A Modeling Feasibility Study Indicates Seismic AVO has Potential to Discriminate between Brine and Hydrocarbon in Middle East Carbonate Reservoir

Abstract

Abstract A seismic Amplitude Variation with Offset (AVO) feasibility study was successfully conducted to investigate the potential for fluid discrimination in a high porosity carbonate reservoir from a producing oil field in the Middle East. Gassmann fluid substitution was used to model the available well log data, which included compressional and shear sonic logs and density logs to produce synthetic well logs representing the reservoir at 100% fluid saturations of brine, oil and gas at reservoir pressure and temperature conditions. The modeled brine, oil and gas logs were used to calculate the AVO responses at the top and base of the reservoir layer using the Zoeppritz equations. The responses for all three fluids were found to be a Class-4 type AVO. The AVO results on the synthetic CDP gathers suggests that brine can be discriminated from hydrocarbon. These encouraging AVO results on synthetic data suggest that with good quality seismic data it might be possible to see a difference in AVO response between brine and hydrocarbon filled porous reservoir. An AVO case study was performed using available relative amplitude CMP gathers along a 2D seismic line extracted from a 3D seismic volume. The effects of key reservoir properties on AVO response were examined to help establish interpretation guidelines and better understand the potential for misinterpretation.