Designing Wells to Optimize Performance and Efficiency - ICWT

Designing Wells to Optimize Performance and Efficiency
How to Minimize Frictional and Financial Losses
Well Efficiency
Optimizing Production and Cost
2012 Water Technology Conference
May 3, 2012
Kevin McGillicuddy, P.G.
Roscoe Moss Company

Efficient Well Design and Operation:
Topics
• Factors contributing to pumping drawdown
• Steps taken to reduce losses
• Calculation of Well Efficiency
• Cost Implications

Pumping Well Terminology
Cone Of Depression
Discharge Rate
Static (non pumping) Level
Pumping Level
Drawdown in Well
Aquifer Loss
Well Loss
AQUIFER
3

Well Efficiency
Defined as : drawdown in the aquifer
total drawdown in the well
4

Critical Components in Designing
Efficient Gravel Envelope Wells
• Understanding factors contributing to pumping
drawdown
– Aquifer losses
– Well losses
• Selection of Appropriate Gravel Pack
• Selection of Screen Slot Size
• Application of Rigorous and Thorough Well Development
Techniques

Collect Representative Borehole Samples

Select Samples for Sieve Tests

Determine Gradation
of Aquifer Sediments

Wt. % Finer
(passing)
20-48
50-60
68-86
Sump
0
1/4 x 10
4 x 16
4x20
4x16.2
Sieve Analysis
U.S. Sieve Sizes
20 16 14 12 8 6
100
90
80
70
60
50
10
6 - 9 x multiplier
Slot size 0.070"
40
30
20
10
0
0.0010 0.0100 0.1000 1.0000
Grain Size (inches )

Slot Size Selection
• Sized to pass 10 to 20% gravel pack
• Slot size more critical than % open area
• Open area of 3 – 5% = 90+ % efficient
• Entrance velocity of 2 – 4 fps = 90+% efficient
(1)
(1)
(1) Modern Techniques in Well Design, Journal AWWA Williams, D.E.,Ph.D, 1985

Efficiency Case Study – Big Pine, CA
Well #374 Well #375
1000 ft
Depth : 450’ 450’
Diameter : 18” 18”
Perforations : 260 - 440’ 260 - 440’
Slot Size: 0.080” 0.080”
Screen Type : wire-wrap louvered
% open area: 27% 5 %

Efficiency Results
Well #374 Well #375
27% open area 5 % open area
Step Q E Q E
(gpm) (%) (gpm) (%)
1 873 91.1 883 93.9
2 1803 83.3 1855 88
3 2078 81.3 2034 87
4 2617 77.5 2607 83.9

Properly Designed Gravel Envelope &
Screen Slot Size
Well Screen Filter Pack Aquifer

Well Development
Any process used to improve permeability of an aquifer and
repair drilling damage.
Accomplished by removing fines through the gravel pack and well
screen.
Must be aggressive and directed.

Damage Zone
Repair Drilling Damage

Phases of Well Development
Pre-development : Controlling drilling fluids during drilling
and construction
Preliminary development : swabbing, jetting, flushing,
airlifting, and bailing
Final development : pumping, surging, and backwashing

Predevelopment
• Predevelopment consists of the procedures followed during
drilling and construction that minimize damage to the aquifer
• The single most important procedure here is the control of
drilling fluid properties; weight, viscosity, and sand content
• Always condition drilling fluids to the proper characteristics
before casing and gravel pack installation.

Failure to Account for Mud Properties

Collapse Due to Slot Plugging

Preliminary Development
• Preliminary development comprises those procedures
performed by the drill rig immediately after casing, screen,
and gravel installation.
• These procedures include Swabbing and Circulating, Jetting,
Wire-line Swabbing and bailing, and simultaneous Swabbing
and Airlifting.
• Chemical Development is included here.

Swabbing and Circulating
• Preliminary development should begin immediately following
construction
• Historically done with a single swab on the bottom of the drill
string while fresh water is pumped down the drill pipe
• Current construction techniques favor the dual swab and
simultaneous air-lift method
• Swabs should fit snugly inside screen and be supported by
steel plates

Wire-Line Swabbing
• Single swab attached to a cable tool
scow or bailer.
• Line swabbing normally begins at the
top of the screen section in short (20 to
40’) sections.
• The swab is repeatedly hoisted with
increased speed and length of haul.
• The well must be frequently bailed of
debris

Development by Swabbing

Single Swab

Single Swab Development
• Beginning at the bottom of the
screen, the swab is vigorously raised
and lowered.
• Consolidates gravel, flushes fines and
filter cake from the gravel for removal
by the circulating fluid.
• Performed 2 or more times through
the screen section, as long as gravel
movement is noted.

Dual Swab Development
• Very similar to the single swab
technique.
• The dual swab is vigorously
raised and lowered while fresh
water is pumped down the drill
pipe.
• The effectiveness of swabbing is
measured by the amount of fine
particles pulled in thru the
screen.

Double Swab

Dual Swab and Simultaneous Airlift
• The well is mechanically swabbed
by raising and dropping the drill
pipe equipped with a tight fitting
dual swab on the bottom.
• During swabbing, water is airlifted
from the well.
• Swabbing is started at the top of
the screen to minimize the risk of
sand locking the swabs.

Final Development / Pump Development

Pump Development
• Final development step
• Stresses larger area of aquifer around the
well
• Provides data for subsequent pump and
aquifer tests

Final Development
• Final Development is accomplished by an extensive program
of pumping, surging, and backwashing the well to remove
any fine silts or sands from the gravel pack and borehole
wall.
• To accomplish this, mobilize a development pump capable of
150% of anticipated capacity.
• Begin development slowly by pumping at about 20% of
anticipated capacity, surge and backwash gently. Gradually
increase efforts as well shows improvement.
• Develop well to its maximum capacity while recording
drawdown and sand content.

Roscoe Moss Company

Rossum
Sand
Tester

Specific Drawdown, s/Q (ft/GPM)
Specific Drawdown, s/Q (ft/GPM)
Specific Drawdown, s/Q (ft/GPM)
Specific Drawdown, s/Q (ft/GPM)
Well Development Type I - Under Developed
0.16
0.07
• Five Types of well development
0.14
0.12
0.1
• Examples of Jurupa
0.08
0.06
0.04
• LACWD 40 4-68
0.02
Figure 6.6 Well Development Types
0.06
0.05
0.04
0.03
0.02
0.01
Well Development Type II - Transitional
0
0 20 40 60 80 100 120 140 160 180 200
Flow Rate, Q (GPM)
Type I
0
0 20 40 60 80 100 120 140 160 180 200
Flow Rate, Q (GPM)
Type II
Well Development Type III - Fully Developed
0.1
0.09
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0
0 20 40 60 80 100 120 140 160 180 200
Flow Rate, Q (GPM)
0.25
0.2
0.15
0.1
0.05
Well Development Type IV & V
Fully Developed at Low Flow Rates - Transitional at High Flow Rates
0
0 20 40 60 80 100 120 140 160 180 200
Flow Rate, Q (GPM)
Type III
TypeIV
Type V

Specific Drawdown, s/Q
0.080
Well Development and Completion
6-Jul-05
• In this case the well was screened from 465 feet bgs to
7-Jul-05
8-Jul-05
0.070
11-Jul-05
795 feet bgs. Blank well casing was installed 12-Jul-05from
13-Jul-05
0.060
ground surface to 465 feet bgs, and again from 795
14-Jul-05
Linear (8-Jul-05)
0.050 feet bgs to 815 feet bgs.
• Development that took place on this well over the
0.040
course of seven days.
0.030
Figure 10.8
Development for Example Well
Linear (8-Jul-05)
Linear (11-Jul-05)
Linear (12-Jul-05)
Linear (14-Jul-05)
Linear (14-Jul-05)
• From this figure we see the well starts as a Type 1
0.020
development and
Trendlines
transition into a Type II and finally
0.010 into a Type III development.
0.000
0 500 1,000 1,500 2,000 2,500 3,000
Discharge Rate, gpm
38

Well Efficiency
Defined as : drawdown in the aquifer
total drawdown in the well
39

Water Level in Pumping Well
Well Loss

Calculating Well Efficiency
E = Aquifer Losses
Total Drawdown
E = Aquifer Losses (BQ)
Aquifer Losses + Well Losses (CQ²)
E % = 100 x
(BQ)
(BQ + CQ²)
41

Ground Surface
Q
Static Water Level
Drawdown in Pumping Well
Pumping Water Level
Aquifer Loss
(BQ)
Well Loss
2
(CQ )
Laminar flow losses
B = Aquifer Loss Coefficient
Turbulent flow losses
C = Well Loss Coefficient
Total Drawdown in Well
= BQ + CQ 2

Drawdown, ft
Calculating Well Efficiency Using Step Drawdown Test
0
1
Time Since Pumping Began, Min
10 100 1000
50
43

Pumping Step Test
Discharge (Q) GPM
STATIC WATER LEVEL
Step 1 Pumping Level ---->
Step 2 Pumping Level ---->
Step 3 Pumping Level ---->
Specific Specific
Discharge Drawdown Capacity Drawdown
. Q s Q/s s/Q
500 gpm 20 ft 25 gpm/ft .04 ft/gpm
1000 gpm 52 ft 19 gpm/ft .05 ft/gpm
1500 gpm 92 ft 16 gpm/ft .06 ft/gpm
AQUIFER
44

SPECIFIC DRAWDOWN, s/Q, ft/gpm
Solving for Aquifer and Well Loss Coefficients -
Specific Drawdown Plot
0.06
0.04
C = 0.000025 ft/gpm (Well Loss Coefficient)
0.02
B = 0.025 ft/gpm (Aquifer Loss Coefficient)
0
0 500 1000 1500
DISCHARGE, Q, [gpm]
45

Data
Discharge Drawdown Specific
Capacity
Specific
Drawdown
Aquifer
Loss
Well
Loss
Well
Efficiency
Q gpm S ft Q/s gpm/ft s/Q ft/gpm BQ CQ %
500 20 25 .04 12.5 6.3 67
1000 52 19 .05 25 25 48
1500 92 16 .06 37 56 40
2
B = 0.025 ft/gpm
C = 0.000025 ft/gpm
E % = 100 x
BQ
BQ + CQ²

Drawdown (s), ft
Well Efficiency (E), %
Specific Capacity Diagram – Design Discharge Rate
0
Discharge Rate (Q), gpm
0 500
1000 1500 2000
Formation Loss (BQ)
100
80
Design
Total Drawdown
Well Loss (CQ 2 )
60
100
Well Efficiency
40
20
200
0

Maintaining Well Efficiency
• Increased well losses (biological, physical clogging)
• Decreased Specific Capacity
• Decreased Efficiency
• Higher Operating Costs

Biological Fouling
Scanning Electron Microscope Magnification = x 3850
49

50
Physical Clogging

Water Level in Pumping Well
Well Loss

Example of Energy Cost
Case 1: New Well
Efficiency = 75%
TDH = 308 ft
Case 2: Well with 50 ft Additional Lift
Efficiency = 65%
TDH = 358 ft
Where:
Cost/Hour = gpm x TDH x 0.746 x Cost/kwh
3960 x Efficiency

Annual Cost
Parameter Case 1 Case 2
Pumping Rate 1500 gpm 1500 gpm
Pumping Level 250 ft 300 ft
Discharge Pressure 58 ft 58 ft
TDH 308 ft 358 ft
Power Cost $ 0.10/kwh $ 0.10/kwh
Well Efficiency 75 % 65%
Annual Operation 4,380 hours 4,380 hours
Annual Cost $50,595 $67,856
Differential = $17,261

SUMMARY
• The efficiency of the well should be considered during
initial planning and design
• Designing efficient wells requires minimizing well losses
and understanding the relationship between the aquifer,
filter pack and well screen
• Achieve full production potential of the well by ensuring
that it has been fully developed
• Monitor the specific capacity and efficiency of the well to
minimize operational costs

Questions
Kevin McGillicuddy, P.G.
(323) 263-4111
Email: kmc@roscoemoss.com
Website: www.roscoemoss.com