Abstract:In recent years, the acid microemulsion has attracted significant attention from the petroleum industry due to its great potential for formation modification. However, the acid microemulsion will become unstable under high formation temperature, which hampers its wide application for deep reservoirs. In this work, an emulsifying formula mainly composed of SMT-3 and SRA-5 was screened through orthogonal experiments and its static and dynamic properties were thoroughly investigated. It was found that the developed acid microemulsion, which showed an average particle size of 30nm, could remain stable at 100℃ for at least 10 hours. It was also able to withstand the Ca2+ as high as 20%. It remained clear and transparent under the shearing rate of 170s-1 for 2 hours, demonstrating its outstanding capacity to resist the shearing force. As the acid droplets were well separated by the oil, the acid microemulsion presented much lower corrosion rate on N80 steel slide and much slower dissolution rate limestone, compared to those of hydrochloric acid and thickening acid with identical concentrations. The rotating disk experiments indicated acid microemulsion had a reaction rate constant 30 times lower than that of hydrochloric acid, which enabled it to penetrate far in the reservoir. The core flooding experiments showed that the permeability had been increased by 500% after acidification and the formation damage was negligible. Overall, the proposed acid microemulsion may be applied as an ideal acidifying fluid for high temperature limestone reservoirs.