## 5 Discussion
### Mechanism of Aperture Development
#### 5.3.1 Sedimentary Tectonic Factors  
Sedimentation and structure are the main reasons for the initial formation and burial depth of strata [37]. Different sedimentary environments and different material sources have great influence on the formation of reservoirs. By clarifying the sedimentary environment, we can understand the sedimentary types in the sedimentary period, so as to clarify the reservoir lithology in the study area, and divide the shale and sandstone interlayers. By clarifying the material sources, we can understand the mineral types and contents of the constituent rocks, and make a more detailed division of the shale types. In addition, different minerals have different physical properties, which will have different effects on the formation of pores [38; 39]. The Fengcheng Formation in Mahu Sag mainly develops three subfacies deposits from bottom to top: semi-deep lacustrine subfacies, shallow lacustrine subfacies, and lakeshoe subfacies, and mainly develops felsic shale. In addition, there are well-sorted siltstone interlayers in the shallow lake subphase. In the water environment of semi-deep lacustrine subfacies and shallow lacustrine subfacies, carbonate minerals are well preserved, so the content of carbonate minerals is relatively high in some strata. Besides felsic shale, dolomitic felsic shale also develops. But in semi-deep lacustrine subfacies, massive structures (Figure 10a) and horizontal bedding (Figure 10d) are mainly developed. In shallow lacustrine subfacies, the laminae (Figure 10f), dolomite bands (Figure 10e), and siltstone interlayers with anti-rhythmic bedding from fine to coarse (Figure 10c) are mainly developed. Due to the proximity of lakeshoe subfacies to the land, carbonate minerals are susceptible to weathering and terrigenous clastic minerals are abundant; in addition to felsic shale, clay-bearing felsic shale is also developed, and the structure is mainly dominated by wavy bedding (Figure 10b). The mineral composition of shale has a certain influence on the pore and fracture development of shale. As shown in Figure 11, the relationship between various mineral contents and porosity was determined with plotting envelope curves, and the influence of different minerals on porosity was analyzed. Siliceous and carbonate minerals are both brittle minerals; the higher their content, the larger the porosity and the more developed the pore structure. A comparative analysis of Figure 11a,b reveals that, relatively speaking, carbonate minerals exhibit a higher correlation with porosity, with a steeper slope, indicating a stronger positive effect on pore development. An increase in the carbonate mineral content favors pore formation, consistent with the conclusions drawn from the comparison of porosity between different lithofacies in the previous section. On the other hand, as depicted in Figure 11c, the envelope curve slopes downward, indicating that clay minerals have an inhibitory effect on pore formation. A higher clay mineral content corresponds to poorer pore development, aligning with the findings obtained earlier. Figure 11: Relationship between minerals and porosity. (**a**) Relationship between porosity and siliceous minerals; (**b**) Relationship between porosity and carbonate minerals; (**c**) Relationship between porosity and clay minerals. Figure 10: Schematic diagram of sedimentary structure. (**a**) Blocky structure; (**b**) wavy bedding; (**c**) anti-rhythmic bedding; (**d**) horizontal bedding; (**e**) dolomite band; and (**f**) dolomite layers. In addition to the influence of different mineral components caused by provenance on the development of pores and fractures, the different pressure caused by the buried depth of sedimentary strata will also have a certain impact on the development of pores and fractures. Affected by the formation pressure, with the increase of burial depth, the porosity of the reservoir gradually decreases, and the occasional increase in porosity is due to the increase in porosity caused by the dissolution of diagenesis.