Basement highs: Definitions, characterisation and origins

A glossary of commonly used terms related to the geometric forms and geological settings of basement highs is presented to assist cross‐disciplinary understanding, qualifying prefixes for the term basement are discussed and a scheme for characterising basement highs is presented. This scheme is designed to standardise, and to add rigour to, description of basement highs. It will thereby enhance basement high comparisons and assist understanding of basement highs across technical disciplines. The scheme enables systematic characterisation of: the geometry of a basement high; the lithologic units and structures in, above and around it; timings; tectonics and origins of the basement high and play elements relating to resource prospectivity. Use of this scheme is demonstrated using the southern Rona Ridge (West of Shetland, UK Continental Shelf). The tectonic, isostatic, erosional and stratigraphic processes that form basement highs are also discussed, and examples in proven petroleum systems are presented. Example of geometric features of a basement high, illustrated using the south Rona Ridge 3D Top Basement depth structure map. A = Lancaster Field oil‐water contact at 1678 m true vertical depth sub sea level (TVDSS) (Hurricane Energy, 2019c). B = Lincoln oil discovery “oil down to” at 2258 m TVDSS. C = Whirlwind Discovery “oil down to” at TVDSS. The basement high covers an area of ~ 1200 km , so it is a 4th order basement high. It has an approximately trapezoid shape in map view shape (including the Whirlwind downthrown block). The topography of the upper surface can be described as an undulating wedge (area i) and an undulating planar slope (areas labelled ii). Structures segmenting the basement high include: 1 = Westray Fault Zone; 2 = Brynhild Fault Zone. Contour increment 100 m.