摘要
Reliable subsurface time-lapse seismic monitoring is crucial for many geo-physical applications,such as enhanced geothermal system characterization,geologic carbon utilization and storage,and conventional and unconventional oil/gas reservoir characterization,etc.We develop an elastic-wave sensitivity propagation method for optimal design of cost-effective time-lapse seismic surveys considering the fact that most of subsurface geologic layers and fractured reservoirs are anisotropic instead of isotropic.For anisotropic media,we define monitoring criteria using qP-and qS-wave sensitivity energies after decomposing qP-and qS-wave components from the total elastic-wave sensitivity wavefield using a hybrid time-and frequency-domain approach.Geophones should therefore be placed at locations with significant qP-and qS-wave sensitivity energies for cost-effective time-lapse seismic monitoring in an anisotropic geology setting.Our numerical modeling results for a modified anisotropic Hess model demonstrate that,compared with the isotropic case,subsurface anisotropy changes the spatial distributions of elastic-wave sensitivity energies.Consequently,it is necessary to consider subsurface anisotropies when designing the spatial distri-bution of geophones for cost-effective time-lapse seismic monitoring.This finding suggests that it is essential to use our new anisotropic elastic-wave sensitivity modeling method for optimal design of time-lapse seismic surveys to reliably monitor the changes in subsurface reservoirs,fracture zones or target monitoring regions.
