## 6 Conclusions  
(1) Based on the analysis of sedimentary facies, logging facies, seismic facies, and the biogenic development characteristics during the Changxing period, the sedimentary system types of the Changxing Formation in the eastern Sichuan region have been clearly defined. During the early Changxing period, the overall sedimentary environment was dominated by carbonate deep-shallow ramp deposition. In the middle to late Changxing period, carbonate platform deposition developed, featuring open platform facies, platform margin facies, and slope-basin facies. These facies can be further subdivided into subfacies such as platform flat, intra-platform depressions, platform margin reefs, and platform margin shoals. (2) The paleo-topography of the Wolong River-Yangdu platform inner depression shows that the paleogeomorphology of the northern margin of the platform was higher than that of the southern margin, the bio-refer and shoal assemblage on the northern edge primarily develops in the lower part of the Changxing Formation, sections 2 and 3, while on the southern edge, it mainly develops in the upper part of section 3 of the Changxing Formation. (3) The Changxing Formation in the eastern Sichuan region exhibits significant heterogeneity. The platform reef and shoal facies represent the most favorable depositional  
Figure 10: Relationship between the degree of dolomitization and sedimentary microfacles in the core section of the Changxing Formation at well W118. environment for reservoir development. Reef limestone (dolomitic limestone) and grain dolomite are the primary lithologies of the reservoir. Reservoirs are primarily developed during periods of relative sea-level fall. The distribution of the dominant reservoirs also exhibits distinct characteristics. On the northern side of the platform depression, the Changing Formation reservoirs have undergone relatively low levels of dolomitization, predominantly consisting of limestone reservoirs. In contrast, the southern side of the platform depression is primarily composed of crystalline dolomite and residual biosparite dolomite reservoirs. The main types of reservoir space are inter-crystalline (dissolution) pores, moldic pores, and intraparticle dissolution pores. Some well sections also show the development of fractures. (4) Through the analysis of petrophysical data from multiple well locations, it was found that the reservoirs in this region generally exhibit low porosity and low permeability characteristics. This study indicates that the reservoirs primarily develop during periods of relative sea-level fall. The diagenetic processes that favor reservoir development include dolomitization, dissolution, and fracturing. Dissolution promotes the further development and enlargement of pores, while fracturing plays a key role in improving the petrophysical properties of the reservoir. Dolomitization, particularly burial dolomitization, is the most widespread and significant diagenetic process in the Changxing Formation reservoir. It plays a crucial role in enhancing the reservoir properties by increasing porosity and permeability in specific intervals, thus promoting the development of favorable reservoirs. (5) This study also indicates that basin subsidence has a significant impact on compaction and cementation, which in turn influences the development of primary porosity and secondary pores. Tectonic subsidence, changes in bathymetry, and diagenetic processes (such as early cementation, dissolution, and dolomitization) collectively control the heterogeneity and distribution of the Changxing Formation reservoirs. (6) The development of dominant reservoirs is often controlled by factors such as depositional conditions, sea-level fluctuations, and diagenetic processes. Paleogeomorphological conditions determine the distribution of relatively high-energy facies belts, which provide the material foundation for reservoir development.