Abstract The ability to predict coal units from seismic data has become important for hydrocarbon exploration, especially in areas away from traditional play sweetspots. An understanding of coal distribution/thickness from seismic data can influence the risking of basin source-rock presence/charge efficiency. A selection of wells is presented from the Carboniferous of the Elbow Spit Platform (Netherlands), the Mid North Sea High (UK) and adjacent areas. These wells penetrated various coal thicknesses, as well as sandstones, mudstones and thin limestones in different stratigraphic configurations. For each well, full-stack synthetic seismograms (acoustic impedance domain) using a conventional seismic wavelet are generated along with supporting rock physics. This analysis suggests, as a guideline, that coal thickness needs to meet a threshold of 25–35% of loop thickness to be uniquely distinguishable from the surrounding lithologies (discernible soft kick). If the coals are thinner than this threshold, they will be comparable to soft sandstone-related kicks, although some exceptions exist where thin coals directly overlie soft sandstone intervals. The exact percentage value will depend on seismic-data quality and rock properties. This study highlights the need for careful consideration of thin-coal seismic expression when devising interpretation strategies and risking source-rock presence.

Abstract A review of recent Triassic research across the Southern Permian Basin area demonstrates the role that high-resolution stratigraphic correlation has in identifying the main controls on sedimentary facies and, subsequently, the distribution of hydrocarbon reservoirs. The depositional and structural evolution of these sedimentary successions was the product of polyphase rifting controlled by antecedent structuration and halokinesis, fluctuating climate, and repeated marine flooding, leading to a wide range of reservoir types in a variety of structural configurations. Triassic hydrocarbon accumulations form an important energy resource across the basin, not only in the established Buntsandstein fairway but also in Rogenstein oolites and Muschelkalk carbonates. In addition, sand-prone sections in the Late Triassic, such as the Schilfsandstein, have the potential to be hydrocarbon reservoirs. Several Triassic intervals are now the focus for developing geothermal projects. A detailed understanding of Triassic reservoir quality and distribution is one of the main keys to efficiently unlocking the geothermal and remaining hydrocarbon potential across the basin.

Abstract An analysis of the Lower Triassic ‘Buntsandstein’ gas play in the underexplored Mesozoic rift system of the German–Danish Horn Graben is presented. Dry hole information from four well penetrations is analysed alongside the development of a 3D basin model. It is demonstrated that the dry holes do not preclude the existence of a working hydrocarbon system. Reservoir and seal elements are present, although details of quality and distribution are uncertain. Carboniferous coal preservation is likely, in a limited area, within the graben and can be constrained through seismic mapping. Vertical gas migration through the Zechstein interval is considered likely due to a large thickness variability (driven by halokinesis and facies changes). The overlap of peak gas-expulsion timing and halokinetic movements make rollover/turtle-back traps risky in terms of breaching or underfill. Dry wells in Denmark are explained by a combination of this relative timing and uncertainty over longer distance migration. This play analysis demonstrates a general agreement with previously published 1D basin models with respect to gas-expulsion timing. However, in contrast to published examples, it is shown that the Zechstein interval can allow for vertical gas migration. Considerable uncertainty in parameters, such as depth conversion, amount of erosion and migration paths, are recognized. Exploration opportunities remain, albeit relatively high risk, in the German area of the graben both in the ‘Buntsandstein’ play and at other stratigraphic levels.

Abstract This study presents an integrated seismic, well and core-based analysis of the Maureen Formation in the Central Graben of the North Sea. Facies analysis reveals that it is possible to divide the Maureen sandstones into amalgamated, sand- and mud-prone divisions, but that the related chalk facies are complex and imply a range of depositional processes including pelagic fallout, debris flows and turbidity currents. These chalk deposits have an impact on the interpretation of amplitude-based seismic attribute volumes. Detailed petrophysical mapping, supported by seismic analysis, reveals that the Maureen sandstones were deposited in distinct western and eastern fairways controlled by the relict Mesozoic rift topography (although offset stacking is an important intragraben process). The spatial extent of the Maureen sandstones is similar to the overlying Sele and Lista formations and suggests that the broad controls on sediment routing were the same throughout the Lower Palaeogene. Other similarities between these systems include the role of sandstone texture in controlling reservoir quality (although the heterolithic nature of the Maureen sandstones means that porosities and permeabilities are lower). A pattern of intraformational progradation and late-stage backstepping of the sandstone units is likely related to sea-level variability.

Abstract Detrital garnet suites have been demonstrated to be reliable indicators of the mineralogical and lithological characteristics of sediment source areas. This study applies garnet analysis to the Paleocene to Eocene Sele Formation deep-water sandstone units of the central North Sea. These stratigraphic units are economically important as they represent one of the main hydrocarbon reservoir intervals in this mature basin. The routing of turbidity currents into the Central Graben has been demonstrated to be related to axial fans (ultimately sourced from Lewisian and Moine basement rocks and Triassic sandstones to the NW) and lateral fans (ultimately sourced from the Dalradian basement rocks to the west). Garnet analysis suggests the majority of samples can be attributed to the axial fan system and that the lateral system contributed little to sandstone deposition east of the Gannet Fields. This contradicts previous seismic mapping work, which suggested that the lateral fan system dominated sedimentation as far east as the Merganser Field. This reinterpretation is potentially important for our understanding of sediment routing and its impact on the distribution of reservoir quality, particularly as this is believed to relate directly to proximity to the shelf.