In the East Shetland basin, Late Jurassic rifting formed tilted fault blocks and unconformity traps sealed by onlapping Cretaceous mudstones. Important oil-bearing reservoirs are Middle and Lower Jurassic marginal/nonmarine sheet sandstones and restricted Upper Jurassic submarine fan/shallow-marine sandstones. Mature Upper Jurassic mudstone and Middle Jurassic coal source rocks located in half grabens downdip of the major fields, and in the flanking western Viking graben, generated oil in Eocene to Miocene time.

Study of reservoir pressures, distribution, and structure defines the major Jurassic aquifers in the East Shetland basin. The geometric relationship of these aquifers to the source rock kitchens defines the volumes of source rock drained by the major oil fields. Quantitative modeling of the volume of oil generated and expelled from the source rocks (from geochemical and compaction data) accounts for the inplace reserves of the fields.

In the Viking graben, deeply buried Jurassic fault blocks that now contain mainly gas condensate and high pressure salt water were sourced with oil in the Late Cretaceous to Eocene, and with gas in the late Eocene to Recent. Extensive vertical migration of oil has occurred from Jurassic source rocks and reservoirs through thick, microfractured, overpressured Cretaceous mudstones, up the fault zones reactivated in the Tertiary, and into an extensive Paleocene/lower Eocene aquifer sealed by Eocene mudstones. The oil was probably degraded during Miocene freshwater flushing, and displaced out of lower Tertiary traps up onto the East Shetland platform by subsequent gas migration.

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