高孔隙度砂岩断裂带内部结构及侧向封闭能力主控因素

Research on internal structure and main controlling factors of lateral sealing capacity of fault zone in highporosity sandstone

根据野外露头和岩心观察,应用高压低速环形剪切装置,开展不同因素下高孔隙度砂岩断裂带环形剪切变形物理模拟实验,结合微观变形特征,明确影响断层侧向封闭能力的主控因素。结果表明:高孔隙性砂岩主要发生碎裂作用,形成典型的碎裂型变形带,与母岩相比,断裂带颗粒粒径明显降低;断裂带渗透率相较于母岩的明显降低,最大可降低2~3个数量级;其他条件不变,随剪切位移增加,初期断裂带渗透性明显降低,当达到一定位移条件时,断裂带渗透性逐渐平稳,甚至不再变化;断面正应力和泥质质量分数与断裂带渗透性呈负相关关系。泥质质量分数、断面正应力和剪切位移共同决定同层砂岩对接型断层的侧向封闭能力。该结果为明确断裂带渗透性变化规律与评价同层砂岩对接型断层侧向封闭能力提供支撑。

According to the field outcrop and core description,the experimental apparatus of high pressure and low speed ring shear is developed to carry out the experimental physical simulation of ring shearing deformation with different factors,combining with the characteristics of microscopic deformation,the main controlling factors that affect the lateral sealing capacity of faults are determined.The results show that:the high-porosity sandstones are mainly cataclasis,and the typical cataclastic deformation zone is formed.Compared with the host rock,the particle size of the fault zone is obviously reduced,and the permeability of the fault zone is also obviously reduced,the permeability can be reduced by 2—3 orders of magnitude.Under the same normal stress and clay content conditions,as the sheare displacement increases,the permeability of the fault zone decreases obviously at the initial stage on the fault surface.When a certain displacement condition is reached,the permeability of the fault zone gradually stabilizes,even no longer changes.The normal stress and clay content are negative correlation with the permeability of the fault zone.The clay content,normal stress on the fault surface and shear displacement determine the lateral sealing capacity for sandstone layer juxtaposed against itself across the fault.The results provide an support for understanding the permeability change law of fault zone and evaluating the sealing capacity of sandstone layer juxtaposed against itself across the fault.