Sparse acquisition VSP: a time-lapse physical modelling experiment

Kevin L. Bertram, Joe Wong

Seismic monitoring of industrial processes such as CO₂ sequestration in geological formations is a legal requirement. Because of cost of fully detailed 4D seismic surveys, sparse acquisition is being investigated for its efficacy in tracking a growing CO₂ plume. To investigate one particular sparse acquisition method, we conducted multi-azimuth marine VSP surveys over a 3D physical model representing a layered structure with an embedded sand-filled mound. The acquisition geometry consisted of a single vertical observation well for receiver positions and 247 surface source points covering an area of 4000m by 4000m. Acoustic seismic data were first acquired with the mound filled with water-saturated sand. With the acquisition geometry unchanged, data were recorded again after injecting air into the mound to replace the water in the pores between sand grains. The two VSP datasets simulate results for time-lapse VSP surveys in a carbon sequestration project. Different levels of sparse acquisition can be investigated by analyzing different numbers of VSP gathers.