Sequestration of CO₂ in Geothermal Areas

Quintessa is providing numerical modelling support to a project investigating the feasibility of sequestering atmospheric CO2 in geothermal areas. This sequestration strategy is one possible means for mitigating the effects of climate change caused by anthropogenic CO2 emissions.

The work is being carried out in collaboration with Mitsubishi Materials Corporation (MMC), the Research Institute of Innovative Technology for the Earth (RITE) and the Central Research Institute of Electric Power Industry (CRIEPI). Funding is being provided by Japan's New Energy Development Organisation (NEDO).

A potential advantage of sequestering CO2 in geothermal areas, where high temperatures (to several hundred °C) occur, is that reactions between CO2-charged water and rock will be more rapid than in rocks at lower temperatures. In turn these reactions could potentially favour the trapping of CO2 in solid mineral phases such as calcite. To evaluate the feasibility of this sequestration option the coupled flow-reaction processes that would accompany CO2 injection must be understood. If the reaction rates are too fast and the rocks' porosity and permeability decrease near to the CO2 injection point, further CO2 injection might be prevented. On the other hand, if reactions are too slow or porosity increases too much, then injected CO2 might migrate too far and leak from the rock reservoir.

Quintessa has evaluated various aspects of this coupling, by theoretical modelling using a combination of widely used geochemical simulation codes (PHREEQC and Geochemist's Workbench) and Quintessa's own Raiden3. Raiden3 fully couples simulations of flow and reactions while taking into account reaction kinetics. One application of Raiden3 in the present project has been to develop an improved understanding of the processes that occur during the migration of CO2-saturated water through granodiorite at 200°C and 100 bars.