Electrical resistance tomographic monitoring of CO2 movement in deep geologic reservoirs

• The world's deepest electrical resistance tomography (ERT) array.
• A challenging environment of high temperature, high pressure and low pH.
• Effective data processing methods to salvage extremely noisy data.
• Effective detection of CO2 breakthroughs and saturation changes with time.
• A near real time remote monitoring tool for tracking CO2 migration with time lapse tomographic images of CO2 saturation.

Deep geologic sequestration of carbon dioxide (CO2) is being evaluated internationally to mitigate the impact of greenhouse gases produced during oil- and coal-based energy generation and manufacturing. Natural gas producing fields are particularly attractive sites for sequestration activities owing to the assumption that the same geologic barrier or cap rock permitting the subsurface regime to act as a long term natural gas reservoir will also serve to permanently contain the injected supercritical CO2. Electrical resistance tomography (ERT) can potentially track the movement and concentration of the injectate as well as the degree of geologic containment using time lapse electrical resistivity changes resulting from injecting the super-critical fluid into the reservoir formation. An experimental cross-well ERT system operated successfully for more than one year obtaining time lapse electrical resistivity images during the injection of approximately one-million tons of CO2 at a depth exceeding 3000 m in an oil and gas field in Cranfield, MS, representing the deepest application of the method to date. When converted to CO2 saturation, the resultant images provide information about the movement of the injected CO2 within a complex geologic formation and the development of the saturation distribution with time. ERT demonstrated significant potential for near real-time assessment of the degree of geologic containment and for updating risk analyses of the sequestration process. Furthermore, electrical resistivity imaging of the developing CO2 distribution may provide crucial input about the developing reservoir pressure field that is required for active reservoir management to prevent the occurrence of cap-rock-damaging seismic activity.