Abstract

The present study deals with post-stack inversion of time-lapse 3D data for monitoring in-situ combustion process in a pilot area of Balol Field of Cambay basin, India. The base 3D dataset pertains to survey conducted prior to the commencement of in-situ combustion process in the already identified set of injector wells. The monitor 3D survey was carried out 12 months thereafter for studying the changes in the reservoir due to this thermal process. The two data sets were acquired with the same acquisition parameters and processed identically. We performed post-stack inversion of these 3D datasets to arrive at clear 4D anomalies in terms of impedance that could be meaningfully interpreted and validated with reservoir engineering and production data. Although various inversion workflows were applied, 4D impedance anomalies are best seen in case of inversion of cross-equalized datasets through a matching procedure using identically processed PSTM gathers. The possible fairways of flue gases and/or propagation of combustion have also been brought out through attribute studies. The study indicates the preferential movement of flue gases towards north through the finer N-S discontinuities. This observation is supported by production behavior of wells in the area.