gas locked pumps are not gas locked! - alrdc - home€¦ · gas locked pumps are not gas locked!...

9th Annual Sucker Rod Pumping

Workshop

Renaissance Hotel

Oklahoma City, Oklahoma

September 17 - 20, 2013

Gas Locked Pumps are NOT Gas Locked!

Lynn Rowlan

Ken Skinner

Echometer Company

1. Best to Keep Gas Out of the Tubing by Setting the Pump

Intake Below the Perforations (Horizontal Wells?)

2. Or Use an Effective Downhole Gas Separator

3. Use a specialty pump such as a VSP® pump to discharge

gas into tubing.

4. Use longer stroke length to increase compression ratio

5. Proper Spacing to minimize dead space at bottom of stroke

6. Slippage thru Pump Clearances Partially Fills Pump

Chamber

7. Sufficient Backpressure can Prevent Tubing Fluids from

Unloading

• Unloading usually Caused by Poor Downhole Gas

Separation with Gas Pumped into the Tubing

• Tubing Fluids Lighten and Tubing Liquids Flow Off.

Introduction Gas Locked Pumps are NOT Gas Locked!

Sept. 17 - 20, 2013 2013 Sucker Rod Pumping Workshop 2


What is a Gas Locked Pump

• Both traveling valve, TV, and standing valve,

SV, remain closed during the entire stroke

• Pump is completely filled with gas

• Gas Lock occurs if:

– Downstroke the tubing pressure on top of the plunger is always

greater than the compressed pressure inside pump chamber

– Upstroke the expanding pump chamber pressure is always

greater than the outside wellbore pressure at the pump intake.

• TV and SV open if pressure below the valve is greater

than the pressure above the valve.


Synthetic Pump Card Shape: Gas Locked Pump

Gas Locked Pump...Both valves

remain closed because the

discharge tubing pressure, (Pd), is

greater the pump chamber

pressure, (Pchamber), which is also

greater than the pump intake

pressure, Pint. The compression

ratio of the sucker rod pump is too

small, with the result that neither

valve opens until the clearance

space between valves fills by

slippage of fluids past the plunger,

or the fluid level is allowed to rise

so that a smaller compression ratio

is required to discharge gas from

the pump into the tubing.

Pd > Pchamber > Pint

Pd > Pchamber at

bottom of stroke

Pchamber > Pint

at top of stroke

Zero Load Line FoDn = 0

Fo from Fluid Level

Expansion

Should Open SV Compression

Should Open TV Zero Load Reached Pchamber > PD

Fo reached when Pchamber < Pint

Pint Pint

PD

PD


Vint

VD

PIVI PDVD

Intake (-----) = (------) Discharge

ZI ZD

Iso-thermal

No Change in Rs

Up Stroke

Gas Interference: Incomplete Pump Fillage and High Fluid Level

Fo

Rods

Fo Well

Fluid Level

Above Pump

Fo Pump < Fo Max


Synthetic Pump Card Example: Gas Interference

Gas Interference is causing decrease in pump Fillage. Pump

components are functioning properly. Usually unstable pump

fillage and EPT changes from stroke-to-stroke. When gas

interference is present expect increased rod-on-tubing wear

due to rod buckling compressing gas in pump barrel.

Tubing anchored, EPT<MPT.

Unanchored tubing, EPT<MPT

Fo Fluid Level

Fo Max


Steps C - D in Pump Operation Pump acts as a Compressor on Down Stroke A

B C

D

Incomplete Pump Fillage Occurs from C to D on Pump Card

C) Standing Valve closes, when plunger reaches top of stroke, rods start to un-stretch to transfer fluid load, Fo, from rods [C] onto tubing [D].

D) Traveling Valve Opens when pressure in pump chamber >= Pump Discharge Pressure, PD.

C-D) Plunger applies

pressure to fluids

inside pump chamber,

to compress fluids in

Pump chamber and

increase pressure.

at [C] PB = PI

at [D] PB = PD PD - Discharge Pressure

PB - Pressure in Chamber

PI - Intake Pressure


2013 Sucker Rod Pumping Workshop

High Compression Ratio Prevents “Gas Lock” By Pumping Gas into Tubing

A

Stroke

Length

(Swept

Volume)

Unswept

Volume

Compression

Ratio = (Swept+Unswept) Vol.

Unswept Vol.

For TV to Open:

PD - Pump Barrel Discharge Pressure =

Intake Pressure x compression ratio

PD Must be greater than Pressure in

Tubing at Top of Plunger

PIVI PDVD

(-----) = (------)

ZI ZD

Assume ZI = ZD

PD = PIVI / VD

Space Pump High

or High Tubing

Pressure CR is

Reduced

Compression Ratio (CR) = VI / VD

VI

VD

9

Effect of PIP on Gas Compression i.e. Gas Interference or Fluid Pound

Liquid

Gas

PIVI PDVD

(-----) = (------)

ZI ZD

Intake Discharge

Iso-thermal

No Change in Rs

Intake

Discharge

10

Gas Lock Cycles

0 53.9-1.0

-0.5

0

0.5

1.0

1.5

2.0

2.5

Fo Max Stroke 45

0 53.9-1.0

-0.5

0

0.5

1.0

1.5

2.0

2.5

Fo Max

Stroke 51

0 54.0-1.0

-0.5

0

0.5

1.0

1.5

2.0

2.5

Fo Max

Stroke 77

0 54.3-1.0

-0.5

0

0.5

1.0

1.5

2.0

2.5

Fo Max

Stroke 84

0 53.9-1.0

-0.5

0

0.5

1.0

1.5

2.0

2.5

Fo Max

Stroke 139


“Gas Lock” Occurs, When Both: 1) Point “A” is Above 0 Line 2) Point “C” is Below Fo From the Fluid Level

A

C

Tag

Tag Bad for Equipment, but

Many tag due to “Gas Locking”

Fo From the Fluid Level

2013 Sucker Rod Pumping Workshop 12 Sept. 17 - 20, 2013

NOT GAS LOCKED

Pump Gas Up the Tubing

Gas Locked?

13

Pump Gas Up the Tubing


2013 Sucker Rod Pumping Workshop Sept. 11 - 14, 2007

Spacing HF Variable Slippage Pump

Spacing at the well site:

a. Touch bottom with tubing loaded with fluid

b. Pick up overtravel length

c. Pick up spacing allowance, normally 12"

d. The lower end of the plunger should slightly enter the start of the VSP® taper. This position gives the least amount of bypass slippage. After well has stabilized, space the plunger higher in small increments for more bypass slippage to achieve desired results.

Re-space well as needed after stabilized:

a. Lower rods for a light tag at pump, then raise slightly for stroking close to bottom without entering VSP® taper.

b. After accomplishing raise rods in 6 inch increments until bottom of plunger enters taper.

"Spacing allowance: 30" down to 4,000 feet well depth, then add 6" for every 1,000 feet well depth below 4,000 feet.

Stroke

Length

Tapered

Barrel

Beginning (Upstroke) Top

Tubing

Liquid

Well

Fluids

Oil

Water

Gas

Gas Displaced by

Liquid thru Tapered

Pump Gas into Tubing

with VSP

15

Using a Backpressure Valve can Prevent Unloading from in Gas Tubing Gas Flowing through Pump OR Pumped into Tubing

• Back-pressure valve maintains high tubing pressure to

prevent gas from blowing all of the liquid out of tubing

• Without BPV Pump action erratic & discharge may STOP

Flow

Harbison-Fischer

Model Illustrated

Increase Pressure by Compressing Spring Pressure

Gage

Spring Force

BPV


Control Excessive Amount of Gas

Pumped Into Tubing 1. ONLY Apply Backpressure to Gassy Wells that

Unload Liquids from the Tubing and Downhole

Pump Action Stops!!!!

2. Backpressure May Increases Operating Cost,

But Allows You to Pump the Well

3. Backpressure Maintains Pump Action

4. Reduced Well Intervention by the Operator

5. Significantly Reduced Stuffing Box Leaks

6. More Consistent Production From Day-to-Day.


Backpressure Recommendations 1. Gassy Wells Difficult to Sucker Rod Pump

2. Horizontal Laterals can Unload a LOT OF GAS

3. Sufficient Backpressure on Tubing can Improve the

performance of Gassy Rod Pumped Wells

4. Sucker rod loading can be incorrect, because of the

piston force, rod loading below the surface will be

higher than measured

5. Use Backpressure ONLY IF a well is Flowing Off due to

TOO Much Gas Produced Up the Tubing

6. If the tubing unloads and pump action stops, then try

200-300 Psi of backpressure on the tubing BUT use

more if required by well


2013 Sucker Rod Pumping Workshop

Compression Ratio High if VD fills with Liquid then Gas Pumped into Tubing

A

Stroke

Length

(Swept

Volume)

Unswept

Volume

Compression

Ratio = (Swept+Unswept) Vol.

Unswept Vol.

Guarantee TV Always Opens:

• Force VD to equal Zero

• Fill Unswept Volume with Liquid

• CR becomes Infinity

If Unswepth Volume Fills with Liquid,

then Pump Chamber Pressure at

Bottom of the Stroke Always Greater

than Tubing Pressure on Top of

Plunger at Discharge.

TV ALWAYS OPENS IF VD=0

Space Pump High

or High Tubing

Pressure CR is

Reduced

Compression Ratio (CR) = VI / VD

VI

VD

19

BPD Tank = BPD Pump

- Slippage

Pump Slippage can Fill Unswept Volume

with Liquid

1) Fluid that leaks back into

pump between the Plunger OD

and the Barrel ID

2) Leaks into the pump chamber

between the standing valve

and traveling valve

3) When traveling ball is on Seat.

Pump Efficiency =

BPD Tank / BPD Pump

Slippage % =

Slippage BPD / BPD Pump


Recommended Procedure to Select Pump Clearances

1. Use QRod predictive sucker rod design program to calculate pump displacement, assume 100% liquid pump fillage.

2. Input correct well parameters into QRod Tool - “Pump Slippage Calculator”, be sure to adjust water viscosity for the temperature at the pump

3. Examine Plot of “Patterson Equation Pump Slippage vs Clearance” and select pump clearance that gives the desired percentage of pump slippage.


651 BPD


QRod Slippage Plot vs Clearance


New pump w/ no wear or damage, Installed 0.009 in.

clearance w/ 2.25 inch diameter & 4 foot plunger

Pump Depth 7156’

Stroke = 145” SPM=9.52 Depth= 7156’ 4’ plunger % of BPD Production Rate or % of Each Stroke lost to Slippage

2-5 % minimum is needed for plunger/barrel lubrication


Leaky

Pump

Well Data Showing No Gas Interference

with High Clearance Pump ~ 1 BPD

26 Sept. 17 - 20, 2013 2013 Sucker Rod Pumping Workshop

Leaky

Pump

Pump Slippage Calculations

10,029’ Pump Depth ~ 1.5” Plunger

27

Leaky

Pump 1) Unswept Space in Pump Filled with

Liquid With 0.002” Clearance

2) IF Compression Ratio were 0, Liquid in

Pump would Displace TV Ball off Seat.

Gas Locked Pumps are NOT Gas Locked

Slippage Can Fill Unswept Pump Volume


When Operator has a Gas Locked Pump the Pump Card Always Looks Like This

1) TV Stuck Open - Pump card on Zero Load, Looks like

Deep Rod Part but often can tag or jar the rods and knock

the debris out of the pump and re-start pump action.

2) SV Stuck Open – Plots on the Fo from the Fluid Level line

3) Tubing Blown Dry – Missing Buoyancy, plots as a flat line

@ a height of Wra-Wrf lbs above the zero load line..


Summary • Pressure in barrel is a function of plunger travel

and compressibility of fluid in barrel.

• A Sucker Rod Pump Intakes Well Fluids and Discharges into the Tubing

• Gas Pumped into the Tubing can be Detrimental to the Operation of the Sucker Rod Pumping System

• No Pump Action can Occur when too Much Gas is Pumped into the Tubing.

• Backpressure may be needed to Maintain Pump Action

• If the Pump has Clearance, then it is Impossible to Gas Lock a Pump



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gas locked pumps are not gas locked! - alrdc - home€¦ · gas locked pumps are not gas locked!...

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