热力耦合作用下钻井围岩稳定性及其破坏临界条件

发布时间：2018-03-28 16:41

  本文选题：热力耦合　切入点：花岗岩钻井　出处：《太原理工大学》2017年硕士论文

【摘要】：在深部能源开发中,不论是传统的油气资源开采,还是绿色的干热岩地热资源的开发,首先需要解决的核心问题就是高温高应力耦合作用下,深钻施工及钻井稳定性控制问题。深钻施工过程中,由于较高地应力及地温的影响,钻井稳定性大幅降低,维护费用增加,严重制约着深部能源的开发。针对深钻施工中遇到地层为花岗岩,在分析、总结课题组“高温-高应力下花岗岩钻井围岩力学实验”的基础上,通过数值模拟方法,借助MATLAB及COMSOL Multiphysics5.2软件,研究了热力耦合作用下花岗岩钻井围岩热弹性变形规律、热力耦合作用下花岗岩钻井围岩蠕变破坏规律、分析了钻孔破坏半径与加载应力及温度之间的关系,最终得到热力耦合作用下花岗岩钻井围岩失稳破坏临界条件。(1)分析课题组“高温-高应力下花岗岩钻井围岩力学实验”数据,得到以下结论:1)热力耦合作用下花岗岩钻孔在不同温度区间内,钻孔热应变增长趋势不同;不同温度下花岗岩钻孔热应变随埋深应力的增大,其数值有降低的趋势。2)热力耦合作用下花岗岩钻孔蠕变破坏失稳存在较为显著的阈值,即应力阈值为4000米埋深应力,温度阈值为480℃。3)热力耦合作用下钻孔围岩破坏特征具有显著端部效应、缩颈、钻孔内壁破坏;沿位移等值线存在较为显著的错动、滑移,有显著的剪切破坏痕迹,最终围绕钻孔形成锥字形破坏面。4)高温对花岗岩基本力学参数影响显著,其基本力学参数弹性模量E、泊松比μ、热膨胀系数α等均可看做是温度的函数。(2)研究热力耦合作用下花岗岩钻井围岩热弹性变形规律,得到以下结论:1)试件在加温过程中存在显著的温度梯度,且温度梯度产生的热应力只在加热过程中对钻孔围岩热应变产生影响;热力耦合作用下花岗岩试件内部主要受压应力作用,其最大值位于试件外侧,钻孔内壁压应力值较小;位移最大值位于试件外侧,最小值位于钻孔内壁。2)热力耦合作用下花岗岩钻孔热弹性变形产生破坏的温度阈值:3000米埋深应力下的温度阈值为210℃;4000米、5000米埋深应力下的温度阈值为195℃。3)在热力耦合作用下花岗岩钻孔热弹性变形中,存在端部效应且破坏沿着位移等值线产生显著的滑移、错动,造成钻孔内壁附近发生流变破坏。(3)研究热力耦合作用下花岗岩钻井围岩蠕变规律,得到以下结论:1)不同热力耦合作用下花岗岩钻孔围岩流变位移规律一致,即钻孔内壁处流变位移最大,沿着钻孔径向方向,流变位移逐渐减小。2)在相同埋深应力及加载温度条件下,考虑蠕变效应后,钻孔围岩的流变位移显著增大,使得钻孔围岩产生破坏的阈值降低,即为:2000米埋深应力温度200℃,且相同条件下流变产生破坏区半径远大于热弹性变形时产生的破坏半径。(4)热力耦合作用下钻井围岩失稳破坏临界条件为σ=241.9-0.3998·T。
[Abstract]:In deep energy development, whether traditional oil and gas resources exploitation or green dry hot rock geothermal resources development, the first need to solve the core problem is the coupling of high temperature and high stress. Deep drilling and drilling stability control. During deep drilling, due to the influence of high ground stress and ground temperature, the drilling stability is greatly reduced and the maintenance cost is increased. The development of deep energy resources is seriously restricted. In view of the granite formation encountered in deep drilling construction, on the basis of analyzing and summarizing the "mechanics experiment of granite drilling surrounding rock under high temperature and high stress", the numerical simulation method is adopted. With the help of MATLAB and COMSOL Multiphysics5.2 software, the thermoelastic deformation law of surrounding rock in granite drilling under thermal coupling and creep failure law of surrounding rock in granite drilling under thermal coupling are studied. The relationship between borehole failure radius and loading stress and temperature is analyzed. Finally, the critical condition of failure failure of surrounding rock in granite drilling under thermal-mechanical coupling is obtained.) the data of "Mechanical experiment of surrounding Rock in Granite drilling under High temperature and High stress" are analyzed by our research group. The following conclusions are obtained: (1) the thermal strain growth trend of granite borehole is different in different temperature range, and the thermal strain of granite borehole increases with buried depth stress at different temperature. The numerical value has a decreasing tendency. 2) the creep failure instability of granite borehole under the coupling of heat and heat has a significant threshold, that is, the stress threshold is 4000 meters buried depth stress. When the temperature threshold is 480 鈩，

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