Numerical Modelling Of Cyclic Steam Stimulation In Cold Lake Oil Sands
Authors: Pethrick W.D. , Sennhauser E.S. , Harding T.G. 
Published: March 2010

Prior to start-up of the Wolf Lake Project in the Cold Lake oil sands, two-dimensional areal simulation studies were conducted using a fully implicit thermal simulator, with the objective of optimizing the operating strategies/or the different well spacings used in the project. Fractures, required to achieve reasonable steam injection rates in the field, were modeled by a line of thin grid blocks with high transmissibility in the preferred fracture (on-trend) direction. Single well optimization studies determined steam slug sizes and production period lengths for eight cycles of operation. Using the single well operating strategies, multiple well studies were conducted. These indicated that interactions among neighbouring wells significantly affected the recovery process. Fractures linking injection and production wells cause high water production. Pressure support via matrix communication results in increased production rates in wells not linked by fractures.

Introduction

The Wolf Lake Project (1,2), jointly owned by Petro-Canada and BP Resources Canada Limited and operated by the latter, is a small-scale commercial project designed to produce bitumen at an average rate of 1100 m3/d for a period of 25 years. The project is located in northeast Alberta on BP's Marguerite Lake lease (Fig. I). Approximately 1100 hectares of the lease will be developed. Also shown in Figure 1 is the location of the Phase A pilot(2,3). Phase A results justified commercial development and the pilot is currently being operated to collect data to Justify the incorporation of oxygen combustion into the Wolf Lake Project in the early 1990s.

Bitumen is produced from the Lower Cretaceous Clearwater Formation(4) at a depth of approximately 460 m. Cyclic steam stimulation is used to heat and recover the highly viscous bitumen. Steam is injected above formation fracture pressure in order to attain reasonable injection rates. Wolf Lake Project wells are expected to undergo six or seven injection and production cycles.

Before start-up, 224 wells were drilled from twelve central pads, or satellites(5). To maintain or exceed the target production rate of 1100 m3/d, new wells will be drilled as they are required. The average number of operating wells required tosustain production after the initial start-up period is expected to be around 250. Steam required for the stimulation process is generated at a central plant and distributed to the satellites and individual wells. The bitumen, gas and water production from the wells will flow through pipelines to the central plant where the bitumen is separated. The satellite layout and pipeline routing is shown in Figure 2.

Figure 3 shows the well location on the east side of the project area. Wells are predominantly in 220 m by 100m 5-spot configurations, although 330m by 80 m 5-spot, 270m by 120m 5-spot and 220 m by 50 m rectangular well spacings are also being tested. Future pads will utilize the optimum well spacing.

A pre-start up simulation program was conceived in early 1983 to assist in the design of the operating strategy for the project.