Diagenesis and Pore Evolution of the Lower Cambrian Niutitang Formation Shale in Northern Guizhou, in South China

The Lower Cambrian Niutitang Formation shale in northern Guizhou is characterized by high organic matter abundance and was deposited in a deep‐water, low‐energy sedimentary environment, making it an important target for shale gas exploration. In this study, the diagenetic evolution and pore development characteristics of the Niutitang Formation shales were systematically investigated through integrated analyses of core observations, x‐ray diffraction (XRD), scanning electron microscopy (SEM), total organic carbon (TOC), vitrinite reflectance ( R o ), and nuclear magnetic resonance (NMR). The results indicate that the shales experienced complex and multistage diagenetic processes, including mechanical compaction, cementation, dissolution, clay mineral transformation, and thermal evolution of organic matter. Inorganic diagenesis primarily governed the formation and modification of the mineral framework, whereas organic diagenesis controlled the generation and preservation of nanoscale organic pores. Pore evolution exhibits distinct stage‐dependent characteristics. During the early diagenetic stage, strong mechanical compaction and cementation resulted in an extensive destruction of primary intergranular pores. In the middle diagenetic stage, hydrocarbon generation and localized mineral dissolution promoted the development of abundant nanoscale organic pores and secondary dissolution pores. During the late diagenetic stage, enhanced cementation and late‐stage compaction became dominant, resulting in a significant reduction of the pore system, although locally developed microfractures partially improved reservoir connectivity. It further demonstrates that the interconnected effects of organic and inorganic diagenesis are the primary controls on pore evolution in the Niutitang Formation, governing the formation, evolution, and preservation of reservoir space.