Study on the Influence of Reservoir Heterogeneity on Oil Recovery Factor in Yanchang Formation of Ordos Basin

The reservoirs of Yanchang Formation in Ordos Basin are typical tight sandstone reservoirs with low porosity and ultra-low permeability, and reservoir heterogeneity is the core factor restricting the improvement of oil recovery factor. To clarify the influence law and mechanism of heterogeneity on oil recovery factor, taking the Chang 6 and Chang 8 oil-bearing intervals of Yanchang Formation as the research objects, this paper systematically characterized the reservoir heterogeneity characteristics from four dimensions, namely plane, interlayer, intralayer and microcosm, by comprehensively using methods such as core analysis, thin section identification, well logging interpretation and numerical simulation. The influence of reservoir heterogeneity on oil recovery factor was quantified through laboratory experiments and field dynamic data, and targeted development optimization strategies were put forward. The results show that the porosity of Yanchang Formation reservoirs ranges from 7.8% to 14.1%, the permeability is concentrated in 0.05×10⁻³μm² to 9.1×10⁻³μm², and the permeability ratio varies from 1.03 to 43.7. The plane heterogeneity is characterized by the interbedded distribution of channel sand bodies and flood plains, the thickness of interlayer barriers and intercalations is 0.6-2.4 m, and the micro-pore-throat ratio is 5-25. Experimental and simulation results indicate that the water flooding recovery factor decreases by 4.2%-6.8% with every 10 increase in permeability ratio, the water flooding recovery factor of reservoirs with strong heterogeneity is only 20.3%, and air foam flooding can increase the recovery factor by 28%. Reservoir heterogeneity restricts oil recovery factor by controlling fluid seepage paths, affecting displacement efficiency and residual oil distribution. The research results provide theoretical basis and practical reference for the efficient development and residual oil tapping of Yanchang Formation reservoirs.