Algorithms for EOR imaging using crosshole seismic data: an experiment with scale model data

Seismic velocities are influenced by many enhanced oil recovery (EOR) techniques. The crosshole seismic survey is well suited to the mapping of injection fluids or fracture patterns following reservoir stimulation. Both traveltime tomography and wave-equation techniques can be used to monitor and map changes in the seismic velocities, given pre-stimulation and post-stimulation crosshole seismic data. In order to evaluate algorithms for EOR mapping using crosshole seismic surveys, data were ob-tained from a scale model of a crosshole seismic survey. The epoxy resin model contained simulated geological structures with strong velocity contrasts. Two versions of the same model were constructed, both with and without a simulated “flood ” zone of a known geometry. Traveltime tomography and tow wave-equation algorithms, the inverse generalized Radon transform (inverse CRT) and fre-quency-domain wave-equation imaging,were used to attempt to locate the extent and velocities of the perturbation. The results of this experiment show that traveltime tomography suffices to locate the flood zone and to determine the magnitude of the velocity perturbations. However, images that resolve the ge-ometry of the flood zone were only obtained when the full waveform was utilized, using either th