We present an approach to use formation brine, N2, and CO2 to (1) generate cost-competitive, dispatchable, renewable power that can quickly respond to electric grid imbalances, (2) stabilize the grid by efficiently storing larger quantities of energy for longer periods than current bulk energy storage technologies, (3) enable seasonal storage of solar thermal energy for grid integration, (4) produce brine for power-plant cooling, all which (5) increase CO2 value, rendering CO2 capture to be commercially viable, while (6) sequestering huge quantities of CO2. Conventional geothermal power systems recirculate brine as the working fluid to extract heat, but the parasitic load for this recirculation can consume a large portion of gross power. Recently, CO2 has been considered as a working fluid because its advantageous properties reduce this parasitic loss. We expand on this idea by using multiple working fluids: brine, CO2, and N2. N2 is advantageous because it can be separated from air at lower cost than captured CO2, it is not corrosive and will not react with the formation, and enable bulk energy storage, while reducing operational risk. Extracting heat from geothermal reservoirs often requires submersible pumps to lift brine, but these pumps consume much of the generated electricity. In contrast, our approach drives fluid recirculation by injecting supplemental, compressible fluids (CO2, and N2) with high coefficients of thermal expansion. These fluids augment reservoir pressure to generate artesian flow at the producers, which reduces the parasitic load. Pressure augmentation is improved by the thermosiphon effect that results from injecting cold/dense CO2 and N2. These fluids are heated to reservoir temperature, greatly expand, and increase artesian flow at the producers. Rather than using pumps, the thermosiphon effect directly converts reservoir thermal energy into mechanical energy for fluid recirculation. Because stored pressure drives fluid production, the response time is faster than that of conventional geothermal. Our approach is achieved by an arrangement of concentric rings of horizontal producers and injectors, designed to create a hydraulic divide to conserve supplemental fluid and pressure, store energy, and maximize artesian flow at the producers. These rings can be arranged at different levels to use gravity-drainage double-displacement to enhance brine recovery and provide operational flexibility to improve heat sweep. Key questions include how well this approach performs in heterogeneous geologic settings and how effectively the productivity of horizontal wells is leveraged. For conventional geothermal power, the parasitic power load is in phase with gross power output. In contrast, our approach can time-shift much of the parasitic power load, which is dominated by the power required to separate N2 from air and compress it for injection. Because N2 is readily available, it can be injected intermittently. Thus, most of the parasitic power load can be shifted to coincide with minimum power demand or when there is a surplus of renewable power. Such a time-shift also allows net power output to be nearly equal to gross power output during peak demand. Energy storage can be almost 100 percent efficient because it is achieved by shifting the parasitic load, which is more efficient than other methods used to store energy. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory (LLNL) under Contract DE-AC52-07NA27344.

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