The Midnight Sun Oil Pool is located in and adjacent to the Prudhoe Bay Unit ("PBU").  It was discovered in 1997 by the Sambuca #1 exploratory well (later renamed PBU MDS E-100), and confirmed by the Midnight Sun #1 delineation well  (later renamed the PBU MDS E-101) in 1998.  This pool comprises an accumulation of oil and gas trapped within the Lower Cretaceous-aged Kuparuk River Formation ("Kuparuk") that correlate with the interval from 11,662’ and 11,805’measured depth (~8,000’ below sea level) in PBU MDS E-100.   The pool has low structural dip, good vertical permeability, contains a relatively large gas cap, and has gross sand thickness of about 110 feet. Free gas volume associated with the gas cap is estimated to range between 60 and 80 BSCF.  Total gas in place is estimated to be 100 to 130 BSCF.  Production from the pool began in October of 1998. 

Within the pool, the Kuparuk is complex, displaying rapid changes in thickness, sedimentary facies and local diagenetic cementation. At Midnight Sun, the Kuparuk is informally divided into lower and upper units. The lower Kuparuk unit is about 40’ thick, and is, in turn, subdivided into two lithologic intervals. The basal non-productive sandstone is discontinuous, ranging up to 5’ thick, and contains abundant glauconite and minor detrital shale. The overlying unit is continuous, very fine to fine grained, quartz-rich sandstone. Mean porosity and permeability in the reservoir-quality portions of the lower Kuparuk unit are 27.3% and 760 md, respectively. The upper unit ranges from 0’ to 70’ in thickness, and consists of poor to well sorted, glauconitic- and siderite-bearing sandstone interbedded with minor amounts of muddy siltstone. Changes in intergranular siderite cementation and compaction cause localized reductions in porosity and permeability.  In the upper unit,  mean porosity is 20.7% and mean permeability is 200 md. Structural and stratigraphic elements combine to trap this oil pool.  It is bounded to the N by the Sambuca fault, to the W by the Prudhoe Mid-Field Fault, to the S by the Prudhoe-bounding fault system, and to the E by an apparent stratigraphic pinch out. No oil-water contact has been observed, but heavy oil was encountered below a true vertical depth of 8,107’in PBU E-101. The areal extent of this heavy oil accumulation is uncertain. A gas-oil contact lies at 8,010’ true vertical depth subsea.  API gravity of the oil is about 25.5 degrees.