The Alba Field: evolution of the depositional model

Abstract

The Alba Field; discovered in 1984 by Well 16/26-5, is situated in UK Block 16/26, approximately 225 km northeast of Aberdeen. The field overlies the Mesozoic Witch Ground Graben, south of the Fladen Ground Spur, and north of the Renee Ridge. The main field is 9 km in length, elongate along a northwest-southeast axis. Field delineation was based upon 2D seismic data, the latest of which were acquired in 1988. Sixteen wells, inclusive of sidetracks, have been drilled to appraise the 16/26-5 discovery. Annex B approval was granted in 1991, and first oil production is expected in 1993.The Middle Eocene sands which comprise the reservoir at Alba display remarkable petrographic uniformity, and are thought to have been deposited by high-density turbidity currents. The presence of water-escape structures and sand injection features suggests rapid deposition and burial.Previous workers have favoured deposition of the reservoir sands within an aggradational channel/levee complex. This model was reviewed by the current authors to assess possible variations of sand quality and shale distribution, and their impact on reservoir performance. A revised model, based on interpretation of a 3D seismic survey acquired in 1989, re-examination of core, and a comprehensive review of recent literature on deep-water depositional processes, proposes that high-density turbidity currents rapidly deposited large volumes of petrographically uniform sand into a previously eroded channel-like feature. The erosional and depositional processes are interpreted to have been largely independent of one another.