Origin of the Magnetic Signature of Hydrocarbons

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From aeromagnetic surveys there is evidence of large magnetic anomalies around some hydrocarbon reservoirs. Direct sampling of cores from Venezuela, China and the US has revealed the presence of an abundance of distinctive magnetite framboids at these anomalies, however, we still do not understand how these magnetic minerals form and how they relate to the hydrocarbons. If we can understand the formation mechanisms and environment, and the migration behaviour of these magnetite framboids, then this has the potential to will help us to better understand hydrocarbon reservoirs. This cross-disciplinary proposal aims to understand these processes.In a preliminary study, to test for the universality of these magnetic signatures, we have already studied samples from the oil sand out-crops near Wytch Farm oil field, Dorset, from the North Sea core repository at the BGS in Edinburgh, from Athabasca, the Alberta basin, Canada, and Llanos Foreland, Columbia. Within these samples we have found magnetic framboids and a direct correlation between the abundance of magnetic minerals determined by the magnetic susceptibility and organic matter content. However, there are a number of key questions, which as yet remain unanswered, which are important if we are to apply mineral magnetic techniques to hydrocarbon research: 1) What is the origin of the magnetic minerals?, 2) What is the relationship between the biodegradation state of oil and the magnetic signature?, and 3) Do the magnetic minerals migrate, and if so, 4) can we identify the migration distance? As part of this proposal we plan to answer these questions.To address our objectives, we aim to complement our suite of samples with samples Wytch Farm drill cores (BGS core store at Keyworth) and with bitumen from the celebrated Tar Tunnel in Shropshire, UK. The samples from Shropshire will be collected from a different sections so that migration paths can be assessed.The plan of research plan combines magnetic and scanning and transmission electron microscopy of the samples to determine the abundance, morphology, size and mineralogy of the magnetic minerals, with gas-chromatography mass spectrometry and other chemical analysis. Migration processes will be determined by sampling through an oil reservoir. If the magnetic minerals migrate, then it is likely that the greater framboids will travel a greater distance than the smaller ones. Given that magnetic properties are highly dependent on magnetic grain-size, we aim to determine a magnetic proxy to identify migration distance.