Regional Rock Physics For Exploration in the West of Shetlands

Oil and gas has been found in clastic reservoirs of Eocene, Palaeocene, Cretaceous and Jurassic age and in fractured basement of Devonian/Carboniferous age in the West of Shetland area. The majority of discoveries have been in Palaeocene age reservoirs. Successful prospects tend to be in combination structural/stratigraphic plays which rely on pinch-out or facies changes up dip to the east as seen at Laggan. Most of the wells targeting Tertiary prospects were drilled on amplitude or AVO anomalies. Roughly three quarters of these wells failed to find hydrocarbons. A rock physics analysis of 35 wells in the WOS was performed on a well by well and subsequently regional basis. The analysis identifies the possibility for additional mechanisms which may help to explain the amplitudes encountered during seismic interpretation in terms of not only rock and fluid properties, but of these properties within the context of complex burial and uplift histories and changing pressure regimes. The study utilises geological reports, digital well logs, pressure data, core data, biostratigraphy, AFTA analysis and temperature data along with rock physics techniques to enhance our understanding of the WOS petroleum system.