Modelling of anisotropic coal swelling and its impact on permeability behaviour for primary and enhanced coalbed methane recovery

Coal swelling/shrinkage during gas adsorption/desorption is a well-known phenomenon. For some coals the swelling/shrinkage shows strong anisotropy, with more swelling in the direction perpendicular to the bedding than that parallel to the bedding. Experimental measurements performed in this work on an Australian coal found strong anisotropic swelling behaviour in gases including nitrogen, methane and carbon dioxide, with swelling in the direction perpendicular to the bedding almost double that parallel to the bedding. It is proposed here that this anisotropy is caused by anisotropy in the coal's mechanical properties and matrix structure. The Pan and Connell coal swelling model, which applies an energy balance approach where the surface energy change caused by adsorption is equal to the elastic energy change of the coal solid, is further developed to describe the anisotropic swelling behaviour incorporating coal property and structure anisotropy. The developed anisotropic swelling model is able to accurately describe the experimental data mentioned above, with one set of parameters to describe the coal's properties and matrix structure and three gas adsorption isotherms. This developed model is also applied to describe anisotropic swelling measurements from the literature where the model was found to provide excellent agreement with the measurement. The anisotropic coal swelling model is also applied to an anisotropic permeability model to describe permeability behaviour for primary and enhanced coalbed methane recovery. It was found that the permeability calculation applying anisotropic coal swelling differs significantly to the permeability calculated using isotropic volumetric coal swelling strain. This demonstrates that for coals with strong anisotropic swelling, anisotropic swelling and permeability models should be applied to more accurately describe coal permeability behaviour for both primary and enhanced coalbed methane recovery processes.

[1]  Edward J. Garboczi,et al.  Modelling drying shrinkage in reconstructed porous materials: application to porous Vycor glass , 1998 .

[2]  A. Myers.  Thermodynamics of adsorption in porous materials , 2002 .

[3]  Roger Beckie,et al.  Flow of Coal-Bed Methane to a Gallery , 2000 .

[4]  Luke D. Connell,et al.  Coupled flow and geomechanical processes during enhanced coal seam methane recovery through CO2 sequestration , 2009 .

[5]  Nathan Deisman,et al.  Geomechanical properties and permeability of coals from the Foothills and Mountain regions of western Canada , 2007 .

[6]  P. J. Reucroft,et al.  Gas-induced swelling in coal , 1986 .

[7]  Luke D. Connell,et al.  Laboratory characterisation of coal reservoir permeability for primary and enhanced coalbed methane recovery , 2010 .

[8]  Badie I. Morsi,et al.  CO2 adsorption capacity of argonne premium coals , 2004 .

[9]  R. Gayer,et al.  Coalbed Methane And Coal Geology , 1996 .

[10]  I. Gray,et al.  Reservoir Engineering in Coal Seams: Part 1-The Physical Process of Gas Storage and Movement in Coal Seams , 1987 .

[11]  C. Özgen Karacan,et al.  Swelling-Induced Volumetric Strains Internal to a Stressed Coal Associated with CO2 Sorption , 2007 .

[12]  G. Scherer.  Dilatation of Porous Glass , 1986 .

[13]  R. Chalaturnyk,et al.  Permeability and porosity models considering anisotropy and discontinuity of coalbeds and application in coupled simulation , 2010 .

[14]  John R. Seidle,et al.  Experimental Measurement of Coal Matrix Shrinkage Due to Gas Desorption and Implications for Cleat Permeability Increases , 1995 .

[15]  J. C. Jaeger,et al.  Fundamentals of rock mechanics , 1969 .

[16]  Phillip M. Halleck,et al.  Three-dimensional carbon dioxide-induced strain distribution within a confined bituminous coal , 2009 .

[17]  R. Marc Bustin,et al.  Volumetric strain associated with methane desorption and its impact on coalbed gas production from deep coal seams , 2005 .

[18]  Jeffrey R. Levine,et al.  Model study of the influence of matrix shrinkage on absolute permeability of coal bed reservoirs , 1996, Geological Society, London, Special Publications.

[19]  Luke D. Connell,et al.  Coupled flow and geomechanical processes during gas production from coal seams , 2009 .

[20]  Luke D. Connell,et al.  Effects of matrix moisture on gas diffusion and flow in coal , 2010 .

[21]  X. Miao,et al.  Evaluation of stress-controlled coal swelling processes , 2010 .

[22]  Victor Rudolph,et al.  An improved permeability model of coal for coalbed methane recovery and CO2 geosequestration , 2009 .

[23]  Sevket Durucan,et al.  Drawdown Induced Changes in Permeability of Coalbeds: A New Interpretation of the Reservoir Response to Primary Recovery , 2004 .

[24]  Tim J. Tambach,et al.  Molecular Exchange of CH4 and CO2 in Coal: Enhanced Coalbed Methane on a Nanoscale† , 2009 .

[25]  Sevket Durucan,et al.  A model for changes in coalbed permeability during primary and enhanced methane, recovery , 2005 .

[26]  R. Lama,et al.  Management of outburst in underground coal mines , 1998 .

[27]  Richard L. Christiansen,et al.  Measurement of Sorption-Induced Strain , 2005 .

[28]  Ian D. Palmer,et al.  How Permeability Depends on Stress and Pore Pressure in Coalbeds: A New Model , 1998 .

[29]  Christopher R. Clarkson,et al.  Predicting Sorption-Induced Strain and Permeability Increase With Depletion for Coalbed-Methane Reservoirs , 2010 .

[30]  John W. Larsen,et al.  The effects of dissolved CO2 on coal structure and properties , 2004 .

[31]  O. Mahajan.  Physical characterization of coal , 1984 .

[32]  L. Connell,et al.  A theoretical model for gas adsorption-induced coal swelling , 2007 .

[33]  R. Marc Bustin,et al.  Adsorption-induced coal swelling and stress: Implications for methane production and acid gas sequestration into coal seams , 2007 .

[34]  P. J. Reucroft,et al.  Effect of pressure on carbon dioxide induced coal swelling , 1987 .

[35]  Xiexing Miao,et al.  Development of anisotropic permeability during coalbed methane production , 2010 .

[36]  Khaled A. M. Gasem,et al.  Adsorption of methane, nitrogen, carbon dioxide and their mixtures on wet Tiffany coal , 2005 .

[37]  M. A. Barakat,et al.  The change in effective stress associated with shrinkage from gas desorption in coal , 2001 .

[38]  C. Özgen Karacan,et al.  Heterogeneous Sorption and Swelling in a Confined and Stressed Coal during CO2 Injection , 2003 .

[39]  Stuart Day,et al.  Swelling of Australian coals in supercritical CO2 , 2008 .