Can clay-rich reservoirs in predominantly-freshwater lacustrine shale systems serve as primary exploration targets in low-medium maturity? A case study of the Triassic Yanchang Formation of the Ordos Basin

作者：Enze Wang, Maowen Li, Xiaoxiao Ma, Menhui Qian, Tingting Cao, Zhiming Li, Sen Li, Zhijun Jin · 发表于：Petroleum Science · 年份：2025 · DOI：10.1016/j.petsci.2025.06.020 · 被引用次数：5 · 研究领域：Hydrocarbon exploration and reservoir analysis、Geological Studies and Exploration、Geological and Geophysical Studies

ABSTRACT Whether clay-rich shale reservoirs with low-medium maturity can serve as primary exploration targets remains a focal point of debate in the academic community. Clarifying the exploration potential of clay-rich shale reservoirs is crucial for the future exploration and development of lacustrine shale. The Triassic Yanchang Formation in the Ordos Basin has been one of most productive lacustrine shale oil systems in China, with substantial oil production capacity already established. While the primary productive layers are currently fine-grained siltstone interbeds, however, it remains a highly debated issue whether the volumetrically more significant clay-rich reservoirs can become viable exploration targets in the near future. To address this issue, we examined the exploration potential of different lithofacies assemblages in Member 7 (Mbr 7) of the Triassic Yanchang Formation, using a borehole in the Tongchuan area of the southern Ordos Basin as an example. We identified favorable exploration targets and assessed whether clay-rich reservoirs formed predominantly-freshwater conditions can become viable exploration targets. The results indicate the presence of six lithofacies in clay-rich reservoirs of Mbr 7 of the Yanchang Formation, with two main lithofacies assemblages: laminated organic-rich shale and massive mudstone. From the perspective of sandstone distribution, the sandstone interlayers within laminated organic-rich shale are primarily formed by gravity (hyper...