HU P, YIN J, WANG Z Q, et al． Diagenetic and diagenetic facies in the first member of Dainan Formation of the Paleogene in Gaoyou Sag, Subei Basin[J]. Journal of Henan Polytechnic University( Natural Science) ， doi: 10.16186/j.cnki.1673-9787.2025120096.

doi: 10.16186/j.cnki.1673-9787.2025120096

Received： 2025-12-29

Revised： 2026-04-21

Online： 2026-07-06

Diagenetic and diagenetic facies in the first member of Dainan Formation of the Paleogene in Gaoyou Sag, Subei Basin (Online)

Hu Ping, Yin Jie, Wang Zhenqi, Wu Nan, Ye Lin, Duan Mingyang

School of Geosciences, Yangtze University, Wuhan 430100,Hubei,China

Abstract: Objectives This study aims to elucidate the genetic mechanisms and porosity evolution pathways of heterogeneous reservoirs, and to investigate the distribution of diagenetic facies based on quantitative diagenetic parameters and sedimentary microfacies. Methods Taking the first member of the Paleogene Dainan Formation (E₂d₁) in the Gaoyou Sag of the Subei Basin as the research object, this study comprehensively employs thin-section petrography, X-ray diffraction (XRD), scanning electron microscopy (SEM), high-pressure mercury intrusion porosimetry (HPMIP), and nuclear magnetic resonance (NMR) to systematically characterize reservoir properties and diagenetic processes. Results The reservoir space of the E₂d₁ is dominated by residual primary pores and intragranular dissolution pores, with secondary intergranular dissolution pores and fractures. The pore-throat connectivity is relatively poor, characterized by a combination of micrometer-scale pores and sub-micrometer throats. The reservoir primarily underwent three evolutionary stages: compaction and cementation in the early diagenetic stage B, dissolution in the middle diagenetic stage A1 sub-stage, and late cementation in the A2 sub-stage. It is currently in the transition from middle diagenetic stage A to B. Mechanical compaction and early calcite cementation destroyed a significant amount of primary porosity, which is the main reason for reservoir quality degradation. The dissolution of feldspar and unstable lithic fragments created secondary porosity, playing a constructive role in improving reservoir properties. The E₂d₁ can be classified into four diagenetic facies. The weakly compacted-weakly dissolved facies and moderately compactied-medium dissolved facies exhibit better physical properties and are mainly developed in underwater distributary channels within delta front and fan-delta front microfacies, representing favorable reservoirs in the study area. The moderately compacted-carbonate cemented facies and strongly compacted-clay mineral cemented facies essentially possess no reservoir potential. Conclusions The E₂d₁ reservoir is a typical "poor initial endowment, modified later" type. The development of high-quality reservoirs followed a process of "foundation by favorable sedimentary facies, preservation through early weak destruction, and modification by mid-term dissolution." Future exploration should focus on the spatial distribution patterns of the weak compaction-weak dissolution and medium compaction-medium dissolution diagenetic facies to provide a geological basis for oil and gas exploration and development.

Keywords: reservoir characteristics; diagenesis; diagenetic facies; Paleogene;E₂d₁; Gaoyou Sag