南海北部陆坡构造坡折带中的天然气水合物

Gas Hydrates in the SSBZ in the North Slope of the South China Sea

构造坡折带是由同沉积构造长期活动引起的沉积斜坡明显突变的地带,对盆地充填的可容纳空间和沉积作用可产生重要的影响,构造坡折带和油气资源分布有着较为密切的关系。本文首次把"构造坡折带"概念引入到天然气水合物调查研究中,认为:构造坡折带是天然气水合物发育和赋存的重要构造单元。论文从海底坡降、断层发育以及温压场环境等角度讨论了构造坡折带对天然气水合物的控制作用,发现BSR发育位置的海底坡降一般在10×10-2～30×10-2之间;利用论文中设计的相对构造强度的算法计算了南海北部陆坡D区的相对构造强度,发现相对构造强度的次高值区有利于水合物赋存;根据高分辨率地震数据计算的构造坡折带的温压场环境,发现构造坡折带中连续变化的温压场环境能够使游离气运移到适宜的温压场中并形成水合物。在对上述研究进行总结归纳的基础上,初步提出了南海北部陆坡构造坡折带中天然气水合物的成藏模式。

The structural slope break zone （ SSBZ）, which constrains the change in the accommodation space of the basins, controlling the development of the depositional sequence and the distribution of the depositional system tracts and the sand bodies, resulting in the abrupt change of the depositional slope, is initiated by the long term activity of syndepositional structure. Researches show that distribution of petroleum is closely connected with the SSBZ. The paper introduce the term of ＂Structural Slope-Break Zone＂ into the investigation and research of gas hydrate first time and concludes that SSBZ is an important structural unit for the formation and accumulation of gas hydrate. Further- more, the paper analyzes the role of SSBZ controlling in gas hydrate in view of gradient of seafloor, fault, temperature, and pressure. Statistics show that the average ＂gradient of the seafloor where BSR is recognized is between 10×10^-2～30×10^-2. The paper calculates the structural intensity of area D in the north slope of the SCS by introduction of structural intensity and design of algorithm, which shows that there are some favorable relationship between areas of hypo-value of structural intensity and BSR. The paper calculates the temperature and pressure in SSBZ based on high resolution seismic data and finds that the free gas can always meet the favorable P-T environment and form gas hydrates when the gas transfers in the SSBZ because of the continuously various P-T environment in the structure. We put forward a model of the accumulation of gas hydrate in SSBZ primarily in the end based on the summarizing of the achievements mentioned above.