How Permeability Depends on Stress and Pore Pressure in Coalbeds: A New Model

Palmer, Ian; Mansoori, J.

doi:10.2118/36737-ms

Cited by 187 publications

(49 citation statements)

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“…The volumetric strain is approximately linearly proportional to the volume of gas adsorbate (Figure 1). Thus the effects of gas sorption on the deformation of isothermal coal seams are treated analogously to the effects of temperature on nonisothermal elastic porous medium [e.g., Palmer and Mansoori, 1996]. Similar to the constitutive equations of nonisothermal poroelastic medium [e.g., Palciauskas and Domenico, 1982;Neuzil, 2003], the stress (s ij ) and strain (e ij ) relation for deforming coal seams can be described as…”

Section: Stress-strain Constitutive Equationmentioning

confidence: 99%

“…[35] Different models have been proposed to describe the permeability change of coal seams during coal bed methane recovery in this paper and in previous studies [e.g., Palmer and Mansoori, 1996;Sawyer et al, 1990;Shi and Durucan, 2004]. Most of those models utilize an exponential dependence of porosity and permeability on stress and pressure except for the linear dependence of porosity in the model proposed by Palmer and Mansoori [1996].…”

Section: Model Limitations and Implicationsmentioning

confidence: 99%

“…Most of those models utilize an exponential dependence of porosity and permeability on stress and pressure except for the linear dependence of porosity in the model proposed by Palmer and Mansoori [1996]. These models also treat the sorption-induced strain analogously to the thermal strain for a poroelastic medium except for the model of Sawyer et al [1990] which does not consider volumetric strains.…”

Section: Model Limitations and Implicationsmentioning

confidence: 99%

“…[36] In order to simplify the problem most previous studies [e.g., Shi and Durucan, 2004;Palmer and Mansoori, 1996] have assumed purely vertical strain or uniaxial strain to determine the stress distribution around the wellbore. The model proposed by Shi and Durucan [2004] is similar to the uniaxial strain model (U model) in the present study except for slight differences in how volumetric strain is calculated.…”

Section: Model Limitations and Implicationsmentioning

confidence: 99%

“…In contrast, adsorption of acid gas induces strong swelling of coals, consequently narrowing the cleat aperture and reducing the permeability. Models have been formulated to account for the dynamic permeability changes during primary coal bed methane recovery [e.g., Palmer and Mansoori, 1996;Pekot and Reeves, 2003;Sawyer et al, 1990;Shi and Durucan, 2004]. These studies were mainly limited to modeling CH 4 recovery and few studies have considered the impact on permeability of CO 2 or H 2 S injection.…”

Section: Introductionmentioning

confidence: 99%

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Adsorption‐induced coal swelling and stress: Implications for methane production and acid gas sequestration into coal seams

2007

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[1] Sequestration of CO 2 and H 2 S into deep unminable coal seams is an attractive option to reduce their emission into atmosphere and at the same time displace preadsorbed CH 4 which is a clean energy resource. High coal seam permeability is required for efficient and practical sequestration of CO 2 and H 2 S and recovery of CH 4 . However, adsorption of CO 2 and H 2 S into coals induces strong swelling of the coal matrix (volumetric strain) and thus reduces significantly coal permeability by narrowing and even closing fracture apertures. Our experimental data on three western Canadian coals show that the adsorption-induced volumetric strain is approximately linearly proportional to the volume of adsorbed gas, and for the same gas, different coals have very similar volumetric strain coefficient. Impacts of adsorption-induced swelling on stress and permeability around wellbores were analytically investigated using our developed stress and permeability models. Our model results indicate that adsorption-induced volumetric strain has significant controls on stress and permeability of producing and sequestrating coal seams and consequently the potential of acid gas sequestration. Coal seams may undergo >10 times enhancement of permeability around CH 4 -producing wellbores due to a reduction in effective stress as a result of coal shrinking caused by methane desorption accompanying a reduction in reservoir pressure. Injection of H 2 S and CO 2 on the other hand results in strong sorption-induced swelling and a marked increase in effective stress which in turn leads to a reduction of coal seam permeability of up to several orders of magnitude. Injection of mixtures of N 2 and CO 2 such as found in flue gas results in weaker swelling, the amount of which varies with gas composition, and provides the greatest opportunity of sequestering CO 2 and secondary recovery of CH 4 for most coals. Because of the marked swelling of coal in the presence of H 2 S, even minor amounts of H 2 S result in a marked reduction in permeability, and hence sequestration of H 2 S in deep coals will be likely impractical. Furthermore, high stresses resulting from sorption of acid gases will potentially cause the coal to yield, fracture or slip, and produce fine particles, which further affect permeability and thus methane production and acid gas sequestration.Citation: Cui, X., R. M. Bustin, and L. Chikatamarla (2007), Adsorption-induced coal swelling and stress: Implications for methane production and acid gas sequestration into coal seams,

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Section: Stress-strain Constitutive Equationmentioning

confidence: 99%

Section: Model Limitations and Implicationsmentioning

confidence: 99%

Section: Model Limitations and Implicationsmentioning

confidence: 99%

Section: Model Limitations and Implicationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Adsorption‐induced coal swelling and stress: Implications for methane production and acid gas sequestration into coal seams

2007

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Modeling gas displacement kinetics in coal with Maxwell‐Stefan diffusion theory

et al. 2007

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in Wiley InterScience (www.interscience.wiley.com).The kinetics of binary gas counter-diffusion and Darcy flow in a large coal sample were modeled, and the results compared with data from experimental laboratory investigations. The study aimed for a better understanding of the CO 2 -sequestration enhanced coalbed methane (ECBM) recovery process. The transport model used was based on the bidisperse diffusion mechanism and Maxwell-Stefan (MS) diffusion theory. This provides an alternative approach to simulate multicomponent gas diffusion and flow in bulk coals. A series of high-stress core flush tests were performed on a large coal sample sourced from a Bowen Basin coal mine in Queensland, Australia to investigate the kinetics of one gas displacing another. These experimental results were used to derive gas diffusivities, and to examine the predictive capability of the diffusion model. The simulations show good agreements with the displacement experiments, revealing that MS diffusion theory is superior for describing diffusion of mixed gases in coals compared with the constant Fick diffusivity model. The optimized effective micropore and macropore diffusivities are comparable with experimental measurements achieved by other researchers.

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