D Oilfield has entered the late stage of ultra-high water cut, facing challenges such as small-scale and scattered remaining oil enrichment zones, a high proportion of low-productivity and inefficient wells, and limited effectiveness of conventional potential tapping measures. Numerical simulation methods were systematically employed to investigate the formation conditions of remaining oil enrichment zones at the fault margins and sand body facies transition zones in D Oilfield. Based on the break-even principle, the economic thresholds for sidetracking horizontal wells were determined, and the optimal range of dimensionless lengths for the horizontal sections of sidetracked wells was clarified. According to the equivalent circle conversion diameter, the area thresholds of enrichment zones for potential tapping by different types of sidetracked horizontal wells were provided. Taking Block X as an example, based on detailed reservoir description, remaining oil enrichment zones were screened according to thickness and area thresholds, and a planar distribution map was created by superimposing enrichment zones from various layers. Personalized potential tapping plans were designed according to the technical characteristics of sidetracked horizontal wells and the types of remaining oil enrichment zones. Eight inefficient wells were selected for on-site window sidetracking, achieving significant production increase. The formation conditions of remaining oil enrichment zones established in this paper are highly consistent with on-site realities, and the proposed horizontal well screening thresholds are more precise and reasonable, providing important guidance for the application of sidetracked horizontal well technology in the management of ultra-high water cut inefficient wells and precise potential tapping.