Characteristics and Models for Deposition and Accumulation of Gas Hydrate in Northern Continental Slope, South China Sea

Wang, Jianzhong; Yu, Xinghe; Li, Shengli; Zeng, Xiaoming; Li, Wen

South China Sea (SCS) has been confirmed that has good gas hydrate deposits accumulation conditions and exploration prospects. BSR (Bottom Simulating Reflector) was developed and distributed in SCS widely, and it is acknowledged as the most important geophysical indicator for identifying gas hydrate. Under the theory guidance of seismic stratigraphy and sequence stratigraphy, through the method of detailed interpretation and sequence division of more than 150 2-D seismic profiles and 115 3-D seismic profiles in the SCS, based on a integrated analysis of the regional gas source, migration conditions, depositional conditions (deposition facies, deposition rate, sand content rate, lithologic features, etc.) and special depositional body (structural slope, slump block), combined with the BSR distribution characteristics in each sequence and on the plane, the features of gas hydrate deposition accumulation was systematic analyzed in the northern SCS, and two typical deposition accumulation models has been established. The first model is with significant structural slope break, BSR has relationship with slope break zones, deep-water gravity flow and contourites. The rapid sediment unloading area can provide the favorable sedimentary reservoir and cover conditions for gas hydrate. The gas source was mainly from the superficial layer and mostly of biogenic gas, and the mainly migration manner is lateral migration, and the critical condition for gas hydrate formation and accumulation is capping conditions. The second model is with significant submarine bulges. The major BSRs are located in the steep and undulated zone with long-term successional uplift and subsidence on the seaward side. Since the depositional process was regression, it was favorable to the development of gravity-flow deposits in the slope zone, which can provide a suitable reservoir space for the formation of gas hydrates. Also a small number of BSR distributed in relatively simple and flat topography areas, where the water was deeper, just with gravity flow was weak and bottom current was more activity. The gas source of hydrate was mainly from the deep thermogenic gas, the key to gas hydrate formation and accumulation lies in the transport and migration conditions. The first model is mostly distributed in the northeast region of the northern SCS, and the second model mostly distributed in the southwest region of the northern SCS.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013