不同围压下砂岩孔渗规律试验研究

采用三轴岩石力学试验系统分析了砂岩储层岩石在全应力—应变过程中渗透率的变化规律和不同围压下岩石的孔渗性，建立了砂岩岩石应力—应变与渗透率之间的定性定量关系。研究表明；岩石在全应力—应变过程中，渗透率的变化的总体规律是在弹性阶段渗透率随应力的增大而略有降低，进入弹塑性阶段后随着新生裂隙的扩展、贯穿，岩石的渗透率先是缓慢增加然后急剧增大，在峰前或峰后达到极大值，残余流动阶段原有裂隙开始压密闭合，渗透率开始降低。砂岩的孔渗性与其所承受的有效侧压大小密切相关，表现为岩石的孔隙度和渗透率均随侧压的增大而减小，且服从对数函数变化规律；成岩作用不同的砂岩孔隙度和渗透率减小的速度和程度不同，表现为在侧压的作用下，成岩作用程度较弱的砂岩储层的孔隙度或渗透率减小的速度和程度明显地高于成岩作用程度较强的砂岩。

TESTING STUDY ON PORE RATIO AND PERMEABILITY OF SANDSTONE UNDER DIFFERENT CONFINING PRESSURES

By using the triaxial rock mechanics experimental system, testing study is made to analyse the change rule of permeability during the whole stress-strain process and the pore ratio and permeability of sandstone under different confining pressures, and the qualitative and quantitative relationship is established among stress-strain and pore ratio permeability of sandstone. It is shown that during the whole stress-strain process, the permeability reduces slightly with the increase of stress in the elastic stage, after coming the elastic and plastic stage, along with expanding and breakthrough of the induced fracture, the permeability of the rock increases slowly at first and then sharply reaches the maximum value before or after peak point, and at residual flowage stage the existent fracture is pressed closely, and the permeability begins decreasing. The pore ratio and permeability of the sandstone are closely related to the effective confining pressure. The pore ratio and permeability decrease along with the accretion of confining pressure, and conform to the change rule of logarithm function. The sandstone of different diagenesis has different speed and degree in decreasing of pore ratio and permeability. It is shown that under confining pressure the pore ratio and permeability of the sandstone with weaker diagenesis are evidently higher than those of sandstone with stronger diagenesis at decreasing speed and degree. The results obtained from the testing study can be applied into the project of petroleum and gas exploitation, where the variation of in-situ stresses affect the pore ratio and permeability of strata evidently.