Estimation of Pressure and Saturation Changes from 4D Seismic AVO and Time-shift Analysis

An inversion scheme that solves for reservoir pressure and fluid saturation changes from time-lapse pre-stack seismic attributes and post-stack seismic timeshifts is presented. It makes use of three equations expressing the production induced changes as a function of changes in zero-offset and gradient reflectivity and of compressional wave time-shifts. The equations related to the AVO (amplitude-versus-offset) response are a revised form of Landro's (2001) equations. The inversion scheme has been successfully tested on a synthetic reservoir where seismic data have been modeled before and after two years production. The results show that changes in fluid properties can be approximated with fairly high accuracy.