Depositional Setting and Reservoir Geology of Kuparuk River Oil Field, North Slope, Alaska: ABSTRACT

Abstract

The Kuparuk River field is located approximately 20 mi (32 km) west of the Prudhoe Bay field and produces from the Lower Cretaceous Kuparuk River formation. The lower member of the Kuparuk is a sequence of interbedded sandstone, siltstone, and mudstone. Individual sandstone beds in the lower member are up to 5 ft (1.5 m) thick and consist of fine-grained, well-sorted quartzarenite. The basal part of the lower member contains five sandstone-rich cycles that prograde to the southeast. Each individual cycle strikes northeast-southwest and is up to 80 ft (254 m) thick, 40 mi (64 km) long, and 15 mi (25 km) wide. The lower member sandstones are interpreted to be storm deposits derived from a northerly source and deposited on a broad marine shelf. The upper member was deposited on an erosional unconformity and contains two sandstone intervals. These sandstone intervals are quartzose, glauconitic, very fine to coarse grained, poorly to moderately sorted, and intensely bioturbated. Both upper member sandstones are interpreted to have been deposited as subtidal sand bodies. The upper and lower member sandstones have similar average porosities (23%), but the average permeability of upper member sandstone is considerably higher than the average permeability of the lower member. Natural fractures in siderite-cemented zones enhance the permeability of the upper member sandstone. Reservoir performance indicates that permeability is greatest in a north-south direction in upper member sandstones, and that a north-south directional permeability may also exist in lower member sandstones. North-south-oriented line-drive waterflood patterns will be utilized in areas where a north-south directional permeability is suspected. End_of_Article - Last_Page 674------------