钻井液对页岩力学特性及井壁稳定性的影响

Effects of drilling fluids on shale mechanical properties and wellbore stability

罗鸣 高德利 黄洪林 李军 杨宏伟 张更 刘楷

LUO Ming GAO Deli HUANG Honglin LI Jun YANG Hongwei ZHANG Geng LIU Kai

中国石油大学(北京) 中海石油(中国)有限公司海南分公司 中国石油大学(北京)克拉玛依校区

College of Petroleum Engineering, China University of Petroleum (Beijing), Changping 102249, Beijing, China CNOOC Limited Hainan Branch, Haikou 524000, Hainan, China China University of Petroleum-Beijing at Karamay, Karamay 934000, Xinjiang, China

钻井液长期浸泡会对层理性页岩产生影响，进而影响到页岩地层的井壁稳定性。利用川南地区龙马溪组页岩开展了不同钻井液浸泡后页岩单、三轴力学实验，分析了其力学特性及破坏形式的变化特征，并探讨了井壁失稳机理。结果表明：受层理影响，页岩力学特性具有明显的各向异性特征，且具有围压效应；油基钻井液对层理面的润滑作用增强了各向异性，页岩沿层理面发生剪切破坏，破坏形式受层理面控制；水基钻井液对页岩造成水化损伤，微裂缝扩展沟通层理，降低了各向异性，易发生复合破坏，破坏形式受基质体和层理面双重控制，井壁更易失稳；黏土矿物水化作用和孔缝毛细管效应是页岩地层井壁失稳的根本原因。该研究可为层理性页岩井壁稳定分析提供参考。

Long-term soaking in drilling fluids has vital effects on shale with well-developed bedding and subsequently wellbore stability in shale. The uni- and tri- axial compression tests were performed using the Longmaxi Formation shale samples from South Sichuan that have been immersed in different drilling fluids, to investigate the variation of mechanical characteristics and failure modes and also the mechanisms of wellbore instability. The results showed that due to the bedding development, the shale presents considerable mechanical anisotropy and dependency on confining pressure. The lubrication effect of oil-based drilling fluids on bedding planes strengthens the anisotropy, shale is found with the shear failure along bedding planes, and the failure mode is controlled by bedding planes. In the case of water-based drilling fluids, hydration damage is caused to shale, and the anisotropy is reduced due to the propagation and bedding connection of micro fractures. The failure is often composite, and the failure mode is controlled jointly by the matrix and bedding plane, which leads to high proneness to wellbore instability. The root causes of wellbore instability are hydration of clay minerals and capillary effects of pores and fractures. The findings of this research provide references for wellbore stability analysis of shale with well-developed bedding.

10.13639/j.odpt.2022.06.005