Anisotropic Model For Permeability Change In Coalbed Methane Wells (original) (raw)

SPE Western North American and Rocky Mountain Joint Meeting, 2014

Abstract

With depletion of coalbed methane (CBM) wells in the San Juan Basin, permeability rises by 10 to 100 times. Similar permeability increases are found in other CBM basins around the world. Models previously advanced to explain this behavior combine a compaction mechanism (which closes cleats) with matrix shrinkage (which opens cleats). In this paper, the original model (Palmer-Mansoori model) is extended to include the transversely isotropic elastic response found in vertically cleated coals. This new version of the model has been calibrated by laboratory measurements on San Juan Basin coal loaded under uniaxial-strain conditions to simulate reservoir depletion. The result is a predictive model characterized by two measured Young's moduli and three measured Poisson's ratios. To our knowledge, a rigorous geomechanical analysis of anisotropic coal has not before been incorporated into efforts to match large permeability increases observed in the field. We have been able to match...

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