The Ugnu deposit, located on the North Slope of Alaska, contains more than 6 billion bbl [954 × 106 m 3] of oil in place (OIP) in the Kuparuk area. The oil has been biodegraded. At reservoir temperature, the dead-oil viscosity varies from 100,000 to 10,000,000 cp [100 to 10 000 Pa·s]. The paper provides reservoir and geological descriptions of the resource and discusses the key aspects affecting development. These aspects include high-temperature formation damage, the projected production performance, and the design considerations for injecting steam through a thick permafrost interval.
The Ugnu oil sands overlie the West Sak and Kuparuk reservoirs on the Alaskan North Slope. The thickest portion of the Ugnu reservoir is located over the northern portion of the Kuparuk River Unit (KRU) (Fig. 1). The resource extends under the Beaufort Sea to the west and into the Milne Point Unit in the east.
Although the Ugnu was discovered more than 20 years ago, until recently its database was extremely limited and consisted of only a few cores and logs taken mostly during drilling to the Kuparuk, the producing zone in both the KRU and the Milne Point Unit. In the early 1980's, delineation and development drilling for the deeper Kuparuk formation provided an initial estimate of the areal extent of the resource. At that time, it was thought that the Ugnu contained between 11 and 19 billion bbl [1.7 and 3 × 109 m3] of oil having a gravity of 8 to 11° API [1.0 to 0.99 g/m3] and a viscosity between 10,000 and 100,000 cp [10 and 100 Pa·s].
In the mid- to late 1980' s, drilling of the northern Kuparuk drillsites delineated areas of the deposit with a thick, vertically contiguous sand interval (Fig. 1). Then, an extensive study was undertaken between 1988 and 1990 to quantify the resource quality and to evaluate the development potential of this resource. As part of that program, a dedicated Ugnu well (Well DS2-0B1) was drilled and injection tested in 1989. This paper describes the main findings from that study.