Abstract: The appearance,distribution and depth of stable zones for the methane gas hydrate in the Okinawa trough are analyzed according to the geological conditions of Okinawa trough,the measured temperatures of bottom water, the measured geothermal gradients and the phase conditions of methane gas hydrate.The results suggest that the Okinawa trough is suitable for the formation of methane gas hydrate. In the northern district of the Okinawa trough,natural gas hydrate appears at the see depth over 600 meters,and the thickness of stable zone for gas hydrate is less than 50 meters.In the middle and southern parts,gas hydrate appears at the sea depth over 500 meters,and the responding thickness of stable zones ranges 25 to 115 meters and 90 to 365 meters,respectively.The stable zones of gas hydrate become thicker and thicker from the north Okinawa to south Okinawa and from the middle part of the trough to the two sides.These conclusions were obtained on the hypotheses of methane gas hydrate,seawater and measured geothermal gradients.If the hypotheses are changed,the natural gas hydrate in the Okinawa trough may be more abundant,and the thickness of stable zones will be greater than the data based on the hypotheses.

Key words: Okinawa trough, natural gas hydrate, development, stable zone, distribution

摘要： 依据冲绳海槽的地质背景、实测底层水温度、地热梯度以及天然气水合物形成与稳定存在的压力和温度条件,分析了冲绳海槽内天然气水合物存在、分布及规模.结果表明:冲绳海槽适合天然气水合物形成,在冲绳海槽北部,天然气水合物分布于水深大于600m的海域,水合物稳定带厚度小于50m;在海槽中部及南部,天然气水合物分布于水深大于500m的海域,水合物稳定带厚度分别为25～115m和90～365m.从冲绳海槽北部到南部、从中央向两侧天然气水合物厚度呈逐渐增加的趋势.上述规律是假设纯甲烷天然气、海水介质以及实测地热梯度等前提下得到的,属于较保守的估计.当假设条件改变时,冲绳海槽天然气水合物稳定带的厚度将会增加.

关键词: 冲绳海槽, 天然气水合物, 发育, 水合物稳定带, 分布