W/O emulsions generated by heavy oil in porous medium and its effect on re-emulsification

Abstract

Water/hot water flooding and steam stimulation are usually used for heavy oil recovery. However, W/O emulsions are generated when heavy oil and water flow in porous medium of formations, which can seriously restrict the recovery effect in the middle or late stage. First, the influence of the W/O emulsion on efficient heavy oil recovery is analyzed by the production dynamics and produced fluid emulsified states of oilfields. Then, the W/O emulsion generation process during heavy oil entrapment and water flooding recovery was simulated. The effects of permeability, porous medium shearing distance and heavy oil viscosity on the emulsified state of W/O emulsions were studied. The properties of W/O emulsions were tested. Before reaching the final emulsified state, the lower the permeability and the longer the porous medium shearing distance, the more fully emulsified of the W/O emulsion. In the final emulsified state, the droplet sizes of the W/O emulsions generated by different viscosities of heavy oil are basically the same at the same water content. As the water content increases, the W/O emulsion droplet size grows first, then tends to stabilize, and finally stabilizes at between 2 and 3 μm. The viscosity of the W/O emulsion increases as water content increases and its viscosity increases significantly at high water contents. The lower the viscosity of dehydrated heavy oil is, the greater the increase of the viscosity of W/O emulsion increase. The viscosity of 70% the water content W/O emulsion is more than 15 times that of the dehydrated heavy oil. Finally, the effects of the water content, surfactant concentration, oil–water ratio on the emulsified state, droplet size distribution and its fluidity in porous medium were studied by simulating the re-emulsification process of W/O emulsion and surfactant solution. A W/O/W emulsion would formed by re-emulsification of the W/O emulsion and surfactant solution. As the water content of W/O emulsion increases, the droplet size of the W/O/W emulsion formed by re-emulsification increases, and its fluidity in porous medium decreases. The average emulsion droplet size (50% water content) after re-emulsification is 6.29 times that of emulsions formed by dehydrated heavy oil, and the apparent viscosity in porous medium is 15.05 higher. This study provides significant information for understanding the key issues in the efficient development of heavy oil reservoirs throughout their life time and the research and development of high-efficiency emulsion flooding systems.