The impact of late Cenozoic uplift and erosion on hydrocarbon exploration: offshore Norway and some other uplifted basins

Uplift and erosion of sedimentary basins can have a wide range of effects, both positive and negative, on hydrocarbon prospectivity. These phenomena are discussed with special reference to the Norwegian Continental Shelf. Late Cenozoic uplift and erosion have affected large expanses of the shelf, and in particular the Barents Sea. Up to 3000 m of sedimentary overburden have been removed from the Barents shelf, and this process is widely held to be responsible for disappointing results in petroleum exploration. Negative effects identified include spillage of hydrocarbons from accumulations, expansion of gas and evacuation of structures, potential for seal failure and cooling of source rocks. We argue, however, that these aspects have been overstated based on a limited database. Many of the worldʹs hydrocarbon basins (and most of the worldʹs petroleum reserves) lie on land. Most of these basins must have been recently uplifted in order to be above sea level today. Using some of these examples, we show that in other areas with a similar magnitude of uplift and erosion to the Barents Sea sealing capacity (particularly that of evaporites) has been preserved. Hydrocarbon systems have remained intact despite phase changes and redistribution of hydrocarbons. Several enhancing effects of the uplift are documented, including the development of fracture permeability in reservoirs, the remigration of hydrocarbons to shallower subsurface levels and the exsolution of light oil (retrograde condensate). Looking to a future in which natural gas may have increased value, potential exists in uplifted basins such as the Barents Sea for vast volumes of methane formed by exsolution from formation brines. We stress the importance of studying such worldwide analogues in order to throw new light on Norwegian shelf problems. Attention is drawn to some striking similarities between the hydrocarbon systems of the Western Canada Basin and those of the Barents Sea. Examination of the massive databases in the Western Canada Basin and other analogous provinces, rather than a continuing locally-centred approach, will probably help to focus exploration directions in the Barents Sea and may help to distinguish between the effects of uplift and erosion per se and those of more specific, local phenomena such as ice loading and rapid deglaciation.