对琼东南盆地Q深水区块天然气水合物的几点探讨

此文分析了琼东南盆地Q深水区块的水深、海底温度和地温梯度条件，并在此基础上计算了此区块天然气水合物稳定域（GHSZ，gas hydrate stable zone），计算结果为:（1）在此区块的海底温度和地热梯度条件下，水深大于600 m的海域才能满足在海底形成天然气水合物的温度和压力条件；（2）天然气水合物稳定域的厚度与水深成正比，此区块范围内GHSZ最大厚度在350 m左右。另外，分析了琼东南盆地Q深水区块三维地震资料，并同韩国郁陵盆地的高分辨率地震资料进行了对比，两者有类似的地震异常:都发现了大量的浅层气、碎屑流堆积体、气烟囱等。韩国已在郁陵盆地相应地震异常区域获得了不同类型的水合物实物样品。可以推测，在琼东南类似地震特征处也可能取到相应类型的水合物。通过天然气水合物温度和压力条件计算得出的天然气水合物稳定域底界埋藏深度，可以作为一个约束条件，指导地震剖面中浅层气与水合物的解释。

Discussion on Gas Hydrate in Block Q of Qiongdongnan Basin

Based on analysis of water depth, seabed temperature and geothermal gradient etc. conditions in Deepwater Block Q of Qiongdongnan Basin, the authors calculated GHSZ (gas hydrate stable zone). It reveals two key points. Firstly, under the specific seabed temperature and geothermal gradient conditions in this block, the temperature and pressure requirements for gas hydrate formation can be met only in the sea area with water depth larger that 600 m; secondly, the thickness of GHSZ is proportionate with water depth, and the maximum thickness of GHSZ in this block is 350 m. Comparison of 3D seismic data from Block Q with the highresolution seismic data from Ulleung Basin of South Korea shows that they both have some similar abnormal seismic reflects such as abundant shallow gases, detrital flow accumulation bodies and gas chimney etc.. It is speculated that gas hydrate samples may be acquired from the abnormal reflects which indicate the gas hydrate. The bottom depth of GHSZ inferred from the T-P conditions in Qiongdongnan Basin can be used as constrain condition for the interpretation of shallow gas and gas hydrate.