Investigation of Waterflooding Model Considering Dynamic Fracture Propagation in Ultra-Low Permeability Reservoirs with High-Angle Fractures

High-angle fractures are widely developed in ultra-low permeability reservoirs in the Ordos Basin, and their propagation has a significant influence on waterflooding performance. However, few studies have focused on the identification of high-angle fractures, let alone the impact of their propagation on waterflooding performance. Therefore, a waterflooding model considering dynamic fracture propagation was developed to evaluate the impact of fracture propagation on waterflooding performance in this study. Firstly, based on the logging response characteristics of high-angle fracture intervals, the high-angle fracture identification model was established by the fuzzy comprehensive evaluation method, and a comprehensive index was proposed to identify high-angle fracture intervals. A threshold of approximately 70 effectively distinguishes high-angle fracture intervals from non-high-angle fracture intervals. After that, the waterflooding model considering dynamic fracture propagation was established to investigate the effect of its parameters on waterflooding performance. A smaller initial leak-off coefficient and a faster decline rate reduce fluid loss, promote fracture propagation, and ultimately improve oil recovery. Higher injection rates promote dynamic fracture propagation, accelerate water cut rise, mitigate production decline, and enhance cumulative oil production, while improving the waterflooding response of wells along the fracture direction. Optimal well group performance is achieved at a fracture orientation of 45°, beyond which production declines. Increasing well spacing reduces the water cut rise rate and the production decline rate, thereby improving cumulative oil production. However, it leads to a faster production decline in the early development stage. This work could provide theoretical guidance for waterflooding in ultra-low permeability reservoirs.