真三轴应力下低渗储层砂岩应力应变特征分析

Stress-strain characteristics analysis of low permeability reservoir sandstone under true triaxial stress

为搞清楚低渗砂岩在复杂应力状态下的变形和破坏特征,以华庆地区三叠系延长组低渗砂岩为原型,根据相似原理做成相似模型,通过对相似模型应力-应变的分析来判断原型所发生的力学现象。利用新研制的YSZS-2000多功能电液伺服岩石真三轴试验机对相似材料进行了4个系列真三轴实验。研究表明:在真三轴应力作用下,峰值强度受中间主应力的影响显著,随着中间主应力的增大而增大;试样杨氏模量随中间主应力的增大有增加的趋势;在相同最小主应力条件下,随着中间主应力的增大,峰值应变逐渐减小。当最小主应力增大时,峰值应变降低的幅度减弱;黏聚力随着中间主应力的增大而增大,内摩擦角则随之减小。

In order to understand the deformation and failure characteristics of low permeability sandstone under complex stress state,the low permeability sandstone of Yanchang Formation of Triassic in Huaqing area is taken as the prototype,a similar model is made based on similar principle and the mechanical phenomenon of prototype is judged by analyzing the stress-strain of the similar model.4-series true triaxial tests of similar material were car⁃ried out by using YSZS-2000 type multi-functional electric hydraulic servo-controlled rock true triaxial testing machine.The experimental results indicate that the peak strength is significantly affected by the intermediate principal stress under the effects of true triaxial stress,the peak strength increases with the increase of the intermediate principal stress.The Young’s modulus of the sample increases with the increase of the intermediate principal stress.Whereas,the peak strain decreases with the increase of the intermediate principal stress(σ2)for a given minimum principal stress(σ3).When the minimum principal stress(σ3)increases,the amplitude of peak strain decreases.With the increace of the intermediate principal stress,the cohesion force increases and the internal friction angle decreases.