Application of Integrated Geophysical Prospecting Technology in Deep Oil and Gas Exploration of the Erlian Basin: A Case Study of the Gaolihan Sag

Exploration of the Gaolihan (GLH) Sag in the Erlian Basin remains low due to the discontinuity of early-stage 2D seismic surveys that have failed to provide regional coverage, leaving the deep geological framework unclear and hindering hydrocarbon breakthroughs. To address this problem and to evaluate the resource potential of the pre-Cretaceous formation, this study applied an integrated geophysical workflow combining 1:50,000 high-precision gravity–magnetic surveys, gravity–magnetic well–seismic joining in the forward and inversion directions, layer stripping, and time–frequency electromagnetic method (TFEM) profiling. Using logging resistivity curves from wells GC1 and LT1 for electrical calibration, we delineated the fault system, stratigraphic framework, and deep lithology of the GLH Sag. The key results include the following: (1) identification of 12 faults defining a “three sags and three uplifts” structural pattern; (2) burial depths of the Cretaceous, Jurassic, and Carboniferous–Permian basements ranging from 3000 to 3300 m, 4400 to 4600 m, and 6500 to 6700 m, respectively; and (3) recognition of three electrical layers within the Jurassic, with high-resistivity intervals indicating basalt and low-resistivity intervals interpreted as coal-bearing formation of the Lower Jurassic Hongqi formation. Quantitative validation against wells GC1 and LT1 demonstrates that the TFEM-inverted resistivity values show an average absolute deviation of ~2.5 Ω·m from measured logs (relative error <12% for resistivities >5 Ω·m), with an overall stratigraphic boundary consistency exceeding 85%. Lithologic prediction accuracies reach 88% for sandstone/siltstone and 82% for mudstone/carbonaceous mudstone. This integrated workflow proves effective for deep structural imaging and lithology prediction in volcanic-covered, seismically poor areas, and provides a practical reference for similar low-exploration basins.