## 5 Discussion
### Genetic Mechanisms of Reservoir Pore Structures in Different Sedimentary Systems  
The pore structure characteristics of the tight sandstone reservoirs in Es3 in Linnan Subsag are controlled mainly by both sedimentation and diagenetic processes. Based on these findings, a genetic model of the pore structure under the control of lithofacies and diagenetic facies has been established (Figure 14), clarifying the mechanisms of heterogeneity in reservoir pore structures in different sedimentary systems. Figure 14: Genetic model of microscopic pore structure and oil-bearing characteristics of tight sandstone reservoirs under different sedimentary systems. Notes: (**a\({}_{1}\)–f\({}_{1}\)**) Sequentially display the corresponding lithofacies for pore structure Type A–F. (**a\({}_{2}\)–f\({}_{2}\)**) Sequentially display the corresponding diagenetic facies for pore structure Type A–F. (**a\({}_{3}\)–f\({}_{3}\)**) Sequentially display the pore structure Type A–F. (**a\({}_{4}\)–f\({}_{4}\)**) Sequentially display the corresponding oil content for pore structure Type A–F through fluorescence sections. (**g**) Sedimentary model in Es\({}_{3}\)\({}^{3}\), [PERSON]. Previous studies have demonstrated that marine tight sandstone reservoirs, such as the Northlet Formation along the northern Gulf of Mexico, exhibit relatively homogeneous pore structures with minor vertical variation in the porosity and permeability. This phenomenon reflects both the development of a consistent grain framework under continuous, stable marine depositional conditions and the subsequent approximately synchronous diagenetic processes (the compaction-cementation-dissolution cycle) throughout the tight sandstones [78; 79]. However, the study area of this paper is the lacustrine tight sandstone reservoirs, which are governed by both the gravity flow and delta sedimentary systems, resulting in pronounced heterogeneity. Sedimentation and diagenesis determine the pore evolution of tight reservoirs through dynamic coupling. Sedimentation controls the initial grain packing structure and pore distribution and limits the geometry of the primary pores. Diagenesis, under the conditions of a deepening burial, increasing temperature, and fluid chemical changes, progressively reduces primary pores and generates secondary pores through compaction, cementation, and dissolution, causing the primary pore structures and connectivity to undergo cycles of reduction and reconstruction. Ultimately, the interaction coupling of sedimentary and diagenetic processes governs the development of multi-scale and multi-type pore structures in tight sandstones, directly affecting the fluid flow capacity, reservoir quality, and petroleum occurrence characteristics. During the shallow burial and weak diagenetic stage, the primary pores are relatively well-preserved compared to the deep layers, with slight clay cementation and initial compaction. Some soluble rock debris dissolves in weakly acidic formation water, generating a small number of secondary dissolution pores. During the stage of intermediate burial with strong compaction and cementation, compaction and carbonate cementation dominate, significantly reducing the primary pores and filling most of the pore spaces with cements, resulting in a decline in pore connectivity. Under the spatiotemporal coupling effect of sedimentary and diagenetic facies, the compaction intensities, cementation type, and degrees in sandstones of different lithologies controlled and developed by the two sets of sedimentary systems exhibit differences. Consequently, multiple pore-throat combinations develop within these sandstones. During the deep-burial, pore-remodeling stage, secondary dissolution predominates: in turbidite sandstones adjacent to two sets of source rock layers, the hydrocarbon-generating organic acids promote the dissolution intensity to be higher than that of the delta fronts. Therefore, turbidite sandstones develop more secondary pores, increasing both the porosity and permeability.