The Captain Field, Block 13/22a, UK North Sea

Abstract

The Captain Field is located in Block 13/22a in the Western Moray Firth Basin of the UK North Sea, 80 miles NE 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 consist of turbidite sandstones of Lower Cretaceous age which have been informally subdivided into two stratigraphic units comprising the Upper and Lower Captain Sandstones. At the base of the preserved Jurassic section the Heather Sandstone, Oxfordian in age, provides a secondary reservoir. Reservoir quality is uniformly excellent in the Lower Cretaceous with in situ, Klinkenberg corrected permeability averaging 7 Darcies and porosity in the range 28-34%. The reservoir is generally poorly consolidated sandstone with the depth to the crest of the field at -2700 ft TVDss. The reservoirs contain a total oil-in-place of 1000 MMBO. The Upper Captain Sandstone has a small associated gas cap containing 16 BCF gas-in-place. The oil is heavy, by North Sea standards, with oil gravity ranging from 19° to 21° API and has high in situ viscosity, 150 to 47 cP, at the mean reservoir temperature of 87°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 8000 ft, are drilled 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). The field is being developed in two phases, Area A and Area B. First oil production commenced from the Captain platform in March 1997 from Area A and the field now produces at between 50000 and 70000 BOPD. Area B development is now underway with first oil planned for December 2000. Completion of this phase of the development will increase the plateau production rate to 85000 BOPD.

Lower Cretaceous reservoir development in the North Sea Central Graben, and potential analogue settings in the Southern Permian Basin and South Viking Graben

“…Tectonic activity furthermore modified the region's bathymetry and redirected sediment transport fairways (Jeremiah 2000;Aas et al 2010). These deep marine sandstones represent Lower Cretaceous reservoirs in stratigraphic or combination structural/stratigraphic traps in for instance the Britannia, Scapa and Captain fields (McGann et al 1991;Jones et al 1999;Pinnock et al 2003).…”

Carbon dioxide storage in the Captain Sandstone aquifer: determination of in situ stresses and fault-stability analysis

“…The pore-pressure measurements are slightly above an assumed hydrostatic gradient of 10 MPa km -1 from the surface level, but as the Lower Cretaceous penetrated by these wells contains hydrocarbons, and given the lack of information regarding brine salinity variations with depth, a porepressure gradient of 10 MPa km -1 to the surface is assumed over the wider area. Despite the history of oil and gas production from the Captain Sandstone, widespread pressure depletion of the reservoir pore pressure is unlikely in the area west of the Kopervik Fairway due to pressure maintenance in the Captain and Blake oil fields (Du et al 2000;Pinnock & Clitheroe 2003). Owing to the good fit of the assumed gradient to the observed data, the variation in the porepressure gradient is expected to be small and should not significantly affect the results of the fault-stability analysis.…”

The performance of leaching experiments to assess the potential mobilization of trace elements during CO2 injection

“…The Captain Sandstone Member is a Lower Cretaceous mass-flow sandstone-dominated unit of up to 200 m thickness (Pinnock et al, 2003) covering c. 4000 km 2 (from maps in SCCS, 2011). The sandstone forms the reservoir for several commercial hydrocarbon fields, including the Captain Field.…”

“…The sandstone forms the reservoir for several commercial hydrocarbon fields, including the Captain Field. The porewaters within the Captain Sandstone Member are below seawater salinity (12 -25,000 ppm TDS; Pinnock et al, 2003), and have been routinely discharged into the North Sea during hydrocarbon production. The Captain Sandstone Member in the Blake Field, the source of the experimental samples, is reported to be at 56°C and c. 330 bars pressure (Melvin et al, 2008), representing a significant overpressure.…”