Monitoring carbon dioxide sequestration using Electrical Resistance Tomography (ERT): A minimally invasive method

Successful geologic sequestration of carbon dioxide (CO2), will require monitoring the CO2 injection to confirm the performance of the caprock/reservoir system, assess leaks and flow paths, and understand the geophysical and geochemical interactions between the CO2 and the geologic minerals and fluids. Electrical methods are especially well suited for monitoring processes involving fluids, as electrical properties are sensitive to the presence and nature of the formation fluids. High resolution tomographs of electrical properties are now used for site characterization and to monitor subsurface migration of fluids (i.e., leaking underground tanks, infiltration events, steam floods, contaminant movement, and to assess the integrity of engineered barriers). When electrical resistance tomography (ERT) imaging can be performed using existing well casings as long electrodes, the method is nearly transparent to reservoir operators, and reduces the need for additional drilling. Using numerical simulations and laboratory experiments, we have conducted sensitivity studies to determine the potential of ERT methods to detect and monitor the migration Of CO2 in the subsurface. These studies have in turn been applied to the design and implementation of the first field casing surveys conducted in an oil field undergoing a CO2 flood.