## 5 Conclusions  
This paper studied three kinds of low-permeability cores of K \(>\) 1 mD, 0.1 mD \(<\) K \(<\) 1 mD, and K \(>\) 1 mD using pore-throat structure, displacement course analysis, and pore-throat utilization characteristics. The main conclusions are as follows:  
1. By using ordered clustering to segment the pore-throat interval, the influence of subjective factors is eliminated, and the accuracy of pore structure characterization is improved. The actual r curve and the converted r curve almost coincide. The improved method can be applied to all cores subjected to HPMI and NMR tests, regardless of the type of pore-throat distribution, and has a wide range of applications. 2. CO\({}_{2}\) has almost no seepage resistance in a low permeability core, and the gas flooding development effect is the best (miscible flooding 80-89%, immiscible flooding (62-66%)). Although CO\({}_{2}\) has a specific resistance to percolation in ultra-low permeability cores, the gas flooding results are relatively good (miscible flooding 74-77%, immiscible flooding 45-51%). Supercritical CO\({}_{2}\) flooding has a good development effect in K \(>\) 0.1 mD reservoirs. The seepage resistance of CO\({}_{2}\) in super-low permeability core is large, and the development effect is the worst (miscible flooding 36-45%, immiscible flooding 28-35%). Miscible flooding can effectively improve the recovery degree in low permeability cores, and the effect of the ultra-low permeability core is the best (20-25%). The effect in an ordinary-low permeability core is slightly worse (18-22%), and the effect in an ultra-low permeability core is the worst (8-12%). 3. The lower the core permeability, the lower the oil and gas seepage capacity. The decrease in core permeability weakens the oil's flow capacity much more than the gas's, resulting in the deterioration of the oil-carrying capacity of oil and gas and the increase of the cumulative gas-oil ratio. In the late phase of K \(<\) 1 mD core displacement, the cumulative gas-oil ratio of miscible flooding is higher than that of  
Figure 16: Line diagram of pore-throat utilization in miscible and immiscible flooding. immiscible flooding. Still, in the early phase of displacement, due to the presence of the back pressure valve, the cumulative gas-oil ratio of immiscible flooding is higher than that of miscible flooding. The cumulative gas-oil ratio of miscible flooding is higher than that of immiscible flooding in the displacement stage of the ordinary low permeability core, and no inversion occurs. 4. The application degree of immiscible flooding to the <10 nm pore-throat region is low (up to 35%), and the higher the core permeability, the lower the application degree of the <10 nm pore-throat region. Miscible flooding can effectively improve the utilization degree of the pore-throat in the entire aperture range, and the higher the permeability, the better the utilization degree. The highest utilization degree of the <3.7 nm pore-throat region is 73%. Conceptualization, Y.S. and C.Z. ; methodology, X.L. and X.W. ; software, J.Z. and B.H. ; validation, X.T. and M.L. ; formal analysis, K.S. and Y.S. ; investigation, C.Z. and X.L. ; resources, X.W. ; data curation, J.Z. ; writing--original draft preparation, B.H., X.T. and M.L. ; writing--review and editing, K.S. and Y.S. ; visualization, C.Z. ; supervision X.L. ; project administration, X.W. ; funding acquisition, J.Z. and B.H. All authors have read and agreed to the published version of the manuscript. This work was support by the National Natural Science Foundation of China (U23B2090), National Key R&D Program of China (2023 YFB4104200), and the CNOOC's \"14 th Five-Year Plan\" major science and technology project (KJGG-2022-12-CCUS-0203). Not applicable. The raw data supporting the conclusions of this article will be made available by the authors on request. Thanks to [PERSON] and [PERSON] of Hebei Ruiniu Company for their experimental technical guidance.