Associate Professor Miao Shi
Hebei GEO University, China
Title: Paleoredox conditions and shale gas potential of the Niutitang Formation(South China): Insights from pyrite morphology, Fe speciation, and Fe–S isotopes
Abstract:
The redox conditions of seawater in the shallow-water to deep-water facies of the Early Cambrian Niutitang Formation exhibited significant differences, which controlledthe deposition of black shales.These conditions further affect the porosity of shale, and the evolution of pores is also influenced by subsequent diagenesis, thus leading to a close correlation with the mechanism of shale gas accumulation.In this study, shale samples from the Niutitang Formation in Well Cenye–1 (CY–1), Cengong region, Guizhou Province, were analyzed to reconstruct paleoredox conditions and their impact on shale gas enrichment. An integrated approach combining pyrite morphology, Fe speciation, and Fe–S isotope geochemistry was employed. The research shows three primary morphological types of pyrite: framboidal, euhedral to subhedral, and anhedral (typically amorphous in nature). These different types of pyrite indicate distinct sedimentary environments. Framboidal pyrite indicates a ferruginous-euxinic environment, euhedral to subhedral pyrite suggests an euxinic environment, and anhedral pyrite implies hydrothermal activity during shale deposition. The FeHR/FeT ratios (0.68–0.99) and Fepy/FeHR ratios (0.7–0.98) both indicate that the predominant sedimentary environment was euxinic. The δ56Fe values (0.31‰ to 1.57‰)exhibit a distinct positive drift, while the δ34Spyvalues (-7.76‰ to 17.05‰)display a significant negative drift. The Fe–S isotope trends further confirm that the Niutitang Formation shale was euxinic sedimentary environment. Pyrite exerts a significant control on the enrichment and preservation of organic matter as the intergranular pores within framboidal pyrite aggregates serve as a carrier for the adsorption, preservation, and migration of shale gas. In an euxinic environment, weaker hydrodynamic conditions combined with a more reducing sedimentary environment are more favorable for the preservation of organic matter in shale gas reservoirs, resulting in an increased amount of generated and expelled hydrocarbons.This study systematically elucidates the critical role of pyrite in indicating the depositional environment of shale and the shale gas enrichment process. It provides an important theoretical foundation and key geochemical indicators for optimizing exploration targets in structurally complex regions.
Biography:
Miao Shi, Ph.D., is an Associate Professor and Master's Supervisor at Hebei GEO University, specializing in sedimentary petrology and unconventional petroleum geology. Her research focuses on the characterization of shale oil and gas reservoirs, employing advanced mineralogical and geochemical analyses to investigate key issues such as pyrite genesis, organic pore evolution, and paleoenvironmental reconstruction in marine shales. As a principal investigator, she has led multiple competitive research projects funded by the National Natural Science Foundation of China, the Hebei Provincial Natural Science Foundation, and the China Postdoctoral Science Foundation. Her work addresses critical challenges in shale gas resource evaluation and development, by integrating experimental simulations with field-based studies. Dr. Shi has authored over 30 SCI/EI-indexed publications in high-impact journals including Ore Geology Reviews, Marine and Petroleum Geology, and ACS Earth and Space Chemistry. She is also the author of the monograph Sedimentary Environment and Diagenesis of Organic-Rich Shale, recognized as a National Key Publication during China's 13th Five-Year Plan period. In addition, she holds three national invention patents related to shale composition analysis and pyrite growth simulation. An active member of the Chinese Geological Society and the American Association of Petroleum Geologists (AAPG), Dr. Shi continues to contribute to advancements in the geosciences through interdisciplinary research and academic collaboration.