Crosshole seismic reflection processing is demonstrated in this research work. Reflected upgoing and downgoing wavefields are studied here with respect to their geometrical concepts and exploration applications. Conventional processing techniques are followed to separate the two wavefields. Unlike Vertical Seismic Profiling (VSP) processing, downgoing primary reflections are selected and processed to contribute with the upgoing reflections in obtaining a subsurface image for the media between the boreholes. As in VSP processing, crosshole data are transformed into surface distance and subsurface depth domain. This method was first applied in 1984 with a constant velocity model assumption. Here, we contribute the multi-layered model and derive the analytical solution of the constant velocity transformation (XHL-CDP Transformation). A subsurface image is obtained by summing multiple transformed records. Depth migration is also applied to provide a correlation with the mapped data. Crosshole geometry is shown to have an extended subsurface coverage between the boreholes which delineates the horizon lateral continuity and complements the interpretation of well logs and VSP data.
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