Oil migration makes the difference: regional distribution of carbonate cement 13C in northern North Sea Tertiary sandstones
Abstract:Carbonate cements in Tertiary reservoir sandstones from the northern North Sea have distinctive carbon isotopic compositions (13C). Oil migration up faults from deeper structures and biodegradation of oil pools are factors of particular importance in influencing the 13C of carbonate cements in these sandstones. As a result, 13C can be used as an exploration guide to locating the positions of vertical leakoff points from the Jurassic source rocks. The histogram distribution of 13C in these carbonate cements is trimodal, with peaks at around -26, -3 and +12‰ (ranges -22 to -30, +2 to -10 and +8 to +18‰, respectively). Bacterial processes played major roles in determining this distribution, with oxidative biodegradation of oil resulting in carbonate cements with very negative compositions and bacterial fermentation resulting in the positive 13C cements. 13C distribution patterns may be used to differentiate Tertiary reservoir sandstones from Jurassic in the northern North Sea, and these regional carbonate cement 13C datasets allow geologically useful inferences to be drawn from 13C data from new sample locations.
Document Type: Research Article
Publication date: March 1, 2000