Well Production Challenges and Solutions in a Mature, Very Low-Pressure Coalbed Methane Reservoir

Okotie, Victoria Uduak; Moore, Robert L.

doi:10.2118/137317-ms

Cited by 11 publications

(4 citation statements)

References 7 publications

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“…In the event of complete failure, the problem of creation of fines may arise, requiring well "cleanout," although the permeability increase due to increased cleat porosity may continue after recommencement of production. This hypothesis explains the observations in some areas of the fairway in the San Juan basin [Okotie and Moore, 2010]. Finally, if this can be confirmed in the future studies, the true impact of the finding would be CBM production from deeper coals, where the initial vertical stress is very high and the initial permeability very low.…”

Section: Initial State Of Stresssupporting

confidence: 61%

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Evaluation of in situ stress changes with gas depletion of coalbed methane reservoirs

Liu

Harpalani

2014

JGR Solid Earth

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A sound knowledge of the stress path for coalbed methane (CBM) reservoirs is critical for a variety of applications, including dynamic formation stability evaluation, long-term gas production management, and carbon sequestration in coals. Although this problem has been extensively studied for traditional oil and gas reservoirs, it is somewhat unclear for CBM reservoirs. The difference between the stress paths followed in the two reservoir types is expected to be significant given the unique sorption-induced deformation phenomenon associated with gas production from coal. This results in an additional reservoir volumetric strain, which induces a rather "abnormal" loss of horizontal stress with depletion, leading to continuous changes in the subsurface formation stresses, both effective as well as total. It is suspected that stress changes within the reservoir triggers formation failure after significant depletion. This paper describes an experimental study, carried out to measure the horizontal stress under in situ depletion conditions. The results show that the horizontal stress decreases linearly with depletion under in situ conditions. The dynamic stress evolution is theoretically analyzed, based on modified poroelasticity associated with sorption-induced strain effect. Additionally, the failure tendency of the reservoir under in situ conditions is analyzed using the traditional Mohr-Coulomb failure criterion. The results indicate that depletion may lead to coal failure, particularly in deeper coalbeds and ones exhibiting large matrix shrinkage.

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Section: Initial State Of Stresssupporting

confidence: 61%

“…Hence, the coal formation may, in fact, fail at low pressures. This would explain the increasing amounts of coal fines during production and the loss in permeability observed in some low pressure (mature) CBM wells in the San Juan Fairway [Okotie and Moore, 2010].…”

Section: Coal Formation Stability Analysismentioning

confidence: 98%

Evaluation of in situ stress changes with gas depletion of coalbed methane reservoirs

Liu

Harpalani

2014

JGR Solid Earth

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“…A simple logarithmic correlation based on Terzaghi's effective stress seems to be appropriate over a defined stress range. Yet, coal seams subjected to CH 4 depletion and/or CO 2 injection under in-situ conditions may experience significant shear stresses which promotes fracture slip and dilation and coal fines production with a significant impact on seam permeability as well (Okotie and Moore, 2010;Palmer, 2008).…”

Section: Model Predictionsmentioning

confidence: 99%

Measurement and modeling of adsorptive–poromechanical properties of bituminous coal cores exposed to CO2: Adsorption, swelling strains, swelling stresses and impact on fracture permeability

Espinoza

Vandamme

Pereira

et al. 2014

International Journal of Coal Geology

104

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International audienceThe reservoir response of unmineable coal seams to primary and enhanced natural gas recovery is strongly affected by gas sorption and the swelling properties of the coal reservoir rock. In-depth understanding of the process of gas sorption/desorption in the coal matrix, induced deformation and measurement of relevant physical parameters are critical for predictive reservoir management. Models used in industry practice are based on swelling strains measured in “free” swelling coal or on empirical correlations between strain and adsorption, and predict permeability changes based on changes of porosity or stress calculated assuming an analogy with thermoelasticity. However, not only coal seams are subjected to in-situ stresses and geometrical boundary conditions but also sorption and strain are strongly coupled. Representative experiments and a truly coupled model for coal seams are needed in challenging applications. We present a set of triaxial testing measurements on 38 mm diameter fractured sub-bituminous/bituminous coal cores exposed to CO2. Testing includes the measurement of fluid uptake, adsorption-induced strains and stresses, and the impact on simultaneously measured permeability. Noteworthy, we measured increases in effective stress of up to 29 MPa when injecting CO2 at 5 MPa and preventing the coal core to swell. The results are analyzed with a poromechanical model in which coal matrix microporosity and adsorption-induced phenomena are embedded into a fractured reservoir rock with transverse isotropic properties. The adsorptive–mechanical coupling in the coal matrix is integrated through an adsorption stress function and fractured coal permeability is estimated as a function of Terzaghi's effective stresses (parallel and perpendicular to the bedding plane). The experimental results and model predictions help identify the characteristic response of coal microporosity and cleat macroporosity on the poromechanical response of coal cores, and suggest that order of magnitude changes of reservoir permeability observed in the field are linked to sorption-induced change on Terzaghi's effective horizontal stress under laterally constrained displacement condition. Together, the modeling and experimental characterization offer unprecedented insights into the mechanics of coal

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“…(EUR) Permeability growth followed by permeability loss as reservoir pressure depletes(Okotie and Moore, 2010).…”

mentioning

confidence: 99%

Selected topics in coalbed methane reservoirs

Morad

2012

Journal of Natural Gas Science and Engineering

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Well Production Challenges and Solutions in a Mature, Very Low-Pressure Coalbed Methane Reservoir

Cited by 11 publications

References 7 publications

Evaluation of in situ stress changes with gas depletion of coalbed methane reservoirs

Evaluation of in situ stress changes with gas depletion of coalbed methane reservoirs

Measurement and modeling of adsorptive–poromechanical properties of bituminous coal cores exposed to CO2: Adsorption, swelling strains, swelling stresses and impact on fracture permeability

Selected topics in coalbed methane reservoirs

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