硬脆性页岩微细观组构及力学性能研究

Study on Microstructure and Mechanical Properties of Hard Brittle Shale

硬脆性页岩地层在钻井过程中很容易出现井壁剥落掉块的情况,使得钻井过程中遇到一定的阻碍。针对小塘子组页岩钻进过程中发生井壁掉落的情况,本文通过开展小塘子组页岩被钻井液浸泡前后微细观组构及力学性能变化的实验进行了井壁失稳因素的分析。研究结果表明:小塘子组地层是典型的硬脆性页岩,主要以石英矿物为主,黏土矿物含量不高,黏土矿物主要以弱膨胀性的伊利石和绿泥石为主,含少量的伊蒙混层;水化膨胀分散性能弱,岩性脆,发育有平行层理和微裂缝;小塘子组页岩井壁失稳主要受钻井液浸泡效应和层理走向及力学弱面效应的影响,尤其当取心角度为40°~60°时,钻井液浸泡后硬脆性页岩受层理缝弱面效应的影响最为明显,力学强度降到最低。

When the drilling operation happens in the hard brittle shale formation,it is easy for the borehole wall to flake off,which makes the drilling process encounter some obstacles.In view of the occurrence of borehole wall falling in the drilling process of Xiaotangzi formation shale,the borehole wall instability factors of Xiaotangzi formation shale were analyzed by the experimental study on the changes of microstructure and mechanical properties before and after the shale was soaked by drilling fluid.The results show that Xiaotangzi formation is a typical hard brittle shale,it is mainly composed of quartz minerals,and the content of clay minerals are not high.Besides clay minerals are mainly composed of weak expansive illite and chlorite,with a small amount of the mixed-layer minerals of illite and smectite.The hydration expansion dispersion property is weak and the lithology is brittle,and parallel bedding and micro fractures are developed.The borehole wall instability of shale in Xiaotangzi formation is mainly affected by drilling fluid immersion effect,bedding trend and mechanical weak plane effect.When the coring angle is from 40°to 60°,the hard brittle shale affected by bedding fracture and weak plane effect after the drilling fluid immersion is most obvious,and the mechanical strength is reduced to the minimum.