Coupled hydrogeomechanical impacts of carbon sequestration

Long-term storage or sequestration of anthropogenic "greenhouse gases" such as CO₂ is a proposed approach to managing climate change. Deep subsurface brine reservoirs In geological sedimentary basins are possible sites for sequestration, given their ubiquitous nature. We used a mathematical sedimentary basin model, including full coupling of multiphase CO₂-groundwater flow, heat flow, and rock deformation, to evaluate effects of CO₂ Injection on fluid pressures and rock strain. We also analyzed residence times and migration patterns of CO₂ in possible brine reservoir storage sites. Study areas Include the Ulnta and Paradox basins of Utah, and the Permian basin of west Texas. Regional-scale hydrologic and mechanical properties, including the presence of fracture zones, were calibrated using laboratory measurements and field data. Our initial results suggest that, in general, long-term (~100 years or more) sequestration in deep brine reservoirs is possible, if guided by robust rock mechanical and hydrologic data. However, specific processes must be addressed to characterize and minimize risks. In addition to CO₂ migration from target sequestration reservoirs into other reservoirs or to the land surface, another environmental issue is displacement of brines into freshwater aquifers. We evaluated the potential for such unintended aquifer contamination by displacement of brines out of adjacent sealing layers such as marine shales. Results suggest that sustained injection of CO₂ may incur significant brine displacement out of adjacent sealing layers, depending on the injection history, initial brine composition, and hydrologic properties of both reservoirs and seals. Model simulations also suggest that as injection can induce abnormally high fluid pressures, or overpressures. Results indicate that injection-induced overpressures may migrate, and effective stresses may follow this migration under some conditions, as will associated rock strain. Such "strain migration" may lead to induced or reactivated fractures or faults, but can be controlled through reservoir engineering.