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.

Crosswell seismic is an emerging technology which provides highly detailed images of the subsurface at the reservoir scale. The technology has the potential not only to delineate complex structure but also to monitor the effectiveness of hydrocarbon recovery and CO2 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 hydrocarbon recovery and CO2 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 CO2 injection for improved oil recovery and sequestration respectively. 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. These 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 both improved recovery and sequestration.

Resolution and measurement diversity are impo rtant parameters that help characterize the subsurface and help optimize reservoir management. While traditional well log data provide a variety of high-resolution measurements of the formation very close to the wellbore, surface-based methods provide larger investigation volume but coarser resolution. Crosswell measurements help to bridge the gap by imaging the inter-well space at reservoir scale.Crosswell seismic data provide high resolution reflection images of reservoir architecture with resolution that is up to 10 times better than that of surface seismic data. Crosswell Electromagnetics (EM) expands the scale investigated by tradition al resistivity logging to deliver, a more extensive understanding of fluid distribution and movement at reservoir scale, away from the wells. Not only do these techniques complement each other, but integrating the measured data with conventional logs and surface data into the modeling workflow gives new insight into reservoir structure and fluid movement in the formation.Recent surveys in v arious improved recovery projects show that these complementary measurements provide a new way to help subsurface teams accurately image geology and map injection fronts.

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