Introduction
The Sooner Unit area encloses approximately 1440 acres (Figure 1) and produces 40° API oil from the lower-most Upper Cretaceous D Sandstone. The sandstone reservoir was deposited in a fluvial and estuarine setting with the majority of clastic sediments being deposited in an erosional valley as sea level rose. The D Sandstone has an average net thickness of 17 ft at a depth of 6200 ft. Reservoir rock has an average porosity of 11.5 percent with a geometric-mean absolute permeability of 20 md to air from core study. The reservoir consists of several stacked, sandstone packages as shown in figure 2. The depositional environment of the reservoir has resulted in strong north-south anisotropy. North-south well pairs often demonstrate fluid communication while east-west well pairs do not.
Production from the D Sandstone was established in 1969 in the Sooner Field one mile east from the Sooner “D” Sand Unit (Sooner Unit) in section 27, T.8N., R.58W. Methods used for exploration and development in the area were geology from well logs and wildcatting. The field consisted of a single well until 1980, when four additional wells were completed. The first productive D Sandstone oil well within the confines of the current Sooner Unit boundary (NWSE section 28, T.8N., R58W.) was completed in December 1985. By 1988, the productive surface area of the Sooner Unit reservoir was defined at about 720 acres with wells spaced on regular 40- acre production units. The 1440-acre Sooner Unit was created in September 1989. At that time, the unitized area had produced 772,000 stock-tank bbl (stb) of oil and 3,000,000 mcf of gas. The reservoir did not have a gas cap or free-water contact. Negligible formation water produced during primary depletion. Estimates of original-oil-in-place (OOIP) at the time the Sooner Unit was formed ranged from 5,300,000 to 5,900,000 stb. Estimates of ultimate primary recovery of oil by the unitization technical committee averaged 900,000 bbl and ranged from 850,000 to 1,100,000 bbl. Current estimate of OOIP is 6,900,000 stbafter information from additional drilling and seismic data.
