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基于上覆岩层应力场和裂缝场演化的采动井套管破断特征及防控对策

Breakage characteristics of casing and prevention and control measures in mining wells based on the evolution law of stress and crack fields in overlying strata

  • 摘要: 准确确定出煤矿采动井套管破断特征并提出相应的防控对策,能为井筒长期稳定提供重要保障。以平顶山矿区的二1煤层及上覆岩层为研究对象,采用理论计算与数值模拟软件模拟方法,确定出上覆岩层离层段应力和位移分布规律,分析了上覆岩层高度、距工作面水平距离与应力、位移的相关性,拟合出上覆岩层高度、距工作面水平距离与应力、位移的关系式;根据研究区采动井的实际开发经验,确定出最佳布井区域下的套管主要破断类型,结合常用套管力学参数,得出“两场”演化下的套管破断位置及长度等特征;对常用的采动井局部防护技术进行总结,并提出对应的防控对策。结果表明:工作面推进过程中,上覆岩层应力呈现出“波动−线性降低”的变化规律,位移呈现出“几乎未发生变化−类双曲线型”的变化规律。最佳布井区域下的采动井套管主要以拉伸缩径和剪切破断为主,选择施加套管加强件对采动井套管进行加固。研究区地面采动井三开段采用N80套管时,需在煤层上部46 m亚关键层处、54 m软硬互层处分别加设抗拉伸套管加强件和抗剪切加强件;采用P110套管时,需在煤层上部46 m亚关键层处加设抗拉伸加强件。建议研究区地面采动井三开段均采用P110套管,增加采动井的井筒稳定性。该研究成果为平顶山矿区及相似条件下采动井预防套管破断提供了理论指导。

     

    Abstract: Accurately determining the casing breakage characteristics in mining wells and proposing corresponding preventive and control measures can provide an important guarantee for the long-term stability of the wellbore. Taking the No. 21 coal seam and overlying strata in the Pingdingshan mining area as the research object, theoretical calculations and numerical simulation were used to determine the stress and displacement distribution law of separation section in the overlying strata. The correlation between the height of the overlying strata, the horizontal distance from the working face and stress and displacement were analyzed, and the relationship between the height of the overlying strata, the horizontal distance from the working face and the stress and displacement were fitted. Based on the actual development experience of mining wells in the research area, the main types of casing breakage in the optimal well layout area were determined. Combined with the commonly used casing mechanical parameters, the casing breakage location and length under the “two field” evolution were characterized. The commonly used local protection technologies for mining wells was summarized and the corresponding preventive and control measures were proposed. The results shown that, in the process of working face advancement, the stress of the overlying strata shown a change pattern of from fluctuation to linear decrease, and the displacement shown a change pattern of from almost unchanged to hyperbolic type. The casing in the optimal well layout area was mainly characterized by tensile shrinkage and shear fracture, and the casing reinforcement was applied to reinforce the casing in mining well. When N80 casing was used in the third section of the ground mining well in the research area, it was necessary to install anti- tensile and shear casing reinforcement in the upper 46 m of the coal seam at the sub-critical layer and in the upper 54 m of the coal seam at the soft/hard interlayer. When P110 casing was used, it is necessary to install anti-tensile reinforcement in the upper 46 m of the coal seam at the sub-critical layer. It is recommended to use P110 casing for all three sections of the surface mining wells in the research area to increase the wellbore stability in mining well. The research achievement can provide theoretical guidance for preventing casing breakage in the Pingdingshan mine and mining wells under similar conditions.

     

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