Imposing Geological and Geomechanical Constraints on Time-lapse Time Strain Inversion

Production from hydrocarbon fields induces velocity changes and strains in the subsurface, which create time shifts between vintages of time-lapse seismic data. Recovering these time shifts can be useful for reservoir management, particularly through calibration of geomechanical models. These shifts can be estimated using non-linear inversion. However, such inversions are hampered by the limited bandwidth of seismic data and noise. Regularization is needed to obtain a suitable solution. We introduce a new constraint into a time-lapse non-linear inversion for time strain. A geologically consistent regularization scheme is imposed through the use of interpreted horizons as constraints. The horizons define layers within which coefficients of a function that describes the expected variation of time strain are inverted for. This decreases the reliance on classical damping parameters for noise suppression and reduces the size of the model space. The resulting time strain model depends on the function chosen to describe its expected variation and the layering scheme, both of which can be driven by geological and geomechanical understanding of the field. We show that this enables accurate recovery of the magnitude, shape and localization of time shift and time strain signals from beneath the reservoir, within the reservoir and throughout the overburden.