The Wizard Lake D-3A Pool Miscible Flood

Abstract

A hydrocarbon miscible flood was initiated in the Wizard Lake D-3A Pool in late 1969. The scheme involved placing a slug of LPG at the gas-oil interface, displacing it vertically down-ward with dry gas while injecting water to stabilize the oil-water contact. Ultimate recovery is expected to be 51.33 × 106 m3 (323 MMSTB), 84 percent of the original oil-in-place and 10.9 × 106 m3 (69 MMSTB) higher than under primary depletion. The Wizard Lake D-3A pool, located in central Alberta, is one of nine Devonian reef pools connected to the Cooking Lake aquifer. pools connected to the Cooking Lake aquifer. It is a dolomitized bioherm reef with a maximum original oil zone of 197.5 metres (648 feet). The pool was considered an ideal candidate for a miscible displacement process because of its vertical relief, small areal extent and the absence of any barriers that would be detrimental to displacement of the slug. This paper reviews the implementation, monitoring techniques and performance of the miscible flood scheme. Introduction The Wizard Lake D-3A pool, located 55 kilometres (35 miles) southwest of Edmonton, Alberta as shown in Figure 1, was discovered in April, 1951 with the drilling of Texaco Wizard Lake Crown B-1 in 12-22-48-27 W4M. The pool, drilled on 40 acre spacing, was fully delineated by the late nineteen fifties. The reservoir is a dolomitized bioherm reef of Devonian age which is part of a prolific chain of Leduc member reefs appropriately known as the Golden Trend. The productive horizon attained a maximum recorded height of 197.5 metres (648 feet) above the Cooking Lake aquifer in which reef growth was initiated. The Cooking Lake aquifer pinches out to the west but is extensive in the other three directions. This aquifer is very active and is common to other oil and gas accumulations which give rise to interference between pools (Figures 2 and 3). The oil column covered an area of 1 507 hectares (3,725 acres) at the original oil-water contact of 1 230 metres subsea (4,034 feet subsea). Figure 4 presents a structure contour map of the top of the pool based on the gross reef section. The initial oil-in-place is estimated to be 61.2 × 106 m3 (385 MMSTB) with some 6.5 × 109 m3 (231 BCF) of solution gas dissolved in it. The primary recovery mechanism, identified as a combination gas expansion, water drive and gravity segregation, was allowed to continue until 1969 when a slug type hydrocarbon miscible scheme was initiated (Figure 5). In 1965, a secondary gas cap began to form and by the end of 1969 there existed a 24 metre (78 foot) gas column containing approximately 152 × 106 m3 (5.4 BCF). Also, by 1969 the oil-water contact had risen 15 metres (50 feet) leaving an oil column of 158.5 metres (520 feet). The performance of this reservoir since 1969 provides a case history of crestal injection and vertical displacement for miscible processes. RESERVOIR ROCK AND FLUID PROPERTIES The Wizard Lake D-3A pool is a dolomitized carbonate reservoir and the porosity, a combination of matrix and vugular, is well developed throughout the reef interior.