【作者】 于洪金；

【导师】 崔海清； 艾池；

【作者基本信息】 大庆石油学院 ， 油气井工程， 2008， 博士

【摘要】 套管损坏问题是世界范围亟待解决的难题。国内外许多学者对套管损坏问题进行了多方面的研究,但是均无法从根本上解决套管损坏问题。通过套管损坏机理的分析可以得出套管损坏问题实质是套管损坏力学计算与判定问题。套管损坏力学计算与判定不仅与原始地应力分布状态、地层岩体和流体渗流场的流固耦合作用存在紧密的关系,而且还涉及到储层产生的应力重新分布直接对套管、水泥环产生外挤应力作用的载荷计算与该载荷下的套管损坏的屈服强度判定问题。本文在全面分析国内外的套管损坏井现状、套管损坏原因、机理和套管损坏井类型以及套管损坏井影响因素的基础上,着重研究了套管损坏井区域的应力场;引入流固耦合理论建立地应力及流体压力数学模型;建立反映套管损坏井在复杂地质条件下的力学模型,应用非线性力学分析的有限单元法进行求解计算;建立外挤载荷作用下的套管和水泥环应力计算模型,分析套管强度影响因素,建立产生套管附加应力的数学模型;建立套管屈服强度的力学判定计算模型。该论文的研究合理地解释套管损坏的机理,为套管设计提供理论依据,为建立套管损坏判定标准奠定坚实的基础。对影响套管损坏的地质和工程因素进行分析得出泥岩吸水蠕变和岩体的膨胀、岩体地层出砂、高压注水以及断层活动和地层活动为套管损坏主要地质影响因素;井网部署、固井完井作业以及套管材质强度为主要的工程影响因素。建立了垂直地应力和水平地应力计算模型和井眼周围应力分布的数学模型。建立套管损坏井周围二维和三维的流固耦合数学-力学模型,运用有限元法求解得出流体地层压力发生变化时,初始状态的岩体的变形和应力变化比较显著,随着时间的推移逐渐趋于平稳,即初始阶段是导致套管损坏井产生的主要阶段;应用三维线弹性流固耦合模型和弹塑性流固耦合模型进行有限元模拟计算得出了储层和套管的应力变化和变形,计算结果与实际情况吻合较好。建立射孔作用条件下的套管-水泥环应力模型,分析了射孔下套管和水泥环的应力分布规律,以及孔眼形态对应力的影响。油层出砂在套管周围砂岩形成局部空洞而产生附加应力,本文建立油层出砂条件下套管-水泥环的应力模型,运用力学模型分析了油层出砂导致套管易损坏的原因。泥岩蠕变过程中,泥岩产生位错而滑动,建立泥岩蠕变损伤本构模型,分析了泥岩蠕变导致套管损坏的原因。建立泥岩地层条件下的套管力学本构模型。分析水泥环对套管抗挤强度的影响程度,有限元计算结果表明,水泥环的弹性模型减小,套管在相同外载条件下的应力增大。建立套管抗挤强度的力学判定模型,考虑到在套管下放之后、未固井之前,自由悬持于钻井液中的套管在自身重力、浮力等应力的作用下,发生轴向拉伸和径向压缩,在太和-建增抗挤强度标准的基础上推导了新的套管屈服力学判定标准。更多还原

【Abstract】 Casing failure is a problem to be solved in the world. A lot of scholars researched on the problem of casing failure in many fields at home and abroad,but they can’t resolve it fundamentally.Through analyzing the mechanism of casing failure,we know the essence of casing failure is the calculation and decision of casing failure mechanics.Since the calculation and decision of casing failure mechanics are not only related with the distribution of original earth stress,formation body and the fluid-solid coupling action of fluid vadose field,but also related with the loading calculation of casing-cement mantle’s external stress because of reservoir stress redistributed and the decision of casing failure’s yield strength under the loading. The article analyses the present situation of casing damaged wells,casing failure reasons and mechanism,the types and affecting factors of casing damaged wells comprehensively.It highlights the stress field of the area around the casing damaged wells,and establishes earth stress and fluid pressure’mathematical model on the base of fluid-solid coupling theory.It establishes mechanical model that reflects casing damaged wells under the complex geologic condition, and calculates used of FEM analysed by nonlinear mechanics.It establishes the calculated model of casing-cement mantle’s stress under the external stress,analyses the affecting factors of casing strength,and establishes the mathematical model gived casing’s extra stress and the calculated model of the mechanical decision of casing failure’s yield strength.The article expounds the mechanism of casing failure reasonably, offers theoretical criterion for designing casing and lays the compact foundation for the establishment of casing failure’s criterion.Analyzing the geologic and engineering factors that affect casing failure, we know that mudstone’s hygroscopic afterflow,rock’s bloating,rock’s sand production,high pressure water injection,fault activity and formation activity are main geological factors of casing failure;well network deployment,cementing-completion operation and casing strength are main engineering factors.The calculated models of the erect and horizontal crustal stress and the mathematical model of the stress distribution in the area of wellbore are established.Two and three-dimensional fluid-solid coupling mathematics-mechanics models in the area of casing damaged wells are established. When fluid-formation pressure changed computed by FEM,the changement of strain and stress of initial body is distinguished,and smoothes out along with time-lapse,that means the original phase is main phase in which casing damaged wells buildup.The changement of strain and stress of reservoir and casing is calculated by three-dimensional linear elastic and elasticoplastic fluid-solid coupling model.The results agree well with the actual situation.A model of casing-cement sheath stress is established by perforating, the distribution rule of casing-cement sheath stress and the affection of perforation form on stress are analysed in such case.Sand inflowing in reservoirs helps formatting local empty in the sand around casing and forms additional stress.A model of casing-cement sheath stress is established under sand inflowing in reservoirs, using the stress model the cause of casing failure in such case is analyse.In the process of mudstone creeping, mudstone bits error and slips, the constitutive model of mudstone creeping is established,the cause that mudstone creeping make casing broken is analysed.Casing mechanic constitutive model of mudstone formation conditions is established. The influence of cement sheath on casing is analysed, FEM calculation results show that, the elastic modulus of cement cylindrical decreases,the stress of casing increases at the same condition.The mechanical estimation models of casing collapse resistance is established, we consider that after the casing set down, before cemented, the casing hanging in a drilling fluid will be stretched axially and compressed radially because of the axial stress caused by its gravity and buoyancy and the radial and circumferential stress caused by its inside and outside force. Based on Yitaihe-jianceng collapse resistance criterion we fetch the new casing yield mechanical criterion.更多还原