Slug Catchers in Natural Gas Production - NTNU

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Karam – Slug Catchers in Natural Gas Production CHAPTER 5 NORWEGIAN FIELDS AND SLUG CATCHERS This chapter will describe four different slug catchers from four different fields lying in the Norwegian continental shelf. The Troll field is linked to an onshore processing plant known as Kollsnes whereas the Heidrun field has its gas processing activity in Tjeldbergodden methanol processing plant. The Melkøya plant receives the gas from the Snøhvit field while the Nyhamna plant receives the gas streams from the Ormen Lange field. Following that, relevant data are collected and organized in two tables, Tables 2 and 3, to allow a HYSYS simulation of the amount of liquid to be expected in the slug catcher and discuss the design. 5.1 Troll and Kollsnes Statoil-owned processing plant, Kollsnes, located 67 km west of Bergen started operations in October 1996. The location of the plant made it possible to build a simpler platform than what was originally planned. The gas from the Troll field is transported to the Kollsnes plant. In 2005, the gas from both Kvitebjørn and Visund fields started coming also to the Kollsnes processing plant. The original capacity of the plant was 120 million standard cubic meters per day with the presence of 5 compressors; it is now raised up to 143 million standard cubic meters per day due to the installation of a sixth compressor. It can also handle 69 000 barrels of Natural Gas Liquids (NGL) per day (Hydrocarbons Technology, 2012). The new plant, which can handle 26 million standard cubic meters of gas, is now able to process gas from further field developments. Natural Gas Liquid is separated from the rich gas at the Kollsnes gas plant and then sent to Mongstad refinery through the Vestprosess pipeline in order to fractionate gas into propane, butanes and naphtha. Pressurized dry gas is driven by the large compressors and transported to customers through gas trunklines. There are four trunklines: Statpipe, Zeepipe, Europipe I and Franpipe transporting the gas to 7 continental European countries: France, Netherlands, Belgium, Germany, Czech Republic, Austria and Spain. It should be noticed that the previously listed trunklines do not all originate from the Kollsnes plant. Along with the Kårstø processing plant, they constitute 70% of the gas transported from Norway to Europe. Page 22 of 56
Karam – Slug Catchers in Natural Gas Production The Troll oil and gas field is located in the 31/2, 31,3, 31/5 and 31/6 blocks in the North Sea. The Troll gas is sent from the Troll A wellhead platform to the Kollsnes plant through two 36’’ gas-condensate pipelines as a multiphase flow is being transported. The receiving terminal consists of a dual-slope multi-pipe slug catcher. The design of this slug catcher is shown in Figure 11. A general view of the two slug catchers at the Kollsnes plant are shown in Figure 12. There are two slug catcher sets which are 575 feet or 175.26 meters long. They consist of four pipe sections each with a 48 inch diameter (Thaule & Postvoll, 1996). 5.2 Heidrun and Tjeldbergodden The Heidrun field, an oil field associated with a gas cap, is located 175 km offshore the Norwegian coast. It is located at a 345 meters water depth. It is located mainly on the south end of the SW-NW trending Norland ridge and extending towards the less faulted Halten terrace (Mitcha et al., 1996). It is the first field where the first Tension Leg Platform (TLP) has ever been used. The gas is transported through a 250 km long 16 inches pipeline known as the Haltenpipe to a methanol plant, Tjeldbergodden. The Tjeldbergodden complex is located in mid-Norway, in the Aure commune between Kristiansund and Trondheim. It occupies an area of 150 hectares and is designed to handle up to 900,000 tons of methanol per year. It is mainly composed of four constituents: a receiving terminal for gas, a methanol plant, an air separation plant and a gas liquefaction plant (Statoil, 2011). It is known as the most environmentally friendly petrochemical plant. Two combined techniques in handling and treating methanol were chosen with precaution; therefore, the production of carbon dioxide and nitrogen oxides per ton of methanol will be very minimal and the energy consumption is set as the lowest in the world (Hansen, 1997). The Tjeldbergodden plant has some limitations and specifications. The plant production is limited due to a restricted production capacity of 6.3 MSm 3 /d (Gustavsen & Tøndel). The gas reaches the receiving terminal with an inlet pressure of 50 bars compared to the normal operating pressure in the pipeline which ranges between 120 and 170 bars. As for the temperature, it is increased by 40 °C at the inlet of the slug catcher. Page 23 of 56
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Slug Catchers in Natural Gas Production - NTNU

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