<p>In rift basins, the spatial arrangement of extensional faults can influence the facies and the thickness distribution of the syn- and post-sedimentary infill, which can harbour good potential for geothermal systems. In this framework, unravelling the tectono-stratigraphic evolution of a rift basin is decisive, as it can influence one of the key parameters for planning geothermal doublets: aquifer thickness.</p> <p>In our study, the West Netherlands Basin, located in one of the Netherlands most densely populated areas, is used as a case study. Up to 2022, 14 geothermal doublets were realized in the area, with the main target being the syn-rift deposits of the Late Jurassic Nieuwerkerk Formation. As a NW-SE &#160;oriented transtensional basin, the West Netherlands Basin developed as consequence of Mesozoic extensional tectonics, after which it became inverted during the Late Cretaceous and Cenozoic. Using publicly available seismic 3D and well data, our renewed interpretation of the study area shows two important rift events. The first one during the Early-Mid Jurassic and the second one, partly controlled by structures of the former, during the Late Jurassic, coinciding with the deposition of the Nieuwerkerk Formation.</p> <p>Our study adds to the understanding of a multiple stage rifting history in the West Netherlands Basin. This is important, as the process influences reservoir thicknesses and with that, the amount of MW that can be extracted from geothermal aquifers. Therefore, this study forms a bridge between providing an integrated picture of the West Netherlands Basin and how the basins geological history affects its geothermal resources.</p>
<p>Meso-scale (sub-seismic) sedimentary injectites are inferred to play an important role in controlling subsurface fluid flow as documented in many hydrocarbon plays at various scales. Detailed characterisation of such units, usually unresolvable at the seismic scale, can be directly achieved at outcrop scale. In this framework, two sedimentary injection complexes have been analysed in the middle Jurassic-lower Cretaceous Agardhfjellet Formation exposed at Deltaneset (central Spitsbergen) at different stratigraphic levels. The upper complex comprises two main isolated, decimetres-thick clastic dykes characterized by different orientation and consolidation, tapering out vertically (up- and downward) within a stratigraphic thickness and a lateral extension of more than 50 m and 200 m, respectively. The lower complex is coarser-grained, made up by a network of interconnected dykes and sills, branching off from isolated lenticular bodies, interpreted to be linked to seafloor extrusion structures (sand volcano). Petrographic and micromorphologic analysis were used to identify the possible source of the remobilized material for both the upper and lower complexes within the over- and under-burden formations. Our results reveal that such granular material is likely sourced by the underlying coarse-grained lithologies of the late Triassic to middle Jurassic Wilhelm&#248;ya Subgroup. The lower complex was firstly emplaced during the Late Jurassic at shallow burial conditions, while the upper complex developed at higher confinement pressure, probably during the Late Cretaceous, with the progressive reworking of the same granular material. Field data allow detailed characterisation of complex structural-stratigraphic architectures of sedimentary intrusions, which can be used to constrain their spatial-temporal relationships with subsurface fluid flow.</p>
Abstract. The tectonic evolution of rift basins can strongly influence the petrophysical properties of its sedimentary infills at various scales and, therefore, influence the characteristics of present resources. Understanding the tectonic evolution of a rift basin is therefore decisive, as it can have consequences for the parameters that influence the planning of geothermal doublets. In this framework, this study gives a detailed interpretation of the syn- and post-rift episodes in the West Netherlands Basin, since Jurassic times. Despite multiple studies on the geotectonic setting of the West Netherlands Basin, a detailed understanding of its syn- and post-rift phases in the context of geothermal exploration is still fundamentally lacking. With a renewed interpretation of a seismic 3D cube, covering a large portion of the onshore section of the basin, we identified two important Jurassic rifting episodes and one Cretaceous inversion event. Rifting caused compartmentalisation of the main producing geothermal target in the area; the Late Jurassic Nieuwerkerk Formation. Yet, the central portions of the half-grabens show good potential for geothermal exploration. Subsequent inversion could have caused local breaching of the aquifer, forming a potential risk. Therefore, only non to moderately inverted areas should be considered for geothermal exploration. This study provides a better understanding of the multi-phase rifting history in the West Netherlands Basin, providing important constraints on the reservoir-seal integrity and with that, the amount of heat that can be safely produced from a geothermal reservoir rock. Aiming to contribute to the energy transition, this study provides an integrated picture of the West Netherlands Basin and shows how a basin’s geological history can affect its geothermal resources.
Sedimentary injectites are increasingly documented in many hydrocarbon plays at various scales, either interpreted as potential risks (e.g., top-seal bypass, a drilling hazard) or benefits (e.g., reservoir interconnection, increased hydrocarbon volumes) for production operations. As such, they have potential critical implications for the assessment of suitability for CO2 injection and sequestration. Detailed characterization of such units, especially in terms of diagenesis and (paleo) fluid flow, is directly achievable at outcrop scale, overcoming dimensional and time constraints otherwise unresolvable at seismic scale. Two sedimentary injection complexes have been recognized in the succession of the Middle Jurassic–Lower Cretaceous Agardhfjellet Formation exposed at Deltaneset, central Spitsbergen, Norway, at different stratigraphic levels. The upper complex comprises two main clastic dikes characterized by different orientation and consolidation, tapering out vertically (upward and downward) within a stratigraphic thickness and lateral extent of more than 50 m and 200 m, respectively. The lower complex is coarser grained, made up by a network of interconnected dikes and sills, shooting off from isolated lenticular and morphologically articulated bodies, interpreted as sedimentary intrusions linked to seafloor extrusion (sand volcano). Petrographic and micromorphological analyses were used to identify the underlying lithologies of the Late Triassic to Middle Jurassic Wilhelmøya Subgroup as the possible source of this remobilized material for both the upper and lower complexes. This subsurface remobilization and consequent intrusion were first achieved in the lower complex during the Late Jurassic at shallow burial conditions, and then at higher confinement pressure for the upper complex, probably during the Late Cretaceous. These results highlight how field data can be used to constrain long-lived spatiotemporal relationships of sedimentary intrusions, allowing a finely tuned upscaling of seismic data and interpretations.
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