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Reservoir case studies |
1 Central North Sea Field Development Team, BP plc, Farburn Industrial Estate, Aberdeen AB21 7PB, UK (e-mail: casabid{at}bp.com)
2 BP Azerbaijan, BP plc, Chertsey Road, Sunbury Upon Thames TW16 7LN, UK
The Machar Oil Field is a fractured Chalk Group reservoir, of Late Cretaceous age, developed above a salt diapir in the Central Graben of the UK Continental Shelf. From 1998 to the present the field has been produced through a water injection scheme sanctioned on the basis of data acquired during a water injection pilot test carried out in 1996. After three years of strong production, performance was affected by an unexpectedly fast rise in water-cut. This prompted the field management team to review the available data and rebuild the reservoir model to serve as the basis for a revised development plan. This paper describes the data used and the lines of evidence followed by the team in order to identify, describe and model the key subsurface characteristics, and related uncertainties, controlling field behaviour and impacting reservoir management and development options. Key uncertainties are the nature and flow significance of an extensive network of faults, the presence, nature and significance of a system of sub-seismic background fractures and the role played by the matrix capillary and wettability properties in controlling recovery through imbibition levels and rates. The successful integration of a wide range of subsurface static data, such as biostratigraphy, fracture identification, stress identification, seismic fault mapping and dynamic data, such as production logs, pressure build-up tests and tracer recovery, resulted in improved reservoir characterization. The ensuing new reservoir model explained the field historic performance and suggested two redevelopment options, which were sanctioned and executed between 2003 and 2004, and resulted in improved field performance.
