Research on low-viscosity high-elastic fracturing fluid system with specific recognition and supramolecular assembly

Fracturing fluids for tight sandstone reservoirs often suffer from issues such as low sand-carrying efficiency, difficulties in fracturing and gel breaking caused by high viscosity, and increased costs in practical applications. Therefore, there is an urgent need to develop a high-performance friction reducer system that combines both low viscosity and high elasticity. In this study, a chemical reduced-friction system (CRS-10, a polymer) with specific recognition capability is synthesized via aqueous solution polymerization. The monomer ratio used is acrylamide/acrylic acid/quaternary ammonium hydrophobic monomer at 86.5:12.5:1.0. Subsequently, through electrostatic assembly with anionic nano-emulsion, a stable supramolecular three-dimensional network structure is successfully constructed. This system exhibited notably low viscosity alongside high elasticity. At the same polymer concentration, the elastic modulus at zero shear rate of the CRS fluid system increases by 9376.97 times after assembly, and at the same viscosity, its elastic modulus increases by 2570.19 times. Under high-temperature conditions (120 °C) and high shear rate (170 s -1 ), the system's viscosity remains stable above 30 mPa·s, demonstrating excellent temperature and shear resistance. Sand-carrying performance tests show that CRS fluid system can carry sand particles for up to 5 h under static conditions without significant settling, and its yield stress far exceeds the net gravity of the sand particles. In dynamic sand-carrying tests, the sand equilibrium bank height reaches only about 30% of the fracture height, indicating outstanding sand-carrying capacity. The system's friction reduction rate exceeds 70%, consistent with conventional friction reduction models. The gel-breaking fluid is clear and transparent, with residue content below 50 mg/L. Furthermore, laboratory tight sandstone imbibition tests confirm a significant increase in oil recovery rate, reaching as high as 42.7%. Mechanistic analysis using nuclear magnetic resonance (NMR) and transmission electron microscopy (TEM) reveals that the strong electrostatic interaction between the quaternary ammonium cations and sulfonate anions drives the supramolecular assembly to form a three-dimensional network with a wall thickness of 17.96 μm, which provides a physical basis for CRS fluid system's high elasticity. Conductivity tests show that the interaction between anions and cations leads to a turning point change in conductivity and a significant decrease in the surface tension as polymer concentration increases, verifying that the polymer promotes surfactant adsorption and enrichment at the interface, thereby stabilizing the supramolecular structure. This supports the correlation between the assembly mechanism and improved rheological properties. In summary, the CRS fracturing fluid system based on specific recognition and supramolecular assembly effectively overcomes the limitations of weak sand-carrying capacity and high viscosity costs associated with traditional slickwater fluids, offering a novel slickwater system with promising applications for efficient fracturing of tight sandstone reservoirs.