Review on High-Temperature-Resistant Viscoelastic Surfactant Fracturing Fluids: State-of-the-Art and Perspectives

A viscoelastic surfactant (VES) fluid is an important part of a water-based fracturing fluid. As oil and gas exploration expands into deep, high-temperature, low-permeability reservoirs, the conventional VES fracturing fluid has shown great limitations. The high-temperature-resistance mechanisms of the high-temperature-resistant VES fracturing fluids in publicly available literature were analyzed from five aspects: single-chain surfactant system, oligomeric surfactant system, counterion effect, blended surfactant system, and nano-enhanced VES system. The friction-reduction performance, sand-carrying performance, gel-breaking performance, and core-damage performance of these systems were summarized. The results show that oligomeric surfactants with a monounsaturated hydrophobic long chain (>C21) are most likely to be used for VES fracturing fluids in high-temperature reservoirs, but the loading of the surfactants is still relatively high (3–5 wt %). By reducing the repulsion among polar headgroups to effectively decrease the area of head groups, or/and penetrating into the nonpolar cores based on hydrophobic interaction to increase the average hydrophobic volume of hydrophobic tails, counterions affect the performance of VESs. The aromatic counterion salts are preferred choices for improving the temperature resistance, friction reduction, and suspended sand performance of VES fluids. The blended surfactant/synthetic polymer systems based on noncovalent interaction improve the temperature resistance of VES fluids and reduce the loading of the surfactants to a certain extent. Based on the "pseudo-cross-linking" of nanomaterials and wormlike micelles, a very small amount of nanomaterials can improve the temperature resistance of VES fluids and reduce the loading of the surfactants. The most essential and effective method to improve the temperature resistance of VES fluids for fracturing is the molecular structure design based on the packing parameter theory. However, the synthesis process or route still needs further optimization to reduce production costs. In addition, given the excellent performance of VES fluids enhanced by nanomaterials, further research should be conducted on the influence mechanism of nanomaterial type and geometric features on the performance of VESs, as well as the potential harmfulness of nanomaterials, to promote the field-scale application of nano-enhanced VES fluids.