Abstract:In response to the poor water flooding effect, high water cut (≥75%), low recovery rate (14.7%), and the inability of reservoir measures to further resolve the development contradictions in the Chang 6 tight oil reservoir of the Yanchang Oilfield, which is characterized by high salinity formation water (≥120,000 mg/L), high calcium and magnesium (Ca2+≥20,000 mg/L, Mg2+≥400 mg/L), and strong heterogeneity (range = 50), and the current foam systems" inability to adapt to these conditions, eight Gemini surfactants were evaluated for their foaming performance, half-life, and comprehensive foam index under simulated reservoir conditions using a high-temperature and high-pressure foam instrument and a tight reservoir imbibition system. The best foaming agent, main agent, and their concentrations were selected to construct a low interfacial tension, calcium and magnesium resistant, and oxygen-reduced air foam system. The effects of different temperatures, Ca2+ and Mg2+ contents, oil saturation, and pH values on the foaming volume and half-life of the system were evaluated, and the oil displacement efficiency and imbibition efficiency of the system in heterogeneous reservoirs were investigated. The results show that 0.4% LY-12 (dodecyldodecyl hydroxysulfonate) + 0.1% LX-14 (tetradecyl amino acid salt) is the best foam system. Temperature, Ca2+ ion content, oil saturation, and pH have a significant impact on the foaming volume and foam half-life, while the effect of Mg2+ content is relatively small. The best foam performance can be guaranteed under conditions of temperature ≤ 45°C, Ca2+ ion content ≤ 20,000 mg/L, oil saturation ≤ 30%, and neutral pH, with a comprehensive foam index ≥ 12,000 mL.min and an interfacial tension of 6.63×10-2 mN/m. When the permeability contrast is 50, the continuous foam flooding in heterogeneous reservoirs has a 7% higher comprehensive oil displacement efficiency than the foam slug followed by water flooding. When the permeability is 0.96×10-3 μm2, the imbibition efficiency reaches 42.88%, demonstrating good adaptability in low-permeability reservoirs.
