水合物储层的毛细封闭效应及高压突破机制

Capillary Sealing Effect and High-pressure Breakthrough Mechanism of Hydrate Reservoir

含下伏气的天然气水合物储藏是我国海洋水合物矿藏的重要类型,天然气水合物开采过程中,必须考虑下伏气存在产生的影响。目前,仍缺少针对下伏气产生机理的相关研究。本文利用核磁共振可视化实验装置,探究了水合物藏对其下伏气的封闭作用。结果表明,高饱和度水合物藏对外来流体具有阻碍作用,即毛细封闭作用。水合物的存在减小了孔喉半径,使多孔介质内存在较大的毛细管力,最终形成了抑制下伏气运移的水合物封闭层。水合物储层的封闭效应是下伏气稳定存在的基础。此外,降压过程产生的高压差会诱发水合物封闭层的高压突破现象、进而会引起压力骤降,威胁水合物安全开采。水合物开采过程应该考虑避免出现水合物储层高压突破。

Storage of gas hydrate containing underlying gas is the main type of marine hydrate reservoir in our country,in which the influence of underlying gas must be considered during hydrate exploitation process.At present,there are few kinds of research on the formation mechanism of underlying gas.In this paper,the sealing mechanism of hydrate reservoir to its underlying gas has been explored using MRI visualization apparatus.The results show that the hydrate reservoir with high hydrate saturation has a capillary sealing effect on the external fluid.The existence of hydrate reduces the pore throat radius,which causes a large capillary force in the porous medium,and finally forms a hydrate sealing layer that hinders the migration of the underlying gas.The sealing effect of hydrate reservoir is the basis for the stable existence of the underlying gas.In addition,the pressure difference caused by the depressurization will induce the high-pressure breakthrough phenomenon of the hydrate sealing layer,resulting in the sudden drop of pressure,which threatens the safe exploitation of hydrate.High-pressure breakthrough of hydrate reservoir should be avoided in the process of hydrate exploitation.