The East Swan Hills Unit Waterflood Optimization Study: A Multi-Disciplinary Approach

Abstract

Abstract The East Swan Hills Unit No. 1 is located on the eastern flank of the Swan Hills Beaverhill Lake "A" and "B" Pools. The reservoir is now in an advanced stage of depletion like many of Alberta's oil reservoirs. Optimization of a geologically complex reservoir, such as is found in the Beaverhill Lake, is a major undertaking and requires a multi-disciplinary approach. To evaluate waterflood performance a study consisting of petrophysical data reduction, geological mapping, spreadsheet analysis of recovery and reservoir simulation was carried out. This paper highlights three major contributions which were essential in the analysis.The significance of geological mapping which has identified layerirlg/ heterogeneity within the Swan Hills formation and the potential in the underlying Slave Point formation.Manual waterflood calculations have enhanced the understanding of the reservoir and confirmed Slave Point production, prior to proceeding with numerical simulation.The methodology used to simulate a multilayer reservoir under waterflood is described. Incremental recovery is predicted by improved waterflooding in selected areas of the Unit. A program consisting of injection testing, production testing, single well tracers and selective cased-hole logging has been designed, prior to proceeding with field implementation. Introduction The East Swan Hills Unit is located in the province of Alberta approximately 200 km northwest of Edmonton as shown in Figure 1. This field was discovered in early 1963 with primary production commencing in the same year. Commingled production is derived primarily from the Swan Hills formation as well as from the underlying Slave Point formation. There are 76 wells in the Unit. The field was produced by primary fluid expansion drive since there was no gas cap or no acquifer support. Unitization occurred in 1967 for the purposes of waterflooding. Peak oil production of 1959 m3/day occurred in 1969 after which oil production declined at 20% per year. An aggressive workover program was initiated in 1984 to arrest the production decline. The program was successful as indicated by the oil production rate which has remained flat over the last five years. The current oil rate is 100 m3/day with a water cut of 90%. As the Unit was approaching its economic limit, it was concluded that a detailed reservoir engineering study should be carried out to determine if improved waterflooding could be achieved. This paper documents the results of the study and the methodology used.. The paper has been divided into three main sections: Geological - Petrophysical Studies, Conventional Reservoir Engineering Review and Reservoir Simulation. The Optimization Program developed from these three studies is then discussed. Finally, the conclusions of the paper are presented. Geological- Petrophysical Studies Method of Study When the East Swan Hills pool was being developed and unitized a fairly simple geological model was used. Two reservoirs, the Swan Hills member and the Slave Point member were recognized, These became known colloquially as the "Light Brown" and "Dark Brown". respectively. The Light Brown member was known to be of substantially better reservoir quality; hence most development was aimed at this pay.