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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 the CO2 sequestration in coal seams (CBM) which can enhance the coal bed methane production (ECBM). However, this process depends on many factors, among which coal wettability is of particular importance especially because of its pressure and temperature dependency. In order to evaluate this process, coal wettability was tested by measuring the contact angle of CO2/water as a function of pressure, temperature and salinity (DI water and brine: 5wt% NaCl+1wt% KCl). 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 consequent methane recovery. Furthermore, we demonstrated that CO2 density, which is very simple to determine, correlates well with coal wettability.

Permeability variation is one of the key factors influencing the injectivity of CO2in CO2sequestration projects. Despite the research carried out on the subject, the results are highly inconsistent. In this study, the injection of brine (5 wt % NaCl + 1 wt % KCl), CO2-saturated (live) brine, and supercritical CO2was performed on three homogeneous Berea sandstone plugs with a low clay content and two Bandera Gray sandstone plugs with a high clay content at reservoir conditions (10 MPa and 323 K). Porosity and permeability of the samples were measured using nuclear magnetic resonance (T2relaxation time), and a dynamic (during flooding) permeability measurement technique, respectively, at different injection rates and injection durations. The mercury intrusion test was also performed on each sample to further evaluate its pore throat size distributions. From the results of this study, it was revealed that the CO2injection rate is unlikely to affect the permeability significantly. It was also shown that the permeability can be influenced depending upon sandstone pore throat size distribution and the distribution/structure of the clay minerals in the sample.