Abstract
The 3D seismic data acquired in the central Qiongdongnan Basin, northwestern South China Sea, reveal the presence of shallow gas hydrate, free gas, and focused fluid flow in the study area, which are indicated by multiple seismic anomalies, including bottom simulating reflectors, polarity reverses, pulldowns, minor faults, and gas chimneys intensively emplaced within the shallow strata. A new cold seep is also discovered at approximately 1520 m water depths with an ~40 m wide crater in the west part of the study area. Water column imaging, seafloor observation, and sampling using the remotely operated vehicle “Haima” demonstrate ongoing gas seepages and shallow gas hydrates at this site. Thermogenic gas in the study area migrates from the deep reservoir through the gas hydrate stability zone along deep faults and gas chimneys, forms shallow gas hydrate and free gas, and sustains localized gas seepage within this cold seep. The results provide insight into the relationship between shallow gas hydrate accumulation and deep hydrocarbon generation and migration and simultaneously have important implications for hydrocarbon explorations in the Qiongdongnan Basin, northwestern South China Sea.
Highlights
According to hydrocarbon supplies and metallogenic characteristics, gas hydrates can be characterized into two categories: diffusive and leakage types
A variety of seismic anomalies are observed in the 3D seismic sections (Figures 3 and 4), including polarity reverses, pulldowns, minor faults, gas chimneys, and bottom simulating reflectors (BSRs), which indicate the presence of focused fluid flows, free gas, and shallow gas hydrates in the central Qiongdongnan Basin (QDNB), northwestern South China Sea (SCS)
The first type of seismic anomaly is polarity reverse. It marks a localized decrease in acoustic impedance [36, 37], which indicates the presence of free gas in the strata [38]
Summary
According to hydrocarbon supplies and metallogenic characteristics, gas hydrates can be characterized into two categories: diffusive and leakage types. The diffusive gas hydrates markedly indicated by bottom simulating reflectors (BSRs) dominantly develop in the Shenhu area, northern South China Sea (SCS), and have received extensive and comprehensive research studies [1,2,3]. Both the Shenhu area and the deepwater slope area of the Qiongdongnan Basin (QDNB) provide favorable conditions for leakage gas hydrate formation. Gas hydrate destabilization may occur and release methane which migrates along faults, fractures, pipes, mud diapirs, gas chimneys, etc., into oceans and will nourish cold seeps on the seafloor
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call