Swelling and mechanical property change of shale and sandstone in supercritical CO2

Abstract

In this study, a method is devised to implement a supercritical CO2(scCO2) injection environment on a laboratory scale and to investigate the effects of scCO2on the properties of rock specimens. Specimens of shale and sandstone normally constituting the cap rock and reservoir rock, respectively, were kept in a laboratory reactor chamber with scCO2 for two weeks.From this stage, a chemical reaction between rock surface and the scCO2 was induced. The effect of saline water was also investigated by comparing three conditions(scCO2-rock, scCO2-H2O-rock and scCO2-brine(1M)-rock).Finally, we checked the changes in the propertiesbefore and after the reactionby destructive and nondestructive testing procedures.The swelling of shale was a main concern in this case. The experimental results suggested that scCO2 has a greater effect on the swelling of the shale than pure water and brine. It was also observed that the largest swelling displacement of shale occurred after a reaction with the H2O-scCO2 solution. The results of a series of the destructive and nondestructive tests indicate that althougheach of the property changes of the rock differed depending on the reaction conditions, the H2O-scCO2 solution had the greatest effect. In this study, shale was highly sensitive to the reaction conditions.These results provide fundamental information pertaining to the stabilityof CO2storagesites due to physical and chemical reactions between the rocks in these sites and scCO2.