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A new 3D seismic reflection data volume acquired in 2012 has allowed for the detailed mapping and characterization of gas hydrate distribution in the Pearl River Mouth Basin in the South China Sea. Previous studies of core and logging data showed that gas hydrate occurrence at high concentrations is controlled by the presence of relatively coarse-grained sediment and the upward migration of thermogenic gas from the deeper sediment section into the overlying gas hydrate stability zone (BGHSZ); however, the spatial distribution of the gas hydrate remains poorly defined. We used a constrained sparse spike inversion technique to generate acoustic-impedance images of the hydrate-bearing sedimentary section from the newly acquired 3D seismic data volume. High-amplitude reflections just above the bottom-simulating reflectors (BSRs) were interpreted to be associated with the accumulation of gas hydrate with elevated saturations. Enhanced seismic reflections below the BSRs were interpreted to indicate the presence of free gas. The base of the BGHSZ was established using the occurrence of BSRs. In areas absent of well-developed BSRs, the BGHSZ was calculated from a model using the inverted P-wave velocity and subsurface temperature data. Seismic attributes were also extracted along the BGHSZ that indicate variations reservoir properties and inferred hydrocarbon accumulations at each site. Gas hydrate saturations estimated from the inversion of acoustic impedance of conventional 3D seismic data, along with well-log-derived rock-physics models were also used to estimate gas hydrate saturations. Our analysis determined that the gas hydrate petroleum system varies significantly across the Pearl River Mouth Basin and that variability in sedimentary properties as a product of depositional processes and the upward migration of gas from deeper thermogenic sources control the distribution of gas hydrates in this basin.

For understanding the Cenozoic subsidence and lithospheric stretching deformation of the Baiyun deepwater area, two seismic profiles are selected for backstripping and stretching factor calculating. Results show that Cenozoic Empty Basin Subsidence (EBS) of this area can be divided into four episodes from fast to slow, (1) 65~24.4 Ma, (2) 24.4~18.5 Ma, (3) 18.5~13.8 Ma, (4) 13.8~0 Ma; Moreover, three periods of fast post‐rift EBS (24.4~21 Ma, 18.5~16.5 Ma, and 13.8~10.5 Ma) and four periods of slow post‐rift EBS (30~24.4 Ma, 21~ 18.5 Ma, 16.5~13.8 Ma, and 10.5~0 Ma) are identified. Syn‐rift EBS of 200~2100 m and post‐rift EBS of 1000~1500 m in the Baiyun deepwater were affected significantly by basement structural relief, which increased gradually towards the continent‐ocean boundary. Lithospheric stretching factors 1~7 calculated based on the syn‐rift EBS have the same trend as whole crust with greater lithosphere stretching than whole crust in the sag and equivalent of both in basement high and continent‐ocean boundary. There is 300~700 m post‐rift anomalous EBS inversely correlated with the basement structural relief, that is, there is less post‐rift anomalous EBS of about 300 m in the sag, but about 600 m in basement high which may be related to the breakup of lithosphere.

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