Combined interpretation of marine CSEM and reflection seismic data for gas hydrate characterization in the Shenhu area, South China Sea

To investigate the accumulation characteristics of gas hydrates in the Shenhu Area of the South China Sea from a multi-property perspective, we performed a joint interpretation of marine Controlled-Source Electromagnetic (CSEM) and multi-channel seismic data. The four stratigraphic interfaces identified from the 2D constrained inversion resistivity profiles of two marine CSEM lines correlate well with seismic interfaces T1–T4. A deeply-rooted high-resistivity anomaly zone, extending upward over 3 km in width, couples with chaotic seismic reflections. This correlation confirms the development of mud diapirs and indicates a high thermal maturity of deep source rocks, thereby establishing a foundation for thermogenic gas supply. The CSEM resistivity profiles demonstrate significant advantages in delineating gas migration pathways and reservoir boundaries. They reveal that fault systems control the vertical transport of thermogenic gas, directly influencing the spatial distribution of gas hydrate and free gas. This underscores the effectiveness of integrated seismic-electromagnetic interpretation in analyzing the reservoir transport system. Furthermore, the inverted resistivity values are consistent with drilling results: intervals within the gas hydrate stability zone exhibit high-resistivity anomalies (approximately 5 ~ 10 Ωm), whereas sections without hydrate show no such anomalies. The saturation distribution profile, obtained through joint seismic-CSEM inversion, clearly delineates the saturation characteristics of gas hydrate and free gas. The average saturations at wells W02 and W07 are 0.35 and 0.34, respectively, which deviate by less than 10% from the mean log-derived saturation values (0.32 and 0.33). The integration of marine CSEM and multi-channel seismic data significantly enhances the understanding of gas migration and reservoir systems, thereby contributing to reduced drilling risks.