Heat as a by-product or sub-product of CO₂ storage in mafic and ultramafic rocks

Since carbonates are at a lower energy state than free CO₂, storage through carbonation of silicate rocks is thermodynamically favoured and proceeds spontaneously by releasing heat. In an in-situ CO₂ injection site, the heat released in these exothermic reactions can be exploited in a geothermal power-plant, effectively contributing toward the economic viability of the storage process. Our calculations suggest the possibility of generating up to about 25 TWh of electrical energy while capturing permanently about 240 Mton CO₂ per 1 km3 of peridotite or basalt rock. That broadly corresponds to exploring an electric power plant having up to 60 MW gross output during a period of 50 years. These results show that geothermal energy and CO₂ storage, often portrayed as conflicting uses of the subsurface, can actually work together, enhancing the economic feasibility of each other in case mafic and/or ultramafic rock formations are used as reservoirs.