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.