Effects of Glacial Loading and Unloading on the Petroleum Systems of the South-Western Barents Sea as Revealed by Basin Modelling

Di Primio, Rolando¹, Andrew Cavanagh², Magdalena Scheck-Wenderoth², Brian Horsfield² (1) GeoForschungsZentrum Potsdam, D-14473 Potsdam, Germany (2) GeoForschungsZentrum Potsdam, DE-14473 Potsdam, Germany

The south-western Barents Sea is a frontier area for exploration on the Norwegian Margin. The juxtaposition of the North Atlantic rift system with the northern borderlands of the Eurasian continental shelf makes for an unusual basin evolution with oil- and gas-prone petroleum systems. Petroleum exploration in this area has yielded giant gas discoveries, very little oil and evidence of significant inversion during the Cenozoic. These findings are typical of peripheral North Atlantic basins that have undergone exhumation. Using 2D basin modelling calibrated to vitrinite reflectance, temperature and apatite fission track data we demonstrate that the main period of inversion must have been related to the Late Cenozoic glacial erosion. Modelling results assuming glacial erosion, effects of ice loading and related temperature changes on the basin evolution using a temporal resolution of 20000 years per timestep indicate that all had profound implications for the temperature and pressure conditions encountered within the Jurassic reservoirs. We estimate that for the Snohvit field, a Jurassic reservoir containg gas with a thin oil leg, a minimum of twenty episodes of extraordinary hydrostatic pressure fluctuations in excess of 5 MPa and a related temperature drop of 20° Celsius during the last 1.6 My occurred. Such fluctuations would have direct consequences for the dynamics of hydrocarbon leakage from gas reservoirs, essentially focussing periods of leakage to initial stages of interglacial conditions.