## 5 Discussion
### The Impact of Sedimentation on Reservoir Pore Structure in Two Sedimentary Systems
#### 5.2.1 Impact of Diagenesis on Pore Structure
Overall, the impact of cementation on the pore structure of the tight reservoirs in the two sets of sedimentary systems indicates that carbonate cementation is the primary influencing factor, clay cementation is a secondary factor, and siliceous cementation has a minimal effect. The cementation in the delta front reservoirs is generally stronger than that in the turbidite reservoirs, resulting in a greater degree of heterogeneity in the pore structures of the delta front subfacies than in those of the turbidite facies. (6) Dissolution  
In the study area's tight sandstone reservoirs, dissolution constitutes the principal mechanism for generating secondary pores. Compared to a primary pore space, these dissolution-induced pores exhibit larger dimensions and greater abundance, which lead to increased pore-throat radii and enhanced connectivity within the pore network. Consequently, the overall pore network becomes more continuous, thereby facilitat  
Figure 12: Conceptual pattern of differential diagenetic processes in turbidite and delta front sandstone reservoirs. ing fluid flow, and the spatial heterogeneity of pore structures decreases relative to the pre-dissolution condition. There are three main types of dissolution in Es3. The direct dissolution of rock fragment particles such as feldspar, debris, and quartz to varying extents results in the formation of intergranular and intragranular pores. The dissolution of carbonate cements results in the formation of intergranular solution pores. The initial replacement of clastic particles by carbonate minerals is followed by the dissolution of the replacement minerals, which causes the indirect dissolution of clastic particles, leading to expanded secondary intergranular pores and intragranular solution pores [32]. Additionally, a small amount of clay matrix dissolution occurs in rocks with relatively high matrix contents. However, owing to the complex nature of the matrix, which is primarily composed of clay minerals, while dissolution can occur under certain temperature, pressure, and physicochemical conditions, the nature of the matrix means that dissolution has a minimal impact on porosity and permeability and does not significantly improve the pore structure. Feldspar dissolution is most common throughout the study area and can occur throughout the burial process, although to varying degrees. Rock fragment particles are affected primarily by the dissolution of plagioclase feldspar. In shallow reservoirs, the intensity is low, whereas in middle-to-deep reservoirs, it is high. Dissolved plagioclase feldspar often has bay-like edges, with some dissolving along cleavage planes to form honeycomb or lattice structures. Strongly dissolved plagioclase feldspars appear as debris or even casts (Figure 5b,f,i,l). Additionally, SEM reveals honeycomb structures formed by feldspar dissolution (Figure 5t). Rock debris dissolution mainly creates intragranular pores (Figure 5a,c,k), whereas quartz particles easily dissolve into bay-like structures, forming secondary intergranular solution pores (Figure 5a,e). Feldspar dissolution is more intense than that of rock debris and quartz particles. The secondary dissolution of intergranular pores is due mainly to the dissolution of carbonate cements in addition to clastic particle dissolution (Figure 5b,d,l,o). A comparison of numerous thin sections and SEM images reveals that the dissolution of rock debris and secondary dissolution of carbonate cements in turbidite reservoirs are significantly greater than those in delta front reservoirs. However, feldspar dissolution is slightly weaker in turbidite reservoirs than in delta front reservoirs. The dissolution of the quartz particles shows little difference (Figure 12). Overall, the intensity of dissolution in turbidite reservoirs is greater than that in the delta front, leading to a greater improvement in the pore structure and the better homogeneity and connectivity of the pores. The occurrence of reservoir dissolution is closely related to the activity of formation fluids.