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 molar ratio of acrylamide to acrylic acid to quaternary ammonium hydrophobic monomer is 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-10 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 ℃) 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-10 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, tight sandstone imbibition tests conducted in the laboratory 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 the high elasticity of the CRS-10 fluid system. 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 the polymer concentration increases. This verifies 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-10 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.

Slickwater-based fracturing fluid has recently garnered significant attention as the major fluid for volumetric fracturing; however, lots of challenges and limitations such as low viscosity, poor salt tolerance, and possible formation damage hinder the application of the conventional simple slickwater-based fracturing fluid. In addition, nanomaterials have proven to be potential solutions or improvements to a number of challenges associated with the slickwater. In this paper, molybdenum disulfide (MoS₂) nanosheets were chemically synthesized by hydrothermal method and applied to improve the performance of conventional slickwater-based fracturing fluid. Firstly, the microstructure characteristics and crystal type of the MoS₂ nanosheets were analyzed by SEM, EDS, TEM, XPS, and Raman spectroscopy techniques. Then, a series of evaluation experiments were carried out to compare the performance of MoS₂ nanosheet-modified slickwater with the conventional slickwater, including rheology, drag reduction, and sand suspension. Finally, the enhanced imbibition capacity and potential mechanism of the nanosheet-modified slickwater were systematically investigated. The results showed that the self-synthesized MoS₂ nanosheets displayed a distinct ultrathin flake-like morphology and a lateral size in the range of tens of nanometers. In the nano-composites, each MoS₂ nanosheet plays the role of cross-linking point, so as to make the spatial structure of the entire system more compact. Moreover, nanosheet-modified slickwater demonstrates more excellent properties in rheology, drag reduction, and sand suspension. The nanosheet-modified slickwater has a higher apparent viscosity after shearing 120 min under 90 ℃ and 170 s⁻¹. The maximum drag reduction rate achieved 76.3% at 20 ℃, and the sand settling time of proppants with different mesh in the nano-composites was prolonged. Spontaneous imbibition experiments showed that the gel-breaking fluid of nanosheet-modified slickwater exhibited excellent capability of oil-detaching, and increase the oil recovery to ~35.43%. By observing and analyzing the interfacial behavior of MoS₂ nanosheets under stimulated reservoir conditions, it was found that the presence of an interfacial tension gradient and the formation of a climbing film may play an essential role in the spontaneous imbibition mechanism. This work innovatively uses two-dimensional MoS₂ nanosheets to modify regular slickwater and confirms the feasibility of flake-like nanomaterials to improve the performance of slickwater. The study also reveals the underlying mechanism of enhanced imbibition efficiency of the nano-composites.