Geological and Geochemical Characterization of Transitional Shale of the Permian Shanxi Formation in the Eastern Ordos Basin, North China

ABSTRACT The Lower Permian Shanxi Formation in the Eastern Ordos Basin, North China, is a key exploration target for transitional shale gas. Based on facies markers and elemental characteristics, the Shanxi transitional organic‐rich shale are divided into estuary shale and lagoon shale. Various techniques (low‐temperature N 2 /CO 2 physisorption, etc.) are applied to reveal pore structure differences between estuary shale and lagoon shale. The results indicate that the estuary shale exhibit better macroscopic characteristics (organic matter [OM] component, mineral composition, porosity, and gas content) and nanoscale pore structure than those of lagoon shale. The OM enrichment model reveals the differences in OM components, and estuary shale is supplied by both terrestrial and marine OM. During the hydrocarbon generation and evolution process, the marine‐origin sapropelinite has the capacity to generate more organic pores. Organic pores still occupy an important position in estuary organic‐rich shale. Lagoon shale is greatly influenced by terrestrial sources, with most of the OM components being terrestrial OM, along with is primary OM showing poor pore‐forming abilities. Estuary shale reservoir belongs to a pore‐fracture type comprising organic pores, inorganic pores, and microfractures, while lagoon shale reservoir is microfractures type.