Abstract Over the last 50 years, the North Sea and the Atlantic Margin and, more recently the Barents Sea, represented key study areas for academic and professionals interested in the exploration for and production of hydrocarbon from the Earth's subsurface. Nowadays, these areas may play a major role in the so-called ‘energy transition’, with the energy industry now seeking to reduce emissions related to hydrocarbon consumption, and leading the development of carbon capture and storage activities, such as the Northern Light project ( https://northernlightsccs.com ). Consequently, there is an increasing interest in advancing our knowledge regarding the stratigraphy, sedimentology and tectonic development of the North Sea, Atlantic Margin and Barents Sea with a cross-border approach.

Abstract The geometry of faults exposed in the field is at least partly controlled by host-rock lithology. However, little work has been published on the effect of lithology on the geometry of very large faults imaged in seismic data. This paper presents such a study for seismic-scale faults in the Norwegian Barents Sea. Gamma-ray data are used to extract clay volumes of the host rock. These clay volume logs are used to populate 3D seismic cubes with lithology information. Finally, the clay volume cubes are co-rendered with seismic coherence cubes using opacity blending. This makes it possible to visualize both lithology information and fault geometries in the same volume. Intervals of different lithologies are studied in order to compare fault geometries. The results show some differences between claystone-rich intervals and the more sandstone-dominated intervals. The fault zone is more segmented and wider in the claystones, while the sandy intervals are narrower and more localized with less segmentation. Larger displacement faults penetrate into deeper stratigraphic levels than smaller displacement faults, and their basal tips are unrelated to lithological decoupling.

Abstract While the Triassic is comparatively a tectonically quiescent period in the dynamic development of the Barents Shelf, the depositional infill was strongly influenced by structural elements and there is a marked difference between lower and middle Triassic sedimentation. Southwards-propagating uplift of north–south-orientated elements along the incipient North Atlantic margin, from the mid-Carboniferous to the Early Triassic, generated uplift, tilt and erosion of the Sørkapp–Hornsund and palaeo-Stappen highs, and the Ringsel and Selis ridges. Progressive onlap along the flanks with probably no deposition until the Ladinian, which is probably condensed/partly missing, characterized the ensuing sedimentation. Late Permian–Early Triassic uplift of the Selis Ridge was concurrent with uplift and erosion of the Capria Ridge. Both elements also experienced a phase of Anisian–Ladinian erosion. The Gardarbanken High underwent a later Early Triassic uplift and a complex, probably condensed, deposition associated with the infill of advancing deltaic systems. The Ladinian, and more dominantly the Carnian, saw even blanketing of large parts of the Barents Shelf, almost wholly unaffected by the structural elements. The most noticeable influence at the time is the thinning of the progradational system approaching the Svalbard Platform, which remained comparatively shallow, as witnessed by the lowered clinoform angle and rapid deposition.

Abstract The growth of faults and folds in basins formed under transtension has been less studied than that in their extensional counterparts. In this study, we capitalize on 3D seismic reflection data to investigate the evolution of faults and folds that evolved coevally during suborthogonal partitioned extension and shortening, respectively, in the Sørvestsnaget Basin, Western Barents Sea. We use quantitative techniques to constrain the distribution of normal fault throw, shortening accommodated by folds and thrusts, and stratigraphic thickness variations, to analyse the relative temporal and spatial evolution of faults and folds. Our results show that normal faults display a similar evolution to those occurring in extensional basins, where they grew by lateral- and dip-linkage of individual fault segments as well as upward propagation. Notably, we show that shortening-related fold growth affected the fault growth patterns, skewing their throw distributions, and shifting the location of accommodation away from the evolving folds. Thus, fold amplification caused lateral migration of normal fault hanging-wall depocentres. Our results shed new light on fault-and-fold growth processes in transtensional basins and contribute to an improved understanding of the structural evolution of basins forming along sheared continental margins, which has economic implications for sheared-margin basins targeted for hydrocarbon exploration.

Abstract Fractured crystalline basement reservoirs (basement) on the UK Continental Shelf (UKCS) and the Norwegian Continental Shelf (NCS) have been underexplored. Over the last 12 years, Hurricane Energy has deliberately set out to explore basement potential by exploring and appraising the Rona Ridge, West of Shetland; and the Rona Ridge Lancaster Field is now being progressed towards being the first UK basement field development. The Norwegian basement play is also recognized as a potentially material resource through serendipitous oil discoveries, with the 16/1-15 well, drilled in 2011, being the first successful full-scale basement test on the NCS. Building on this success, the 2018 Rolvsnes appraisal well (16/1-28 S) has demonstrated the significant basement potential of the extensive Utsira High and confirmed the materiality of a Norwegian basement play. The Rona Ridge and Utsira basement discoveries are used as a comparison with two other, yet to be evaluated, prospective basement plays on the NCS, with the objective of establishing technical subject areas where future UKCS and NCS collaboration would aid in accelerating understanding of the UKCS–NCS basement play.

Abstract The NE Atlantic volcanic rifted margins include vast underexplored basin areas neighbouring mature petroleum-producing regions. We appraise the cross-border prospectivity of the outer and central Faroe–Shetland, Møre and southern Vøring basins and present insights from extensive new 3D seismic surveys. Regional seismic surfaces are used to compile a cross-border seismic profile highlighting key discoveries from the UK Rosebank field in the SW to the Norwegian Ormen Lange field in the NE. Cretaceous to Paleocene reservoirs remain the main exploration focus seaward of the platform areas, and the presence of several large untested structures presents important exploration targets in the mid-Norway region. Improved imaging of the areas affected by Paleogene igneous rocks reveals major untested sub-basalt structures including some regions on the marginal highs where the basalt cover has been entirely removed by erosion, revealing sub-basalt stratigraphy and structures with pre-Cretaceous potential prospectivity. The influence of igneous rocks on both discovered and prospective hydrocarbon systems is discussed. Neogene sand injectite fields and Quaternary glacial sand bodies are extremely well imaged in the Møre Basin, documenting shallow prospectivity supported by the presence of successful regional analogue plays. New 3D seismic data are revealing previously unseen prospectivity in frontier and underexplored regions.

Abstract Extensional rift basin systems have been a focus of study for hydrocarbon exploration and have provided significant economic reserves in recent decades, which has led to advances in our understanding of their tectono-sedimentary evolution. However, with the increasing maturity of such settings, focus is shifting from pre-rift structures to the underexplored syn- and late-rift plays. This change in focus brings with it a significant increase in complexity when trying to develop an integrated understanding of the sedimentological, sequence stratigraphic and structural conditions that control the distribution of syn-rift reservoirs. Here we present a subsurface example from offshore Norway of a small, confined, syn-tectonic basin sourced from a local basement high. 3D seismic data, sedimentary facies analysis and stratigraphic correlations based on well and core data from six key wells constrain the local and regional tectonic controls. The PL586 licence partners drilled several wells between 2014 and 2015 targeting syn-rift Upper Jurassic stratigraphy on the southern Halten Terrace. The wells penetrated a complete syn-rift stratigraphic sequence, which provided an excellent subsurface record of the inherent complexities encountered in small, confined (3 by 5 km) syn-rift basins. Seismic data reveals that the Late Jurassic hanging-wall basin architecture and the footwall hinterland of the Frøya High were controlled by activity on the basin-bounding Vingleia Fault Complex. Facies analysis from well and core data reflects a complete syn-rift succession. The early-rift succession comprises mainly mud and siltstone with minor fine-grained sandstones interpreted to be deposited by sediment gravity flows in isolated mini-basins. The peak-rift deposits comprise coarse-grained sediment gravity flows that were sourced locally from the uplifting footwall and deposited as coarse-grained submarine fan systems in the immediate hanging wall. Significant footwall uplift during the peak-rift phase resulted in fault scarp instability and the emplacement of several large landslide complexes into the basin. The late-rift phase is dominated by a mud-rich sequence with minor coarse-grained apron fans shedding sediment off the basin bounding fault and shoreface deposits flanking the hanging-wall dip-slope and subtle intra-basinal highs. This subsurface study from the southern Halten Terrace is significant in the number of wells that have specifically targeted syn-rift stratigraphy and the level of detail at which it captures the stratigraphic variability of these deposits within a small, confined basin system. Integration of seismic geomorphology and well data with robust provenance, dating and stratigraphic correlation has enabled the development of a tectono-stratigraphic model specific to the scale and local tectonic setting. The model reveals that structural evolution ultimately controlled the development of sediment supply routes, their age and distribution, and allows several conclusions to be drawn: The stratigraphy of small, confined syn-rift basins is broadly comparable with more typically documented larger syn-rift settings, although lateral facies changes occur more rapidly. The cannibalistic nature of syn-rift systems, where a large volume of pre- and syn-rift sediments are uplifted and eroded then rapidly re-deposited makes determining the relative age of laterally variable depositional settings difficult. In order to adequately constrain the timing and depositional extent of syn-rift stratigraphy, it is essential to understand the structural evolution of the system and integrate this information with other disciplines and datasets. This integrated understanding will ultimately improve predictions of reservoir presence and quality.

Abstract Deep-marine gravity-driven deposits represent one of the more investigated depositional systems owing to their potential interest as targets for exploration and carbon capture and storage activities, as well as an important record of the depositional history of a basin through time. Although the Halten Terrace (Norwegian Sea) is one of the main successful exploration areas, we still have poor understanding of the post-rift Cretaceous interval. Here, 3D seismic reflection and borehole data are integrated to investigate the stratigraphic distribution and sedimentological characteristics of the Cenomanian–Turonian intra Lange Sandstones in the Gimsan Basin and Grinda Graben. The Lange Fm records the deposition in a deep-marine environment of a 1000 m-thick shale unit punctuated by gravity-driven coarse-grained sandstone intervals that are tens of metres-thick and sourced from the Norwegian mainland. The presence of gravity-driven deposits and the deep-marine setting are supported by seismic interpretation, architectural elements and the facies analysis of cored material acquired within the studied stratigraphic interval. Borehole data indicate the presence of both turbidites and hybrid-event beds rich in mud content. The results of this study have implications for understanding the distribution and reservoir potentiality of the Late Cretaceous Lange Fm in the Halten Terrace.

Abstract Onshore exposures of the North Atlantic Igneous Province have been studied in detail for over 200 years, whereas the more extensive offshore volcanic stratigraphy is significantly less well constrained with the exception of a small number of boreholes. Within this study we integrate seismic and well data across the northern Faroe–Shetland Basin and Møre Marginal High to improve understanding of the volcanic stratigraphy and its relationship to rifting in the NE Atlantic. Volcanic seismic facies, including compound and tabular lavas and hyaloclastites (representing subaerial and subaqueous emplacement), are interpreted across the study area, calibrated by the Lagavulin borehole. The volcanic sequence was erupted between c. 56.1 and 55.2 Ma, when subaerial conditions dominated in the region, but extensive lava deltas developed in a seaway east of the main lava field. Geochemical and thickness variations within the volcanic pile have important implications for the regional rifting history. MORB-like lavas at the base of Lagavulin, which thicken substantially northward, support an early onset of rifting near the Møre Marginal High prior to major thinning associated with continental breakup to the south and north. Following a period of erosion, smaller-degree melting caused the eruption of higher-TiO 2 /Zr lavas, marking the final ‘pre-breakup’ volcanism before emplacement of seaward-dipping reflectors.

Abstract The most prolific reservoir package in the SW Barents Sea is currently the Upper Triassic–Middle Jurassic Realgrunnen Subgroup, comprising the main hydrocarbon accumulations in the Goliat, Snøhvit and Johan Castberg fields and the Wisting discovery. The interval continues to be the main target as hydrocarbon exploration ventures further into this region. However, the package varies considerably in thickness and reservoir quality throughout the basin, and it is therefore very important to understand how this package developed and what has affected it in the time since it was deposited. Here we review controls on the tectonostratigraphic evolution and facies distribution within the Realgrunnen Subgroup, and exemplify the variability in reservoir characteristics within the subgroup by comparing some key wells in relation to their depositional environment and provenance. New provenance data that record a turnover from reworked Triassic- to Caledonian-sourced mature sediment support facies observations which suggest temporal changes in the depositional environment from marine to fluvial. Much of the variability within the subgroup is attributed the tectonostratigraphic development of the basin that controlled accommodation, facies transitions and sediment distribution. This variability is reflected in subtle differences in reservoir quality important both for exploration and production in the remaining underexplored basin.

Abstract A dataset with pore pressures from more than 1000 exploration wells has been used to investigate the dynamics of aquifer systems in the Norwegian Continental Shelf (NCS). Variations in aquifer pressures reflect flow of porewater through permeable rocks over geological time. Strongly overpressured regimes are formed within confined aquifers in subsiding areas, where fluid flow out of the aquifer is controlled by vertical seepage. In transitional pressure regimes, fluid flows within permeable beds towards areas with hydrostatic pressures. In the hydrostatic regime, pressure differences result from density differences due to varying formation water salinity and by hydrocarbon columns. An underpressured regime has been encountered in confined aquifers in the platform areas of the Barents Sea, and is related to net uplift and erosion. In the case studies, pressure differences are interpreted in the context of the relevant pressure regime, and with a dynamic approach where segment boundaries and cap rocks are regarded as low-permeability restrictions rather than barriers. The present distribution of pressure regimes was developed over the last few million years due to rapid Pleistocene sedimentation and erosion processes.

Abstract The most recent advance in infrared spectroscopy is in the use of real-time imaging reflectance spectrometers to study cores and cuttings. These are non-contact and non-destructive, and acquire continuous mineral and hydrocarbon data in a detailed sub-millimetre pixel image format. The main strength of this approach is the unique ability to accurately discriminate and quantify the clays, carbonates and sulfates, along with hydrocarbon information. Three hyperspectral core-scanning projects from the UK and Norwegian Continental Shelf highlight how these detailed, continuous mineral and hydrocarbon data can be used in geological and petrophysical evaluations. In the Dunbar Field of the Northern North Sea, UK, the spectral recognition of illite and kaolinite polytypes associated with faulted sandstone units contributed to a successful revision of lithostratigraphic correlation between wells with core material and those with only cuttings. These had been hitherto problematical. In Norway, hyperspectral mineral data from mixed carbonate–siliciclastic sequences across the Permo-Triassic boundary in the Alta Field, Barents Sea, helped in the delineation of a karstified dolomitic reservoir. A kaolinite cyclicity associated with an Upper Triassic stacked alluvial fan sequence was also identified in the Lorry Prospect, Norwegian Sea. Finally, it is demonstrated how hyperspectral data can be applied quantitatively to help to calibrate downhole petrophysical data, improve gamma log scaling for shale volume calculations and link mineralogy to permeability.

This volume offers an up-to-date ‘geology-without-borders’ view of the stratigraphy, sedimentology, tectonics and oil-and-gas exploration trends of the entire Atlantic Margin and Barents Sea basin. The challenges associated with data continuity and nomenclature differences across median lines are discussed and mitigated. Examples of under-exploited cross-border plays and discoveries are discussed.

Abstract The North Sea has reached an ultra-mature state as a petroleum basin, entering a phase of infrastructure-led exploration in an attempt to extend the economic lives of the main fields and reduce the rate of production decline. At the same time, the transition to a future low-carbon use of the basin is also in progress. As the papers in this volume demonstrate, in order to find, appraise and develop the mostly smaller near-field opportunities as well as making sure to grasp the opportunities of the near-future energy transition, a regional understanding of the North Sea is still critical. Even more so, a cross-border approach is essential because: (1) some of the plays currently being targeted have a clear cross-border element; (2) it allows a comparison of stratigraphic names throughout the entire basin; and (3) it enables explorers to learn lessons from one part of the rift to be applied somewhere else. This volume offers an up-to-date ‘geology-without-borders’ view of the stratigraphy, sedimentology, tectonics and oil-and-gas exploration trends of the entire North Sea Basin. The challenges associated with data continuity and nomenclature differences across median lines are discussed and mitigated. Examples of under-exploited cross-border plays and discoveries are discussed.

Abstract The Devonian–Recent tectono-stratigraphic history of the Northern, Central and Southern North Sea is here reviewed at a regional scale and four novel cross-border pseudo-Wheeler diagrams are presented to summarize the stratigraphic evolution of the cycles of basin fill and uplift/erosion. In this scheme, six first-order megasequence boundaries have been defined, characterized by extensive and long-lasting erosional hiatuses and major coastal regressions: (1) Caledonian (or Base Devonian) Unconformity; (2) Variscan–Saalian (or Base Permian) Unconformity; (3) Mid Cimmerian (or Intra-Aalenian) Unconformity; (4) Late Cimmerian (or Base Cretaceous) Unconformity; (5) Atlantean (or Near-Base Tertiary) Unconformity; and (6) Eridanos (or Mid-Miocene) Unconformity. These surfaces have been linked to regional causal factors ranging from orogenesis-related compressional uplifts, in either active plate margin settings (1) or foreland basin settings (2), to intra-plate dynamically supported uplifts associated with the development of mantle plumes (3, 5 and 6) and the end-of-rifting and associated widespread erosion of tilted fault block crests (4). The aforementioned megasequence boundaries punctuate the geodynamic evolution of the North Sea area and facilitate the subdivision of the entire the North Sea sedimentary basin fill into six megasequences, named here A–F. All of the lithostratigraphic units of the North Sea (formations and members) have been described within the context of this first-order tectono-stratigraphic framework. The correlation powers of certain stratigraphic markers are also compared and contrasted, together with the potential cross-border equivalence of sedimentary units on different sides of the political median lines.