Rock and porewater characterisation on drillcores from the Schlattingen borehole

Radioactive waste in Switzerland is foreseen to be disposed in deep-seated low permeability sedimentary formations. Currently, the siting process is taking place within the so-called Sachplan procedure, in which Nagra has proposed six potential siting areas. One of these areas lies in the region "Zürich Nordost" where a large geological campaign within the project Opalinus Clay, a demonstration of feasibility (Entsorgungsnachweis), was carried out until 2002. In 2011, a deep borehole for geothermal purposes was drilled down to a depth of 1'508 m below surface (well head at 416.6 m above sea level) in Schlattingen (TG)1. It is located west of the village of Schlattingen, about 10 km NE of the Benken borehole, which was drilled within the feasibility demonstration study Entsorgungsnachweis. Nagra had the opportunity to accompany the borehole drilling in Schlattingen with an extensive investigation programme. The scope thereof is to gain further information and understanding on the geology of the area, focussing in particular on the low permeability Jurassic sedimentary rocks. Thus, the section 731.5 – 988.9 m (Malm till base Lias) as well as a deeper section in the Muschelkalk were cored and sampled for rock mechanical, geological and geochemical purposes. Geophysical logging was conducted for almost the entire borehole length (130 – 1'508 m depth). Hydrotesting was performed in a number of test intervals in the Jurassic, Triassic and Permian formations and in the underlying crystalline rock. Finally, primary stress measurements were conducted at selected depth levels. The Rock-Water Interaction (RWI) group of University of Bern has participated in this investigation programme by on-site work (geological mapping and sampling of the drillcores, coordination and distribution of samples to different laboratories), as well as extensive laboratory studies. These were performed to a large extent in-house, but partly also contracted to other laboratories. The focus is on the sediments dominated by clay-rich lithologies from the Malm to the lower Lias, including the Effingen Member, the 'Brauner Dogger', the Opalinus Clay and the underlying Lias unit (also referred to as lower confining unit). The objectives are: - to complement the mineralogical and geochemical database of the Jurassic rocks in Northern Switzerland, - to improve the geochemical and hydrogeological process understanding of the porewaters of these rocks, - to test and to improve new methods for characterising porewater chemistry. The main scope of this report is to present: - a comprehensive mineralogical dataset, - a comprehensive petrophysical dataset (densities, porosities, surface areas), - a comprehensive dataset on conservative porewater tracers (2H, 18O and Cl-) and on anion-acessible porosity, - additional data on porewater composition: cation concentrations, pH/pCO2 conditions, cation exchange data, - data on thermal maturity of organic matter, - information on diagenetic processes and vein mineralisations, including isotope studies