Geothermal energy production from actively-managed CO ₂ storage in saline formations

Increased reliance on geothermal energy and CO ₂ capture and sequestration (CCS) in deep geological formations are both regarded as a promising means of lowering the amount of CO ₂ emitted to the atmosphere and thereby mitigate climate change. We investigate an approach to produce geothermal energy and to sequester CO ₂ at low cost and risk by integrating geothermal production with CCS in saline, sedimentary formations where a significant portion of the U.S. geothermal resource base resides. For industrial-scale CO ₂ injection in saline formations, pressure increase can be a limiting factor in storage capacity and security, while geothermal energy production can be limited by pressure depletion. Our approach utilizes Active CO ₂ Reservoir Management, which combines brine production with CO ₂ injection to enable more cost-effective and secure CO ₂ storage. The complementary CCS and geothermal systems are integrated synergistically, with CO ₂ injection providing pressure support to maintain productivity of geothermal wells, while brine production provides pressure relief and improved injectivity for CO ₂ injectors. A volumetric balance between injected and produced fluids mitigates the environmental and economic risks of reservoir overpressure (CCS concern) or underpressure (geothermal concern), including induced seismicity, insufficient well productivity or injectivity, subsidence, and fluid leakage either to or from overlying formations. We investigate the tradeoff between pressure relief at CO ₂ injectors and CO ₂ breakthrough time at geothermal brine producers for both vertical and horizontal wells, and address the influence of formation dip and permeability heterogeneity. The combined influence of buoyancy and layered heterogeneity delays CO ₂ breakthrough at geothermal production wells, particularly when the permeability contrast is large. Our results indicate adequate pressure relief at CO ₂ injectors can be attained, while delaying CO ₂ breakthrough at production wells for 30 or more years, thus enabling sustainable geothermal power.