Study on the Construction and Key Performance Recyclable CO2 Foam Fracturing Fluid: Reducing CO2 Utilisation Costs

Abstract The CO2 foam fracturing fluid is a popular CO2 utilization strategy, as it significantly alleviates the economic burden of carbon capture and storage (CCS), reduces CO2 emissions, and allows partial sequestration of CO2 underground. However, the CO2 foam fracturing fluid contains a large amount of surfactants, resulting in high costs and potential environmental risks. To address this issue, this study developed a recyclable CO2 foam fracturing fluid system based on CO2-responsive surfactants and commercial viscoelastic surfactants. This new system serves as an efficient, economic, and environmentally friendly candidate for CO2 utilization. The fracturing fluid was also evaluated in this study. First, using a self-developed high-temperature and high-pressure (HTHP) foam fracturing fluid performance evaluation apparatus, the optimal types of CO2-responsive surfactants and commercial viscoelastic surfactants were selected based on the foam drainage half-life time at 80°C and 20 MPa, resulting in an excellent foam system. Next, to ensure compatibility, necessary organic salt additives were incorporated into the selected foam system to formulate a recyclable CO2 foam fracturing fluid system. Subsequently, the foam stabilization mechanism was elucidated through rheological and transmission electron microscopy tests (TEM). Finally, the rheological properties, high-pressure proppant-carrying capacity, damage potential, and recyclability of the fracturing fluid were evaluated to demonstrate its practical feasibility. At 80°C and 20 MPa, erucamidopropyl hydroxysulfobetaine (EHSB) and oleamidopropyl dimethylamine (DOAPA) exhibit a high comprehensive foam value. Under the promotion of potassium chloride (KCl), the foam drainage half-life reached 134 minutes. Therefore, the optimal system is determined to be 1.5 wt% EHSB + 1.5 wt% DOAPA + 2 wt% KCl. Rheological tests and TEM results indicated that the strong synergistic effect of the mixed system formed worm-like micelles, significantly enhancing foam stability. As pressure increased (10-20 MPa), the sedimentation rate of proppants in the fluid decreased from 2.2 to 0.48cm/min, demonstrating excellent proppant-carrying performance under high pressure. By removing/introducing CO2, the foam fracturing fluid could switch between stable and unstable states, enabling its recyclability. Furthermore, damage evaluation showed that this fracturing fluid caused only about 30% of the core damage compared to traditional guar-based fracturing fluids, making it highly suitable for unconventional oil and gas reservoir stimulation. The recyclable CO2 foam fracturing fluid demonstrated excellent performance and recyclability, effectively reducing CO2 utilization costs and mitigating potential environmental risks. It shows promising application potential and warrants further research. The fluid is expected to be applicable not only for fracturing but also in fields such as Enhanced Oil Recovery (EOR) and foam-based well cleaning technology.