Publications

Crosswell seismic is an emerging technology that provides high resolution imaging of the subsurface at the reservoir scale. The technology is used for delineating complex structure and monitoring the effectiveness of hydrocarbon recovery using timelapse techniques. The technique employs tomographic surveying, whereby a transmitter and receiver are deployed downhole in separate wells. As a result of the inherent source-receiver geometry, interwell velocity profiling and structure can be obtained from direct wave and reflection processing respectively. In difficult seismic areas, such as the project area, with high attenuation in the weathered layer and difficult surface access issues, the ability to use existing wellbores to conduct a crosswell seismic survey is a unique advantage of the crossewell seismic method further enhanced by the inherent high-resolution characteristics of the crosswell seismic method. With hydrocarbon recovery becoming increasingly difficult day by day in mature fields, there is a need to improve the existing seismic interpretation to be able to track the reservoirs with more confidence. The presence of small-scale faulting that is difficult to map using the existing surface seismic can explain or complement the production results. Hence, there is a need for alternative enhanced resolution imaging and improved seismic in difficult surface seismic areas.A total of eleven (11) crosswell seismic profiles and four (4) reverse VSP are being acquired in a mature field in East Kalimantan, Indonesia.The objective of the crosswell campaign is to provide a better image of the reservoir dominantly represented by sandshale formations to ultimately aid in defining new well locations. The reward will be better infill well locations to locate bypassed pay areas such as the recently drilled 5000 bbl / day well, that demonstrated significant future potential for this brownfield reservoir. The use of crosswell seismic technology was chosen to minimise known attenuation effects produced by near surface layers, static corrections and the presence of coal streaks in the area. As the well to well configuration is less affected by these problems placing sources and receivers below the highly attenuative near surface layers, it allows for better illumination of the reservoir.In this paper, results from two (2) of the profiles acquired and processed will be discussed with the focus on enhanced resolution. Initially, 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. Two main products were obtained from each profile: tomographic velocities and reflection images.Tomographic velocity images showed high correlation with sonic velocities extracted from acoustic logs available in the area. The crosswell seismic reflection profiles show improved seismic imaging in comparison to the surface seismic previously acquired in the area. Once, the crosswell seismic compaign concludes, all profiles acquired will be integrated with the surface seismic and interpreted.