Identifying flooded areas and determining remaining oil potential areas are important research topics in oilfield development. There are many methods for studying remaining oil distribution, but each method has its own limitations in application. Production logging technology can measure the oil/water production rate of each perforation interval in the wellbore, while casing hole saturation logging technology can provide the distribution ratio of oil and water in the reservoir nearby wellbore. However, their detection range can only cover the vicinity of the wellbore, and the logging data cannot fully represent the reservoir characteristics far from wellbore. Reservoir numerical simulation technology can predict the three-dimensional remaining oil distribution of the entire reservoir, but the modeling work is complex, and the simulation accuracy highly depends on geological understanding, resulting in significant uncertainty in the prediction results. Borehole-to-surface electrical potential image technology is an electromagnetic exploration technique that utilizes the significant differences between the electrical signals (potential and electric field) of oil, gas, and water to study the distribution characteristics of oil and water in reservoirs. The detection radius can reach several hundred meters, which can effectively evaluate the inter-well remaining oil, determine the potential area of remaining oil between wells, and improve the success rate of infill wells. In the WB oilfield, 23 wells were selected for electrical potential image data acquisition, covering the entire oil-bearing area. The three-dimensional distribution of remaining oil was obtained by processing and interpreting the acquisition data. The interpretation results indicate that the remaining oil is mainly distributed in layer B1a and B1b. Based on the understanding of remaining oil and production performance analysis, infill well had been proposed and drilled the target oil zones, with a good oil production, achieving good economic benefits. The successful application of borehole-to-surface electrical potential image technology in WB oilfield indicates that it is an effective technology for evaluating inter-well remaining oil.