海底多相流作用下的含水合物沉积地层静水力学性质分析

Hydrostatic Properties of Hydrate-bearing Sediments in Seafloor Multiphase Flow Zone

海底多相流动区域沉积物孔隙内流体迁移-甲烷输运-水合物形成是一种普遍模式,形成的水合物在孔隙内沉淀并与多孔介质骨架胶结从而改变当地的地层结构和性质。水合物的不断形成将减少沉积地层孔隙度,改变孔隙内各相间界面张力,增大当地孔隙的进入压力及毛细压力,增强地层滞后效应,降低地层渗透率,同时多相流体流动前缘气液分离带变厚而使得气柱变长。建立了在这类环境里水合物-水-气-盐共同作用下的水合物成藏模型,选择合适的参数分析了水合物形成对沉积地层静水力学性质等的影响关系。最后根据资料估算了南海北部神狐海域沉积物内甲烷气柱的分布,结果表明:随着水合物在沉积物孔隙内逐渐饱和,临界甲烷气柱长度将在接近海底面处达到最大,约为0.9 m。

The process of liquid flow,methane transport and hydrate formation in seafloor leakage sediments was a widespread phenomenon.The formed hydrate precipitated in porous pores and cemented with in-situ grain matrix,thereby changed the skeleton structures and hydrostatic properties.In this paper a multiphase flow model of hydrate reservoir described the hydrate-water-gas-salt interaction in sediment pores in leakage environment had been established.The evolution of capillary pressure,porosity,relative and intrinsic permeability of sedimentary strata during hydrate forming had been estimated.According to this model the distribution of gas column in Shenhu area of north South China Sea had also been predicted.The results showed that with the continuously hydrate forming and growing in the sediment pores,the gas column would gradually become longer,and at last near the seabed the critical gas column length could achieve its most height to be about 0.9 m.