Abstract The appellation ‘Belgian black “marbles”’ usually designates dark fine-grained limestones present in the Paleozoic substrate of south Belgium. They have been extracted mostly in Frasnian (Upper Devonian) and Viséan (Lower Carboniferous) strata, in various different localities (Namur, Dinant, Theux, Basècles, Mazy-Golzinne among others). Nearly devoid of fossils and veins, they take a mirror-like polished finish, with a pure black colour. These limestones were already known during Antiquity but were only intensively exploited from the Middle Ages. Many different uses were made of these stones, for architecture, decoration or sculpture, in religious or civil contexts, following all the successive styles, Romanesque, Gothic, Renaissance, baroque and so on. All these products, architectural, decorative and sculptural, were probably manufactured close to the quarries and were first exported to neighbouring countries (France and the Netherlands), then to all of Europe (Italy, Germany, Denmark, Poland, Baltic states, etc.) and, by the beginning of the nineteenth century, worldwide. They were always considered as high value-added objects, which allowed them to travel great distances from their origin. Thousands of references document the widespread use of these exceptional natural stones. They were employed, among other famous applications, as the black background of the Pietre dure marquetry of Florence. Some other lesser uses were either for musical instruments or lithographic stones. Today only one underground quarry exploits the black ‘marble’, at Golzinne (close to Namur). This prestigious material, with its dark aura, is suitable for recognition as a Global Heritage Stone Resource.

Abstract The speciation of selenium (Se) in clay-rich host rocks is important within the framework of geological disposal of radioactive waste since it affects its migration. Removal of selenite from formation water can be caused by reduction and adsorption. Reduction could potentially be inhibited or delayed by adsorption. Here, the interplay of adsorption and reduction of selenite was investigated in batch experiments with Boom Clay and its separated size fractions. In all experiments, dissolved Se concentrations (Se aq ) showed a fast initial decrease that was followed by a slower decline until removal was almost complete. X-ray absorption spectroscopy indicated that adsorption of selenite accounted for the fast removal of Se aq followed by slower selenite reduction. Eventually, almost all solid-bound Se IV became reduced to Se 0 in all experiments. The progress of Se aq removal and Se IV reduction to Se 0 could be described by a kinetic model involving reversible adsorption on clay minerals and reduction by pyrite. This implies that the reduction of selenite to Se 0 is not significantly hindered or delayed by selenite adsorption on clay minerals. Pyrite is probably the most relevant reductant for selenite in Boom Clay, although reduction by Fe II structurally bound in clay minerals might provide an additional pathway for selenite reduction in clay rocks. Supplementary Material: X-ray diffractograms of separated clay-size, silt-size and total BC material are available as Supplementary Material . Also provided are particle size distributions of all materials and extra information on XANES and EXAFS results, Se concentrations through time for experiments with standard clay minerals and figures of the sensitivity analysis of the kinetic model. The information is available at https://doi.org/10.6084/m9.figshare.c.4363826

Abstract A geological understanding of the way fluids flow through a reservoir is crucial when considering waterflood developments in heterogeneous reservoirs. Recent integrated production geoscience and reservoir engineering studies on the Holland Greensand oil reservoir (Aptian) of the Rotterdam Field in the West Netherlands Basin, are used to illustrate the geological controls on fluid flow through rocks deposited in a clastic inner shelf depositional setting. An integrated understanding of the subsurface has been gained through core, log and production data analysis. Analogous Early Cretaceous Upper Greensand Formation coastal exposures in SW England have been used to gauge the scale of lateral and vertical heterogeneity, and its impact on hydrocarbon and water flow paths. Argillaceous sandstones deposited at the distal margins of a subtidal sand-sheet provide internal reservoir baffles, while fluids are believed to preferentially follow flow paths through associated laterally extensive tempestites. Cemented layers observable in wells are interpreted to be laterally restricted and are not considered as major baffles. These observations have been used to steer static reservoir model construction and subsequent simulation. Results from field testing by production logging tool analysis support the geological concepts developed and the modelling approach used. This work has important implications for defining the approach for future reservoir management and redevelopment in the Rotterdam Field, in particular the well type and configuration and completion strategies post-reservoir flooding. The application of methodologies employed in this study is recommended for similar waterflood developments.

Abstract: The mechanical strength, porosity and permeability of chalk are affected by chemical and mineralogical changes induced by fluids that are chemically out of equilibrium with the host rock. Here, two high-porosity Upper Cretaceous chalk cores from Liège were tested at effective stresses beyond yield at 130°C during flooding with MgCl 2 and NaCl brines. Core L1 (flooded by MgCl 2 brine) deformed more than L2 (flooded with NaCl brine), with volumetric strains of 9.4% and 5.1%, respectively. The porosity losses estimated from strain measurements alone are 5.82% for L1 and 3.01% for L2. However, this approach does not account for dissolution and precipitation reactions. Porosity calculations that are based on strain measurements in combination with (i) the weight difference between saturated and dry cores and (ii) the solid density measurement before and after flooding show an average porosity reduction of 3.69% between the two methods for L1. This discrepancy was not observed for core L2 (with the NaCl brine). The rock and effluent chemistry show that Ca 2+ dissolved and Mg 2+ is retained within the core for the L1 experiment. Therefore, accurate porosity calculations in chalk cores that are flooded by non-equilibrium brines (e.g. MgCl 2 ) require both the volumetric strain and chemical alteration to be considered.