Permeability, Elastic, and Carbon Dioxide-Sorption Properties of Upper Freeport Coalbed Cores from a Carbon Dioxide Sequestration/Enhanced Coalbed Methane Field Project

摘要

The National Energy Technology Laboratory (NETL) of the U.S. Department of Energy is aiding its industrial and academic partners in a field project to assess the suitability of unmineable coal seams for sequestration of carbon dioxide and enhanced coalbed methane production. The permeability behavior of bituminous and sub-bituminous coals is know to be quite complex. According to laboratory data and various models, the permeability depends on the fluid composition, the network of cleats in the coal, the fluid pressure, the lithostatic or coriflning pressure, and the Young's modulus and Poisson's ratio of the coal. In the laboratory experiments reported here, steady-state permeabilities to helium, methane, or carbon dioxide were measured for Upper Freeport cores from a field sequestration project. Bulk compressibilities were measured by compressing the sample in an X-ray CT (computer tomography) scanner and calculating changes of sample density. Fluid pressure, confining pressure, history of pressure changes (i.e., pressure hysteresis), and fluid composition were extensively explored and found to have important effects on the permeability. Results were found which appeared to confirm that useful permeabilities depend on flow through the cleats, and that under certain conditions permeabilities can be reduced by several orders of magnitude due to cleat closure. These experiments may suggest additional measurements or models for the permeabilities of various coals and their dependence on elastic, gas sorption, and swelling and shrinkage parameters.