青海木里三露天天然气水合物钻孔岩心构造裂隙特征

通过对三露天井田天然气水合物钻孔岩心观察与统计分析，从线密度、倾角、充填程度等方面对裂隙的特征进行讨论，明确研究区天然气水合物赋存类型以及构造裂隙的基本特征，最后讨论了裂隙对天然气水合物形成的作用。结果表明：井田内 天然气水合物绝大多数赋存于粉砂岩、暗色泥岩、油页岩中，其中62.5%赋存于构造裂隙中；研究区构造裂隙以低倾角(占50.37%)、未被充填裂隙为主(占73.68%)，且水合物上覆地层裂隙 密度均不同程度减小。研究区裂隙的发育特征对天然气水合物成藏起到重要的作用：研究区73.68%的裂隙为未充填，为烃类气体的运移和聚集提供了空间；50.37%的裂隙为低倾角，垂直方 向上的渗透率值较小，不同层位的连通性差，极大地限制了烃类气体向上扩散，使其得以聚集保存；最后，裂隙发育程度的降低，同样抑制了烃类气体向上扩散，起到了相对“盖层”的作用 。

Structural Fracture Characteristics of Cores from Gas-hydrate Drillholes in Sanlutian of Muli Coalfield,Qinghai

Through observation and statistical analysis of gas-hydrate drilling cores in Sanlutian mining area, the characteristics of fractures were discussed from the point of linear density, dip angle and filling degree. The occurrence type of gas hydrates and the basic feature of structural fractures in the study area were confirmed. The influence of fractures on the formation of gas hydrate was also discussed. The results showed that the gas hydrate mainly occurred in siltstone, dark mudstone and oil shale, and about 62.5% of gas hydrate occurred in structural fractures,which are mainly low-dip angle fractures and unfilled fractures with proportion of 50.37% and 73.68%, respectively;in addition, the density of fractures in the overlying strata reduced to some extent. It is concluded that the development of fractures has important effect on the formation of gas hydrate in the study area: firstly, the unfilled fractures have provided migration passages and accumulation spaces for hydrocarbon gases;secondly, the fractures with low-dip angles make the strata have low permeability vertically and formations have poor connectivity, greatly limiting the upward diffusion of hydrocarbon gases; finally, the reduction of fractures in the overlying strata also inhibits the upward diffusion of hydrocarbon gases, playing the role of cap rocks.