Optimization of the SAGD Preheating for the Athabasca Oil Sands Reservoir with a Water Transition Zone

In oil sands reservoirs with a water transition zone, steam assisted gravity drainage (SAGD) well-pairs are drilled at least 5m above the water transition zone to avoid decreasing the thermal efficiency of the steam and the resulting reduction in SAGD productivity. This renders a significant amount of oil in the excluded lower net reservoir zone unrecoverable. However, a transition zone with high water saturation is favorable for steam flow, allowing more heat to be transferred to the reservoir during steam injection. This allows for the faster completion of the preheating stage, which is a non-productive period of SAGD, and the early start-up of production stage, which improves productivity. In this study, through a sensitivity analysis of various preheating methods and operating conditions according to the drilling elevation of the producer, we identify sensitive operating conditions in the preheating stage and propose an optimized operation of the SAGD preheating stage and recovery improvement by utilizing the flow characteristics of the transition zone, if it exists.