Facies analysis of the Kopervik sand interval, Kilda Field, Block 16/26, UK North Sea

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Abstract
The Kilda Field is a large gas condensate accumulation located in UK Block 16/26. The reservoir sands, informally termed Kopervik, are Lower Cretaceous in age and are developed on the southern dip slope of the Fladen Ground Spur. They represent a localized sandy development within the lower Sola and upper Valhall formations, associated with the Austrian orogeny. Sands were carried out into the basin by a variety of sediment gravity flow processes, and were deposited as an apron near the foot of the slope. Their distribution is controlled largely by the nature of the flow and by pre-existing topography. Six main sand facies have been recognized, three of which are high-density turbidite (HDT) types and contain virtually all reservoir quality rock. HDT S 3 sands resulted from suspension collapse. They exhibit porosities around 15%, and permeabilities around 40 md. HDT Laminated sands probably formed from traction sedimentation. They have similar average porosities but reduced permeabilities between 10 and 15 md. Sands of the Marginal facies are of an inferior reservoir quality. The remaining three facies consist of non-reservoir quality sands deposited by liquefaction, debris or low-density turbidite flow. Post-depositional disturbance suggests that deposition took place on an unstable palaeoslope. Subsequent porosity loss within clean sand intervals has been dominantly through compaction.