西沙海域南部天然气水合物发育特征及成藏模式

Distribution Features and Accumulation Model of Natural Gas Hydrate in the South of Xisha Islands Seas, South China Sea

根据新的三维地震资料,在西沙海域南部发现的天然气水合物具有三个主要地震识别标志:(1)似海底反射现象明显,表现为强振幅强连续反射、与海底反射极性相反、与海底近平行及有穿层现象等四个特征;(2)具有空白反射带,且与似海底反射伴生;(3)随偏移距增加,振幅明显增强。研究区天然气水合物平面上具有分块展布的特点,单块内水合物中部富集、向周缘丰度减小。估算水合物稳定带厚度约为120m。通过地质类比研究认为,西沙海域南部天然气水合物成藏主要受气源条件、温度-压力条件和构造-沉积条件三个因素共同控制。据此建立了研究区天然气水合物的成藏模式。

According to the new 3D seismic data, three seismic identifications of natural gas hydrate are discovered in south of Xisha Islands seas, South China Sea： （1） Obvious bot om simulating reflector （BSR） shows strong amplitude and continuous reflection, opposite polarity in contrast to the seafloor reflection, and nearly paral el to sea floor and translayer phenomena. （2） There are blanking zones（BZ） accompanied with BSR. （3） Amplitude enhances versus increasing offset. Natural gas hydrate distributes in dispersive blocks in plane and gas hydrate enriches in center but gets reducing toward periphery within a single block. It is estimated that the stable zone of gas hydrate is about 120m thick. The result of geology analogy shows that gas hydrate accumulation is commonly effected by some conditions in-cluding gas source, temperature-pressure and structure-sedimentation. A geological model of gas hydrate accumu-lation is established.