ACTIVE CO2 RESERVOIR MANAGEMENT: COMBINING BRINE EXTRACTION, DESALINATION, AND RESIDUAL-BRINE REINJECTION WITH CO2 STORAGE IN SALINE FORMATIONS

The injection of CO₂ in deep saline aquifers will increase pressure in the storage formation and confining seal units, and result in CO₂ and brine migration away from the injection zone. We consider how to actively manage that migration so that it is beneficial. We analyze the concept of Active CO₂ Reservoir Management, which is engineered CO₂ and brine migration via injection/extraction/reinjection strategies, and contrast it with the conventional CCS approach, which can be called Passive CO₂ Reservoir Management. Combining brine extraction with CO₂ injection causes “push-pull” manipulation of the CO₂ plume, which can enable exposing less of the caprock seal to CO₂ and more of the storage aquifer to CO₂, with a greater fraction of the aquifer utilized for trapping mechanisms. Because CO₂ storage capacity is greatly increased and brine migration is minimized, the area required for securing mineral rights is reduced per unit of stored CO₂. If an extraction ratio of one is used, which is defined as the net extracted volume of brine divided by the injected CO₂ volume, pressure buildup is minimized, which greatly reduces the Area of Review, as well as the risk of induced seismicity. Because the migration of CO₂ and brine will be unaffected by neighboring CO₂ operations, planning, assessing, and conducting each CO₂ operation within a basin can be carried out independently. In addition, the extracted brine is available as a feedstock for desalination technologies, such as Reverse Osmosis (RO). Depending on the extraction ratio, Enhanced Water Recovery may also be possible. All of these benefits will be useful during the regulatory approval process and for gaining public acceptance.