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 has been synthesized and characterized using 1HNMR, FTIR, and TGA. These 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 is 1:1 wt/wt percent with CaCl2 (10-30%) solutions at a temperature range of RT to 90oC 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 oC 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 polymer c-PEI and CTAB may potentially offer a more robust and efficient system for recovering hydrocarbons from oil reservoirs.

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

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