Seismic interpretation and generation of key depth structure surfaces within the Carboniferous and Devonian of the Orcadian Study Area, Quadrants 7-9, 11-15 and 19-21

摘要

This report details the rationale, methodology and results of a regional seismic interpretation of the 21CXRM Palaeozoic ‘Orcadian study area’, specifically the Inner Moray Firth and western Outer Moray Firth basins (Quadrants 11–15), the East Orkney Basin (Quadrant 13) and the Grampian High area (Quadrants 19–21). The aim of the interpretation was to create Two-Way Travel Time (TWTT) and depth maps that show the distribution of Palaeozoic basins and highs, and where possible interpret key Devono-Carboniferous surfaces and main structural elements in order to contribute a tectono-stratigraphic model of the Palaeozoic succession. Some 35,000 line kilometres of predominantly 2D seismic data have been interpreted and tied to key released wells in the study area.udIn total, 8 depth structure maps of key horizons have been produced for the pre-Permian succession. The maps do not cover the entire study area as it was not possible to interpret a specific seismic reflector everywhere due both to seismic resolution and also current day extents (as a result of non-deposition and/or erosion). These maps provide a key element to aid assessment of the petroleum systems of the Palaeozoic sequence within the study area.udWhere present, the surfaces with a grid spacing of 5000 m, give a regional view of the topography of the horizons, and comprise:udInner and Outer Moray Firth and East Orkney Basin areaud Base Zechstein;ud Top Firth Coal Formation;ud Top Eday Marl Formation;ud Top Orcadia Formation;ud Base Orcadia Formation;ud Top Struie Formation;ud Top Basement.udThe geological succession over the Grampian High area was such that only the following surfaces were generated:ud Base Zechstein;ud Base Carboniferous/ Top Devonian;ud Top Basement.udThe regional structure map of the area constructed for this report, and observations made from the seismic data, have been integrated with peer reviewed published information to describe a tectonic synthesis for the region (Leslie et. al., 2016).udA new pre-Permian subcrop map is presented here that builds on existing publications (Smith, 1985; Marshall and Hewett 2003) and incorporates relevant new well penetrations since the previous maps were published. The well dataset has been either validated or re-interpreted before being integrated with the new seismic interpretation. The map extends the interpretation of the pre-Permian subcrop northwards from the published Central North Sea map (Arsenikos et al., 2015).