VSP found the lost reservoir

We acquired a VSP survey for look-ahead purpose in a deviated well in the tectonically complex area of Kohat Plateau, North-West Pakistan. The dips from VSP image were found contradicting with the surface seismic image. Because of the very small lateral extent of VSP image at the reservoir level, the VSP image alone could not provide confidence in the structural interpretation. For that reason, we analyzed various VSP migration techniques to analyze the reflections from top of the reservoir. The uncertainty due to non-uniqueness of the tomographic inversion of VSP travel times and the reflector geometry was reduced by iterative numerical modeling of VSP wavefield. The VSP image showed that the reservoir had been missed because the well had entered into the fault block. After validating the interpretation by drilling further 100 m, a side track was drilled based on the VSP image. The side-track hit the reservoir as predicted.