Abstract

The Captain Field is located in Block 13/22a in the Western Moray Firth Basin of the UK North Sea, 80 miles northeast of Aberdeen in a water depth of 340 ft. Hydrocarbons are trapped in two geographical regions, the Main and Eastern closures, both with a significant stratigraphic pinchout component. The principal reservoirs are the Lower Cretaceous Upper and Lower Captain Sands, which are predominantly of turbiditic origin. Reservoir quality is uniformly excellent with in situ permeability averaging 7 D and porosity in the range 28-34%. The reservoir is largely unconsolidated sandstone with the depth to the crest of the field at "2700 ft TVDSS. The reservoirs contain a total oil-in-place of 1500 MMBO. The Upper Captain Sand has a small associated gas cap containing 29 BCF gas-in-place. The oil is heavy, by North Sea standards, with oil gravity ranging from 19 degrees and 21 degrees API and in situ viscosity between 88 and 47 cP, at the mean reservoir temperature of 87 degrees F. The fluid properties and offshore location necessitate the employment of innovative horizontal drilling methods, completion design and artificial lift technology in order to achieve an economically viable field development. Extended reach horizontal wells, with reservoir completion lengths of up to 6500 ft, are proposed for all oil producers and water injectors. Development risks were significantly reduced following two appraisal drilling campaigns in 1990 and 1993 culminating with the successful drilling and extended testing of a prototype horizontal field development well (13/22a-10). First oil production commenced from the Captain platform in early 1997.

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