A New Viscoelastic Surfactant for High Temperature Carbonate Acidizing

Abstract

Abstract Diverting agents have been widely used during matrix acidizing treatments to accomplish the uniform distribution of acid solutions across the target zones. One of the most popular formulas is based on viscoelastic surfactants (VES) which showed good results in the lab and field tests. A major limitation with the conventional VES is temperature. Most of these surfactants do not hold viscosity at temperatures greater than 250°F. A new VES that can be used at higher temperatures was developed. The apparent viscosity of the spent VES-based acids was measured as a function of temperature and shear rate at 300 psi. Various corrosion inhibitors were mixed together with the new VES to find out the most compatible formula. A coreflood test was conducted on a 20 in. long carbonate core to examine the performance of the new surfactant. The core was CAT scanned before and after the experiment to observe the wormholes created by the new system. The acid contained 20 wt% HCl and 4 vol% VES. Spent acids of the new VES had a high viscosity up to 325°F. Several corrosion inhibitors were identified that can be mixed with the new system without affecting the apparent viscosity of the spent acid. Similar to current VES, mutual solvent is recommended in the post flush to reduce the fluid viscosity and remove any gel from the core. CAT scan of the core show wider and tortuous wormholes, indicative of good retardation of the new VES-based acid system.