MontTerri projects

The Mont Terri Rock Laboratory provides an underground infrastructure for conducting long-term experiments (years to decades) in clay rock, the Opalinus Clay, at a decametric to hectometer scale. This facility uniquely bridges the gap between typical laboratory experiments and pilot projects, incorporating the complexity of an in-situ setting while maintaining a high level of control over the experimental environment due to the extensive understanding of the clay formation.

SED, as partner in the Mont Terri Consortium, is active since many years in multiple experiments, as of principal investigator (*) or in partnership with other scientific and industrial organizations. The SED provides in-kind contributions as well as direct funding from European and/or national funding agencies. The projects cover a large variety of research topics, and often have an immediate applicability for industry.
Current experiments where the SED is involved are:

CL: CO2LPIE - CO2 Long-term Pulse Injection Experiment (2023-2028) examines the thermal, hydraulic, mechanical, and chemical (THMC) effects of CO2 injection into intact Opalinus Clay at in-situ conditions. It begins with a four-year phase, and could be extended over a decade. The goal is to improve understanding of caprock behavior and integrity, which is crucial for subsurface uses, particularly CO2 storage. Insights into geochemical reactions are vital due to their impact on clay-rock composition and hydro-geomechanical properties. Accurate experimental data on reaction rates and barrier properties are essential for reliable reactive transport simulations, which are foundational for storage site characterization and long-term storage risk assessment.

CS-E (*): Mini-fracturing and Sealing (2021-2027) builds on the observations of the previous CS-D experiment (2018-2021). The primary objective is to understand the reactivation of individual, small fractures within the Mont Terri Main Fault. This involves a series of low flow rate, high pressure "mini-stimulations" to open pre-existing small fractures. The experiment aims to develop strategies to mitigate caprock failure during storage activities, and investigates on the use of sealants to be injected into the fault zone. It addresses critical research questions under geological conditions relevant to Switzerland, supporting the implementation of the Swiss national roadmap on carbon capture and storage.

FS-B: Imaging the long term loss of fault rock integrity (2015-2027) aims to image short-term fluid flow, permeability, and stress variations through a minor fault to evaluate the performance of radioactive waste repositories in shale. Its results can also inform CO2 storage security and cap-rock integrity. FS-B involves repeated seismic imaging of fluid flow and stress variations during controlled fault activation by fluid injection, with continued monitoring afterward to characterize the permeability evolution of the stimulated fault.

FS-E: Distributed hydromechanical response during fault damage and fault self-sealing evolution (2023-2027). Using an unprecedented 10cm resolution distributed optical fiber method, the goal of the experiment is to explore the in situ time-lapse coupling of pore pressure, strain, and structures associated with the long-term sealing process following the fault zone activation (after the FS-B activation). Few studies have investigated the long-term hydromechanical behavior of a fault years after activation. FS-E results could also be used to assess the long-term integrity and security of host rocks and CO2 storage.

GT: Gas transport models and the behavior of clay rocks under gas pressure (2022-2026). In geological waste repositories, gas is mainly generated by the corrosion of metals. The low permeability of clay rock can cause gas accumulation, increasing pressure and potentially fracturing the host rock. Waste processing or engineered gas transport systems are proposed as mitigation measures. In clay-rich formations, it is uncertain whether gas can escape without causing fractures and creating pathways for groundwater transport. Understanding these processes is incomplete, and a comprehensive mathematical framework is still lacking. The experiment includes both laboratory and field components.

PF-A: Progressive evolution of structurally controlled overbreaks - Long-term monitoring, hydromechanical simulation and rock testing (2023-2026).  From 2020 to 2023, the PF experiment investigated damage initiation and propagation in faulted Opalinus Clay rock above a large-diameter borehole. Initially, it examined the effects of ventilation and rock desaturation, followed by re-saturation. With the ongoing PF-A experiment the focus move on the long-term (3.5 to 7.5 years) evolution of rock mass damage and structurally-controlled over-breaks. Novel survey and monitoring techniques revealed reduced rock resistivities and subtle changes in seismic velocities, indicating evolving water flow paths linked to rock mass damage. Numerical simulations assessed the short-term mechanical behavior of the faulted rock mass. PF-A continues in-situ surveying and monitoring at a reduced frequency to establish long-term datasets. Advanced simulations aim to develop a 3D model for coupled flow and deformation phenomena, investigate subcritical crack growth effects on overbreaks, and validate a numerical model for predicting repository tunnel behavior in fractured rock.