CAJ | 학술논문

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。
감우아국혈암기개발시험구수평정유기찬정액찬정과정중，빈번출현엄중적정벽실은、정루등정하복잡정황，선취투동남룡마계조로두혈암위실험암양，개전료찬정액침포전후혈암암석역학성질적측시，기우유한원수치모의법건립료련통정통단조수직렬봉정황하적렬봉동태관도예측모형，연구료찬정액침포후혈암렬봉관도변화적행위，수정화완선료기우유한원적렬봉동태관도예측방법，병토론료렬봉관도변화모의재루실성저층보호화정벽실은공제방면적응용。결과표명，찬정액침포후혈암탄성모량감소，박송비증가，암석강도명현강저；찬정액침포후혈암렬봉동태관도대정통압력변화경가민감，각렬봉장도화정통정압차조건하적반봉관증량균비침포전증가료약8%，차반봉관증량수정통정압차적증가이대폭도증가，동태봉관가체수호미량급；찬정액밀도-렬봉관도-가교봉도과립립경삼자긴밀상관。연구획득적렬봉동태관도삼수대우선찬정도루재료화립경급배、공제합리찬정액밀도、공제정루화정벽실은구유중요적의의。
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.