Abstract
Background: At later development stages of oil fields using reservoir pressure maintenance technology, residual recoverable reserves undergo significant transformation, evolving from a mobile to a low-mobile and, eventually, to an immobile state. These reserves are primarily concentrated in formations and reservoir zones that are not affected by water flooding. Identifying, localising, and developing such reserves are critical for maximizing the ultimate oil recovery factor in mature fields. This issue is particularly relevant for the Uzen field, which is characterized by a high depletion level and significant water cut. When combined, these factors necessitate the optimization of geological and technical measures. Aim: To develop and justify an integrated approach to assessing the localisation of residual oil reserves at the late stage of field development. Materials and methods: This approach implements methodology for the construction of depletion maps based on the analytical modelling of drainage radii of production wells, as well as analysis of changes in reservoir fluid mineralization based on laboratory measurement of the composition of produced and injected water. . Results: The results of this study demonstrate that the developed approach is highly informative. It provides a detailed picture of distribution of residual oil reserves, allows for a quantitative assessment of how different zones are involved in development, and helps improve the efficiency of the waterflooding system. Conclusion: The proposed integrated methodological approach is an effective tool for enhanced oil recovery in mature fields, which facilitate rational management of residual oil reserves and allows for systematic implementation of production stimulation measures in conditions of high field depletion.