Novel Viscoelastic Surfactant-Based Self-Diverting Acid Systems for Carbonate Acidizing

Abstract

Novel viscoelastic self-diverting acid (VDA) systems with and without cosurfactant (sodium dodecylbenzenesulfonate, SDBS) added to enhance reaction retardation and to improve the conventional VDA system are studied. The novel system viscosifies at a pH of ~0.6 and attains a viscosity of ~500 mPa·s. The system without added SDBS viscosifies at a pH of ~2.2 and reaches a final viscosity of 403 mPa·s. Studies of the limestone—acid reaction kinetics showed that the reaction rate fell from 1.37·10^–4 mol/(cm²·s) for 20 wt. % HCl solution to 13.2·10^–6 and 6.5·10^–6 mol/(cm²·s) for VDA solutions without and with added SDBS, respectively. The reaction rate constants (k) for the negative sample control and VDA systems I and II were 1.0740·10^–1 (mol/cm³)^(–0.3092)·(cm/s), 5.5221·10^–4 (mol/cm³)^(0.2822)·(cm/s), and 6.3154·10^–5 (mol/cm)^(0.5554)·(cm/s), respectively. A dual-core flow test showed that wormholes were produced in both cores for the VDA systems rather than a large single channel in a high-permeability core when 20 wt.% HCl solution is used. Thus, a smaller volume of SDBS is needed for flow formation when VDA solution is added. The studies revealed that the novel VDA system retards reaction considerably, improves acid diversion, and has tremendous potential for field applications.