Gas hydrate accumulation associated with fluid escape structure in the western margin of South China Sea

Gas hydrates have been found in the western continental margin of South China Sea, which are revealed by widespread bottom simulating reflectors (BSRs) imaged from a three-dimensional (3D) seismic volume near the Guangle carbonate platform in the western South China Sea. Fluid-escape structures (faults and gas chimneys) are originated below BSR were distinguished. A comprehensive model in three-level structure was proposed to depict the gas hydrate accumulation in the study area. In Level 1, regional major faults and gas chimneys provide the first pathways of upward migration of gas near basement. In Level 2, pervasive polygonal faults in carbonate layer promote the migration of gas. In Level 3, gases sourced from near-basement accumulate within shallow sediment layers and form gas hydrate above the unit with faults once appropriate temperature and pressure occur. The gas hydrates in the study area are mainly in microbial origin, and their accumulation occurs only when fluid-escape structures align in all the three levels. The proposed model of the gas hydrate accumulation in western SCS margin provides new insights for further studies in this poorly studied area.