In the Pt. McIntyre area, the Kuparuk River Formation is stratigraphically complex. It consists predominantly of sandstone, pebbly sandstone, siltstone and sandy mudstone, and is characterized by rapid changes in thickness, lithology, and local diagenetic cementation. Two informal subdivisions, the lower and upper units, are recognized. The basal portion of the lower unit is tight, non-productive, silty sandstone, siltstone and sandy mudstone that are overlain by about 200 feet of porous, very fine- to fine-grained, well sorted sandstone. The thickness of the lower unit is relatively constant, suggesting it was deposited prior to faulting. The upper unit consists of interbedded, glauconitic, well to poorly sorted sandstone and pebbly to muddy sandstone. Local areas of siderite cementation and compaction reduce porosity and permeability, especially on the western side of the field where cementation forms a permeability barrier that contributes to hydrocarbon trapping. The upper unit is variable in thickness and is thought to have been influenced by syndepositional faulting.7
The overlying Kalubik Formation consists mainly of shale and shaly mudstone that also exhibits abrupt changes in lithology and thickness.8
The oil-bearing portions of the Kalubik Formation are restricted to the western portion of the Pt. McIntyre area.
The Pt. McIntyre reservoir is a faulted, gently north-plunging anticline that is bound to the south by the east-trending, large-displacement, down-to-the-north Pt. McIntyre fault. This fault was the primary control for Kuparuk deposition and preservation. North of the fault, Kuparuk sediments are thick and preserved; south of the fault, equivalent Kuparuk sediments are very thin to absent. Other controls on Kuparuk distribution were paleogeography and erosion truncation. Numerous moderate displacement normal faults cut the reservoirs. Fluid contact and pressure data indicate these faults are non-sealing.9
The Pt. McIntyre Oil Pool is trapped by a combination of structural and stratigraphic elements. To the south, the Pt. McIntyre fault juxtaposes reservoir rock against impermeable shale. The northern limit of the pool is established by structural dip. To the west, cementation of the reservoir sediments creates a permeability barrier in the upper portion of the Kuparuk, and to the east, structural dip and diminishing reservoir quality limit the extent of the accumulation.10
Average porosity for the Kuparuk River reservoir ranges from 19% to 25%. Average horizontal permeability ranges from 50 to 300 millidarcies in the Upper Kuparuk and 100 to 600 millidarcies in the Lower Kuparuk. Initial water saturation values for the oil column range from 16% to 65% and average 33%. Gas-cap initial water saturation is about 15%. Reservoir oil gravity is 27 degrees API, and the oil viscosity is 0.9 centipoise at the bubble-point pressure of 4,308 psia. The solution gas-oil ratio is 806 scf/stb, and the formation volume factor is 1.39 rvb/stb. Initial reservoir temperature ranges from 176 to 184 deg F at 8800' true vertical depth below sea level.11