Pressure dependence of the contact angle in a CO2–H2O–coal system

Carbon dioxide 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, contact angles in the coal–water–CO2 system have been measured using the captive bubble technique in the pressure range between atmospheric pressure and 141 bar at a temperature of 45 °C. At atmospheric pressure the contact angle of a shrinking CO2 droplet increases with time, but stays below 90°. At higher pressures (>2.6 bar) the contact angle increases beyond 90°. The pressure dependence of the contact can be represented by θ=(111°±10.5°)+(0.17±0.14)P [bar]θ=(111°±10.5°)+(0.17±0.14)P [bar]. The exceptional behavior at atmospheric pressure is possibly related to the stability of water patches on the coal surface. It is concluded that water is the non-wetting phase in this coal–water–CO2 system.

Graphical abstractContact angles in the coal–water–CO2 system have been measured using the captive bubble technique between 1 and 141 bar at 45 °C. The pressure dependence of the contact can be represented by θ=(111°±10.5°)+(0.17±0.14)P [bar]θ=(111°±10.5°)+(0.17±0.14)P [bar].Figure optionsDownload full-size imageDownload as PowerPoint slide