Design and Evaluation of a CO2-Responsive Fracturing Fluid for Coalbed Methane Recovery

Abstract

This study focuses on constructing a CO2-responsive and low-residue fracturing fluid tailored for coalbed methane (CBM) extraction, aiming to overcome the issues of poor flowback and high residue commonly observed in traditional systems. A novel tertiary amine-based surfactant (HDD) was synthesized via a nucleophilic substitution reaction, and its structural characteristics, interfacial properties, viscosity responsiveness, thermal-shear stability, and gel-breaking behavior were systematically evaluated. The molecular structure was confirmed by 1H NMR spectroscopy, while performance tests were conducted using a rheometer and an interfacial tensiometer to explore the reversible response mechanism under CO2/N2 stimulation. It was observed that the surfactant quickly assembled into wormlike micelles upon CO2 exposure, significantly enhancing the system’s viscosity. Even at 110 °C and a shear rate of 170 s−1, the viscosity remained above 56 mPa·s, indicating remarkable resistance to thermal and shear stress. Upon N2 introduction, rapid gel breaking was achieved, indicating excellent flowback performance. The addition of K+ ions as co-agents significantly increased the viscosity to 69.9 mPa·s, suggesting enhanced micelle network formation. In addition, the system exhibited good CO2/N2 reversible responsiveness and cycling stability. This study proposes a CO2-responsive clean fracturing fluid system that combines rapid responsiveness, high-temperature stability, and controllable gel breaking, providing a novel approach for low-damage and efficient CBM extraction, while also offering a viable strategy for synergistic CO2 utilization and sustainable energy development.