【作者】 于桂杰；

【导师】 王瑞和；

【作者基本信息】 中国石油大学 ， 油气井工程， 2009， 博士

【摘要】 本文针对固井状态下因套管长期服役引起的损坏问题,建立了长效地应力机制下套管应力与抗挤强度的研究方法,研究了固井状态套管存在的非载荷固井套管应力,长效地应力机制下固井状态井眼周围地应力分布和套管应力分布,不同固井状态下因地应力长期作用产生的套管应力和变形以及套管可能的破环位置与载荷。该理论研究方法的建立为解释实际工况条件下套管的局部损坏,制定防治套管损坏的工艺技术和钻井井身结构设计,提供了简单有效的方法。通过对固井实际状况的分析,建立了三种固井物理模型和套管应力分析力学模型。通过分析工艺技术,提出了固井过程因水泥水化和凝固在套管内产生固井套管环向应力的概念,这种固井套管环向应力和其它载荷产生的轴向应力同时被封固在套管中,形成了非载荷作用下套管的原始应力,套管的原始应力对套管抗挤压性能产生不利影响。通过试验测试了固井套管环向应力,证明了固井套管原始应力的存在。应用经典弹性力学中的半逆解法和叠加法,首次建立了长效地应力机制下固井状态井眼周围地应力的分布理论,提出了井壁径向应力、环向应力和剪切应力不为零的观点。认为优质固井状态井壁的应力呈周期变化,得出了优质固井状态地应力长期作用下套管应力分布的理论计算公式,指出了破坏的局部性,该理论可以直接应用于工程计算,简单、方便。用能量法分析研究了一般固井状态下的套管应力,得出了地层应力越均匀套管越不容易损坏,长效地应力作用下套管易于局部损坏的结论。首次应用相邻平衡准则法探讨了偏心固井状态套管的稳定临界载荷,提出了偏心固井状态套管安全工作的载荷是由强度条件和稳定条件共同决定的概念。首次应用薄壳理论分析了任意缺陷固井状态套管应力和变形,分析了水泥环刚性和弹性约束局部环状固井缺陷下的套管受力变形,通过半逆解法试算,合理地确定了待定边界问题,给出了符合边界条件和微分方程的位移、应力解和应力分布状况,确定了刚性和弹性两种约束条件下套管破损危险主要发生于缺陷中部,刚性约束时套管损坏一般发生在缺陷边缘,建立了该环境下的套管强度设计和套管损坏条件;初步建立了局部块状固井缺陷下的套管受力变形分析方法,为进一步分析套管局部损坏原因提出了新的思路。分别采用有限元方法和工程实例分析计算了不同固井状态套管应力和变形,验证了理论分析方法的正确性。解析解和数值解的结果都表明:水泥环能够极大的提高套管的抗挤能力;四种固井状态长效地应力机制下套管都具有损坏的可能性,有效地解释了固井状态套管多发生局部变形的实际工程现象。工程实例、常用理论的计算结果证明了本论文理论分析方法的正确性,而且,本理论分析方法对分析套管应力和抗挤强度更具广泛性,理论计算简单、方便、结果准确,对合理的固井设计及施工,制定具体的套管挤毁防治措施具有重要的指导意义。更多还原

【Abstract】 In this paper, for the problem of casing collapse on cementing status caused by long-term In-Situ Stresses, it puts forward the research method of casing stress and anti-collapse strength under long-term In-Situ Stresses. The following contents were analyzed and studied by this method: Original casing stress generated by non-load on cementing status; The stress distribution on casing and stratum around the cementing borehole under long-term In-Situ Stresses; To determine the casing stress & deformation and possible location of casing collapse & load under In-Situ Stresses on different cementing status; The theoretical methods provided a effective simple means for explaining the partial casing damage on engineering practice, establishing technology of preventing casing collapse and casing drilling program.Through analyzing the actual cementing technique, it summarized and founded three solid models and casing stress mechanical ones for casing cementing status. By analyzing the cementing technology, it put forward the concept of casing cementing circumferential stress generated by cementing hydration and solidification. This cementing circumferential and the axial stress caused by other load are fixed in the casing at the same time, and called the casing original stress in the casing by no-loading.The casing original stress had an adverse effect on casing anti-collapse. It tested the circumferential stress of cementing casing by experimentation and proved the existence of casing original stress on cementing.By applying the classical theory of elasticity of the semi-inverse method and the superposition one, it set up firstly the distribution theory of stress in stratum around the cementing borehole under long-term In-Situ Stresses, put forward the opinion that the radial, annulus and shear stress are not zero on the well wall. The paper reckoned that the stress on the wall is cycle at cementing status. Distribution theory of casing stress is obtained at cementing status under long-term In-Situ Stresses. It pointed out the collapse is partial. The theory in the paper could be applied to engineering calculations directly. It is simple and convenient.Analyzed the casing stress at general cementing status, the conclusion was obtained that more homogeneous stratum stress less easily damaged and in contrary the casing were easily damaged partially under long-term In-Situ Stresses. Firstly applied adjacent balance criterion to discuss the steady critical load for eccentric cementing status, it provided the opinion that the security working load for eccentric cementing was decided by the strength and stability. Firstly applied the thin-shell theory to analyze the casing stress and deformation on random lacuna cementing, it analyzed the casing stress and deformation under cement sheath rigidity and elastic partial annular cementing lacuna, by trial calculation with the semi-inverse method, it determined the border issues problem, solved the displacement , stress and stress distribution that consisted with the boundary conditions and differential equations, identified that casing collapse occurred mainly in the central lacuna under two types of constraints , and on the edge under rigid constraint, set up the condition of casing strength design and failure ones under this environment. It simply studied the casing stress and deformation under elastic partial square lacuna cementing, and put forward new ideas deeply to analyse casing partial collapse.The casing stress and deformation at different lacuna cementing were calculated with FEM and engineering example.The result proved that the theory and method were right. Analytical and numerical results indicated that the cement sheath can greatly enhance the casing anti-collapse at scope of stress range by combined the analytical and numerical solutions; The conclusions that casing had the possibility of collapse under long-term In-Situ Stresses at four cementing status would explain availably the engineering facts that the partial collapse is taken place on cementing casing. The engineering example and the academic result in common use proved that the analyses theory was validity and more universality for casing stress and anti-collapse strength. The theoretical calculation is simple, convenient and exact.There would be high significance in engineering for reasonable cementing technology, formulating prevention for casing collapse.更多还原