APPLICATION OF CROSSWELL AND SINGLE WELL SEISMIC METHODS FOR MAPPING CO2 MOVEMENT

Two different seismic experiments at two different scales were conducted prior to CO2 injection for enhanced oil recovery and sequestration applications. One experiment was conducted at Chevron's Lost Hills California CO2 pilot project in the Belridge Diatomite. In this experiment two closely spaced vertical wells (25 meters) on either side of the CO2 injection well were used to image a 300 meter section of the diatomite formation using crosswell seismic and single well seismic. Two different sources were used for both methods, a piezoelectric source (200 hertz to 3000 hertz) and a mechanical orbital vibratory (50 hertz to 400 hertz). The recording of the data was done with hydrophones and three component geophones. The single well used the piezoelectric source and 16 hydrophones. In the second case, hydrophones deployed inside of coiled tubing (48 channels) were used with a piezoelectric source (200 hertz to 2000 hertz) in two horizontal wells 275 meters apart and at a depth of 1350 meters with a horizontal section of 1000 meters, in a carbonate formation at PanCanadian's Weyburn field in Southern Saskatchewan, to perform a high resolution crosswell experiment. In both cases, the objective was to image prior and after CO2 injection to determine the path and rate of CO2 movement. In both cases high resolution images were obtained that will serve as baselines for future repeat imaging. Innovative methods had to be developed to successfully deploy the seismic instruments and obtain the high frequency data. The results to date show in the Lost Hills case the geologic structure (bedding and faults) with indication of the induced hydrofrature between the two imaging wells. In the Weyburn case the data indicate severe wave guide effects from the reservoir section which can be used to perform dipersion tomography. Follow-up surveys in the spring of 2001 will be done to map the path of the CO2.