Carbon dioxide (CO₂) foam fracturing fluid features the advantages of low water consumption, weak reservoir damage, and excellent stimulation performance, making it particularly suitable for the extraction of water⁃sensitive unconventional shale oil and gas as well as coalbed methane. To address the poor stability of traditional CO₂ foam fracturing fluids, flake⁃structured nano⁃graphene oxide (GO) was used to modify the CO2 foam fracturing fluid. The CO₂ foam fracturing fluid was prepared in a sealed reactor, and the variation of foam half⁃life with surfactant type was investigated by visual observation to optimize the formulas. Subsequently, the effects of surfactant type, concentration, and temperature on the stability of the CO₂ foam fracturing fluid were studied. The results show that the addition of GO to the octadecyltrimethylammonium chloride (OTAC) system leads to a large amount of flocculent material and fails to stabilize the foam. In contrast, the α⁃olefin sulfonate (AOS) system exhibits good compatibility with GO. The formula of 0.50%AOS+1.00%NaCl+0.25%GO presents high foam quality, and the introduction of GO significantly improves the temperature resistance of the foam system. A foam liquid film model was constructed using Materials Studio, and molecular dynamics simulations were performed to reveal the synergistic foam⁃stabilizing mechanism and failure mechanism of GO at the molecular level. This study provides a theoretical basis and technical support for the development of oil and gas reservoirs.

This article simulated three mortar systems including mineral filler⁃asphalt,mineral filler⁃emulsified asphalt residue and cement⁃emulsified asphalt residue in cold recycled mixture with emulsified asphalt. The results show that cement⁃emulsified asphalt residue mortar owns higher modulus than the other two mortars because of cement hydration. The change of modulus and phase angle is different from that of ordinary mineral powder⁃asphalt mortar and mineral powder⁃emulsified asphalt mortar, and does not change linearly monotonously with powder⁃to⁃binder ratio. At the same time, the interface adhesive ability of cement⁃ emulsified asphalt residue is similar to that of the mineral filler⁃asphalt mortar, and much higher than that of the mineral filler⁃emulsified asphalt residue mortar in a lower filler dosage. In the process of mixture production, emulsified asphalt provides the initial stability of the mixture, and cement hydration and the formation of composite mortar system are the guarantee of the final cold recycled mixture strength.