Reflection processing of crosswell seismic data: Midale field, Saskatchewan

Ashraf A. Abdalla, Robert R. Stewart, David C. Henley

A development study is presented here for the analysis and processing of crosswell seismic data. This work uses direct arrivals and reflections to construct an image. Use of reflections in addition to transmissions promises to provide higher resolution sections.

To this end, high frequency crosswell data, from the Midale field of southeastern Saskatchewan, have been processed for reflections. The data were acquired by Shell Development Company for Shell Canada Ltd. as part of their EOR monitoring studies. Raw field data showed a complex assortment of wave modes that included direct compressional and shear waves, head waves, guided waves, converted transmitted waves and reflected shear waves. A traveltime inversion technique (layer-stripping via raytracing) was developed to obtain P- and S-wave interval velocities from the respective direct arrivals. Further analysis of the receiver-gathered data showed evidence of primary reflected downgoing arrivals as well as the primary reflected upgoing arrivals. Downgoing primary reflections were selected and processed with the upgoing reflections to obtain a subsurface image. The reconstruction method used is similar to conventional VSPCDP mapping. Crosswell geometry is shown to provide an extended subsurface coverage away from the borehole which can complement the interpretation of well logs.