Gas Well Deliquification Workshop
Sheraton Hotel, Denver, Colorado
February 17 – 20, 2013
Downhole Gas Separator Selection
James N. McCoy & Lynn Rowlan
Many operators with medium to high capacity
wells who have low production rates and low
pump fillage ask the question:
What kind of downhole separator should be used?
Downhole Gas Separator Selection
Feb. 17 – 20, 2013 2 2013 Gas Well Deliquification Workshop
Denver, Colorado
Gas Separator
Liquid Capacity
is Based on the
Following
Principle:
GAS BUBBLES FLOW UPWARD IN OIL OR WATER AT A RATE OF
APPROXIMATELY 6 INCHES PER SECOND. THUS, GAS BUBBLES WILL BE
RELEASED FROM A LIQUID COLUMN IF THE DOWNWARD LIQUID VELOCITY IS
LESS THAN 6 INCHES PER SECOND.
A LIQUID COLUMN HAVING AN AREA OF 1 SQUARE INCH TRAVELLING AT
6 INCHES PER SECOND IS A RATE OF 50 BPD.
Downhole Gas Separator
Principle of Operation
Feb. 17 – 20, 2013 3
2013 Gas Well Deliquification Workshop
Denver, Colorado
The outer pipe can be
the casing or the outer
barrel of a gas
separator. The inner
tube is the inlet to the
pump.
ESP Producing 5 MMCF/D of CO2 Gas
Free Gas flows in the annulus, if the casing
pressure builds up after the casing valve is closed.
What Kind of Separator is Needed?
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Denver, Colorado
2013 Gas Well Deliquification Workshop
Denver, Colorado
Dynamometer and Acoustic Analysis of Seating
Nipple Type Gas Separator Performance
88.6” Effective Plunger Stroke
with 87% Pump Fillage
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Casing Pressure Buildup
4.13 psi/min ~ 298 MscfD
Annular Gas Flow Rate
Gas Separator with Seating Nipple
Natural Gas
Separator
The most efficient downhole gas separators locate the pump intake below the lowest gas entry point.
Gas is not pulled down to the pump perforations unless the liquid velocity is greater than 6 inches per second.
Maximum capacity is obtained using casing annulus.
6
Natural Gas Anchor
Feb. 17 – 20, 2013 7 2013 Gas Well Deliquification Workshop
Denver, Colorado
liquid in
separator
pump
slip
gas in
separator
Tubing Conveyed Downhole Separator System
Gravity separation is
the governing principle
for downhole gas
separators.
Insert Separator has
less capacity than
using the casing ID.
Downward Liquid
velocity greater than 6
inches per second in
separator pulls gas into
pump.
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2013 Gas Well Deliquification Workshop
Denver, Colorado
Sorry “Poor Boy” Gas Separator
Seating Nipple
Collar
Perforated Sub
Collar
Joint of Tubing
Dip Tube
Tubing Collars
prevent
perforated sub
from laying
against casing
wall where
liquid
accumulates
Casing
Limited
Flow Area
and Small
Holes
Feb. 17 – 20, 2013 9
“Poor Boy” Gas Separator
Liquid Capacity
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Denver, Colorado
2013 Gas Well Deliquification Workshop
Denver, Colorado
Many Modifications of
“Poor Boy” Gas Separator
Seating Nipple
Collar
Perforated Sub
Collar
Joint of Tubing
Dip Tube
Casing
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2013 Gas Well Deliquification Workshop
Denver, Colorado
Collar Size Separator
Eliminates Poor Boy
Deficiencies
A good separator must
balance annular flow area,
separator flow area, dip
tube diameter and pressure
drop.
Outer barrel OD same as
collar OD.
Thin short wall outer barrel
and short dip tube.
Large inlet ports distributed
around outer barrel
facilitate entry of liquid.
Feb. 17 – 20, 2013 12
Collar-Sized Gas Separator
Specifications Designed with thin-wall tubing, large ports and
minimum lengths to optimize gas separation
from the liquid that enters the pump.
Set 5.5 foot long separator 3 joints below tubing
anchor.
OD of outer barrel of gas separator is the same
OD as the tubing collar.
Collar at the top of separator attaches to
bottom of pump seating nipple.
Optimum size dip tube is permanently mounted
inside the outer barrel.
A bull plugged joint of tubing can be run below
the bottom half-collar for a solids collection
chamber if desired instead of the bull plug.
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Denver, Colorado
To get gas capacity of a specific installation multiply the
table value by the Pressure at the Pump Intake (psi)
and divide by 14.7 14 2013 Gas Well Deliquification Workshop
Denver, Colorado
Collar Size Separator - Gas and Liquid Capacity
2013 Gas Well Deliquification Workshop
Denver, Colorado
Poor Boy Separator Franks #1
34.4” Effective Plunger Stroke
with 34% Pump Fillage
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Casing Pressure Buildup
.25 psi/min ~ 18 MscfD
Annular Gas Flow Rate
2013 Gas Well Deliquification Workshop
Denver, Colorado
Collar Sized Gas Separator Franks #1
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Production of 100 BPD
with a Full Pump
Casing Pressure Buildup
1.8 psi/min ~ 161 MscfD
Annular Gas Flow Rate
MIST
FLOW
Gas Velocity
should be less
than 10 ft/sec
in Annulus
Between ID of
Casing and
OD of Gas
Separator
GAS Should NOT Flow Too Fast
Past Outside Gas Separator
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Liquid Moves Slower in Separator
Than Inside Pump Chamber
4.17 sec
SV Closes
1.8 sec
SV Opens
Pump Plunger
Velocity
Liquid Velocity
Inside Separator
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Denver, Colorado 18
Feb. 17 – 20, 2013
Bubble Size Impacts Rise Velocity
Clift, Grace and Webber (1978)
1 in/sec
3 in/sec
6 in/sec
Feb. 17 – 20, 2013 2013 Gas Well Deliquification Workshop
Denver, Colorado
During 5th Stroke 1 in/sec Bubble is
Pulled into Bottom of the Dip Tube Plunger Dia. 1.25 Inch
Plunger Area 1.227 sq.in.
Pump Depth 10,540 feet
Begin 0 - SV Opens 1.8 - SV Closes 4.17 – End 8.633 sec.
6.95 SPM
2 3/8" Collar Sized Gas Separator
Area between Dip Tube and Barrel
ID - OD 4.581 sq.in.
Collar Sized Gas Separator
Results of Early Field Tests
Installed in over 300 wells
Increased production by an average of 25% in those wells with additional production capacity.
Reduced pumping time by an average 50% in wells with Pump-Off controllers.
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Denver, Colorado
Packer Gas Separator
Inner tube can hold a pump or
simply be a long small dip tube to
a pump landed above.
Uses gravity separation like the
“Poor Boy” except more
separation area and capacity.
Higher cost and higher risk of
mechanical and sand problems.
Page Oil Tools 1957
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2013 Gas Well Deliquification Workshop
Denver, Colorado
Gas Separator Design Top
Collar
Bottom
Collar Formation
Fluids
Formation Fluid
Outlet
Pump
Seating Nipple
Pump Inlets
Fluids from the formation flow
upward to the gas separator and
then flow through a concentric
annulus to an outlet at the top of
the separator which discharges on
one side into the casing annulus.
The gas rises and the liquid falls in
the casing annulus.
The pump inlet is located at the
bottom of the gas separator
causing the pressure drop from the
liquid at the bottom of the separator
to the pump inlet to be negligible.
Diverter Cups or a packer or tail
pipe with packer is located below
the Separator to force formation
fluids into the separator.
Casing
Diverter cups or
Packer or Stinger 23
Gas Separator Selection Criteria
Use Packer Type when dP/dT >2
Use Collar Type when dP/dT <2
24 Feb. 17 – 20, 2013
Average
of all data
2013 Gas Well Deliquification Workshop
Denver, Colorado
Determine
Gaseous
Liquid
Column
Gradient
Below
Liquid Level
Adjusted Liquid Level
Transition from
Collar Sized to
Packer Type
Gas Separator
25
If Liquid Rate is
Low, Poor Boy
Gas Separator
May be OK
Downhole Gas Separator Selection Criteria
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Denver, Colorado
Conclusions
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2013 Gas Well Deliquification Workshop
Denver, Colorado
• Best gas separation performance is obtained by locating
the pump intake below the gas entry point.
• Proper gas separator selection when pump intake is
above the formation must take into account casing
annulus gas production rate and well liquid production
rate.
• Use casing pressure buildup rate to help select Gas
Separator Type.
• Use % Liquid Surrounding Separator with % Pump Fillage
to Determine Separator Performance
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Denver, Colorado 28
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Feb. 17 – 20, 2013 2013 Gas Well Deliquification Workshop
Denver, Colorado
29
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The Artificial Lift Research and Development Council and its officers and trustees, and the Gas Well Deliquification Workshop Steering Committee members, and their supporting organizations and companies (here-in-after referred to as the Sponsoring Organizations), and the author(s) of this Technical Presentation or Continuing Education Training Course and their company(ies), provide this presentation and/or training material at the Gas Well Deliquification Workshop "as is" without any warranty of any kind, express or implied, as to the accuracy of the information or the products or services referred to by any presenter (in so far as such warranties may be excluded under any relevant law) and these members and their companies will not be liable for unlawful actions and any losses or damage that may result from use of any presentation as a consequence of any inaccuracies in, or any omission from, the information which therein may be contained.
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5 Seconds
10 Seconds
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Start
The problem of separating the gas from the liquid before
the liquid enters the pump may be related to the creation
of small gas bubbles from the drop in pressure of liquid in
the dip tube as the oil travels to the pump inlet.
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Denver, Colorado
Feb. 17 – 20, 2013