Seismic Response of CO2 Saturated Red Wildmoor Sandstone under Varying Temperatures and Pressures

Underground geological sequestration of CO2 is considered as one of the most promising solutions for overcoming the global warming problem. Time lapse seismic monitoring enables us to monitor the CO2 plume migration and is considered as an integral component of a geological CO2 sequestration project because the seismic behavior of the rock is a function of both mineralogical composition and also the physical properties of the pore fluids. CO2 can be presented as gaseous, liquid and supercritical states at the uppermost kilometer of the sedimentary basin while in CO2 sequestration operation the supercritical and liquid states of CO2 are preferred due to the higher sweep efficiency. In this study, both compressional (Vp) and shear (Vs) wave velocities of a CO2 saturated Red Wildmoor sandstone sample under different temperature and pressure conditions are measured in a uniaxial hydrostatic cell equipped with acoustic transmitting and receiving transducers. The observed velocities illustrate that by introducing CO2 into the dry core, the resultant wave velocities decrease up until the critical condition in which by further increasing the CO2 pressure the Vs remains unchanged while the Vp gradually increases up to the maximum pressured applied in this study. Also it was observed that at lower temperature, the gas to liquid CO2 phase transition occurs with a sudden decrease in the amounts of the observed velocities while at higher temperature the velocity reduction is smoother possibly due to reaching the supercritical state. The observed velocities are in good agreement with Gassmann predicted velocities as well as literature data.