West Netherlands Basin Research Articles

Multiple phase rifting and subsequent inversion in the West Netherlands Basin: implications for geothermal reservoir characterization

Abstract. Aiming to contribute to the energy transition, this study provides an integrated picture of the geothermal system hosted in the West Netherlands Basin and shows how the reconstruction of the basin's geological history can contribute to the correct exploration and exploitation of its geothermal resources. In the West Netherlands Basin, the main geothermal targets are found in the Cretaceous and Jurassic strata that were deposited during the rifting and post-rifting stages and were deformed during the subsequent basin inversion. Despite multiple studies on the tectonic setting, the timing and tectono-stratigraphic architecture of the rift system and its overall control on the development and evolution of geothermal systems are still to be fully deciphered. In this study, a detailed seismo-stratigraphic interpretation of the syn- and post-rift intervals in the West Netherlands Basin will be given within the framework of geothermal exploration. A recently released and reprocessed 3D seismic cube is used, covering a large portion of the onshore section of the basin. We identified two major Jurassic rifting episodes and a Late Cretaceous inversion event. During the Jurassic rifting phases, the compartmentalization of the basin and the creation of accommodation space led to the deposition of the Late Jurassic Nieuwerkerk Formation, which is the main regional geothermal producing target. Within this formation, we individuate growth synclines located in the central portions of the Jurassic half-grabens as sites that show good potential for geothermal exploration.

The impact of natural fractures on heat extraction from tight Triassic sandstones in the West Netherlands Basin: a case study combining well, seismic and numerical data

AbstractThe positive impact that natural fractures can have on geothermal heat production from low-permeability reservoirs has become increasingly recognised and proven by subsurface case studies. In this study, we assess the potential impact of natural fractures on heat extraction from the tight Lower Buntsandstein Subgroup targeted by the recently drilled NLW-GT-01 well (West Netherlands Basin (WNB)). We integrate: (1) reservoir property characterisation using petrophysical analysis and geostatistical inversion, (2) image-log and core interpretation, (3) large-scale seismic fault extraction and characterisation, (4) Discrete Fracture Network (DFN) modelling and permeability upscaling, and (5) fluid-flow and temperature modelling. First, the results of the petrophysical analysis and geostatistical inversion indicate that the Volpriehausen has almost no intrinsic porosity or permeability in the rock volume surrounding the NLW-GT-01 well. The Detfurth and Hardegsen sandstones show better reservoir properties. Second, the image-log interpretation shows predominately NW–SE-orientated fractures, which are hydraulically conductive and show log-normal and negative-power-law behaviour for their length and aperture, respectively. Third, the faults extracted from the seismic data have four different orientations: NW–SE, N–S, NE–SW and E–W, with faults in proximity to the NLW-GT-01 having a similar strike to the observed fractures. Fourth, inspection of the reservoir-scale 2D DFNs, upscaled permeability models and fluid-flow/temperature simulations indicates that these potentially open natural fractures significantly enhance the effective permeability and heat production of the normally tight reservoir volume. However, our modelling results also show that when the natural fractures are closed, production values are negligible. Furthermore, because active well tests were not performed prior to the abandonment of the Triassic formations targeted by the NLW-GT-01, no conclusive data exist on whether the observed natural fractures are connected and hydraulically conductive under subsurface conditions. Therefore, based on the presented findings and remaining uncertainties, we propose that measures which can test the potential of fracture-enhanced permeability under subsurface conditions should become standard procedure in projects targeting deep and potentially fractured geothermal reservoirs.

Geology of the Upper Jurassic to Lower Cretaceous geothermal aquifers in the West Netherlands Basin – an overview

AbstractIn the past 10 years the mature hydrocarbon province the West Netherlands Basin has hosted rapidly expanding geothermal development. Upper Jurassic to Lower Cretaceous strata from which gas and oil had been produced since the 1950s became targets for geothermal exploitation. The extensive publicly available subsurface data including seismic surveys, several cores and logs from hundreds of hydrocarbon wells, combined with understanding of the geology after decades of hydrocarbon exploitation, facilitated the offtake of geothermal exploitation. Whilst the first geothermal projects proved the suitability of the permeable Upper Jurassic to Lower Cretaceous sandstones for geothermal heat production, they also made clear that much detail of the aquifer geology is not yet fully understood. The aquifer architecture varies significantly across the basin because of the syn-tectonic sedimentation. The graben fault blocks that contain the geothermal targets experienced a different tectonic history compared to the horst and pop-up structures that host the hydrocarbon fields from which most subsurface data are derived. Accurate prediction of the continuity and thickness of aquifers is a prerequisite for efficient geothermal well deployment that aims at increasing heat recovery while avoiding the risk of early cold-water breakthrough. The potential recoverable heat and the current challenges to enhance further expansion of heat exploitation from this basin are evident. This paper presents an overview of the current understanding and uncertainties of the aquifer geology of the Upper Jurassic to Lower Cretaceous strata and discusses new sequence-stratigraphic updates of the regional sedimentary aquifer architecture.

Investigation of the synergy potential of oil and geothermal energy from a fluvial oil reservoir

Geothermal projects, as renewable energy projects, are not economically attractive in most places of the world at the current state of development; for this reason, subsidies are required by energy and environmental authorities in order to increase the interest in such projects. In this paper, we assess and model strategies for integration of geothermal energy with oil productions of the Moerkapelle oil field in the Netherlands. To do so, numerical simulations have been employed to analyse the feasibility of a fluvial oil reservoir for the synergy potential of oil and geothermal energy exploitation. In order to implement the simulation studies, single phase and two-phase non-isothermal fluid flow modelling are utilized for the geothermal well doublet system and for water flooding in an oil reservoir (including facies heterogeneity), respectively. A series of simulations have been conducted to investigate how hot water from a geothermal reservoir beneath a heavy oil reservoir in the fluvial sedimentary system of the West Netherlands Basin can be used for Thermal Enhanced Oil Recovery (TEOR) and geothermal energy production.This study finds that the high degree of heterogeneity in fluvial oil reservoirs could significantly affect oil recovery improvement and hence the synergy strategy. High values of a) Net to gross (N/G) b) Bottom Hole Pressure (BHP) and c) horizontal wellbore length are favourable for oil recovery. In contrast, wide horizontal wellbore spacing and high oil viscosity have an adverse effect on oil recovery enhancement. Furthermore, the results display that the enhanced oil production helps to reduce the required subsidy for a single doublet geothermal project up to 100%. Consequently, the extra amount of oil produced by utilising the geothermal energy, could make the geothermal business case independent and profitable.

Towards optimisation of geothermal heat recovery: An example from the West Netherlands Basin

The Netherlands experienced the fastest European expansion of geothermal energy exploitation in the past decade. The first Dutch geothermal sites proved that Hot Sedimentary Aquifers exploitation can play an important role in a future low-carbon energy mix. In this study, we estimate that with the expansion rate of the past four years, geothermal heat production from Lower Cretaceous Hot Sedimentary Aquifers could cover up to 20% of the heat demand in the province of Zuid-Holland by 2050. Although this is a significant amount, we show in this study that only 1% of the potentially recoverable heat will be recovered by 2050. This is because of inefficient doublet deployment on a ‘first-come, first served’ basis with operational parameters that focus on objectives of small decentralised heat grid demands. Instead, similar to the common-practise approach in the hydrocarbon industry, a regional coordinated ‘masterplan’ approach could be used to increase heat recovery. Utilising numerical simulations for flow and heat transfer in the subsurface, we showed that the heat recovery efficiency could be increased by tens of percentages with such coordinated doublet deployment. Based on calculations of the Levelized Costs Of Heat for both deployment strategies, we also show that current financial support schemes do not favour heat recovery optimisation. This study emphasises that although Hot Sedimentary Aquifer resources have the potential to cover a significant part of our energy demand, a radical change in financial support schemes and legislation are required to unlock their true potential.

Reservoir architecture model of the Nieuwerkerk Formation (Early Cretaceous, West Netherlands Basin): diachronous development of sand-prone fluvial deposits

Abstract The sand-prone fluvial Delft Sandstone Member of the Nieuwerkerk Formation is the main target for geothermal exploitation in the West Netherlands Basin. Uncertainty reduction in the modelling of permeability heterogeneity and connectivity of the sandstone reservoir units is of prime importance in the low-profit geothermal energy market. Lithostratigraphic correlation of the Delft Sandstone Member dates back to the 1970s, and considers the fluvial deposits as Valanginian (140–134 Ma) in age and synchronously deposited throughout the basin. Analysis of newly-acquired palynological data, in combination with well-log correlation and seismic interpretation, enabled the construction of a sequence-stratigraphic framework for the Nieuwerkerk Formation, in which the fluvial sandstones were deposited in a much wider age range than previously believed, from Late Ryazanian to Valanginian (142–134 Ma). The depocentre of fluvial deposition shifted in time from NE to SW across the width of the basin. This diachronous development resulted in a discontinuous spatial arrangement of fluvial sandstones. The new reservoir architecture model will aid in the well placement of geothermal doublets and the assessment of interference risk of adjacent geothermal projects.

The impact of heterogeneity on waterflood developments in clastic inner shelf reservoirs: an example from the Holland Greensand Member, Rotterdam Field, The Netherlands

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.

Regional geothermal aquifer architecture of the fluvial Lower Cretaceous Nieuwerkerk Formation – a palynological analysis

AbstractThe primary challenge for efficient geothermal doublet design and deployment is the adequate prediction of the size, shape, lateral extent and thickness (or aquifer architecture) of aquifers. In the West Netherlands Basin, fluvial Lower Cretaceous sandstone-rich successions form the main aquifers for geothermal heat exploitation. Large variations in the thickness of these successions are recognised in currently active doublet systems that cannot be explained. This creates an uncertainty in aquifer thickness prediction, which increases the uncertainty in doublet lifetime prediction as it has an impact on net aquifer volume. The goal of this study was to improve our understanding of the thickness variations and regional aquifer architecture of the Nieuwerkerk Formation geothermal aquifers. For this purpose, new palynological data were evaluated to correlate aquifers in currently active doublet systems based on their chronostratigraphic position and regional Maximum Flooding Surfaces. Based on the palynological cuttings analysis, the fluvial interval of the Nieuwerkerk Formation was subdivided into two successions: a Late Ryazanian to Early Valanginian succession and a Valanginian succession. Within these successions trends were identified in sandstone content. In combination with seismic interpretation, maps were constructed that predict aquifer thickness and their lateral extent in the basin. The study emphasises the value of palynological analyses to reduce the uncertainty of fluvial hot sedimentary aquifer exploitation.

The crustal structure beneath The Netherlands derived from ambient seismic noise

This work presents the first comprehensive 3-D model of the crust beneath The Netherlands. To obtain this model, we designed the NARS-Netherlands project, a dense deployment of broadband stations in the area. Rayleigh and Love wave group velocity dispersion was measured from ambient noise cross-correlations. Azimuthally anisotropic group velocity maps were then constructed and the isotropic part was used to determine a shear wave speed model that includes the effects of radial anisotropy. Employing the Neighbourhood Algorithm for the depth inversion, we obtained probabilistic estimates of the radially anisotropic model parameters. We found that the variations in the thickness of the top layer largely match the transition from sediments of Permian age to those of Carboniferous age. Regions of high faulting density such as the West Netherlands Basin and Roer Valley Graben are recognized in our model by their negative radial anisotropy (VSH−VSV < 0). The model has a mid-crustal discontinuity at a depth of around 13km and the average Moho depth is 33km, with most of its depth variations within 2km. Specifically, a localized Moho uplift to a depth of 29km is found within Roer Valley Graben, in the Campine region in Belgium. Furthermore, our Rayleigh and Love wave group velocity data at periods of around 20s show evidence for azimuthal anisotropy with a NW-SE fast direction. This anisotropy is likely related to NW-SE rock fabric in the lower crust thought to originate from the Caledonian deformation.

Molybdenum‐isotope chemostratigraphy and paleoceanography of the Toarcian Oceanic Anoxic Event (Early Jurassic)

AbstractMolybdenum (Mo)‐isotope chemostratigraphy of organic‐rich mudrocks has been a valuable tool for testing the hypothesis that the Toarcian Oceanic Anoxic Event (T‐OAE, Early Jurassic, ~183 Ma) was characterized by the spread of marine euxinia (and organic matter burial) at a global scale. However, the interpretation of existing Mo‐isotope data for the T‐OAE (from Yorkshire, Cleveland Basin, U.K.) is equivocal. In this study, three new Mo‐isotope profiles are presented: from Dotternhausen Quarry (South German Basin, Germany), the Rijswijk core (West Netherlands Basin, Netherlands), and the Dogna core (Belluno Basin, northern Italy). Precise biostratigraphic and chemostratigraphic correlation between the three sites allows a direct comparison of the data, enabling some key conclusions to be reached: (i) The Mo‐isotope composition of seawater during the peak of the T‐OAE was probably close to ~1.45‰, implicating a greater removal flux of sulphides from seawater, and a larger extent of global seafloor euxinia compared to the present day; (ii) Mo‐isotope cycles previously identified in the Yorkshire sedimentary succession are attributed to changes in the degree of local Mo drawdown from overlying Cleveland Basin seawater; (iii) The consistency of the new multisite Mo‐isotope data set indicates a secular reduction in the burial of Mo globally in the late stages of the T‐OAE, implying a contraction in the extent of global marine euxinia; (iv) Subtle differences in the Mo‐isotope composition of deposits formed in different euxinic subbasins of the European epicontinental shelf were probably governed by local variations in basin hydrography and rates of water renewal.

The impact of reduction of doublet well spacing on the Net Present Value and the life time of fluvial Hot Sedimentary Aquifer doublets

This paper evaluates the impact of reduction of doublet well spacing, below the current West Netherlands Basin standard of 1000–1500m, on the Net Present Value (NPV) and the life time of fluvial Hot Sedimentary Aquifer (HSA) doublets. First, a sensitivity analysis is used to show the possible advantage of such reduction on the NPV. The parameter value ranges are derived from West Netherlands Basin HSA doublet examples. The results indicate that a reduction of well spacing from 1400 to 1000m could already improve NPV by up to 15%. This effect would be larger in more marginally economic HSA doublets compared to the West Netherlands Basin base case scenario. The possibility to reduce well spacing is supported by finite element production simulations, utilizing detailed facies architecture models. Furthermore, our results underline the necessity of detailed facies architecture models to assess the potential and risks of HSA doublets. This factor significantly affects doublet life time and net energy production of the doublet.

High-resolution quantitative reconstruction of Late Cretaceous-Tertiary erosion in the West Netherlands Basin using multi-formation compaction trends and seismic data: implications for geothermal exploration

A workflow is presented to determine the detailed, high-resolution pattern of erosion in maturely explored Sedimentary Basins by analysing the sonic log-based interval velocity patterns of nine stratigraphic intervals complemented by a geometrical approach involving the extrapolation of 3-D seismic reflectors. The jointly evaluated results of the two approaches not only provide important constraints on the inversion tectonics of a basin, but are also used to better constrain its maturity history and reservoir quality for geothermal energy. The developed workflow is demonstrated for the West Netherlands Basin. The pattern of erosion, which is consistent with observed subcrop maps, shows increasing amount of erosion towards the East and reflects the complex deformation of the basin, in which the reactivation of faults played a major role. Indirectly the results also indicate that continuous, syn-inversion sedimentation was taking place on the flanks of the basin during the Late Cretaceous, while its centre was characterised by non-deposition or slight erosion. For geothermal exploration the inferred variations of amount of erosion has implications for the spatial distribution of porosity which is an important parameter for the assessment of reservoir quality.

On the connectivity anisotropy in fluvial Hot Sedimentary Aquifers and its influence on geothermal doublet performance

This study finds that the geothermal doublet layout with respect to the paleo flow direction in fluvial sedimentary reservoirs could significantly affect pump energy losses. These losses can be reduced by up to 10% if a doublet well pair is oriented parallel to the paleo flow trend compared to perpendicular. The chance that flow paths are formed perpendicular to this trend strongly depends on the net sandstone volume in the reservoir. Detailed fluvial facies architecture realisations which are used in this study, are generated with a process-based approach utilizing geological data from the Lower Cretaceous Nieuwerkerk Formation in the West Netherlands Basin. Finally, this study emphasizes the importance of detailed facies architecture modelling for the assessment of both risks and production strategies in Hot Sedimentary Aquifers.

Microstructures of Early Jurassic (Toarcian) shales of Northern Europe

The Toarcian (Early Jurassic) Posidonia Shale Formation is a possible unconventional gas source in Northern Europe and occurs within the Cleveland Basin (United Kingdom), the Anglo-Paris Basin (France), the Lower Saxony Basin and the Southwest Germany Basin (Germany), and the Roer Valley Graben, the West Netherlands Basin, Broad Fourteens Basin, the Central Netherlands Basin and the Dutch Central Graben in The Netherlands. Outcrops can be found in the United Kingdom and Germany. Since the Posidonia Shale Formation does not outcrop in the Netherlands, sample material suitable for experimental studies is not easily available. Here we have investigated lateral equivalent shale samples from six different locations across Northern Europe (Germany, The Netherlands, The North sea and United Kingdom) to compare the microstructure and composition of Toarcian shales. The objective is to determine how homogeneous or heterogeneous the shale deposits are across the basins, using a combination of Ion Beam polishing, Scanning Electron Microscopy and X-ray diffraction. The work presented here shows that the Toarcian shales of Northern Europe display considerable homogeneity in mineralogy and microstructure in the different investigated samples and formations, where the largest variability is the carbonate content ranging from almost zero up to 80%. We conclude that the outcrop locations in Germany and the United Kingdom are suitable analogues with respect to their mineralogy and microstructure for experimental studies on the Posidonia Shale in the Dutch subsurface.

The influence of facies heterogeneity on the doublet performance in low-enthalpy geothermal sedimentary reservoirs

A three-dimensional model is used to study the influence of facies heterogeneity on energy production under different operational conditions of low-enthalpy geothermal doublet systems. Process-based facies modelling is utilised for the Nieuwerkerk sedimentary formation in the West Netherlands Basin to construct realistic reservoir models honouring geological heterogeneity. A finite element based reservoir simulator is used to model the fluid flow and heat transfer over time. A series of simulations is carried out to examine the effects of reservoir heterogeneity (Net-to-Gross ratio, N/G) on the life time and the energy recovery rate for different discharge rates and the production temperature (Tmin) above which the doublet is working. With respect to the results, we propose a design model to estimate the life time and energy recovery rate of the geothermal doublet. The life time is estimated as a function of N/G, Tmin and discharge rate, while the design model for the energy recovery rate is only a function of N/G and Tmin. Both life time and recovery show a positive relation with an increasing N/G. Further our results suggest that neglecting details of process-based facies modelling may lead to significant errors in predicting the life time of low-enthalpy geothermal systems for N/G values below 70%.

Variations of organo-mineral microfacies of Posidonia Shale from the Lower Saxony Basin and the West Netherlands Basin: Application to paleoenvironmental reconstruction

High resolution organic petrological analysis has been carried out on core samples of the Posidonia Shale from four wells, two located in northwestern Germany (Lower Saxony Basin) and two in the western Netherlands (West Netherlands Basin). The organo-mineral microfacies defined by maceral composition and associated mineral matter show a wide range of variations related to the proportions of individual liptinite macerals of marine origin and of terrestrial macerals (macerals of vitrinite, inertinite groups and sporinite). Variations in organo-mineral microfacies, in which the organic components are sensitive to paleoenvironmental changes, are considered as a potential indicator of changes in depositional conditions.Sedimentation of organic matter is controlled by several factors, the most important in the marine environment being primary biomass productivity and influx of transported terrestrial organic matter, biological degradation related to bacterial activity, and the oxygen content of the bottom water. The level of degradation in organic-rich sediments is mainly related to oxygen availability which, in turn, influences the diversity of algae and the quality and quantity of the preserved organic matter. These two factors can be directly linked to maceral preservation and the organo-mineral microfacies. In order to evaluate the relationships between different types of organic matter and paleoenvironmental conditions, two indices, the oxidation index and the degradation index have been proposed. These indices illustrate the transition from highly degraded to well preserved macerals, provide information on the types of organic matter, and permit recognition of precursors for degraded amorphous organic matter (AOM).Use of these indices not only enables determination of the organo-mineral microfacies, but also sheds light on the AOM precursors in the Posidonia Shale. Information derived from the indices can also be used to reconstruct the paleoenvironments.

Sweet spot identification in underexplored shales using multidisciplinary reservoir characterization and key performance indicators: Example of the Posidonia Shale Formation in the Netherlands

Sweet spot identification in underexplored shale gas basins needs to be based on a limited amount of data on shale properties in combination with upfront geological characterization and modelling, because actual production data is usually absent. Multidisciplinary reservoir characterization and integration of modelling approaches can aid initial site selection for exploratory drilling and de-risk exploration efforts. In this study, the potential of hydrocarbon production across underexplored shale basins is analyzed using key performance indicators. A mean indicator is defined as the harmonic mean of three performance indicators that describe the potential for hydrocarbon generation, storage, and flow stimulation. The performance indicators are based on a limited number of local shale properties, i.e. vitrinite reflectance, porosity, depth, thickness, sorbed gas content and brittleness index. Values for the indicators are calculated relative to prospective North American shales (Marcellus, Bakken, Haynesville and Barnett), so that the mean indicator can be used to rank the prospectivity of an underexplored shale relative to hydrocarbon producing shales. The mean performance indicator is also used to map out the potential for gas production in the underexplored Posidonia Shale Formation in the West Netherlands Basin. The analysis shows that the performance indicator is lower for the Posidonia than for the North American Shales, mainly due to low maturity and brittleness. Local maxima of the indicator correlate with local maxima in vitrinite reflectance and depth. Besides the low potential for flow stimulation, the potential for hydrocarbon generation and storage capacity of the Posidonia are comparable to oil-window thermal-maturity Barnett Shale. Upfront simulations of hydraulic fracture properties and gas production in the Posidonia Shale Formation are in rough agreement with observed average gas flow for Barnett wells in non-core areas that are oil mature. It shows that key performance indicators can be applied to underexplored shales to quantify prospectivity and map out sweet spots across shale basins.

Shale oil potential and thermal maturity of the Lower Toarcian Posidonia Shale in NW Europe

A suite of drilling cores and outcrop samples of the Lower Toarcian Posidonia Shale (PS) were collected from multiple locations including the Swabian Alb and Franconian Alb of Southwest-Germany, Runswick Bay of UK and Loon op Zand well (LOZ-1) of the West Netherlands Basin. In order to assess the thermal maturity and quantify the petroleum generation potential of the rocks, elemental analysis, Rock-Eval pyrolysis, organic petrographic investigations and molecular hydrocarbon analyses were performed. Available literature data of the Posidonia Shale from Luxembourg and northwest Germany were used for comparison in the discussion.The Lower Toarcian Shale is more carbonate-rich (about 30% on average) in SW-Germany, NW-Germany and Luxembourg, and is instead more silicate-rich in UK and NL with carbonate contents of about 15% on average. This coincides with the relative distances of the depositional settings to the clastic source areas on the continents during the early Jurassic. However, HI values are similar, approx. 500–700mgHC/g TOC on average at all sampling localities, exhibiting typical type II kerogen with excellent hydrocarbon generation potential. Differences in relative abundance of terrigenous organic matter input are deduced from molecular indicators, Rock-Eval data and organic petrography. The highest abundance of terrigenous organic matter is evident for Runswick Bay, UK.Samples from outcrops of the Lower Toarcian Shale from Runswick Bay, UK, have reached the early stage of the oil window, with quite uniform Tmax values (425–438°C, avg. 433°C) and a narrow range of PI (production index) values (0.10–0.19), substantiated by mature fluorescing characteristics of telalginite and lamalginite and vitrinite reflectance values of 0.6–0.7%. Wider ranges of Tmax values (421–443°C, avg. 427°C), vitrinite reflectance (0.4–0.8%) and production indices (0.06–0.29) suggest more variable thermal maturation ranging from immature to almost peak oil generation at the LOZ-1 well, NL, although only some intervals indicate advanced thermal maturity there. In contrast, the Lower Toarcian marlstones from the Swabian and Franconian Alb of SW-Germany are clearly immature, similar to the samples from Luxembourg. In NW-Germany, the Posidonia Shale covers a wide spectrum of maturity ranging from immature to overmature.Source potential index (SPI) indicates the highest value in the LOZ-1, NL followed by Wickensen, NW-Germany and Esch-sur-Alzette, LU, mainly due to differences in thickness of the studied sections. The lowest value was observed in SW-Germany. The Lower Toarcian (Jet Rock) in Runswick Bay, UK, is assumed to have a high shale oil potential because of its advanced thermal maturity, although its SPI is not high due to the limited thickness of the section studied. The PS in SW-Germany has low shale oil potential due to low thermal maturity and limited thickness.

Thermal evolution and shale gas potential estimation of the Wealden and Posidonia Shale in NW‐Germany and the Netherlands: a 3D basin modelling study

AbstractSedimentary basins in NW‐Germany and the Netherlands represent potential targets for shale gas exploration in Europe due to the presence of Cretaceous (Wealden) and Jurassic (Posidonia) marlstones/shales as well as various Carboniferous black shales. In order to assess the regional shale gas prospectivity of this area, a 3D high‐resolution petroleum system model has been compiled and used to reconstruct the source‐rock maturation based on calibrated burial and thermal histories. Different basal heat flow scenarios and accordingly, different high‐resolution scenarios of erosional amount distribution were constructed, incorporating all major uplift events that affected the study area. The model delivers an independent 3D reappraisal of the tectonic and thermal history that controlled the differential geodynamic evolution and provides a high‐resolution image of the maturity distribution and evolution throughout the study area and the different basins. Pressure, temperature and TOC‐dependent gas storage capacity and gas contents of the Posidonia Shale and Wealden were calculated based on experimentally derived Langmuir sorption parameters and newly compiled source‐rock thickness maps indicating shale gas potential of the Lower Saxony Basin, southern Gifhorn Trough and West Netherlands Basin.

Implications of continuous structural inversion in the West Netherlands Basin for understanding controls on Palaeogene deformation in NW Europe

A detailed analysis of high-quality 3D seismic and borehole data provides new insights into the Palaeogene tectonic history and inversion of the West Netherlands Basin. The inversion characteristics are compared with those of other basins in the region, to provide constraints on the Palaeogene compressional tectonic movements in NW Europe. The inversion of the West Netherlands Basin, which is characterized by the doming of the basin centre and by the reactivation of pre-existing faults in a reverse mode, was found to be the result of a continuous inversion process rather than a distinct tectonic pulse. The intensity of the tectonic movements was not uniform throughout the Eocene and was strongest during the Latest Eocene. These characteristics are similar to those of other basins in the southern North Sea region and in the English Channel area. In addition, a good correlation exists between Alpine tectonic events and the Palaeogene inversion phases. In light of these observations the Latest Eocene inversion pulse in the southern North Sea region can be considered as the culmination of a long-term inversion process that originated from the Alpine collision.