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

摘要

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 center dot s. The system without added SDBS viscosifies at a pH of 2.2 and reaches a final viscosity of 403 mPa center dot s. Studies of the limestone-acid reaction kinetics showed that the reaction rate fell from 1.37 center dot 10(-4) mol/(cm(2)center dot s) for 20 wt. % HCl solution to 13.2 center dot 10(-6) and 6.5 center dot 10(-6) mol/(cm(2)center dot 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 center dot 10(-1) (mol/cm(3))((-0.3092))center dot(cm/s), 5.5221 center dot 10(-4) (mol/cm(3))((0.2822))center dot(cm/s), and 6.3154 center dot 10(-5) (mol/cm)((0.5554))center dot(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.