Pore characteristics of lacustrine shale within the oil window in the Upper Triassic Yanchang Formation, southeastern Ordos Basin, China

摘要

Organic matter (OM)-rich shale in the Yanchang Formation is recognized as a promising hybrid shale oil/shale gas system in lacustrine strata in China. Being mainly in the oil window, both the type and distribution of the pores in the shale have been affected by several factors, including petroleum expulsion and retention, mineral and organic composition, and compaction. To obtain a better understanding of the factors controlling OM pore development, 10 core samples were selected with various OM content from the Chang 7 and Chang 9 members of the Yanchang Formation for pore characterization. The investigation combined microscopic observation, both of thin sections and ion milled surfaces of samples with low-pressure carbon dioxide and nitrogen adsorption and bulk porosity measurements, with the main emphasis being on OM-associated pores.