## 4 Results
### Pore Systems  
#### 4.3.1 Qualitative Analysis  
Based on the comprehensive observations and analysis of thin section and SEM images of 17 tight sandstone cores from the different sedimentary facies of the turbidity current and delta front in the Linnan Subsag, there are five main pore types in the study area: intergranular residual pores, intergranular dissolution pores, intragranular dissolution pores, intergranular micropores, and microfractures (Figure 5a-t). Among them, the intergranular pores are composed of residual intergranular pores and intergranular dissolution pores, with the largest proportion of pores. There are few primary residual intergranular pores (Figure 5b), which are mainly intergranular dissolution pores. They are specifically manifested as feldspar particles, quartz particles, debris, and carbonate cementation dissolution pores (Figure 5a,b,d). The second largest proportion of pores are intragranular dissolution pores, which are composed mainly of feldspar and debris dissolution pores in the study area (Figure 5c,f). However, quartz intragranular dissolution pores are occasionally found in the tight reservoirs of the delta front sedimentary system (Figure 5q). Feldspar particles are the main component of both intergranular and intragranular dissolution. Intergranular micropores are mainly intergranular micropores of clay minerals (Figure 5h,s). In addition, diagenetic shrinkage microfractures have developed in argillaceous layers in tight sandstones (Figure 5p). The primary intergranular residual pores of the turbidite reservoirs of sand Group 2 in Es\({}_{3}\)3 are clearly developed, and there are also many intragranular and granular margin dissolution pores. Overall, the intergranular zone is partially filled with carbonate cementation and clay gap filler (Figure 5a-h). Under the microscope, quartz secondary enlargement is observed (Figure 5e). The degree of pore development is moderate. The intragranular dissolution pores are mainly debris and feldspar dissolution pores (Figure 5a,b,f), whereas the intergranular dissolution pores are mainly felsic particle margin dissolution and carbonate cement dissolution (Figure 5b,d). In addition, obvious feldspar alteration can be observed (Figure 5g). The main pore spaces are the primary residual intergranular pores, debris dissolution pores, feldspar dissolution pores, mineral particle intergranular dissolution pores, and carbonate cement intergranular dissolution pores. In addition, the secondary pore spaces are clay mineral intergranular micropores (Figure 5h). The overall surface pore rate is between 2.12% and 6.68%, and the average surface pore rate is 4.12%. Figure 4: Physical properties of different sedimentary reservoirs for 68 samples: (**a**) Porosity distribution; (**b**) Permeability distribution; (**c**) Correlation between porosity and permeability. Figure 5: Microscopic characteristics of tight sandstone reservoirs in Es\({}_{3}\)\({}^{3}\) in Linnan Subsag. Notes: (**a**) Dissolution pores, well TX307, turbidite sandstone, 4231.8 m (CTS, \(-\)). (**b**) Feldspar dissolution pores, residual intergranular pores and carbonate cement dissolution pores, well TX307, turbidite sandstone, 4230.6 m (CTS, \(-\)). (**c**) Debris dissolution pores, well T305, turbidite sandstone, 4032.07 m (CTS, \(-\)). (**d**) Carbonate cement, carbonate cement dissolution pores, well T305, turbidite sandstone, 4057.02 m (CTS, \(-\)). (**e**) Quartz overgrowth edge, authigenic quartz microcrystalline and residual intergranular pores, well L86, turbidite sandstone, 3935.58 m (SEM). (**f**) Feldspar intragranular dissolution pores, residual intergranular pores, well TX307, turbidite sandstone, 4227.1 m (SEM). (**g**) Feldspar alteration, well T305, turbidite sandstone, 4057.02 m (SEM). (**h**) Clay mineral interstitial material and intercrystalline micropores, well T305, turbidite sandstone, 4032.07 m (SEM). (**i**) Intergranular dissolution pores of feldspar, residual intergranular pores, well L86, delta front sandstone, 4096.6 m (CTS, \(-\)).