非均匀地应力条件下水泥环失效特征研究

发布时间：2019-04-13 19:48

【摘要】：固井后井筒内压力的变化可能导致水泥环发生密封失效,将井筒内压力的变化过程分为两个阶段:加压阶段、卸压阶段。在加压阶段中,在高套压和地应力的作用下水泥环本体发生塑性变形、同时当水泥环应力分布达到剪切强度和抗张强度时水泥环本体会发生失效。在卸压阶段中,由于此前水泥环本体已经发生塑性变形,因此在该阶段中,由于套管、水泥环和地层的形变能力不同,就可能会在固井第一界面或第二界面处产生微环隙,从而发生层间窜流以及环空带压,继而造成油田无法安全生产、降低油田产量等一系列后果。本文基于弹性力学理论、Mohr-Coulomb准则以及最大拉应力准则,考虑套管和地层为弹性体,水泥环为弹塑性体,重点研究了固井第一界面和水泥环本体的密封完整性。判断了在加压过程中水泥环本体可能发生剪切破坏以及张性破坏的区域。然后通过分析微环隙的形成机理,对卸压阶段中的微环隙宽度进行建模,得出微环隙宽度的理论计算模型。并通过Jackson室内试验,ABAQUS软件以及现场实例对理论模型性进行了验证。然后应用理论模型,分析了现场实际条件下,水泥环弹性模量和泊松比对水泥环破坏区域面积的关系。分析结果表明:水泥环本体的在加压阶段中发生破坏(剪切破坏和张性破裂),其剪切破坏区域面积随着弹性模量的增加而变大,随着泊松比的增加而减小;其张性破坏区域面积随着弹性模量的增加而变大,随着泊松比的增加而减小。本论文研究结果可以用来计算实际工况下水泥环本体破坏区域的范围,套管水泥环胶结面微环隙的宽度,也可为固井水泥体系的设计提供理论依据。
[Abstract]:The change of pressure in the wellbore after cementing may lead to seal failure of cement sheath. The change process of pressure in the wellbore can be divided into two stages: pressure stage and pressure relief stage. In the compression stage, the plastic deformation of cement sheath occurs under the action of high casing pressure and in-situ stress. At the same time, when the stress distribution of cement ring reaches the shear strength and tensile strength, the cement sheath will fail. In the pressure relief phase, since the plastic deformation of the cement sheath has already taken place before, in this stage, due to the different deformation capacity of the casing, the cement sheath and the formation, microannular gaps may occur at the first or second interface of the cementing. As a result, inter-layer channeling and annulus pressure occur, resulting in a series of consequences, such as failure to safely produce oil fields and reducing oil production and so on. Based on the elastic mechanics theory, Mohr-Coulomb criterion and maximum tensile stress criterion, considering the casing and formation as elastomer and cement sheath as elastomer, this paper focuses on the sealing integrity of the first interface of cementing and cement sheath body. The regions where shear failure and tensile failure of cement sheath may occur in the process of compression are judged. Then through the analysis of the formation mechanism of the micro-ring gap, the micro-ring gap width in the pressure relief phase is modeled, and the theoretical calculation model of the micro-ring gap width is obtained. The theoretical model is verified by Jackson indoor test, ABAQUS software and field examples. Then, the relationship between the elastic modulus of cement sheath and Poisson's ratio to the failure area of cement sheath is analyzed by using the theoretical model. The results show that the area of shear failure region increases with the increase of elastic modulus and decreases with the increase of Poisson's ratio when the failure of cement sheath occurs in the compression stage (shear failure and tensile fracture). The results show that the shear failure area increases with the increase of elastic modulus and decreases with the increase of Poisson's ratio. The area of tensile failure region increases with the increase of elastic modulus and decreases with the increase of Poisson's ratio. The results of this paper can be used to calculate the scope of failure zone of cement sheath under actual working conditions and the width of micro-annular gap on caking surface of casing cement ring. It can also provide a theoretical basis for the design of cementing cement system.
【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】：TE256

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