低速酸性水化学溶液作用下砂岩损伤时效特性

Aging Characteristics of Sandstone Damage Under the Action of Low-Velocity Flowing Acidic Hydrochemical Solution

为探究流动酸性溶液作用下砂岩损伤时效特性,在不同pH水化学溶液(pH=3,5,7)浸泡处理的基础上设置不同流速的浸泡环境(v=0,500 mm/s),利用扫描电镜和MTS-815岩石力学试验系统分析浸泡后砂岩试件的微细观结构变化与宏观力学性能劣化规律,并在不同时间节点测量试件的质量与尺寸变化。试验结果表明:(1)同一时间内,酸性溶液pH越低、流速越快,试件的孔隙率、质量与直径尺寸变化较大,且在各环境下,初期变化程度最大,后期逐渐趋于稳定;(2)砂岩表面微观结构损伤与溶液pH呈负相关,与流速呈正相关,溶液pH越低,次生孔隙数量增多,微裂隙发育良好,结构框架疏松度上升;(3)与干燥状态相比,经pH=3的溶液浸泡后的试件峰值偏应力强度在5 MPa、10 MPa和15 MPa围压下分别下降32.85%,36.47%和39.14%,而模拟流速v=500 mm/s、pH=3的溶液环境下,峰值强度分别累计下降41.91%,44.77%和42.56%,且随时间逐渐趋于平缓;同时其黏聚力与内摩擦角也随时间延长而衰减,且黏聚力对酸性溶液的敏感度更高;(4)综合试件在流动酸性溶液环境下腐蚀深度的变化规律建立的强度模型与试验结果吻合度高。

In order to explore the aging characteristics of sandstone damage under the action of flowing acid solution,the immersion environment with different flow velocities(v=0,300,500 mm/s)was set on the basis of immersion treatment of hydrochemical solution with different pH(pH=3,5,7).Scanning electron microscopy and MTS-815 rock mechanics test system were used to analyze the microstructure changes and macromechanical property deterioration laws of sandstone specimens after immersion,and the mass and diameter dimensions changes of specimens were measured at different time nodes.The test results are concluded as follows.Firstly,the lower the pH value and the faster the flow velocity of acidic solution at the same time,the larger the changes of porosity,mass and diameter dimensions of the specimens.And in each environment,the degree of change was the greatest at the beginning and gradually stabilized at the later stage.Secondly,the microstructural damage on the surface of sandstone is negatively correlated with the solution pH and positively correlated with the flow velocity.the lower the solution pH,the more the secondary pores,the better the development of microcracks,and the higher the sparseness of the structural framework.Thirdly,compared with the dry state,the peak partial stress intensity of the specimens immersed by the solution with pH of 3 decreases by 32.85%,36.47%and 39.14%under the circumferential pressure of 5 MPa,10 MPa and 15 MPa,respectively.While the peak intensity decreases cumulatively by 41.91%,44.77%and 42.56%under the simulated solution environment with flow velocity of 500 mm/s and pH of 3,and gradually levels off with time.In addition,the cohesion and internal friction angle also decay with time,and the cohesion is more sensitive to the acidic solution.Fourthly,the strength model established by the change law of corrosion depth of the specimens in the flowing acidic solution environment is in a good agreement with the test results.