为解决页岩气开发中井壁失稳崩塌问题,基于单轴压缩实验和声发射技术,以龙马溪组页岩为研究对象,探究岩石层理倾角对页岩破坏、裂纹类型的影响以及压缩过程中声发射特征参数变化过程。结果表明:倾角为30°的岩样的主裂缝穿过层理面,岩石破坏主要受岩石基质控制且存在一定层理弱面影响,致使倾斜的宏观裂纹不完全沿层理面扩展;倾角为45°、60°的岩样发生耦合破坏,岩石破坏主要受层理面控制,引起明显的滑移破坏,沿层理弱面的破坏平面穿透整个岩样;倾角为90°的岩样以劈裂破坏为主,裂纹扩展受层理面影响,岩石破坏由层理弱面和岩石基质共同控制。声发射振铃计数呈波动趋势且存在差距,在应力峰值前夕和岩样即将破坏时,振铃计数迅速增长到最大值;大部分时间内声发射能量数值微小,裂纹扩展时声发射能量增大,在岩样发生断裂破坏时,声发射能量释放达到最大值。通过聚类算法处理后的定位点显示模型对单一集中的岩石宏观表面裂缝、脱落区域的表达优于Geiger算法定位模型。该研究可为页岩气开发中井壁稳定性分析提供理论参考。
To address the issue of wellbore instability and collapse in shale gas development,with Longmaxi shale as the research subject,based on uniaxial compression experiments and acoustic emission technology,the influences of bedding dip angles on shale failure,crack types,and the variation process of characteristic parameters of acoustic emission during the compression process were investigated.The results indicate that the main crack of the rock sample inclined at an angle of 30° traverses the bedding plane.The failure of the rock is predominantly governed by the rock matrix,and a certain bedding weak plane exists,resulting in the inclined macrocrack not fully propagating along the bedding plane.The coupling failure of rock samples with dip angles of 45° and 60° occurs.The rock failure is mainly controlled by the bedding plane,resulting in conspicuous slip failure.The failure plane along the bedding weak plane penetrates the entire rock sample.The rock sample with a dip angle of 90° is dominated by splitting failure.The crack propagation is influenced by the bedding plane,and the rock failure is governed by the weak bedding plane and the rock matrix.The count of acoustic emission ringing exhibits a fluctuating pattern and a disparity exists.Prior to the peak stress and when the rock sample is on the verge of being destroyed,the count of ringing increases rapidly to the maximum value.For the majority of the time,the acoustic emission energy is relatively low,and the acoustic emission energy rises as the crack propagates.When the rock sample fractures,the release of acoustic emission energy attains the maximum value.The positioning point display model processed by the clustering algorithm is superior to the Geiger algorithm positioning model in the expression of single concentrated rock macro-surface cracks and shedding areas.This study can provide a theoretical reference for wellbore stability analysis in shale gas development.
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