摘要
分析裂纹扩展演化机理是认识井壁坍塌失稳的关键,尤其是层理和脆性特征显著的页岩地层,伴有节理与微裂隙发育,研究其裂纹扩展演化机制对于确定钻井导向、钻速及井眼尺寸更显重要。为此利用材料试验机开展了考虑层理倾角、加载速率与试件尺寸的页岩裂纹扩展演化试验研究。结果表明页岩层理平行于载荷时,裂纹沿层理呈张性破坏。层理倾角由0°~30°时,裂纹扩展形态由张性破坏向剪切破坏转变;当层理与轴向应力呈30°倾角时,剪切破坏最为明显,裂纹的平均扩展速率最大,且抗压强度最小;层理倾角由30°~90°时,裂纹由剪切破坏;逐渐转向张性破坏,当层理与轴向载荷垂直时,试件裂纹切割层理片层发生张性破坏。随加载率的增加,页岩峰值应力增大,裂纹长度逐渐减小,但加载速率越小,破坏后的页岩越为碎裂;在侧向尺寸不变的条件下,试件高度越大,越呈现张性破坏,主裂纹越长,且破碎后的页岩越呈现片状。
The analysis of crack propagation mechanism is the key to understanding the instability and collapse of the borehole wall,especially for bedding and obvious brittle shale formation accompanied by joint and micro fracture.Therefore,the research of shale formation evolution plays an important role in determining the drilling orientation,drilling speed and hole size.The shale crack propagation experimental study which considering the bedding obliquity,loading rate and specimen size was carried out by using material testing machine.The results show that the crack along bedding extensional damage when the shale bedding is parallel to the load.The crack morphology changes from tensile failure to shear failure,when the bedding angle ranges 0°~30°.The shear failure is most obvious when the stratification and axial stress is 30°.Under this condition,the average crack growth rate reaches to the maximum,and the compressive strength decreases to minimum.The crack morphology changes from shear failure to tensile failure,when the bedding angle ranges 30°~90°.The tensile failure occurrs when the specimen crack cuts bedding layer,if the vertical stratification perpendiculars to the axial load.With the increase of loading rate,the peak stress increases,and the crack length decreases.However,if the loading rate is lower,the broken shale will fracture more seriously.Under the condition of constant lateral dimension,if the height of sample is larger,the main fracture will be longer,the tensile failure and flake will be more obvious after broken.
作者
范翔宇
郭东亚
张千贵
徐烽淋
梁永昌
卢鑫伟
倪涛
FAN Xiang-yu;GUO Dong-ya;ZHANG Qian-gui;XU Feng-lin;LIANG Yong-chang;LU Xin-wei;NI Tao(State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation,Southwest Petroleum University,Chengdu 610500,China;College of Petroleum Engineering,Southwest Petroleum University,Chengdu 610500,China)
出处
《科学技术与工程》
北大核心
2018年第9期63-71,共9页
Science Technology and Engineering
基金
中国博士后科学基金(2014M560728)、国家重点基础研究发展计划(973)(2013CB228003)和国家自然科学基金(51474185)资助
关键词
页岩
层理性
加载速率
尺寸效应
裂纹扩展
试验研究
shale
bedding
loading rate
size effect
crack propagation
experimental study
