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Stratigraphic column for the southern margin of the Mid North Sea High adapted from Archer et al. (2022) and Patruno et al. (2017). In this area, the Upper Permian Zechstein Supergroup rests directly on truncated Carboniferous strata and the Rotliegend is absent.
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This paper provides an updated understanding of the reservoir stratigraphy, sedimentology, palaeogeography and diagenesis of the Upper Permian Hauptdolomit Formation of the Zechstein Supergroup (“Hauptdolomit”) in a study area on the southern margin of the Mid North Sea High. The paper is based on the examination and description of core and cutting...
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... by Variscan compression and more recent Triassic and Tertiary extension (Grant et al., 2019). There is a dramatic change in structural style between the pre-and post-Zechstein successions. Pre-Zechstein sediments largely show evidence of extension and varying degrees of inversion, and the Carboniferous sediments beneath the Variscan unconformity (Fig. 2) show evidence of compression in the form of large open folds with a variety of orientations. These folds occur both on-and offshore and create pre-Permian prospectivity in the ...
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... the initial transgression at the beginning of each Zechstein cycle, carbonates such as the Z2 Hauptdolomit Formation were deposited before the water body became increasingly restricted and more saline, leading to evaporite deposition. Across the basin, up to seven Zechstein cycles are recorded although only five are observed within the study area (Fig. 2). The increased evaporation during later cycles resulted in the deposition of more complex salts, for example carnallite, sylvite and potash. The first two Zechstein cycles (Z1 and Z2) are the focus of this study. The development of sulphate platforms during the first Zechstein cycle (Z1) was influenced by the antecedent topography; the ...
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... extension in an intracontinental setting continued in the Mid North Sea High area throughout the Triassic, and sedimentation in Triassic grabens initiated a first phase of salt movement; the mobilisation of Zechstein evaporites and the development of salt pillows took place in the Late Triassic (Stewart and Coward, 1995). Much of the subsequent Jurassic sedimentation was removed by Mid to Late Jurassic "Cimmerian" uplift which produced a prominent angular unconformity at the base of the Cretaceous (Fig 2) ( Duguid and Underhill, 2010). Rapid subsidence resumed in the Early Cretaceous with a rise in global sea-level, leading to widespread deposition of the Chalk Group ( Grant et al., 2019). ...
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... Hauptdolomit and Werraanhydrit seismic events. There is less rafting of the Hauptanhydrit/ Plattendolomit in this area, and there is a zone of increased porosity at the base of the Hauptdolomit which has resulted in a greater AI contrast. Anhydrite of the Z2 Basalanhydrit typically overlies the Hauptdolomit in platform wells in the study area ( Fig. 2). Well 43/05-1, however, is an exception in that halite rather than anhydrite is present in the overlying Stassfurt Halite and forms a strong peak. Sedimentologically, the Hauptdolomit in wells 43/05-1 and 42/04-1 is dominated by fine crystalline dolomites ( Fig. 7; Fig. 8a, photomicrographs 2, 5 and 6; Fig. 8b, photomicrographs 1, 2, ...
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... final cement phase which affects all Hauptdolomit sediments to variable degrees is a late anhydrite which occludes pores in both the microbial and the oolitic facies ( Fig. 9a photomicrograph 2; Fig. 9b photomicrograph 2; Fig. 8a photomicrograph 4; Fig. 11a, photomicrograph 3; Fig. 11b, photomicrograph 2; Fig. 16a and i), and is also the final cement phase in vugs in the basinal dedolomites (Fig. 17k). Anhydrite cementation has therefore reduced overall reservoir quality significantly. The cement is coarse and blocky or ...
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... final cement phase which affects all Hauptdolomit sediments to variable degrees is a late anhydrite which occludes pores in both the microbial and the oolitic facies ( Fig. 9a photomicrograph 2; Fig. 9b photomicrograph 2; Fig. 8a photomicrograph 4; Fig. 11a, photomicrograph 3; Fig. 11b, photomicrograph 2; Fig. 16a and i), and is also the final cement phase in vugs in the basinal dedolomites (Fig. 17k). Anhydrite cementation has therefore reduced overall reservoir quality significantly. The cement is coarse and blocky or bladed, with crystals generally ...
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... porosities are most common in oolitic grainstones (Fig. 9a, photomicrographs 3, 4, 5; Fig. 9b, photomicrographs 2, 3), whilst framework and mouldic porosities are locally preserved in microbial build-ups (i.e. cored interval in well 38/22-1; Fig. 21). Anhydrite cementation is the diagenetic process most detrimental to reservoir quality (Fig. 9a, photomicrograph 2 Fig. 8a photomicrograph 4; Fig. 11a photomicrograph 1; Fig. 21), but despite detailed evaluation the distribution and intensity of late anhydrite cement is difficult to ...
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... that wind-generated, high energy ooid shoals developed along the windward faces of the platform margins as a result of persistent wave action. The shoals formed resistant bars, and relatively minor amounts of sediment were reworked onto the slope but instead formed thick, aggradational packages at the shelf margin (Van de Sande et al., 1996; Fig. 22). On leeward margins by contrast, sediment was comparatively easily shed from the platform to the slope, creating a gently dipping slope with thicker slope facies (Van de Sande et al., 1996; Fig. 22). At the wells evaluated in this study, the Hauptdolomit margin resembles the aggradational margin of Van de Sande et al. (1996), and ...
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... amounts of sediment were reworked onto the slope but instead formed thick, aggradational packages at the shelf margin (Van de Sande et al., 1996; Fig. 22). On leeward margins by contrast, sediment was comparatively easily shed from the platform to the slope, creating a gently dipping slope with thicker slope facies (Van de Sande et al., 1996; Fig. 22). At the wells evaluated in this study, the Hauptdolomit margin resembles the aggradational margin of Van de Sande et al. (1996), and slope facies are relatively thin. However, there may be local variations in the slope configuration and careful mapping may identify toe-of-slope deposits similar to those recorded at the LMG field ...
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... correspond to localities with high-energy ooidal bars at the platform margin (Harris, 2018). Tidal shoals are focussed where there is a change in geometry of the platform or where there is an embayment resulting in the funnelling of tidal currents, and similar influences may have controlled the distribution of Hauptdolomit shelf margin facies (Fig. ...
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... is often a focal point for the development of shallow-water, high energy shoals. In the study area in the Mid North Sea High, the antecedent topography at the level of the Base Permian Unconformity had a significant influence on the position and development of the Werraanhydrit sulphate platforms, and maybe also on Hauptdolomit deposition (Fig. ...
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... very limited availability of core plug or test data from the study area means that permeability measurements for the Hauptdolomit are in general lacking. However analogue data has been published in studies from Germany, the Netherlands and Poland (Fig. 24), although the Hauptdolomit in these areas may not have undergone the same diagenetic or burial pathways as it has in the Mid North Sea High. In the analogue examples, ooid grainstones are the main reservoir facies in the Hauptdolomit, and mouldic and vuggy porosity are the main pore types. Leaching is most often proposed to explain ...
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... the whole, the relatively limited poroperm dataset for the MNSH compares favourably with its Southern Permian Basin counterparts (Fig. 24). For example, in NW Germany and Poland, the porositypermeability of the Hauptdolomit may be lower than predicted for the Mid North Sea High because of significantly deeper burial (to almost 5 km), which will have resulted in increased compaction and cementation. In the Netherlands, faults and fractures in the Hauptdolomit are more ...
Citations
... Limited halite and the presence of continuous carbonates implies marginal Zechstein facies in a predominantly platform-slope environment (Smith 1989;Tucker 1991). This is further supported by the presence of thick Z1 Hayton Anhydrite confirming the onshore extension of the Z1 Werraanhydrit Platform (Garland et al. 2023;Houghton et al. 2024). Thickening of the Z1 Cadeby Formation towards well Whenby-1 suggests more platform-associated facies towards the west which is consistent with published Z1 paleogeographical models (Smith 1989;Fyfe and Underhill 2023a, b). ...
The Vale of Pickering (VoP) in North Yorkshire has played host to several small gas discoveries that have come to the end of their production life. Now that the fields have ceased production, there is an opportunity to repurpose them and their infrastructure for the energy transition. Using an extensive, well-constrained seismic dataset, mapping of the VoP has revealed the presence of a NNE-SSW striking Carboniferous basin precursor, the (newly defined) Slingsby Trough, containing Visean (syn-rift) organic shales that source the gas reservoirs and Namurian sandstones (post-rift) that form secondary reservoirs. Structural inversion of the half graben because of foreland deformation during the Variscan orogeny led to uplift, folding, and peneplanation by the Base Permian Unconformity. The area was subsequently overlain by Upper Permian Zechstein Group carbonates and evaporites deposited on the margins of the Anglo-Polish Basin, creating the main reservoir-seal pair and a local petroleum system. ESE-WNW striking Mesozoic faults transected the area and created 3-way, fault-bound footwall closures, forming a hydrocarbon ‘sweet-spot’ in the VoP through the coalescence of traps, a reservoir-seal pair, and a mature source rock. This study improves our understanding of the various geological conditions that lead to its hydrocarbon prospectivity, explains why interest was shown in its unconventional resource potential, and provides a basis for evaluating the feasibility of re-imagining these fields as viable onshore storage and geothermal sites to aid the decarbonisation of NE England.
... During marine regressions (low-stand systems tracts), increased basin restriction and salinity enabled the precipitation of sulfate platforms (A1, A2, A3, and A4), which prograded over the carbonate platforms in Z1, Z2, and Z3 and over basal shale in Z4, respectively (Taylor, 1998). Basinward, sulfate deposits were restricted in terms of thickness and preservation due to lower precipitation rate and bacterial sulfate reduction processes in an anoxic deepwater environment (Garland et al., 2023;van de Sande et al., 1996). With the exception of Z1, sulfates in each cycle were capped by halite units followed by K-Mg salts, which developed in depocenters under maximal drawdown conditions likely linked to the lowest eustatic levels (Na2, Na3, and Na4) (Tucker, 1991) (Fig. 5). ...
... Polyhalite layers reported at the base of this halite unit were most likely deposited during the transition stage between sulfate and halite saturation phases and may record freshening events. Polyhalite wedge shapes locally reported along the southern side of the Mid North Sea High platform (Garland et al., 2023) suggest that primary anhydrite to polyhalite deposits kept prograding over the margin platform. Pichat (2022) also proposed that part of these polyhalite layers in the basin center formed from anhydrite turbidites having reworked margin sulfate platforms (platform A2). ...
The Zechstein Group in the Northern Permian Basin (UK and south Norway sectors of the North Sea) is subdivided into four halite-rich evaporitic sequences. These sequences contain K-Mg salts, the amount and distribution of which are still poorly constrained. Understanding the lithological variations of the evaporites is important for understanding the syn- to post-salt basin evolution and for predicting the development of salt caverns. We compiled well data to perform intra-salt correlations and to constrain the stratal architecture of the halite-rich units. Our results enable refinement of depositional zones of the Zechstein Group in the Northern Permian Basin with emphasis on the spatial distribution of the K-Mg salt deposits. Our analysis suggests that K-Mg salts were preferentially precipitated in the Forth Approaches Basin and north of the West Central Shelf. This was likely the result of geographic position restricting the direct influx of marine water and early halokinetic movements associated with salt relief that promoted the development of isolated intra-salt minibasins. We then use the revised stratigraphy of the Zechstein Group to propose an evolutionary scenario of the Zechstein Group that considers both the Northern Permian Basin and the Southern Permian Basin and that highlights discrepancies in the bathymetric conditions of halite deposition and the spatial repartition of the K-Mg salts. Finally, our results allow an assessment of the potential risk of finding insoluble deposits or K-Mg salts in bedded salt, salt pillows, or salt diapirs that are otherwise suitable in terms of depth and thickness for the development of salt caverns in the Northern Permian Basin.
... Recent studies and subsequent drilling campaigns have revealed a play fairway within the Upper Permian Zechstein Group across Quadrants 41-43 on the MNSH (Patruno et al., 2018;Browning-Stamp et al., 2023). Recent success involving the Ossian-Darach, Crosgan and Pensacola discoveries have demonstrated hydrocarbon prospectivity in the Zechstein Z2 Hauptdolomit Fm. 3D seismic and sedimentological facies mapping (Garland et al., 2023;Browning-Stamp et al., 2023) unveiled the Orchard Platform: A Z2 Hauptdolomit Fm. carbonate platform spanning Quadrants 36-38 and 42-44 (Fig. 2). Whilst our understanding of the characteristics of the Orchard Platform has improved significantly, the greatest uncertainty now resides with the overlying Zechstein Group formations which must be analysed to de-risk future exploration of the Zechstein system on the MNSH. ...
... Shallow marine Z2 Hauptdolomit Fm. progradation on top of Z1 Werraanhydrit Fm. clinoforms helped to create a tabular carbonate system known as the Orchard Platform ( Fig. 3; Patruno et al., 2018;Garland et al., 2023) at the southern entrance to Jenyon's Channel (Fig. 2a). As straits and seaways control the exchange of nutrients between basins (Bahr et al., 2022), it is envisaged that nutrient-rich waters arriving via Jenyon's Channel could have helped stimulate the growth of the Z2 Orchard Platform at its intersection with the Anglo-Polish Basin. ...
... Map of the Orchard Platform study area including the subset of the 3D seismic volume (rectangle) and the locations of the local well penetrations that were tied to guide seismic interpretation. The shape of the carbonate platform is after Browning-Stamp et al. (2023) and Garland et al. (2023). ...
The influence of the Mid North Sea High and Seaway on the distribution of salts in the Northern and Southern North Seas during the Zechstein.
The Mid North Sea High (MNSH) region represents one of the least explored areas for the Late Permian Zechstein Hauptdolomit play in the Southern Permian Basin although some of the first offshore wells drilled in the UK were located here. In other parts of the basin such as onshore Poland, the Hauptdolomit Formation (“Hauptdolomit”) is an active and attractive exploration target, with oil and gas production from commercial‐sized fields. In the UK, the play has been overshadowed by drilling campaigns in areas to the south of the MNSH which tested plays in the underlying Rotliegend and Carboniferous successions. However, with these areas now in decline, there is increased exploration interest in the Hauptdolomit in the MNSH region, particularly since 2019 when 3D seismic data were acquired and the first hydrocarbon discovery was made at Ossian (well 42/04‐01/1Z). Geochemical data from the latter discovery have pointed to the presence of a prolific petroleum system with the potential for Hauptdolomit reservoirs to be charged both by Zechstein‐generated oils and Carboniferous condensate/gas. With regard to hydrocarbon migration and preservation in the southern MNSH, a detailed evaluation of the effects of the Mid Miocene Unconformity has allowed for a greater understanding of the main factors controlling hydrocarbon preservation and remigration. Reservoir characterization of the Hauptdolomit play has been achieved by integrating petrographic microfacies analyses, core data and petrophysical interpretations. The most important factors controlling reservoir quality are the presence and extent of anhydrite cementation and the presence of high energy shoal facies. Thicker and coarser grained shoal facies are expected to occur along the yet‐to‐be explored Orchard platform margin where numerous prospects have been mapped and refined using recently acquired 3D seismic data.
A multidisciplinary approach combining geological mapping based on seismic and well data with petrographic analyses of core and cuttings samples was used to gain a better understanding of the distribution of Upper Permian (Zechstein, Z2) Hauptdolomit platforms and their depositional facies around the Elbow Spit High in the northern Dutch offshore. A detailed understanding of the Hauptdolomit's lateral facies variability is of great importance for assessing its reservoir potential, since both the thickness and reservoir properties of these carbonate platforms greatly depend on local accommodation within different palaeo‐depositional environments. The platforms generally contain the thickest Hauptdolomit sequences and are largely characterised by a mix of oolitic and coated grainstones, as well as by some dolomicrites. Porosities of around 15% are reached at well E02‐02 within the grainstone intervals, and interconnectivity between the pores is generally present. Seismic mapping has indicated a rim of isolated Hauptdolomit platforms, which are up to 10 km wide, around the southern and NW margins of the Elbow Spit High. No Hauptdolomit platforms are present on the NE margin of the High, likely because the palaeo‐ basin margin was too steep and hence lacked accommodation for carbonate growth. Discoveries made in recent years in the UK sector of the southern North Sea have highlighted the importance of the Hauptdolomit hydrocarbon play, and the results of the current study provide a solid base for assessing the reservoir potential of this play in the relatively underexplored northern part of the Dutch offshore.
