Effects of supercritical CO2 treatment time, pressure, and temperature on microstructure of shale

Supercritical CO2 (SC-CO2) fluid is capable of extracting organic matter in shale and dissolving the primary pores and fractures. To determine how well SC-CO2 can influence the microstructure at different traditions, shale samples were treated at different times, pressures and temperatures with SC-CO2. The results showed that crystal water was released from clay mineral in the shale after treatment. The specific surface area and porosity of the shale increased with time and pressure; pressure was significant at transforming shale's microstructure. Under low pressure, SC-CO2 treatment of shale at different temperatures does not have a clear influence on the microstructure of the shale. The porosity had a linear relationship with the specific surface area. The mechanism of changing the microstructure of the shale by SC-CO2 is as follows: as treatment time, pressure and temperature increase, the SC-CO2 fluid increases its density and dissolving capability and can extract more organic matter from the pores and fractures in shale. Concurrently, it increases the number of shale gas seepage channels and widens them. This research lays a foundation for efficient shale gas exploitation with SC-CO2 fluid.