Carbon sequestration in coal-beds with structural deformation effects

Abstract

Carbon dioxide sequestration in a coal-bed is a profitable method to reduce the concentration of greenhouse gas in the atmosphere and to recover byproduct methane from the coal seam. The important factor to be considered is the stability of the coal-bed with the increased carbon dioxide injection. It is crucial to avoid carbon dioxide escaping from the coal seam caused by structural deformation. Meanwhile, structural deformation also depends on such properties of the geological coal basin as fracture state and phase equilibrium, especially the porosity, permeability and saturation of the coal seam. In this study, a structural deformation effect was simulated with the purpose of predicting carbon dioxide storage in the environment of a typical unmineable coal seam. As an example, Appalachian Basin is considered in the deformation analysis of carbon dioxide sequestration based on the variable saturation model. Moreover, the comparison between simulations with and without the account of structural deformation is given. The results indicate that modeling of structural deformation in carbon sequestration is feasible by directly coupling structure terms to a variable saturated model. Moreover, introducing structural deformation effects into carbon sequestration modeling is important because it affects the fluid flow and leads to a faster drop of the resulting capillary pressure and relative permeability of the gas phase. This faster drop directly results in the diminished carbon dioxide storage capacity in a coal-bed basin. In addition, structural deformation modeling in carbon sequestration simulations can provide important insights into how to avoid carbon leakage and seepage by monitoring the effective stress and displacement of coal-bed basin during carbon dioxide injection.