Experimental study of the rheology of cellulose nanocrystals-enhanced C22-tailed zwitterionic wormlike micelles

Abstract

Nano-materials enhanced zwitterionic surfactants fracturing fluids with greatly improved rheological properties are extensively employed in foam fracturing to stimulate unconventional gas/oil reservoirs. In this study, a novel worm-like micelles (WLMs) system composed of erucyl dimethyl amidopropyl betaine (EDAB, C22), alkyl polyglucoside (APG) and cellulose nanocrystals (CNC) is proposed. A series of rheology and dynamic light scattering tests were conducted to determine the optimal concentration, and the influence of various factors, including temperature, pH, and inorganic salts, on the viscoelasticity and structural morphology of WLMs systems were also analyzed. The results show that a 0.3 wt% EDAB/APG/CNC system exhibits optimal viscosity and viscoelastic fluid behavior. The increase of temperature accelerates the breaking rate of WLMs, resulting in a decrease in viscosity, but its shear viscosity can still maintain 87.42 mPa·s at 90 °C and is an order of magnitude greater than that of other systems. The change of pH can disturb the equilibrium state under the electrostatic interaction of EDAB and CNC, and the negative ions in EDAB and CNC molecules are easily protonated in acid medium, resulting in a lower viscosity than alkaline medium and much lower than neutral medium. The viscosity of the EDAB/APG/CNC system increases first and then decreases with the increase of inorganic salt concentration, and reaches a peak at 2.5 wt%. Proppant critical settling velocity tests show that the CNC improves the proppant-carrying capacity of the EDAB/APG/CNC system with favourable critical settling velocity. The CNC enhanced C22-tailed EDAB system provides a basis for optimizing foaming fracturing in unconventional reservoirs.