【作者】 张应安；

【导师】 艾池； 王峰；

【作者基本信息】 东北石油大学 ， 油气井工程， 2011， 博士

【摘要】 对于水平井压裂施工,多封隔器压裂管柱顺利下入井底和上提出井是压裂施工成功的必要条件。多封隔器压裂管柱下入过程,压裂管柱及封隔器与套管内壁之间存在摩擦作用,当管柱自重不足以使其顺利入井时,需要在井口施加一定的轴向载荷。而压裂管柱具有壁薄、刚度小等特点,在轴向载荷作用下将发生屈曲变形,且存在多封隔器时管柱变形情况更为复杂,使管柱与套管内壁产生新接触点,造成压裂管柱下入摩阻力增大。轴向载荷越大,新接触点越多,摩阻力越大,需要井口提供的轴向载荷也越大,当压裂管柱屈曲变形到一定程度,管柱与套管间产生摩擦锁死,此时轴向力无法向下传递,使压裂管柱下入受阻；压裂液返排过程,井口压力迅速降低,使地层裂缝与井筒流体之间形成较大压差,压裂液回流至井筒,压裂液压力作用在套管射孔孔眼上产生较强的应力集中,可能导致套管发生塑性变形或失稳挤扁等而使多封隔器压裂管柱在上提过程中遇卡。为了解决水平井多封隔器压裂管柱下入与上提遇阻的难题,本论文创新性地开展了多封隔器压裂管柱弯曲和屈曲变形力学分析,建立了考虑多封隔器压裂管柱刚度的摩阻力计算模型；考虑压裂液返排速度对套管受力的影响,建立压裂管柱上提出井的压裂液临界返排速度计算模型,为多封隔器压裂管柱顺利上提出井,提出一种预判方法。本文的主要研究工作与研究成果体现在以下几个方面：首先,根据材料力学弯曲梁理论,建立了两封隔器之间的压裂管柱弯曲变形挠度计算模型,分析了压裂管柱在套管内挠度变化的极限值,提出了封隔器之间压裂管柱出现新接触点的判定方法,为摩阻力计算提供了基础判定条件。其次,分别对压裂管柱发生屈曲变形的垂直井段、弯曲段、水平段的屈曲临界载荷问题开展研究。在垂直段,考虑压裂管柱重力对压裂管柱屈曲变形的影响,根据静力学平衡方程,建立了垂直段压裂管柱正弦屈曲及螺旋屈曲临界载荷计算模型；在弯曲段,考虑井眼弯曲作用对压裂管柱屈曲变形的影响,建立了不同曲率半径下弯曲段压裂管柱正弦屈曲及螺旋屈曲临界载荷计算模型；在水平段,考虑压裂管柱重力对压裂管柱屈曲变形的影响,建立了水平段压裂管柱正弦屈曲及螺旋屈曲临界载荷计算模型。考虑封隔器对压裂管柱屈曲变形的约束作用,建立了带封隔器的压裂管柱屈曲变形分析力学模型。得出了紧靠封隔器的非螺旋屈曲段压裂管柱长度计算方法。为屈曲摩阻力计算奠定了基础。根据弯曲梁挠度微分方程,建立了压裂管柱发生螺旋弯曲时压裂管柱截面最大弯矩计算模型,进而得出压裂管柱界面最大弯曲应力计算方法。计算得出了不同轴向载荷作用下,弯矩及弯曲应力变化规律,为压裂管柱强度分析提供了依据。再次,考虑了压裂管柱刚度作用对压裂管柱摩阻力的影响,根据静力学平衡方程,建立了水平井压裂管柱弯曲段摩阻力计算模型。考虑压裂管柱屈曲变形作用产生的正压力,建立了水平井压裂管柱屈曲摩阻力计算模型。为压裂管柱顺利下入提供一种新的下入方法。最后,对压裂液返排过程裂缝内流体压力分布展开研究,建立了裂缝中的压裂液压力随压裂液返排速度变化的计算模型；在此基础上,依据弹塑性力学理论,结合射孔套管的强度条件,建立了压裂液返排时引起套管径向上塑性变形或失稳的压裂液临界返排速度计算模型,为多封隔器压裂管柱顺利上提出井筒提出一种预判方法；将弹性力学理论与复变函数结合,研究了多孔套管孔眼周围的应力集中系数问题,并应用有限元模拟软件计算了多孔套管孔眼周围应力集中系数,分析了不同射孔组合对多孔套管孔眼周围应力集中系数的影响。更多还原

【Abstract】 In the process of horizontal well fracture treatment, whether the multi-packers fracturing string can be successfully tripped into the target layer and picked up is the key to success. When the fracturing string tripped in, the existence of certain friction resistance between fracturing string and borehole requires the axial load in the well head in order to ensure the fracturing string easily tripped in. because the wall of fracturing string is thin and stiffness is small, buckling deformation appears under axial load. Meantime there forms several contact point between fracturing string and casing, which causes the friction resistance increase. The more axial load increased the more contact point comes out, so that the friction resistance much harder and that requires more axial load. By the time the buckling occurs to a certain extent, the axial force can’t transmit down, so that the fracturing trapped and can’t be tripped in. When fracturing fluid flows back, well head pressure dropped sharply and fracturing fluid flow back to the bore hole, pressure between fractures and the wellbore fluid effects on the casing bullet hole which creating strong stress concentration. The stress concentration leads to the casing plastic deformation or unstability collapsed which causing the casing stuck during fracturing string pick up work. In order to solve the difficult problem of multi-packers fracturing strings pass ability in horizontal well, mechanics analysis of multi-packer fracturing string buckling deformation is innovative developed in this paper. We put forward a new model for friction resistance. Casing deformation research is carried out in the process of fracturing fluid flowback under the condition of different perforation combination, which provides an anticipation method for the fracturing string easily picked up. The main research work and research results can be described in the following respects.Firstly, the mechanical model of fracturing string bending deformation analysis is established according to the bending beam deflection differential equation. After analyzing the bending deflection limit value of fracturing string in the casing, this paper puts forward a new method for determine contact point which afford evidence for friction resistance calculation.Secondly, the critical load problems on the vertical interval, bending interval and horizontal interval where the fracturing string buckling is respectively researched. In vertical interval, considering the effects of the gravity of the string on fracturing string buckling, sine buckling and spiral buckling critical load calculation model of fracturing string is established according to the static equilibrium equations. In bending interval, considering the influence of wellbore bending on the gyrose deformation of fracturing string, sine buckling and spiral buckling critical load calculate model is established under different curvature radius. In the horizontal interval, considering the affection of the gravity of fracture on fracturing string buckling, sine buckling and spiral buckling critical load calculate model of the fracturing string is established on the horizontal interval. Moreover, taking into account the constrained effect of packer on the buckling of fracturing string, the mechanical analysis model of packer section fracturing string buckling is established. A computational method calculated the length of string and the constrained force of fracturing string which abuts the packer has been devised.According the deflection differential equation of flexed beam, when fracturing string occurs helical buckling, a calculation model of fracturing string section maximum bending moment is established, moreover, the calculation method of maximum bending stress in fracturing string section is achieved. Using this method, the variation rules of bending moment and bending stress in different axial force can be calculated, and providing the evidence for fracturing string intensive analysis.Moreover, considering the effect of stiffness action to friction resistance of fracturing string, the calculation model of friction resistance in curved section of horizontal well fracturing string is established according to the static equilibrium equation. Considering the normal pressure exerted from the effect of fracturing string buckle deformation, the calculation model of buckle friction resistance of horizontal well fracturing string is established, which provides a new method for fracturing string tripped in easily.Finally, analyzing the pressure of casing perforation orifice in the process of fracturing flowback, the calculation model of flowback pressure of casing perforation orifice is established. Researching the relation between the stress and the variation on casing perforation orifice by the elastoplasticity theory, the mechanical analyzing model of the relation between flowback velocity and variation of fracturing fluid is established. Analyzing the effect of different perforating combination on the casing deformation, and the correctness of the model can be verified by comparing the results of calculation and simulation. This model can be used as a prediction method for lifting to the well head of the multi-packers fracturing casing. By putting elastic mechanics theory and complex-variable function together, this paper researched stress concentration problem of casing eyehole, calculated the stress concentration factor by using finite element simulation software and analyzed different perforating combination effecting on the casing eyehole stress concentration factor problem.更多还原