Time-Lapse Cross-Well Pressure Tomography for Monitoring CO2 Plumes and Detecting Leaks: Efficient Approaches to Inversion

Downhole monitoring techniques for CO2 plumes have some advantages over surface seismic, particularly reduced surface footprint and environmental impact. Of possible downhole techniques, pressure monitoring has the merit of accessing the saturation/permeability/porosity distribution relatively directly, as opposed to indirect inferences from elastic impedances via seismic, or resistivity via EM methods. We have developed a range of plume imaging/inversion techniques for time-lapse cross-well pressure tests, based on an efficient, single phase, effective-compressibility model of reservoir flow which closely approximates multiphase pressure response at large scale. Inversion implementations using both object-based plume models with classical methods, and voxelised plume representations using nonlinear adjoint theory, are shown to be useful in imaging plume movement in time.