Monitoring and detecting CO2 injected into water-saturated sandstone with joint seismic and resistivity measurements

As part of basic studies of monitoring carbon dioxide (CO2) storage using electrical and seismic surveys, laboratory experiments have been conducted to measure resistivity and P-wave velocity changes due to the injection of CO2 into water-saturated sandstone. The rock sample used is a cylinder of Berea sandstone. CO2 was injected under supercritical conditions (10 MPa, 40 degrees C). The experimental results show that resistivity increases monotonously throughout the injection period, while P-wave velocity and amplitude decrease drastically due to the supercritical CO2 injection. A reconstructed P-wave velocity tomogram clearly images CO2 migration in the sandstone sample. Both resistivity and seismic velocity are useful for monitoring CO2 behaviour. P-wave velocity, however, is less sensitive than resistivity when the CO2 saturation is greater than similar to 20%. The result indicates that the saturation estimation from resistivity can effectively complement the difficulty of CO2 saturation estimations from seismic velocity variations. By combining resistivity and seismic velocity we were able to estimate CO2 saturation distribution and the injected CO2 behaviour in our sample.