Exploring the reservoir potential of Lower Cretaceous Clinoforms in the Fingerdjupet Subbasin, Norwegian Barents Sea

Abstract

Sandy clinothems are of interest as hydrocarbon reservoirs but there is no proven, economic, clinothem reservoir in the Norwegian Barents Sea. We used high‐resolution, 2D and 3D seismic, including proprietary data, to identify a previously untested, Barremian, clinoform wedge in the Fingerdjupet Subbasin (FSB). Data from recent well 7322/7‐1 plus seismic have been used to characterize this wedge and older Lower Cretaceous clinoforms in the FSB. In the latest Hauterivian – early Barremian, during post‐rift tectonic quiescence, shelf‐edge clinoforms (foreset height > 150 m) prograded into an under‐filled basin. Increased sediment input was related to regional uplift of the hinterland (northern Barents Shelf). Early Barremian erosion in the north‐western FSB and mass wasting towards the SE were followed by deposition of delta‐scale (<80 m high), high‐angle (c. 8°) clinoform sets seaward of older shelf‐edge clinoforms. This may be the local expression of a regional, early Barremian, regressive event. By the close of the Barremian, clinoforms had prograded, within a narrow, elongate basin, across the FSB and towards the uplifted Loppa High. A seismic wedge of high‐angle (10–12°), low‐relief, delta‐scale (25–80 m) clinoform sets occurs between shelf‐edge clinoforms to the NW and the uplifted area to the SE. Well 7322/7‐1, positioned on a direct hydrocarbon indicator, <1 km NNW of the high‐angle, low‐relief, delta‐scale clinoforms, found upward coarsening siltstone‐cycles linked to relative sea‐level fluctuations on a marine shelf. Sand may have accumulated, offshore from the well, in high‐angle, low‐relief foresets of the delta‐scale clinothems (which are typical geometries elsewhere interpreted as ‘delta‐scale, sand‐prone subaqueous clinoforms’). Deposition was controlled by the paleosurface, storms and longshore currents on an otherwise mud‐dominated shelf. The study highlights challenges associated with exploration for sandstone reservoirs in seismic wedges on an outer shelf.

Clinoforms and clinothems: Fundamental elements of basin infill

“…Amorosi et al, 2019;Plink-Bjorklund, 2019) to shelf-edge scale (e.g. Bryn et al, 2019;Gamberi et al, 2019;Gan, Steel, Olariu, & Almeida Jr, 2019;Olariu et al, 2019;Patruno et al, 2019;Steel et al, 2019) and continental-margin scale (Chen, Steel, Wang, Zhao, & Olariu, 2019;Midtkandal et al, 2019). Continuous and repeated erosion is commonplace in the topset areas, F I G U R E 3 Conceptual section of nested clinoforms as the result of incremental margin growth: as in Matryoshka dolls, progressively smaller-scale clinoforms and clinothems 'appear' as we gradually zoom into a continental margin succession.…”

“…Amorosi et al, 2019; Plink‐Bjorklund, 2019) to shelf‐edge scale (e.g. Bryn et al, 2019; Gamberi et al, 2019; Gan, Steel, Olariu, & Almeida Jr, 2019; Olariu et al, 2019; Patruno et al, 2019; Steel et al, 2019) and continental‐margin scale (Chen, Steel, Wang, Zhao, & Olariu, 2019; Midtkandal et al, 2019). Continuous and repeated erosion is commonplace in the topset areas, as highlighted by frequent downcutting of fluvial and delta‐distributary channels (Gan et al, 2019) and by shelf‐edge incisions (Olariu et al, 2019).…”

“…As a consequence, care is needed when interpreting the palaeophysiographic significance of ancient rollover points, to pinpoint the shelf break, to identify the shoreline and to estimate palaeo‐water depths from clinoforms (Bryn et al, 2019; Gamberi et al, 2019; Patruno et al, 2015; Patruno et al, 2019; Schattner et al, 2019; Steel et al, 2019; Trincardi et al, 2019).…”

“…Other present‐day research on clinoform parameters focuses on how process regime impacts the morphology of delta‐scale clinoforms (e.g. Bryn et al, 2019, and Plink‐Bjorklund, 2019). In differentiating coarse‐ and fine‐grained delta‐scale subaqueous clinforms, also Patruno et al (2015) emphasized the gradient of the foreset.…”

“…This gradient is likely controlled by the interplay of: (a) clinoform height, with higher clinoforms generally characterized by steeper profiles, as previously mentioned (if the sediment grain size is similar); and (b) sediment calibre, where coarser‐grained clinothems are typically characterized by steeper angles of repose than fine‐grained ones with similar heights. However, Bryn et al, (2019) suggest that there may be ‘black swan’ examples of steep fine‐grained subaqueous clinoforms, and hypothesize that such occurrences highlight the somewhat underappreciated role that process regime and availability of specific sediment grain sizes may have on the final morphology of the clinothem. This topic is further dealt with in the U.S. Western Interior and Spitsbergen outcrops by Plink‐Bjorklund (2019).…”