Analysis of water drive characteristics and influencing factors of Chang 10 reservoir in Mid-Western Ordos Basin

To further explore the water-driven oil seepage characteristics of the ultra-low permeability reservoir in the west-central Ordos Basin Chang 10 reservoir, clarify the reservoir seepage mechanism, and provide theoretical guidance for the effective development of the region. Taking Wuqi area as the research object, the microscopic pore throat structure, water-driven oil seepage characteristics and influencing factors of the Chang 10 reservoir in the study area were analyzed by using analytical tests such as physical analysis, cast thin section, scanning electron microscopy, high-pressure mercury compression, visualization microscopic water-driven oil experiment and core multiphase seepage experiment. The study shows that the pore type of the Chang 10 reservoir in the study area is mainly intergranular pores, followed by feldspathic and zeolitic pores, and the throat type is mainly lamellar and curved lamellar throats. The pore-throat structure can be divided into three categories: Ⅰ, Ⅱ and Ⅲ. For reservoirs with different categories of pore structure, the main mode of water-driven oil replacement in the reservoir pore channels is piston replacement, while non-piston replacement is rare; for reservoirs with different categories of pore structure, the replacement characteristics of injected water in the pore network vary greatly. The repulsion mode of Class Ⅰ reservoir is mainly uniform repulsion and reticulation-uniform repulsion, that of Class Ⅱ reservoir is mainly reticulation, and that of Class Ⅲ reservoir is mainly finger repulsion and reticulation-finger repulsion. The seepage characteristics and replacement efficiency of water-driven oil are mainly influenced by the reservoir properties, pore throat structure and replacement pressure, water injection multiplier and other factors. The study concludes that: the reservoir physical properties and pore throat structure deteriorate from Class Ⅰ to Class Ⅲ, and the water repelling mode in the pore network changes from homogeneous-reticulated-finger-like, and the water repelling efficiency decreases; the size of the reservoir throat is the most important factor affecting the efficiency of water dive, the larger the radius of the reservoir throat, the higher the oil drive efficiency; increasing the repelling pressure and water injection multiplier can improve the water repelling efficiency within a certain range.