Dewatering Requirements for Low Productivity Gas...

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Gas Well Deliquification Workshop Sheraton Hotel, Denver, Colorado February 22 - 24, 2010 Dewatering Requirements for Low Productivity Gas Wells Michael W. Conway Stim-Lab, Inc.

Transcript of Dewatering Requirements for Low Productivity Gas...

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Gas Well Deliquification WorkshopSheraton Hotel, Denver, Colorado

February 22 - 24, 2010

Dewatering Requirements forLow Productivity Gas Wells

Michael W. Conway

Stim-Lab, Inc.

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Low Rate Gas Well Completionsin North America

• There are a large number of commerciallysuccessful Gas Wells in the US

• Detailed analysis of many of those wellscontinues to show that the completion efficiencyas measured by apparent fracture half length anddrainage area is surprising low in a large numberof cases

• These wells have a lot more potential than we aresending down the pipeline

Feb. 22 - 24, 2010 2010 Gas Well Deliquification WorkshopDenver, Colorado

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Premise

• Two primary factors limiting productionfrom Low Potential Gas Wells in NorthAmerica are:

– Inability to consistently maintain fluid level inthe casing below the perforations

– Excessive drawdown which significantlyreduces the flow capacity of

• Unpropped natural/induced fractures

• Proppant filled fractures

The topic of this discussion is managementof fluid levels in gas wells

Feb. 22 - 24, 2010 2010 Gas Well Deliquification WorkshopDenver, Colorado

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Historical Example With Travis Peak Production

• In the mid ’80’s Enserch conducted an extensive field study inthe Travis Peak to answer the following question:

– Why can we complete 250’ (1 stage) or 1000’ (4 stages) and still make2.5 MMcfd?

• They concluded the following:

• The tubing tail was placed 50’ above the upper mostperforation

• The standing level of water averaged 140’ below the tubing tail

• There was no gas production below the standing level ofwater

The following recent well appears to be headed forthat same production condition

Feb. 22 - 24, 2010 2010 Gas Well Deliquification WorkshopDenver, Colorado

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Travis PeakCompletion Profile

• Note the fluid level inthe lower part of theinterval and the froth upto the tubing

Frac Stage Interval (ft) Water(b/d) % Water Gas(Mscf/d) % GasStage 4 7506-7618 193 36.14% 207 10.91%Stage 3 8363-8528 19 3.56% 1200 63.26%Stage 2 8642-8862 6 1.12% 268 14.13%Stage 1 8881-9216 316 59.18% 222 11.70%

Tubing

Feb. 22 - 24, 2010

2010 Gas Well Deliquification WorkshopDenver, Colorado

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Field Data From Pumping Coalbed Methane Well

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10

100

1000

1/11/94 4/21/94 7/30/94 11/7/94 2/15/95 5/26/95 9/3/95 12/12/95 3/21/96 6/29/96

MONTH/DAY/YEAR

GA

SR

AT

E(M

CF

D)

0.1

1

10

100

Line PressureMCFGPD

LINE

PR

ES

SU

RE

(psi)

Refrac withwater and sand

Lower pump 30 ft(now below perfs)

Pump Down

1

10

100

1000

1/11/94 4/21/94 7/30/94 11/7/94 2/15/95 5/26/95 9/3/95 12/12/95 3/21/96 6/29/96

MONTH/DAY/YEAR

GA

SR

AT

E(M

CF

D)

0.1

1

10

100

Line PressureMCFGPD

LINE

PR

ES

SU

RE

(psi)

Refrac withwater and sand

Lower pump 30 ft(now below perfs)

Pump Down

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Effect of A Standing Level of Water

• We contend that the negative impact of a standing levelof water is not due to the backpressure

• The relative permeability effects are much moresignificant

– Gas flow capacity in the proppant pack

– Development of gas relative permeability in the reservoir

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Proppant Pack Desaturation:Saturation Profile with 48 sL/min Gas

and 650 ml/min WaterSaturation very quick, desaturation exceedingly slow

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Summary of Experimental ResultsEffect of Water in Wellbore on Gas Permeability

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20

40

60

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120

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Below

Perfs

Above

Perfs

Below

Perfs

MidPer

f

Above

Perfs

Below

Perfs

MidPer

f

Above

Perfs

Below

Perfs

MidPer

f

Above

Perfs

Below

Perfs

MidPer

f

Above

Perfs

Wellbore Water Level

Per

mea

bili

ty(D

)

GAS-L/min

WATER-ml/min

37650

5.3650

5350

2.5300

8.6100

StrongProducer

WeakProducer

Actual Gas and Water Rates cannot be related to a well productionconditions. The relative ratio’s however, are relevant.Feb. 22 - 24, 2010 9

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Implications

• These tests were conducted with an active waterdrive which is different from recovering stimulationfluids with gas drive fluid production

• This does not include the impact of water level in theproppant pack on saturation in reservoir

– Capillary end effect will force near 100% Sw at the fractureface and water imbibition will continue to hinder dewatering

Feb. 22 - 24, 2010 2010 Gas Well Deliquification WorkshopDenver, Colorado

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Evaluation of Additives to Promote Dewatering

• Horizontal Wells require that the fracturebelow the lateral produce water againstgravity to develop gas flow capacity

– To produce water, continuous relative permeabilityto water must be maintained through the proppantpack and is difficult to achieve when the tendencyis for water to gravity segregate to the bottom ofthe fracture

• Studies are currently being conducted for theStim-Lab Proppant Consortium since 2006

Feb. 22 - 24, 2010 2010 Gas Well Deliquification WorkshopDenver, Colorado

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STIM-LAB PROPPANT CONSORTIUM:8” x 6’ Vertical Slot Dewatering Experiment

• A 0.3” proppant pack is packed into the slotwhich has a Plexiglas™ front to allow view of theflow patterns

• A sandstone porous media is on the back of theslot

• The whole system is initially water saturated withdyed water

• Nitrogen is flowed through the injection ports tothe back side of the 8” x 6’ slot and percolatedthrough the sandstone backing to dewater thesystem

– Initially, any or all of the valves can be opened

• A constant pressure gas displacement isconducted starting with a gas pressure of 3 psi ormore, which is slightly higher than the initialhydrostatic head in the system of ~2.6 psi

Sandstone

Proppant

Plexiglass

Gas

End View

Feb. 22 - 24, 2010 2010 Gas Well Deliquification WorkshopDenver, Colorado

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Slot System Setup

MistHumidifying

System

6’ Slot

Gas Separator and Balance

Mass FlowController

Water pump for humidifier

Valve 1

Valve 2

Valve 3

Valve 4

Valve 5

Valve 6

Dp

Horizontal Well

Orifice Gas Meter

Feb. 22 - 24, 2010 2010 Gas Well Deliquification WorkshopDenver, Colorado

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WaterProduced

0 352 489.5 559.6 591 620.3 634.7 Shut-in13 min14

MobileWater ~1400 gm

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Potential Technologies to AchieveMaximum Production from Gas Wells• Most vertical gas shale wells do not have

adequate gas velocity potential to unload tubinglet alone the casing across from the perforations

• A successful production strategy needs to:

– positively maintain water level below perforations

– Provide the mechanism to accurately determining BHFPfrom surface data

• With the trend toward larger water volumes usedin fracture stimulation, most of the cases wehave examined must have active water removalto achieve optimum long term production

– These wells are water wells and must be treated as suchfor the rest of their productive life

Feb. 22 - 24, 2010 2010 Gas Well Deliquification WorkshopDenver, Colorado

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Potential Technologies: Siphon Strings

• Tubing must be run long before it is needed

– It is being run primarily to dewater the wellbore, not reducebottom hole pressure

• Hold backpressure on casing to control pressure

– It should be placed below the perforations

• Must be run while you have adequate flowing bottom holepressure to overcome U tube effects

• This is typically a short lived solution in lowpermeability reservoirs

– Foamers are often used next

• CAUTION: If get in reservoir, can block gas flow

– Plungers are often next before resorting to active technologies

Feb. 22 - 24, 2010 2010 Gas Well Deliquification WorkshopDenver, Colorado

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Example: Plunger Lift Does Not MaintainWater Level Below Perforations

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1/7/2009 1/27/2009 2/16/2009 3/8/2009 3/28/2009 4/17/2009 5/7/2009 5/27/2009 6/16/2009

Date

Pre

ssu

re(p

si),

Gas

Rat

e(m

cfd

)

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6200

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6600

6800

7000

7200

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7600

7800

8000

Flu

idL

evel

(ft)

Casing Pressure Tubing Pressure Gas Rate Fluid Level

Shale

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Potential Technologies: Rod Pumps

• Conventional systems can dewater the wellbore ifand only if:

• The tubing tail is below the perforations

• Often challenged with gas locking whenback pressure is applied to the system

• Adequate rat hole is critical for optimumdewatering

Feb. 22 - 24, 2010 2010 Gas Well Deliquification WorkshopDenver, Colorado

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Rod Pumps and Controls

• Modern Pumping Systems Allow Control of BottomHole Pressure Using Surface Measurements

– Inferred Pump Load is Determined From Surface RodLoad and Down Hole Rod Modeling

– Inferred Pump Load Coupled With Surface Tubingand Casing Pressure Measurements Allow BottomHole Pressure Estimate

– Down Hole Dynamometer Plots Derived FromInferred Pump Load and Position Provide PositiveFeedback of Casing Fluid Level at the Pump Intake

– Pumping Speed is Continuously Adjusted toMaintain Desired Casing Fluid Level

Feb. 22 - 24, 2010 2010 Gas Well Deliquification WorkshopDenver, Colorado

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Example Control SystemLinear Rod Pump for Sucker Rod Pumping:

Contact: Chri=com Unico USFeb. 22 - 24, 2010 20

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Dynamometer Analysis:Compute Liquid Rate and BHFP

gross pump stroke

pump fill

tubing stretch

net pump stroke

rod strokerod stretch

buoyant rod weight

gas compression

gas or fluid pound

pump load

rod dynamicsSurface

Downhole

Position, inches

Load

,lbs

Feb. 22 - 24, 2010 2010 Gas Well Deliquification WorkshopDenver, Colorado

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Potential Technologies: Gas LiftBelow Packer Annular Gas Lift with Velocity Enhancement

ProductionLift Gas

Technology is owned byMarathon Oil Company

•Technology is licensed toProduction Control Services

Contact Information

Stuart Harlow, PCS

Houston, Texas

281-350-2084

Feb. 22 - 24, 2010 2010 Gas Well Deliquification WorkshopDenver, Colorado

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Below Packer Annular Gas Liftwith Velocity Enhancement

• Above the packer, the gas injection is through the tubing-casing annulus and the production is up the tubing

• Below the packer, gas injection is inside the tubing andproduction through the tubing-casing annulus– Allows for using standard wireline retrievable gas lift valves

below the packer

• Packer and cross over system set in the vertical section ofthe hole in Horizontal Wells– Tail pipe is run into the horizontal section with the end of the

tubing placed at the low point in the section

– An orifice check is run in the end of the tubing for gasinjection

• Injection and production is crossed over at the packer.

Feb. 22 - 24, 2010 2010 Gas Well Deliquification WorkshopDenver, Colorado

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The Prize: Relative Permeability Effects

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3400 3500 3600 3700 3800 3900 4000 4100 4200 4300

Flow Time (min)

Dif

fere

nti

alF

low

ing

Pre

ssu

e(p

sid

)

0.001

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10000

Con

ductivity

(μD

-ft),Rate

(mL/m

in)

Net

Co

nfining

Stress

(psi)

Fresh Water Nitrogen NCS Conductivity Rate

XTO Energy Inc Doss N #1H Barnett Shale from 5216.6'

Water and Gas Conductivity & Pressure Response

7189T154

T = 154 °F

4.35 µD-ft (Gas)

0.2 µD-ft (Fresh water)

In Naturally Fractured Reservoirs (Shales)

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Conclusion

How You Produce a WellMay be More Important

than How YouStimulated it!

Feb. 22 - 24, 2010 2010 Gas Well Deliquification WorkshopDenver, Colorado

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– Display the presentation at the Workshop.

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Other use of this presentation is prohibited without the expressedwritten permission of the author(s). The owner company(ies) and/orauthor(s) may publish this material in other journals or magazines ifthey refer to the Gas Well Deliquification Workshop where it wasfirst presented.

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