3D-basin modelling of the Hammerfest Basin (southwestern Barents Sea): A quantitative assessment of petroleum generation, migration and leakage

3D basin modelling of the Hammerfest Basin (southwestern Barents Sea) was performed in order to address the masses of petroleum generated, accumulated and lost during the evolution of the basin. Calibration of the model, based on observed maturity (vitrinite reflectance) and present-day temperatures, took into account (1) two main erosion episodes: an Oligocene–Miocene event, due to tectonic uplift and a Plio-Pleistocene glacial erosion event, and (2) variable heat flow from Late Palaeozoic to Cenozoic. The maturity levels of the main source rocks (Kobbe, Snadd and Hekkingen formations) were reconstructed and show that the highest maturities have been reached in the western and northwestern margin of the basin. The beginning of petroleum generation in the Kobbe, Snadd and Hekkingen source rocks has been predicted to occur during Late Triassic, Early Cretaceous and Late Cretaceous, respectively. Our model reproduces satisfactorily the distribution of the main oil and gas fields and discoveries that have been found in the study area. Our results indicate that two events of hydrocarbons redistribution occurred in the basin. The first event resulted in the main oil redistribution episode, which took place during the Oligocene–Miocene associated with tectonic uplift and gas expansion, and the second was related to the main gas leakage events that occurred during the Pliocene–Pleistocene glacialinterglacial cycles in general and the episodes of glacial retreat in particular. Glacial loading and unloading cycles resulted in overpressure fluctuations in the subsurface reservoirs. Modelling results indicate that during these episodes a portion (at least 0.247 Gt) of thermogenic gas leaked from the main Stø Formation reservoirs reached the sediment interface and was released to the surface in the Hammerfest Basin.