A smart recyclable VES fluid for high temperature and high pressure fracturing

The visco-elastic surfactant (VES) fluid has acquired great attention in the development of tight oil & gas reservoir due to low damage to the formation. However, the high cost and undesirable viscosity reduction at high temperature have seriously restricted the development of the VES fluids. In this paper, a functional VES fracturing fluid with good viscoelastic switchability under high temperature and high pressure was designed and constructed by CO2 responsive surfactant, erucamidopropyl dimethylamine (abbreviated as EA). It was interestingly found that this VES fluid can exhibits excellent rheological properties even at high temperatures in the presence of supercritical CO2 or CO2, and the rheological property can be reclaimed more than three times without reduction. The shear viscosity of 4 wt% EA + NaSal solution under 120 degrees C can meet the requirement of fracturing application in presence of CO2 pressure, and it is significantly rare in the literature where the surfactant solution is capable of withstanding such temperature. Cryogenic scanning electron microscopy (cryo-SEM) was used to study the aggregation structure. The self-assembly mode and the self-healing mechanism of this VES fluid was proposed to further understand its mechanism from the molecular level. The results of tests demonstrate that this functional VES fluid provides potential in the application of smart VES fracturing fluid.