This study systematically evaluates the adaptability of viscoelastic surfactant (VES) fracturing fluids under deep coalbed methane (CBM) reservoir conditions. The rheological properties of three VES fluids—single-chain cationic (B), Gemini cationic (C), and nano-SiO2-modified Gemini (D)—were investigated at 303.15, 323.15, and 343.15 K. Four formulations, including de-ionized water (A), were assessed for their impact on coal permeability under coupled temperature–pressure conditions. Coal samples were soaked for 12 h at each temperature and at pressures of 3, 5, and 7 MPa, followed by porosity, permeability, and x-ray diffraction (XRD) characterization. Results show that coal permeability is strongly influenced by temperature–pressure conditions and fracturing fluid formulation. Group D achieved the greatest permeability enhancement, with an increase in up to 199.18 ± 19.06% at 343.15 K and 7 MPa. Rheological analysis revealed that, unlike Groups B and C—where the consistency index decreased markedly with rising temperature—the nano-SiO2-modified Group D maintained stable consistency (10.00–13.87) and exhibited a higher elastic modulus (G′ = 16.83), indicating superior thermal stability. XRD analysis showed that the synergistic interaction between nanoparticles and micelles in Group D significantly disrupted the vertical stacking of aromatic layers within the coal matrix, resulting in the largest reduction in microcrystalline stacking height (Lc) by 23.69%. This promoted the expansion and interconnection of pores and fractures, enhancing coal permeability. The study establishes a multi-scale mechanistic relationship among fracturing fluid composition, microstructural transformation, and permeability evolution, providing theoretical support for optimizing fracturing strategies in deep CBM reservoirs.
Wang et al. (2025) studied this question.