This paper examines the use of surfactant gels during acid injection and describes the optimization of these fluids. Unlike available viscoelastic surfactants used today in the field, this surfactant is cationic at low pH values. If used in live acids, the fluid has relatively low viscosity when pumped. However, once the acid is spent the surfactant molecules significantly increase the fluid viscosity. To further enhance diversion, the acidic fluid can also be foamed. Alternately, brine gelled with surfactants can be foamed and utilized for diversion.
Rheological measurements were conducted on Hastelloy fitted rotational viscometers at temperatures from 70 to 300°F. The effects of surfactant concentration and acid additives on the apparent viscosity of various surfactant-based fluids were investigated in detail.
The surfactant was found to be stable and compatible with most acid additives. Some corrosion inhibitors adversely affected the apparent viscosity of surfactant solutions. The apparent viscosity increased with salt concentration. The apparent viscosity of the surfactant solutions can be predicted using Carreau-Yasuda model. Coreflood tests indicated that the surfactant delayed acid breakthrough in carbonate cores. Acceptable corrosion rates were obtained when this surfactant was added to the acid.
The performance of this surfactant was validated with field trials. The surfactant was used in more than fifty field treatments. It was used with up to 28 wt% HCl as in-situ acid diverter. It was also used to enhance the stability and apparent viscosity of foams used for acid diversion in power water injectors.