【摘要】 根据天然气水合物的产出条件,海洋环境水合物可以分为二类扩散系统水合物和渗漏系统水合物。扩散系统水合物分布广泛,在水合物稳定带内是水-水合物两相共存的热力学平衡体系,游离气仅发育于稳定带之下,在地震剖面上发育有指示水合物底界的强反射面(BSR)。该类水合物含量低,埋藏深。除温度和压力外,水合物的沉淀受甲烷溶解度和扩散速度的控制,并与气体组分、孔隙水盐度、天然气供应和有机碳转化等有关。渗漏系统与断层等通道相伴生,水合物发育于渗漏系统整个水合物稳定带,是水-水合物-游离气三相共存的热力学非平衡体系,水合物的沉淀受动力学控制。该类水合物含量高,埋藏浅,但一般不发育BSR。而且,天然气渗漏活动在海底沉积物和上覆水体中形成了一系列特殊的地质、地球物理、地球化学和特异生物群异常。更多还原

【Abstract】 The hydrates in marine environment can be grouped into two categories, diffusion system and venting system, according to hydrate occurrences. The first type of hydrate occurs widely in the world. Water-hydrate (two-phase) only coexists in gas hydrate stability zone (GHSZ) where a thermodynamic equilibrium system occurs. Free gas occurs beneath the base of the GHSZ only, inducing a bottom simulation reflection (BSR) to indicate the base of the hydrate occurrence zone. The hydrate buries deeply beneath seafloor and shows a low concentration relatively. Its precipitation is controlled by methane solubility and diffusion in addition to temperature and pressure, and affected by gas compositions, pore water salinity, gas supply and conversion ratios of organic carbon to methane. But the second type of hydrate is related to the conduits, such as fault especially, and occurs in the whole GHSZ where water-hydrate-free gas (three-phase) coexists in the system, so demonstrating no BSR in seismic section. This system is a thermodynamic unequilibrium system, and the hydrate accumulation is controlled by kinetics. This type of hydrate occurs in shallow water and shows a high concentration. Furthermore, a series of special phenomena in terms of geology, geophysics, geochemistry and biology arising from the activities of gas seeping occur in the sediments and in the overlying water column.更多还原