## 5 Discussion
### Genetic Mechanisms of Reservoir Pore Structures in Different Sedimentary Systems
Meanwhile, secondary dissolution products can provide the material basis for the subsequent cementation, leading to a new round of the cementation-dissolution cycle and further complicating the pore-throat structures. For turbidite reservoirs, the highest-quality pore structure type in the study area is the coarse pore-coarse throat (Type A), which results from the combined effects of fine sandstone lithofacies and medium compaction-medium cementation-strong dissolution diagenetic facies. It has developed mainly at the bottom of sand Group 2 in the low-lying areas of the central part of the study area. The pore structure exhibits favorable petrophysical properties, with porosities of up to 12.565% and permeabilities approaching 10 mD. It has the least complex pore structure and minimal heterogeneity, with the predominant pore type being residual intergranular pores (84.65%) and intergranular and intragranular dissolution pores accounting for approximately 11% of the total pores. The pore diameter ranges widely from 1.92 to 25.37 um, with an average of 10.84 um. In contrast, based on siltstone lithofacies and influenced by medium compaction-medium cementation-weak dissolution diagenetic facies, the reservoirs developed a medium pore-medium throat pore structure type (Type B), with pore diameters significantly smaller than those of Type A. This type developed at the top of sand Group 2 in the eastern part of the study area. The porosity is mainly between 8% and 11%, whereas the permeability is generally less than 1 mD. The pores are predominantly residual intergranular pores (93.59%), with overall pore diameters ranging from 0.46 to 14.14 um, with an average of 3.26 um. In addition to the fine sandstone and siltstone facies, significant amounts of argillaceous siltstone lithofacies are present in the turbidite reservoirs. These lithofacies are characterized by variable sedimentary structures and beddings, including load structures, flame structures, and wavy migration microcrossbedding layers. In these lithofacies, diagenesis primarily involves medium compaction, strong cementation, and weak dissolution, resulting in a fine pore-medium throat pore structure type (Type C) with the smallest average pore diameter in the turbidite sedimentary system. The porosity ranges from 4-8%, and the permeability is between 0.3 and 1 mD. Although the pores are primarily composed of residual intergranular pores (81.91%), the increased clay mineral content has led to a significant increase in the proportion of intercrystalline micropores and microfractures, totaling approximately 11%. The pore diameter distribution ranges from 0.35 to 9.52 um, with an average of 1.93 um. Type C pore structures are distributed in the western part of the Linnan Subsag and are located mainly at the bottom of turbidite sedimentary reservoirs. The formation of the pore structure in delta front sedimentary systems is also controlled by lithofacies and diagenetic facies. Within this sedimentary system, the optimal pore structure is characterized by a medium pore-coarse throat (Type D) developed in the fine-siltstone lithofacies, with a few mudstone bands. This type of reservoir is generally located at the top of delta front sedimentary reservoirs in the structurally high area of the eastern part of the study area. During diagenesis, cementation and dissolution are relatively strong, whereas compaction is of a medium intensity. The type D pore structure is optimal for the delta front facies, with porosities ranging from 8-12% and permeabilities ranging from 0.08 to 3 mD. The pore types are diverse, with dissolution pores being the most prevalent (approximately 44%), followed by residual intergranular pores (39.20%), and intercrystalline micropores being the least common. The range of pore diameters is small, from 0.54 to 4.43 um, with an average pore diameter of 2.12 um, which is the largest among the delta front facies.