Guar gum fracturing fluid is widely used in hydraulic fracturing due to its excellent viscoelastic and proppant-carrying properties. With the increasing burial depth of oil and gas resources, strengthening the temperature and shear resistance of guar gum fracturing fluid is a significant engineering issue. Although graphene oxide is known to be effective in enhancing the structural strength of materials, few studies reported its ability to enhance guar gum fracturing fluid properties. To address this issue, herein, we prepared a boron-functionalized colloidal graphene oxide crosslinker (GOB) to enhance the temperature and shear resistance of guar gum fracturing fluid. Colloidal graphene oxide crosslinkers have a larger size and more crosslinking sites, reducing the amount of self and guar gum. Compared with organoboron crosslinkers under the same conditions, GOB can improve the temperature resistance of fracturing fluid by 8.9 °C and viscosity by 20−50 mPa•s. It was observed by vacuum freeze-drying combined with scanning electron microscopy that guar gum exists as irregular linear structures when dissolved in water. The addition of crosslinkers makes the irregular linear structures bind to each other and form a continuous membrane structure. Meanwhile, the distribution of graphene oxide crosslinker on the surface of the continuum film enhances the membrane's tensile strength, resulting in the enhanced water retention capacity of the fracturing fluid gel at high temperatures. Thereby, the temperature and shear resistance of the gel is enhanced. In addition, this work reveals in detail the effects of pH and crosslinker dosage on the gel properties of fracturing fluid formed by graphene oxide crosslinker. It has significant significance for further improving the GOB's properties and developing other types of nanomaterials in guar gum fracturing fluids.

In this study, the foaming properties of a compound surfactant formula containing cetyltrimethylammonium chloride (CTAC), cocamidopropyl betaine (CDAB), fatty alcohol polyoxyethylene ether-7 (AEO7) and sodium alpha-olefin sulfonate (AOST) were evaluated to meet the application requirements for foam generation and foam drainage in gas wells. The results exhibited that the foaming volume and the half-life of the compound surfactant solution (0.05 wt % CTAC + 0.7 wt % CDAB + 0.6 wt % AEO7 + 0.05 wt % AOST) can reach the values of 550 mL and 23 min, respectively, which suggested that the foaming ability and stability were improved in comparison with each solution containing a single surfactant. It showed that the surface tension can be lowered to 22.4 mN/m with the presence of the compound surfactants. Simultaneously, the microstructure of the foam was observed using a polarizing microscope, and it was found that there were almost no polyhedron structures in the foam within a certain range of formula concentrations. The results of the experiments also clarify that the formula has well properties of temperature resistance and salt resistance (measured using a high-speed agitator).