Experimental Study on Improving SAGD Performance in Ultra-Heavy Oil Reservoirs by Flue Gas Assistance

Abstract

Steam assisted gravity drainage (SAGD) is an advanced technique for ultra-heavy oil recovery that generally yields high oil recovery factors. However, in the mid-to-late stages of SAGD operation, several issues emerge, including severe steam override toward the upper oil layer, a low oil-to-steam ratio, and substantial heat losses, all of which impair overall performance. Therefore, effective improvement strategies are urgently needed. In this work, laboratory experiments were carried out using a physical simulation system, a PVT analyzer, a spectrophotometer, and other instruments to examine how flue gas affects the properties of reservoir crude oil, as well as the heat losses to overlying formations after flue gas injection, the evolution of the steam chamber morphology, and production behavior. The results show that injecting flue gas during SAGD can markedly lower the viscosity of reservoir crude oil, improve its flowability, enlarge the steam swept zone, and boost the elastic energy of the formation. Compared with the conventional SAGD process, the flue-gas-assisted SAGD method slows the vertical propagation of the steam chamber while accelerating its lateral expansion, thereby suppressing steam override. The flue gas accumulates above the steam chamber, creating an insulating layer that reduces heat loss into the overlying strata and enhances thermal efficiency. By co-injecting flue gas, the required steam volume is reduced, the oil-to-steam ratio is increased, and the overall development outcome is improved. Comprehensive analysis indicates that flue gas assistance is an effective approach to enhancing SAGD performance in the later stages.