Abstract Due to their particularly good mechanical and self-healing properties combined with exceptionally efficient cation adsorbents and exchanger capacities, clay minerals and clay rock formations are considered as suitable geological barriers for radioactive waste disposal. The Middle Jurassic Opalinus Clay Formation has been identified as a potential host rock. Logging data were measured at the Benken borehole drilled through this formation in northern Switzerland. This paper presents a statistical methodology to improve the description of the physical properties of the clay rock based on the well-log data. The methodology involves the classification of a set of local statistics, calculated from a reduced number of principal components computed from well-log properties. The use of a kernel-based method to calculate local statistics allows an analysis of spatial variability to be carried out at different scales, and with different scale effects. The first-order layering was found to be robust and independent of kernel size (i.e. observation scale), while preserving small-scale heterogeneities that are useful for further interpretation. The log units can be more clearly interpreted in terms of stationary or transitional log units, depending on the behaviour of local statistics. Finally, the derived spatial variability of the log-units properties are compared with earlier lithological descriptions and stratigraphic data. Supplementary material: A spreadsheet summary with the determination of clustering parameters for a kernel size of 3 m is available at https://doi.org/10.6084/m9.figshare.c.4315991

Abstract The inversion of a sedimentary basin could be associated with compressional reactivation of basin-forming normal faults, upwards movement of the basement blocks and partial or complete erosion of its sedimentary infill. Basin inversion might be also related to whole-basin uplift that is not linked to the reactivation of basement faults, and results in the development of regional stratigraphic gaps and unconformities. Both types of basin inversion have been documented in SE Poland using seismic data. Regional NW–SE seismic profiles illustrate earliest Late Jurassic (earliest Oxfordian) and earliest Late Cretaceous (Cenomanian) regional unconformities related to regional basin-scale uplifts in the SE segment of the Polish Basin. Late Cretaceous (Turonian?–Maastrichtian) progressive uplift of the Mid-Polish Swell has been documented along the NE border zone of this regional anticlinal structure. The Upper Cretaceous inversion-related sedimentary succession is characterized by an overall progradational character directed from the SW towards the NE. Buried contourite drifts that were detected within the Upper Cretaceous succession using seismic data indicate the existence of contour currents encircling inversion-related intrabasinal morphological barriers. A new tectonic scenario of the Mesozoic evolution of SE Poland would have a significant impact on the modelling of tectonic subsidence and the history of petroleum systems.

Abstract The North German Basin yields enormous geothermal resources of more than 13 000 EJ (exajoule: 1 EJ = 1 × 10 18 J) heat in place bound to Paleozoic petrothermal and Mesozoic hydrothermal reservoirs. So far, these resources are only exploited at a few localities. Thus, geothermal energy is considered an underutilized energy resource. Despite long-term experience in exploiting Rhaetian hydrothermal reservoirs, the exploration risk remains high, which is mainly related to high expectations on reservoir thickness and quality. Previous exploration campaigns have identified potential hydrothermal reservoirs in six Mesozoic reservoir complexes. But, as high-resolution subsurface maps are not available, the reliable prediction and targeting of reservoirs remains an unsolved problem. As such, an exploration strategy integrating methods of sedimentology, palaeontology, petrography and reservoir characterization was applied to a large database of cores and wireline logs. This contribution details the key results of the exploration of Upper Keuper and Middle Jurassic reservoir complexes, including high-resolution subsurface facies, sandstone thickness and reservoir quality maps. Sets of these maps enable the reliable prediction and targeting of individual hydrothermal reservoirs, and, thus, make a significant contribution to a lowered exploration risk.

Abstract A detailed 3D petroleum system model was constructed for the Schleswig-Holstein area in northern Germany. Salt movement and the Quaternary ice episodes were implemented in order to reconstruct their impact on temperature, maturity and pressure. Burial, temperature and maturity histories were calculated for the Jurassic troughs and the Glueckstadt Graben showing both differences and similarities. For example, all locations reached (almost) deepest burial at present day, whilst subsidence and long-term sedimentation rate was highest in Glueckstadt Graben during the Triassic. The Jurassic troughs received their major subsidence and sedimentation pulse later, and were strongly affected by a later salt movement. The implementation of Quaternary glacial episodes does not have a strong impact on petroleum generation from the major source rock (Lower Toarcian Posidonia Shale). In the case of the Posidonia Shale reaching the stage of petroleum expulsion (outside of the study area), the effect of ‘glacial pumping’(i.e. the development of high pore pressures during glaciation followed by expulsion and subsequent pressure release during deglaciation) can be deduced from the model. Petroleum accumulations in the reservoir layers (Dogger sandstones) are also seen to have been affected. This finding is of interest for exploration, as it might control petroleum composition, biodegradation and leakage through cap rocks.

Abstract: The properties of sandstones are strongly affected by formation of minerals in the pore space during diagenesis. In many sandstones, quartz overgrowths are the most important pore-filling cements and show a characteristic trace element composition. The most important impurities are Al, Li, H and Ge. The Al concentration of quartz may reach up to several 1000 µmol mol −1 and is assumed to reflect the composition of the porewater. Geochemical modelling of the activity ratio of Al and Si revealed a minimum at nearly neutral to slightly acid conditions. This minimum shifts to lower pH with increasing temperatures. Due to complexing, organic acids may strongly affect the Al solubility especially in acidic water at low temperatures. There is a linear correlation between Al and Li, indicating their incorporation in a combined [AlO 4 |Li] centre. Since Li only accounts for 10–30% of the Al concentration, the remaining Al needs to be balanced by H. The ratio of Li/H-compensated Al centres seems to depend on the Li activity and the pH in the aqueous solution. Germanium concentrations in quartz cements are slightly higher than the crustal average and they show a weak correlation with Al. The excess of Ge in authigenic quartz requires pre-enrichment, probably by formation of kaolinite. Possible applications of trace element analyses of authigenic quartz include discrimination of different sources that contribute to the supply of silica, enhanced understanding of inhomogeneities that are related to cementation and possible tracking of fluid migration.