A Time-Depth Conversion Method Capable of Correcting Shallow Gas Effects

The presence of shallow gas or overlying gas reservoirs often degrades the imaging accuracy of underlying structural formations. To address the “pull-down” effect of deep structural reflectors caused by low-velocity shallow gas anomalies, this study takes the X Gas Field in the Pearl River Mouth Basin as an example. By using spectral attenuation attributes, we finely characterize the planar distribution and temporal thickness of the shallow gas. On this basis, a shallow gas anomaly thickness correction method is established. This approach integrates the temporal thickness of shallow gas (derived from spectral attenuation), characteristics of the seismic velocity field, and velocity differences calibrated by well logs to compute specific depth correction values. Application results, validated through blind well tests, show that the accuracy of the structural map can be improved to within 5 m. This multi-data integration strategy, which combines lateral velocity variation with vertical correction, offers a valuable reference for the detailed characterization of hydrocarbon reservoirs under similar geological conditions.