Abstract

In our paper presented at the CIM 1993 Annual Technical Conference in Calgary, we have outlined the design principles of the Combustion Override Split production Horizontal-well Process (COSH). This process has been conceived to combine the beneficial features of gravity drainage, horizontal wells, split production of gas and liquid phases and low energy costs. Because of its unique well arrangement, COSH is expected to provide much better recovery performance than standard combustion processes and eliminate most of the common combustion related problems. Furthermore, its high degree of operating freedom permits the operator to tailor the process parameters to suit the conditions of aarge variety of conventional, heavy oil and oil sand reservoirs. In this paper, simulation results will be resented to demonstrate how this may be achieved in a heavy oil reservoir.

Introduction

In the design of heavy oil and oil sands thermal recovery processes, one of the greatest challenges is to place the heat at the desired reservoir location. For example. in cyclic steam stimulation projects, steam has to be injected at fracturing pressures to achieve reasonable injectivities. However, heat distribution is usually limited to the vicinity of the fractures. In conventional steamflood and fireflood projects, injectors and producers are separated by large cold Zones. The propagation of heat is very slow even though high Injection pressures are used. It often takes a long time to see thermal effects at producers and the heat distribution is usually uneven because of reservoir heterogeneity. The heat distribution problem is particularly bad in conventional fireflood projects. The heating process is extremely difficult to control once gas communication channels are established in the reservoir.

Recent progress in horizontal wells has opened up tremendous opportunities for the development of gravity assisted recovery methods (References 1,2 and 3). Since high differential pressures are not needed to force thejection medium into the reservoir, the gravity dominated processes are less susceptible to reservoir quality variations than the pressure dominated processes. The gravity assisted processes are therefore less problematic, easier to control and more predictable.

The Combustion Override Split-production Horizontal-well (COSH) process was conceived by combining the high recovery potential of gravity drainage with the high energy efficiency of combustion. Because of its unique split-production design, most of the combustion related problems can, in principle, be minimized. The operator can have a high degree of freedom to control the operating conditions and optimize the production performance. This paper will present simulation results to illustrate how the COSH operating parameters may be controlled to optimize the performance results.

In March 1994, Alberta Energy Oil Sands and Research Division (formerly AOSTRA) and the industry formed a task force to further assess and develop the COSH Process he focuses of the task force are: to carry out a laboratory research program and to perform a pilot project scoping study. Since then, significant progress has been made. A 3-dimensional physical model project proposed by the niversity of Calgary has been reviewed. Simulation work has been conducted for Athabasca, Cold Lake, Provost and Battrum to determine the commercial potential of COSH in these areas.

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