the university of texas at austin downhole gas separator performance in sucker rod pumping system...
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The University of Texas at Austin
Downhole Gas Separator Performance In Sucker Rod Pumping System
Beam Pumping WorkshopHouston, Texas
October 4 - 7, 2005
Manuel GuzmanAugusto Podio
Overview
Description of the problem
System schematic
Bubble flow forecast
Gas separation testing facilities
Pump volumetric efficiency for actual wells
Conclusions
What Is The Problem?
Design and selection of downhole gas separators are usually made using heuristics.
Generally the performance is much below than expected.
V liquid in V liquid in anchoranchor
V plungerV plunger
V slipV slip
V gas in V gas in anchoranchor
Downhole Separator System
Gas Velocity Inside the Anchor
V V plungerplunger
Net gas velocityNet gas velocity is difference is difference
between between gas slip gas slip velocity (up)velocity (up)
liquid velocity liquid velocity (down)(down)
Liquid velocity
depends on:
• ID of anchor
• OD of dip tube
• Plunger diameter and velocity
Instantaneous Liquid Flow Rate
Conventional
Dplunger=1 in
Ls=86 in
8.45 SPM
200 BPD
Upstroke Downstroke
Forecast for Different Bubble Sizes
Clift, Grace and Webber (1978)
Stroke 1 Stroke 2 Stroke 3
Bubble motion inside a separator with rod pump.Diam. Dip tube=1.5 in Plung. Diam.=1.5 in
Conventional Unit, Ls=86.3 in, 8.45 SPM. Flow rate=151 BPD
Gas Separator Testing – Univ. of Texas
BHP
Air purge Hyd
rost
atic
Co
lum
n
Flow Controlto keep BHPconstant
Air Supply
Air out
Manifold
Mix Pump
L.C.
50 ft high/ 6 in. diam.
Gas Separator Testing – Univ. of Texas
PerforationsSeparator Inlet Slots
Dip Tube Separator Tube
Casing
Liquid rate of the pump
the well (BPD)
Gas rate entering
the well (MSCF/D)
Gas
Rate
thro
ugh
Separa
tor
(MSC
F/D
)
1
2
3
45
6
78
SEPARATOR TYPE: Echometer 1 (2 x 4" slots)
Air and water entering below ports @ 10 psi
2
5
8
Separator Performance (Continuous Flow)
Downhole gas separator selection
With several options of separators it is difficult to select the right one.
Two common situations: I have a well with specific conditions, which
separator is my best choice? I have a separator, In which kind of well can I
use it efficiently?
Separator Selector Spreadsheet
Designed for using with Excel©
Determine separator performance for continuous flow
Input: Average liquid rate Gas rate Casing diameter
Output: Separator that offers the greatest liquid fillage
for the given conditions
Example
200 BPD and 100MSCFD with a 7” casing Patterson 1 using a 3 1/2” separator would offer
the best performance
Inputs (liq. rate, gas rate, csg. diam.)
Region of zero gas thru pump
Gas is entering the pump
Boundary obtained with lab data
Outputs (separator, dimensions)
Superficial Liquid Velocity
inside Separator (in/sec)
Superficial Gas Velocity
in casing annulus (in/sec)
Gas
Rate
th
rou
gh
S
ep
ara
tor
(MS
CF/
day)
1
6
5
2
3
4
PATTERSON 1(OD DIP TUBE = 1”; # OF SLOTS =8; DIMEN. OF THE SLOTS =8" x 1/8")
Pc = 10 psi; POSITION OF THE SEP. = ABOVE THE PERFORATIONS
What If This Were a Rod Pumped Well?
Superficial Liquid
Velocity varies during
the stroke
Sucker Rod Simulator
A special butterfly valve was built and installed in the return line It will be automatically operated to obtain the desired on/off time Flow will be measured using a mass flow meter after the valve
Pipe
½ in shaft2
in
Motor
z
x
6 in
Driv
e
Intermittent Flow Behavior
Gas enters the pump only during a fraction of the 5 sec. upstroke.
Gas column moves uniformly during each stroke.
Bubble size distribution changes with during stroke.
Patterson 8Flow rate = 275 BPD
Gas rate = 55 MSCFDPump speed =6 SPM (1 stroke = 10 sec)
Calculated Pump Liquid Fraction (Fluid Entering Below Ports)
A reduction in pump liquid fraction was found when dip tube diameter was increased (Echometer 2 & Patterson 5)
Up to 87% of liquid fillage can be achieved None of the evaluated separators reached the goal of 100%
Conventional Unit, fluid entering below anchor portsDplunger=1.5, Ls=90, SPM=8.37, PIP=10psi 151 BPD
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Echometer 1 Echometer 2 Patterson 3 Patterson 5 Poorboy
Pum
p fill
per
centa
ge
(%)
.
50
35
20
Vg (in/s)
Conclusions
The instantaneous flow rate during the pump stroke should be used for the separator design.
The gas flow rate in the casing has a major effect on the gas separation efficiency.
Separator efficiency depends on the stroke length (Ls), plunger speed and the dip tube diameter, for each given geometry in a rod pump well.
Visual observation confirms that the best way to maximize the gas separation is to set the intake below the perforations, if possible.
Future work: carry out additional intermittent flow tests to validate the mathematical predictions.
Special thanks to: Yates Petroleum
Q&A Session
The University of Texas at Austin
Downhole Gas Separator Performance In Sucker Rod Pumping System
Beam Pumping WorkshopHouston, Texas
October 4 - 7, 2005
Effect of Geometry
Liquid rate entering
the well (BPD)
Gas rate entering
the well (MSCF/D)
Gas
Rate
th
rou
gh
S
ep
ara
tor
(M
SC
F/d
ay)
Liquid rate entering
the well (BPD)
Gas rate entering
the well (in/sec)
Gas
Rate
th
rou
gh
S
ep
ara
tor
(MS
CF/
day)
Poorboy Patterson 3
Number of holes: 12 Diameter: 3/8” Area 1.3 in2
Number of slots: 8Dimension: 8" x 1/2“Area 32 in2
Background Research
Understanding and Combating Gas Interference in Pumping Wells. Joe Clegg, 1963
Another Look at Gas Anchors. Joe Clegg, 1989
Characterization of Static Downhole Gas Separators. Jorge Robles, 1996
The Effect of Geometry on the Efficiency of Downhole Gas Separator. Omar Lisigurski, 2004
Mark II (3”OD, 1” Dip Tube)
Rotaflex (3”OD, 1” Dip Tube)
Liquid Fraction (Mark II, fluid entering below the anchor ports)