Abstract: An Integrated Strategy for Carbon Management Combining Geological CO2 Sequestration, Displaced Fluid Production, and Water Treatment

Abstract The preliminary numerical simulations of commercial-scale geological carbon dioxide (CO2) sequestration at the Rock Springs Uplift, southwestern Wyoming, presented in this study strongly suggest that displaced fluids resulting from subsurface CO2 injection must be managed. To solve this problem, the Wyoming State Geological Survey and Los Alamos National Laboratory propose a strategy that includes integration of fluid production and treatment with injection of CO2. Using this strategy, 750 million tonnes (Mt) of CO2 can be injected and contained in a 16 km × 16 km (10 mile × 10 mile) storage domain over a 50-year period. The primary CO2 sequestration reservoir on the Rock Springs Uplift is the Weber Sandstone, and the secondary sequestration reservoir is the Madison Limestone. The numerical simulations demonstrate that, over the course of 50 years with an injection rate of 15 Mt of CO2 per year (750 Mt total), these sequestration reservoirs can accommodate the injected CO2; however, as pressure in the reservoir returns to background over the 50 years following injection, the sequestered CO2 will displace 1 cubic kilometer of formation fluid. For successful CO2 sequestration, this displaced fluid (6 billion barrels over 75 years) must leave the storage domain and find accommodation space elsewhere. To reduce the risk of large-scale hydrofracture, especially at intraformational fluid-flow barriers and faults, reservoir pressure must be managed. In the suggested strategy, pressure management is accomplished by production of the displaced fluids, with subsequent treatment at surface facilities, yielding 10,000 acre-feet of potable water per year. In the context of this paper, management of displaced fluids means that the pressure effect of these fluids is confined to the CO2 storage domain (16 km × 16 km). Without management, the pressure evolution caused by CO2 injection will migrate over an area larger than 50 km × 50 km. The potential for pressure migration over such large distances greatly increases the need for data that can help us predict possible fluid migration along high-permeability vertical pathways. Also, long migration distances substantially increase the potential for interference with adjacent mineral estates. The cost of monitoring unmanaged fluid flow would be extremely high and characterized by significant uncertainty. In addition, the large quantity and low quality of the displaced fluids (> 20,000 ppm TDS) makes management obligatory.