Pressure Dependence of the CO2 Contact Angle on Bituminous Coal and Semi - Anthracite in Water

Carbon dioxide (CO2) injection into coal layers serves the dual purpose to enhance coal bed methane production (ECBM) and to store CO2. The efficiency of this process is expected to be much higher if water is the non-wetting phase in the coal-water-gas system. Therefore, carbon dioxide contact angles in two coal-water-CO2 systems have been measured. The captive bubble technique was used within a pressure range from atmospheric pressure and 140 bar at a constant temperature of 45° C.

Two sets of measurements have been performed, one on a polished semi-anthracite, the second set on a polished high volatile bituminous B coal sample. For the anthracite the following observations have been made. At atmospheric pressure, the contact angle of a CO2 droplet increases with time, but stays below 90°. At higher pressures (>3 bar) the contact angle increases beyond 90°. This shows that the semianthracite coal sample behaves CO2-wet at system pressures above 3 bar.