Composite fluids are comprised of particles and polymers and are used for fracking and the in‐situ treatment of subsurface contaminants. This study investigates the correlation between the shear viscoelasticity of guar aqueous solutions and their effectiveness in suspending sand, which is a common fracking proppant. In the absence of a crosslinker, the shear viscous modulus (G”) of 5 g/L guar solutions was greater than the shear elastic modulus (G’). When the crosslinker borax was added, the guar solutions behaved as yield stress fluids (G’ > G”). Sand was well‐suspended in the crosslinked guar solutions but settled in non‐crosslinked fluids. Similar results were obtained with fenugreek gum. This study also investigates the correlation between particle settling and the effect of particle addition on the rheology of the fluids. Granulated activated carbon (GAC) particles are utilized to remediate polluted sites and were used as model particles. Guar and xanthan effectively suspended the GAC. Anionic polyacrylamide effectively suspended the GAC but not after soaking in sodium dodecyl sulphate. Zetag 8167 did not effectively suspend the GAC. The addition of 10 g/L of GAC did not affect the shear rheology of the fluids that suspended them, but decreased the shear viscoelastic moduli of the polymeric fluids that could not suspend them.
This study investigated the potential effect of shear rheology and humic acids (HA) on the subsurface transport of polymeric fluids used for the remediation of contaminants. Polymeric fluids were prepared with guar, scleroglucan, and carboxymethyl cellulose (CMC). Guar fluids can be used to suspend reactive particles for contaminant degradation. Fluids prepared with 2.5 g/L of guar in water were viscous, and the crosslinker borax (1 g/L) made them viscoelastic. Microfluidics experiments showed that the increase in elasticity blocked the flow of guar in 350 μm channels. Guar, CMC, or scleroglucan fluids containing sodium thiosulfate can be used to trap toxic Cr(VI) in the subsurface and reduce it to harmless Cr(III). Trapping of Cr(VI) is achieved by the gelation of the fluids upon contact with chromium. Before mixing with chromium, HA did not affect the flow of CMC, guar, and scleroglucan in microfluidic channels. Quartz-crystal microbalance with dissipation monitoring experiments indicates that HA reduced sorption of guar onto silica, potentially promoting the transport of guar fluids in sandy aquifers. While HA slightly decreased the rate of gelation of CMC and scleroglucan upon contact with chromium, it did not affect the fast gelation rate of guar.
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