The Alba Field: A Middle Eocene Deep Water Channel System in the UK North Sea
The end of the appraisal stage of the Alba field has opened the way for the first development of a middle Eocene reservoir in the North Sea.
The Alba field is located in the Witch Ground graben between the Fladen Ground spur to the north and the Renee ridge to the south, entirely in UKCS (U.K. continental shelf) Block 16/26. In 1984, oil was discovered in a sand within the middle Eocene Alba Formation at a depth of 6100 ft (1860 m) subsea. Seventeen subsequent wells, including sidetracks, have been drilled to appraise the discovery. This drilling indicates that the Alba field is a stratigraphic trap covering an area of approximately 3400 ac (1375 ha).
The sands represent a brief interruption in the hemipelagic sedimentation that dominated this part of the Witch Ground graben during the middle Eocene. Sediment was supplied intermittently from a shelf area to the northwest, into a deep-water environment. Well correlations, seismic mapping, and core analyses indicate that these sands were deposited from turbidity flows as part of a constructional channel/levee complex, within a mud-rich, shelf-sourced, submarine channel system. The cap, updip, and lateral seals of the reservoir are shale.
The reservoir is predominantly a homogeneous, very fine to fine-grained, unconsolidated sand. The average reservoir porosity is 35% and the average permeability is 2.8 darcys. Oil in place is estimated to be 1.1 billion bbl of 20° API biodegraded crude oil.