Reservoir identification using full stack seismic inversion technique: A case study from Cambay basin oilfields, India

Full stack seismic data in Cambay basin, India, shows limited contrast between sandstone reservoirs and other lithologies. The seismic inversion result has been used here to convert the seismic reflection data into impedance log at each point and the ratio of every point. Wavelet estimations have been carried out for four wells namely, AM-11, AM-12, AM-13 and AM-14 lying between Sanand and Nawagam oilfields located in the Ahmedabad-Mehsana block of Cambay basin. The combination of P-impedance and compressional wave velocity (Vp) to shear wave velocity (Vs) ratio has been used to delineate the pay sand. Reservoir pay sand in Eocene pay formation has been delineated from these wells. The cross plotting technique between Vp/Vs (from four wells AM-11 to AM-14 under the study area) and P-impedance values has differentiated sand and shale. It is observed that the high P-impedance sand is associated with low porosity (15-18%) values while the low P-impedance sand is associated with relatively high porosity (20-25%) values.