## 5 Discussion
### The Impact of Sedimentation on Reservoir Pore Structure in Two Sedimentary Systems
#### 5.2.2 The Impact of Diagenetic Facies on Pore Structure
Medium compaction-strong cementation-strong dissolution diagenetic facies (according to the Type D pore structure): The diagenetic facies developed in the fine-silstone lithofacies are located at the high structural position of the delta front facies. Although these diagenetic facies experience stronger compaction than the three types in turbidite reservoirs, they remain the least compacted within the delta front facies because of their relatively shallow burial depth, with an overall moderate degree of compaction. Delta front reservoirs generally exhibit high cementation contents and strong cementation characteristics, with fewer residual primary pores. Additionally, the intergranular filling consists of carbonate cements and clay infill. The high feldspar content in the fine-silstone lithofacies is subject to the stronger dissolution of feldspar than that of debris and carbonate cements. In other words, strong dissolution leads to both well-developed intergranular and intragranular dissolution pores, ultimately resulting in a medium pore-coarse throat pore structure with an average surface pore rate of 1.99% (Figure 13d1,d2). 5. Strong compaction-strong cementation-medium dissolution diagenetic facies (according to the Type E pore structure): These facies develop in the calcareous siltstone lithofacies and are controlled by the delta sedimentary system in the study area, corresponding to a medium pore-fine throat pore structure with an average surface pore rate of 1.68%. This diagenetic facies exhibit significant compaction, with quartz grains showing pressure dissolution and sutured contacts. Moreover, the calcareous siltstone lithofacies show strong carbonate cementation. Under the combined effects of strong compaction and cementation, a small number of primary pores are preserved. The degree of dissolution is moderate, with the observable dissolution of feldspar and intergranular carbonate cements, resulting in complex and variable pore-throat types. Occasional occurrences of feldspar transforming into kaolinite are noted, and this kaolinitization process can also generate a small number of secondary pores (Figure 13e1,e2). 6. Strong compaction-strong cementation-weak dissolution diagenetic facies (according to the Type F pore structure): The diagenetic facies developed in the argillaceous layered siltstone lithofacies in the central and western parts of the study area are characterized by a relatively low quartz content and weak compaction resistance but a high degree of compaction. The high mud content is accompanied by significant cementation, which preserves only a small number of intergranular residual primary pores. In addition, the intergranular spaces are generally filled with carbonate cements. There are few easily dissolvable minerals, leading to weak dissolution effects. Therefore, fine pore diameters and strong heterogeneity can be found within reservoirs. These diagenetic facies correspond to a fine pore-fine throat pore structure with an average surface pore rate of only 0.86%. However, notably, intercrystalline micropores account for a large proportion of the total pore area, which consists of micropores within kaolinite minerals (Figure 13f1,f2).