A Series of Examples
1 August 2014

Crystalline basement provides the reservoir for a large number of commercial oil and gas fields in more than thirty countries, including major discoveries in the Sirte Basin, Libya (Nafoora-Aguila Field), offshore Vietnam (including the Cuu Long Basin; e.g. the Bach Ho Field - Cuong and Warren, 2009) and Yemen (Kharir, Sunah and Habban fields). In these examples basement reservoirs consist of variably fractured granites or granitegneiss with reservoir characteristics locally enhanced by strong weathering and/or hydrothermal alteration. These reservoirs are "buried hill" subconformity traps developed on deeply eroded basement highs or fault blocks sealed by onlapping and overlying claystones and shales; which include the hydrocarbon source. These fields bear comparison with oil discoveries made upon the flanks of the Viking Graben and along the Rona Ridge on the margin of the Faroe-Shetland Basin. The establishment of the Pilot Exploration Task Force, a joint Government/industry initiative, highlights the interest in fractured basement as an unconventional and under-explored plays on the UKCS. Recent and ongoing exploration and appraisal drilling in the West of Shetlands and Viking Graben areas demonstrates the potential of this play type, which may include one of the largest discoveries made on the UKCS in recent years. These include Lancaster and Whirlwind on the Rona Ridge and Cairngorm in the Viking Graben.