The Lower Cretaceous plays of the Central and Northern North Sea: Atlantean drainage models and enhanced hydrocarbon potential

Abstract

In the Central North Sea, the Apto-Albian play appears to be confined to patchy areas within the Moray Firth basins. In this area, it is widely believed reservoir-quality sands were sourced from local residual Late Cimmerian highs, with resultant limited distributions of commercial fairways. Local hydrocarbon modelling proves that most hydrocarbons discovered to date occur within stratigraphic traps, discovered largely by serendipity during appraisal of older structurally defined reservoirs. Re-appraisal of Jurassic to Cretaceous tectonic models shows how tectonic trends within the Moray Firth basins are optimized for discovery of Lower Cretaceous reserves. These models also suggest considerable upside potential in under-explored areas of the Viking Graben and Central Trough, where complex basin geometries and halokinesis conspire to hide potential fairways. The search for Aptian reserves is severely hampered by a widespread inability to see or interpret sand and/or hydrocarbon presence using seismic data alone, resulting in a very high dependence on geological modelling to evaluate potential sweet spots within wide fairway tracts. This style of modelling has been reliant on a ‘Jurassic-upwards’ technique, with limited success. Recent re-modelling of the entire North-West European area has shown that established models of Paleocene sand distribution can be projected downwards to find sweet spots in potential Aptian fairways. Using this approach has resulted in a new plate-wide tectono-sedimentological and drainage pattern model for the Aptian, which suggests that most sand fairways, dominated by deep marine facies, were sourced from an active Atlantic Margin Arch via northwest–southeast-oriented fluvial and shelfal feeder systems. Application of this model to Central and Northern North Sea hydrocarbon fairways suggests a gross current underestimate of Aptian sand volumes and considerable upside potential both within the Moray Firth basins and unappraised exploration territory in the Viking Graben and Central Trough.