油套管特殊螺纹连接强度和密封理论研究

发布时间：2018-07-17 01:19

【摘要】：油套管特殊螺纹具有连接强度高和密封性能好的优点,它己成为解决高温高压含腐蚀介质等复杂恶劣工况下气井井筒完整性的关键技术之一。然而,即使是采用国际公认先进的油套管特殊螺纹,螺纹开裂或断裂及密封失效问题仍时有发生。目前关于特殊螺纹的研究主要采用有限元分析和试验法,此类方法较难以揭示螺纹连接失效机理及普遍规律。同时,油套管特殊螺纹目前无公认的技术标准,但相信各主流油套管公司均具有各自核心的密封结构形式以及相关的核心设计理论和分析软件。本文主要采用理论建模的方法对油套管特殊螺纹连接强度和密封理论进行了较系统的研究,包括油套管特殊螺纹上扣扭矩理论模型、拧紧和轴向工作力学理论模型、连接强度理论模型、密封面接触应力理论模型、气体泄漏率理论模型、密封性能定性定量评价理论方法、密封结构参数设计理论方法、腐蚀泄漏机理和材料接触应力松弛泄漏机理等。研究的主要内容概括如下：(1)调研了国内外油套管螺纹连接理论、有限元和试验研究现状,分析了特殊螺纹连接研究领域目前存在的主要问题,提出了论文的研究思路和主要内容。(2)分析了油套管特殊螺纹上扣扭矩构成,在此基础上基于弹性力学厚壁圆筒理论和旋转台肩法尔公式建立了上扣扭矩理论模型。以某Φ88.9mm油管特殊螺纹为例,对上扣扭矩及其构成的影响因素进行了敏感性分析,得出了螺纹径向过盈量、密封面径向过盈量、台肩面轴向过盈量以及螺纹脂摩擦系数对上扣总扭矩以及台肩面作用扭矩比例的影响规律,从而为油套管特殊螺纹参数优化设计提供了理论依据。(3)基于弹性力学和螺纹牙三维空间曲面描述建立了油套管特殊螺纹拧紧轴向载荷分布和螺纹牙平均接触应力理论模型并通过有限元实例对比分析验证了理论模型的有效性,同时得出了拧紧时螺纹轴向载荷分布规律。结果表明：台肩预紧力主要由距离台肩面附近的4-6个螺纹牙承担,仅最后一牙就承担了47.7%。为防止螺纹粘扣,应避免台肩过扭矩。同时必须考虑台肩预紧力对螺纹连接强度和密封性能的影响。(4)基于弹性力学建立了油套管特殊螺纹轴向拉压工作时力学理论模型,以某Φ88.9mm油管特殊螺纹为例分析得出了轴向拉伸和压缩载荷作用下螺纹旋合段载荷分布规律,明确了油套管特殊螺纹主要失效位置和失效形式,从而为建立特殊螺纹连接强度公式奠定了理论基础。(5)分析了API螺纹连接强度公式的不足,建立了考虑台肩面预紧力、螺纹连接强度、防止台肩面分离和屈服的油套管特殊螺纹轴向受拉受压连接强度理论模型。以某088.9mm非外加厚、外加厚和特殊间隙接箍油管特殊螺纹为例开展了实例计算,得出了油套管特殊螺纹失效规律,提出了采用端部内外加厚、厚壁油管避免使用特殊间隙接箍并合理控制台肩面上扣作用扭矩有利于提高特殊螺纹连接强度和连接效率。(6)针对协调式(锥面对锥面)和非协调式(球面对锥面、球面对柱面及球面对球面)接触主密封结构,分别采用弹性力学厚壁圆筒过盈配合理论和Hretze弹性接触力学理论建立了主密封面径向过盈接触应力理论模型并对影响过盈接触应力的密封结构参数进行了敏感性分析,得出了锥面锥度、油套管壁厚、球面半径以及涂敷合金弹性模量对主密封面过盈接触应力的影响规律。提出了合理控制锥面锥度、采用球对球内接触或球面对柱面主密封结构、密封面涂敷低弹性模量合金有利于提高油套管特殊螺纹主密封性能。(7)基于管柱力学理论建立了井下载荷工况下主密封面和台肩面实际接触应力理论模型,并以锥对锥和球对柱主密封结构为例进行了密封接触应力分布敏感性分析,得出了轴向拉伸、轴向压缩、气体内压、环空外压、井筒温度升高以及复合载荷工况对主密封面接触长度、主密封面和台肩面平均接触应力的影响规律。提出了应避免环空带压和合理控制台肩面上扣作用扭矩,以提高特殊螺纹密封性能。(8)建立了基于密封接触能机理和密封面极限屈服条件的特殊螺纹气密封性能定性评价方法并绘制了气密封包络线,评价了不同井下载荷工况下主密封面和台肩面密封性能,提出了油套管特殊螺纹主密封结构参数设计理论方法。(9)基于粗糙表面弹塑性分形接触力学和不可压缩层流流动理论,建立了气体通过特殊螺纹锥对锥主密封微小间隙的泄漏率理论模型,并通过基于Murtagian试验的气密封包络线验证了理论模型的有效性。同时,通过实例分析得出了密封面平均接触应力、有效接触长度和密封面粗糙度对气体泄漏率的影响规律。建立的气体泄漏率理论模型为揭示特殊螺纹泄漏本质、定性评价密封性能、优化设计密封结构参数提供了理论依据。(10)开展了13CrS-110和普通碳钢管段试样模拟实际井底、井口温度压力以及地层水和C02腐蚀环境下的腐蚀对比试验和13CrS-110油套管特殊螺纹应力腐蚀试验,揭示了管材腐蚀导致油套管特殊螺纹密封失效机理和规律。提出了密封面接触应力松弛导致缝隙腐蚀和泄漏的观点,并评价了油气井常用管材接触应力松弛性能。创新性地提出了高钢级和低钢级油套管特殊螺纹应采取不同的密封设计准则。总之,通过本文的研究工作,首次较系统地建立了一套油套管特殊螺纹连接强度和密封理论体系,这不仅为分析油套管特殊螺纹工作力学行为、评价特殊螺纹连接性能,设计开发新型特殊螺纹提供了理论依据和方法,同时对于降低油套管特殊螺纹连接失效、提高高温高压气井井筒完整性具有重要意义。因此,本文的研究工作不仅具有重要的理论意义和学术价值,而且具有重大的工程意义和广泛的应用前景。
[Abstract]:The special thread of oil and casing has the advantages of high connection strength and good sealing performance. It has become one of the key technologies to solve the wellbore integrity of gas well under complicated and harsh conditions, such as high temperature and high pressure corrosion medium. However, even if the international recognized advanced oil and casing threads are used, the problem of thread cracking or fracture and sealing failure still exists. At present, the research on special thread mainly adopts the finite element analysis and test method. This method is difficult to reveal the failure mechanism and universal law of threaded connection. At the same time, there is no accepted technical standard for the special thread of oil and casing, but it is believed that all the main oil and casing companies have their own core seal structure form and related core. In this paper, the theoretical modeling method is used to make a systematic research on the strength and sealing theory of the special thread connection of oil and casing, including the theoretical model of the torque of the special thread, the theoretical model of tightening and axial working mechanics, the theoretical model of the connection strength and the theoretical model of the contact stress of the seal face. The theoretical model of gas leakage rate, the qualitative and quantitative evaluation theory method of sealing performance, the theory method of sealing structure parameter design, the mechanism of corrosion leakage and the mechanism of material contact stress relaxation leakage. The main contents of the research are summarized as follows: (1) investigation on the theory of thread connection of oil and casing at home and abroad, the present situation of finite element and experimental research, and the analysis of the characteristics of the theory of finite element and test. The main problems existing in the research field of the special thread connection are present, and the research ideas and main contents of the paper are put forward. (2) the torque composition of the special thread on the casing thread is analyzed. Based on this, the theoretical model of the upper torque is established based on the theory of elastic thick wall cylinder and the rotary table shoulder formula, with a special thread of a certain 88.9mm tubing. For example, the sensitivity analysis is carried out on the influence factors of the torque and its composition, and the influence rules of the screw radial interference, the radial interference of the seal face, the axial interference amount of the shoulder surface and the friction coefficient of the screw grease on the total torque of the upper buckle and the ratio of the torque to the shoulder face are obtained, so as to optimize the design of the special thread parameters of the oil and casing. The theoretical basis is provided. (3) based on the description of the elastic mechanics and the three-dimensional curved surface of the threaded teeth, the theoretical model of the axial load distribution and the average contact stress of the threaded teeth is established and the validity of the theoretical model is verified by the comparison and analysis of the finite element examples. At the same time, the axial load distribution law of the screw thread is obtained. The results show that the pretension of the shoulder is mainly borne by the 4-6 threaded teeth near the shoulder surface. Only the last one bears the 47.7%. to prevent the thread sticking, and the over torque of the shoulder should be avoided. At the same time, the influence of the shoulder pretension on the strength of the thread connection and the sealing performance must be considered. (4) the special thread shaft of the oil and sleeve is established based on the elasticity mechanics. The mechanical theoretical model of the tension and pressure work is made. Taking the special thread of a certain 88.9mm tubing as an example, the load distribution law of the screw rotation section under the action of axial tension and compression load is obtained. The main failure position and failure form of the special thread of the oil and casing are clarified, which lays a theoretical foundation for the establishment of the special screw connection strength formula. (5) The deficiency of the strength formula of API thread connection is analyzed. The theoretical model of axial compression connection strength is established, which takes the pretension force of the shoulder surface and the strength of the thread connection to prevent the separation and yield of the shoulder surface. A case calculation is carried out with the example of a 088.9mm non external thickening, the extra thick and special clearance tubing special thread of the tubing. The failure law of special thread of oil and casing is given. It is proposed that the internal and external thickening of the end part, the thick wall tubing to avoid the use of special gap collar and the reasonable control of the torque on the shoulder face can improve the connection strength and connection efficiency of the special thread. (6) the coordination type (cone face to conical surface) and uncoordinated type (ball face conical surface, ball face cylinder face and The spherical surface of the ball is in contact with the main sealing structure. The theoretical model of radial interference contact stress of the main cover is established by using the theory of elastic thick wall cylinder interference fit and Hretze elastic contact mechanics, and the sensitivity analysis is made for the sealing structure parameters affecting the interference contact stress, and the cone surface taper, the thickness of the casing wall and the ball are obtained. The influence of the surface radius and the elastic modulus of the coating alloy on the interference contact stress of the cover cover is put forward. A reasonable control of the conical taper is put forward, the ball is used to contact the ball or the ball face the main seal structure, and the seal surface coating with low modulus of elasticity is beneficial to the improvement of the special seal performance of the oil casing. (7) based on the mechanical theory of the tube column The theoretical model of the actual contact stress of the main cover and the shoulder surface under the loading condition is downloaded, and the sensitivity analysis of the seal contact stress distribution is carried out with the cone and the ball to the main seal structure. The axial tension, axial compression, internal pressure of gas, outer pressure of the annular space, the rise of the wellbore temperature and the compound load condition on the main cover are obtained. The influence law of the contact length, the main cover and the average contact stress of the shoulder surface is proposed. It is proposed that the ring air pressure should be avoided and the torque on the shoulder surface is reasonably controlled to improve the sealing performance of the special thread. (8) the qualitative evaluation method of the special threaded gas seal performance based on the sealing contact energy mechanism and the limit yield condition of the sealing surface is established. The enveloping line of gas seal is drawn and the sealing performance of the main cover and shoulder surface under the loading condition of different wells is evaluated. The theoretical method of designing the main seal structure parameters of the special thread of the oil casing is proposed. (9) based on the rough surface elastoplastic fractal contact mechanics and the incompressible laminar flow theory, the gas through the special thread cone is established to the cone main. The theoretical model of leakage rate is sealed with small gap, and the validity of the theoretical model is verified by the air seal envelope based on Murtagian test. At the same time, the effect of the average contact stress, the effective contact length and the seal surface roughness on the gas leakage rate is obtained by the case analysis. The theoretical model of the gas leakage rate is established. It provides a theoretical basis for revealing the essence of leakage of special thread, evaluating the sealing performance qualitatively and optimizing the design of sealing structure parameters. (10) the simulated actual bottom of 13CrS-110 and common carbon steel tube specimens, the temperature pressure of the wellhead and the corrosion against test and the special thread stress corrosion of the 13CrS-110 oil casing under the formation water and the C02 corrosion environment The failure mechanism and law of the special thread sealing of the casing pipe caused by the pipe corrosion were revealed. The viewpoint of the gap corrosion and leakage caused by the contact stress relaxation of the sealing surface was put forward, and the contact stress relaxation performance of the common pipe material used in the oil and gas wells was evaluated. The special thread of the high steel grade and low steel grade oil casing should be innovatively adopted. In summary, through the research work of this paper, a set of special thread connection strength and sealing theory system of oil and casing is set up for the first time. It not only provides a theoretical basis and method for analyzing the mechanical behavior of the special thread of oil and casing, evaluating the connection performance of special thread, and designing and developing new special thread. In order to reduce the failure of the special thread connection of the oil and casing, it is of great significance to improve the wellbore integrity of high temperature and high pressure gas well. Therefore, the research work of this paper not only has important theoretical significance and academic value, but also has great engineering significance and wide application prospect.
【学位授予单位】：西南石油大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TE931.2

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