In consideration of the fact that, during drilling of horizontal wells with oil-base mud in the pilot area for development of shale gas in our country, down-hole troubles like severe wellbore instability and lost circulation frequently occur, the outcrops of Longmaxi shale in the southeast of Chongqing were taken as experimental objects in order to carry out the tests of shale rock mechani-cal properties before and after immersion in drilling lfuid;based on ifnite element numerical model, a model was built for predicting the dynamic fracture under the condition of single vertical fracture connecting the wellbore, the behaviour of shale fracture width variation after immersion was studied, the method for prediction of dynamic fracture width based on ifnite element was corrected and improved, and the application of fracture width variation simulation was discussed to the protection of leaking reservoirs and control of wellbore instability. The results show that, after immersion in drilling lfuid, the elasticity modulus of shale decreased, the Poisson’s ratio increased and the rock strength reduced signiifcantly;after immersion, the dynamic shale fracture width was more sensite to changes in wellbore pressures;the half-fracture width increment under posite pressure differential of each fracture length and wellbore all increased by about 8%compared with pre-immersion;and the increment of half width increased greatly with the increase of posite pressure differential in the wellbore, and the dynamic fracture width could be up to several millimeter order;the three factors:drilling density, fracture width and bridging grain sizes were closely related. The parameters of dynamic fracture width obtained by the research work are very signiifcant for selecting the LCM materials and grain size grading, controlling proper drilling lfuid density and hence more effectely protecting the reservoir, controlling lost circulation and wellbore instability.%鉴于我国页岩气开发试验区水平井油基钻井液钻井过程中，频繁出现严重的井壁失稳、井漏等井下复杂情况，选取渝东南龙马溪组露头页岩为实验岩样，开展了钻井液浸泡前后页岩岩石力学性质的测试，基于有限元数值模拟法建立了连通井筒单条垂直裂缝情况下的裂缝动态宽度预测模型，研究了钻井液浸泡后页岩裂缝宽度变化的行为，修正和完善了基于有限元的裂缝动态宽度预测方法，并讨论了裂缝宽度变化模拟在漏失性储层保护和井壁失稳控制方面的应用。结果表明，钻井液浸泡后页岩弹性模量减小，泊松比增加，岩石强度明显降低；钻井液浸泡后页岩裂缝动态宽度对井筒压力变化更加敏感，各裂缝长度和井筒正压差条件下的半缝宽增量均比浸泡前增加了约8%，且半缝宽增量随井筒正压差的增加而大幅度增加，动态缝宽可达数毫米量级；钻井液密度-裂缝宽度-架桥封堵颗粒粒径三者紧密相关。研究获得的裂缝动态宽度参数对优选钻井堵漏材料和粒径级配、控制合理钻井液密度、控制井漏和井壁失稳具有重要的意义。
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