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The Devonian–Carboniferous Clair Group reservoir succession in the Clair Field, located west of Shetland on the UK continental shelf, comprises over 1000 m of clastic sediment deposited in a range of fluvial, lacustrine, and eolian environments. Owing to the unfavorable depositional conditions, palynomorphs and microfossils are almost entirely absent, precluding development of a high-resolution biostratigraphic framework for reservoir correlation. An alternative approach to reservoir subdivision and correlation is therefore necessary in order to establish a viable reservoir model prior to field development. Heavy-mineral analysis, which subdivides clastic successions on the basis of changes in provenance and sediment transport history, has proved successful in establishing a high-resolution correlation framework for the Clair Field. This paper concentrates on the heavy-mineral stratigraphy of the Lower Clair Group, which is the target for the first phase of the field development. The key parameters that have been used to erect the correlation framework are provenance-sensitive ratios of heavy minerals (notably garnet:zircon, rutile:zircon, and apatite:tourmaline), grain morphology (apatite roundness), and mineral chemistry (garnet composition). The Lower Clair–Upper Clair boundary is a major heavy-mineral event related to a fundamental change in provenance. Six major units (I–VI) and a number of subunits have been recognized within the Lower Clair Group, boundaries being related to more subtle changes in provenance and sediment transport history. The successful application of integrated heavy-mineral analysis in the Clair Field demonstrates that the method can be reliably applied to correlation of clastic hydrocarbon reservoirs. The technique is successful because it generates data that are independent of factors such as hydrodynamics and diagenesis, and therefore directly reflect correlatable geological events such as changes in provenance, sediment transport history, and climate. Furthermore, the method can be used on the full range of geological samples acquired during hydrocarbon exploration, since data are acquired from the constituent components of the sample rather than from the bulk sample, thereby enabling contamination from drilling additives and caving to be filtered out.

Application of Modern Stratigraphic Techniques: Theory and Case Histories

SEPM Special Publication No. 94, Copyright © 2010

SEPM (Society for Sedimentary Geology), ISBN 978-1-56576-199-5, p. 183–199.

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