FIGURE 7 - uploaded by Joanna Garland
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Fig. 7. Depositional models for Hauptdolomit platforms in the study area; well locations in Fig. 1: (above) large-scale attached platform; (below) isolated platform. Note that platform interior facies are more areally important in attached platforms. The models were built from core and cuttings microfacies observations from 25 wells. Wells marked in red are key wells discussed in the text; wells marked in grey are additional wells which were evaluated in order to build the models.
Source publication
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...
Citations
... 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.
