Abstract Spatially and temporally variable Tournaisian to Namurian Carboniferous fluvial, fluvio-deltaic, platform carbonate and shale-dominated basin sedimentary successions up to 3.5 km thick are preserved in a complex series of basins from the Outer Moray Firth (Quadrant 14) to the Silverpit Basin (Quadrant 44). Differences in stratigraphic nomenclature in the areas surrounding the Mid North Sea High and onshore, combined with sparse biostratigraphic data, have hindered the systematic regional understanding of the timing and controls on stacked source and reservoir rock intervals. Over 125 well reinterpretations, tied to seismic interpretations, provide evidence of the inception and extent of a delta system. Regional time slices highlight a long-lived laterally equivalent basinal, mud-rich succession across Quadrants 41–44. They also show that the area from the Outer Moray Firth to the Silverpit Basin was part of the same sedimentary system up to at least Namurian times. All of this is placed within a simplified stratigraphic framework. Supplementary material: Appendix A in the Supplementary Material contains the stratigraphic intervals interpreted on each well and highlights which intervals have biostratigraphic control. Supplemental Figures 1 and 2 are larger scale versions of Figures 6 – 8 . The Supplementary Material is available at https://doi.org/10.6084/m9.figshare.c.4087046

Abstract A seismic stratigraphic analysis constrained by well and wireline log data has been undertaken on the Paleocene and earliest Eocene succession of the South Buchan Graben (Quadrants 20 and 21), Outer Moray Firth Basin (OMFB). Two principal sequences have been described relating to two regressive/transgressive second-order cycles of relative sea-level change. The Maureen, Andrew, Glamis Tuff and Balmoral sandstone members are expressed as a stacked set of lowstand basin floor fans separated by mudstone intervals representing four cycles of third-order relative sea-level change. The Sele and Balder formations contain both basinal and shelfal packages as an expression of two cycles of third-order relative sea-level change. The Forties Sandstone Member is deposited within highly mounded, levee-confined channels downlapped by a prograding slope succession with well-defined clinoforms and deltaic topsets attributed to the Dornoch and Beauly formations. The individual parasequences of the prograding wedge are related to higher-order eustatic fluctuations with incision and slope fans, attributed to the Cromarty Sandstone Member, deposited during periods of relative sea-level lowstand. It is demonstrated that through the integration of lithostratigraphic, seismic geomorphological and sequence stratigraphic analyses an understanding of depositional environments and the distribution of facies within them can be obtained. The identification of basinal and slope features with reservoir potential, along with an understanding of their chronostratigraphic relationship to sealing facies, play an important role in regional play fairway mapping and risk analysis in this area and beyond. Future prospectivity within mature basins, such as the OMFB, relies on subtle stratigraphic traps typical of lowstand systems tracts, where the main risk is associated with reservoir quality and containment.

Abstract Despite a number of targeted and serendipitous discoveries above deeper Jurassic targets in the 1970s and 1980s, the high-quality Albo-Aptian sand fairway of the Outer Moray Firth, informally known as the Kopervik fairway, still remained relatively unexplored until the late 1990s. Following the Hannay and Goldeneye discoveries in 1996, the renewed impetus in exploration drilling on the trend generated a series of commercial oil and gas discoveries. This most recent exploration phase proceeded with a high ratio of well success to failure, despite the significant technical challenges specific to the Kopervik reservoir sands. For the most part, the explorationist has to contend with a play fairway consisting of subtle trapping mechanisms. The recognition of these traps is hampered by the acoustically transparent nature of the sand, ambiguous seismic imaging and depth conversion issues. The subsequent development of this high permeability reservoir remains equally challenging. Many discoveries have low hydrocarbon column heights with an active aquifer and/or mixed phased fluids, which lead to well deliverability and fluid processing issues. In spite of the technical complications, these discoveries are now being swiftly developed by various operators along the trend. In this paper, we discuss how interest in the fairway was renewed only recently, review how the technical concept was developed in an attempt to reduce exploration risk, and how, following a number of early and surprising discoveries, the fairway was rapidly and effectively appraised. Finally, as an example, we review how the application of joint development concepts will lead to the commercialization of the fallow Cromarty Field and the neighbouring Atlantic discoveries.

Abstract Kilometre-scale sandstone intrusions have recently been documented from the Palaeogene deep-water sequences of the northern North Sea. The distribution of Eocene sandstones within a 126 km 2 3D4C seismic survey located in the Outer Moray Firth was mapped using surface and volume based interpretation of converted wave seismic data calibrated to a number of boreholes. About 35 conical sandstone intrusions, a few tens of metres thick and 1–1.5 km wide, were mapped within the lower Eocene. The intrusions are inclined about 15–20° and crosscut some 100–200 m of lower Eocene mudstones, terminating upward at the Middle Eocene unconformity, below the oil-charged, upper Eocene sandstones of the Alba and Chestnut reservoirs. Individual sandstone intrusions may contain millions of cubic metres of sandstone and often have excellent reservoir properties. Previous studies failed to define a viable migration path for the oil in the Alba/Chestnut reservoirs because they appeared to be completely encased in poorly permeable Eocene mudstones. However, detailed mapping and volume visualization of the converted wave seismic data demonstrates that the upper Eocene reservoirs have suffered post-depositional remobilization and that the conical intrusions provide a viable migration path between the Alba/Chestnut reservoirs and the underlying Paleocene aquifers. Despite more than two decades of exploration activity in the Outer Moray Firth, the widespread occurrence of conical intrusions in the lower Eocene is still not widely recognized, and it is likely that the sandstones may pose a hazard when drilling for deeper targets. However, it is also possible that large conical intrusions that do not connect with overlying sandstones may contain economical quantities of hydrocarbons.

Abstract Largely due to inadequacies of mapping software and complexities of data management, faults are traditionally treated as vertical planes for each separate reservoir zone or throughout the total reservoir within volumetric field models. This simplified approach results in errors in geometry and volume calculations. We discuss a software system which automates the volumetric modeling of multiple horizons exhibiting nonvertical faulting. The modeling is based upon the construction of fault plane grids from digitized fault traces and a set of attributes to describe the attitude of the fault. The fault plane grids are intersected with structural and isochore grids for each reservoir zone, producing a realistic set of migrated fault traces for each structural horizon. This greatly enhances the structural definition for volumetric analysis. Extensional fault models, incorporating normal, listric, and strike-slip faults can currently be built. The resulting horizon and fault grids may form the input for more advanced three-dimensional modeling software, providing a better structural framework. The Full Fault Modeling System (FFMS) is a stand-alone module. It has been designed to work closely with Radian’s CPS-3 Advanced Mapping Software, but can equally operate with any computer mapping package which uses rectangular grids. The FFMS software provides a structurally consistent approach to computer-based modeling of multiple surfaces affected by nonvertical faulting. The Ivanhoe field, situated in the Outer Moray Firth of the U.K. North Sea, has been used as a case history to demonstrate the application of the software and its methodology.

Abstract The Carboniferous strata of the Central and Northern North Sea occupy a depositional basin that is laterally contiguous with, and located to the east of, the Midland Valley of Scotland (Chapter 14). The Carboniferous strata of the Southern North Sea occupy a depositional basin located between the Mid North Sea High to the north and the Wales-Brabant High to the south (Fig. 46). It is laterally contiguous with the Pennine Basin complex. An isolated area of Carboniferous strata has also been proved in the Clair Basin of the NW Approaches, west of the Shetland Isles. The Tournaisian and oldest Visean strata have been proved beneath Permian and younger cover in the Central and Northern North Sea, within the Outer Moray Firth, Western Platform and Central Graben, eastwards from the coast of SE Scotland along the crest and southern flanks of the Mid North Sea High and in the Clair Basin, west of Shetland (Fig. 46). The strata are dominated by red, fluvial and playa-lake deposits (Upper Old Red Group). Younger Visean strata include the grey, fluvio-lacustrine deposits within the Forth Approaches Basin and Outer Moray Firth Basin of the Central and Northern North Sea (Firth Coal Formation). Visean to lower Namurian lacustrine, marine, fluvial and fluvio-deltaic sediments are proved in the Southern North Sea eastwards from the Northumberland coast along the western crest and southern flanks of the Mid North Sea High (Farne Group).

Abstract Many of the stratigraphic sequences recognized in North Sea Jurassic well sections correspond to mappable surfaces on seismic sections. Typically, however, sequences are only mappable seismically within individual sub-basins, and seismic correlation between sub-basins, or across highs, is generally impossible without independent control from wells. Particularly prominent seismic sequence boundaries occur at near-base J54 in the Inner Moray Firth (‘Intra-Oxfordian Event’) the Viking Graben (‘Top Heather’ in this area), base J62 (‘Top Heather’, Moray Firth), base J66 (‘Top Lower Hot Shale’, Inner and Outer Moray Firth), base J71 (East Shetland Platform), base J73 (‘Top Siltstone Member’, Moray Firth) and top J70/base K10 (‘Base Cretaceous Unconformity’ (BCU), basin-wide). The BCU is the most frequently mapped seismic horizon in the North Sea Basin in Jurassic–basal Cretaceous studies. This surface, at the base of the Cromer Knoll Group, separates synrift sediments from post-rift successions above and marks a major shift in the tectonic evolution of the North Sea Basin.

Abstract The sequence stratigraphic analysis of the Lower to Upper Jurassic (Hettangian to Kimmeridgian) succession of the Moray Firth basin synthesizes sedimentological and paleontological data from approximately 400 wells in the offshore domain with scattered outcrops along the eastern coastline of Scotland. The stratigraphic framework produced provides a consistent framework for understanding and predicting basin-wide sedimentary facies distribution. Three hierarchies of sedimentary cycles are distinguished: (i) major transgressive/regressive (T/R) cycles (with durations between 10 and 50 my), (ii) transgressive/regressive (T/R) facies cycles (with durations between 3 and 10 my), and (iii) regressive/transgressive (R/T) cycles (with durations between 0.5 and 3 my). Two major T/R cycles are identified, which are bounded by three important surfaces of maximum regression. These boundaries, which generally correspond to regionally extensive subaerial unconformities, occur close to the Triassic/Jurassic boundary, the Lower/Middle Jurassic boundary (often termed the “Mid-Cimmerian” unconformity) and the Ryazanian/Valangian boundary (often termed the “Base Cretaceous” unconformity). Each major T/R cycle can be subdivided into component T/R facies cycles, which are also bounded by surfaces of maximum regression. Both types of cycle are synchronous across the basin, although high sediment flux locally affects the timing of peak transgression. Difficulties exist in objectively defining and correlating most higher-frequency (so-called 3rd-order) sequence boundaries in distal depositional settings. Instead maximum flooding surfaces have proven to be the most reliable, distinctive and easy-to-date surfaces with which to define a rigorous sequence stratigraphic framework. Consequently, higher-frequency cycles are bounded by maximum flooding surfaces, are centered upon transgressive surfaces and hence are termed regressive/transgressive (R/T) cycles. Fourteen R/T cycles are defined, each of which developed simultaneously across the Moray Firth basin. The fact that these R/T cycles can be correlated from both subbasin to subbasin, and from the Inner Moray Firth to Outer Moray Firth basin, indicates that local tectonics had little effect upon controlling the timing of 3rd-order cycle development, even during the Middle and Late Jurassic Epochs when extensional rifting is known to have exerted a pronounced control upon basin development.