numerical model analysis of gas production in unconventional gas reservoir

8/10/2019 Numerical Model Analysis of Gas Production in Unconventional Gas Reservoir

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Outline

Introduction Purpose Reservoir Model Case Study

Numerical Model Analysis Conclusion


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Introduction

The convectional representation-elementary-volume is notaccurate in estimating gas flow in unconventional gas reservoir

because they are usually located in hostile environment with hightemperature, high pressure with extremely low permeability and

porosity.

Two examples of common unconventional Gas reservoirs are:Tight Gas Reservoir

Shale Reservoir Coalbed Methane


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Tight gas reservoirs are more compact than brick block with very

low porosity and permeability properties Tight gas reservoir has permeability in the range of nanoDarcy to microDarcy .

Shale gas reservoir has a lower rock qualities that tight gasreservoirs and permeability are usually in nanoDarcy.

The use of horizontal completion andhydraulic fracturing has make it

economically possible to recover gasfrom unconventional reservoir

Introduction

http://www.total.com/en/energies-expertise/oil-gas/exploration-production/strategic-sectors/unconventionalgas/presentation/three-main-sources-unconventional-gas?%FFbw=kludge1%FF


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Known Unconventional Gas Resources in the Continental United States

North America Unconventional Gas Reserves- Estimated Gas in Place ~ 8,228 TCF

- Proved reserves ~ 2,074 TCF- US consumption ~ 23 TCF (EIA )

Introduction

http://americanenergyinnovation.org/wp-content/uploads/2013/03/Case-Unconventional-Gas.pdf


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Purpose

Quantifying flow in unconventional gas reservoir has been asignificant challenge.

This presentation explains an analysis model that is incorporatessome of the complexities that unconventional reservoirs aresubjected to.


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Reservoir Model In this model, it is assumed that there is no natural fracture

in the formation and only the Stimulated Reservoir Volume(SRV) around the hydraulic fracture are active. HydraulicFracture will improve the well productivity by:

Increasing pore pressure

Reducing effective stressImproved permeability


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From the case study data above, it will deduced that tpf/tpm >>1.Production is strictly controlled by the hydraulic fracture

Case Study


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Numerical Model Analysis

Klinkenberg effect with threedifferent matrix permeability

Klinkenberg effect is highestat low pressure and lowervalues of permeability

Klinkenberg beta factor estimations for three permeability values

Klinkenberg Effect


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Time, years

Klinkenberg effect of Unconventional Gas Flow

Case without Klinkenberg

Case with Klinkenberg

The figure shows the difference in production with and without theKlinkenberg effect. Including the

Klinkenberg uncertainty in thesimulation improves theunderstanding of the unconventionalreservoir and increases the total gas

production by approximately 9%.

Numerical Model AnalysisKlinkenberg Effect


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Amount of gas adsorbed is determined according to the Langmuir s

isotherm as a function of reservoir pressure. Reservoir pressure drop = moreadsorbed gas released from solid to free gas phase.

Gas Adsorption


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TIme, years

Gas production from free gas and adsorbed gas

Free Gas Produced

Adsorbed Gas Produced

Total Gas Production


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The effective porosity, permeability, and capillary pressure of rock areassumed to correlate with the mean effective stress

Geomechanics Effect

Effective stress increases as pore pressure decreased due to production. This leads to reservoirrock deformation and significantdrop in permeability. IfGeomechanics effect is not

consider in the simulation, it willlead to overestimation of gas production



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In the early stage production, not considering the non-Darcy flowleads to overestimation of gas production by approximately 5%.After 40 years of production, gas flow behaves in the well behavesexactly as Darcy flow .

Non-Darcy Flow



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Conclusion

The incorporation of the complexuncertainty associated with unconventionalreservoir in this analysis improves our

understanding of gas flow behavior andultimately produce a more accurate

production forecast.


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SourcesCipolla, C.L., E.P. Lolon, J.C. Erdle, and B. Rubin,Reservoir Modeling in Shale-Gas Reservoirs, Reservoir

Evaluation & Engineering , August 2010

Wu, Y.S., "Numerical Simulation of Single-Phase and Multiphase Non-Darcy Flow in Porous and Fractured

Reservoirs,"

Wu, Y.S., et al, "A Generalized Framework Model for Gas Production in Unconventional Gas Reservoir,"

SPE 163609, present at the SPE Reservoir Simulation Symposium held in Woodlands, TX, USA, 18-20February 2013

Konopczynski, Michael. "Smart Completions, Oilfield Sensors and Sensor Technology Intelligent

Completion". PTE 587, USC. 3 February, 2011. Lecture."4D Reservoir Monitoring

USSI US Seismic Systems Inc. Web. 23 April 2014

Bob Godfrey: "Geophysical monitoring of heavy oil production", June 2010, Schlumberger: Heavy Oil, pp. 1


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numerical model analysis of gas production in unconventional gas reservoir

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