Microscopic evaluation of emulsion stability and formula optimization for emulsified acid

Emulsified acid has gradually become an acid system commonly used in deep-penetration acid fracturing because of its good retardation. However, it is difficult to evaluate the stability of under reservoir condition, which results in unreasonable acid fracturing design. A quantitative and intuitive method has been presented for evaluation of emulsified acid properties under field application conditions. The conductivity is tested under different formulas, temperature and acid/rock reaction time by use of conductivity meter. The lower electric conductivity values emulsified acid gets, the better emulsified property it is. Emulsified acid stability and the processes of emulsion and demulsification are observed under different conditions by use of microscopy. From the results, it is shown that the microscopic characteristics of emulsified acid have a determinative role on the emulsion stability. The acid with good emulsion performance has following micro-characteristic: even droplet sizes, tight placement and small diameter. Also, a new emulsified acid formula with optimum stability has been derived. It provides important guidance for the field application of emulsified acid in acid fracturing. © 2013 Springer-Verlag.