Exploring the continental shelf for low geological risk nuclear waste repository sites using petroleum industry databases: a UK case study

Site selection for deep disposal of intermediate and high level radioactive waste in the UK to date has not taken full advantage of oil industry databases that cover offshore areas. The shallow water area of the UK continental shelf is twice that of the onshore area and due to variations in regional geology, many geological settings occur that are not found onshore. The geology and hydrogeology of the UK continental shelf contrast in many respects with that of onshore areas. The geology of the North Sea in particular is constrained by over 3000 deep (>2 km) exploration wells, 50,000 km2 of 3D seismic data and several million line kilometres of 2D seismic data—vastly more than the coverage of data constraining the deep geology onshore. Combined with detailed studies of oil and gas fields, this data has led to a greater technical understanding of many aspects of offshore geology relative to that onshore. These data represent an original investment of £20bn by oil and gas companies, but are now in the public domain. These databases are used here to compare onshore and offshore settings in terms of criteria such as structural geology, fault activity and uplift/subsidence. Clear differences emerge, such as risk of seismicity, exhumation and the variety of hydrogeological systems. The distribution and geometry of candidate repository sites throughout the North Sea (salt structures, shale basins, sealed sandstone reservoirs and basement highs) are illustrated. Several lines of petroleum-related research have yielded lessons that may be useful in assessing deep repository locations, such as migration of hydrocarbons through shale seals. The exceptional combination of seismic data and well control means that offshore areas on the continental shelf and the North Sea in particular can now be thoroughly explored in this context and contribute candidate sites into a nationwide portfolio of deep geological disposal options, in the event of site selection being pursued in the UK. An example framework for this process is presented here.