Reaction kinetics of an emulsified acid using a mixed emulsifier and carbonate rocks

Abstract

For successful emulsified acid treatment, it is imperative to have emulsified acid that can maintain a water-in-oil emulsion state for 24 h at room temperature and 4 h at high temperatures. As a result, a hybrid emulsified acid was developed by combining cationic and nonionic emulsifiers, guaranteeing stability at both room and high temperatures. We assessed its viscosity and explored the interaction dynamics of the emulsified acid with carbonate rock samples using rotating disk apparatus experiments. Viscosity measurements revealed a non-Newtonian shear-thinning behavior modeled using a power-law approach. We examined limestone, dolomite, and chalk disks to evaluate weight loss tendencies, dissolution rates, and diffusion coefficients when exposed to the emulsified acid and hydrochloric acid (HCl). Both the weight loss and dissolution rate demonstrated that the reactivity of HCl surpasses that of the emulsified acid by up to 2.4 times at the same rotating speed. This indicates that the emulsified acid in our study can significantly slow the rapid reaction between acid and rock due to the diffusion barrier created by the oil phase. The diffusion coefficient for the limestone sample with emulsified acid was 1.46 times greater than that of dolomite (limestone: 1.64 E–7 cm2/s, dolomite: 1.12 E–8 cm2/s, and chalk: 1.47 E–8 cm2/s). Consequently, understanding the rock/mineral composition of the targeted reservoir is crucial when designing matrix acidizing with emulsified acid in carbonates. In summary, it is vital to account for the impact of emulsified acid on acid-rock reaction kinetics when establishing injection parameters for carbonate acidizing.