Fracturing fluid applications of carboxylate-terminated low molecular weight PEI and CTAB formulations

It is imperative to develop new viscoelastic surfactants (VES) based fluid formulations that show promise as fracturing fluids for a more efficient hydrocarbon recovery. In this study, a novel hyperbranched polymer having multiple terminal carboxylate (C-PEI) functional groups was prepared using a simple one-pot, two-step synthesis method and characterized using ¹HNMR, FTIR, and TGA. The terminal carboxylate moieties are employed as a chelating agent along with a cationic surfactant cetyltrimethylammonium bromide (CTAB) to develop different viscoelastic formulations of a low molecular weight polymer and a surfactant system. The amounts of C-PEI (2.5–7.5%) and CTAB (2.5–7.5%) that were used in 1:1 wt/wt percent with CaCl₂ (10–30%) solutions at a temperature range of RT to 90 °C under the influence of shear rate (1–100 s⁻¹) to find an optimum formulation and the most convenient conditions for exhibition of better viscoelastic properties. The shear-based viscosity was investigated to ascertain the typical viscoelastic behavior of a carboxylate terminated polymer and a cationic surfactant using a rheometer. The results showed that the concentrations of C-PEI and CTAB (7.5%:7.5% wt/wt) in the presence of 30% CaCl₂ solution (85%) exhibited apparent viscosity of ~680 cPs at 90 °C under a shear rate of 100 s⁻¹. The stability of optimized viscoelastic formulations was also assessed, and it was realized that there was no appreciable change in viscosity with respect to time. The gel-breaking results indicate that the addition of ~8.5% commercial diesel reduced the maximum apparent viscosity 682 cPs to 12 cPs at 90 °C. This novel viscoelastic system comprising of a low molecular weight hyperbranched polymer C-PEI and CTAB may potentially offer a more robust and efficient system for enhanced recovery of hydrocarbons from oil reservoirs.