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Palaeomagnetic Properties of Hydrocarbon Reservoirs |
1 School of Earth Sciences, University of Birmingham, Birmingham B15 2TT, UK
2 Department of Geology and Petroleum Geology, Meston Building, King’s College, Aberdeen AB9 2UE, UK
3 Facultad de Ciencias Geologica, Universidad de Vigo, Spain
Although rocks of the Carboniferous Barren Red Measures in the UK southern North Sea are often primarily reddened, they also show secondary reddening by fine-grained hematite precipitated as a result of deep weathering below the Permian unconformity. However, palaeomagnetic and petrographic analyses of samples from wells 49/1–3 and 49/2–3 have shown that a third phase of hematite was precipitated in the Triassic. The specularite grains associated with this magnetization are larger than those precipitated in the Permian and also contain a more dominant magnetic signature. Although Permian hematite precipitation was largely produced as a result of oxidation through vertical percolation, the occurrence of Triassic hematite grains appears to be related to distinct fluvial channels. It is suggested that lateral fluid flow is responsible for the precipitation of hematite in the Triassic and that this is associated with fluvial channel sandstones which have the best permeabilities and interconnectivities. The palaeomagnetic technique is therefore useful for assessing the degree of lateral communication in reservoir sandstones.
