Instant gel formation of viscoelastic surfactant fracturing fluids by diluting through lamellar liquid crystal

• Addition of cosurfactant forms lamellar liquid crystal in concentrate range.
• Presence of lamellar structure in diluting path increases VES dissolution rate.
• Viscosity and elasticity of mixed VES fluids increases at high temperature.

In application of viscoelastic surfactants (VES) as hydraulic fracturing fluids, some VES fluids take a long time to dissolve and build up viscosity in the field operation when it is diluted from concentrate. Amphoteric surfactant is studied to understand the mechanism. The phase behavior of the surfactant–solvent–water was investigated. It was found that a three phase range consisted of liquid crystal gel was passed during diluting process. It consisted of a highly viscose hexagonal liquid crystal phase, which took a long time to dissolve and formed VES gel. A cosurfactant was added to concentrate, which increases the dissolving rate. The hexagonal liquid crystal gel is transformed to soft lamellar liquid crystal gel in the present of cosurfactant. The mixed surfactants form VES gel within 1 minute. Addition of cosurfactant also increases viscosity at higher temperature.