Comprehensive recognition and distribution prediction of semi-deep and deep lacustrine source rock of the Lower Paleocene Yueguifeng Formation in Jiaojiang Sag

The Jiaojiang Sag is a low-level exploration area in the East China Sea Basin where hydrocarbon generation has been confirmed but no commercial discoveries yet have been made. Implementation of the development and scale of semi-deep lake-deep lake facies source rocks in the Yueguifeng Formation, the main source rock, is an urgent issue in the next step of oil and gas exploration. Based on the newly acquired 3D seismic, drilling, paleontological and organic geochemical data, the lake facies of the Yueguifeng Formation in the Jiaojiang Dong Subsag was developed in four aspects of rifting, paleogeomorphic background, source area parental rock lithology, and organic matter abundance and type. High-quality source rocks are precisely identified, and their planar distribution and scale are quantitatively predicted through seismic facies analogy analysis. Results show that the development of semi-deep lake to deep lake source rocks in the Yueguifeng Formation in Jiaojiang Dong Subsag is jointly controlled by strong faulting, moderately hilly palaeogeomorphic setting, and the igneous provenance area. As a whole, it is a good to excellent quality source rock, mainly composed of type Ⅱ₁-Ⅱ₂ kerogen. The organic matter is mainly composed of lower aquatic organisms with partly contributions from higher terrestrial plants, and the typical seismic facies shows low frequency continuous strong amplitude parallel reflection. Controlled by the sag structure, the semi-deep lake to deep lake source rocks of the Yueguifeng Formation in Jiaojiang Dong Subsag are mainly developed in the central area and on one side of the steep slope belt of Jiaojiang Dong Subsag. The typical seismic phase is characterized by low-frequency continuous strong amplitude parallel reflection. Using multi-attribute neural network deep-learning technology, we predicted that the maximum area and total volume of the semi-deep lake to deep lake source rock of the Yueguifeng Formation in the subsag are 294 km² and 109 km³, respectively. Overall, we believed that Jiaojiang Dong Subsag has good potential for oil and gas resources and exploration prospect.