含水合物地层井壁力学状态的弹塑性解析分析
作者:
作者单位:

1.同济大学 航空航天与力学学院,上海 200092;2.同济大学 土木工程防灾国家重点实验室,上海 200092;3.天津大学 建筑工程学院,天津 300350

作者简介:

王华宁(1975—),女,教授,博士生导师,工学博士,主要研究方向为岩土工程中的数值与解析方法。E-mail:wanghn@tongji.edu.cn

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基金项目:

国家自然科学基金(11872281,51639008);同济大学土木工程防灾国家重点实验室自主课题(SLDRCE19-A-06)


Elastoplastic Analytical Investigation of Mechanical Response of Wellbore in Methane Hydrate-bearing Sediments
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Affiliation:

1.School of Aerospace Engineering and Applied Mechanics, Tongji University, Shanghai 200092, China;2.State Key Laboratory of Disaster Reduction in Civil Engineering, Tongji University, Shanghai 200092, China;3.School of Civil Engineering, Tianjin University, Tianjin 300350, China

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    摘要:

    含水合物地层钻井引发井壁周边温度和渗流压力变化,可能导致水合物分解,对井壁安全产生不利影响。基于Mohrp-Coulomb准则、理想弹塑性模型以及非关联流动法则,针对含水合物地层中井壁力学分析, 建立了稳态轴对称平面应变模型,考虑水合物分解对地层温度、渗流和力学特性的影响,得到了欠压和过压钻井条件下井周应力及位移的解析解答,与相同假定下有限元模型、复杂数值模型的结果吻合较好。结果表明一定范围内水合物分解范围的增大会引起塑性区显著扩展。水合物分解引起的弹性模量劣化在欠压条件下将引起塑性区范围减小,在过压条件下则引起塑性区范围增大。

    Abstract:

    When drilling in methane hydrate-bearing sediments, the variation of temperature and seepage pressure around the wellbore likely leads to the hydrate dissociation, reducing the safety of wellbore. The analytical solution for wellbore mechanical analysis is derived accounting for the ideal elastic-plastic behavior of the formation, the Mohr-Coulomb yield criterion and non-associated flow rule. Based on a steady-state axisymmetric plane strain model considering the effect of hydrate dissociation on temperature, seepage flow and mechanical property, the stress and displacement solutions are presented under unbalanced and overbalanced drilling conditions. The analytical solutions agree well with the results by numerical methods under the same assumptions, as well as the complex conditions. The results show that the increase of the size of dissociated region leads to the expanding of plastic zone obviously within a certain range. The size of plastic zone is decreased with the reduction of Young's modulus of dissociated region under unbalanced drilling condition, while the result is inverse under overbalanced drilling condition.

    图1 水合物地层中井壁稳定力学模型Fig.1 Mechanical model for wellbore drilling in methane hydrate-bearing sediments
    图2 力场、渗流场和温度场的耦合关系Fig.2 Coupling relationship between mechanics, seepage and temperature field
    图3 应力与增量位移计算Fig.3 Models for stress and incremental displacement calculation
    图4 轴对称有限元模型Fig.4 Axisymmetric model in finite element method
    图5 解析解与有限元结果比对Fig.5 Comparison between analytical solution and finite element results
    图6 解析解与复杂模型数值结果比对Fig.6 Comparison between analytical solution and numerical solution under complex conditions
    图7 欠压钻井时钻井液压力对应力和位移的影响Fig.7 Influence of drilling fluid pressure on stress and displacement under underbalanced drilling condition
    图8 过压钻井时钻井液压力对应力和位移的影响Fig.8 Influence of drilling fluid pressure on stress and displacement under overbalanced drilling condition
    图9 分解域大小对塑性区半径的影响Fig.9 Influence of the size of dissociation region on the radius of plastic zone
    图10 欠压钻井时弹性模量劣化程度对应力和位移的影响Fig.10 Influence of the reduction of elastic modulus on stress and displacement under underbalanced drilling condition
    图11 过压钻井时弹性模量劣化程度对应力和位移的影响Fig.11 Influence of the reduction of elastic modulus on stress and displacement under overbalanced drilling condition
    图12 黏聚力劣化程度对塑性区大小的影响Fig.12 Influence of the reduction of cohesive on plastic radius
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王华宁,郭振宇,高翔,蒋明镜.含水合物地层井壁力学状态的弹塑性解析分析[J].同济大学学报(自然科学版),2020,48(12):1696~1706

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  • 收稿日期:2020-04-17
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  • 在线发布日期: 2020-12-31