The use of Potential Fields in the Search for Potential Fields in the Faroe-Shetland Area

Abstract

Abstract In the UK the exploration effort has shifted from the maturing North Sea basins to the frontier province between the Shetland/Hebridean Platform and the continental margin W of the Faroe Islands, bringing with it over 23 years of hydrocarbon finding experience. Fundamental geological and environmental differences exist between the basins of the North Sea and the basins of the NW European continental margin, and strategies for success in the North Sea have not necessarily transferred directly to the continental margin. As a result, exploration outcomes to date have been somewhat disappointing, with one or two notable exceptions. Furthermore, a change in the approach to acreage evaluation places increasing levels of reliance on seismic data, specifically 3D data, to tie down prospects prior to drilling. This approach focusses down rapidly to the prospect scale and although allowing detailed analysis of target structures, runs the risk of creating a gap in understanding between the geological processes observed at the basin scale and those at the prospect scale. A strategy to bridge this gap has drawn upon the wider family of geophysical data, namely gravity and magnetic data, in conjunction with a conventional, broad regional grid of 2D seismic data. These data have been worked together in order to construct a basin scale framework into which 3D seismic data acquisition can be planned and the results interpreted. The results of this approach in the Faroe-Shetland area have revealed a basin framework with implications for hydrocarbon prospectivity which extend beyond the region. At the regional scale, satellite-derived gravity coverage has enabled the removal of the effects of Tertiary sea-floor spreading, allowing structures on the NW European continental margin be viewed in context with the geology of East Greenland. At the basin scale, basinal elements have been identified and correlated between seismic, gravity and magnetic data. Controlling faults have been mapped and the timing of basin formation inferred from trend and geometry, with implications for source rock distribution. At the licence block scale, the segmentation of basin margins has been revealed by high spatial resolution magnetic data with implications for both trapping potential and the control of sediment supply into the basins. The fusion of interpretations made from the different types of geophysical data creates a scale of observation range which stretches from tectonic plates to prospective structures. The resulting geological framework has sufficient scale overlap to relate immediately to the level of detail available from 3D seismic data. Moreover, the broader perspective may ensure that those seismic data are acquired in the correct part of the basin in the first place. Introduction The region of the NW European continental shelf between the Shetland-Hebridean Platforms and the continental margin to the west of the Faroe Islands has been progressively opened for hydrocarbon exploration since the 4th UK licencing round in 1971. P. 301^