Estimation of effective pressure and water saturation by viscoelastic inversion of synthetic time-lapse seismic data for a gas sandstone reservoir

Inversion of synthetic seismic data for a viscoelastic reservoir model provides estimates of changes in effective pressure (P,) and water saturation (S,) over time. Application is to analysis of simulated time-lapse seismic data for a gas sandstone reservoir. Estimation of unique values of P, and S. from two independent seismic data [such as P-wave velocity (V-p) and S-wave quality factor (Q(s))] is theoretically feasible, if the other reservoir properties are known. In the S.-P, plane, the solution corresponds to a point for noise-free data and a region for noisy data. For the reservoir properties [porosity (0), clay content, permeability (k)], and the dominant seismic frequency (40 Hz) used in the synthetic examples, density, Q(s) and Q(s)/Q(p) are primarily dependent on S-w, V-p is primarily dependent on P-e, and Vs, Q(p) and V-p/V-s are dependent on both S-w and P-e.