## 5 Discussion
### The Impact of Sedimentation on Reservoir Pore Structure in Two Sedimentary Systems
#### 5.1.2 Impact of Lithofacies on Pore Structure  
The tight sandstone reservoirs controlled by two different sedimentary systems exhibit diverse lithofacies types, but the impact and control of these lithofacies on the microscopic pore structure of the reservoirs remain unclear. Therefore, it is necessary to discuss the sedimentary processes under the control of the gravity flow and delta front subfacies at both macro- and microscales to clarify the relationships between different lithofacies and the microscopic pore structures of reservoirs. The turbidite sandstones are generally coarse, are predominantly composed of fine sandstone and siltstone, and exhibit distinctive gravity flow sedimentary structures. The delta front reservoirs are primarily composed of fine siltstone and calcareous siltstone. The sedimentary structures are relatively sparse, with some mudstone bands developed. Summarizing the lithofacies classification results, different pore structure types correspond to the following lithofacies, as shown in Figure 10. In turbidite sandstone reservoirs, the Type A pore structure is associated with fine sandstone lithofacies, which predominantly consists of massive fine sandstone, with some cores displaying disturbed structures and minor mudstone bands. The type B pore structure corresponds to siltstone lithofacies, which consists mainly of massive siltstone, but also features cross-bedding and convolute bedding. The type C pore structure is linked to argillaceous siltstone lithofacies, which are characterized by variable sedimentary structures and bedding, with load structures and flame structures developed, and occasional wavy migrating microcross-bedding. Under the influence of the delta front subfacies, the Type D pore structure corresponds to the fine siltstone lithofacies, which predominantly consists of massive structures with minor mudstone bands. The type E pore structure includes a variety of lithofacies, such as calcareous siltstone lithofacies and argillaceous layered siltstone lithofacies. The former is mainly massive, whereas the latter features feathery sedimentary structures. The Type F pore structure is associated with silty mudstone lithofacies and is characterized mainly by massive structures, although some cores contain debris or sandy masses. The lithofacies description and spatial distribution characteristics are illustrated in Figure 10. In turbidite sandstone reservoirs, the first type of lithofacies is fine sandstone, which predominantly consists of massive fine sandstone, with some core samples displaying disturbed structures and a small number of mudstone bands. These lithofacies are present mainly at the bottom of the turbidite sandstone reservoirs (sand Group 2), which are in the relatively low-lying area at the center of the subsidence zone within the study area. The second type are siltstone lithofacies, which primarily consist of massive siltstone, but have a visible development of cross-bedding and encapsulated bedding. These lithofacies are present mainly at the top of the gravity flow sedimentary reservoirs in the eastern part of the study area. The final type of lithofacies in the turbidite sandstones is argillaceous siltstone. It is characterized by variable sedimentary structures and bedding, specifically showing the development of load structures and flame structures, while occasional wavy migration microcrossbedding can also be observed. These lithofacies are distributed primarily in the western area of Linnan Subsag and is located mainly at the bottom of turbidite sedimentary reservoirs. With respect to the three types of lithofacies in the gravity flow reservoirs, the fine sandstone and argillaceous siltstone lithofacies both develop at the bottom of sand Group 2, which is in the central and western areas of the study area. In contrast, the siltstone lithofacies are present at the top of sand Group 2, which is primarily situated in the eastern part of the study area.