Investigation for shale gas using potential field methods: A case study of the Youjiang Basin in Guangxi, China

Abstract China is rich in shale gas resources, and the Youjiang Basin in Guangxi is a major potential area and exploration region for shale gas. To determine the depth of the gas-rich layers in the Youjiang Basin of Guangxi and delineate prospective areas, potential field methods were used to explore the Youjiang Basin. Combined with geological and drilling data from the Youjiang Basin, the nonseismic geophysical data were processed and comprehensively studied. Gravity data were fitted quantitatively using 2.5D visualization forward modeling, and magnetotelluric data were inverted using 2D nonlinear conjugate gradient inversion. This yielded the density and electrical resistivity distribution characteristics within the study area of the Youjiang Basin. The basement, structural features, spatial distribution of mudstone and shale, as well as the thickness and burial depth of the target layers, were evaluated. The results show that the top interface of the Luzhai Formation, the main shale gas reservoir, is buried at depths ranging from 0 to 2600 m, with an average depth of approximately 1000–1500 m. The top interface of the Luofu Formation is buried at depths between 550 and 3900 m, with an average depth of around 2000–2800 m. Potential field methods have proven effective, reliable, and credible in detecting shale gas in the Youjiang Basin of Guangxi. These methods have revealed the geological structures of the shale gas reservoirs in the Youjiang Basin, providing important geophysical evidence for evaluating shale gas prospective areas in this area.