Shallow Gas Distribution in the Southwest of Qiongdongnan Basin: Evidence from Geophysical Attributes

Shallow gas, a newly recognized natural gas resource found in deep-water settings, has been identified within the shallow sand-rich sediments in the LS 36-1 area, the Qiongdongnan Basin. These sand-rich sediments display a tongue-shaped Quaternary submarine fan system transported from the western part of the South China Sea. To clearly delineate the spatial distribution of shallow gas in the southwestern area of the Qiongdongnan Basin, we integrated multiple geophysical anomalies that are derived from prestack simultaneous inversion, amplitude-versus-offset (AVO) analysis, forward modeling, and Bayesian lithology-fluid discrimination, thereby delineating the occurrence and distribution of shallow gas. Our results revealed that shallow gas to the south of the Qiongdongnan Basin occurs in layered, heterogeneous submarine fan sediments, as evidenced by seismic data. Although AVO analysis alone cannot discriminate shallow gas in thin layers, combining it with Poisson’s ratio, ratio of P-wave to S-wave velocity, and gas probability derived from AVO inversion significantly improves prediction accuracy. This study demonstrates that shallow gas is widely distributed in a coarse-grained submarine channel-levee system with high saturation, indicating its potential as an unconventional future global deep-water resource.