Computer simulations of the flow and diffusion of H2O, CH4, and CO2 through unmineable coal seams are integral parts of the design, implementation, and interpretation of carbon sequestration field projects. Although it has seldom been discussed in the literature, coal seams may also effect-ively serve as “cap rock” for sequestration into underlying formations (brine-saturated, oil and gas reservoirs, or other coal seams). In this case, the very large sorption capacities of coal, even at low CO2 pressures; the blockage of CO2 flow through cleats when they are saturated with H2O; and the tendency of coal to swell when it sorbs CO2, thus reducing cleat apertures and Darcy flow, all may contribute to make coal seams effective caprock.

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