Reservoir Characteristics and Shale Oil Enrichment of Shale Laminae in the Chang 7 Member, Ordos Basin

The laminae of lacustrine shale in China have been systematically identified and characterized by a combination of core/slice observations, mineral compositions, geochemical analysis, pore structure characterization, and oil-bearing evaluation. The shale of the Chang 7 Member, Yanchang Formation, Ordos Basin was examined as an example in the study. Four types of laminae are developed in the Chang 7 Member, including felsic laminae (FQL), clay laminae (CLL), organic matter laminae (OML), and tuff laminae (TUL). The shale reservoirs exhibit significant heterogeneity. Of these, FQL and TUL have superior reservoir characteristics. The pore diameter of TUL is primarily composed of micrometer-sized secondary pores that are generated during the diagenesis process, while mesopore and macropore development are dominant in FQL. The main source laminae in the Chang 7 Member of the Ordos Basin are the OML and CLL, while the main reservoir laminae are the FQL and TUL. Some of the hydrocarbons produced by hydrocarbon generation are stored in the pore space inside the laminae, while the majority migrate to the inorganic pores of the adjacent FQL and TUL. It confirms that OML and CLL afford abundant shale oil, the combination of organic pores and inorganic pores in FQL and TUL serve as reservoir space, and the “clay generation-siliceous reservoir” shale oil enrichment model is established in the Chang 7 Member of Ordos Basin.