Abstract

An inverted nine spot waterflood pattern was selected and initiated in Boundary Lake Unit No. 2 in 1965. Following indications of gas/oil ratio response, it was estimated that even with full gas/oil ratio control, production capacity of the Unit would still be less than half of the established waterflood allowable. Infill drilling was selected as a means of increasing productivity and accelerating recovery.

Reservoir simulations were performed to establish the optimum location of infill wells. Based on these studies it was concluded that wells should be located at one third of the distance between the corner and side wells of a pattern.

Included in the paper is a review of pre-infill unit performance as well as performance of the infill wells. A total of 42 successful wells were drilled which contributed to a more than threefold increase over pre-unit production levels.

Introduction

The Boundary Lake Triassic oil field in northeast British Columbia, Canada, as shown in Figure 1, was discovered in 1954 with the drilling of Texaco NFA Boundary Lake A-1. The pool, however, was not extensively developed until 1962 following completion of a pipeline connection. In early 1963 reservoir studies indicated that pressure maintenance would be required to offset future increases in gas/oil ratios and to enhance the relatively low primary recovery. The northern half of the pool was unitized in 1964 and an inverted nine spot pattern waterflood was implemented in May of 1965 following completion of a successful pilot waterflood. The specific pattern was selected to minimize loss of production through well conversions and to utilize the indicated high well injectvities. Following indications of gas/oil ratio response, a review of well productivity indicated that Boundary Lake Unit No.2 would be capable of producing about 10,200 BOPD or 45 percent of the waterflood allowable. Since markets existed for additional crude and predictions indicated producing lives in the order of seventy years, infill drilling was investigated as a means of accelerating production from the Unit.

Various infill configurations were investigated with a 2-D reservoir simulator. Infill wells in all cases were located between the corner and side wells of an inverted nine spot pattern. It was concluded that locating infl11 wells at one third the distance from the corner to side well would result in a modest improvement in recovery and delayed water breakthrough compared to infill wells located nearer to the Side wells.

A total of 42 successful infill wells were drilled during the period from late 1968 to early 1971. As a result of waterflood operations gas/oil ratios have been reduced to near solution COR levels. Pressure maintenance coupled with infill drilling has more than tripled unit production to a peak of 13,400 barrels of oil per day compared to pre-unit levels of approximately 4,000 barrels of oil per day.

GEOLOGY AND DEVELOPMENT

The Boundary Lake zone reservoir is a porous carbonate body within the Triassic Schooler Creek group approximately 250 feet below the Triassic top or at a total depth of 4,200 feet (l,800 feet subsea).

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