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Abstract This study investigated the characteristics and genesis of reservoirs in the 2nd and 4th members of Sinian Dengying Formation in northern Sichuan and its surrounding areas, on the basis of outcrop, drilling cores and thin section observation and geochemical analysis. The reservoirs of 2nd member are distributed in the middle part of the stratum. The reservoir quality is controlled by supergene karst and the distribution of mound-shoal complex. The bedded elongated isolated algal framework solution-cave and the residual "grape-lace" cave, which are partially filled with multi-stage dolosparite, constituted the main reservoir space of the 2nd member. There is no asphalt distribution in the pores. The pore connectivity is poor, and the porosity and permeability of the reservoir is relatively low. The reservoirs of 4th member were distributed in the upper and top part of the stratum. The reservoir quality is controlled by burial dissolution and the distribution of mound-shoal complex. The bedded algal framework solution-pores or caves, intercrystalline pores and intercrystalline dissolved pores constituted the main reservoir space of the 4th member. It's partially filled with asphalt and quartz, without any dolosparite fillings in the pores and caves. The pore connectivity is good. Most of the 4th member reservoirs had medium-low porosity and low permeability, and, locally, medium-high porosity and medium permeability. Affected by the development of mound-shoal complex and heterogeneous dissolution, the platform margin along Ningqiang, Guangyuan, Jiange and Langzhong is the most favorable region for reservoir development. Deep buried Dengying Formation in the guangyuan and langzhong areas should be the most important hydrocarbon target for the future exploration. [ABSTRACT FROM AUTHOR]

The Dengying Formation is an important stratum of exploration in the Gaoshiti-Moxi structure belt in the Sichuan Basin. Therefore, this study combines core, thin section, mud logging data and geochemical analysis (C, O and Sr isotopes) with seismic section data to investigate the basic characteristics and genesis of the Dengying Formation reservoir. Observations indicate that the reservoir rocks mainly consist of sand crumb dolomites, algae laminated dolomite and breccia. The reservoir space is dominated by porous dissolved holes, dissolved pores (or holes) along the direction of algal laminae, intra-grit holes and residual “grape lace” holes. The reservoir has the characteristics of low porosity and medium-permeability. There are three types of reservoir: porous reservoir, fractured porous reservoir and cave reservoir. The reservoir was formed by the common action of deposition, diagenesis and tectogenesis. Sedimentation is the basis and presupposition for reservoir development, but the effective reservoir is mainly controlled by the algal flat microfacies; Furthermore, compaction, cementation and filling are the main causes of reservoir density; Recrystallization is the basis for the formation of porous reservoir; Supergene dissolution is the key to reservoir formation; Buried dissolution also promotes the formation of a high quality reservoir. The fractures formed by tectogenesis significantly improve the permeability of the reservoir and contribute very little to porosity. The reservoir gradually evolved and formed under the control of various geological and diagenetic activities. This study provides important information and references for oil and gas exploitation and development in central Sichuan. [ABSTRACT FROM AUTHOR]