Waterflood Behaviour of the Low-Gravity Wainwright Pool

This paper outlines the development and performance of the Wainwright fieldin east-central Alberta, where the Wainwright sand produces 20–22-gravity oilfrom a depth of approximately 2,100 feet. The field was the first heavy oilpool in Alberta in which pressure maintenance by waterflooding was undertaken.Although pressure maintenance has been in progress for only three years, theperformance during this period is indicative of the project's success. To forestall the adverse effects of rapid pressure decline and increasinggas-oil ratios in this solution gas drive reservoir unitization as aprerequisite to full-scale pressure maintenance was instituted. The field wasunitized as five separate units, with pressure maintenance conducted by two operators. To the end of 1965, the cumulative oil production from the field wasapproximately 8,600,000 barrels. In December, 1965, oil production was 4,560barrels per day, with pressure maintenance accounting for approximately 70 percent of this. The ultimate recovery (primary plus waterflood) for the field hasbeen estimated at 31,300,000 barrels, which is more than double the recoveryanticipated by natural depletion. Introduction The Wainwright Sand reservoir is located on the southwestern flank of theheavy oil region of east-central Alberta. This is shown in Figure 1. Thefield was the first heavy oil pool in Alberta in which pressure maintenance bywaterflooding was undertaken. The reservoir was developed on 20-acre spacing, and the unitized areas include 202 producing wells. Reservoir characteristicsare included in Table I. The reservoir has a gas cap and an aquifer. During primary depletion, itproduced principally as a solution gas drive reservoir with some gas capexpansion. This was evidenced by rapidly declining reservoir pressures andincreasing gas-oil ratios. Although some water was produced from down-dip wellsalong the southwest rim of the present producing limits, and there was anoticeable encroachment of water before unitized operations began, there was noappreciable recovery resulting from the water influx. Early in 1959, it wasobvious that the natural energy of the reservoir was going to produce only asmall fraction of the original oil-in-place.