Abstract A dataset with pore pressures from more than 1000 exploration wells has been used to investigate the dynamics of aquifer systems in the Norwegian Continental Shelf (NCS). Variations in aquifer pressures reflect flow of porewater through permeable rocks over geological time. Strongly overpressured regimes are formed within confined aquifers in subsiding areas, where fluid flow out of the aquifer is controlled by vertical seepage. In transitional pressure regimes, fluid flows within permeable beds towards areas with hydrostatic pressures. In the hydrostatic regime, pressure differences result from density differences due to varying formation water salinity and by hydrocarbon columns. An underpressured regime has been encountered in confined aquifers in the platform areas of the Barents Sea, and is related to net uplift and erosion. In the case studies, pressure differences are interpreted in the context of the relevant pressure regime, and with a dynamic approach where segment boundaries and cap rocks are regarded as low-permeability restrictions rather than barriers. The present distribution of pressure regimes was developed over the last few million years due to rapid Pleistocene sedimentation and erosion processes.

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: Petroleum systems represent complex multiphase subsurface environments. The properties of the noble gases as conservative physical tracers allow them to be used to gain insight into the physical behaviour occurring within hydrocarbon systems. This can be used to better understand the mechanisms of hydrocarbon migration, residence time of fluids, and measurement of the scale of the subsurface fluid system involved in the transport and trapping of the hydrocarbon phase. The noble gases in the subsurface derive from different sources with distinct isotopic compositions, allowing them to be resolved in any crustal fluid. We discuss the processes within petroleum systems that incorporate the noble gases from each of these sources into hydrocarbon accumulations. The dominant mechanism controlling the introduction of air-derived noble gases into petroleum systems is via subsurface groundwater, and this records key information about the interaction of the petroleum system with the hydrogeological regime. Radiogenic noble gases accumulate over time, recording information about the age and relative timing of processes within the petroleum system. We review the conceptual framework and quantitative models describing these processes using examples from previous studies, and discuss both their current limitations and the potential for their application to unconventional hydrocarbon systems.

The particle-size distribution of oil-sands tailings has always figured prominently in the mine planning and overall operations and closure strategy in surface-mined oil sands. In oil-sands applications, the convention is to define the sand as the mineral components >44 μm in size and the fines as the mineral component which is <44 μm. The water-based extraction process uses 2 m 3 of water to extract the bitumen from 1 m 3 of oil sand, and as the bulk of this water is recycled, large containment areas are required to maintain a supply of extraction water. A significant proportion of water that is not recycled is retained in both the sand and fines components of the resulting tailings streams and the essence of tailings management comes down to separating and managing the water that can be recovered from the tailings. As the mining operations have become larger, and ore properties vary over wider ranges, the designation of sand and fines was simply inadequate in explaining the behavior of many of the tailings and a thorough understanding of the entire particle-size distribution became more important. Due in part to the upgrading and refinery operations often associated with bitumen production, the oil sands industry is relatively sophisticated in its approach to tailings characterization and tailings management. As a result, any discussion of clays can, and often does, include both a size and mineralogy component. In any case, there is no doubt about the importance of understanding and quantifying the clay component of any tailings stream when defining a dewatering or management strategy. Historically, it might have been argued that the strong correlation between clay content and fines content would be an adequate characterization and tailings-planning parameter. Although this is still largely true, the clay to fines correlations can sometimes be measurably different from operation to operation, resulting in varying tailings performance. In addition, some tailings-management options such as thickeners and centrifuges can separate the fines fraction and even the clay fraction in a fluid fine tailings stream. These upset operational modes can create what are known colloquially as Franken-Fines, a stream with a very disproportionately high clay content that can create an equally disproportionate tailings problem. The tailings strategies that will be discussed include composite/consolidated/non-segregating tailings, thickening, freeze-thaw processes, rim ditching, thin lift dewatering, and centrifugation. The present chapter outlines the evolution of many of these tailings-management strategies that have been tested extensively or are currently in use in the surface-mined oil-sands industry, with a particular emphasis on the importance of understanding the clay size and clay mineralogy in the evaluation and understanding of tailings dewatering performance.

The whole Earth geohydrologic cycle describes the occurrence and movement of water from the clouds to the core. Reservoirs that comprise the conventional hydrologic cycle define the exosphere, whereas those reservoirs that are part of the solid Earth represent the geosphere. Exosphere reservoirs thus include the atmosphere, the oceans, surface water, glaciers and polar ice, the biosphere, and groundwater. Continental crust, oceanic crust, upper mantle, transition zone, lower mantle and the core make up the geosphere. The exosphere and geosphere are linked through the active plate tectonic processes of subduction and volcanism. While the storage capacities of reservoirs in the geosphere have been reasonably well constrained by experimental and observational studies, much uncertainty exists concerning the actual amount of water held in the geosphere. Assuming that the amount of water in the upper mantle, transition zone, and lower mantle represents only 10%, 10%, and 50% of their storage capacities, respectively, the total amount of water in the Earth's mantle (1.2 × 10 21 kg) is comparable to the amount of water held in the world's oceans (1.37 × 10 21 kg). Fluxes between reservoirs in the geohydrologic cycle vary by ~7 orders of magnitude, and range from 4.25 × 10 17 kg/yr between the oceans and atmosphere, to 5 × 10 10 kg/yr between the lower mantle and transition zone. Residence times for water in the various reservoirs of the geohydrologic cycle also show wide variation, and range from 2.6 × 10 -2 yr (~10 days) for water in the atmosphere, to 6.6 × 10 9 yr for water in the transition zone.