Improving pressure-limited CO2 storage capacity in saline formations by means of brine extraction

The carbon dioxide (CO₂) storage capacity of saline formations may be constrained by reservoir pressure limitations. Brine extraction could be necessary to increase the CO₂ storage capacity of a given formation, manage the extent of the underground CO₂ plume and induced pressure front, and control the migration direction. To estimate the additional CO₂ storage capacity of a saline formation that can be made accessible by extraction of in-situ brines, a three-dimensional (3D) generic cubic cell containing one CO₂ injector in the middle surrounded by four brine extractors at each corner of the cell was assumed. A series of Tough2-ECO2N reservoir simulations were constructed with varying reservoir properties and run. Based on a series of scenarios, a mechanism was developed and demonstrated that resulted in derivation of a function to provide estimates of the ratio of total CO₂ injection over the brine extraction rate for a given scenario. We selected multiple saline formations in U.S. basins and evaluated the potential to increase the combined dynamic CO₂ storage capacity of the selected saline formations to over 1000 million metric tonnes per year (Mt/yr) of CO₂ for 100 years by means of brine extraction. Such storage capacities may be adequate to accommodate the CO₂ injection rates suggested for the United States under a “beyond two-degree Celsius scenario” (B2DS) that has been proposed to maintain global temperature rise to less than 2°C above pre-industrial reported levels. The results suggest that B2DS goals could be achieved with a volume ratio of brine extraction to CO₂injection as low as 1:4, which is far lower than the ratios that have been commonly assumed in the literature.