页岩气井压裂液返排过程套管损坏机理研究

发布时间：2018-10-05 09:11

【摘要】：页岩层理较发育且非均质性较强,压裂液返排过程中,近井筒周围已产生较多的形态复杂的裂缝,裂缝产生的诱导应力导致页岩储层地应力大小和方向发生变化,变化后的应力值完全作用于套管周围的水泥环和套管本身,使套管发生弹塑性变形并损坏。页岩气井压裂液返排过程中,套管损坏问题始终存在,为了准确计算页岩储层大规模压裂返排过程套管的应力状态,预测套管的损坏情况,需要提出一种套管受力分析计算的新方法。本文主要应用弹性力学理论,分别研究了水泥环、套管椭圆率与套管抗挤强度系数的关系,建立了压裂液返排过程中套管的抗挤强度理论计算模型。然后,分析了人工裂缝产生的诱导应力对原始地应力的影响,根据应力叠加原理,建立了页岩气井压裂液返排过程中井筒周围应力场计算模型,在此基础上,根据弹性力学理论,对套管孔眼处的受力情况进行了详细的分析,建立了压裂液返排过程中套管管壁单孔所受应力情况计算模型。最终,对页岩气井压裂液返排过程中套管所受应力进行研究。通过页岩储层岩心的岩石力学实验,获取不同取心方向页岩单轴抗拉强度、三轴抗压强度和弹性模量、泊松比等关键力学参数。以实验结果为依据,建立压裂返排过程页岩储层-水泥环-套管有限元计算模型。根据模拟结果可知,压裂液返排过程,页岩压裂层段与上、下非压裂层段岩石弹性模量和泊松比差异对套管受力影响显著。通过本文研究,能够为页岩储层大规模水力压裂返排过程套管应力计算研究提供新思路,为套管失稳损坏的判别和合理压裂方案的制定提供依据。
[Abstract]:Shale bedding is relatively developed and heterogeneity is strong. In the process of fracturing fluid backflow, there have been many complicated fractures near wellbore, and induced stress caused by fractures leads to changes in the size and direction of in-situ stress in shale reservoir. The stress values completely affect the cement sheath around the casing and the casing itself, resulting in elastic-plastic deformation and damage of the casing. In order to accurately calculate the casing stress state and predict the casing damage in shale gas well fracturing fluid backflow process, casing damage exists all the time, in order to accurately calculate the casing stress state during large-scale fracturing and drainage in shale reservoir, A new method of casing stress analysis and calculation is needed. Based on the theory of elasticity, this paper studies the relationship among cement sheath, casing ellipse ratio and casing anti-squeezing strength coefficient, and establishes the theoretical calculation model of casing anti-extrusion strength in the process of fracturing fluid backflow. Then, the influence of induced stress produced by artificial fracture on the original in-situ stress is analyzed. According to the principle of stress superposition, the stress field calculation model around the wellbore in the process of fracturing fluid reflux in shale gas well is established. According to the theory of elastic mechanics, the stress of casing hole is analyzed in detail, and the stress calculation model of single hole in casing wall during the process of fracturing fluid backflow is established. Finally, the stress of casing in the process of back discharge of fracturing fluid in shale gas well is studied. The key mechanical parameters of shale core such as uniaxial tensile strength triaxial compressive strength and elastic modulus Poisson's ratio and so on are obtained through rock mechanics experiments of shale reservoir core. Based on the experimental results, a finite element model of shale reservoir, cement sheath and casing is established. According to the simulation results, the difference of rock elastic modulus and Poisson's ratio between shale fracturing zone and upper and lower fracturing layers has significant influence on casing stress. Through the research in this paper, it can provide a new idea for the calculation of casing stress during large-scale hydraulic fracturing in shale reservoir, and provide the basis for distinguishing casing instability damage and making reasonable fracturing scheme.
【学位授予单位】：东北石油大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TE931.2

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