Seismic Scale Injected Sandstones in the South Viking Graben, North Sea; Implications for Exploration of the Palaeogene Succession

Sletten, Elisabeth Bøhle¹, Reza Ramsumair², Eirik Larsen¹, Nicholas Satur³, ingrid Nilsson¹, trond Ødegård⁴ (1) Statoil ASA, Stavanger, Norway (2) University of Aberdeen, Aberdeen AB24 3UE, United Kingdom (3) STATOIL, Stavanger, Norway (4) Envision AS, Stavanger, Norway

The Palaeogene Hordaland Group of the Viking Graben, North Sea, comprises abundant seismic amplitude anomalies with various geometries that cross-cut the otherwise conformable stratigraphy. These anomalies are interpreted as seismic reflections from injected sand bodies. Analysis of the regional facies variability and stratigraphic distribution of seismically detected injected sands improve our ability to assess the risk and opportunities associated with exploring the Palaeogene succession. 3D seismic reveals the reflection character, geometric variability and spatial distribution of seismic anomalies. A series of seismic facies interpreted as injected sandstones are identified, and their spatial distribution varies with stratigraphic position. They range from laterally extensive (up to 160 km2) compound units of chaotic seismic facies dominating the lower section, to smaller (~0.1 km2) isolated conical anomalies in the upper section. Lithology and fluid content of the injected sands is determined from analysis of well data. Porous and cemented sand units range in thickness from a few centimetres to several tens of metres. Water, gas and oil have been encountered in these sands. Seismic modelling analyses the variability in reflection character, and links the seismic and well observations. Mapping of injections improves our understanding of their implications on 1) leakage of hydrocarbons, 2) increased reservoir volume, 3) unusual HC contacts, 4) migration from Palaeocene into shallower traps, with either in-situ reservoir sands or reservoirs formed by injected sands. The results of this study improve our understanding of the risk and opportunities associated with the deliberate search for hydrocarbons in injected sands.