Effect of Liquid Crystal on Gel Formation Rate of Viscoelastic Surfactant for Hydraulic Fracturing

Abstract

Abstract The viscoelastic surfactant (VES) as low formation damage fluids can be used in hydraulic fracturing and acidizing of low permeability oil and gas reservoir. The physical association and entanglement of wormlike micelle in diluted range gives viscoelastic properties, which gives similar properties as polymer. Compared with traditional polymer fluids, VES fluids used few additives and were easy to prepare in the wellsite. However, some VES fluids could take a long time to dissolve and build up viscosity in the field operation when it is diluted from concentrate. Amphoteric VES is hereby studied to understand the cause of such problems. 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 hexagonal liquid crystal phase. Hexagonal liquid crystal is highly viscose rod-like aggregate, it took longer time, up to several hours, to dissolve to form VES in the lab and field test. A cosurfactant was added to concentrate to increase the dissolve rate. Transient hexagonal liquid crystal gel is transformed to lamellar liquid crystal gel upon addition of co-surfactant. The microstructure of liquid crystal is confirmed by cross-polarizer microscope and small angle X-ray diffraction. The lamellar liquid crystal with multi-layer structure has low viscosity. It forms VES and builds up in viscosity within 2 minutes in the lab tested, and can form VES on-the-fly in field blending. Addition of cosurfactant didn't change performance of the prepared fluid at high temperature. Hence, the liquid crystal phase structure is the critical factor for dissolving rate of VES concentrate in the field operation.