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Current research status of flow units: Main views of scholars over time, and the current state of research abroad. In 1984, Hearn CL and others first classified the sandstones in a particular region into 5 sedimentary lithofacies zones; taking into account the combined effects of sedimentation, diagenesis, subsequent tectonic activities, as well as the actions of fluids within the rock pores, they proposed classifying the sandstones in that region into 5 “flow units”. It is also emphasized that the various flow units are not isolated bands, but rather interconnected; within the same flow unit, the permeability varies in both the vertical and horizontal directions, and is not homogeneous. 1986: The continuity of the Weber reservoir, its permeability heterogeneity, various barriers, and various cross-flow conditions all constitute the pathways through which fluids flow within the reservoir. 1987: Embanks further subdivided rock bodies based on the geological and physical variations that affect fluid flow in rocks. 1992: BARR DC refers to rock bodies with similar hydraulic characteristics within a given rock. 1993: Amaefule denotes layers within a given rock that have similar hydraulic characteristics; these are representative basic volumes within the total volume of the reservoir rocks, where the physical properties affecting fluid flow remain constant and allow them to be distinguished from other rock volumes. 1994: Canas used the Inter-well Flow Capacity Index (IFCI) to identify flow units. The research findings show that if two wells are located in the same flow unit, the ratio of their formation coefficients is closely correlated with the ratio of their flow rates ； Otherwise, the correlation is poor. From this, it is possible to determine the distribution range and connectivity of the flow units. In 1995, Guangming Ti et al. first proposed that, based on stratigraphic stratification, correlation, and facies classification, the permeability coefficient (KHe/μ), storage coefficient (ΦHeCt), and net thickness ratio should be calculated for each layer in the cored wells (with μ and Ct not being considered in the actual calculations). Subsequently, clustering was carried out, with each cluster representing a flow unit; these flow units were then extended to wells without cores, using inter-well stratigraphic correlation to establish the inter-well distribution of these flow units. In 2000, Barclay utilized fluid inclusion stratigraphy, specifically FIS (Fluid Inclusion Stratigraphy), to identify oil-water interfaces and flow barriers, and supplemented this with production logging and pressure data to identify flow units. It is worth noting that when there are differences in the physicochemical properties of fluid inclusions between adjacent wells, it indicates the presence of a barrier layer ； And when there are no differences in the physicochemical properties of fluid inclusions between adjacent wells, it cannot be concluded that a barrier layer does not exist. In 2002, R. Aguilera et al. identified flow units by the constant lines of the integrated transport velocity K/Φ on Pickett diagrams. Studies show that for formations with a constant transmission speed K/Φ, the Pickett diagram of effective porosity versus true resistivity consists of a series of parallel lines. The slope of the straight line is related to the porosity index m, the water saturation index n, and the constant in the absolute permeability equation. Through these straight lines, the capillary pressure and pore radius of each type of flow unit at any water saturation can be determined directly, and it is considered that flow units can be characterized comprehensively using Pickett diagrams in single logarithmic coordinates, capillary pressure, pore radius, and Winland’s R35. Main viewpoints of time geologists and the current status of research in China: In 1994, Xiong Qihua discussed the extension from well points to surface levels of sedimentary microfacies, diagenetic reservoir facies, and fracture facies; these elements combine with each other to form the geometric characteristics of the existing pore network, which are characterized by different rock physical properties. In 1994, Feng Xiaohong and others used core data along with the flow zone index FZI to divide Layer II5 into 5 flow units with distinctly different characteristics that could be replicated; each flow unit represents a combination of lithological, physical, oil-bearing capacity, and water-washing characteristics. From 1994 to 1995, Li Sitian and others (1994) as well as Jiao Yangquan and others (1995) noted that within river channel complexes, flow units are bounded by barrier layers; these barrier layers reorganize the various structural units within the sand bodies to form multiple isolated or semi-connected spatial-fluid flow units. Barrier layers are related to level 3 and level 4 interfaces, and the scale of a flow unit may be equivalent to that of one or several point-bar growth units. In 1995, Yao Guangqing and others stated that the rock physical phase is the most fundamental rock unit of flow units; from the perspective of seepage characteristics, the rock physical phase can be regarded as a “hydraulic unit”. In this way, research on the petrophysical phases of rocks can all be regarded as research on flow units. Yao Guangqing, Lü Xiaoguang, et al. (1997) studied the rock physical phases of cored wells using the flow zone index FZI, and by applying an improved permeability calculation method, they effectively enhanced the prediction accuracy of the permeability in uncored zones. In 1996, Qiu Yinan noted that due to the heterogeneity of reservoirs, barriers, and flow bypass conditions, the injected water drives oil along pathways formed by geological structures, which are natural fluid flow channels. In 1999, Wu Shenghe and others proposed a reservoir hierarchical analysis method based on geological research, integrating the principles of high-resolution sequence stratigraphy, hierarchical interface analysis, and quantitative classification of flow units, while applying hierarchical analysis concepts. This method has a clear conceptual framework; it emphasizes the causes and distribution of seepage barriers in flow units, and incorporates the advantages of multi-parameter analysis methods. It is a relatively advanced and comprehensive approach for the study of flow units at present. In 1999, Yan Changhui noted that reservoir rocks with continuous vertical and lateral properties that affect fluid flow and are similar in characteristics require a comprehensive evaluation using multiple parameters related to both the rock and the fluid; fuzzy cluster analysis is employed to classify these rocks into different flow units. In 1999, Sun Laixi and others used the production pressure difference to predict flow units, based on the assumption that fluid flow in oil-water mixtures follows Darcy’s law, and they developed formulas for calculating the production pressure difference for various flow units. This method can avoid the waste of resources resulting from well shutdown pressure testing, as well as the issue of limited data available from stratified pressure testing. Its accuracy depends on factors such as the precision of the parameters chosen and the reliability of the segmentation into flow units. In 2002, Liu Jiyu and others defined a flow unit as a reservoir unit with identical permeability characteristics, suggesting that flow units possess relativity, hierarchy, and scale. After analyzing the basic characteristics of flow units, a classification scheme for their formation was proposed, dividing flow units into 7 categories controlled by faults, barriers, interlayers, permeability variations, stratification structures, fractures, and pore structures. Flow units of different origins reflect the scale and stratification of reservoir heterogeneity, and their research contents and methods vary. In 2002, Zeng Daqian and others applied the principles and methods of high-resolution sequence stratigraphy to study the types of sea-level cycles in the upper Sha3 member of the Pucheng Oil Field in the Dongpu Depression; they established a high-precision sequence stratigraphic framework. By utilizing the correlation between the stratification of reservoir heterogeneity and the stratification of flow units, as well as between this and the hierarchy of sea-level cycles, they classified the reservoir flow units and further analyzed their characteristics and patterns of variation. In 2002, Song Guoying and others applied the principles of high-resolution sequence stratigraphy to further divide flow units. The steps involved using comprehensive analysis of seismic data, well logs, and core samples to determine reference levels, establishing a framework for segmenting the profiles, and then using sedimentary facies to further divide the flow units. In 2005, Zhang Jichun and others utilized drilling data from different stages, logging information, laboratory displacement experiments, as well as various production performance metrics to reveal and characterize the evolution of the properties of flow units throughout the development process. By employing advanced technical methods such as computer workstations, they achieved three-dimensional visual simulation of the various property parameters of these flow units at different development stages, thereby creating a four-dimensional model of the flow units. It not only accurately reflects the changing characteristics of its underground property features in the spatial domain, but also depicts the process of change in these properties over time, thereby revealing and predicting the patterns of oil and water movement within flow units at different development stages as well as the distribution of remaining oil.