Influence of glaciations on North Sea petroleum systems

Abstract

Abstract Even in tectonically inactive areas/times, the vertical motions of the Earth's interior may be significant due to glaciation. The most recent ice age massively changed the surface of northern Europe, leading to isostatic re-equilibration. We quantify the vertical motions resulting from three glacial-related mass redistribution mechanisms using, as an example, the North Sea throughout the Quaternary: (1) ice-sheet loading, (2) erosion, including glacial carving of fjords; (3) and sediment deposition. These processes yielded up to 1 km of vertical displacement of the lithosphere across the North Sea, and the corresponding sediment-tilting changed the geometry of petroleum systems and hydrocarbon migration routes. Using the Base Cretaceous Unconformity as a top seal proxy, we analyse the consequences in the Norwegian North Sea. Comparing well data to models, we suggest that tilting the Troll Field back towards its early Quaternary position flattens the palaeo-oil–water contact (palaeo-OWC), which today is tilted by up to 70 m. The Johan Sverdrup Field shows a more complex history. Hints of a palaeo-OWC tilted can be seen in permeable reservoirs, whereas deeper sporadic oil shows cannot be explained by simple tilt models. Our study illustrates how glacial-related processes may influence the development of giant oil and gas accumulations.