Coal Wettability after CO₂ Injection

Increasing energy demand and associated global warming are unarguably the two major challenges that the world currently faces. One of the ideas to reduce the carbon footprint while increasing the efficiency of the energy extraction is CO₂ sequestration in coal seams. This can additionally enhance the coal-bed methane production. However, this process depends on many factors, among which coal wettability is of particular importance especially because of its pressure and temperature dependency. To evaluate this process, coal wettability was tested by measuring the contact angle of CO₂ and water as a function of pressure, temperature, and salinity (DI water and brine (5 wt % NaCl + 1 wt % KCl), i.e., wt % is the weight percentage of salt to water. The results show that the CO₂-water contact angle increases significantly, with increasing pressure, temperature, and salinity indicating more-effective CO₂ wetness of coal. This, in turn, can reduce the CO₂ residual trapping capacities and increase methane recovery. Furthermore, we demonstrated that CO₂ density correlates well with coal wettability.