## 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  
The diagenesis of the six types of pore structures is summarized via a diagenetic facies classification method, reflecting the impact of multiple factors on pore changes under the control of different sedimentary systems during the processes of sandstone reservoir compaction and porosity enhancement. Additionally, by integrating studies on formation water properties, diagenetic characteristics, and diagenetic evolution sequences and considering the compaction strength characteristics observed between elastic particles, the tight sandstone reservoirs in the study area can ultimately be classified into six diagenetic facies corresponding to lithofacies and pore structure types (Figure 13). 1. Medium compaction-medium cementation-strong dissolution diagenetic facies (according to the Type A pore structure): The diagenetic facies developed in the fine sandstone lithofacies, with moderate grain compaction primarily characterized by point contacts and residual primary pores were relatively well preserved. In addition, both carbonate and clay cementation are moderate. Influenced by the proximity to source rocks rich in organic acids, the dissolution process is pronounced, resulting in noticeable intergranular carbonate cement dissolution pores and intragranular debris dissolution pores, ultimately forming a coarse pore-coarse throat pore structure with an average surface pore rate of 6.68% (Figure 13a1,a2). 2. Medium compaction-medium cementation-weak dissolution diagenetic facies (according to the Type B pore structure): The diagenetic facies as a whole exhibit moderate compaction, predominantly characterized by point and point-line contacts. While some primary pores are well preserved, the cementation is moderate, with a degree of cementation like that of the previous diagenetic facies. These diagenetic facies have developed mainly in the siltstone lithofacies of turbidite reservoirs. Influenced by the mineral composition of the rocks, the debris content is relatively low and the dissolution process is weak, ultimately forming a medium-porosity pore structure with an average surface pore rate of 4.41% (Figure 13b1,b2). 3 Medium compaction-strong cementation-weak dissolution diagenetic facies (according to the Type C pore structure): This type of diagenetic facies developed in the reservoirs of argillaceous siltstone lithofacies and exhibited moderate compaction but strong cementation. Compared with that in delta front reservoirs, the overall cementation in turbidite sedimentary reservoirs is relatively weak. However, the high clay content in the argillaceous siltstone lithofacies led to strong clay cementation. Additionally, influenced by the lithofacies, the high clay content and low abundance of easily dissolvable minerals result in weak dissolution. Owing to the comprehensive effects of various diagenses, the reservoirs in these diagenetic facies feature partially filled intergranular carbonate cements and clay-filled materials, with  
Figure 13: Diagenetic intensity and diagenetic facies classification of tight sandstone reservoirs under different sedimentary systems. Notes: (**a1**) Well TX307, turbidite sandstone, 4227.10 m (cl). (**a2**) Well TX307, turbidite sandstone, 4229.35 m (-). (**b1**) Well T305, turbidite sandstone, 4060.55 m (cl). (**b2**) Well T305, turbidite sandstone, 4032.8 m (-). (**c1**) Well L86, turbidite sandstone, 3937.18 m (cl). (**c2**) Well L81, turbidite sandstone, 3852.76 m (SEM). (**d1**) Well T306, delta front sandstone, 4017.76 m (cl). (**d2**) Well T306, delta front sandstone, 4015.59 m (SEM). (**e1**) Well T305, delta front sandstone, 4205 m (cl). (**e2**) Well T305, delta front sandstone, 4205 m (SEM). (**f1**) Well L98, delta front sandstone, 4294.58 m (cl). (**f2**) Well TX307, delta deta front sandstone, 4364.7 m (SEM). -clay minerals primarily consisting of illite and illite/smectite mixed layers. Therefore, the average surface pore rate is 2.12%, with a fine pore-medium throat pore structure (Figure 13c1,c2). 4.