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分支井筒稳定的塑性力学模型及分析
张广清
0
(中国石油大学石油工程学院,北京 102249)
摘要:
针对分支井钻进过程中普遍存在的井壁稳定问题,建立考虑地层、水泥环、套管和支井井筒的分支井稳定性分析三维弹塑性有限元模型。模型中将水泥环、地层和套管分别视为不同的塑性材料,同时通过建立应力各向异性地层中模型转换方法,消除不同支井方位之间的模型误差。通过弹塑性有限元模拟研究支井方位对分支井稳定性的影响。结果表明:方位角小于15°时,地层与水泥环最大等效应力位于主井筒上,有利于分支井井眼稳定;方位角为75°时,等效应力最大值位于分支井井壁上,不利于井壁稳定;从套管侧窗变形的角度来看,分支井方位应尽量靠近水平最大地应力方向;当支井方位角大于30°时,主井眼水泥环的破坏可引起支井钻进问题;在分支井井身结构设计中,采用较小方位角,同时避免采用50°~80°的分支井方位角,以保证水泥环-地层-套管-井筒系统的稳定性和安全性。
关键词:  钻井  分支井  井壁稳定  支井方位  有限元方法
DOI:10.3969/j.issn.1673-5005.2013.05.012
投稿时间:2013-07-03
基金项目:国家自然科学基金项目(51274216; 51234006);国家科技重大专项(2011ZX05013-004)
Plastic mechanics model for wellbore stability analysis of branched wells
ZHANG Guang-qing
(College of Petroleum Engineering in China University of Petroleum, Beijing 102249, China)
Abstract:
Three-dimensional elasto-plastic models based on finite element method were developed for studying wellbore stability during branch well drilling, in which a mechanical system incorporating rock formation, cement sheath, casing and branch junction was considered. In the models, cement, rock formation and casing were treated as different materials with a plastic feature. Model transformation was established for stress anisotropic formations to maintain the same geometry for various branch orientations and avoid the errors caused by differential geometry model. The influence of branch orientation on wellbore stability during branch drilling was analyzed using the elasto-plastic finite element simulation. The results indicate that, when the branch azimuth angle is less than 15°, the maximum equivalent stress of the formation and cement sheath appears on the main wellbore system, which is favorable to the stability of branch wellbores. When the branch azimuth angle is greater than 75°, the maximum stress will appear on the branch wellbore, which may cause stability problems of the branch wellbores. To reduce deformation around the opening of the casing, the branch orientation should be very close to the direction of the maximum horizontal stress. Failure of the cement sheath in the main wellbore may cause problems during branch drilling, especially when the branch azimuth angle is greater than 30°. Small branch azimuth angle should be used in terms of the distribution of equivalent stress, casing deformation and cement 's plastic deformation. Azimuth angle range of 50°- 80° should also be avoided in order to ensure the stability of the wellbore.
Key words:  drilling  branch well  wellbore stability  branch well orientation  finite element method
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