【摘要】 中国南方上扬子地台四川盆地下古生界发育多套海相富有机质页岩。其埋藏深、构造复杂,大位移水平井的井壁失稳问题突出。基于露头、岩心等资料,以宏观形貌、微观结构和岩石力学为重点,对富有机质页岩的各向异性特征进行表征,指出基质页岩是典型的横观各向同性介质,平行和贯穿基质页岩层理的成岩缝和构造缝等弱结构面使页岩地层具有显著的强度各向异性。在考虑地应力、孔隙弹性和地层弹性各向异性对井周应力影响的基础上,通过坐标转换分别得到了应力在斜井井筒和弱面上的分布公式,并根据页岩发生本体破坏和发生多弱面-油基钻井液耦合破坏的不同机制,建立了油基钻井液条件下考虑地层各向异性的大位移井井壁稳定模型。研究结果表明,工程地质因素诸如地层弹性和强度各向异性、地层产状以及地应力各向异性将对井筒稳定性产生规律性影响。实例预测结果与现场情况较为一致,验证了新模型的精度和适用性。更多还原

【Abstract】 Several marine organic- rich shale intervals exist in the Lower Paleozoic of Sichuan Basin in Upper Yangtze area,China. However,wellbore collapse phenomena and accidents frequently occur during drilling operations in extended reach wells of organic- rich shale reservoir due to its burial depth and complicated structure. The anisotropy features of organic- rich shale were investigated based on characterization and analysis of macro profile,microstructure and rock mechanics of outcrop and core datum. Results show that shale matrices are representative anisotropy media,and strength anisotropy of shale formation is noticeable as the diagenetic fissure and tectonic joint parallel or across the weak bedding. Therefore,incorporating the effect of in- situ stress,pore elasticity and elastic anisotropy on stress concentration,stress distribution of borehole rock mass and weakness plane was calculated using reference coordinate systems and its rotation matrices. Meanwhile,considering the different failure mechanism of rock mass and weakness plane,wellbore stability coupling mode was proposed in a circumstanceof oil- base mud considering anisotropy of media and strength.The numerical simulation shows that wellbore instability is affected regularly when anisotropy is considered such as elasticity,strength,and in- situ stress of organic- rich shale formation.Prediction result agrees with the field case,verifying the accuracy and applicability of the model.更多还原