High-Resolution Reservoir Monitoring Using Crosswell Seismic

摘要

Crosswell seismic is an emerging technology that provides highly detailed images of the subsurface at the reservoir scale. The technology has the potential not only to delineate complex structures, but also to monitor the effectiveness of hydrocarbon-recovery and CO_2-sequestration strategies. The technique employs tomographic surveying, whereby a transmitter and receiver are deployed in separate wells. With this setup, interwell velocity profiling and structure can be obtained from direct-wave and reflection processing, respectively. With increased hydrocarbon recovery and CO_2 sequestration becoming more prominent in the oil and gas industry, the ability to monitor the efficiency of these strategies is paramount. In this paper, two case studies of crosswell seismic surveying are discussed, with the focus on high-resolution imaging and monitoring during CO_2 injection for improved oil recovery. A brief description of the measurement theory and its capabilities is provided, followed by a description of the processing workflow and, finally, a discussion of the acquired results. The two cases discussed demonstrate that crosswell seismic was able to successfully monitor the injection through velocity profiling in time lapse and provide answers as to why and how the flow has occurred through interpretation of the crosswell reflection seismic section. The results clearly show that crosswell seismic could significantly reduce the uncertainty and risk associated with injection processes for improved recovery and can extend the technique to sequestration monitoring.