Experimental Study on Viscosity-Reducing Foam Flooding in Fractured-Vuggy Reservoirs

The crude oil reserves of fractured-vuggy reservoirs are large, but most of them are heavy oil and ultraheavy oil reservoirs. They have the characteristics of high heavy metal ion concentration, high asphaltene content, high viscosity and density, and deep burial. They are difficult to exploit. Therefore, it is necessary to reduce the viscosity of the heavy oil to improve crude oil recovery. In this paper, the use of a viscosity-reducing foamer is investigated. First, the optimal concentration screening, temperature resistance, salt resistance, aging resistance, viscosity-reducing ability, ability to reduce oil–water interfacial tension, and ability to reduce gas–liquid surface tension were evaluated for DXY-03 viscosity-reducing foamer and DXY-08 viscosity-reducing foamer. Then, an oil displacement experiment on the viscosity-reducing foam was carried out under different placement conditions by using a visual fractured-vuggy model. The experimental results showed that the DXY-08 viscosity-reducing foamer has better temperature resistance, salt resistance, viscosity-reducing ability, and ability to reduce gas–liquid interfacial tension than the DXY-03 viscosity-reducing foamer. Therefore, the DXY-08 viscosity-reducing foam was selected for visual oil displacement experiments. The results of the visual oil displacement experiments showed that the DXY-08 viscosity-reducing foamer has good flooding ability, can effectively use the remaining oil in the fractures and holes in the middle of a reservoir, can also block large-opening fractures, and can effectively use the remaining oil in small- and medium-sized fractures. In addition, a liquid phase and a gas phase are produced after the disproportionation of the viscosity-reducing foamer. The liquid phase can emulsify and reduce the viscosity of crude oil, and the gas phase replaces the oil remaining in the fracture hole at the top of the reservoir under the action of gravity, which greatly improves oil recovery.