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Hamilton Oil Company Ltd, Devonshire House, Piccadilly, London W1X 6AQ, UK
The Douglas oil field lies entirely within UK Block 110/13, Licence P710, awarded in 1989 in the Eleventh Round to a group comprising Hamilton, Ultramar and Renown. Following the acquisition of Renown by Monument, Ultramar by Lasmo and the partial sale in 1993 of their interests to Powergen, the current group was established.
The Douglas oil field was discovered in 1990 by the second well on the block, 110/13-2. Appraisal wells 110/13-6 and 10 were drilled in 1991, 110/13-11 in 1992 and 110/13-13 in 1993. Annex B was awarded in October 1993 and first oil will be produced in 1995.
The reservoir for the oil is the Helsby Sandstone Formation of the Sherwood Sandstone Group. In Block 110/13 the Helsby Sandstone is divided into three members: Frodsham, Delamere and Thurstaston. The Frodsham and Thurstaston Members are dominated by aeolian processes. The Delamere Member is predominantly fluvial. The majority of oil initially in place is in the Frodsham Member.
Above the Helsby Sandstone Formation is the Mercia Mudstone Group (MMG), which acts as the seal for the reservoir. Unlike the Hamilton gas fields and the Morecambe gas fields, where the Rossall and Mythop Halite Formations lie in the first 1000 ft above the reservoir, in the Douglas area the only halite present is the Northwich Halite Formation, lying 1200–1500 ft above the reservoir. However, the mudstones of the MMG provide an adequate seal.
The source rock for the Douglas oil is the Dinantian/Namurian Holywell Shale Formation (see Armstrong et al. 1995) directly underlying Block 110/13, which
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