Miscible Flood from Inception: The Brassey Field Development, British Columbia, Canada

Abstract

The Brassey field, located in northeast British Columbia, Canada, is a dune sand reservoir, containing a volatile, under saturated oil. The "Artex" sand is approximately 12 feet thick and is interpreted to be part of a large aeolian complex. Primary recovery is uneconomic, so a miscible flood will be operated from inception. Development of this oil-wet reservoir required the simultaneous integration of petroleum engineering and geoscience disciplines. A British Columbia Provincial Government 24 month royalty holiday program encouraged the pursuit of an aggressive development plan. This resulted in final development drilling being conducted during the miscible flood facility installation. Development was started by implementing an extensive seismic acquisition and pulse testing/pressure transient program to determine reservoir boundaries and continuity. The ultimate well density, pattern design, and well location were altered prior to startup, based on this program. Fundamental reservoir engineering methods were applied in determining oil-in-place, performance predictions, and the necessary EOR process. Introduction The Brassey field is a Triassic stratigraphic trap in northeast British Columbia, Canada (Figure 1). In 1980, an areally-limited Artex sand reservoir was discovered, but a followup well proved to be dry, and interest in the area waned. In August 1987, another Artex well was drilled by Canadian Hunter Exploration Ltd., operator of a joint venture with BP Exploration. The well penetrated an overpressured Artex sand and blew penetrated an overpressured Artex sand and blew out for 24 days. A subsequent 3.5 mile stepout well was completed producing 2400 BOPD. Subsequent drilling has identified five separate Artex oil pools in the Brassey field (Figure 2). The field is approximately 60 miles from the nearest oil pipeline, and 20 miles from the nearest gas tie-in point. Commercial production will start in August 1989, simultaneous with the initiation of a miscible flood. The reservoir is at a depth of 9850 feet. The Artex is a thin aeolian sand and exhibits excellent reservoir properties. Brassey oil is a volatile undersaturated fluid. The fluid and formation properties have been evaluated extensively to enhance the understanding of this complex system. In 1986, the British Columbia Provincial Government initiated a royalty exemption incentive program to promote exploration and development drilling. In order to qualify for 24 months of royalty-free status, a well had to be capable of production by June 30, 1989. The program limits operators to December 31, 1991 to program limits operators to December 31, 1991 to produce the 24 royalty-free months. Crown produce the 24 royalty-free months. Crown royalty in British Columbia is normally about 30 percent of wellhead revenue. Brassey field percent of wellhead revenue. Brassey field development drilling was conducted simultaneously with the implementation of the miscible flood scheme, as encouraged by the incentive program. The development was a team effort requiring a detailed geological description. It involved a reservoir study incorporating reservoir simulation and pressure transient analysis, extensive laboratory support including special core analysis and PVT testing, and an operating strategy complementing the results. P. 279