Slug Catchers in Natural Gas Production - NTNU
Slug Catchers in Natural Gas Production - NTNU
Slug Catchers in Natural Gas Production - NTNU
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<strong>Slug</strong> <strong>Catchers</strong> <strong>in</strong> <strong>Natural</strong> <strong>Gas</strong><br />
<strong>Production</strong><br />
Thereza Karam<br />
Trondheim<br />
December 2012
Karam – <strong>Slug</strong> <strong>Catchers</strong> <strong>in</strong> <strong>Natural</strong> <strong>Gas</strong> <strong>Production</strong><br />
ABSTRACT<br />
Operations <strong>in</strong> deep, far and remote areas as well as cold environments have raised the problem of slug<br />
formation. Irregular sea floor is the ma<strong>in</strong> concern and major reason beh<strong>in</strong>d the formation of these slugs. Their<br />
presence <strong>in</strong> the pipel<strong>in</strong>es has raised the flow assurance concerns. Several methods are used to <strong>in</strong>hibit such<br />
occurrences as the use of MEG besides the erection of slug catchers at the receiv<strong>in</strong>g term<strong>in</strong>als. The design of<br />
the latter challenges eng<strong>in</strong>eers due to the difficulty of predict<strong>in</strong>g accurately slug length and volumes.<br />
The project will focus on the design of slug catchers and then on four different field cases ly<strong>in</strong>g <strong>in</strong> the<br />
Norwegian Cont<strong>in</strong>ental Shelf. The analysis of a set of articles and theses made it possible to gather the needed<br />
<strong>in</strong>formation. HYSYS was one tool <strong>in</strong> hand to calculate the gas, liquid and condensate fractions <strong>in</strong> the models.<br />
Input data to the model were either assumed, found from previous literature work or calculated from several<br />
correlations.<br />
The project deliberates about two major parts. The first focuses on multiphase flow problems and slug<br />
formation along with the different types of slug catchers available. As for the second part, the methods beh<strong>in</strong>d<br />
the design of a slug catcher are brought <strong>in</strong>to light. A HYSYS simulation was associated with the model to<br />
verify the percentage of the different phases and check whether the size of the slug catcher is suitable.<br />
As a result, the design of a slug catcher was dependent upon three major parameters. These are the length and<br />
the <strong>in</strong>cl<strong>in</strong>ation of the f<strong>in</strong>gers of the multi-pipe catcher, the diameter of the pipel<strong>in</strong>e head<strong>in</strong>g to the <strong>in</strong>let of the<br />
slug catcher and the liquid accumulation volumes expected to be formed <strong>in</strong> the pipel<strong>in</strong>es. The analysis showed<br />
that the multi-pipe type is the mostly used especially for large slug volumes.<br />
Regard<strong>in</strong>g the simulations, HYSYS is not an accurate tool for multiphase flow analysis and estimation of<br />
phase volumes due to the limitations of the program and the simplifications assumed. The MEG quantity<br />
<strong>in</strong>jected was smaller than what is actually used <strong>in</strong> the fields. Likewise, the volume or size of the slug catchers<br />
should be smaller than their current size; this discrepancy is due to the larger amount of slug expected to be<br />
formed and to the simplifications attributed to the model.<br />
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Karam – <strong>Slug</strong> <strong>Catchers</strong> <strong>in</strong> <strong>Natural</strong> <strong>Gas</strong> <strong>Production</strong><br />
ACKNOWLEDGMENT<br />
The project was completed <strong>in</strong> partial fulfillment of the requirements for my Master’s degree <strong>in</strong><br />
Petroleum <strong>Production</strong> at <strong>NTNU</strong>. The project was completed under the supervision of Professor JÒn<br />
Ste<strong>in</strong>ar Gudmundsson at the Department of Petroleum Eng<strong>in</strong>eer<strong>in</strong>g and Applied Geophysics at<br />
<strong>NTNU</strong>.<br />
I would like to thank Professor JÒn Ste<strong>in</strong>ar Gudmundsson for his cont<strong>in</strong>uous support and guidance<br />
throughout the process and for the time he <strong>in</strong>vested <strong>in</strong> read<strong>in</strong>g and comment<strong>in</strong>g my report. I am<br />
grateful for the advices and help I got dur<strong>in</strong>g our discussions.<br />
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LIST OF CONTENT<br />
ABSTRACT .......................................................................................................................................... ii<br />
ACKNOWLEDGMENT...................................................................................................................... iii<br />
LIST OF CONTENT ........................................................................................................................... iv<br />
LIST OF TABLES ............................................................................................................................... vi<br />
LIST OF FIGURES ............................................................................................................................ vii<br />
CHAPTER 1 INTRODUCTION .......................................................................................................... 1<br />
CHAPTER 2 MULTIPHASE FLOW AND SLUGS ........................................................................... 3<br />
2.1 Multiphase flow and flow patterns .............................................................................................. 3<br />
2.2 <strong>Slug</strong> Flow .................................................................................................................................... 4<br />
CHAPTER 3 SLUG CATCHERS ........................................................................................................ 8<br />
3.1 <strong>Slug</strong> Catcher types ....................................................................................................................... 8<br />
3.2 Vessel slug catcher vs. Multi-pipe slug catcher .......................................................................... 9<br />
CHAPTER 4 SLUG CATCHERS DESIGN GUIDELINES ............................................................. 11<br />
4.1 Steps and calculation process .................................................................................................... 11<br />
4.2 Close-up on the formulas beh<strong>in</strong>d the design ............................................................................. 12<br />
4.3 Components and specifications ................................................................................................. 16<br />
CHAPTER 5 NORWEGIAN FIELDS AND SLUG CATCHERS .................................................... 22<br />
5.1 Troll and Kollsnes ..................................................................................................................... 22<br />
5.2 Heidrun and Tjeldbergodden ..................................................................................................... 23<br />
5.3 Snøhvit and Melkøya ................................................................................................................ 24<br />
5.4 Ormen Lange and Nyhamna ..................................................................................................... 24<br />
CHAPTER 6 HYSYS SIMULATIONS ............................................................................................. 26<br />
6.1 Model Setup with a close up on the Ormen Lange case ........................................................... 26<br />
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6.2 MEG Injection to the model ...................................................................................................... 28<br />
CHAPTER 7 DISCUSSION ............................................................................................................... 29<br />
CHAPTER 8 CONCLUSION............................................................................................................. 32<br />
CHAPTER 9 NOMENCLATURE ..................................................................................................... 33<br />
CHAPTER 10 WORKS CITED ........................................................................................................ 34<br />
CHAPTER 11 TABLES ..................................................................................................................... 37<br />
CHAPTER 12 FIGURES .................................................................................................................... 39<br />
APPENDIX I - GENERAL INFORMATION ABOUT THE FIELDS USED FOR THE HYSYS<br />
SIMULATION .................................................................................................................................... 52<br />
I.A – Troll Field .............................................................................................................................. 52<br />
I.B – Heidrun Field.......................................................................................................................... 54<br />
I.C – Snøhvit Field .......................................................................................................................... 55<br />
I.D – Ormen Lange Field ................................................................................................................ 56<br />
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LIST OF TABLES<br />
Table 1: The different slug catcher characteristics of both the f<strong>in</strong>ger type and the vessel type<br />
(Contreras & Foucart, 2007) ................................................................................................ 37<br />
Table 2: Data from the reservoir and the pipel<strong>in</strong>es of the four different fields .................................. 38<br />
Table 3: Data related to the wells and the slug catchers collected for the four different fields ......... 38<br />
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Karam – <strong>Slug</strong> <strong>Catchers</strong> <strong>in</strong> <strong>Natural</strong> <strong>Gas</strong> <strong>Production</strong><br />
LIST OF FIGURES<br />
Figure 1: The six different flow patterns that form depend<strong>in</strong>g on the flow speed <strong>in</strong> the channel. (Aker<br />
Solution, 2011) ......................................................................................................................... 39<br />
Figure 2: The slug formation process <strong>in</strong> three steps start<strong>in</strong>g with the Kelv<strong>in</strong>-Helmholtz Wave Growth,<br />
then by a slug nose <strong>in</strong>gress and tail shedd<strong>in</strong>g to gas entrapment (Feesa, 2003) ...................... 40<br />
Figure 3: The effect of pipel<strong>in</strong>e <strong>in</strong>cl<strong>in</strong>ation on slug formation (Feesa, 2003) ....................................... 40<br />
Figure 4: Idealized slug unit show<strong>in</strong>g all four different elements: the mix<strong>in</strong>g zone, the slug body, the<br />
film and the bubble (Scott et al., 1989) .................................................................................... 41<br />
Figure 5: Representation of the slug unit and unit length with both the slug and film zones (Marquez et<br />
al., 2009) ................................................................................................................................... 41<br />
Figure 6: Flow map of a 20-<strong>in</strong> horizontal slug catcher show<strong>in</strong>g the operational po<strong>in</strong>t (Sarica et al.,<br />
1990) ......................................................................................................................................... 42<br />
Figure 7: Flow map of a 26-<strong>in</strong> horizontal slug catcher show<strong>in</strong>g the operational po<strong>in</strong>t (Sarica et al.,<br />
1990) ......................................................................................................................................... 42<br />
Figure 8: The appropriate design of a constrictor (Shell, 1998). ........................................................... 43<br />
Figure 9: View of the <strong>in</strong>let side of a multi-pipe slug catcher (Patel, 2007) ........................................... 44<br />
Figure 10: View of the liquid header side of a multi-pipe slug catcher (Patel, 2007) ........................... 44<br />
Figure 11: The bottle geometry of the slug catcher for Troll field <strong>in</strong> the Kollsnes process<strong>in</strong>g plant<br />
(Shell, 1998) ............................................................................................................................ 45<br />
Figure 12: A general view of the two slug catchers at the Kollsnes Process<strong>in</strong>g plant (Klemp, 2011) .. 45<br />
Figure 13: The different components of the Hammerfest process<strong>in</strong>g plant of the Snøhvit field<br />
(Pettersen J. , 2011). ................................................................................................................ 46<br />
Figure 14: Representation of the Storegga Slide (left) and the location of the field (right) (Bryna et al.,<br />
2005) ....................................................................................................................................... 46<br />
Figure 15: A general Overview of one of the two multi-pipe slug catchers at Ormen Lange (Gupta,<br />
2012) ....................................................................................................................................... 47<br />
Figure 16: Setup of the HYSYS model (MEG <strong>in</strong>jection was not <strong>in</strong>cluded <strong>in</strong> this setup) ...................... 47<br />
Figure 17: Elevation profile of the Ormen Lange big bore well retrieved from the HYSYS model..... 48<br />
Figure 18: Elevation Profile of the Ormen Lange flowl<strong>in</strong>e (Christiansen, 2012 from Biørnstad, 2006)<br />
................................................................................................................................................. 48<br />
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Karam – <strong>Slug</strong> <strong>Catchers</strong> <strong>in</strong> <strong>Natural</strong> <strong>Gas</strong> <strong>Production</strong><br />
Figure 19: The digitized elevation profile of the Ormen Lange flowl<strong>in</strong>e <strong>in</strong> HYSYS ............................ 49<br />
Figure 20: The slug tool results show<strong>in</strong>g the position, length, frequency and velocity of slugs along<br />
with different flow regimes <strong>in</strong> the Ormen Lange pipel<strong>in</strong>e. ................................................... 49<br />
Figure 21: The elevation profile of the Snøhvit flowl<strong>in</strong>e (Christiansen, 2012) ..................................... 50<br />
Figure 22: The digitized elevation profile of the Snøhvit field as it is implemented <strong>in</strong> HYSYS .......... 50<br />
Figure 23: The elevation profile of the Troll flowl<strong>in</strong>e. H=-350 m and L=67 km (Albrechtsen &<br />
Sletfjerd<strong>in</strong>g, 2003) .................................................................................................................. 51<br />
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Karam – <strong>Slug</strong> <strong>Catchers</strong> <strong>in</strong> <strong>Natural</strong> <strong>Gas</strong> <strong>Production</strong><br />
CHAPTER 1 INTRODUCTION<br />
<strong>Natural</strong> gas reserves around the world have shown a remarkable <strong>in</strong>crease. As the population around<br />
the world is grow<strong>in</strong>g, especially <strong>in</strong> underdeveloped countries, the oil/gas <strong>in</strong>dustry is forced to f<strong>in</strong>d<br />
some additional sources of energy besides oil. Thus, researches for new fields and new alternatives<br />
were carried on and <strong>in</strong>tensified. Due to that, the approved reserves of natural gas, accord<strong>in</strong>g to BP’s<br />
statistical energy review 2011, have <strong>in</strong>creased from 106.86 trillion cubic meters <strong>in</strong> 1987 to 208.4<br />
trillion cubic meters <strong>in</strong> 2011. At the end of 2011, the world’s natural gas production, which is show<strong>in</strong>g<br />
an <strong>in</strong>creas<strong>in</strong>g trend, accounts for 3276.2 billion cubic meters.<br />
<strong>Natural</strong> gas is essential and accounts for a great portion of the world’s energy supply. It constitutes up<br />
to 24% of the worldwide supply of energy. It is currently used for electricity and power sectors which<br />
feed, <strong>in</strong> turn, both residential and commercial sectors. The <strong>in</strong>dustrial sector and transportation are both<br />
us<strong>in</strong>g natural gas for energy supply. It is considered as the cleanest source of energy implemented at<br />
the present time <strong>in</strong> the <strong>in</strong>dustry, thus mak<strong>in</strong>g the usage of it more popular. Its ability to produce a large<br />
deal of energy with the least emission possible made of natural gas a highly demanded energy source<br />
especially with the <strong>in</strong>creas<strong>in</strong>g environmental concerns.<br />
The production of natural gas presents many challenges among which the transport of gas from the<br />
templates up to the receiv<strong>in</strong>g facilities stand out. Many of the receiv<strong>in</strong>g term<strong>in</strong>als do not receive only<br />
natural gas <strong>in</strong> the pipel<strong>in</strong>es: gas is often associated with condensed hydrocarbons and condensed water.<br />
Both the condensate and the water tend to form slugs <strong>in</strong> the pipel<strong>in</strong>es lead<strong>in</strong>g to blocked pipes and to<br />
irregular arrival to term<strong>in</strong>als with large volume rates. These rates cannot be handled by the facilities<br />
without the presence of some buffer volumes known as slug catchers.<br />
<strong>Slug</strong> catchers have been used <strong>in</strong> many of the receiv<strong>in</strong>g facilities <strong>in</strong> Norway. Troll, Heidrun, Ormen<br />
Lange and Snøhvit are four different fields offshore Norway. The first three lie <strong>in</strong> the Norwegian Sea<br />
whereas the last one is located <strong>in</strong> the Barents Sea. The four different fields are l<strong>in</strong>ked to the receiv<strong>in</strong>g<br />
facilities through subsea pipel<strong>in</strong>es. <strong>Slug</strong> catchers are the first facilities receiv<strong>in</strong>g the flow from the<br />
pipel<strong>in</strong>es. In order to determ<strong>in</strong>e the size of the slug catcher, the approximate volumes assumed to be<br />
form<strong>in</strong>g <strong>in</strong> the pipel<strong>in</strong>es have to be estimated. To do so, HYSYS has been used to implement some<br />
simulations, estimate the cont<strong>in</strong>uous amount of gas, condensate and liquid water and then discuss the<br />
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Karam – <strong>Slug</strong> <strong>Catchers</strong> <strong>in</strong> <strong>Natural</strong> <strong>Gas</strong> <strong>Production</strong><br />
suitability of the current design. However, it should be noticed that when simulat<strong>in</strong>g multiphase flow<br />
<strong>in</strong> pipel<strong>in</strong>es, results can be undependable due to the difficulty of an accurate representation.<br />
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Karam – <strong>Slug</strong> <strong>Catchers</strong> <strong>in</strong> <strong>Natural</strong> <strong>Gas</strong> <strong>Production</strong><br />
CHAPTER 2 MULTIPHASE FLOW AND SLUGS<br />
2.1 Multiphase flow and flow patterns<br />
Multiphase flow is the mostly common and dom<strong>in</strong>at<strong>in</strong>g flow <strong>in</strong> pipel<strong>in</strong>es. A s<strong>in</strong>gle phase flow is rarely<br />
found <strong>in</strong> the oil <strong>in</strong>dustry as the high pressure <strong>in</strong> the reservoir will cause a portion of the gas from the<br />
gas cap to get dissolved <strong>in</strong> the oil or water to be dissolved <strong>in</strong> the gas. As the pressure is reduced due to<br />
production, the gas will come out of solution; similarly, water will come out of solution <strong>in</strong> the form of<br />
water droplets. In a more general description, two different sets of simultaneous flows constitute the<br />
multiphase flow. Simultaneous flow of materials of two different states such as liquid, solid or gas<br />
occurr<strong>in</strong>g at the same time <strong>in</strong> the same mixture is classified as multiphase flow. On the other hand,<br />
simultaneous flow of materials of different chemical properties belong<strong>in</strong>g to the same state or phase<br />
such as oil droplets <strong>in</strong> water is also considered as a multiphase flow (Bakker, 2005). As for the<br />
nomenclature of the phases, the cont<strong>in</strong>uous one is considered primary while the second phase(s) is<br />
considered secondary as it is dispersed <strong>in</strong> the first.<br />
Several multiphase flow regimes take place <strong>in</strong> horizontal pipel<strong>in</strong>es. The two-phase gas-liquid flow is<br />
considered <strong>in</strong> the section below. Phase separation usually occurs when the gravity effect is<br />
perpendicular to the pipe axis. Six different patterns can appear <strong>in</strong> the horizontal pipe and are<br />
represented <strong>in</strong> Figure 1. The follow<strong>in</strong>g flow regimes are mentioned as a function of <strong>in</strong>creas<strong>in</strong>g flow<br />
rate velocities. Stratified smooth (SS) pattern is the flow regime that is tak<strong>in</strong>g place more frequently <strong>in</strong><br />
pipes as both gas and liquid streams are be<strong>in</strong>g separated and parallel due to gravity. The gas overlies<br />
the liquid and the <strong>in</strong>terface is smooth. Stratified wavy (SW) pattern occurs as the gas velocity<br />
<strong>in</strong>creases slightly and causes waves to form on the gas-liquid <strong>in</strong>terface.<br />
The considerable <strong>in</strong>crease <strong>in</strong> gas velocity <strong>in</strong> the pipes leads to more complicated flow regimes.<br />
Elongated bubble flow (EB), also known as plug flow, shows elongated gas bubbles that separate the<br />
liquid plugs. The elongated bubbles have a large diameter so that the liquid phase is ly<strong>in</strong>g cont<strong>in</strong>uously<br />
at the bottom of the pipe. The elongated bubbles will grow <strong>in</strong> size with <strong>in</strong>creas<strong>in</strong>g flow velocity until<br />
they reach a diameter similar to that of the channel leav<strong>in</strong>g beh<strong>in</strong>d some liquid slugs. This is known as<br />
the slug flow (I). The latter bubbles are known as the Taylor bubbles which will be coated by a liquid<br />
film. Dispersed bubble (DB) flow takes place where the gas phase is extensively distributed <strong>in</strong> the<br />
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Karam – <strong>Slug</strong> <strong>Catchers</strong> <strong>in</strong> <strong>Natural</strong> <strong>Gas</strong> <strong>Production</strong><br />
form of bubbles or droplets <strong>in</strong> the cont<strong>in</strong>uous liquid phase. Annular (wavy) flow (A-AW) arises when<br />
the flow rate is the highest. Hence, the liquid will form an annular film around the tube; but the film is<br />
thicker at the bottom than at the top of the tube. Some small amplitude waves disrupt the <strong>in</strong>terface<br />
between the liquid film and the gas; as well, some droplets may be found <strong>in</strong> the gaseous phase<br />
(Walveribne Tube Inc, 2007, Azzopardi, 2010 and Bratland, 2010).<br />
Counter-current flow represents one of the aspects encountered <strong>in</strong> multiphase flow. Counter-current<br />
takes place normally as the flow is flow<strong>in</strong>g <strong>in</strong> an upward direction. Hence, gravity plays a major role;<br />
it pulls the heavier phase of the gas-liquid mixture downwards. Each layer drags the other one<br />
oppositely to its flow direction. In such a flow type, double holdups are always expected. The bubble<br />
<strong>in</strong>stability leads to a difficulty <strong>in</strong> the prediction of the flow’s velocity. Counter-current flow limitation<br />
takes place when the gas flow rate <strong>in</strong>creases. This <strong>in</strong>crease causes a decrease <strong>in</strong> the delivered liquid<br />
flow rate.<br />
Liquid fallback can be <strong>in</strong>hibited by a pressure difference applied on the fluids and an <strong>in</strong>terfacial shear<br />
between the two phases present <strong>in</strong> the pipe. In order to <strong>in</strong>hibit this occurrence, the <strong>in</strong>terfacial shear<br />
should be high. This is ma<strong>in</strong>ly implemented with an <strong>in</strong>crease <strong>in</strong> the gas flow rate which should be able<br />
to lift the liquid exist<strong>in</strong>g <strong>in</strong> the form of either a film or droplets. Furthermore, the pressure differential<br />
should be high as well <strong>in</strong> order to overcome the liquid-wall stress and the gravity that pull the liquid <strong>in</strong><br />
the other direction. To simplify, the direction of the liquid-wall shear determ<strong>in</strong>es whether the flow is a<br />
co-current or counter-current flow. A positive shear corresponds to a co-current flow while a negative<br />
shear corresponds to a counter-current flow.<br />
2.2 <strong>Slug</strong> Flow<br />
<strong>Slug</strong>, which is a lump of liquid, has been one of the major concerns of the <strong>in</strong>dustry when it comes to<br />
transport of flow <strong>in</strong> multiphase flowl<strong>in</strong>es. The slug normally forms as a result of retrograde<br />
condensation when the reservoir pressure drops below the dew po<strong>in</strong>t. The presence of a slug flow <strong>in</strong><br />
the flowl<strong>in</strong>es leads to an unsteady hydrodynamic behavior. The latter is the consequence of an<br />
alternat<strong>in</strong>g flow of liquid slugs and gas pockets. The liquid level <strong>in</strong> the <strong>in</strong>let separator will be affected;<br />
a good separation is <strong>in</strong>hibited and <strong>in</strong> the worst case scenario, a flood<strong>in</strong>g of the separator will occur.<br />
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The slug formation is a three step process that is represented <strong>in</strong> Figure 2. The first pipel<strong>in</strong>e section<br />
shows a stratified flow where the gas is overly<strong>in</strong>g the liquid and usually flow<strong>in</strong>g at a higher velocity.<br />
The <strong>in</strong>terface between these two phases is not a straight l<strong>in</strong>e but a wave-like boundary. As soon as the<br />
gas hits the wave, a pressure drop will take place followed by a pressure recovery. The latter will<br />
create a small force that will be sufficient to lift the wave upwards until it reaches the top of the pipe<br />
form<strong>in</strong>g the slug shape. This is ma<strong>in</strong>ly generated by the Kelv<strong>in</strong>-Helmholtz <strong>in</strong>stability. The slug shape<br />
formed consists of a nose and a tail. The first is shown on the right side of part 2 of Figure 2 extracted<br />
from the Feesa case study; as for the second, it is located to the left side. The slug is ma<strong>in</strong>ly pushed by<br />
the gas at a higher rate than the liquid. Hence, the presence of the tail can be expla<strong>in</strong>ed and leads to a<br />
liquid entrance <strong>in</strong> the slug nose. Jet formation is, then, the outcome of such an <strong>in</strong>cident. The result is a<br />
bubble formation which will, <strong>in</strong> turn, reduce the liquid holdup <strong>in</strong>creas<strong>in</strong>g thus the turbulence <strong>in</strong> the<br />
slug due to <strong>in</strong>terference with the liquid <strong>in</strong>gress process.<br />
The amount of liquid to be formed <strong>in</strong> the pipel<strong>in</strong>es depends upon several variables. The velocity<br />
between the liquid and gas surface is one factor that determ<strong>in</strong>es the amount of the slug be<strong>in</strong>g formed; a<br />
slip <strong>in</strong> velocity between the two phases will cause the liquid to accumulate. The length of the twophase<br />
flow pipel<strong>in</strong>es through which the liquid is transported under steady-state conditions affects also<br />
the amount of liquid be<strong>in</strong>g deposited; the longer the distance of transport, the more liquid is deposited.<br />
The slug that comes out from the pipel<strong>in</strong>e under steady state condition is changed <strong>in</strong>to operat<strong>in</strong>g<br />
conditions when the volume flow might change. In other words, by a change of velocity which is<br />
normally up to 12 m/s <strong>in</strong> gas pipel<strong>in</strong>es or by pigg<strong>in</strong>g, the slug will come out of the pipel<strong>in</strong>e. Pigg<strong>in</strong>g<br />
produces the largest amount of slugs. It should be noticed that the slug flow characteristics are difficult<br />
to predict and cause some challenges due to the vary<strong>in</strong>g slug length and frequency, liquid holdup and<br />
pressure drop.<br />
The size of the slug and its degree of persistence <strong>in</strong> the flowl<strong>in</strong>e depend ma<strong>in</strong>ly on the flow rate, the<br />
liquid <strong>in</strong>gress and how it will affect the turbulence with<strong>in</strong> the slug. The latter is also governed by<br />
several parameters such as the fluid properties <strong>in</strong> the pipel<strong>in</strong>e, the pipel<strong>in</strong>e <strong>in</strong>cl<strong>in</strong>ation and the local<br />
flow<strong>in</strong>g conditions as it was stated <strong>in</strong> the case study ‘Hydrodynamic <strong>Slug</strong> Size <strong>in</strong> Multiphase<br />
Pipel<strong>in</strong>es’ completed by Feesa. The <strong>in</strong>cl<strong>in</strong>ation of the pipe is one of the most sensitive parameters that<br />
affect the slug formation; an <strong>in</strong>cl<strong>in</strong>ation of less than 1° can cause an unbalanced state <strong>in</strong> the pipe.<br />
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Karam – <strong>Slug</strong> <strong>Catchers</strong> <strong>in</strong> <strong>Natural</strong> <strong>Gas</strong> <strong>Production</strong><br />
The difference <strong>in</strong> the slug formation <strong>in</strong> both a horizontal and an undulant pipe is shown <strong>in</strong> Figure 3. In<br />
the first case of a horizontal pipe, only slug flow regime is occurr<strong>in</strong>g while both slug and stratified<br />
flow regime are encountered <strong>in</strong> the undulant pipe imply<strong>in</strong>g a vary<strong>in</strong>g range of slug sizes and pressure<br />
drops. The turbulent region <strong>in</strong> the slug, which is also affected by the gas bubble formation, affects the<br />
frictional pressure losses. It should be noticed that the horizontal pipes are rarely used due to different<br />
topographies and bathymetries that require more or less undulat<strong>in</strong>g pipes. For the four different fields<br />
<strong>in</strong> question <strong>in</strong> this paper, rough terra<strong>in</strong>s and large slides formed huge challenges. Thus, horizontal<br />
pipes were only small sections of the elevation profile for each of the fields.<br />
Several types of slugs can form. The hydrodynamic slug, one of the mostly known slug types, forms <strong>in</strong><br />
near horizontal parts of the flowl<strong>in</strong>es due to the small amount of liquids compared to the free volume<br />
<strong>in</strong> the separator. The accumulated liquids must be handled as they come out from the pipel<strong>in</strong>es without<br />
any reduction <strong>in</strong> the pipel<strong>in</strong>e flow velocity. On the other hand, riser’s slugg<strong>in</strong>g can cause some<br />
problems for process<strong>in</strong>g as gravity forces can develop riser slugs if the flowl<strong>in</strong>e has a low po<strong>in</strong>t <strong>in</strong><br />
front of the riser. The reasons beh<strong>in</strong>d the riser slug formation are ma<strong>in</strong>ly low flow rates and low<br />
pressure <strong>in</strong> the flowl<strong>in</strong>e around the end of the field lifetime. The low rate can be <strong>in</strong>creased by the use<br />
of a static topside choke. <strong>Slug</strong> removal by flow stabilization has a great economic potential s<strong>in</strong>ce it<br />
reduces the shutdown periods and might improve the oil recovery. The hydrodynamic slug is the only<br />
slug type to be handled by the <strong>in</strong>let separator or slug catchers.<br />
<strong>Slug</strong>s are more or less very complicated to model the 3D turbulent multiphase phenomena. They occur<br />
<strong>in</strong> numbers <strong>in</strong> a pipel<strong>in</strong>e, thus, this adds to the complexity of model<strong>in</strong>g. <strong>Slug</strong>s might be mostly<br />
communicat<strong>in</strong>g whether directly or <strong>in</strong>directly; therefore, each one cannot be treated separately or <strong>in</strong><br />
isolation which further complicates the situation. In order to somehow predict the behavior of the slug,<br />
both the <strong>in</strong>itial and the boundary conditions must be determ<strong>in</strong>ed with precision as the chaotic behavior<br />
of the slug is sensitive to the <strong>in</strong>itial conditions.<br />
The slug flow can be suppressed <strong>in</strong> different manners depend<strong>in</strong>g on the availability of the <strong>in</strong>formation<br />
about slug formation. When slug formation is expected, it is possible to reduce it by chang<strong>in</strong>g the<br />
design of the process equipment. On the other hand, if the slug flow forms unexpectedly, some<br />
<strong>in</strong>tervention methods should be implemented to reduce its effect on the process<strong>in</strong>g part; thus, devices<br />
handl<strong>in</strong>g the slug should be considered <strong>in</strong> the design. To solve the problem, a large <strong>in</strong>let separator can<br />
be built to avoid slug flood<strong>in</strong>g dur<strong>in</strong>g severe slugg<strong>in</strong>g but this method is quite expensive and requires a<br />
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Karam – <strong>Slug</strong> <strong>Catchers</strong> <strong>in</strong> <strong>Natural</strong> <strong>Gas</strong> <strong>Production</strong><br />
large space. This previously stated solution is ma<strong>in</strong>ly implemented for offshore slug formation. The<br />
similar alternative for onshore operations is the use of a slug catcher which is a big tank located at the<br />
receiv<strong>in</strong>g term<strong>in</strong>al. It is the first equipment to collect the flow from the pipel<strong>in</strong>es.<br />
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Karam – <strong>Slug</strong> <strong>Catchers</strong> <strong>in</strong> <strong>Natural</strong> <strong>Gas</strong> <strong>Production</strong><br />
3.1 <strong>Slug</strong> Catcher types<br />
CHAPTER 3 SLUG CATCHERS<br />
A slug catcher, which is a part of the gas pipel<strong>in</strong>e system, is an essential equipment at the receiv<strong>in</strong>g<br />
term<strong>in</strong>al of a multiphase flow process<strong>in</strong>g plant. The specific function of a slug catcher is the separation<br />
of the gas and liquid phases as well as the storage of the liquids temporarily. The gas is then sent for<br />
further treatment <strong>in</strong> the gas-treat<strong>in</strong>g facilities downstream the pipes. The slug catcher is ma<strong>in</strong>ly made<br />
up of two different compartments: the first one <strong>in</strong>cludes the gas-liquid separator under steady flow<br />
conditions while the second consists of the storage where the received liquid is accumulated under<br />
operat<strong>in</strong>g conditions. The gas will be guaranteed to reach the downstream facilities as the accumulated<br />
liquid will displace the exist<strong>in</strong>g gas <strong>in</strong> a relatively cont<strong>in</strong>uous pattern. The size of the slug catcher<br />
should be determ<strong>in</strong>ed by the size of the largest slug that is possible to form <strong>in</strong> the pipel<strong>in</strong>e.<br />
The appropriate design of the slug catcher accounts largely to avoid problems at the receiv<strong>in</strong>g<br />
term<strong>in</strong>als. In order to prevent the acceleration of the gas/liquid mixture, the <strong>in</strong>let diameter of the pipes<br />
enter<strong>in</strong>g the slug catcher should be the same as that of the pipel<strong>in</strong>e. Normally the slug catcher is made<br />
up of a series of pipes that are parallel and <strong>in</strong>cl<strong>in</strong>ed <strong>in</strong> order to give the hold-up volume for the liquid<br />
(Shell, 1998). Each one of these pipes <strong>in</strong> the slug catcher is known as a f<strong>in</strong>ger. The upper end of the<br />
pipes discharges the gas while the bottom end discharges the liquid. A strong structure and foundation<br />
ma<strong>in</strong>ta<strong>in</strong> the pipes so as to support the impact of the slug.<br />
The slug catchers exist <strong>in</strong> three different types: the vessel type, the multi-pipe type and the park<strong>in</strong>g<br />
loop type. The vessel type can range from a simple to a more complicated knock-out vessel which is<br />
ma<strong>in</strong>ly used for limited plot sizes such as offshore platforms due to its small size. For large volumes of<br />
slugs which implies a volume exceed<strong>in</strong>g 100 m 3 , the multi-pipe or park<strong>in</strong>g loop slug catchers are<br />
ma<strong>in</strong>ly used. The multi-pipe slug catcher is made up of a liquid and gas separation entry slot and a<br />
series of parallel tilted bottles where the liquid is stored. The <strong>in</strong>flow of liquid gets first through the<br />
splitter <strong>in</strong>to the <strong>in</strong>let manifold and then down to the bottles mov<strong>in</strong>g thus the exist<strong>in</strong>g gas up to the gas<br />
outlet risers. As a consequence, a cont<strong>in</strong>uous gas flow is ma<strong>in</strong>ta<strong>in</strong>ed to the downstream facilities.<br />
Therefore, the advantage of this slug catcher category is the ease of operation due to a free flow<br />
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Karam – <strong>Slug</strong> <strong>Catchers</strong> <strong>in</strong> <strong>Natural</strong> <strong>Gas</strong> <strong>Production</strong><br />
control measure. The gas <strong>in</strong>let side and the liquid <strong>in</strong>let header are shown <strong>in</strong> Figures 9 and 10,<br />
respectively.<br />
The park<strong>in</strong>g loop slug catcher is designed to handle liquid carry-over that can be easily formed <strong>in</strong> case<br />
of counter-current gas/liquid flow. The separation and storage parts are practically separated but the<br />
liquid and the gas from the <strong>in</strong>com<strong>in</strong>g stream are separated <strong>in</strong> the conta<strong>in</strong>er. A slug arrival <strong>in</strong>to the<br />
separator can be detected by an <strong>in</strong>crease <strong>in</strong> the liquid volume <strong>in</strong> the vessel. For precautious measures,<br />
the gas is controlled by forc<strong>in</strong>g the liquid to get <strong>in</strong>to the pipe-loop where a pig is present. The latter is<br />
responsible for the separation of the liquid and gas. The other side of the loop is now open for the gas<br />
to flow <strong>in</strong> a co-current mode to the downstream facilities. This slug catcher type is ma<strong>in</strong>ly used<br />
offshore where the separator is located on the platform while the loop is mounted on the seabed. It can<br />
also be used onshore to reduce the space used if the pipe-loop is placed parallel to the <strong>in</strong>let pipe.<br />
Multiphase surges can be classified <strong>in</strong>to three different categories. The latters are hydrodynamic slugs,<br />
terra<strong>in</strong> <strong>in</strong>duced slugs and operationally <strong>in</strong>duced surges. Hydrodynamic slugs, as mentioned previously,<br />
form due to an <strong>in</strong>stability <strong>in</strong> the waves at the gas-liquid <strong>in</strong>terface <strong>in</strong> stratified flow regimes. On the<br />
other hand, the terra<strong>in</strong> <strong>in</strong>duced slugs form mostly at low flow rates after accumulation and <strong>in</strong>termittent<br />
removal of liquids <strong>in</strong> dips along the flowl<strong>in</strong>e. The operationally <strong>in</strong>duced surges occur usually as the<br />
system is forced to change from one steady state to the other such as <strong>in</strong> pigg<strong>in</strong>g operations. In order to<br />
say that a pipel<strong>in</strong>e is be<strong>in</strong>g operated under slug flow regime, it should be then filled with a number of<br />
hydrodynamic slugs. Under such regime, the liquid-gas flow shows a chaotic behavior.<br />
3.2 Vessel slug catcher vs. Multi-pipe slug catcher<br />
Multi-pipe slug catcher, also known as f<strong>in</strong>ger slug catcher, is preferably used compared to the vessel<br />
slug catcher. In case of large volumes of slug handl<strong>in</strong>g, which is more frequently experienced <strong>in</strong><br />
operations, multi-pipe slug catcher is more cost effective. As well, less operational problems are<br />
encountered when us<strong>in</strong>g the multi-pipe slug catcher. On the other hand, vessel slug catcher is more<br />
size effective as it does not require a large space <strong>in</strong> the process<strong>in</strong>g plant.<br />
Several criteria and aspects are to be considered when decid<strong>in</strong>g upon which type of slug catcher is<br />
more feasible for the field <strong>in</strong> question. The performance as handl<strong>in</strong>g the <strong>in</strong>com<strong>in</strong>g slug and the<br />
transportation features differentiate the two types of slug catchers. The performance depends chiefly<br />
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Karam – <strong>Slug</strong> <strong>Catchers</strong> <strong>in</strong> <strong>Natural</strong> <strong>Gas</strong> <strong>Production</strong><br />
on the volume of the slug to be handled; this has been mentioned <strong>in</strong> the previous section. The<br />
efficiency to remove the liquid is essential: the vessel type has a high efficiency <strong>in</strong> remov<strong>in</strong>g the small<br />
particles. The weight of the two different catchers is also taken <strong>in</strong>to consideration; the f<strong>in</strong>ger type<br />
weighs much less than a vessel type. The fabrication of the walls of a smaller bottle does not require as<br />
much material as that of the walls of a larger bottle (Mokhatab et al., 2006). The larger bottle should<br />
sometimes handle a higher pressure; therefore, the walls should be thicker than those of a f<strong>in</strong>ger type<br />
catcher. The lighter weight of the f<strong>in</strong>ger type and the smaller size of the pieces to be assembled later<br />
on <strong>in</strong> the field make it easier for the f<strong>in</strong>ger type to be transported than the heavy and bulky vessel type.<br />
The capital cost or CAPEX is also to be accounted for when decid<strong>in</strong>g upon the appropriate slug<br />
catcher type. The capital cost is the money <strong>in</strong>vested <strong>in</strong> acquir<strong>in</strong>g or upgrad<strong>in</strong>g a physical asset. It<br />
depends on the pressure that should be handled by the catchers. The vessel type is expected to handle a<br />
higher pressure but sometimes both types should handle approximately the same pressure. However,<br />
the vessel type is more expensive if transportation and taxes are also <strong>in</strong>cluded (Mokhatab et al., 2006).<br />
The <strong>in</strong>stallation costs and the associated technological risk should be thought of <strong>in</strong> the choice of the<br />
suitable slug catcher type. The <strong>in</strong>stallation costs are higher for a f<strong>in</strong>ger type than a vessel type. The<br />
area required for <strong>in</strong>stall<strong>in</strong>g the catcher, the crew responsible for <strong>in</strong>stallation, the field work and the<br />
erect<strong>in</strong>g time are, as well, all higher for a f<strong>in</strong>ger type slug catcher. The f<strong>in</strong>ger type is constructed <strong>in</strong> a<br />
workshop but needs to be assembled <strong>in</strong> the field and then connected to the exist<strong>in</strong>g equipment.<br />
However, the vessel type is also erected <strong>in</strong> a workshop but needs only to be <strong>in</strong>stalled <strong>in</strong> the field and<br />
connected to the other equipment. This can expla<strong>in</strong> the difference <strong>in</strong> the <strong>in</strong>stallation costs. Both have a<br />
low risk associated to handl<strong>in</strong>g the operations then this is not a criterion that would affect much the<br />
decision (Contreras & Foucart, 2007).<br />
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Karam – <strong>Slug</strong> <strong>Catchers</strong> <strong>in</strong> <strong>Natural</strong> <strong>Gas</strong> <strong>Production</strong><br />
CHAPTER 4 SLUG CATCHERS DESIGN GUIDELINES<br />
4.1 Steps and calculation process<br />
<strong>Slug</strong> catchers, as previously stated, are important equipment <strong>in</strong> the receiv<strong>in</strong>g term<strong>in</strong>als for multiphase<br />
flow pipes. For that purpose, the accurate and appropriate design of these catchers is crucial. More<br />
specifically, the size of the slug catcher and the diameter of either the vessel or the f<strong>in</strong>gers should be<br />
estimated. To do so, a series of steps should be followed (Bai & Bai, 2010).<br />
1- Determ<strong>in</strong><strong>in</strong>g the functions of the slug catcher<br />
2- Determ<strong>in</strong><strong>in</strong>g the location of the slug catcher<br />
3- Select<strong>in</strong>g the primary configuration of the slug catcher<br />
4- Compil<strong>in</strong>g the design data<br />
5- Establish<strong>in</strong>g the design criteria<br />
6- Estimat<strong>in</strong>g the size and the dimensions of the slug catcher<br />
7- Review<strong>in</strong>g of the feasibility of the overall design; review<strong>in</strong>g if necessary<br />
As for the calculation sequence, the preferable order of calculations accord<strong>in</strong>g to Shell’s DEP is the<br />
follow<strong>in</strong>g (Shell, 1998)<br />
1- Calculat<strong>in</strong>g the <strong>in</strong>tercept volume<br />
2- Calculat<strong>in</strong>g the buffer volume based on the process requirements downstream<br />
3- Decid<strong>in</strong>g the size of the bottle<br />
4- Decid<strong>in</strong>g the number of primary bottles<br />
5- Calculat<strong>in</strong>g the distance between the end of the downcomer and the gas riser<br />
6- Calculat<strong>in</strong>g the bottle ‘s storage length <strong>in</strong> a way to conta<strong>in</strong> the volume of the slug catcher<br />
7- Determ<strong>in</strong><strong>in</strong>g the slug catcher’s total width and length and decid<strong>in</strong>g upon the necessity of<br />
secondary bottles depend<strong>in</strong>g on the available length of the plot for the slug catcher<br />
8- Determ<strong>in</strong><strong>in</strong>g with a sketch the configuration and the major dimensions of the slug catcher<br />
9- Analyz<strong>in</strong>g critically the volumes <strong>in</strong> a way to take the volume of the slug catcher calculated <strong>in</strong><br />
step 6 and adjust<strong>in</strong>g accord<strong>in</strong>gly the length and the number of bottles; the necessity for<br />
secondary bottles should be checked aga<strong>in</strong>. Repeat<strong>in</strong>g the steps start<strong>in</strong>g with number 4 <strong>in</strong> case<br />
of adjustments<br />
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Karam – <strong>Slug</strong> <strong>Catchers</strong> <strong>in</strong> <strong>Natural</strong> <strong>Gas</strong> <strong>Production</strong><br />
10- Repeat<strong>in</strong>g the volume calculations after f<strong>in</strong>alization of all dimensions<br />
4.2 Close-up on the formulas beh<strong>in</strong>d the design<br />
<strong>Slug</strong> flow behavior must be determ<strong>in</strong>ed first <strong>in</strong> order to be able to design and size a slug catcher<br />
whether it is a normal slug flow or <strong>in</strong>duced by pigg<strong>in</strong>g. A number of calculations and a set of<br />
equations should be available and used. The slug length, slug holdup, slug velocity and translational<br />
velocity should all be determ<strong>in</strong>ed accord<strong>in</strong>g to Sarica et al. (1990). The slug velocity can be def<strong>in</strong>ed as<br />
the velocity of the mixture <strong>in</strong> steady state flow whereas the translational velocity, , is determ<strong>in</strong>ed by<br />
the equation below:<br />
(1)<br />
where is the velocity of the mixture, is the drift velocity and c is a constant. The drift velocity,<br />
which is the velocity of one phase relative to a surface mov<strong>in</strong>g at the mixture velocity, is expressed<br />
- for normal slug flow <strong>in</strong> vertical pipes, as:<br />
√<br />
(2.a)<br />
- for normal slug flow <strong>in</strong> horizontal pipes, as:<br />
√<br />
(2.b)<br />
- for normal slug flow <strong>in</strong> <strong>in</strong>cl<strong>in</strong>ed pipes based on the Bendiksen correlation (1984), as:<br />
(2.c)<br />
- for pigg<strong>in</strong>g, as:<br />
The constant c depends on the flow type thus if the flow is lam<strong>in</strong>ar, c=2. If the flow is turbulent, then<br />
c=1.2. Otherwise, the Taitel correlation (2000) is used; it is represented as follows,<br />
(2.d)<br />
( ) ( )<br />
(3)<br />
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Karam – <strong>Slug</strong> <strong>Catchers</strong> <strong>in</strong> <strong>Natural</strong> <strong>Gas</strong> <strong>Production</strong><br />
The general slug liquid holdup, which is symbolized by or and affected by the liquid velocity,<br />
is expressed by the Gregory et al. correlation (1978) for a liquid slug with a viscosity less than 500 cP<br />
( ( ) )<br />
(4.a)<br />
If the viscosity of the liquid is greater than 500 cP, the correlation obta<strong>in</strong>ed at PDVSA Intevep is used,<br />
The latter correlation can also be used to determ<strong>in</strong>e the holdup <strong>in</strong> the Taylor bubble,<br />
(4.b)<br />
(5)<br />
The Beggs correlation (1991) is used to calculate the gas void fraction which is the fraction of a<br />
volume element <strong>in</strong> the two-phase flow occupied by the gas phase <strong>in</strong> the slug zone.<br />
(6)<br />
Accord<strong>in</strong>g to Sarica et al. (1990), the average slug length for large diameter pipes up to 24 <strong>in</strong>ches can<br />
be determ<strong>in</strong>ed by the Norris correlation which is based on the Prudhoe Bay experiment. It is<br />
represented <strong>in</strong> the equations below.<br />
̅<br />
(7.a)<br />
̅<br />
(7.b)<br />
Thus, the maximum anticipated slug length can be determ<strong>in</strong>ed us<strong>in</strong>g the results of eq. (7.b),<br />
̅ (8)<br />
Equation (7.b) has some limitations; thus, it uses a limited set of data which fall with<strong>in</strong> a small range<br />
of flow rates. This will narrow the applicability of this correlation to other systems; hence, it is<br />
<strong>in</strong>applicable to pipe diameters larger than 24 <strong>in</strong>ches.<br />
An alternative correlation has been developed by Shoham (2000) to determ<strong>in</strong>e the slug length. The<br />
latter requires a known film length of the slug. Thus, a film length of the slug, which is ma<strong>in</strong>ly the<br />
length of the Taylor-bubble as it constitutes the majority of the film zone, was developed by PDVSA<br />
Intevep and then, <strong>in</strong>cluded <strong>in</strong> the general formula for the slug length calculation. A representation of<br />
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Karam – <strong>Slug</strong> <strong>Catchers</strong> <strong>in</strong> <strong>Natural</strong> <strong>Gas</strong> <strong>Production</strong><br />
the slug and film length and zone are shown <strong>in</strong> Figures 4 and 5. The film length of the slug and the<br />
slug length for a hydrodynamic flow are represented, respectively, as follows,<br />
( ) (9)<br />
( )<br />
(10)<br />
The slug frequency denot<strong>in</strong>g the rate of <strong>in</strong>termittence of the slug through the pipel<strong>in</strong>e, is expressed as<br />
(11)<br />
with L U , the slug unit length, be<strong>in</strong>g the sum of the slug length L S and the film length L L .<br />
The <strong>in</strong>stantaneous <strong>in</strong>let flow rates of both gas and liquid are important slug characterization features<br />
and crucial for the design of the slug catchers. These rates have been calculated by us<strong>in</strong>g the Miyoshi<br />
et al model (1988). The equations are as follow:<br />
- for the liquid: (12.a)<br />
- for the gas: (12.b)<br />
The liquid accumulation <strong>in</strong> the slug catcher should be determ<strong>in</strong>ed <strong>in</strong> order to def<strong>in</strong>e the size of the slug<br />
catcher. Accord<strong>in</strong>g to Sarica et al. (1990), a mass balance between the <strong>in</strong>let and outlet liquid rate of the<br />
slug catcher can be used to calculate the accumulated liquid rate and thus the accumulated liquid<br />
volume.<br />
[ ] [ ] [ ]<br />
To solve the mass balance, the different parts of the equation should be determ<strong>in</strong>ed separately. As<br />
expressed earlier, the liquid <strong>in</strong>put mass rate can be calculated with the Miyoshi et al. (1998) model<br />
similarly to equation (12.a). The liquid discharge mass rate represents the flow rate at the outlet of the<br />
slug catcher which is, <strong>in</strong> turn, dependent upon the flow control valve (Marquez et al., 2009). The<br />
liquid accumulation rate can be calculated from equation (13) with the assumption of a constant liquid<br />
density <strong>in</strong> the slug catcher and no acceleration while slug production (Sarica et al., 1990). On the other<br />
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Karam – <strong>Slug</strong> <strong>Catchers</strong> <strong>in</strong> <strong>Natural</strong> <strong>Gas</strong> <strong>Production</strong><br />
hand, what counts more for the design and model<strong>in</strong>g of the slug catcher is the liquid accumulation<br />
volume calculated from the mass balance as <strong>in</strong> equation (14). The m<strong>in</strong>imum rate is preferably used <strong>in</strong><br />
case of fluctuation of the discharge rate.<br />
(13)<br />
[ ] (14)<br />
The dimensions of the f<strong>in</strong>gers of a multi-pipe slug catcher are very important <strong>in</strong> the overall design.<br />
One of the parameters to be determ<strong>in</strong>ed is the diameter of the f<strong>in</strong>gers. It is required to ensure an <strong>in</strong>let<br />
stratified flow <strong>in</strong>to the slug catcher <strong>in</strong>stead of gett<strong>in</strong>g a slug flow. Two measures can be implemented<br />
to satisfy the stated requirement. The first is to <strong>in</strong>crease the diameter of the slug catcher while the<br />
second is to have a downward <strong>in</strong>cl<strong>in</strong>ation of the slug catcher. Therefore, the m<strong>in</strong>imum diameter<br />
required lead<strong>in</strong>g to a stratified flow can be calculated from the transition criterion given by Taitel et al<br />
(2000) based on the <strong>in</strong>viscid Kelv<strong>in</strong> Helmholtz <strong>in</strong>stability criterion. This is shown <strong>in</strong> equation (15).<br />
( ) √<br />
(15)<br />
The viscous Kelv<strong>in</strong> Helmholtz <strong>in</strong>stability criterion accord<strong>in</strong>g to Marquez et al (1990) is a better<br />
representation of the transition between slug and stratified flows. The transition is applicable for a<br />
wider range of viscosities (100-5000 cP). The transition can be then represented by:<br />
√ ( ) (16)<br />
K V is a correction factor calculated from the follow<strong>in</strong>g equation:<br />
√<br />
(17)<br />
Several <strong>in</strong>dications would simplify the recognition of a stratified flow at the <strong>in</strong>let of the catcher. The<br />
stratified flow will take place when the actual gas velocity is lower than the transitional gas<br />
velocity,<br />
. Some flow pattern maps for specific diameters of slug catchers can be used to<br />
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Karam – <strong>Slug</strong> <strong>Catchers</strong> <strong>in</strong> <strong>Natural</strong> <strong>Gas</strong> <strong>Production</strong><br />
position the operational and the transitional po<strong>in</strong>ts which will assist <strong>in</strong> determ<strong>in</strong><strong>in</strong>g if the flow is<br />
stratified or not. Two flow pattern maps are shown <strong>in</strong> Figures 6 and 7; the first illustrates a map for a<br />
20 <strong>in</strong>ch diameter horizontal slug catcher while the second is for a 26 <strong>in</strong>ch diameter horizontal slug<br />
catcher. The two maps show that an <strong>in</strong>creased diameter will provide a better stratification of the flow<br />
<strong>in</strong> the catcher.<br />
The volume needed to handle the enter<strong>in</strong>g liquid flow has to be decided upon after determ<strong>in</strong><strong>in</strong>g the<br />
m<strong>in</strong>imum diameter of the slug catcher. The latter has to be <strong>in</strong>creased <strong>in</strong> order to accommodate the<br />
accumulat<strong>in</strong>g liquid and avoid carryovers. The accumulat<strong>in</strong>g liquid will destabilize the flow <strong>in</strong> the<br />
catcher and stratified flow is consequently not ma<strong>in</strong>ta<strong>in</strong>ed with such a pre-determ<strong>in</strong>ed m<strong>in</strong>imum<br />
diameter. The operational liquid holdup, H oper , can be calculated by solv<strong>in</strong>g the comb<strong>in</strong>ed momentum<br />
equation for the stratified flow conditions. It depends on the liquid and gas average flow rates. The<br />
transition equation can be used to determ<strong>in</strong>e the maximum superficial liquid velocity know<strong>in</strong>g the<br />
superficial gas velocity. Thus, the transitional liquid holdup, H tran , can be calculated. The available<br />
volume to accommodate the liquid <strong>in</strong> the slug catcher is represented as the difference between the<br />
operational and the transitional liquid holdup. Thus, the length of the slug catcher for a specific<br />
diameter is calculated us<strong>in</strong>g equation (18).<br />
[ ]<br />
(18)<br />
Larger slug catcher dimensions result from such calculations due to two assumptions considered. The<br />
first consists of hav<strong>in</strong>g a lower accumulated liquid volume than what is calculated <strong>in</strong> equation (14)<br />
s<strong>in</strong>ce the liquid cont<strong>in</strong>ues to be under the gas bubbles <strong>in</strong> the liquid film dur<strong>in</strong>g production. As for the<br />
second, the liquid <strong>in</strong> the slug catcher is represented by H Loper before slug production while this amount<br />
drops as gas pockets and film are produced. The overestimation of the dimensions of the slug catcher<br />
can be considered as an advantage as it is a safety factor <strong>in</strong> production. The set of calculations is<br />
applied to one f<strong>in</strong>ger, but is valid to more than one f<strong>in</strong>ger know<strong>in</strong>g the liquid distribution among the<br />
f<strong>in</strong>gers.<br />
4.3 Components and specifications<br />
The design of the slug catcher follows a series of computational steps us<strong>in</strong>g the equations stated<br />
previously. As a first step, data from the field are required such as temperature, pressure, °API, <strong>in</strong>let<br />
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flow rates of the gas and the liquid, diameter and roughness of the pipes. Afterwards, the operational<br />
po<strong>in</strong>t is to be plotted on the flow pattern map generated for the designated diameter of the <strong>in</strong>let<br />
pipel<strong>in</strong>e to the slug catcher. The operational po<strong>in</strong>t should be <strong>in</strong> the slug flow region of the map<br />
otherwise a slug catcher is not required.<br />
The flow characteristics are also calculated us<strong>in</strong>g the equations stated previously <strong>in</strong> this paper. The<br />
time difference <strong>in</strong> the slug arrival is ma<strong>in</strong>ly determ<strong>in</strong>ed by the nature and the operat<strong>in</strong>g way of<br />
handl<strong>in</strong>g the system. Pigg<strong>in</strong>g can affect greatly the regularity of the slug emergence to the slug catcher<br />
aside from the natural slug flow. The slug catcher, <strong>in</strong> this case, should be designed based on the<br />
<strong>in</strong>terval of pigg<strong>in</strong>g, the volume of slug to be produced from each spher<strong>in</strong>g phase and a cont<strong>in</strong>gency<br />
volume. If pigg<strong>in</strong>g is not to be performed frequently, the maximum sphere-generated volume, SGV, of<br />
liquid should be determ<strong>in</strong>ed by a computer program to size the slug catcher. In normal flow, the size<br />
of the catcher, accord<strong>in</strong>g to Shell (1998), should be designed <strong>in</strong> a way to handle the difference between<br />
the volumes of the steady-state holdup generated by the fluctuat<strong>in</strong>g liquid flow <strong>in</strong> case of no pigg<strong>in</strong>g.<br />
Some complications should be accounted for <strong>in</strong> the siz<strong>in</strong>g process. For long pipes, the pigg<strong>in</strong>g<br />
activities should be controlled as to limit the size of the slug catcher s<strong>in</strong>ce the slug-sphered volumes<br />
(SGV) might be very large. There should be a comparison <strong>in</strong> the cost of hav<strong>in</strong>g a more frequent<br />
pigg<strong>in</strong>g activity and a smaller slug catcher and that of a large slug catcher with occasional pigg<strong>in</strong>g<br />
(Mokhatab, Poe, & Speight, 2006). Siz<strong>in</strong>g slug catchers with very rough elevation profiles of pipel<strong>in</strong>es<br />
needs a specific computer program to simulate the transient flow. This is due to the terra<strong>in</strong> slugs that<br />
will form. By-pass pigg<strong>in</strong>g was also considered to cut the size of the slug catcher as it reduces the rate<br />
of the slug arrival and extends the arrival period of the slug ahead of the pig (Shell, 1998).<br />
The gas and liquid flow rates head<strong>in</strong>g to the f<strong>in</strong>gers’ <strong>in</strong>let are considered <strong>in</strong> the design tak<strong>in</strong>g <strong>in</strong>to<br />
account an even distribution among the different f<strong>in</strong>gers. An even distribution is reta<strong>in</strong>ed by the use of<br />
Tee-junction shaped splitters receiv<strong>in</strong>g the <strong>in</strong>let flow perpendicularly. The splitters’ ma<strong>in</strong> function is to<br />
divide and further divide the flow <strong>in</strong>to 2, 4 and 8 equal and parallel streams go<strong>in</strong>g downwards through<br />
the runs. The runs are constantly adjusted to keep the flow velocity constant and the flow distribution<br />
equal through back pressure <strong>in</strong>duction. The <strong>in</strong>let manifold is located perpendicularly to the splitters<br />
and should be of a large diameter so that the phases are evened before proceed<strong>in</strong>g to the downcomers.<br />
Each <strong>in</strong>let manifold can take up to eight downcomers which will be mounted to a constrictor.<br />
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A constrictor guarantees a good distribution of liquid <strong>in</strong> case of SGV thus it should be m<strong>in</strong>utely<br />
designed. The appropriate constrictor design is shown <strong>in</strong> Figure 8. It has to be positioned eccentrically<br />
and close to the lower wall side of the downcomer. This will ensure a 40% reduction <strong>in</strong> the <strong>in</strong>let<br />
diameter ma<strong>in</strong>ta<strong>in</strong><strong>in</strong>g, thus, an even distribution of flow and then any jett<strong>in</strong>g effect, with the result<strong>in</strong>g<br />
mist/foam formation, will be avoided as the liquid is mov<strong>in</strong>g along the wall. With the gas expansion<br />
down the constrictor, segregation of gas and liquid takes place and will be enhanced <strong>in</strong> case of a 1:1<br />
slope of the downcomer <strong>in</strong>stead of a vertical downcomer. A 45° angle with the horizontal can be used<br />
as an optimal solution for the stratified flow.<br />
The diameter of the downcomer is usually smaller than that of the bottle so that D downcomer < 2/3 D bottle .<br />
A peculiar conical expander is located at the downcomer and bottle jo<strong>in</strong>t. The expander can either<br />
have the flat side up or the flat side down such as <strong>in</strong> the Troll field <strong>in</strong> the North Sea. A slight<br />
preference for the second is observed as the slope of the bottle is cont<strong>in</strong>uous hence the stratified flow<br />
would develop problem free. A further separation of gas and liquid will take place due to expansion.<br />
(Shell, 1998)<br />
The bottle section of the slug catcher, <strong>in</strong>clud<strong>in</strong>g primary and/or secondary bottles, an equalizer system<br />
and a liquid outlet header, is designed with the consideration of several criteria. The first section of the<br />
primary bottles encompasses the gas-liquid separation just upstream the first gas risers. The storage of<br />
liquid takes place downstream the riser. Liquid droplets as small as 600 μm or less are removed from<br />
the gas (Mokhatab et al., 2006). The distance between the riser and the conical expander should be<br />
long enough to ensure more than 99% separation efficiency. Nevertheless, it should not be too large<br />
imply<strong>in</strong>g a gas flow rate less than 2 m/s <strong>in</strong> the bottle. On the other hand, secondary bottles can only<br />
store liquids. The equalizer is used ma<strong>in</strong>ly to ensure a unified pressure <strong>in</strong> the bottles. The use of an<br />
equalizer should be very precautious as the system geometry is very sensitive. An equalizer can lead to<br />
unwanted liquid carryovers.<br />
The choice of the bottles number is very important <strong>in</strong> the design of the slug catcher. The gas flow rate<br />
<strong>in</strong> the pipel<strong>in</strong>e, the required volume of liquid storage and the length of the bottles are crucial for this<br />
choice. It should be noticed that the number of bottles should not exceed eight for flow distribution<br />
reasons but should be an even number to ma<strong>in</strong>ta<strong>in</strong> symmetry. The design should also consider the<br />
possibility for further expansion of the slug catcher along with <strong>in</strong>creas<strong>in</strong>g flow rate. The bottles have<br />
to be <strong>in</strong>cl<strong>in</strong>ed downwards to allow a smooth liquid fill<strong>in</strong>g due to gravity and gas migration to the gas<br />
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outlet system. The most heavily loaded bottle can take an additional 20% compared to an even<br />
distribution thus 120/n pb %. Stratified <strong>in</strong>flow of liquid should be ma<strong>in</strong>ta<strong>in</strong>ed <strong>in</strong> the bottles <strong>in</strong> order to<br />
avoid chocked bottles.<br />
The slope of the bottles and the slope concept beh<strong>in</strong>d the slug catcher design should be decided upon<br />
when choos<strong>in</strong>g the bottles’ number. The bottles’ angle of <strong>in</strong>cl<strong>in</strong>ation has to be determ<strong>in</strong>ed with<br />
precaution. As for the slope concepts, there are ma<strong>in</strong>ly two: the s<strong>in</strong>gle and the dual slope concepts. In<br />
the s<strong>in</strong>gle slope concept, the m<strong>in</strong>imum optimum slope for the bottles should be 1% and the maximum<br />
can reach 3%. The latter will prevent the chock<strong>in</strong>g effect of form<strong>in</strong>g. On the other hand, for the dual<br />
slope concept, the first part of the primary bottles is <strong>in</strong>cl<strong>in</strong>ed at an optimal angle, around 2.5%, that<br />
can ensure a fill<strong>in</strong>g flow rate with no chock<strong>in</strong>g effect. A smaller <strong>in</strong>cl<strong>in</strong>ation angle of 1% can be then<br />
used for the other part of the primary bottles and the secondary bottles. This approach implemented <strong>in</strong><br />
the Kollsnes process<strong>in</strong>g plant takes advantage of the liquid storage capacity of the bottles and uses it<br />
efficiently; as well, high structural designs are avoided. (Shell, 1998)<br />
The diameter of the f<strong>in</strong>gers is also crucial for the number of bottles. It is determ<strong>in</strong>ed by iterations as<br />
the diameter is kept on be<strong>in</strong>g <strong>in</strong>creased until the operat<strong>in</strong>g po<strong>in</strong>t lies <strong>in</strong> the stratified flow region. But<br />
the m<strong>in</strong>imum diameter can be accomplished when the operational po<strong>in</strong>t is superimpos<strong>in</strong>g on the<br />
transition curve between the <strong>in</strong>termittent and stratified flow regions; this po<strong>in</strong>t is called the transition<br />
po<strong>in</strong>t and is seen <strong>in</strong> figure 7. Equation (16) is used for this estimation.<br />
A closer look on the method shows the follow<strong>in</strong>g. The calculations start with a diameter similar to that<br />
of the pipel<strong>in</strong>e, then calculations are made to plot the operational po<strong>in</strong>t on the flow pattern map. As the<br />
transition po<strong>in</strong>t is reached, the m<strong>in</strong>imum diameter of the f<strong>in</strong>ger is <strong>in</strong>creased to the next commercial<br />
pipel<strong>in</strong>e diameter to ensure a stratified flow dur<strong>in</strong>g the operations. The number of f<strong>in</strong>gers used is<br />
determ<strong>in</strong>ed based on the diameter; the latter should be large enough so that more than one f<strong>in</strong>ger is<br />
used. The mostly used f<strong>in</strong>ger number is ma<strong>in</strong>ly four. Their length is calculated us<strong>in</strong>g equation (18).<br />
The weight of the slug catcher is calculated <strong>in</strong> the f<strong>in</strong>al steps of the process as it has to consider the<br />
overall components of the slug catcher. Among those are the <strong>in</strong>let header, the separation zone and both<br />
liquid and gas outlet headers. (Marquez et al., 2010)<br />
The gas outlet section should be designed <strong>in</strong> a way to ensure the optimum separation. This section<br />
<strong>in</strong>cludes the gas risers, the gas outlet headers and the gas outlets. Ensur<strong>in</strong>g a flow of gas out of the unit<br />
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is the ma<strong>in</strong> function of a gas riser along with the prevention from liquid carryovers <strong>in</strong> case of large<br />
volumes of liquid pass<strong>in</strong>g through the lower region of the riser. The risers can sometimes be used as<br />
liquid separators with high gas flow velocities. The capability of the riser <strong>in</strong> separation is based on the<br />
load factor λ, which is expressed as,<br />
√ (19)<br />
The superficial gas volume generated can be calculated from the follow<strong>in</strong>g equations,<br />
( )<br />
(20)<br />
√ (21)<br />
For large droplets with a size greater than 2 mm to setlle out of the stream, λ should be smaller or<br />
equal to 0.2 m/s. This is applied <strong>in</strong> case of pigg<strong>in</strong>g-formed slugs and when the riser is mounted <strong>in</strong> the<br />
primary bottles with a receiv<strong>in</strong>g capacity of 120/n pb %. A high gas flow should also be ma<strong>in</strong>ta<strong>in</strong>ed to<br />
avoid liquid flow from the heavily loaded bottles to the other bottles. The bottle has to be reta<strong>in</strong>ed at a<br />
m<strong>in</strong>imum height where the liquid would settle; thus, its height should be at least 5 times or 5 meteres<br />
bigger than its diameter depend<strong>in</strong>g on which value is lower. A second riser is mounted down the first<br />
one to share 20 to 30% of the gas flow and the flow is equally distributed among the two risers by the<br />
use of reducers at the top of the risers. This technique ensures a 100% carryover free and<br />
un<strong>in</strong>terrupted production even when the slug catcher is half function<strong>in</strong>g due to ma<strong>in</strong>tenance. A<br />
maximum of two risers per bottle is allowed for safe and optimal production.<br />
The gas outlet header and the gas outlet are to be designed accurately. Their diameter shouldn’t be too<br />
small as it will lead to a high pressure drop <strong>in</strong> the system. Such a pressure drop can cause an <strong>in</strong>crease<br />
<strong>in</strong> the liquid level closest to the gas outlet system compared to the other bottles. This is known as the<br />
manometer effect. Thus, it is advisable to keep a balanced pressure distribution <strong>in</strong> the system.<br />
Allow<strong>in</strong>g the gas to be released from both ends of the header or us<strong>in</strong>g a reducer for each riser may<br />
ensure such a distribution.<br />
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As for the liquid outlet, it should be of the same diameter as the bottles or m<strong>in</strong>imum 75% of it <strong>in</strong> order<br />
to be able to handle the large liquid volumes without block<strong>in</strong>g the passage. The gas carry-under is to<br />
be taken care of or avoided by hav<strong>in</strong>g the liquid outlet header lower than the lower end of the bottle.<br />
The liquid accumulation <strong>in</strong> the system should be kept as low as possible <strong>in</strong> the manifold. To do so, the<br />
two liquid dra<strong>in</strong>s are added to the system under the lower end of the bottle. Three liquid outlets per<br />
manifold should exist <strong>in</strong> the system. These have to be evenly distributed and positioned at a 45° angle<br />
from the vertical to keep a m<strong>in</strong>imum liquid accumulation. (Shell, 1998).<br />
Last of all, the control of the liquid <strong>in</strong> the slug catcher is given a great importance especially from a<br />
safety side. The presence of water and glycol, the blockage of the bottles due to sludges and the<br />
accumulation of condensed liquid can all affect the liquid level <strong>in</strong> the catcher. Pressure tapp<strong>in</strong>gs are<br />
used as control devices mounted <strong>in</strong> the liquid outlet headers to supress any <strong>in</strong>terruption caused by the<br />
sludge. The maximum allowable operat<strong>in</strong>g pressure (MAOP) <strong>in</strong> the slug catcher should be at least<br />
equal to that of the <strong>in</strong>let pipel<strong>in</strong>e. In case the MAOP of the slug catcher is decided to be lower than<br />
that of the pipel<strong>in</strong>e, an overpressure protection is then <strong>in</strong>cluded <strong>in</strong> the design. A pressure test is<br />
implemented; dur<strong>in</strong>g this test all the loads <strong>in</strong> the catcher are considered. Such loads, accord<strong>in</strong>g to Shell<br />
(1998), can be the pressure, the thermal expansion, the passage of slugs, the settelment, the<br />
environmental loads and the foundation and support reaction. (Shell, 1998)<br />
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CHAPTER 5 NORWEGIAN FIELDS AND SLUG CATCHERS<br />
This chapter will describe four different slug catchers from four different fields ly<strong>in</strong>g <strong>in</strong> the Norwegian<br />
cont<strong>in</strong>ental shelf. The Troll field is l<strong>in</strong>ked to an onshore process<strong>in</strong>g plant known as Kollsnes whereas<br />
the Heidrun field has its gas process<strong>in</strong>g activity <strong>in</strong> Tjeldbergodden methanol process<strong>in</strong>g plant. The<br />
Melkøya plant receives the gas from the Snøhvit field while the Nyhamna plant receives the gas<br />
streams from the Ormen Lange field. Follow<strong>in</strong>g that, relevant data are collected and organized <strong>in</strong> two<br />
tables, Tables 2 and 3, to allow a HYSYS simulation of the amount of liquid to be expected <strong>in</strong> the slug<br />
catcher and discuss the design.<br />
5.1 Troll and Kollsnes<br />
Statoil-owned process<strong>in</strong>g plant, Kollsnes, located 67 km west of Bergen started operations <strong>in</strong> October<br />
1996. The location of the plant made it possible to build a simpler platform than what was orig<strong>in</strong>ally<br />
planned. The gas from the Troll field is transported to the Kollsnes plant. In 2005, the gas from both<br />
Kvitebjørn and Visund fields started com<strong>in</strong>g also to the Kollsnes process<strong>in</strong>g plant. The orig<strong>in</strong>al<br />
capacity of the plant was 120 million standard cubic meters per day with the presence of 5<br />
compressors; it is now raised up to 143 million standard cubic meters per day due to the <strong>in</strong>stallation of<br />
a sixth compressor. It can also handle 69 000 barrels of <strong>Natural</strong> <strong>Gas</strong> Liquids (NGL) per day<br />
(Hydrocarbons Technology, 2012). The new plant, which can handle 26 million standard cubic meters<br />
of gas, is now able to process gas from further field developments.<br />
<strong>Natural</strong> <strong>Gas</strong> Liquid is separated from the rich gas at the Kollsnes gas plant and then sent to Mongstad<br />
ref<strong>in</strong>ery through the Vestprosess pipel<strong>in</strong>e <strong>in</strong> order to fractionate gas <strong>in</strong>to propane, butanes and naphtha.<br />
Pressurized dry gas is driven by the large compressors and transported to customers through gas<br />
trunkl<strong>in</strong>es. There are four trunkl<strong>in</strong>es: Statpipe, Zeepipe, Europipe I and Franpipe transport<strong>in</strong>g the gas<br />
to 7 cont<strong>in</strong>ental European countries: France, Netherlands, Belgium, Germany, Czech Republic,<br />
Austria and Spa<strong>in</strong>. It should be noticed that the previously listed trunkl<strong>in</strong>es do not all orig<strong>in</strong>ate from<br />
the Kollsnes plant. Along with the Kårstø process<strong>in</strong>g plant, they constitute 70% of the gas transported<br />
from Norway to Europe.<br />
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The Troll oil and gas field is located <strong>in</strong> the 31/2, 31,3, 31/5 and 31/6 blocks <strong>in</strong> the North Sea. The Troll<br />
gas is sent from the Troll A wellhead platform to the Kollsnes plant through two 36’’ gas-condensate<br />
pipel<strong>in</strong>es as a multiphase flow is be<strong>in</strong>g transported. The receiv<strong>in</strong>g term<strong>in</strong>al consists of a dual-slope<br />
multi-pipe slug catcher. The design of this slug catcher is shown <strong>in</strong> Figure 11. A general view of the<br />
two slug catchers at the Kollsnes plant are shown <strong>in</strong> Figure 12. There are two slug catcher sets which<br />
are 575 feet or 175.26 meters long. They consist of four pipe sections each with a 48 <strong>in</strong>ch diameter<br />
(Thaule & Postvoll, 1996).<br />
5.2 Heidrun and Tjeldbergodden<br />
The Heidrun field, an oil field associated with a gas cap, is located 175 km offshore the Norwegian<br />
coast. It is located at a 345 meters water depth. It is located ma<strong>in</strong>ly on the south end of the SW-NW<br />
trend<strong>in</strong>g Norland ridge and extend<strong>in</strong>g towards the less faulted Halten terrace (Mitcha et al., 1996). It is<br />
the first field where the first Tension Leg Platform (TLP) has ever been used. The gas is transported<br />
through a 250 km long 16 <strong>in</strong>ches pipel<strong>in</strong>e known as the Haltenpipe to a methanol plant,<br />
Tjeldbergodden.<br />
The Tjeldbergodden complex is located <strong>in</strong> mid-Norway, <strong>in</strong> the Aure commune between Kristiansund<br />
and Trondheim. It occupies an area of 150 hectares and is designed to handle up to 900,000 tons of<br />
methanol per year. It is ma<strong>in</strong>ly composed of four constituents: a receiv<strong>in</strong>g term<strong>in</strong>al for gas, a methanol<br />
plant, an air separation plant and a gas liquefaction plant (Statoil, 2011). It is known as the most<br />
environmentally friendly petrochemical plant. Two comb<strong>in</strong>ed techniques <strong>in</strong> handl<strong>in</strong>g and treat<strong>in</strong>g<br />
methanol were chosen with precaution; therefore, the production of carbon dioxide and nitrogen<br />
oxides per ton of methanol will be very m<strong>in</strong>imal and the energy consumption is set as the lowest <strong>in</strong> the<br />
world (Hansen, 1997).<br />
The Tjeldbergodden plant has some limitations and specifications. The plant production is limited due<br />
to a restricted production capacity of 6.3 MSm 3 /d (Gustavsen & Tøndel). The gas reaches the<br />
receiv<strong>in</strong>g term<strong>in</strong>al with an <strong>in</strong>let pressure of 50 bars compared to the normal operat<strong>in</strong>g pressure <strong>in</strong> the<br />
pipel<strong>in</strong>e which ranges between 120 and 170 bars. As for the temperature, it is <strong>in</strong>creased by 40 °C at the<br />
<strong>in</strong>let of the slug catcher.<br />
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5.3 Snøhvit and Melkøya<br />
The Snøhvit field is located <strong>in</strong> the 7120 and 7121 blocks of the Barents Sea at a 140 km distance from<br />
shore. The development of this field was the first <strong>in</strong> the Barents Sea. Several challenges were faced<br />
throughout the process especially regard<strong>in</strong>g the operation <strong>in</strong> a remote area. The reservoir, which is at a<br />
2400 meters depth, is underly<strong>in</strong>g a water depth rang<strong>in</strong>g from 250 to 340 meters. No platform of any<br />
k<strong>in</strong>d was used for operations and production, a subsea production facility was used <strong>in</strong>stead (Statoil,<br />
2012).<br />
The gas is transported from the reservoir to Melkøya through a 143 km long, 26.8 <strong>in</strong>ches pipel<strong>in</strong>e. The<br />
route followed by the pipel<strong>in</strong>e is quite rough which will cause numerous production problems such as<br />
slug formation. The elevation profile versus the length of the pipe should be determ<strong>in</strong>ed. The cold<br />
water of the Barents Sea and low temperatures at the sea floor can cause some flow assurance<br />
problems as well. Therefore, these specifics have to be accounted for <strong>in</strong> the design. Inhibitors such as<br />
MEG are also be added to the system to reduce the effect of these two previously stated factors.<br />
The Melkøya island, represented <strong>in</strong> Figure 13 with all its components, receives the gas from two other<br />
different fields, the Albatross and the Askeladd fields also located <strong>in</strong> the Barents Sea. The products<br />
generated are LNG, LPG and condensate. This made of Hammerfest the first land based LNG plant.<br />
The gas produced is then shipped to some further treat<strong>in</strong>g term<strong>in</strong>al facilities <strong>in</strong> Bilboa, Huelva and<br />
Cove po<strong>in</strong>t before be<strong>in</strong>g distributed to the European and American markets. LNG tankers are used to<br />
transport the gas <strong>in</strong>stead of the pipel<strong>in</strong>es due to the location of the field and the process<strong>in</strong>g plant with<br />
respect to the targeted markets (Pettersen J. , 2006).<br />
5.4 Ormen Lange and Nyhamna<br />
The Ormen Lange field located <strong>in</strong> the blocks 6305/4, 5, 7 and 8, 121 km north-west of the Møre coast<br />
<strong>in</strong> mid-Norway, is the second largest gas field <strong>in</strong> the Norwegian Sea (Statoil, 2012). Some<br />
geographical patterns of the area such as the well-known Storegga Slide made the transport of gas to<br />
shore challeng<strong>in</strong>g, especially that the field is ly<strong>in</strong>g with<strong>in</strong> this area and close to the steep upper<br />
headwall. The latter has a slope rang<strong>in</strong>g from 25 to 30 degrees and goes from 250 meters of water<br />
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depth at the upper end of the wall down to 500 meters at the foot (Bryna et al., 2005). The Storegga<br />
Slide is represented <strong>in</strong> Figure 14.<br />
The reservoir is located at a depth of 2013 meters and has an <strong>in</strong>itial pressure of 290 bara and an <strong>in</strong>itial<br />
temperature of 96 °C. The Ormen Lange field has a total gas flow rate of 70 MSm 3 /d and it is<br />
produc<strong>in</strong>g from 8 different wells which are located at the same distance from the PLEM. It should be<br />
mentioned that the big-bore wells of this field represent the largest wells drilled <strong>in</strong> 900 meters deep<br />
waters; they have a 9 5/8’’ tub<strong>in</strong>g size and production l<strong>in</strong>er (Biørnstad, 2006).<br />
The Ormen Lange field is tied to the Nyhamna process<strong>in</strong>g plant through two 30’’, 121 km long pipes.<br />
The pipes are not ly<strong>in</strong>g on a flat and horizontal area but they should go through the Storegga Slide<br />
area. The latter has caused many problems and additional work such as add<strong>in</strong>g around 3 million tons<br />
of rock boulders at some po<strong>in</strong>ts <strong>in</strong> order to flatten the area and provide a smoother path for the pipes.<br />
The Nyhamna plant is then export<strong>in</strong>g the gas produced to the UK through Langeled, the longest<br />
pipel<strong>in</strong>e <strong>in</strong> the world with a length of 1200 km. Energy efficiency and reduced energy emission were<br />
the basis on which the whole project has been erected.<br />
Flow assurance is one of the concerns for gas transport to the Nyhamna process<strong>in</strong>g plant. When<br />
pass<strong>in</strong>g through such a rugged seafloor with different elevations, the angles of <strong>in</strong>cl<strong>in</strong>ations of the pipes<br />
will vary greatly and thus will enhance the possibility of water accumulation and slug formation<br />
through the transport s<strong>in</strong>ce all 3 conditions of hydrate formations are present <strong>in</strong> the field <strong>in</strong> question.<br />
The Hydrate <strong>in</strong>hibition <strong>in</strong> the pipel<strong>in</strong>e is then essential; therefore, a 5/8’’ MEG <strong>in</strong>jection was <strong>in</strong>cluded<br />
<strong>in</strong> the design. 97% of the gas production accessibility of the plant is thus ensured. In addition, two<br />
symmetrical multi-pipe slug catchers of a capacity of 1500 m3 are mounted at the end of the two<br />
pipel<strong>in</strong>es. Each of the two-multi-pipe catchers is also divided <strong>in</strong>to two for ma<strong>in</strong>tenance reason. One of<br />
the two multi-pipe slug catchers is represented <strong>in</strong> Figure 15.<br />
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CHAPTER 6 HYSYS SIMULATIONS<br />
6.1 Model Setup with a close up on the Ormen Lange case<br />
Aspen HYSYS V7.3 has been used to determ<strong>in</strong>e the cont<strong>in</strong>uous amount of gas, liquid and condensate.<br />
The simulations have been implemented for the four different fields <strong>in</strong> question. Therefore, data from<br />
all the fields had to be colleted and used as <strong>in</strong>put for the simulation cases. The basis environment is<br />
built separately for every field, it <strong>in</strong>cludes all the fluid properties of that field. Afterwards, the<br />
flowsheet is built <strong>in</strong> order to connect the streams and the <strong>in</strong>put data together. Many simplifications<br />
have been assumed due to the lack of accurate <strong>in</strong>formation.<br />
Ormen Lange is one of the fields to be <strong>in</strong>vestigated. As a first step, the composition of the field has to<br />
be determ<strong>in</strong>ed <strong>in</strong> order to provide the simulator with the make up of the gas be<strong>in</strong>g <strong>in</strong>vestigated. The<br />
Peng-Rob<strong>in</strong>son fluid package was chosen for the analysis. The model is attributed to a steady-state<br />
model which also reflects a simplified aspect of the model. For further simplifications, all wells and<br />
templates are also assumed to be symmetric <strong>in</strong> position and capacity.<br />
Wet gas has to be ensured <strong>in</strong> the reservoir and <strong>in</strong> its representation <strong>in</strong> the model. To do so, the<br />
reservoir gas stream has to be associated with a stream of water. These two are led to a simple vertical<br />
separation to extract the vapor phase which is used as the ma<strong>in</strong> reservoir stream. The <strong>in</strong>itial reservoir<br />
conditions were specified <strong>in</strong> both the reservoir stream and the water stream. The reservoir temperature<br />
is 96 °C and the reservoir pressure is 290 bars. The setup of the field model is shown <strong>in</strong> Figure 16.<br />
The water flow rate has to be determ<strong>in</strong>ed with precision. This is calculated by the water solubility r sw<br />
which is given <strong>in</strong> Kg/MSm 3 . A VBA has been prepared for that purpose where water mole fraction <strong>in</strong><br />
methane and the water mole fraction <strong>in</strong> gas are calculated to get to the water solubility. The <strong>in</strong>puts to<br />
the VBA are the <strong>in</strong>itial pressure and temperature, the gas gravity and the water sal<strong>in</strong>ity. The gas<br />
gravity <strong>in</strong> the case of the Ormen Lange is 0.6 as for the sal<strong>in</strong>ity, it is assumed to be zero ppm. The<br />
water mass rate, which is 1441 Kg/h, is obta<strong>in</strong>ed from the water solubility and the gas flow rate. It<br />
should be noticed that no formation water is produced at the early stages of production.<br />
The flow rate is one of the ma<strong>in</strong> and essential parameters to be <strong>in</strong>cluded <strong>in</strong> the model as it affects the<br />
model’s performance to a great extent. The total gas flow rate of the field is 70 MSm 3 /d that are<br />
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produced from 8 different wells positioned symmetrically away from the PLEM. Two 30’’ pipel<strong>in</strong>es<br />
transport the gas from the PLEM to the receiv<strong>in</strong>g term<strong>in</strong>als onshore.<br />
To simplify and due to symmetry, halv<strong>in</strong>g the wells and the pipel<strong>in</strong>es can be used as a simplification<br />
accord<strong>in</strong>g to Christiansen (2012) and Heskestad (2004). One well was enough to represent the flow<br />
through the wells. Therefore, the flow rate is divided by the number of wells which is thus 8.75<br />
MSm 3 /d. The pressure drop <strong>in</strong> the reservoir, which is around 30 bars, was accounted for through a<br />
graph shown by Christiansen (2004). This pressure drop can be represented <strong>in</strong> the model through a<br />
valve.<br />
The Ormen Lange well is known as the Big Bore Well. It is a 9 5/8’’ tub<strong>in</strong>g well with 8.5’’ <strong>in</strong>ner<br />
diameter. It is not a vertical well. On the contrary, it has four different sections that are represented <strong>in</strong><br />
a well elevation profile shown <strong>in</strong> the Figure 17. It can handle the largest production rates <strong>in</strong> the world<br />
and then can reduce the need for wells for the same production.<br />
As a next step, the flow will enter the pipel<strong>in</strong>e pass<strong>in</strong>g first through a wellhead choke. The two 30’’<br />
pipel<strong>in</strong>es are 121 km long each with an <strong>in</strong>ner diameter of 27.17’’. They are ly<strong>in</strong>g on the irregular and<br />
rough seafloor; therefore, a pipel<strong>in</strong>e elevation profile is needed. It was taken from Christiansen’s paper<br />
(2012) and then digitized <strong>in</strong> HYSYS. The elevation profile to be digitized is represented <strong>in</strong> Figures<br />
18while the digitized profile is shown <strong>in</strong> Figures 19. The wellhead choke should handle a pressure<br />
drop that will ensure the operational <strong>in</strong>let pressure to the pipel<strong>in</strong>e which is around 150 bars.<br />
The next spot to which the flow is head<strong>in</strong>g to is located at the receiv<strong>in</strong>g term<strong>in</strong>al. The slug catcher is<br />
the first equipment to handle the arriv<strong>in</strong>g flow. It is represented by a simple separator <strong>in</strong> the model. It<br />
has a specific <strong>in</strong>let pressure of 90 bars. A choke will be responsible for ensur<strong>in</strong>g a pressure drop<br />
correspond<strong>in</strong>g to the appropriate <strong>in</strong>let pressure. As operations are carried on, the <strong>in</strong>let pressure will be<br />
reduced to75 bars as production rate will decl<strong>in</strong>e to 60 MSm 3 /d (Gupta, 2012).<br />
An expected problem <strong>in</strong> the pipel<strong>in</strong>e system is the formation of slugs. HYSYS allows the detection of<br />
such a h<strong>in</strong>drance; the slug detection should be activated <strong>in</strong> the model. This is done simply by tick<strong>in</strong>g<br />
the ‘Do <strong>Slug</strong> Calculations’ option. The results are then displayed show<strong>in</strong>g the slug position, the status,<br />
slug length, the bubble length, the film holdup, the slug frequency, the velocity and the pressure<br />
gradient. A sample of the results is shown <strong>in</strong> Figure 20.<br />
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6.2 MEG Injection to the model<br />
<strong>Slug</strong> formation <strong>in</strong> the pipel<strong>in</strong>es needs to be <strong>in</strong>hibited. To do so, slug or hydrate <strong>in</strong>hibitors are used. The<br />
most common <strong>in</strong>hibitors used <strong>in</strong> the <strong>in</strong>dustry are Mono-Ethylene Glycol also known as MEG and<br />
Methanol also known as MeOH. For the Ormen Lange field, the <strong>in</strong>hibitor applied is the MEG as it is<br />
easier to regenerate and re-<strong>in</strong>ject. It is <strong>in</strong>jected at the wellhead through two 6’’umbilicals. Only one of<br />
the two umbilicals is used for <strong>in</strong>jection while the second is a spare one.<br />
The amount of MEG to be <strong>in</strong>jected has to be determ<strong>in</strong>ed beforehand. In his book Hydrate Eng<strong>in</strong>eer<strong>in</strong>g,<br />
Sloan has enclosed a CD that helps <strong>in</strong> the calculation of the amount of MEG or MeOH needed by<br />
simply enter<strong>in</strong>g a couple of parameters. By do<strong>in</strong>g so, the amount of MEG needed <strong>in</strong> this particular<br />
case is 746.7 Kg/h; the MEG is <strong>in</strong>jected with water at a 49 wt.%.<br />
The MEG’s use is <strong>in</strong>tended for the <strong>in</strong>hibition of slugs <strong>in</strong> the pipel<strong>in</strong>es. This effect can be tested by the<br />
analysis of the data provided by the slug option present <strong>in</strong> the simulator. The results have shown that<br />
the MEG is reduc<strong>in</strong>g the length of the slug and the bubble as well as the film holdup and the pressure<br />
gradient. On the other hand, the velocity and the length ratio S/B are both <strong>in</strong>creased due to the smaller<br />
length of the slugs.<br />
The same analysis was applied for the Snøhvit field for both cases. Many simplifications were made<br />
due to the lack of all the needed <strong>in</strong>formation to build the model. The elevation profile of the pipel<strong>in</strong>e<br />
was available along with the gas composition. The elevation profile and the digitized elevation profile<br />
of the flowl<strong>in</strong>e are shown <strong>in</strong> Figures 21 and 22, respectively. The well elevation profile was not found,<br />
thus a similar profile of the Ormen Lange was used with a smaller ID (assum<strong>in</strong>g 5 ½’’ production<br />
tub<strong>in</strong>g). The wells <strong>in</strong> Snøhvit are not equally distant from the PLEM, but for simplification, all the<br />
wells are assumed to be at an equal distance. The elevation profile of the Troll flowl<strong>in</strong>e was also<br />
available and is shown <strong>in</strong> Figure 23. As for the wells, they are equally spaced and were assumed to be<br />
similar <strong>in</strong> profile to that of the Ormen Lange except for the smaller ID.<br />
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CHAPTER 7 DISCUSSION<br />
<strong>Slug</strong> formation constitutes one of the major concerns for gas transport from offshore to onshore<br />
facilities. Several conditions <strong>in</strong>duce their formation. High velocity <strong>in</strong> pipel<strong>in</strong>ees would cause a<br />
turbulence and a plug or slug flow regime, <strong>in</strong>creas<strong>in</strong>g thus the tendency of slugs to form. Irregular<br />
bathymetry challenges the eng<strong>in</strong>eer as the pipel<strong>in</strong>es would be follow<strong>in</strong>g the sea floor elevations. <strong>Slug</strong><br />
formation is very sensitive to the angle of <strong>in</strong>cl<strong>in</strong>ation: a change of less than 1° would <strong>in</strong>duce slug<br />
formation <strong>in</strong> significant amounts. The reservoir gas is usually saturated with water; this is another<br />
aspect that enhances slugs <strong>in</strong> horizontal conduits.<br />
Suppression of slug formation is one of the ma<strong>in</strong> flow assurance duties. The <strong>in</strong>jection of <strong>in</strong>hibitors as<br />
MEG and the erection of buffer volumes at the receiv<strong>in</strong>g term<strong>in</strong>als reduce the <strong>in</strong>tensity of slugs. The<br />
buffer volumes also known as slug catchers should be sized <strong>in</strong> a way to handle the largest slug<br />
expected to be formed. Therefore, they should be designed as accurately as possible. Counter-current<br />
flow forms another challenge to be delt with <strong>in</strong> multiphase flow; gravity pulls the heavier component<br />
of the two-phase flow downwards <strong>in</strong> an upward conduit which makes it difficult to predict velocities.<br />
The latter has a great <strong>in</strong>fluence <strong>in</strong> the calculations beh<strong>in</strong>d the slug catcher design.<br />
The slug catchers are found <strong>in</strong> three different types. The vessel type and the multi-pipe type are the<br />
mostly common <strong>in</strong> the <strong>in</strong>dustry. For the fields <strong>in</strong> question, multi-pipe type was chosen due to the<br />
feasibility of the model along with its capacity to handle the slugs with a volume greater than 100 m 3 .<br />
S<strong>in</strong>ce the fields apply to the latter condition, this type of catcher was selected regardless of the ability<br />
of the vessel type to separate particles as small as 10 microns.<br />
Moreover, the f<strong>in</strong>ger type catcher can be designed with either a s<strong>in</strong>gle slope or a dual slope concept.<br />
The latter uses two different <strong>in</strong>cl<strong>in</strong>ation angles of the bottles which prevent chok<strong>in</strong>g effets and makes<br />
efficient use of its liquid storage capacity. Symmetrical systems are essential for the design as they<br />
might reduce the liquid load when it comes to more than one pipel<strong>in</strong>e and/or slug catcher; similarily, it<br />
ensures cont<strong>in</strong>uous production <strong>in</strong> case of ma<strong>in</strong>tenance or pigg<strong>in</strong>g activities.<br />
Liquid accumulation volume and f<strong>in</strong>gers’ length constitute two important parameters to be determ<strong>in</strong>ed<br />
with precision when it comes to the design of the slug catcher. The difficulty faced <strong>in</strong> the design is<br />
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ma<strong>in</strong>ly due to the <strong>in</strong>ability to determ<strong>in</strong>e m<strong>in</strong>utely the velocity and the flow regime under which the<br />
pipe is operat<strong>in</strong>g especially as counter-current flow is frequent and unpredictable <strong>in</strong> mltiphase flow.<br />
The diameter of the f<strong>in</strong>gers is determ<strong>in</strong>ed at a m<strong>in</strong>imum to ensure a stratified flow and then <strong>in</strong>creased<br />
to ma<strong>in</strong>ta<strong>in</strong> the same flow regime at the <strong>in</strong>let of the buffer. Similarily, a downward <strong>in</strong>cl<strong>in</strong>ation of the<br />
f<strong>in</strong>gers ensure a stratified flow.<br />
The dimensions of the slug catcher, based on the method stated <strong>in</strong> this paper, might be larger than<br />
needed. This is due the volume of accumulated liquid assumed to be lower than the calculated volume<br />
as the liquid keeps on be<strong>in</strong>g under the gas bubbles <strong>in</strong> the liquid film dur<strong>in</strong>g production. The<br />
operational liquid holdup used is the one prior to production while <strong>in</strong> reality this value is lower due to<br />
gas pockets and film production. Nevertheless, an overestimation of the slug catcher can be considered<br />
as a safety factor for production. The calculations are also flexible and can be applied to more than one<br />
f<strong>in</strong>ger as long as symmetry is ma<strong>in</strong>ta<strong>in</strong>ed.<br />
HYSYS simulator has been used to generate models reflect<strong>in</strong>g the amount of gas, water and<br />
condensates. The models are not reliable due to the numerous simplifications assumed and the<br />
difficulty <strong>in</strong> simulat<strong>in</strong>g multiphase flow. Multiphase flow is accurately represented by the OLGA<br />
simulator which was not available <strong>in</strong> the HYSYS package I have been us<strong>in</strong>g due to a limited license.<br />
The simplified HTFS homogeneous flow correlation has been used for pipe and well calculations.<br />
Many of the <strong>in</strong>put data were also assumed due to the lack of <strong>in</strong>formation which makes it difficult to<br />
create a model operat<strong>in</strong>g as the real field. The steady state flow is assumed throughout the entire<br />
production.<br />
Ormen Lange model is the most accurate model among the four fields due to the availability of data<br />
and due to symmetry <strong>in</strong> the field design which makes its model<strong>in</strong>g precise. As for the rest, either some<br />
of the ma<strong>in</strong> <strong>in</strong>put data such as the elevation profiles were miss<strong>in</strong>g or the wells are not located<br />
symmetrically or at the same distance from the PLEM. Further assumptions regard<strong>in</strong>g those two<br />
matters made it hard to rely on the HYSYS outcome.<br />
The slug option provided by the HYSYS has shown that some of the results have been affected by the<br />
<strong>in</strong>jection of the MEG and the length of the bubbles as well as that of the slug were reduced. The<br />
amount of MEG <strong>in</strong>jected based on the sheet provided by the Hydrate Eng<strong>in</strong>eer<strong>in</strong>g book was 49 wt%<br />
which is lower than what is currently used <strong>in</strong> the field (~ 60 wt%). This is ma<strong>in</strong>ly due to the <strong>in</strong>puts to<br />
the sheet which are taken from the HYSYS simulator. Furthermore, the volume of water expected to<br />
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form <strong>in</strong> th field is higher, hence a higher percentage of MEG is required. Similarily, the volume of the<br />
liquid to be expected at the slug catcher was estimated by HSYSYS as around 1300 bbl/d which is<br />
way smaller than the size of the slug catcher at the receiv<strong>in</strong>g term<strong>in</strong>al.<br />
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CHAPTER 8 CONCLUSION<br />
<strong>Slug</strong> formation has raised the concern of eng<strong>in</strong>eers when it comes to gas transport from remote and<br />
deep sea templates to shore facilities. <strong>Slug</strong> tends to form as the flow velocity is <strong>in</strong>creased and the flow<br />
is ly<strong>in</strong>g <strong>in</strong> the slug flow regime region. A small pipel<strong>in</strong>e diameter would lead to the same problem.<br />
The irregular and rough sea bed causes some low ly<strong>in</strong>g areas <strong>in</strong> the pipel<strong>in</strong>es where the liquid might<br />
accumulate; additionally, a small variation <strong>in</strong> the angle of <strong>in</strong>cl<strong>in</strong>ation would lead to a change <strong>in</strong> the<br />
flow regime dom<strong>in</strong>at<strong>in</strong>g the pipes.<br />
<strong>Slug</strong> catchers are facilities used for handl<strong>in</strong>g the slug formed from the production of a multiphase<br />
pipel<strong>in</strong>e along with the use of the MEG <strong>in</strong>hibitor. Multi-pipe slug catchers are frequently used <strong>in</strong> the<br />
<strong>in</strong>dustry due to the ease of manipulation of the f<strong>in</strong>gers and to the ability to handle large volumes of<br />
slugs which is the case for all the fields under <strong>in</strong>vestigation. S<strong>in</strong>gle and dual slope concept can be<br />
applied to this type of the catchers; thus, the choice of the concept will be costumed to every field.<br />
Several parameters contribute to the design of the slug catcher. The diameter of the pipel<strong>in</strong>e should be<br />
designed first at the m<strong>in</strong>imal diameter size and then <strong>in</strong>creased to ma<strong>in</strong>ta<strong>in</strong> a stratified flow at the <strong>in</strong>let<br />
of the buffer. The liquid accumulation volume along with the length of the f<strong>in</strong>gers and their <strong>in</strong>cl<strong>in</strong>ation<br />
are essential for determ<strong>in</strong><strong>in</strong>g an accurate and optimal size and design of the slug catcher. The<br />
calculations might lead to a larger size of the slug catcher which may be considered as a safety marg<strong>in</strong>.<br />
<strong>Gas</strong>, liquid and condensate volumes were estimated by the HYSYS simulator. The model for the<br />
Ormen Lange is the most accurate among the four fields <strong>in</strong> question due to the availability of <strong>in</strong>put<br />
data. Regardless that, the numbers estimated were too low compared to the real data because of the<br />
simplified model where a steady state flow was presumed throughout the production. A homogeneous<br />
flow was assumed as well s<strong>in</strong>ce the license that was <strong>in</strong> hand does not support the OLGA multiphase<br />
simulator which gives a more detailed and accurate analysis.<br />
The suitability of the current designs of the slug catchers is hard to be critically discussed due to the<br />
<strong>in</strong>accuracy <strong>in</strong> the model<strong>in</strong>g of the fields <strong>in</strong> HYSYS. Similarly, the data available regard<strong>in</strong>g the sizes of<br />
the slug length enter<strong>in</strong>g the slug catcher was scarce or unavailable. But most of the slug catchers were<br />
designed based on the multi-pipe model with complete symmetry. This is favored due to the reasons<br />
stated earlier.<br />
Page 32 of 56
CHAPTER 9 NOMENCLATURE<br />
Karam – <strong>Slug</strong> <strong>Catchers</strong> <strong>in</strong> <strong>Natural</strong> <strong>Gas</strong> <strong>Production</strong><br />
Nomenclature<br />
A = Cross-sectional area, m 2<br />
c = Bubble velocity proportionality constant<br />
C = Wave velocity<br />
D = Diameter<br />
f s = <strong>Slug</strong> frequency, slugs/s<br />
g = Gravitational acceleration, m/s 2<br />
h = Height, m<br />
Subscripts<br />
accum = Accumulation<br />
CL = Constant Liquid<br />
d = Drift<br />
dis = Discharge<br />
F = Film zone<br />
G = <strong>Gas</strong><br />
Gtran = <strong>Gas</strong> transition<br />
H LLS or E S = Liquid holdup <strong>in</strong> the slug zone<br />
hor = Horizontal<br />
H LTB = Liquid holdup <strong>in</strong> the film (Taylor-Bubble) zone<br />
<strong>in</strong>s = Instantaneous<br />
K V = Coefficient of stability<br />
IV = Invicid<br />
̅ Average length, m L = Liquid<br />
L = Length, m<br />
m = Mixture<br />
m = Number of risers per bottle<br />
max = Maximum<br />
n = Number of bottles<br />
oper = Operational<br />
q = Flow rate, m 3 /s<br />
Re = Reynolds number<br />
t = time, s<br />
v = Velocity, m/s<br />
V = Volume, m 3<br />
Greek Letters<br />
α = <strong>Gas</strong> void fraction<br />
θ = Incl<strong>in</strong>ation angle, degree<br />
ρ = Density, Kg/m 3<br />
λ = Load factor or volumetric fraction of liquid <strong>in</strong><br />
two-phase flow , m/s<br />
p = Pipe<br />
pb = Primary bottle<br />
S = <strong>Slug</strong> zone<br />
SG = Superficial gas<br />
SL = Superficial liquid<br />
t = Translational<br />
U = <strong>Slug</strong> Unit<br />
ver = Vertical<br />
V = Viscous<br />
Page 33 of 56
Karam – <strong>Slug</strong> <strong>Catchers</strong> <strong>in</strong> <strong>Natural</strong> <strong>Gas</strong> <strong>Production</strong><br />
CHAPTER 10 WORKS CITED<br />
Hydrocarbons Technology. (2012). Retrieved from Kollsnes <strong>Gas</strong> Process<strong>in</strong>g Plant, Norway:<br />
http://www.hydrocarbons-technology.com/projects/kollsnes-gas/<br />
Actis, S., Smith, K., & Chenier, D. N. (1993). Plann<strong>in</strong>g and Start-Up of the Heidrun TLP Predrill<strong>in</strong>g Program.<br />
Society of Petroleum Eng<strong>in</strong>eers.<br />
Albrechtsen, R., & Sletfjerd<strong>in</strong>g, E. (2003). Full-scale Multiphase Flow Tests In the Troll Pipel<strong>in</strong>es. PSIG Annual<br />
Meet<strong>in</strong>g, Bern, Switzerland.<br />
Azzopardi, B. (2010). Multiphase Flow-Vol 1. Chemical Eng<strong>in</strong>eer<strong>in</strong>g And Chemical Process Technology.<br />
Bai, Y., & Bai, Q. (2010). In Subsea Structural Eng<strong>in</strong>eer<strong>in</strong>g Handbook (pp. 389-390).<br />
Bakker, A. (2005). Lecture 14 - Multiphase Flows: Applied Computational Fluid Dynamics.<br />
Barnea, D., & Taitel, Y. (1993). A Model for <strong>Slug</strong> Length Distribution <strong>in</strong> <strong>Gas</strong>-Liquid <strong>Slug</strong> Flow. International<br />
Journal of Multiphase Flow, 19, 829-838.<br />
Biørnstad, C. (2006). Ormen Lange og Langeled. Naturgassfaget på <strong>NTNU</strong>.<br />
Bolle, L. (n.d.). Troll Field-Norway's Giant Offshore <strong>Gas</strong> Field.<br />
Bratland, O. (2010). Introduction. Retrieved from The Flow Assurance Site.<br />
Bryna, P., Berga, K., Forsbergb, C. F., Solheimb, A., & Kvalstada, T. J. (2005). Expla<strong>in</strong><strong>in</strong>g the Storegga Slide.<br />
Mar<strong>in</strong>e and Petroleum Geology.<br />
Christiansen, H. E. (2012). Rate of Hydrate Inhibitor <strong>in</strong> Long Subsea Pipel<strong>in</strong>es.<br />
ConocoPhillips. (n.d.). Norway. Retrieved from ConocoPhillips:<br />
http://www.conocophillips.com/EN/about/worldwide_ops/europe/Pages/Norway.aspx<br />
Contreras, M. A., & Foucart, N. (2007). Selection <strong>Slug</strong> Catcher Type. SPE.<br />
Cook, M., & Behnia, M. (1999). <strong>Slug</strong> length prediction <strong>in</strong> near horizontal gas-liquid <strong>in</strong>termittent flow. School of<br />
Mechanical and Manufactur<strong>in</strong>g Eng<strong>in</strong>eer<strong>in</strong>g, University of New South Wales, Australia.<br />
Corrad<strong>in</strong>i, M. L. (1997, August 4). Wiscons<strong>in</strong> Institute of Nuclear Systems. Retrieved from Fundamentals of<br />
Multiphase Flow: http://w<strong>in</strong>s.engr.wisc.edu/teach<strong>in</strong>g/mpfBook/ma<strong>in</strong>.html<br />
Feesa. (2003). Hydrodynamic <strong>Slug</strong> Size <strong>in</strong> Multiphase Pipel<strong>in</strong>es. Feesa Ltd Case Study.<br />
Page 34 of 56
Karam – <strong>Slug</strong> <strong>Catchers</strong> <strong>in</strong> <strong>Natural</strong> <strong>Gas</strong> <strong>Production</strong><br />
Golan, M. (2012). Exercise Set 6-Field Process<strong>in</strong>g. TPG4230-Field Development . Retrieved from<br />
https://files.itslearn<strong>in</strong>g.com/File/Download/GetFile.aspx?FileName=Ex+set+6-<br />
2012.pdf&Path=kKg0zGiHdYtVzUwAHgoFdhz7ABu7nTWQFGwBaqTL1jl3D1WoVbezcdEGcngkzMYE%2b<br />
U2VhDLUTQNJWs9%2bgribGInewMaaKvhsyZ0TfwEF9IkxdrLtkJ%2fehwy10UtQih4J4YMsg%2ff3rqL529<br />
obw4%2bhPThZuSV8<br />
Gustavsen, Ø., & Tøndel, P. (n.d.). <strong>Production</strong> Optimization us<strong>in</strong>g Automatic Control at Heidrun. StatoilHydro.<br />
Hansen, R. (1997). Comb<strong>in</strong>ed Reform<strong>in</strong>g For Methanol <strong>Production</strong>. 15th World Petroleum Congress.<br />
Madsen, T. (1997). The Troll Oil Development: One Billion Barrels of Oil Reserves Created Through Advanced<br />
Well Technology. 15th World Petroleum Congress.<br />
Marquez, J., Manzanilla, C., & Trujillo, J. (2009). <strong>Slug</strong> Catcher Conceptual Design as Separator for Heavy Oil.<br />
SPE.<br />
Marquez, J., Manzanilla, C., & Trujillo, J. (2010). A conceptual Study of F<strong>in</strong>ger-Type <strong>Slug</strong> Catcher for Heavy Oil<br />
Fields. SPE.<br />
Mitcha, J. J., Morrison, C., & De Oliveira, J. (1996). The Heidrun Field - Development Overview. OTC.<br />
Miyoshi, M., Doty, D., & Schmidt, Z. (1988). <strong>Slug</strong>-Catcher Design for Dynamic <strong>Slug</strong>g<strong>in</strong>g <strong>in</strong> an Offshore<br />
<strong>Production</strong> Facility. SPE Prod Eng 3.<br />
Mokhatab, S., Poe, W. A., & Speight, J. G. (2006). In Handbook of <strong>Natural</strong> <strong>Gas</strong> Transmission and Process<strong>in</strong>g (pp.<br />
221-223).<br />
<strong>Natural</strong><strong>Gas</strong>.org. (2011). Background. Retrieved from <strong>Natural</strong><strong>Gas</strong>.org:<br />
http://www.naturalgas.org/overview/background.asp<br />
Patel, R. J. (2007). <strong>Slug</strong> Catcher Inspection Us<strong>in</strong>g The Large Structure Inspection. 4th Middle East NDT<br />
Conference and Exhibition, K<strong>in</strong>gdom of Bahra<strong>in</strong>,.<br />
Pettersen, J. (2006). Hammerfest LNG (Snøhvit).<br />
Pettersen, J. (2011). Snøhvit Field Development.<br />
Sarica, C., Shoham, O., & Brill, J. (1990). A New Approach for F<strong>in</strong>ger Storage <strong>Slug</strong> Catcher Design. OTC.<br />
Scott, S. L., Shoham, O., & Brill, J. P. (1989). Prediction of <strong>Slug</strong> Length <strong>in</strong> Horizontal, Large-Diameter Pipes.<br />
Shell. (1998). Design of Multiple-Pipe <strong>Slug</strong> <strong>Catchers</strong> (Manual).<br />
Shell. (2012). Shell. Retrieved from Ormen Lange - Facts and figures:<br />
http://www.shell.no/home/content/nor/products_services/ep/ormenlange/en/facts/<br />
Shoham, O. (2000). Two-Phase Flow Model<strong>in</strong>g. Thesis. Department of Petroleum Eng<strong>in</strong>eer<strong>in</strong>g, University of<br />
Tulsa, Oklahoma.<br />
Page 35 of 56
Karam – <strong>Slug</strong> <strong>Catchers</strong> <strong>in</strong> <strong>Natural</strong> <strong>Gas</strong> <strong>Production</strong><br />
Statoil. (2007, September 18). Statoil. Retrieved from Kollsnes gas process<strong>in</strong>g plant:<br />
http://www.statoil.com/en/OurOperations/Term<strong>in</strong>alsRef<strong>in</strong><strong>in</strong>g/ProcessComplexKollsnes/Pages/default<br />
.aspx<br />
Statoil. (2007, September 29). Statoil. Retrieved from Troll <strong>Gas</strong>s :<br />
http://www.statoil.com/no/OurOperations/ExplorationProd/ncs/troll/Pages/Troll<strong>Gas</strong>.aspx<br />
Statoil. (2011, August 10). Tjeldbergodden <strong>in</strong>dustrial complex. Retrieved from Statoil:<br />
http://www.statoil.com/en/OurOperations/Term<strong>in</strong>alsRef<strong>in</strong><strong>in</strong>g/Tjeldbergodden/Pages/default.aspx<br />
Statoil. (2012, March 27). Ormen Lange. Retrieved from Statoil:<br />
http://www.statoil.com/en/OurOperations/ExplorationProd/partneroperatedfields/OrmenLange/Pag<br />
es/default.aspx<br />
Statoil. (2012, August 10). Snøhvit. Retrieved from Statoil:<br />
http://www.statoil.com/en/OurOperations/ExplorationProd/ncs/snoehvit/Pages/default.aspx<br />
Taitel, Y., & Barnea, D. (1990). Two Phase <strong>Slug</strong> Flow. In Advances <strong>in</strong> Heat Transfer (pp. Vol 20, 83-132).<br />
Academic Press.<br />
Thaule, S. B., & Postvoll, W. (1996). Experience with Computational Analyses of the Norwegian <strong>Gas</strong> Transport<br />
Network. PSIG.<br />
Time, R. (2011). Flow Assurance and Multiphase Flow. Sem<strong>in</strong>ar at Aker Solutions.<br />
Valberg, T. (2005). Temperature Calculations <strong>in</strong> <strong>Production</strong> and Injection Wells.<br />
Walveribne Tube Inc. (2007). Chapter 12 Two-Phase Flow Patterns. In Eng<strong>in</strong>eer<strong>in</strong>g Data Book III (pp. 3-4).<br />
Page 36 of 56
CHAPTER 11 TABLES<br />
Karam – <strong>Slug</strong> <strong>Catchers</strong> <strong>in</strong> <strong>Natural</strong> <strong>Gas</strong> <strong>Production</strong><br />
Table 1: The different slug catcher characteristics of both the f<strong>in</strong>ger type and the vessel type (Contreras & Foucart,<br />
2007)<br />
<strong>Slug</strong> Catcher Characteristics<br />
F<strong>in</strong>ger Type<br />
Economical way to catch large slugs<br />
Gives predictable particle separation <strong>in</strong> the 50<br />
micron and up sizes<br />
Predictable separation up to tens of thousands of<br />
barrels slug size<br />
Shipp<strong>in</strong>g <strong>in</strong> pieces for field assembly with l<strong>in</strong>e<br />
pipe<br />
When slug size is large enough to justify the<br />
logistics of field assembly, and B31.8 type<br />
construction allowed, the harp type<br />
separator/slug catcher will be considerably<br />
cheaper than vessels<br />
Vessel Type<br />
Can give small particle separation (10 microns)<br />
where there is liquid and lower gas flow<br />
It is possible to be used as a three-phase<br />
separator<br />
Becomes expensive and heavy when large sizes<br />
are required<br />
When the slug size is up to 5-700 bbl., the<br />
separation performance is good<br />
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Karam – <strong>Slug</strong> <strong>Catchers</strong> <strong>in</strong> <strong>Natural</strong> <strong>Gas</strong> <strong>Production</strong><br />
Table 2: Data from the reservoir and the pipel<strong>in</strong>es of the four different fields<br />
Process<strong>in</strong>g<br />
Plant<br />
Field<br />
Start<strong>in</strong>g<br />
<strong>Production</strong><br />
date<br />
Water<br />
Depth<br />
Reservoir<br />
depth<br />
Distance<br />
to the<br />
field<br />
Pipel<strong>in</strong>e<br />
number<br />
Pipel<strong>in</strong>e<br />
OD<br />
Pipel<strong>in</strong>e<br />
OD<br />
Pipel<strong>in</strong>e<br />
ID<br />
Pipel<strong>in</strong>e<br />
ID<br />
[-] [-] [-] [m] [m] [km] [-] [<strong>in</strong>] [mm] [<strong>in</strong>] [mm]<br />
Kollsnes Troll 19/09/1995 350 1400 67 2 36 914.4 35.5 901.7<br />
Heidrun 18/10/1995 345 2300 250 1 16 406.4 14.95 379.8<br />
Melkøya Snøhvit 21/08/2007 250-340 2400 143 1 26.8 680.7 25.80 655.3<br />
Nyhamna<br />
Ormen<br />
Lange<br />
13/09/2007 800-1100 2013 121 2 30 762.0 27.17 690.0<br />
Process<strong>in</strong>g<br />
Plant<br />
Table 3: Data related to the wells and the slug catchers collected for the four different fields (* numbers close to real data)<br />
Field<br />
Field<br />
Flow<br />
Rate<br />
Number<br />
of Wells<br />
Well<br />
Flow<br />
Rate<br />
<strong>Slug</strong><br />
Catcher<br />
Capacity<br />
<strong>Slug</strong><br />
Catcher<br />
Capacity<br />
Page 38 of 56<br />
Number<br />
of <strong>Slug</strong><br />
Catcher<br />
<strong>Slug</strong><br />
Catcher<br />
Total<br />
Capacity<br />
<strong>Slug</strong><br />
Catcher<br />
Total<br />
Capacity<br />
Pipel<strong>in</strong>e<br />
Outlet<br />
Pressure<br />
Pressure<br />
Inlet to<br />
<strong>Slug</strong><br />
catcher<br />
Temperature<br />
Inlet to <strong>Slug</strong><br />
catcher<br />
[-] [-] [MSm 3 /d] [-] [MSm 3 /d] [m 3 ] [ft 3 ] [-] [m 3 ] [ft 3 ] [bar] [bar] [°C]<br />
Kollsnes Troll 100 39 2.56 1250 44150 2 2500 88300 90 ~120 5 – 8*<br />
Tjeldbergodden<br />
Tjeldbergodden<br />
Heidrun 11 10 1.10 2300* 81236 1 2300 81236 120-170<br />
Melkøya Snøhvit 20.8 9 2.31 2800 98896 1 2800 98896 120-90*<br />
Nyhamna<br />
Ormen<br />
Lange<br />
50 (30-<br />
50)<br />
75 (70-<br />
90)<br />
<strong>in</strong>crease of 40<br />
(-5) - (4)<br />
70 8 8.75 1500 52980 2 3000 105960 110-95* 90 2 – 4
Karam – <strong>Slug</strong> <strong>Catchers</strong> <strong>in</strong> <strong>Natural</strong> <strong>Gas</strong> <strong>Production</strong><br />
CHAPTER 12 FIGURES<br />
Figure 1: The six different flow patterns that form depend<strong>in</strong>g on the flow speed <strong>in</strong> the channel. (Aker Solution,<br />
2011)<br />
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Karam – <strong>Slug</strong> <strong>Catchers</strong> <strong>in</strong> <strong>Natural</strong> <strong>Gas</strong> <strong>Production</strong><br />
Figure 2: The slug formation process <strong>in</strong> three steps start<strong>in</strong>g with the Kelv<strong>in</strong>-Helmholtz Wave Growth, then by a<br />
slug nose <strong>in</strong>gress and tail shedd<strong>in</strong>g to gas entrapment (Feesa, 2003)<br />
Figure 3: The effect of pipel<strong>in</strong>e <strong>in</strong>cl<strong>in</strong>ation on slug formation (Feesa, 2003)<br />
Page 40 of 56
Karam – <strong>Slug</strong> <strong>Catchers</strong> <strong>in</strong> <strong>Natural</strong> <strong>Gas</strong> <strong>Production</strong><br />
Figure 4: Idealized slug unit show<strong>in</strong>g all four different elements: the mix<strong>in</strong>g zone, the slug body, the film and the<br />
bubble (Scott et al., 1989)<br />
Figure 5: Representation of the slug unit and unit length with both the slug and film zones (Marquez et al., 2009)<br />
Page 41 of 56
Karam – <strong>Slug</strong> <strong>Catchers</strong> <strong>in</strong> <strong>Natural</strong> <strong>Gas</strong> <strong>Production</strong><br />
Figure 6: Flow map of a 20-<strong>in</strong> horizontal slug catcher show<strong>in</strong>g the operational po<strong>in</strong>t (Sarica et al., 1990)<br />
Figure 7: Flow map of a 26-<strong>in</strong> horizontal slug catcher show<strong>in</strong>g the operational po<strong>in</strong>t (Sarica et al., 1990)<br />
Page 42 of 56
Karam – <strong>Slug</strong> <strong>Catchers</strong> <strong>in</strong> <strong>Natural</strong> <strong>Gas</strong> <strong>Production</strong><br />
Figure 8: The appropriate design of a constrictor (Shell, 1998).<br />
Page 43 of 56
Karam – <strong>Slug</strong> <strong>Catchers</strong> <strong>in</strong> <strong>Natural</strong> <strong>Gas</strong> <strong>Production</strong><br />
Figure 9: View of the <strong>in</strong>let side of a multi-pipe slug catcher (Patel, 2007)<br />
Figure 10: View of the liquid header side of a multi-pipe slug catcher (Patel, 2007)<br />
Page 44 of 56
Karam – <strong>Slug</strong> <strong>Catchers</strong> <strong>in</strong> <strong>Natural</strong> <strong>Gas</strong> <strong>Production</strong><br />
Figure 11: The bottle geometry of the slug catcher for Troll field <strong>in</strong> the Kollsnes process<strong>in</strong>g plant (Shell, 1998)<br />
Figure 12: A general view of the two slug catchers at the Kollsnes Process<strong>in</strong>g plant (Klemp, 2011)<br />
Page 45 of 56
Karam – <strong>Slug</strong> <strong>Catchers</strong> <strong>in</strong> <strong>Natural</strong> <strong>Gas</strong> <strong>Production</strong><br />
Figure 13: The different components of the Hammerfest process<strong>in</strong>g plant of the Snøhvit field (Pettersen J. , 2011).<br />
Figure 14: Representation of the Storegga Slide (left) and the location of the field (right) (Bryna et al., 2005)<br />
Page 46 of 56
Karam – <strong>Slug</strong> <strong>Catchers</strong> <strong>in</strong> <strong>Natural</strong> <strong>Gas</strong> <strong>Production</strong><br />
Figure 15: A general Overview of one of the two multi-pipe slug catchers at Ormen Lange (Gupta, 2012)<br />
Figure 16: Setup of the HYSYS model (MEG <strong>in</strong>jection was not <strong>in</strong>cluded <strong>in</strong> this setup)<br />
Page 47 of 56
Karam – <strong>Slug</strong> <strong>Catchers</strong> <strong>in</strong> <strong>Natural</strong> <strong>Gas</strong> <strong>Production</strong><br />
Figure 17: Elevation profile of the Ormen Lange big bore well retrieved from the HYSYS model<br />
Figure 18: Elevation Profile of the Ormen Lange flowl<strong>in</strong>e (Christiansen, 2012 from Biørnstad, 2006)<br />
Page 48 of 56
Karam – <strong>Slug</strong> <strong>Catchers</strong> <strong>in</strong> <strong>Natural</strong> <strong>Gas</strong> <strong>Production</strong><br />
Figure 19: The digitized elevation profile of the Ormen Lange flowl<strong>in</strong>e <strong>in</strong> HYSYS<br />
Figure 20: The slug tool results show<strong>in</strong>g the position, length, frequency and velocity of slugs along with different<br />
flow regimes <strong>in</strong> the Ormen Lange pipel<strong>in</strong>e.<br />
Page 49 of 56
Karam – <strong>Slug</strong> <strong>Catchers</strong> <strong>in</strong> <strong>Natural</strong> <strong>Gas</strong> <strong>Production</strong><br />
Figure 21: The elevation profile of the Snøhvit flowl<strong>in</strong>e (Christiansen, 2012)<br />
Figure 22: The digitized elevation profile of the Snøhvit field as it is implemented <strong>in</strong> HYSYS<br />
Page 50 of 56
Karam – <strong>Slug</strong> <strong>Catchers</strong> <strong>in</strong> <strong>Natural</strong> <strong>Gas</strong> <strong>Production</strong><br />
Figure 23: The elevation profile of the Troll flowl<strong>in</strong>e. H=-350 m and L=67 km (Albrechtsen & Sletfjerd<strong>in</strong>g, 2003)<br />
Page 51 of 56
Karam – <strong>Slug</strong> <strong>Catchers</strong> <strong>in</strong> <strong>Natural</strong> <strong>Gas</strong> <strong>Production</strong><br />
APPENDIX I - GENERAL INFORMATION ABOUT THE FIELDS<br />
USED FOR THE HYSYS SIMULATION<br />
I.A – Troll Field<br />
The gas composition of the Troll field is represented <strong>in</strong> the table below along with the correspond<strong>in</strong>g<br />
densities for C6 components and above (Madsen, 1997 and Bolle).<br />
Component<br />
Troll <strong>Gas</strong> Composition<br />
Mole<br />
Composition<br />
weight<br />
(mol %)<br />
(g/mole)<br />
N 2 1.749 28.01<br />
Density<br />
(Kg/m3)<br />
CO 2 0.226 44.01<br />
C1 92.815 16.04<br />
C2 3.265 30.07<br />
C3 0.585 44.10<br />
iC4 0.331 58.12<br />
nC4 0.090 58.12<br />
iC5 0.081 72.15<br />
nC5 0.330 72.15<br />
C6 0.110 86.18 664.0<br />
C7 0.185 96.00 738.0<br />
C8 0.118 107.00 765.0<br />
C9 0.051 121.00 781.0<br />
C10+ 0.064 160.13 811.5<br />
S<strong>in</strong>ce the gas arriv<strong>in</strong>g to the Kollsnes plant comes from three different platforms, then the respective<br />
flow rate and the MEG <strong>in</strong>jection rate varies and is represented <strong>in</strong> the table below (Madsen, 1997).<br />
Field/<br />
Platform<br />
Typical <strong>Gas</strong><br />
Rate<br />
(MSm 3 /d)<br />
Typical<br />
MEG<br />
Injection<br />
(m 3 /d)<br />
Troll (ABC) 119 200<br />
Kvitebjørn 20 10<br />
Visund 6 4<br />
Total 145 214<br />
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Karam – <strong>Slug</strong> <strong>Catchers</strong> <strong>in</strong> <strong>Natural</strong> <strong>Gas</strong> <strong>Production</strong><br />
The reservoir and fluid properties are also essential for develop<strong>in</strong>g a HYSYS simulation. The data<br />
required are shown <strong>in</strong> the follow<strong>in</strong>g table (Bolle).<br />
Reservoir and Fluid Properties<br />
Reservoir pressure at 1547m MSL<br />
158 bar<br />
Reservoir temperature 68 °C<br />
<strong>Gas</strong> gravity 0.61<br />
<strong>Gas</strong> quality Sweet, dry, lean 24-29 ° API<br />
<strong>Gas</strong> viscosity<br />
0.018 cP<br />
<strong>Gas</strong> density (at standard conditions) 0.75 Kg/m 3<br />
Oil gravity<br />
0.908 g/cm3<br />
Oil quality<br />
Slightly waxy<br />
Condensate/gas ratio 29 Sm 3 /MSm 3<br />
Condensate gravity<br />
0.802-<br />
0.825<br />
g/cm 3<br />
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Karam – <strong>Slug</strong> <strong>Catchers</strong> <strong>in</strong> <strong>Natural</strong> <strong>Gas</strong> <strong>Production</strong><br />
I.B – Heidrun Field<br />
The gas composition of the Heidrun field can be found <strong>in</strong> the table below (Hansen, 1997).<br />
Component<br />
N2-C1<br />
CO2<br />
C2<br />
C3<br />
C4<br />
C5<br />
C6<br />
C7<br />
C8-C9<br />
C10-C11<br />
C12-C13<br />
C14-C15<br />
C16-C17<br />
C18-C19<br />
C20-C21<br />
C22-C23<br />
C24-C25<br />
C26-C29<br />
C30-C33<br />
C34-C38<br />
C39-C44<br />
C4-C54<br />
C55-C80<br />
Mole<br />
Composition<br />
(%)<br />
8.62E-01<br />
1.23E-02<br />
5.24E-02<br />
2.03E-02<br />
2.27E-02<br />
1.12E-02<br />
3.40E-02<br />
4.12E-03<br />
6.21E-03<br />
2.53E-03<br />
1.60E-03<br />
9.19E-04<br />
4.18E-04<br />
1.69E-04<br />
4.95E-05<br />
2.28E-05<br />
1.08E-05<br />
6.60E-06<br />
9.43E-07<br />
2.06E-07<br />
3.42E-08<br />
5.43E-09<br />
1.36E-09<br />
The basic reservoir properties of the Heidrun field are represented <strong>in</strong> the table below (Actis, Smith,<br />
& Chenier, 1993 and Norway).<br />
Reservoir Properties - Heidrun<br />
Reservoir pressure<br />
267 bar<br />
Reservoir temperature 85 °C<br />
<strong>Gas</strong> <strong>in</strong> Place 50 BSm 3<br />
Oil Gravity 851 Kg/m 3<br />
<strong>Gas</strong> flow rate 11 MSm 3 /d<br />
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Karam – <strong>Slug</strong> <strong>Catchers</strong> <strong>in</strong> <strong>Natural</strong> <strong>Gas</strong> <strong>Production</strong><br />
I.C – Snøhvit Field<br />
The gas composition of the Snøhvit field can be found <strong>in</strong> the table below (Golan, 2012).<br />
Component<br />
Mole Fraction<br />
Nitrogen 0.02525<br />
Carbon dioxide 0.05262<br />
Methane 0.81006<br />
Ethane 0.05027<br />
Propane 0.02534<br />
i-Butane 0.004<br />
n-Butane 0.0083<br />
i-Pentane 0.00281<br />
n-Pentane 0.00308<br />
Hexanes 0.00352<br />
Heptanes 0.00469<br />
Octanes 0.00407<br />
Nonanes 0.00203<br />
Decanes plus 0.00397<br />
Proprieties C 10+ fraction_<br />
Molecular weight (g/gmol) 172<br />
Density (kg/m3) 814<br />
The basic reservoir properties of the Snøhvit field are represented <strong>in</strong> the table below (Christiansen,<br />
2012)<br />
Reservoir Properties - Snøhvit<br />
Reservoir pressure<br />
267 bar<br />
Reservoir temperature 92 °C<br />
<strong>Gas</strong> flow rate 20.8 MSm 3 /d<br />
<strong>Gas</strong> In Place 317 GSm 3<br />
Condensate 34 MSm 3<br />
Page 55 of 56
Karam – <strong>Slug</strong> <strong>Catchers</strong> <strong>in</strong> <strong>Natural</strong> <strong>Gas</strong> <strong>Production</strong><br />
I.D – Ormen Lange Field<br />
The gas composition of the Ormen Lange field can be found <strong>in</strong> the table below (Valberg, 2005).<br />
Component Mole fraction<br />
N2 0.003411<br />
CO2 0.00408<br />
H2O 0.005931<br />
Methane 0.930927<br />
Ethane 0.034719<br />
Propane 0.012177<br />
i-Butane 0.002717<br />
n-Butane 0.00322<br />
i-Pentane 0.00151<br />
n-Pentane 0.001308<br />
The basic reservoir properties of the Ormen Lange field are represented <strong>in</strong> the table below<br />
(Biørnstad, 2006).<br />
Reservoir Properties - Ormen Lange<br />
Reservoir pressure<br />
290 bar<br />
Reservoir temperature 96 °C<br />
<strong>Gas</strong> flow rate 70 MSm 3 /d<br />
Condensate <strong>Production</strong> Rate 6000-8500 GSm 3<br />
<strong>Gas</strong> Molecular weight 17.443<br />
<strong>Gas</strong> Specific Gravity 0.6<br />
Page 56 of 56