Geophysics and Geophysical Exploration ISSN:1229-1064(Print) 2384-051X(Online) 지구물리와 물리탐사

As part of basic studies of monitoring carbon dioxide (CO_2) storage using electrical and seismic surveys,laboratory experiments have been conducted to measure resistivity and P-wave velocity changes due to the injection of CO_2into water-saturated sandstone. The rock sample used is a cylinder of Berea sandstone. CO_2 was injected under supercritical conditions (10 MPa, 40℃). The experimental results show that resistivity increases monotonously throughout the injection period, while P-wave velocity and amplitude decrease drastically due to the supercritical CO_2 injection. A reconstructed P-wave velocity tomogram clearly images CO_2 migration in the sandstone sample. Both resistivity and seismic velocity are useful for monitoring CO_2 behaviour. P-wave velocity, however, is less sensitive than resistivity when the CO_2 saturation is greater than ~20%. The result indicates that the saturation estimation from resistivity can effectively complement the difficulty ofCO_2 saturation estimations from seismic velocity variations. By combining resistivity and seismic velocity we were able to estimate CO_2 saturation distribution and the injected CO_2 behaviour in our sample.