Upfaulted ridges of Neoarchean crystalline basement rocks formed in the Faeroe-Shetland basin as a consequence of Mesozoic rift processes and are an active target for oil exploration. We carried out a comprehensive fault and fracture attribute study on the extensive exposures of geologically equivalent crystalline basement rocks onshore in NW Scotland (Lewisian Gneiss Complex) as an analogue for the offshore oil and gas reservoirs of the uplifted Rona Ridge basement high. Our analysis shows a power-law distribution for fracture sizes (aperture and length), with random to clustered spacing and high connectivity indices. Regional variations between the Scottish mainland and the Outer Hebrides are recognized that compare directly with variations observed along the Rona Ridge in the Faeroe-Shetland basin. Here we develop a model for the scaling properties of the fracture systems in which variations in the aperture attributes are a function of the depth of erosion beneath the top basement unconformity. More generally, the combination of size, spatial and connectivity attributes we found in these basement highs demonstrates that they can form highly effective, well-plumbed reservoir systems in their own right.Supplementary material: Additional methods and results are available at: https://doi.org/10.6084/m9.figshare.c.5017139Thematic collection: This article is part of the The Geology of Fractured Reservoirs collection available at: https://www.lyellcollection.org/cc/the-geology-of-fractured-reservoirs

Fractured gneiss lithologies form a basement-cored high, the Rona Ridge in the Faroe–Shetland Basin. Basement structures are known to play an important role in the petroleum system for the overlying giant Clair Field. An onshore analogue exposure in the Lewisian Gneiss Complex at Kinlochbervie in NW Scotland provides an example of a hanging-wall damage zone of a large basement-hosted normal fault. In this study, we used remote sensing (2D), outcrop line sample methods (1D) and a virtual outcrop created by terrestrial laser scanning methods (3D) to characterize spatial variations of the fracture systems. Spacing distributions from 1D line samples collected from exposures and pseudo-wells constructed through the virtual outcrop show power-law distributions. The virtual outcrop data enable us to extend the scale-invariant description from 1 to 3 orders of magnitude. We developed a novel box-counting workflow to provide an assessment of 2- and 3D variations in the fracture properties. Fracture density and fractal dimension are elevated whereas the number of intersections is decreased within a 220 m-wide volume adjacent to the fault. We discuss how the methods and results from this study can aid the development of analogue for basement reservoirs in the offshore UK continental shelf.