Experimental investigation on improved vertical sweep efficiency by steam-air injection for heavy oil reservoirs

Abstract Steam injection is one of the most widely used technique for heavy oil recovery. There are few laboratory experiments to investigate how to decrease the negative effect of steam override in thick heavy oil reservoirs, thus increasing the vertical sweep efficiency and further improving oil recovery. In this paper, a three-dimensional physical model was introduced to study the sweep efficiency of steam injection and steam/air injection in reservoirs with different rhythms. The mechanisms of improved vertical sweep efficiency by the hybrid injection of steam and air were also analyzed by monitoring the real-time temperature and liquid production of the 3D model. The experimental results indicated that as pure steam was injected, the sweep area mainly located in the upper part of the model. The sweep area decreased from the top to the bottom, and the same to liquid production. The steam override was most serious in negative-rhythm reservoir, followed by the homogeneous and positive-rhythm reservoirs. As steam and air were coinjected, the vertical sweep efficiency of different-type reservoirs was improved to different degrees. The liquid production of in the upper part decreased while that in the lower part increased, among which the liquid production increase at the bottom of negative-rhythm reservoir was most significantly. The investigation of this paper was beneficial to visually recognize steam override by steam injection and provided a guidance to improve the vertical sweep efficiency with the hybrid injection of steam and air in thick heavy oil reservoirs.