Feasibility of inverting compaction-induced traveltime shifts for reservoir pressure

Pore-pressure variations inside producing reservoirs result in excess stress and strain that cause time shifts of reflected waves. Inversion of seismic data for pressure changes requires better understanding of the dependence of compaction-induced time shifts on reservoir pressure reduction. Here, we investigate pressure-dependent behavior of P-, S-, and PS-wave time shifts from reflectors located above and below a rectangular reservoir embedded in a homogeneous half-space. Our geomechanical modeling algorithm generates the excess stress/strain field and the stress-induced stiffness tensor as linear functions of reservoir pressure. Analysis of time shifts obtained from full-waveform synthetic data shows that they vary linearly with pressure for reflectors above the reservoir, but become nonlinear for reflections from the reservoir or deeper interfaces. Time-shift misfit curves computed with respect to noise-contaminated data from a reference reservoir for a wide range of pressure reductions display well-defined minima. Our results indicate that stable pressure estimation requires including multicomponent time shifts from reflectors below the reservoir and applying a nonlinear global inversion algorithm.