Diagenesis of microbial dolomite reservoirs in the second Member of Dengying Formation of Ediacaran in the Penglai area,Sichuan Basin:Insights into the formation and evolution of high-quality reservoirs
[Objective]The microbial dolomite of the second Member of the Dengying Formation(Deng 2 Member)in the Penglai area of the Sichuan Basin is widely distributed and considered a potential target for deep carbonate oil and gas exploration.Unlike conventional high-quality reservoirs characterized by porosity and karst fractures,the carbonate rocks of the Deng 2 Member mainly consist of microbial dolomite.The genesis and diagenetic evolution of these high-quality reservoirs remain unclear.[Methods]This study employed petrographic thin sections,scanning electron microscopy(SEM),cathodoluminescence,and computed tomography(CT)scanning to conduct a detailed analysis of the microbial dolomite reservoirs in the Dengying Formation,using field outcrop and core samples.The aim was to gain a deeper understanding of the effects of diagenesis on pore formation and the development of high-quality reservoirs.[Results and Conclusion]The microbial carbonate reservoirs in the study area were characterized by low porosity and very low permeability,predominantly consisting of fracture-porosity(cavity)type microbial dolomite.The reservoir space was primarily composed of intergranular dissolution pores,residual framework dissolution pores,intragranular dissolution pores,and small to medium-sized dissolution cavities,with minor occurrences of intercrystalline pores and intercrystalline dissolution pores.The Deng 2 Member has undergone multiple diagenetic processes;penecontemporaneous dissolution and early epigenetic dissolution were key factors in enhancing porosity.[Significance]These findings enhance the understanding of the genesis of high-quality microbial carbonate reservoirs in the Ediacaran System of the Sichuan Basin and provide valuable information for deep oil and gas exploration and development in the region.
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