Sedimentology and diagenesis impact on Sanduo formation (E2S) in Zhen 11 block of Gaoyou Sag, East China.

Zhen 11 block is located in the deep sag of Gaoyou Sag, North Jiangsu basin, China. It is the main oil-bearing block in the Zhenwu oilfield, which contains multiple types of faults with complex tectonic structures. The Sanduo formation is the target horizon of the study area that has been divided into two members. The purpose of the current study is to evaluate the sedimentology and diagenetic impact on reservoir characteristics. To fulfill the main objective of the study, the core data analysis, thin-section analysis, SEM, CL, and MICP techniques have been used to evaluate the sedimentary facies, reservoir characteristics, and diagenesis of E₂s₁ in the Zhen 11 block. The reservoir rock of E₂s₁ in the Zhen 11 block is mainly lithic arkoses and feldspathic litharenite. The grain sorting and rounding are poor, with low composition and structural maturity, reflecting the characteristics of near provenance. The formation comprises primary pores, secondary pores, and microfractures. The porosity and permeability range from 10 to 31% and 0.4 × 10⁻³μm² to 8000 × 10⁻³μm², respectively. The diagenesis includes compaction, cementation, alteration of clay minerals, and feldspar dissolution. The dissolution of feldspar developed in the early and late burial stages. The mechanical compaction increases by increasing burial depth, due to that mechanism the reservoir characteristics have been reduced. The dissolution of feldspar and the fracturing mechanism is common that enhance the reservoir quality. Carbonate cement and clay contents block pores and pore throats and significantly reduces reservoir quality. E₂s₁ sandstone is commonly deposited in the braided river and meandering stream depositional environment. It consists of an abundance of quartz and feldspar grains with minor calcite cement. Grains are mostly sub-angular to angular, sub-rounded, and moderate sorting, with primary intergranular porosity that increases the reservoir quality. The meandering channel sandstone is comprised of coarse gravel, sandstone, and siltstone from bottom to top with fair reservoir characteristics. Overall the studied formation consists of moderate to good porosity and permeability that is why it can be acting as a good reservoir. [ABSTRACT FROM AUTHOR]