Structural development and hydrocarbon occurrence of the Carboniferous in the UK Southern North Sea Basin

Abstract

Recent Carboniferous gas discoveries in the UK Southern North Sea display a pronounced structural alignment. Previous efforts to decipher Carboniferous structural development have been hampered by limited well control and poor quality seismic data. The recent increase in exploration activity in the southern area of Quadrant 44 has facilitated a detailed analysis of the Carboniferous. Interpretation of spectral gamma ray logs and biostratigraphic data from more than 40 deep wells have permitted re-correlation of the Carboniferous section. These new well correlations and VSP data from key wells make it possible to relate seismic reflection character to stratigraphy for several Carboniferous units. More than 2000 km of seismic data were interpreted throughout the southern part of Quadrant 44 to map the distribution of these Carboniferous seismic packages below the angular Base Permian Unconformity. This interpretation project has resulted in a new understanding of Carboniferous structural development and its relationship to hydrocarbon occurrence. East–west-trending hangingwall roll-overs, formed during Carboniferous crustal extension, were subsequently transected by northwest-trending regional anticlines, generated during the Variscan orogeny. Hydrocarbons have been discovered in both the regional anticlines and localized roll-over structures.