Subsurface imaging using reversed vertical seismic profiling and crosshole tomographic methods

Abstract

A combined reversed vertical seismic profile (RVSP), crosshole, and surface seismic experiment was performed to image the subsurface between two 1000 ft wells separated by 600 ft. Explosives were used as downhole sources and a 24-channel hydrophone streamer provided the downhole receivers. Surface shots were 1/3 lb dynamite charges and the surface receivers were vertical geophones. RVSP data, consisting of 48 offsets ranging from 25 ft to 1200 ft, were processed with a ray‐tracing method to produce an equivalent stacked seismic section. The crosshole data were processed with an SIRT traveltime transmission tomography algorithm to produce a velocity cross‐section. The stacked RVSP subsurface image and the crosshole tomography velocity cross‐section both have higher resolution than does the surface seismic image. For example, the velocity map from tomography exhibits a rapid lateral velocity change that is not resolved by surface seismic. However, all three methods agree within the limits of their common resolution. The results indicate that RVSP and crosshole tomography can potentially be used to image steeply dipping beds or complex structures, such as small faults, pinchouts, steam‐flooded zones, reef boundaries, or the flanks of salt domes.