Self-similar shear thickening behavior in CTAB/NaSal surfactant solutions

Abstract

The eect of salt concentration C s on the critical shear rateγ c required for the onset of shear thickening and apparent relaxation time λ of the shear-thickened phase, has been investigated systematically for dilute CTAB/NaSal solutions. Experimental data suggest a self-similar behavior ofγ c and λ as functions of C s . Specically,γ c ∼ C s −6 whereas λ ∼ C s 6 such that an eective Weissenberg number We ≡ λγ for the onset of the shear thickened phase is only weakly dependent on C s . A procedure has been developed to collapse the apparent shear viscosity versus shear rate data obtained for various values of C s into a single master curve. The eect of C s on the elastic modulus and mesh size of the shear-induced gel phase for dierent surfactant concentrations is discussed.Experiments performed using dierent ow cells (Couette and cone-and-plate) show thatγ c , λ and the maximum viscosity attained are geometry-independent. The elastic modulus of the gel phase inferred indirectly by employing simplied hydrodynamic instability analysis of a sheared gel-uid interface is in qualitative agreement with that predicted for an entangled phase of living polymers. A qualitative mechanism that combines the eect of C s on average micelle length and Debye parameter with shearinduced congurational changes of rod-like micelles is proposed to rationalize the selfsimilarity of SIS formation.

Wellbore to fracture proppant-placement-fluid rheology

“…Since we are interested however in elastic properties as a means to suspend proppant we focus rather on fluids that exhibit high SIS regime growth. From a Couette rheometer screening of VES formulations for application in fracture and porous matrix flow, (Golombok et al, 2008;Vasudevan et al, 2008; van der Plas and Golombok, 2015a) we identified two fluids for application -30 mM CTAB, 10 mM NaSal (denoted 30/10) and 50 mM CTAB, 14 mM NaSal (denoted 50/14).…”

“…The description above does however give an indication of expected values. We also note that the fluid described here has the ability to be ''tuned" based on additive concentrations and ratio (Vasudevan et al, 2008) allowing the viscous profile to be matched to predicted flow regimes throughout the treatment.…”

“…When CTAB is combined with NaSal two intriguing properties develop; the fluid exhibits elasticity coupled with strong viscous behaviour and also a non-monotonic shear-viscosity response (Vasudevan et al, 2008). NaSal acts as a counter-ion, electrostatically shielding the CTAB's polar head groups from each other.…”

“…At even higher C S concentrations only shear-thinning behaviour occurred Cresseley, 1998, 1997a,b). Vasudevan et al (2008) suggests the shear thickened phase is gel-like and composed of shear induced structures that form a micellar network dispersed within a lower viscosity solution.…”

“…Numerous authors have investigated FIVE systems and CTAB/ NaSal specifically mostly in the context of material properties in a Couette cell (Lin et al, 1994;Vasudevan et al, 2008). For a fixed surfactant concentration C D , micelles extend from spherical to wormlike micelles with increasing co-solute concentration C S .…”