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 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.