Wizard Lake: Reservoir Quality As A Key To Successful Miscible Displacement

Abstract

Abstract The Wizard Lake D-3A pool, discovered in 1951, has been under a vertical gravity stable first contact miscible flood since 1969. In 1983, a tertiary extension to the miscible scheme was implemented. Ultimate oil reserves of 57.8 × 105 m3 or 86% of the original-oil-in-place (OOIP) are predicted for the pool of which 44.2 × 106 m3 is from primary recovery and 13.6 × 105 m3 is the result of miscible displacement. To date (August 1990), 51.9 × 106 m3 of oil or 77% OOIP has been produced. Introduction The Wizard Lake reservoir is one of a chain of Upper Devonian age Leduc reefs located in the Western Canadian Sedimentary Basin in Alberta (Fig. I). The Leduc reefs are aligned approximately north-south to form the Rimbey-Meadowbrook reef trend (Fig. 2). The Leduc reefs in this trend rest on a regionally extensive series of shallow water, platformal carbonate sediments (the Cooking Lake Formation). These form an active aquifer and the reservoirs in the Rimbey-Meadowbrook chain are hydraulically linked as a result. The Wizard Lake reservoir consists of the Leduc reef proper and the uppermost portion of the underlying Cooking Lake Formation. The entire reservoir has been dolomitized and as a result the pool in general has excellent reservoir quality. The Wizard Lake reef is encased in shales and variably argillaceous carbonates of the Ireton and Duvernay formations (Fig. 3), most of which are believed to represent terrigenous sedimentary basin in fill contemporaneous with Leduc reef growth. At the time of its discovery in 1951, the Wizard Lake reservoir was filled with oil to a depth of 1229.6 m subsea. The maximum thickness of the oil column in the pool was 196.5 m, and the pool contained an estimated 67 106 m3 of original-oil-in-place. Cumulative production through August 1990 is 51.9 × 106 m3. Historical Summary of Pool Exploration From 1951 to 1969, the Wizard Lake pool was produced under primary recovery which consisted of vertical water drive from the Cooking Lake aquifer influx with gravity segregation and solution gas drive. By 1954, a gas cap had formed. In 1969, a gravity stable vertical miscible flood was initiated with injection of a 75% HCPV solvent followed by push gas. The pool was repressured by gas and water injection to 14,480 kPa (gauge). The oil-water contact moved up to 1207 mss. This performance is reviewed in Reference 3. In 1983, a tertiary extension of the secondary miscible flood was initiated. Current miscible displacement is now occurring in the lower parts of the reservoir. To fully understand reservoir performance in this area, a geological model must be constructed. Geological Model of Reservoir Setting The geological model presented below is the result of a series of studies initiated in 1986. This work was greatly facilitated by new porosity log data —acquired since 1980 as wells in the reef were redrilled or twinned —and by data provided by the five flank wells drilled since 1987. Additional geological information was obtained from core data from the neighboring, analogous Bonnie Glen Leduc reef.