Development and Characterization of CO2-Responsive Surfactants for Coalbed Methane Fracturing

To address issues of traditional coalbed methane (CBM) fracturing fluids (high displacement, weak sand-carrying, poor stability, severe coal seam damage), this study synthesized CO2-responsive erucamide propyl dimethylamine surfactant (C22ZEA, yield 99%), with molecular structure verified by 1H NMR (400 MHz, CDCl3) matching the target. Molecular simulation showed CO2 protonates C22ZEA into EA+: 1 wt% forms a simple micelle network, while 3 wt% enhances entanglement into a dense 3D network. Experiments indicated: 3 wt% solution reaches 160 mPa·s viscosity in 200 s under CO2 (0.2 L·min−1); 1.5–4.5 wt% solutions are pseudoplastic (n = 0.14–0.18), with G′ > G″ when concentration > 2 wt%; viscosity recovery rate > 95% after alternating shear (170 s−1/10 s−1); viscosity remains > 160 mPa·s after 1 h shear (170 s−1) at 70 °C; gel breaks to 0.01–0.02 Pa·s in 15 min with N2 at 45 °C; 1.0–3.0 wt% solutions meet non-toxic standards via EC50/96 h LC50. This study supports high-efficiency low-damage smart fracturing fluids, boosting CBM extraction efficiency.