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Sand remobilization and injection above an active salt diapir: the Tyr sand of the Nini Field, Eastern North Sea

Authors


Johan Svendsen, DONG Energy, Agern Allé 24-26, DK-2970 Hørsholm, Denmark. E-mail: johbs@dongenergy.dk

ABSTRACT

The Selandien [58 Ma (PP3c-d)] Tyr sand in the Nini area, Siri Fairway, Danish North Sea, is severely influenced by the syn-depositional movement of the Nini Salt Diapir. The sand is faulted and remobilized into a degree where no original depositional signature can be recognized. The Tyr sand is drilled (and cored) by a number of wells, and the sand is never found in the same stratigraphic position. In some wells, the Tyr sand is injected down into the chalk of the Danian Ekofisk Formation, whereas other wells show the Tyr sand embedded in the Selandien Vile Member claystone, with varying degree of remobilization. The Tyr sand is thin (2–7 m) and is therefore below seismic resolution and close to seismic detection. Standard reflection seismic data has proven problematic in determining the actual thickness and spatial distribution of the thin Tyr sand located within or immediately above the chalk. A simultaneous AVO (amplitude vs. offset) inversion using time-aligned angle stack seismic data, has improved resolution of the thin and complex reservoir, allowing a better understanding of the remobilization processes occurring above the rising salt diapir, and thereby an improved understanding of the reservoir and its performance. Three different remobilization features are described: injection into the chalk, injection up along fault planes and compactional driven injection. The force for the remobilization spans in orders of magnitude from metre scale phenomena, to injections of 100s of metres, moving millions of tons of material and fluids.

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