SATELLITE-BASED MEASUREMENTS OF SURFACE DEFORMATION REVEAL FLUID FLOW ASSOCIATED WITH THE GEOLOGICAL STORAGE OF CARBON DIOXIDE

The geological storage of carbon dioxide is likely to be an important tool for preventing CO₂, particularly that emitted from power plants, from entering the atmosphere. However, in order for the storage to be safe and effective the CO₂ must remain at depth. Monitoring will be a key component of in determining our success in immobilizing this greenhouse gas within the Earth. Satellite-based monitoring techniques, even though they are indirect, can be more cost effective, more frequent, and less invasive then seismic or electromagnetic methods. Furthermore, surface deformation is particularly sensitive to the migration of CO₂ to shallower depths. Interferometric Synthetic Aperture Radar (InSAR) gathered over the In Salah CO₂ storage project provides an early indication that satellite-based geodetic methods can be effective in monitoring fluid flow related to geological storage. The injected carbon dioxide produces a measurable signal of approximately 5 mm/year of surface deformation induced by the pressure and volume changes at depth. The pattern of deformation at one injector suggests propagation along a narrow conduit such as a fault or fracture zone. Using inverse methods we are able to infer flow within the reservoir layer and within a hypothesized fracture/fault zone. We find that the fluid pressure changes only occur in the vicinity of the reservoir layer. However, pressure changes associated with the injection of CO₂ have propagated several kilometres within the reservoir, following a suspected fault. One finding from our modelling is that it is crucial to use the best available elastic model when solving the inverse problem. In particular, because the reservoir lies in a low velocity zone, using a uniform elastic model, rather than a more accurate layered model, produces an error of more than 50% in the depth estimate.