Reservoir petrofacies — A tool for characterization of reservoir quality and pore structures in a tight sandstone reservoir: A study from the sixth member of Upper Triassic Yanchang Formation, Ordos Basin, China
التفاصيل البيبلوغرافية
العنوان:
Reservoir petrofacies — A tool for characterization of reservoir quality and pore structures in a tight sandstone reservoir: A study from the sixth member of Upper Triassic Yanchang Formation, Ordos Basin, China
Reservoir petrofacies is an important tool for the better understanding of the key petrographic parameters (primary texture and detrital component, types and processes of diagenetic alteration) that control reservoir properties of tight sandstones. This study aims to investigate sandstone texture and composition, and diagenetic features of the sixth member of Upper Triassic Yanchang Formation (YC6 member), Ordos Basin, China, and to examine controls of diagenesis and petrofacies on reservoir quality and pore structures of tight sandstone reservoirs. This study has been carried out using petrography, XRD, SEM, routine core analysis and mercury intrusion capillary pressure (MICP) test. The YC6 member sandstones are moderately well sorted, very fine- to fine-grained arkoses. The reservoir quality and pore throat distributions are highly heterogeneous in the sandstones. Four reservoir petrofacies are defined based on the combination of sandstone detrital components, diagenetic processes, pore types and reservoir properties. Contrasting diagenetic characteristics between these petrofacies are mainly determined by detrital grain size through ductile grain compaction. Ductile grain compaction has a significant control on porosity and permeability of the sandstones. Especially, the poor quality has been encountered in the petrofacies where ductile grain content is >12%. Calcite cement has helped destroy quality of the petrofacies where the cement is present in amounts >15%. Reservoir quality is best for the petrofacies that is poor in both ductile grain and calcite cement and commensurately is rich in secondary dissolution. Four pore-facies types are defined based on the dominant pore throat dimension of the sandstones. The large pore-throat regime determines permeability and fluid flow of reservoir rocks. A good correlation between pore-facies and petrofacies indicates diagenetic effect on pore structures of the sandstones. The study provides insights into how reservoir quality and pore structures of tight sandstone reservoirs are correlated with reservoir petrofacies.
