Mercury in source rocks on the Norwegian Continental Shelf; link to maturity, depositional environment and age

The source of mercury (Hg) in petroleum is debated in the literature and could stem from; Hg rich black shales producing petroleum, coals, proximity to deep faults acting as migration routes from deep Hg sources, and proximity to large igneous provinces. In an attempt to cast light on the source of Hg in oils on the Norwegian Shelf 268 mainly organic rich core samples from wells in the North Sea, Norwegian and Barents Sea were analysed for Hg and other heavy metals. In addition 5 core samples from Devonian and Permian reservoir sands and 6 oils from the Embla field were analysed. Our study shows that sediments with elevated Hg concentrations are associated with anoxic depositional environments. The study also show that Hg is mobilized in the source rock at the same temperature interval that generates oil and that the concentration of Hg in the source rock decreases with expulsion of oil. It is suggested that Hg in oil may carry information about the origin of the oil; source rock type and age.