Review of experimental sorption studies of CO2 and CH4 in shales

In recent years CO2 injection in shale has been investigated with aim to enhance shale gas recovery (ESGR) and permanently sequester CO2. This paper reviews the state of research on CH4 and CO2 sorption in shale. We present the interaction of CO2 and CH4 with shale rocks and discuss the dependence of gas sorption on shale properties including organic matter content, kerogen type, mineralogy, moisture and temperature as well as shale selectivity for either species. Dynamic CO2-CH4 exchange studies are also summarized together with the geochemical and mechanical impact of gas sorption in shales. We note that most experimental work is still performed on crushed samples rather than whole cores. Also, CO2 is preferentially adsorbed over CH4 when both species co-exist in shale. Both gases are in supercritical state at typical reservoir conditions. Especially CO2 adsorption is not well described by standard isotherm models in this state.