Research on Potential Lacustrine Source Rock Prediction in the Frontier and Ultra‐Deep Water Baiyun Southern Sag, Pearl River Mouth Basin

ABSTRACT The Baiyun Southern (BS) Sag, located in the Zhu‐II Depression in the ultra‐deep waters of the Pearl River Mouth Basin, experienced limited exploration, with its hydrocarbon exploration potential remaining ambiguous. A quantitative source rock assessment within the sag is pivotal for future exploration direction. Though sited in the deep‐water realm, the BS Sag shares a similar early Eocene rifting structure to the shallow‐water sags of the Zhu I Depression in the Pearl River Mouth Basin, where the presence of the Eocene Wenchang Formation's semi‐deep lacustrine source rocks is proven. Guided by these analogues, this study integrates geological analysis and seismic attribute analysis to affirm the presence of lacustrine source rocks and map their spatial distribution. The results show that the BS Sag is characterised by a high rate of subsidence and an optimal sediment flux conducive to the formation of semi‐deep lacustrine source rock. Geochemical biomarkers, particularly the presence of C 30 4‐methylsteranes, possibly derived from aquatic organisms, indicate lacustrine source rocks. Seismic studies in the analogue sags have shown that the semi‐deep lacustrine source rocks exhibit low frequency, high continuity, and strong amplitude anomalies, which are also the seismic characteristics of the WC Formation in the BS Sag. The seismic sweetness attribute emerges as the most effective presenter of the potential source rocks in the BS Sag. The paleogeomorphology data and sweetness attribute are then applied as inputs into a K‐means clustering algorithm to classify the source rock geobodies. The results show that Baiyun Southern Sag could have a large distribution of Wenchang semi‐deep lacustrine source rock with an area of 161 km 2 and a volume of 77 km 3 , which can contribute to 0.3 billion cubic meters of hydrocarbon resource. The study's results can be used to guide future exploration in the Baiyun Southern Sag and other similar paleo‐rift sags and add confidence to pursue deep plays in the ultra‐deepwater.