变内压条件下膨胀水泥与地层机械性能的匹配

以膨胀水泥和地层作为研究对象,以维持井筒完整性为目的,利用弹性力学理论,借助有限元方法模拟分析了套管内压变化条件下膨胀水泥和地层机械性能对井筒完整性的影响,研究了两者机械性能的匹配关系。研究表明:膨胀水泥弹性模量越大,水泥环内最大米塞斯(Mises)应力越大;膨胀水泥泊松比越大,水泥环内最大Mises越小,水泥环内最大周向应力越小。地层弹性模量越大(地层越硬),水泥环内最大Mises应力越大,水泥环内最大周向应力越小;地层泊松比对水泥环内最大Mises应力和最大周向应力的影响较小。建议硬地层(弹性模量大)匹配弹性模量较小、泊松比较大的膨胀水泥,重点预防水泥环的挤压破坏;软地层且内压较小时匹配弹性模量较大、泊松比较大的膨胀水泥,重点预防水泥环的周向拉伸破坏。     

套管和水泥环对井间电磁场测井的影响

本文以电磁场理论为基础,假设地下非均匀介质是关于发射器所在的井轴对称,发射源为处于垂直于井轴放置的通以交流电的多匝线圈,充分考虑套管、水泥环对地层信号的影响因素,建立了井液、套管、水泥环、地层四层媒质模型低频电磁场的求解方法,分析了不同地层电导率、套管和水泥环对井间电阻率测井的影响。研究表明,套管和水泥环的存在,对低阻值地层和高阻值地层电阻率测井都有影响,尤其是对低阻值地层的影响较为明显。接收信号电动势幅度受套管磁导率影响较大,受水泥环磁导率影响较小。     

内壁磨损套管在非均匀地应力作用下的应力强度分析

西南油气田深井内壁磨损套管在地层深部非均匀地应力的作用,受力工况恶化,挤毁风险加大。为了了解地应力非均匀程度、方向及其与磨损位置夹角对套管抗挤强度的影响,本文建立了磨损套管-水泥环-地层系统的有限元力学模型,并进行了算例分析,结果表明:在非均匀载荷作用下,内壁磨损套管受力状况趋于恶化,载荷非均匀性(最大主应力与最小主应力之比)越大,套管的工作应力越高,被挤毁的风险越大;当最大主应力方向与磨损月牙夹角为90°时,磨损引起的套管应力增加和地应力非均匀性导致的应力非均匀分布叠加,套管的受力状态进一步恶化,是最危险的情况。     

基于有限元仿真的套管损坏原理分析

套管损坏影响油井生产,增加后期维护成本。造成套管损坏的主要原因包括地层岩性变化、断层活动、地应力的变化等。本文利用某区块油井井身结构资料和地质测井资料,通过有限元仿真软件建立了套管-水泥环-围岩有限元模型,直观有效地模拟了套管、水泥环在不同地质参数下的应力应变状态,通过分析研究确定了水泥环力学性能、地层岩性、地应力、套管内压变化对套管和水泥环应力状态的影响规律,从而在理论上为降低套管损坏提供指导。     

套管磨损及地应力对深井套管柱强度的影响分析

油田开发过程中,采油套管损坏给油田造成了巨大的经济损失。采用弹性力学解析及有限元方法,给出了考虑磨损时套管剩余抗挤强度、抗内压强度,以及非均匀地应力作用下套管外壁等效外挤载荷的计算方法,分析了非均匀地应力作用下不同套管磨损量对套管强度,以及不同地层性质对套管地应力外挤力的影响。研究表明,当磨损度为10%时,套管的剩余抗外挤强度、剩余抗内压强度降低约30%;套管内壁的M ises应力和套管外壁地应力外挤力随地层弹性模量的增大均明显减小,说明地层越硬,套管将偏于安全。     

固井水泥环性质和厚度对套管承载能力的影响研究

油气井固井注水泥作业主要目的就是要形成质量较好的水泥环,起到支撑及保护套管的作用。但在钻井和开发过程中,水泥环会受到多种不利载荷的影响,如温度应力、地层岩石围压、套管内压力等,使水泥环不能起到有效保护套管的作用。本文以某口井作为研究对象,根据弹性力学的相关理论并结合有限元方法,通过建立有限元模型,利用和操作有限元分析软件ANSYS,系统的研究了水泥环性质、厚度,对套管的承载能力的影响规律,并根据以上情况提出了相应的措施,用于指导现场工程实践。     

大庆深层致密气固井质量对完井套管受力变形规律的影响

为了进一步明确大庆深层气致密储层大规模压裂过程固井质量对完井套管受力变形影响程度,采用有限元数值模拟分析方法,建立了套管、水泥环、地层三维分析模型,模拟不同水泥环缺失工况条件下压裂参数对套管受力变形状态。研究表明,固井水泥环缺失会导致套管受到应力急剧升高,套管存在变形风险。当偏心距离为4mm、8mm、12mm时,随着水泥环厚度的增加,套管受到的最大等效压力呈现不断变大的趋势;当水泥环周向上缺失90°时,固井套管所受等效应力最大,相对于完整水泥环套管承受的最大等效应力增加了66.9%。研究成果可为大庆深层致密气大规模压裂套管变形防治提供依据。     

稠油热采井水泥环拉伸疲劳破坏寿命预测研究

稠油热采井生产过程中水泥环完整性失效严重危害稠油热采井的安全高效开发。已有研究未见稠油热采井水泥环拉伸疲劳破坏寿命预测的研究。本文基于Zhaoguang Yuan等人关于水泥环拉伸应变疲劳寿命研究的方法,提出了适用于稠油热采井水泥环拉伸疲劳破坏寿命预测的应力疲劳寿命预测方法。利用室内实验测试水泥环的疲劳破坏寿命,采用Abaqus有限元软件获取水泥环疲劳破坏对应的应力值,建立了稠油热采井水泥环应力疲劳寿命方程。基于所建立的方法和方程,研究了地层弹性模量、热采井升温周期、水泥环热膨胀倍数对水泥环拉伸破坏疲劳寿命的影响,研究表明地层弹性模量、注蒸汽升温周期、水泥环热膨胀倍数对热采井水泥环的寿命影响较大,硬地层环境、适当增加注蒸汽升温时间、适当增加水泥环的热膨胀倍数均有利于热采井水泥环寿命的延长。     

水泥环封固质量对套管安全影响研究

压裂改造施工是致密油气资源开采的有效技术手段,在改造和生产过程中,油气井在井下面临着复杂的温压工况条件,水泥环封固质量就是套管安全服役的重要基础。根据长庆油田常见井身结构,针对套管试压或压裂工况,建立不同水泥环封固条件下的套管-水泥环-地层力学模型,考虑不同试压或压裂压力、套管壁厚等因素,计算套管应力状态。在此基础之上,根据不同水泥浆上返高度、水泥环封固状态和套管下入深度,开展套管安全状态评价。研究结果表明,水泥环封固完全时,套管等效应力都较小;水泥环出现窜槽缺失,套管应力将迅速增加,甚至超过套管屈服值,套管产生塑性变形;环空水泥环封固高度过低,套管安全系数会大幅降低。因此在固井施工过程中,必须保证环空水泥环封固质量,同时考虑水泥浆上返高度,从而保证套管在井下工况条件安全服役。     

水泥环对磨损套管抗内压强度的影响研究

用弹性有限元方法,建立套管一水泥环的有限元力学模型.对套管--水泥环内壁不同磨损量时的杭内压强度进行了计算,分析了在不同磨损量时,在内压作用下,套管管体达到屈服时,VonMise应力随套管最小壁厚和圆周方向的变化情况,并比较了在相同磨损量下,套管和套管一水泥环之间Von Mise以及抗内压强度之间的大小关系,最后得出了在相同磨损情况下,水泥环对磨损套管抗内压强度的影响效果.     

煤矿地应力测试及应力场反演分析

根据地应力测试的基本概念及原理,结合实际地应力测试工作,介绍了地应力测试过程中的测量原理、测试设备与现场测量方法,并对测试结果进行了分析。在此基础上,根据地应力的测试结果,运用多元线性回归的方法进行了地应力场反演,并以西二采区9号煤反演结果为例进行了分析,结果表明,该采区3个工作面位于应力集中区,冲击危险性较大。     

Hypothalamic Regulation of Corticotropin-Releasing Factor under Stress and Stress Resilience

This review addresses the molecular mechanisms of corticotropin-releasing factor (CRF) regulation in the hypothalamus under stress and stress resilience. CRF in the hypothalamus plays a central role in regulating the stress response. CRF stimulates adrenocorticotropic hormone (ACTH) release from the anterior pituitary. ACTH stimulates glucocorticoid secretion from the adrenal glands. Glucocorticoids are essential for stress coping, stress resilience, and homeostasis. The activated hypothalamic-pituitary-adrenal axis is suppressed by the negative feedback from glucocorticoids. Glucocorticoid-dependent repression of cAMP-stimulated Crf promoter activity is mediated by both the negative glucocorticoid response element and the serum response element. Conversely, the inducible cAMP-early repressor can suppress the stress response via inhibition of the cAMP-dependent Crf gene, as can the suppressor of cytokine signaling-3 in the hypothalamus. CRF receptor type 1 is mainly involved in a stress response, depression, anorexia, and seizure, while CRF receptor type 2 mediates “stress coping” mechanisms such as anxiolysis in the brain. Differential effects of FK506-binding immunophilins, FKBP4 and FKBP5, contribute to the efficiency of glucocorticoids under stress resilience. Together, a variety of factors contribute to stress resilience. All these factors would have the differential roles under stress resilience.     

Running from Stress: Neurobiological Mechanisms of Exercise-Induced Stress Resilience

Chronic stress, even stress of a moderate intensity related to daily life, is widely acknowledged to be a predisposing or precipitating factor in neuropsychiatric diseases. There is a clear relationship between disturbances induced by stressful stimuli, especially long-lasting stimuli, and cognitive deficits in rodent models of affective disorders. Regular physical activity has a positive effect on the central nervous system (CNS) functions, contributes to an improvement in mood and of cognitive abilities (including memory and learning), and is correlated with an increase in the expression of the neurotrophic factors and markers of synaptic plasticity as well as a reduction in the inflammatory factors. Studies published so far show that the energy challenge caused by physical exercise can affect the CNS by improving cellular bioenergetics, stimulating the processes responsible for the removal of damaged organelles and molecules, and attenuating inflammation processes. Regular physical activity brings another important benefit: increased stress robustness. The evidence from animal studies is that a sedentary lifestyle is associated with stress vulnerability, whereas a physically active lifestyle is associated with stress resilience. Here, we have performed a comprehensive PubMed Search Strategy for accomplishing an exhaustive literature review. In this review, we discuss the findings from experimental studies on the molecular and neurobiological mechanisms underlying the impact of exercise on brain resilience. A thorough understanding of the mechanisms underlying the neuroprotective potential of preconditioning exercise and of the role of exercise in stress resilience, among other things, may open further options for prevention and therapy in the treatment of CNS diseases.     

Stress rupture of polypropylene

Tensile stress rupture is an important engineering property of plastics required in desiging parts subject to continuous or intermittent stress over long periods of time, especially in corrosive environments. This paper presents tensile stress rupture results on polypropylene and some of their applications in a program conducted over the past several years. Among the structural and compositonal paramaters studied in this work are the effects of molecular weight, molecular weight distribution, isotactic content, polyblends, and fillers on the shape and slope of the stress rupture-time curve. Data are presented showing the interrelationships between these variables, and the agreement with current stress rupture theories is discussed.     

论应力腐蚀断裂

本文简明扼要地阐述了金属材料在许多环境中同时受应力和腐蚀的作用,产生了裂纹甚至断裂;分析了应力腐蚀产生的机理,介绍了低碳钢和奥氏体不锈钢产生应力腐蚀的原因、现象和影响因素;同时,也提出了防止应力腐蚀裂纹产生的四种方法.     

管道应力分析

阐述了管道应力分析的任务和方法,介绍了如何建立压力管道布置三维立体模型,管道上的荷载及其组合工况,以及如何对管系进行分析计算。     

Stress Relaxation in PZT

Time-dependent deformation in the sonar transducer ceramic, PZT, was studied by stress-relaxation techniques. Logarithmic stress relaxation was not observed but the data could be treated in terms of an analysis of thermally activated deformation by Reed-Hill and Dahlberg. The room-temperature activation energy and activation volume of the rate-controlling deformation mechanism were measured as 25 kcal/mol and 7000 ų, respectively. A dislocation model of the domain processes responsible for deformation, consistent with the experimental data, is presented.     

管壳式换热器部件的应力分析及强度校核

本文对某换热器的前管板在机械载荷和热载荷下利用有限元分析软件ANSYS进行强度分析。在分析时,首先进行热分析得出温度分布,得出温度最大值出现在换热管与管板接触区,且最大值为150.408℃。然后在热分析的基础上进行应力分析,得出最大应力出现在螺栓连接处,且为174 MPa。最后参照JB4732-1995《钢制压力容器分析设计标准》采用线分析法选取7处危险区域进行应力评定,得出3处应力(为机械载荷和热载荷的总应力)最大为174 MPa小于安全值438 MPa。所以该换热器在运行过程中是安全的。     

Influence of Interfacial Shear Stress on First-Matrix Cracking Stress in Ceramic-Matrix Composites

The first-matrix cracking stress and fiber-matrix interfacial shear stress were measured in zircon-matrix composites uniaxially reinforced with either uncoated or BN-coated silicon carbide filaments to study the role of intentional changes in interfacial shear stress on first-matrix cracking stress. The first-matrix cracking stress was measured by mechanical tests performed in either tension or flexure, and the filament-matrix interfacial shear stress was measured by a fiber pushout test. The first-matrix cracking stress was independent of the measured interfacial shear stress and did not conform to the predictions of a number of energy-based micromechanics models. In contrast, the first-matrix cracking stress showed a good correlation with the first-matrix cracking strain, which is hypothesized to be a more realistic criterion for first-matrix cracking in this class of filament-reinforced ceramic-matrix composites.