Elastic-wave sensitivity propagation for optimal time-lapse seismic survey design

Effective and reliable reservoir monitoring is critically important for optimizing oil/gas production and ensuring safe geological carbon sequestration. Reservoir monitoring requires optimal sensor deployment that uses a minimum number of sensors to record the most significant information resulting from reservoir property changes. Conventional monitoring survey designs are typically based on seismic-wavefield illumination analyses, which cannot determine the best receiver locations for effective and reliable monitoring of reservoir property changes. We introduce a new approach for designing optimal seismic monitoring surveys by analyzing sensitivities of elastic waves with respect to reservoir geophysical property changes. The method is based on differentiating the elastic-wave equations with respect to geophysical parameters. The resulting sensitivity equations are solved simultaneously with the elastic-wave equations using a finite-difference scheme. We conduct three numerical tests to demonstrate the efficacy of our elastic-wave sensitivity propagation in facilitating time-lapse seismic survey optimal design, including an elastic SEG-EAGE salt model, a multilayer fault model for CO2 leakage monitoring, and a modified anisotropic Hess model. Our numerical results show that for efficient time-lapse seismic monitoring, receivers should be placed at locations where elastic-wave sensitivity energies are significant. This study indicates that our elastic-wave sensitivity analysis provides a fundamental numerical tool for cost-effective seismic monitoring survey designs.