The article Hydro-mechanical response of Opalinus Clay in the CO₂ long-term periodic injection experiment (CO₂LPIE) at the Mont Terri rock laboratory of the EASY GEO-CARBON team has been published on 29th September.
Guaranteeing the sealing capacity of caprocks becomes paramount as CO₂ storage scales up to the gigaton scale. A significant number of laboratory experiments have been performed with samples of intact rock, showing that low-permeability and high-entry pressure caprocks have excellent sealing capacities to contain CO₂ deep underground. However, discontinuities, such as bedding planes, fractures and faults, affect the rock properties at the field scale, being at the same time challenging to monitor in industrial-scale applications. To bridge these two spatial scales, Underground Research Laboratories (URLs) provide a perfect setting to investigate the field-scale sealing capacity of caprocks under a well-monitored environment. In particular, the CO₂ Long-term Periodic Injection Experiment (CO₂LPIE) at the Mont Terri rock laboratory, Switzerland, aims at quantifying the advance of CO₂ in Opalinus Clay, an anisotropic clay-rich rock with bedding planes dipping 45° at the experiment location.
To assist in the design of CO₂LPIE and have an initial estimate of the system response, we perform plane-strain coupled Hydro-Mechanical simulations using a linear transversely isotropic poroelastic model of periodic CO₂ injection for 20 years. Simulation results show that pore pressure changes and the resulting stress variations are controlled by the anisotropic behavior of the material, producing a preferential advance along the bedding planes. CO₂ cannot penetrate into Opalinus Clay due to the strong capillary effects in the nanoscale pores, but advances dissolved into the resident brine. We find that the pore pressure oscillations imposed at the injection well are attenuated within tens of cm, requiring a close location of the monitoring boreholes with respect to the injection interval to observe the periodic signal.