To clarify the complex water production types and unclear water flooding mechanisms of horizontal well injection and production well patterns in the USH reservoir of Oman D oilfield due to various vertical reservoir stacking patterns, micro-fracture development, and high-permeability channel water breakthrough. By establishing a mechanism model of dominant channels, six typical reservoir superimposed model were constructed. The numerical simulation method was used to analyze the water breakthrough differences under different models, and the characteristics of dominant channels in oil reservoirs were further identified. A typical chart for identifying the characteristics of dominant channels in oil reservoirs was established. The results indicate that the reservoir type characterized by microfractures and pseudo-inverse rhythmicity determines the water flooding pattern, water breakthrough speed, and water cut increase trend in oil wells. Additionally, the types of water production in USH oil reservoirs are classified into four categories: porosity type, fracture type (traversing the middle and upper parts of the D layer), porosity type (traversing the upper part of the D layer), and another type of fracture type. The higher the position of the preferential flow channel in the vertical direction, the more prone it is to channeling. The research findings provide a reliable basis for the subsequent formulation of measures to stabilize oil production and control water influx, and also offer valuable references for the development of similar oilfields in the Middle East.