## 5 Conclusions  
In this paper, in order to explore the gas occurrence state and the flow characteristics of the oil-gas-water three-phase formation fluid in the depletion development process of volatile carbonate reservoir, microscopic displacement experiments of a typical fractured porous reservoir were carried out. The following conclusions can be drawn by analyzing the experimental results:  
1. In the process of depletion development, the first degassing area of the porous carbonate reservoir is around the production well and the large pore throat area in the model, and the main gas migration channel is the small pore throat area. With the increase of the volume of gas, the gas phase in the small pore throat gradually expands, coalesces and migrates. The degassing sequence of the fractured porous carbonate reservoir is fracture, large pore throat region and small pore throat region. 2. The locations of the gas phase increase in the same order. Gas phase state and position and its change rule is as follows: in the early depletion stage, the gas phase occurs in  
Figure 34: Change of displacement efficiency of porous carbonate rock model. (**a**) Original condition; (**b**) Depletion development; (**c**) Water injection development. Figure 35: Change of oil displacement efficiency of fractured pore carbonate model. (**a**) Original condition; (**b**) Depletion development; (**c**) Water injection development. fractures near the matrix, and rapidly forms a continuous gas phase in the fractures. In the middle depletion stage, the occurrence position extends from fractures near the matrix to the large pore throat region. Along with the continuous gas phase formation and migration in the matrix, the occurrence position extends to fractures, the large pore throat region and the small pore throat region. 3. When the depletion development is converted to water injection development, in the early stage of displacement, the injection water preferentially selects the large pore throat or fracture containing only simulated oil as the flow channel, and the displacement process shows an obvious feature of \"displace the oil, not the gas\". As the injected water restores and maintains formation pressure, the dissolved gas dissolves continuously, and the area where re-dissolution occurs gradually expands from the main line to the edge, increasing the effective mobilization of water flooding. 4. Due to the strong heterogeneity of carbonate reservoirs, the remaining oil in this type of oil field is dominated by a contiguous cluster of remaining oil, followed by the dispersed porous remaining oil, and the membranous remaining oil. Moreover, fractures enhance the influence of heterogeneity, so that the water driving mobilization range decreases obviously, and the remaining oil saturation increases. 5. The microfluidic experiment of water-driven live oil can better simulate and observe the whole process of formation fluid seepage in a volatile carbonate reservoir with depletion and waterflooding development. Through analysis and summary, the oil and gas dynamic occurrence law in the depletion development stage and the oil and gas production law in the waterflooding development stage can be obtained. The experimental results show that this method is a feasible and accurate microscopic physical simulation experiment to study the oil-gas-water three-phase flow law in fractured porous carbonate reservoirs. Conceptualization, P.J. and H.G. ; methodology, P.J. ; software, Y.L. ; validation, Y.L., H.G. and H.F.; formal analysis, L.C. ; investigation, P.J. and L.C. ; data curation, Y.L. and H.G. ; writing--original draft preparation, Y.L. and H.F.; writing--review and editing, P.J. ; supervision, L.C. ; project administration, P.J. ; funding acquisition, P.J. All authors have read and agreed to the published version of the manuscript. Not applicable. Due to privacy restrictions, the data from the study period is unavailable. The authors declare no conflict of interest.