【作者】 朱立；

【导师】 刘卫群；

【作者基本信息】 中国矿业大学 ， 固体力学， 2014， 博士

【摘要】 当前，“温室效应”引起的全球升温明显直接导致了自然灾害的频发，造成了巨大的人员伤亡和经济损失。将引起“温室效应”主因的CO2进行地下封存对控制“温室效应”是一个行之有效的方法。本文根据CO2地下封存安全性的需要，针对CO2注入煤层过程煤与盖层的变形和破裂演化特征，开展了实验室实验、理论分析和数值模拟研究。主要研究工作和结论如下：(1)通过含CO2煤变形破坏特征的实验研究，得到了CO2对煤力学性质的影响规律。三轴实验中含CO2煤样的强度、峰值强度和残余强度随着CO2压力的增加逐渐降低，峰值强度的CO2压力效应要比残余强度更为显著。随着CO2压力的增加，应力跌落系数逐渐减小，煤样破坏形式从剪切破坏逐渐转变为近乎平行于轴向的劈裂破坏。常规三轴蠕变情况下，煤样的预定轴向应力远小于煤样的长期强度，煤样只出现了稳定蠕变阶段；小于煤样的长期强度，煤样出现了减速蠕变阶段和稳定蠕变阶段。（2）推导了注气过程中煤层孔隙压力分布函数，当CO2渗透到边界时边界效应不可忽略。利用三层叠层梁模型，联系winkler地基假设得到了盖层的变形和正应力与注气时间的关系，盖层正应力的最大值出现在注气初期，并随着CO2的注入逐渐减小。利用双参数模型对winkler假设进行修正，结果表明考虑地基剪力的煤层对盖层正应力的影响甚微。考虑上下岩层对于盖层和底板的约束作用，采用winkler假设对三层叠层梁模型进行修正，结果表明盖层正应力变化明显减小。在此基础上，考虑了不同注气压力下注气初期盖层正应力的分布情况，得到了完整盖层的最佳注气压力。(3)设计制作了CO2注入煤层过程中上覆岩层变形的相似模型，分析了模型与原型之间的关系。注水过程中，止水条中水所渗透到的地方的上覆岩层会产生向上的变形，随着实验的进行，岩层的变形量不断增加，由于注水管与岩层之间的粘连的影响，造成了离模型井口12cm处的累计变形量大于离井口2cm处。（4）分析了注入CO2对封存环境的影响，得到了相关力学量的变化规律和盖层的损伤演化规律。注气压力的提高会加剧对封存环境相关力学量的影响和盖层的损伤程度。提出了分步提高注气压力的方法，注气间隔为30天时盖层不再损伤。分析了缺陷盖层条件下注入CO2对封存环境的影响，得到了注气过程中存在的两种缺陷对封存环境相关力学量的影响和盖层的损伤演化规律。更多还原

【Abstract】 At present, the "greenhouse effect" has caused a rise in the average globaltemperature, which obviously led to the frequent natural disasters and great casualtiesand economic losses. An effective way of reducing CO2, the main cause of"greenhouse effect", is by storing CO2under the earth surface and hence controllingits greenhouse effect. For geological storage of CO2injection into the coal seam, thelong-term safely storage of CO2requires carefully consideration. This paper focuseson the deformation and fracture evolution characteristics of coal and caprock duringCO2injection into coal seam. A comprehensive study has been conducted usingexperimental, numerical, theoretical and analytical approaches and main researchcontents and conclusions drawn from the study can be listed as follows:(1) An experiment of deformation and failure characteristics of CO2-saturatedcoal is conducted to identify effect of CO2on the mechanical properties of coal. Intriaxial experiment, strength, peak strength and residual strength of CO2-saturatedcoal samples are gradually reducing with the increase of injection pressure. And, thepressure effect on peak strength is much more significant than on residual strength.Also, due to stress drop coefficient gradually decreases with the increasing injectingpressure, the destruction form of coal samples are transformed from shear failure tosplitting failure. In conventional triaxial creep, the predetermined axial stress is muchless than the long-term strength of coal samples, steady creep stage are only shown;the predetermined axial stress is less than the long-term strength of coal samples, coalsamples show the deceleration creep and steady creep stages.(2) Pore pressure distribution function during CO2injection into coal seam isdeduced, which take the boundary effect into consideration when CO2permeate to theboundary. Based on three-layer laminated beam model and Winkler assumption aboutfoundation, the relationship between deformation and normal stress of the caprockand CO2injection time is obtained. The normal stress reaches its maximum in theinitial stage of CO2injection, and then decreases. To modify Winkler assumptionapplying double parameters model, the results show that the coal seam withconsidering shear stress of foundation has little impact on caprock normal stress. Tomodify three-layer laminated beam using Winkler assumption with consideration ofoverburden and underlying rock’s restriction on caprock and base, the results showcaprock normal stress obviously reduces.On this basis, considering normal stress distribution of caprock on initial stage under different CO2injection pressure, the bestCO2injection pressure is obtained.(3) Similarity model on deformation of overburden rock during CO2injection isdesigned and the relationship between the model and the prototype is analyzed.During water injection, the rock over the palace, where water in water-stop strippermeates, will induce uplift deformation. With experiment goes on, the deformationcontinues to increase. Due to the influence of the adhesion between the waterinjection pipe and rock, the accumulative deformation in12cm is larger than in2cmfar away from the wellbore.(4) A study of the influence of CO2injection on sealing environment is conductedto obtain evolution of relative mechanical properties of sealing environment and thedamage degree of caprock. The improvement of CO2injection pressure willincreasingly affects relative mechanical properties of sealing environment and thedamage degree of caprock. A new injection method of improving gas injectionpressure by step is presented. Through this method, no damage would occur incaprock when injection interval is30days. A study of the influence of CO2injectionon sealing environment with imperfect caprock is conducted to obtain relativemechanical properties of sealing environment with two kinds of imperfection and thedamage degree of caprock.更多还原