Gas Well Deliquification Workshop - ALRDCalrdc.com/workshops/2010_2010GasWellWorkshop/Private/VII... · Gas Well Deliquification Workshop Sheraton Hotel, Denver, ... Bin Hu, Rahel

Gas Well Deliquification WorkshopSheraton Hotel, Denver, Colorado

February 22 - 24, 2010

Transient Simulation and Optimization of IntermittentProduction in A Liquid-loaded Gas Well

Authored by

Håvard Holmås, Bin Hu, Rahel Yusuf, SPT Group

Kees Veeken, Shell E&P EuropePresented by

Stephanos Zunez, SPT Group

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

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Contents

• Short on automated intermittent gas production

• OLGA-ROCX modeling

• Simulation results

• Conclusions

• Future work

Gas well liquid loading

• Gas rate is too low

• Annular-mist flow cannot be maintained

• Liquid film starts tofall (collapse) andbridge the flow path

• Flow changes toslug/churn mode andgradually ceasesdepending onreservoir properties


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Reducing Gas Rate


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Production modes after loading

• Irregular intermittent production– Wellhead choke is kept open

– Liquid and gas are bursting up intermittently when producing

– The production interval is irregular and normally short

• Meta-stable production– Gas bubbling up through the liquid column

– In a very low rate, normally not economic

– No or few liquid is observed at the wellhead

• Automated intermittent production

– Wellhead choke is actively controlled

– Liquid is produced out as slug, following by a long period of stable gasproduction

– Well is shut in prior to loading re-occurs, waiting for near-wellbore reservoirpressure to build up


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Irregular Intermittent Gas Production


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Automated intermittent gas production


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OLGA-ROCX modeling

• OLGA

– An transient multiphase flow model for well flow and pipe flow

– Normally uses IPR as inlet boundary

• ROCX

– A small reservoir simulator

– Normally uses constant Pwf as outlet boundary

• For automated intermittent production modeling,

– one needs integrate the wellbore model with the reservoirmodel

– as the process involves dynamic flow interactions betweenthe wellbore and near-wellbore


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Schematically, it looks like• Near-wellbore

reservoirmodeled inROCX

• Wellboremodeled inOLGA

X

Y

Z

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1Oil Saturation

OLGA-ROCX integration

Rocx = plug-in to OLGA

Implicit coupling

Unified PVT

X

Y

Z

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1Oil Saturation

The basic parameters of the sample well

• Well parameters– Tubing depth, 0-3000 m

– Tubing ID, 0.100 m

– Tubing head pressure,20 bara

– Maximum gas rate,2e+06 Sm3/d

• Reservoir parameters– Top Reservoir Depth, 3000 m

– Reservoir thickness, 50 m

– Radius, 560 m

– Porosity, 12%

– Gas Saturation, 75%

– Net-to-gross, 100%

– Gas specific gravity, 0.6

– Reservoir permeability, 5 mD


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How the simulation was set up?

50m

560m

0.1m

3000m

20m

FigureError!Notextof specifiedstyleindocument..1: Schematicof thetubingandnearwellborereservoir.

• Reservoir was descritized into10 numerical layers

• Assuming the well has flow rateand THP sensors, but no BHPsensor

• The wellhead choke iscontrolled to close when thesurface rate is getting close tothe loading rate

• The wellhead choke iscontrolled to reopen when theTHP builds up to the requiredlevel

High Selector FCPC

Wellhead Choke

Wel

lbor

e


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Validation on the OLGA-ROCX model


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Initial conditions prior to "cycling"

Please note the high liquid content in the tubingafter loading


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Simulation matrix

• Different combinations of theshut-in flow rate and re-openpressure build-up were triedin order to find the optimaloperation.

• Reservoir pressure at 41 bara

• The critical rate is around 80KSm3/day

• The simulation was run for aprocess duration of 10 days

• The average gas productionrate is calculated to comparewith metastable rate (withoutcycling)

33.5 32 30

90 x x x

85 x x x

80 x x x

60 x x x

40 x - x

PT_crit

QGS

T_cr

it


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Example of the simulation results in gas rate

Zoom-in view


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Average gas production fromdifferent combinations


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Cycle observed onthe reservoir side

Main observation:•The water goes back andforth to and from the reservoir•There is a net accumulation ofwater in the near-wellboreregion during cycling•The well's cycling capabilityis dependent on the speed ofthe water accumulation


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Conclusions

• OLGA-ROCX can successfully capture the dynamics ofthe intermittent production

– For the simulation presented, the integrated model runs at 10times the real speed

– The model can be used to evaluate the well cycling capabilityand optimize the cycling operation

• There is indeed an optimization issue in the wellcycling operation depending on the availability ofmeasurable signals

– A good combination of shut-in rate and re-open pressure cangive an average rate three times higher than the metastablerate


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Future work

• More investigation to be done on what kind of wells(reservoirs) have the cycling potential

– For example, it is observed from this study that the well hasbad cycling capability if starting the cycle after loading.However additional simulation shows that the well could becycled very long if pro-actively starting the cycling before theloading happens

– Some fractured reservoirs exhibit good cycling capability overthe non-fracture reservoir according to field report. This is tobe confirmed and investigated in the future study

• More control strategy investigation based on theavailabilities of the different well signal measurements


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Copyright

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– Display the presentation at the Workshop.

– Place it on the www.alrdc.com web site, with access to the site to beas directed by the Workshop Steering Committee.

– Place it on a CD for distribution and/or sale as directed by theWorkshop Steering Committee.

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.

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

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Gas Well Deliquification Workshop - ALRDCalrdc.com/workshops/2010_2010GasWellWorkshop/Private/VII... · Gas Well Deliquification Workshop Sheraton Hotel, Denver, ... Bin Hu, Rahel