A model for changes in coalbed permeability during primary and enhanced methane, recovery
- University of London Imperial College of Science Technology & Medicine, London (United Kingdom). Dept. of Environmental Science & Technology
The natural fracture network of a dual-porosity coalbed reservoir is made up of two sets of orthogonal, and usually subvertically oriented, cleats. Coalbed permeability has been shown to vary exponentially with changes in the effective horizontal stress acting across the cleats through the cleat-volume compressibility, which is analogous to pore compressibility in porous rocks. A formulation for changes in the effective horizontal stress of coalbeds during primary methane recovery, which includes a Langmuir type curve shrinkage term, has been proposed previously. This paper presents a new version of the stress formulation by making a direct link between the volumetric matrix strain and the amount of gas desorbed. The resulting permeability model can be extended readily to account for adsorption-induced matrix swelling as well as matrix shrinkage during enhanced methane recovery involving the injection of an inert gas or gas mixture into the seams. The permeability model is validated against a recently published pressure-dependent permeability multiplier curve representative of the San Juan basin coalbeds at post-dewatering production stages. The extended permeability model is then applied successfully to history matching a micropilot test involving the injection of flue gas (consisting mainly of CO{sub 2} and N{sub 2}) at the Fenn Big Valley, Alberta, Canada.
- OSTI ID:
- 20674297
- Journal Information:
- SPE (Society of Petroleum Engineers) Reservoir Evaluation and Engineering, Vol. 8, Issue 4; ISSN 1094-6470
- Country of Publication:
- United States
- Language:
- English
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