Abstract The collaboration between HADES and the Mont Terri rock laboratory started in 1995, when granite was considered the most suitable host rock for radioactive waste disposal in Switzerland. When an alternative host formation was looked for by NAGRA, the choice of clay as host rock became rapidly clear. It was then decided to build an underground research laboratory in the Opalinus Clay taking advantage of the excavation of a motorway tunnel crossing the Mont Terri anticline. Exchanges of knowledge and experience on the behaviour of argillaceous formations were focused on the feasibility of constructing a safe geological repository for high-level radioactive waste: from excavation and gallery lining techniques to geochemistry, diffusion of radionuclides and coupled thermo-hydro-mechanical processes. The research programme at Mont Terri and the growing numbers of partners from four up to nine countries worldwide led to successive extensions of the galleries. The scientific and technical advances made possible by the collaboration between both laboratories dealt with the development of common methods and joint experimental and modelling efforts. This review article summarizes the main scientific lessons learned during these exchanges, stressing the added values of the knowledge transfer between partners and the overall cross-fertilization between HADES and Mont Terri.

Abstract: Reaction transport modelling (RTM) has been successfully used to simulate dolomitization and to predict the lateral extension of dolomitized bodies as potential hydrocarbon reservoirs in the subsurface as well as to give insights into the dolomitization process itself. Geological configurations that have been tested include reflux dolomitization, thermal convection and dolomitization in compactional burial settings. In this study the hydrothermal dolomitization model has been tested with a RTM approach where a limestone reservoir in an intermediate burial setting is fluxed in the presence of deep feeding faults. Hydrothermal fluids migrate upwards from the deep basin areas through extensional fault conduits reaching more permeable levels in the reservoir. The fluids enter the primary interparticle porosity and dolomitize the limestone creating moldic and vuggy porosity. The simulations demonstrate the importance of faulting in this dolomitization process. An effective control on dolomitization is thus exerted by the permeability distribution. Moreover, the type and reactivity of the fluids entering the limestone reservoir exert important controls on the extent of the dolomite bodies.