Fine-grained sedimentary rocks (FGSRs) consist of sediments with grain sizes <62.5 μm. They account for approximately 70% of the total sediments in nature. These rocks are becoming a popular research topic largely due to the increase of unconventional petroleum exploration. Organic-rich FGSRs are important hydrocarbon source rocks in conventional petroleum systems. These rocks can also become reservoirs for shale oil and gas resources. FGSRs are composed of complex lithologies including clay, quartz, carbonates, feldspars, sulfides, biogenic debris (aragonite, opal, and magnesium calcite) and organic matter (OM). They are typically characterized by complex diagenesis, evolution, and fluid-rock interactions. Micro-nano pores generated during diagenesis become important storage spaces and channels for hydrocarbon migration and accumulation. Therefore, the evolution of the diagenetic fluids and associated reservoir responses are key factors controlling the formation of sweet spots in shale oil and gas.

With the rapid development of the shale oil and gas industry, there are several fundamental issues regarding FGSRs that are worth further investigation. Firstly, further studies should be conducted discussing the sources and evolution of the diagenetic fluids associated with complex lithofacies, diagenetic stages, temperature, pressure, etc. Secondly, there need to be further investigations regarding the physical, chemical, and biological processes involved in the diagenesis of FGSRs. Thirdly, studies should investigate the diagenetic path, mass balance, diagenetic fluid transport, and exchange, and organic–inorganic interactions within FGSRs. Finally, there is a need to research the co-evolution of the diagenesis of FGSRs with the thermal evolution of OM, the formation of reservoirs, and their effects on the petrophysical characteristics of reservoirs and hydrocarbon generation, expulsion, and accumulation.

This Special Issue aims to bring together original research and review articles discussing the source and characteristics of diagenetic fluids. Submissions discussing fluid-rock interaction and reservoir response of diagenetic fluids in FGSRs from different basins, sedimentary settings (from marine to lacustrine shales), and geological ages (from Precambrian to Cenozoic) are encouraged. Discussions on the limitations of current models and methods or suggestions for future research on FGSRs are also welcome.

Potential topics include but are not limited to the following:

• Diagenetic fluid types, characteristics, and sources in FGSRs
• Paleo-geofluids in FGSRs
• Diagenetic fluid evolution process in FGSRs
• Diagenetic fluid organic-inorganic interactions in FGSRs
• Hydrocarbons and inorganic fluid occurrence in FGSRs
• Modelling the interaction of fluids and rocks in FGSRs
• Mechanisms of hydrocarbon generation, diagenesis, and pore formation in shales
• Shale reservoir heterogeneity