| Permeability of coal is perhaps the most critical parameter controlling the flow of gas in a coalbed reservoir. The permeability of coal, however, is a dynamic property depending on several parameters like effective stress, gas pressure, water saturation, and matrix shrinkage/swelling due to desorption/adsorption. There have been a few studies that have concluded that matrix volumetric changes resulting from desorption of methane causes the permeability to change. This becomes even more critical when a second gas, like CO2, is injected into a coal reservoir, either to sequester CO2 or enhance the production. Thus an understanding of the physical process of gas flow in coal, primarily the permeability and different parameters affecting it, is critical for CO 2 sequestration and enhanced methane recovery.; Two properties of coal, the permeability, and impact of gas flow on coal structure and its effect on flow behavior, were studied. The results of the experimental work involving measurement of matrix volumetric change indicate that the coal matrix "swells" with injection of CO2. Numerical analysis suggests that this matrix strain can result in a significant reduction in coal permeability. Permeability of coal was also estimated in the laboratory for a well preserved core of coal. The permeability to CO2 was found to be much lower than that of methane, clearly suggesting that CO 2 injection can result in permeability reduction. |
