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The Southern North Sea Basin area, stretching from the UK to the Netherlands, has a rich hydrocarbon exploration and production history. The past, present and expected future hydrocarbon and geothermal exploration trends in this area are discussed for eight key lithostratigraphic intervals, ranging from the Lower Carboniferous to Cenozoic. In the period between 2007 and 2017, a total of 95 new hydrocarbon fields were discovered, particularly in Upper Carboniferous, Rotliegend and Triassic reservoirs. Nineteen geothermal systems were discovered in the Netherlands onshore, mainly targeting aquifers in the Rotliegend and Upper Jurassic/Lower Cretaceous formations. Although the Southern North Sea Basin area is mature in terms of hydrocarbon exploration, it is shown that with existing and new geological insights, additional energy resources are still being proven in new plays such as the basal Upper Rotliegend (Ruby discovery) for natural gas and a new Chalk play for oil. It is predicted that hydrocarbon exploration in the Southern North Sea Basin area will probably experience a slight growth in the coming decade before slowing down, as the energy transition further matures. Geothermal exploration is expected to continue growing in the Netherlands onshore as well as gain more momentum in the UK.

Significant amounts of gas and oil have been produced in the Dutch on/offshore over the last 50 years. The extraction of large volumes of gas has resulted in major pressure depletion of the originally overpressured to highly overpressured gas reservoirs. The impact of local pressure depletion on the virgin pressure systems of aquifers connected to those reservoirs has not been studied in detail. This paper presents and discusses a new approach to assess the distribution and magnitude of such pressure changes in time and space in and around gas fields. The focus will be on Rotliegend gas fields since most gas fields in the Netherlands occur in Rotliegend reservoirs.

Shallow gas in the Dutch offshore predominantly occurs in shallow marine to continental deposits of the Plio-Pleistocene Eridanos delta (Fig. 1). This delta was fed by an ancient fluvio-deltaic system that prograded through Northwestern Europe due to simultaneous uplift of the Fennoscandinavian Shield and accelerated subsidence of the North Sea Basin. The dimensions of its drainage area and the thickness of the deltaic deposits make it one of the largest deltas and complex in the world. The origin of the shallow gas may be deep subsurface thermogenic sources or biogenic sources in shallower strata. It is either structurally trapped in anticlines associated with rising salt domes or occurs in stratigraphic or depositional traps.

The Netherlands represent a mature area for hydrocarbon exploration, and only less obvious targets are left for finding more oil and gas. One of these targets is the Chalk Group. This paper presents selected results of a multidisciplinary project that aims to develop a new stratigraphic trap model and migration/charge model for the Chalk in the Netherlands. Here we focus on the analysis of the Posidonia-Chalk system, with emphasis on both the Posidonia source rock maturity history and the migration and charging conditions of the Chalk in the Dutch Central Graben. The Posidonia Shale Formation is the main oil-prone source rock in the Dutch Central Graben. The only producing oil field in the Chalk in the Netherlands, is the Hanze Field located in block F-2 between the Central Graben and the Step Graben. The strongly naturally fractured reservoir is located in the Ekofisk and in the Maastrichtian part of the Ommelanden Formation of the Chalk Group on top of a major salt diapir. The Chalk Group is absent by erosion in the inverted central part of the graben and its thickness reaches not more than 300 m in most of the graben area. The Chalk is overlain by the sealing Lower Tertiary shales, and is on top of the Lower Cretaceous shales/marls of the Rijnland Group. The Chalk overlies Jurassic units in the inverted centre of the graben. 1D-3D basin modelling (Petromod v.10 of IES) was used to study the Posidonia-Chalk system in the Dutch Central Graben (e.g. Verweij and Souto Carneiro Echternach 2008a), while additional hydrodynamic analysis (e.g. Verweij 2008b) was used to improve our understanding of the hydrocarbon charging and preservation conditions in the Chalk

The application of the empirical Eaton method to calibrated sonic well information and 3D seismic interval velocity data in the southeastern part of the Central North Sea Graben, using the Japsen (Glob. Planet. Change 24 (2000) 189) normal velocitydepth trend, resulted in the identification of an undercompacted and overpressured zone within the shaly Lower North Sea Group. Calculated overpressures near the bottom part of the group increase from east to west, from 3.5 to 5.5 MPa, that is in the direction of increasing sedimentary loading rates in Pliocene - Quaternary times. This ability of the application of sonic and 3D seismic velocity in empirical methods to assess the spatial distribution of overpressures in such shaly units is of importance because measured pressure data are usually not available for shaly sections. © 2003 Elsevier Science B.V. All rights reserved.

Traditionally, geologists focussed their research on the solid part of the subsurface. Increasingly geoscientists are aware of the role of fluids in the structural, sedimentological, mineral and (bio)geochemical evolution of the Earth’s crust. Geofluids research focusses on fluid-related processes on geological timescales. It includes a wide variety of research on physical and chemical aspects of subsurface fluids (groundwater, petroleum, and geothermal, magmatic and metamorphic waters) in the Earth’s crust, on microscopic to continental length scales.The significance of understanding fluid processes and, as a consequence, of geofluids research in exploration, use and sustainable management of natural resources (groundwater, oil, gas, geothermal energy, ore minerals and salt), storage of energy carriers and energy wastes, and prediction of natural geohazards and its consequences is increasingly recognised. The worldwide interest in – and understanding of – fluid flow in relation to various geological processes have advanced rapidly, especially since the early 1990’s (Bethke 1985, 1989; Doligez, 1987; Garven, 1985; Hubbert, 1953; Tóth, 1980, 1987; and since 1990: Al-Aasm et al., 2002; Bredehoeft & Norton, 1990; Dahlberg, 1994; Garven, 1995; Ingebritsen & Sanford, 1998; Jamtveit & Yardley, 1997; Law et al., 1998; Lerche & Thomsen, 1994; Mc- Caffrey et al., 1999; Mitchell & Grauls, 1998; Parnell, 1994, 1998; Pueyo et al., 2000;Van Balen, 1995;Verweij, 1993).The latest overview of geofluids research is presented in the Proceedings of the Geofluids IV: Fourth international conference on fluid evolution, migration and interaction in sedimentary basins and orogenic belts (Verweij et al. 2003). These concepts, theories and methods pertaining to fluid flow in relation to various geological processes in different sedimentary basins have been very valuable for the research in onshore and offshore Netherlands

The reconstruction of the post-Carboniferous hydrogeohistory of the onshore and offshore Netherlands is part of an ongoing TNO project on fluid flow systems analysis on geological timescales. The scope of the project is to assess the present-day hydrogeological and fluid flow conditions of the sedimentary basins in the onshore and offshore Netherlands and to analyse and model the evolution of fluid flow systems in these basins in order to increase the process-based knowledge of the causes of present-day physico-chemical characteristics of rocks and fluids in the sedimentary fill of the Dutch part of the North Sea Basin. This article concerns the first phase of the project and provides an overview of the characteristic features of the post-Carboniferous evolution of external and internal processes acting on the sedimentary fill and their role in shaping the hydrogeological and hydrodynamical setting of the Netherlands. The post-Carboniferous evolution of the fluid flow conditions is described for five geological time periods. During each time period different forces have acted simultaneously on the fluids and different fluid flow systems have coexisted and interacted. The present-day active driving forces and processes influencing fluid flow conditions include sedimentary loading, gas generation, tectonic forces, topographic relief of the water table, fluid density differences and human activities. The article presents a brief outline of the resulting fluid flow systems. Observed direct and indirect indicators of fluid flow (pressure, temperature, salinity, sediment-diagenetic minerals) are consistent with the reconstructed hydrogeological and hydrodynamic setting of the Netherlands.