Pseudo-interpenetrating network viscoelastic surfactant fracturing fluid formed by surface-modified cellulose nanofibril and wormlike micelles

Nano-material enhanced viscoelastic surfactant (VES) systems have attracted considerable attention as clean fracturing fluids due to their improved rheological properties compared to conventional VES systems. In this study, a pseudo-interpenetrating network VES (PINVES) fracturing fluid, which was composed of sodium oleate (NaOA), potassium chloride (KCI) and surface-modified cellulose nanofibril (SMCNF), was proposed. The rheological behavior of the PINVES fracturing fluid and the interaction mechanism between SMCNF and wormlike micelles (WLMs) were comprehensively studied. The zero-shear viscosity of PINVES increased with appropriate SMCNF addition but decreased with excess SMCNF addition. Meanwhile, the typical viscosity-flat of WLMs gradually disappeared when the concentration of SMCNF exceeded the optimum value. The optimum value was closely related to the functional groups on the surface of SMCNF. The SMCNF physically crosslinked the WLMs through hydrogen bonding but the sulfonic groups and hydrophobic groups on the surface of SMCNF destroyed the network of WLMs at relatively high SMCNF concentration. The network formed by SMCNF dominated the rheological behavior of the PINVES fracturing fluid simultaneously. In addition, due to the competition between the network of WLMs and the network of SMCNF, the PINVES fracturing fluid exhibited higher concentration dependence of surfactant in rheological behavior than conventional VES fracturing fluid. The SMCNF network also endowed the PINVES with better temperature-resistance. Furthermore, the relaxation time and elasticity of PINVES fracturing fluid increased with the increase in SMCNF concentration. The static proppant settling tests demonstrated that the addition of SMCNF improved the sand-carrying capability of PINVES fracturing fluid. The results of the study could provide some enlightenments on the application of SMCNFs in reservoir stimulation.

Automated summary

The addition of SMCNF can increase the zero-shear viscosity of PINVES, but excess addition will decrease its viscosity. The functional groups on the surface of SMCNF play an important role in determining the optimum value, and SMCNF acts as a crosslinker for WLMs. The network formed by SMCNF dominates the rheological behavior of the PINVES fracturing fluid.