win德赢

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 (hyperpycnal) flows, while sandstones deposited in delta front environments are typically associated with massive mudstone. Laminated organic-rich shale deposition occurred in an anoxic, deep-water environment characterized by high primary productivity, whereas massive mudstone formed in environments with high sedimentation rates and substantial terrigenous debris influx. Currently, the exploration potential of sandstone interlayers exceeds that of clay-rich reservoirs, with the greatest potential observed in the sandstone interlayers associated with laminated organic-rich shale formed by gravity (hyperpycnal) flows. Comparative analysis reveals that clay-rich reservoirs with low to medium maturity present great challenges for exploitation, making interlayer-type reservoirs the main focus of exploration at this stage. Nevertheless, clay-rich reservoirs in closed systems with high thermal maturity and organic matter content also hold considerable potential.