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Abstract
Time-lapse, or 4D, seismic technology has the potential to monitor enhanced oil recovery and to delineate bypassed hydrocarbon reserves. Characterization of time-lapse 3D seismic data is based on detecting the different reservoir conditions associated with production between two survey times. Properties are estimated from two independent seismic surveys that are performed at two different times (called the base state and the monitor state). From analysis of these observations, conclusions are drawn with respect to fluid changes in the reservoir.
Full wavefield inversions based on elastic and viscoelastic parameterizations give different estimates of the seismic parameters; effects associated with parameters that are not fitted lead to biases in the seismic parameters that are fitted, and hence to errors in the subsequent estimation of the reservoir variables.
Inversion of synthetic seismic data for a viscoelastic reservoir model provides estimates of changes in effective pressure (Pe) and water saturation (Sw) over time. Estimation of unique values of Pe and Sw from two independent seismic data [such as P-wave velocity (V p) and S-wave quality factor (Qs)] is theoretically feasible, if the other reservoir properties are known. In the Sw-Pe plane, the solution corresponds to a point for noise-free data and a region for noisy data.
