Three-dimensional physical simulation experiment study on carbon dioxide and dissolver assisted horizontal well steam stimulation in super heavy oil reservoirs

There is abundant super heavy oil resource in the world, however, due to the very high viscosity and density, conventional steam stimulation process will result in high steam injection pressure and small heating area, leading to very bad development effect. To improve the development effect of steam injection in super heavy oil reservoirs, a compound stimulation enhanced thermal recovery technology is proposed. Steam injection is conducted through horizontal well assisted by carbon dioxide and oil-soluble composite dissolver, so this kind of technology is called HDCS for short. HDCS technology synthetically utilizes the physical and chemical characteristics of dissolver, carbon dioxide and steam, so that viscosity reduction, mixing and mass transfer, increasing energy and assisting cleanup of the three components are combined. In this paper, three-dimensional thermal recovery physical simulation experiment apparatus is used to conduct the comparison experiments between steam stimulation and HDCS stimulation, to analyze the development advantage and mechanisms of HDCS stimulation. Experimental results indicate that HDCS stimulation realizes the rolling replacement of viscosity reduction effect of dissolver, carbon dioxide and steam, keeping the oil in steam front with a low-viscosity, and enlarging the viscosity reduction range of super heavy oil by steam injection. Besides, the dissolver injection beforehand decreases the subsequent steam injection pressure, and the dissolution and release of carbon dioxide in super heavy oil can complement the reservoir energy. Compared with the condition after conventional steam stimulation, after HDCS stimulation the steam has larger swept volume and heating range, and the content of heavy component and viscosity of crude oil decreases by larger amplitude. The properties of super heavy oil are improved better than conventional steam stimulation. HDCS stimulation significantly improves the development effect of steam in super heavy oil reservoirs.