Under the umbrella of the ELEGANCY-ACT project, the group also studied the possibility of caprock leakage of CO2 at a larger scale by in-situ CO2 injection tests at the Mont Terri URL. In a unique setup, the scientists investigated how the exposure to CO2-rich fluid affects the sealing capacities of a caprock hosting a fault – the Mont Terri Main Fault – and evaluated potential leaks.
After characterizing the fault’s transmissivity and permeability by water injection tests, while monitoring for eventual micro-seismic events, the scientists launched a long-term injection of CO2-saturated water at constant pressure and at a rate of approximately 0.04 millilitres per minute, to evaluate rock-CO2 interaction. The first results already after three months were promising, showing fault self-sealing soon after the CO2 injection, probably caused by swelling of the caprock. The injection is ongoing since 13 moths at present.
The final and future goal is to inject CO2-saturated water into the fault core for a few more weeks while monitoring its geo-mechanical response. Additional tracers and transmissivity tests at regular time intervals helped to determine the fluid path evolution and to infer the potential diffusion of CO2 from the water.