Feasibility of In-Situ Combustion in the SAGD Chamber

Abstract

Summary Steam-assisted gravity drainage (SAGD) is a commercially successful bitumen-recovery method that has transformed some of the vast Canadian oil-sand deposits into recoverable reserves. Several SAGD projects have been developed in northern Alberta in the past few years, and many more are in the planning stages. As the projects mature, new operational problems are revealed, demanding new solutions. Because of operational restrictions, it is almost impossible to have the same growth rate in all steam chambers in a SAGD pattern. Hence, interference between a mature chamber and an adjoining immature chamber can become a problem. Steam leakage from the immature chamber into the mature chamber reduces the thermal efficiency of the project and requires a solution to prevent the steam dissipation. Filling the mature chamber with combustion gases is a possible solution for this problem. Carrying out in-situ combustion (ISC) in the mature chamber not only would create the needed combustion gases in the chamber, but also could recover a substantial part of the residual oil in the mature chamber. It is also likely that the combustion would create a reduced-permeability coke (toluene insoluble fraction) zone around the mature chamber, thus isolating it from the rest of the reservoir. To evaluate the merit of this idea, an elevated-pressure experiment was conducted using a 2D physical model. The conventional SAGD process was conducted in the model to develop a steam chamber. Air was then injected through a horizontal well near the top of the model into the SAGD chamber, and a combustion front was established around the air-injection well. By operating combustion in the depleted chamber, residual oil was mobilized and produced. Additional oil recovery was attained by more than 20% over the SAGD operation as a bonus. Initiation and propagation of combustion were confirmed by a large increase in the temperature in the combustion zone. After unpacking the model, it was found that a coke layer formed around the perimeter of the chamber.