Gas Interference EffectsGas Interference EffectsGas Interference Effects

Lynn RowlanLynn Rowlan

2006 2006 International International Sucker Rod Sucker Rod

Pumping Pumping WorkshopWorkshop

Causes of Incomplete Pump FillageCauses of Incomplete Pump FillageBoth gas and liquid are present at Both gas and liquid are present at the pump intake:the pump intake: gas interferencegas interference..

Not enough liquid to fill the pump Not enough liquid to fill the pump barrel: pump flow rate greater than barrel: pump flow rate greater than well production,well production, well pumped offwell pumped off. .

Flow restrictionFlow restriction at the pump intake: at the pump intake: flow through SV less than plunger flow through SV less than plunger displacement.displacement.

Dynamometer Cards DefinitionDynamometer Cards DefinitionDynamometer Cards Definition1) Surface dynamometer

card is the plot of the measured rod loads at the various positions throughout a complete stroke; the load is usually displayed in pounds of force and the position is usually displayed in inches.

2) Pump dynamometer cardis a plot of the calculated loads at various positions of pump stroke andrepresents the fluid load the pump applies to the bottom of the rod string.

Pump Card

Surface Card

Fluid PoundsFluid PoundsFluid Pounds Fluid Pound & Fluid Pound & Gas PoundsGas Pounds A gas A gas pound (Lower Left) pound (Lower Left) does not move does not move progressively to the progressively to the left. It moves back left. It moves back and forth and jumps and forth and jumps around on the trace around on the trace as more or less gas as more or less gas enters the pump and enters the pump and changes where the changes where the valves close and open valves close and open during the during the downstrokedownstroke portion of portion of the pumping cycle.the pumping cycle.

Gas PoundsGas PoundsGas Pounds

11

9797

1122 33 441111

Fluid Load, Fo, Has Two Reference LinesFluid Load, Fluid Load, FoFo, Has Two Reference Lines, Has Two Reference LinesFoFo -- Fluid Load is the load Fluid Load is the load

that the Pump that the Pump applies to the rod applies to the rod string.string.

FoFo = = FoUpFoUp -- FoDnFoDnUpstroke: Upstroke: FoUpFoUp = (Pdis = (Pdis -- Pintk) * ApPintk) * ApDownstroke: Downstroke: FoDnFoDn = 0= 0

Two reference linesTwo reference lines1. 1. FoMaxFoMax = Pdis * Ap= Pdis * Ap

FoMax is the maximum load that the FoMax is the maximum load that the pump would apply to the rod string pump would apply to the rod string assuming pump intake pressure is zero. assuming pump intake pressure is zero. The well would provides no help in The well would provides no help in lifting the fluid to the surface.lifting the fluid to the surface.

2. Zero Load Line2. Zero Load Line0 166.3-1.25

0

1.25

2.50

3.75

5.00

6.25

7.50 Fo Max

FoUp

FoDnFoFo

Increase PIP to PDPIncrease PIP to PDPIncrease PIP to PDPTo Open TVTo Open TVTo Open TV

Fo - Differential Load Required to Open TVFoFo -- Differential Load Required to Open TVDifferential Load Required to Open TV

FoFo (Pump Card(Pump Card ) = () = (FoUpFoUp –– FoDnFoDn))

FoUpFoUp

FoDnFoDn

FoFo (Valve Test) = (TV (Valve Test) = (TV –– SV)SV)

TVTV

SVSV

PIP = Tubing Pressure + Tubing Gradient * Pump Depth (TVD) PIP = Tubing Pressure + Tubing Gradient * Pump Depth (TVD) –– FoFo /Plunger Area/Plunger AreaPDP = Tubing Pressure + Tubing Gradient * Pump Depth (TVD)PDP = Tubing Pressure + Tubing Gradient * Pump Depth (TVD)

Sucker Rod Pump Valve DiagramSucker Rod Pump Valve Diagram1) Main valve components

in the pump are the standing and the traveling valve.

2) Standing valve, intake valve, fixed to tubing considered to be stationary, and acts as a check valve to keep well fluid in the tubing on the downstroke.

3) Traveling valve, discharge valve, moves with the rod string. Acts as a check valve to keep well fluid in the tubing on the upstroke

Steps in the Pump Operation

Steps in the Steps in the Pump Pump OperationOperationB)B) Standing Valve opens, when Standing Valve opens, when

rods stretch to pick up fluid rods stretch to pick up fluid load, Fo, from tubing. load, Fo, from tubing.

BB--C)C) Fluid load, Fo, is carried by Fluid load, Fo, is carried by the rods as well fluids are the rods as well fluids are drawn into the pump. drawn into the pump.

C) C) Standing valve closes, and Standing valve closes, and the traveling valve remains the traveling valve remains closed. Cclosed. C--D pressure inside D pressure inside the pump increases until it is the pump increases until it is slightly greater than the slightly greater than the pump discharge pressure. pump discharge pressure.

AA

BB CC

DD

A) A) Start of the upstroke, the traveling valveStart of the upstroke, the traveling valveand standing valve are both closed.and standing valve are both closed.

D) Pump discharge pressure (Pd) equals the staticD) Pump discharge pressure (Pd) equals the statictubing pressure (Pt), and the traveling valvetubing pressure (Pt), and the traveling valveopens. Fluid load, Fo, is carried by tubing.opens. Fluid load, Fo, is carried by tubing.

D D -- A, the fluid in the A, the fluid in the pump is displaced pump is displaced through the traveling through the traveling valve into the tubing valve into the tubing and and ZEROZERO fluid load fluid load is on rods.is on rods.

Synthetic Pump Cards:Gas InterferenceSynthetic Pump Cards:Gas Interference

Gas Interference is causing decrease of EPT. Pump components 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

Gas Interference: Incomplete Pump Fillage and High Fluid LevelGas Interference: Incomplete Pump Fillage and High Fluid Level

Fo Rods

Fo Well

Gas InterferenceGas Interference

Traveling valve Traveling valve opens when opens when pressure in pressure in barrel exceeds barrel exceeds the pressure at the pressure at the pump the pump discharge at the discharge at the bottom of the bottom of the tubing.tubing.

The dynamometer card indicates gas in the pump. Gas compression occurs during the downstroke from C to D and causes the traveling valve to opened at D.

Effect of PIP onGas Interference and Fluid PoundEffect of PIP onGas Interference and Fluid Pound

Liquid

Gas

Effect of PIP on Pump CardEffect of PIP on Pump Card

Gas

Liquid

Synthetic Pump Cards:Gas Locked PumpSynthetic Pump Cards:Synthetic Pump Cards:Gas Locked PumpGas Locked Pump

Gas Locked Pump...Both valves remain closed because the static tubing pressure, (Pt), is greater the pump discharge pressure, (Pbarrel), 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 leakage of fluids past the plunger, or the fluid level is allowed to rise so that a smaller compression ratio is required to force gas from the pump into the tubing. The pressure relations are:

Tubing anchored or unanchored

Pt > Pbarrel > Pint

Pt > Pbarrel at bottom of stroke

Pbarrel > Pint at top of stroke

Gas interference ?Gas interference ?

High Pressure - Almost Gas LockedHigh Pressure - Almost Gas Locked

Gas LockGas LockGas Lock Low Pressure Gas LockLow Pressure Gas Lock1)1) Surface dynamometer card Surface dynamometer card

located near the calculated located near the calculated traveling valve load test line. traveling valve load test line.

2)2) Both the standing and Both the standing and traveling valves remain traveling valves remain closed closed

3)3) Gas lock condition caused Gas lock condition caused by having too low a by having too low a compression ratio in the compression ratio in the pump when producing both pump when producing both gas and liquid. gas and liquid.

4)4) Waste space in the pump, Waste space in the pump, too short a valve rod or pull too short a valve rod or pull tube, or a the rod string not tube, or a the rod string not being spaced out properly being spaced out properly when the pump is seated when the pump is seated usually causes the low usually causes the low compression problems.compression problems.

5)5) Liquid Slippage into Pump Liquid Slippage into Pump Prevents Gas LockPrevents Gas Lock0 42.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

4.50

5.00

36.1

Fo Max

Wrf

Wrf + Fo Max

Kt

Fluid SlippageFluid SlippageFluid Slippage

Synthetic Pump Cards:Fluid PoundSynthetic Pump Cards:Synthetic Pump Cards:Fluid PoundFluid Pound

Severe fluid pound, well is being pumped off. Pump components functioning properly. BUT, sudden unloading of rods results is reduced equipment life! Shoot fluid level to verify pump intake not blocked and fluid level at pump intake.

Tubing anchored, EPT<MPT. Unanchored tubing, EPT<MPT

Fo Rods

Same Well with Full PumpSame Well with Full Pump

Full

Pound

Pump Capacity Exceeds Inflow of Fluids from Well.

Controlling Pump Run timeImproves Efficiency by Matching Pump Displacement To Inflow of Fluids from Well.

Fluid Level @ Pump - Fluid Pound? Timer or Pump Off Controller CandidateFluid Level @ PumpFluid Level @ Pump -- Fluid Pound? Fluid Pound? Timer or Pump Off Controller CandidateTimer or Pump Off Controller Candidate

Fluid Fluid PoundPound

Rods Buckle (Train Wreck Effect )Rods Buckle (Train Wreck Effect )

Fluid PoundFluid Pound

Plunger Slows to Open TV

Plunger Slows to Open TV

Pump Load & Velocity

Rods Buckle (Train Wreck Effect )Rods Buckle (Train Wreck Effect )

Gas Gas InterferenceInterference

Plunger Slows to Open TV

Pump Load & Velocity

Predicted Surface Dynamometer CardIntake Pressure: 80 psig Pump Fillage: 50% SPM: 8

Predicted Surface Dynamometer CardIntake Pressure: 80 psig Pump Fillage: 50% SPM: 8

0 25 50 75 100 125 150-4

0

4

8

12

16

20

24

28

32Load (1000 lbf)

Position from Bottom of Stroke (in)CASE12.ACP: 8.00 SPM, 144.000 in Stroke, Production = 159.1 bbl/d

Polished Rod

Effective Pump Load

Perm. Load - In Balance

SV/TV Open

CBE

SV

TV

Top of Fluid in Pump

Liquid

Gas InterferenceGas InterferenceGas InterferenceGas in Pump is the Most Common Operational ProblemResults in Lost Pump DisplacementPump and Rod Weight must Compress Gas Inside Pump Barrel on Down StrokeSR Pump is Inefficient CompressorIncreased Rod and Tubing Failures

Gas in Pump is the Most Common Gas in Pump is the Most Common Operational ProblemOperational ProblemResults in Lost Pump Results in Lost Pump DisplacementDisplacementPump and Rod Weight must Pump and Rod Weight must Compress Gas Inside Pump Barrel Compress Gas Inside Pump Barrel on Down Strokeon Down StrokeSR Pump is Inefficient CompressorSR Pump is Inefficient CompressorIncreased Rod and Tubing FailuresIncreased Rod and Tubing Failures

Questions ?Questions ?