南海北部陆坡坳隆断裂带中水合物赋存的温压场环境

天然气水合物的发育和赋存明显受构造条件控制,一些活动和非活动大陆边缘的特殊构造单元,如增生楔、泥火山、泥底辟、海底滑塌体均有利于水合物的发育和赋存。南海北部陆坡天然气水合物调查研究表明:南海北部陆坡的坳隆断裂带是有利于天然气水合物发育和赋存的重要构造之一。选择穿过坳隆断裂带的地震剖面A,根据南海北部陆坡海水深度和海底温度的关系曲线,计算了沉积物的温度;并在拟合沉积物深度与体密度关系曲线的基础上,计算了沉积物中的净岩压力,进一步探讨了测线A的温压场环境。结果表明:坳隆断裂带中存在连续变化的温压场环境,当气体在其中运移时,总能遇到有利的温压场环境,从而形成天然气水合物;另一方面,坳隆断裂带中也不是处处均有利于水合物的发育和赋存,需要进行具体的温压条件分析,从而对水合物稳定域进行准确定位。

The P-T Environment of the Depression-upwelling Faulted Zone for the Existence of Gas Hydrates in the Northern Slope of the South China Sea

The development and existence of the gas hydrates are controlled prominently by the structural conditions.Several special structural units in the active or passive continental margins including accretionary wedge,mud volcano,mud diaper and seafloor slip are favorable structures for the development and existence of gas(hydrates).The investigation and research in the north slope of the South China Sea(SCS) suggest that the(depression-)upwelling faulted zone(DUFZ) is one of the important favorable structural circumstances for gas(hydrates) coming into being.Based on the comprehensive comparison,the temperature in the sediment is calculated from the relationship between the water depth and the seafloor temperature in the northern slope of the SCS,while the lithostatic pressure in the sediment is calculated from the relationship between the sediment depth and body density which was simulated in this paper.Furthermore,the P-T environment of the profile A which traverses the structure of DUFZ is analyzed in detail.The result shows that the free gas can always meet the favorable P-T environment and form gas hydrates when the gas transfers in the DUFZ because of the continuous variation of P-T environment in the structure,but it is not everywhere.The analysis of temperature and pressure in situ is necessary for the location of the gas hydrates.