Imaging reservoirs - a crosswell seismic experiment

Setting sources and receivers down hole limits the investigation to the neighbourhood of the objective, so that we avoid high absorbing, near-surface, low-velocity zones and do not need knowledge of the velocity field outside the region of interest. Most research on crosshole seismic surveys deals with tomography, i.e. inversion of the direct arrival times to update the velocity field. This method by itself does not give a well-resolved image of the objective. Furthermore it implies that the waves should cross the objective on their path from the source to the receivers, which is not always possible, since oil wells generally do not penetrate far below the reservoir.