RESERVOIR DEPLETION INDUCED CHANGES IN COALBED PERMEABILITY AND IMPLICATIONS FOR ENHANCED CBM RECOVERY USING CO INJECTION
Department of Environmental Science and Technology, Imperial College, London, UK. E-mail: j.q.shi@ic.ac.uk
Department of Environmental Science and Technology, Imperial College, London, UK
Department of Environmental Science and Technology, Imperial College, London, UK
Abstract
A model for describing changes in cleat permeability in a gas-desorbing coalbed under uniaxial strain conditions has been developed. An analysis on the possible behaviours of changes in effective horizontal stress (and thus cleat permeability) during reservoir drawdown is presented. The model has been applied to analyse the performance of three coalbed methane wells in the fairway of San Juan basin, USA, where continued increase in the absolute permeability has been observed during the course of primary recovery. The results of this study are presented and discussed. The permeability model has been extended to account for matrix swelling as well as matrix shrinkage that are associated with multi-component gas adsorption/desorption, and therefore providing a first-order estimation on the permeability changes in coalbeds arising from CO2 injection. Preliminary investigation has indicated that matrix swelling associated with CO2 injection could have a detrimental impact on cleat permeability.