Experimental investigation of the failure mechanism of P110SS casing under opposed line load

Many studies focused on casing collapse strength under uniform load have been done, and the API 5C3 and ISO standards have been formed. However, only a limited number of researches on collapse failure mechanism of casing have been done under non-uniform load, especially experimental study, although the non-uniform load has a great impact on casing collapse strength. Hence, the collapse experiment is conducted for P110SS casing under opposed line load by using electro hydraulic servo pressure testing machine. The displacement variation rules of P110SS casing have been obtained under opposed line load. The strain of casing is measured in the process of collapse testing by the method of gluing strain-gauge on the outside surface of P110SS casing. The initial yield load of casing, instability load of casing and the yield load, stress-hardening rate, strain-hardening rate of casing after hardening are obtained. The stress-strain rules of casing after hardening are analyzed. The hardening characteristic and collapse failure mechanism of P110SS casing have been clarified under non-uniform load (under opposed line load). Experimental results can provide important references for the theoretical study on failure mechanism and collapse strength of casing under non-uniform load.     

A failure assessment diagram for strain hardening materials under cyclic and monotonic loading

Strain hardening is introduced in the failure assessment diagram by studying two simple collapse models. These models together with the new failure curves are used both to predict the maximum load of different types of specimens and to assess the stability of these specimens under controlled displacement. The models are also used to study crack growth under a cyclic load high enough to cause gross plastic deformation and thus invalidate Paris law.     

注汽井套管的三轴预应力设计

以暴露于热蒸汽中的目的层套管为研究对象,根据弹性力学理论,首先给出了套管在热应力和非均匀地应力作用下的三轴应力表达式,然后利用对套管施加预应力来降低套管的轴向热应力,以使得套管的有效应力控制在相应温度下套管的最小屈服极限内为原则,得到了热采井套管三轴预应力设计方法,并对辽河油田常用的N80钢级套管进行了预应力设计分析,给出了该套管在不同注汽温度和井深条件下所应使用的径厚比及相应的预应力值。研究表明,在实际注汽过程中适当增加注汽压力可以提高套管的安全性,传统的单轴预应力设计及只考虑热应力的三轴预应力设计结果偏于保守,建议以后注汽井在进行预应力设计时应考虑热应力和实际非均匀地应力的共同作用。     

深井超深井内壁磨损套管剩余强度计算

采用理论分析和有限元相结合的方法,给出了深井超深井套管磨损面积与磨损深度预测模型,以及均布外载条件下内壁磨损套管剩余抗外挤强度和抗内压强度的计算公式。将非均布载荷等效成均布载荷,给出了非均布外载条件下内壁磨损套管剩余抗外挤强度计算公式。将建立的理论公式计算结果与现有实验数据进行了对比,二者较为吻合。建议在深井超深井套管柱强度设计与评价时考虑套管磨损和地层弹性参数的影响,同时开展不同类型磨损套管剩余强度实验研究,进一步验证理论计算结果的精度及适用条件。     

非API套管接头完整性评估计算方法

针对非API套管接头的连接和密封性能提出一套完整的解析评估计算方法。首先建立具有密封和内外螺纹啮合结构的非API套管接头力学分析模型,依据API套管接头失效形式(螺纹跳扣、螺纹剪切破坏和接头断裂)及其机理结合弹塑性力学理论,推导出非API套管接头发生相应连接失效时的临界轴向载荷计算公式。然后,依据螺纹啮合对变形协调方程和单个螺纹牙轴向弹性变形分析,推导出套管接头螺纹牙啮合法向接触力计算方程组,从而获得非API套管接头各个螺纹牙轴向变形量及其承载轴向载荷分布情况数值解。最后,通过对比各个螺纹牙承载轴向载荷与连接失效临界载荷对非API套管接头进行连接性能评估;通过计算轴向载荷和气体内压作用下,套管接头螺纹轴向变形量及其对接头密封过盈配合值的影响,对非API套管接头进行密封性能评估。通过对3种典型非API套管接头完整性评估计算结果表明:在螺距、螺纹啮合中径、螺纹高度等螺纹参数相同情况下,非API套管接头的螺纹牙型设计参数(承载面角度与导向面角度)对其连接和密封性能影响显著。     

Elasticity solution for the casing under linear crustal stress

The integrity of the casing is crucial for oil and gas well. Based on stress function method, a three-dimensional model of the casing-cement sheath-formation system subjected to linear crustal stress is proposed. And then an analytical solution of the model was obtained. In the process of calculation, the casing and cement sheath are simplified as the perfect cylinder. The cement sheath is closely bonded with the casing and formation. The formation is considered to be an isotropic material without the layer-block structure. And the crustal stress is assumed to be linearly increasing with the depth of the well. The analytical solution strictly meets the stress and displacement continuity condition and boundary condition, and exhibits good agreement with finite element method. The results imply that an analytical method to capture the stress and displacement field of the casing under linear crustal stress along the axis is presented. Next, a benchmark for numerical and approximate solutions is provided. In addition, a new idea about solving the casing under the non-linear loads along the axis in some special stratum (such as heterogeneity stratum, salt rock) is proposed. Finally, our understanding for the casing under complex loads will be deepened.     

基于套管屈曲约束的拉挤型GFRP管轴压性能

为解决复合材料空间桁架结构部分关键压杆失稳引发的连续性倒塌问题,提出了一种由不锈钢套管及螺栓连接系组成的玻璃纤维增强树脂复合材料(GFRP)管整体失稳套管屈曲约束装置。为分析该套管屈曲约束装置对拉挤型GFRP管轴压性能的影响,对3个GFRP管试件和4个套管屈曲约束GFRP管试件进行了轴压试验,观察了试件的受力过程和破坏形态,获得了荷载-位移曲线和荷载-应变曲线,对比研究了两者的极限承载力和破坏模式,同时利用有限元模型分析了不同内核长细比、内核与套管间隙及套管壁厚对GFRP管轴压性能的影响。结果表明:该套管屈曲约束装置能有效约束GFRP管整体失稳变形,其极限承载力和延性均得到提升,并使GFRP管从失稳破坏向材料强度破坏发展;内核长细比越大,套管屈曲约束GFRP管极限承载力相比于内核失稳临界荷载的相对提升幅值越高,约束效果越好;内核与套管间隙越大,GFRP管延性越好,但其极限承载力会降低;套管壁厚过薄会降低GFRP管极限承载力,过厚则约束效果不明显。      

TG800碳纤维/聚酰亚胺树脂复合材料带翻边开口圆柱壳机匣件高温气动载荷下的承载性能

基于航空发动机的高温气动载荷环境,对树脂传递模塑(RTM)工艺制备的TG800碳纤维/聚酰亚胺树脂复合材料带安装翻边和壳壁开口的圆柱壳机匣件开展了常温、200℃和260℃高温气动载荷下的仿真分析和承载性能试验。仿真计算得到复合材料机匣件的高应力水平发生在安装翻边和开口处。试验利用所设计的专用试验装置与机匣试验件合围成一套能够解耦内压和轴力的被试腔体结构,通过对被试腔体施加高温气体压力和机械静载联合模拟热气流载荷,相比传统的冲压胶囊加压方式,可以对机匣的翻边和开口处进行充分热压考核。常温、200℃和260℃承载试验后对机匣开口进行了无损检测,得到开口处的分层损伤区域随着载荷增大朝着正方和正圆的趋势扩大,260℃破坏试验得到TG800碳纤维/聚酰亚胺树脂复合材料机匣件的失效模式与传统金属机匣的筒体破裂不同,失效方式为安装翻边断裂。研究表明,RTM工艺TG800碳纤维/聚酰亚胺树脂复合材料结构件的力学性能在200℃以内具备良好的温度稳定性,安装翻边为复合材料机匣件在航空发动机热气流载荷下的薄弱区域,应作为机匣件减重设计的重要优化部位。      

应用同步辐射CT系统研究脆性材料破坏过程

对脆性材料的破坏过程进行实验监测，非常困难。本文应用同步辐射CT系统来尝试对脆性材料的破坏过程进行初步观测。在对聚丙烯纤维增强水泥砂浆的实验过程中，得到了一些初步的比较满意的实验结果。     

碳纳米管增强开孔铝基复合泡沫的疲劳性能

采用原位化学气相沉积、短时球磨和填加造孔剂法相结合的工艺制备了碳纳米管(CNTs)/Al复合泡沫,研究了其在压缩-压缩循环载荷下的力学性能及失效机制。结果表明,CNTs/Al复合泡沫的应变-循环次数曲线经历线弹性、应变硬化及应变快速增长三个阶段。不同于泡沫铝的逐层坍塌变形失效模式,CNTs/Al复合泡沫疲劳失效的主要原因是大量剪切变形带的形成,试样出现快速的塑性变形。此外,CNTs含量为2.5wt%、孔隙率为60%的复合泡沫试样的疲劳强度相比于泡沫铝提高了92%。CNTs的均匀分布及增强相与基体材料之间良好的界面结合性保证了疲劳载荷能够以剪切力的形式从基体传递到CNTs上,使其充分发挥自身高强度、高韧性的特点,进而提高了疲劳性能。      

纤维增强水泥薄板及其复合梁抗弯性能研究

实验研究了纤维对水泥基复合材料抗弯性能的影响.结果表明,聚乙烯醇(PVA)纤维增强挤压脱水成型板材在弯曲荷载作用下呈现多点开裂、应变硬化的特性,具有良好的延性,聚丙烯(PP)纤维增强挤压脱水成型板材呈应变软化的特性,木纤维增强挤压脱水成型板材则呈脆性破坏;与普通混凝土梁相比,冷浇和热浇纤维增强板-混凝土组合梁的抗弯强度...     

酸性油气田C110套管断裂失效分析

为查明酸性油气田某油井C110套管断裂失效原因,通过C110断裂失效套管断口宏观形貌、金相组织、化学成分、力学性能和腐蚀产物成分等综合分析,对酸性油气田某油井C110套管断裂原因进行了探讨。结果表明:套管不居中导致套管产生应力集中,并在套管与卡瓦咬合的第1个齿形成严重机械损伤;同时,地层运动、套压波动等因素导致套管在应力集中部位出现交变载荷。最终,在套管内壁处于高H2S、低p H值环境下,在内表面交变应力集中区域发生腐蚀疲劳开裂。     

On the Collapse of Cotton/Epoxy Tubes under Axial Static Loading

Experimental quasi-static crushing tests and finite element analysis have been carried out for unidirectional filament wound laminated cotton/epoxy tubes. The work focuses on three main factors, which considerably affect the axial collapse load of unidirectional natural composite tubes. These factors are structural geometry, fibre diameter and fibre orientation. Cotton/epoxy tubes with different diameters (50, 70, 90, 110 and 130 mm) were examined and tested. The fibre orientation angles were 80 and 90°. The initial geometric imperfections are measured using the computerised Mistral coordinate measuring machine. The numerical prediction was obtained using commercially available finite element software. A limited agreement between the experimental and computational results was obtained. For all structures considered classical axial collapse eigenvalues were computed. The initial failure crush load computed from the finite element simulation model has been compared with the experiments.     

Comparative evaluation of strain controlled low cycle fatigue behaviour of solution annealed and prior cold worked 316L(N) stainless steel

The effect of 20% prior cold work on low cycle fatigue (LCF) behaviour of type 316L(N) stainless steel (SS) was studied at 873 K by conducting total axial strain controlled tests in air with strain amplitudes in the range ±0.25% to ±1.0%. The cyclic deformation behaviour of 20% prior cold worked (PCW) material was compared with the LCF response of solution annealed (SA) alloy tested under similar conditions. The cyclic stress response (CSR) of 316L(N) SS in the PCW condition was characterized by a short period of hardening followed by prolonged softening prior to failure, whereas SA material exhibited a significant hardening regime followed by stress saturation. Interrupted tests on PCW material were carried out at different stages of CSR in order to determine the underlying mechanisms as reflected in substructural changes. The fatigue life in the solution annealed condition was similar to that of the PCW material at higher strain amplitudes of testing (≥±0.5%) while at lower strain amplitudes, the PCW material exhibited longer life.     

核壳型丁苯胶乳对水泥基复合材料力学性能的影响及其作用机制

针对地层、水泥环、套管三者之间形变不协调而导致的三者层间封隔失效等问题,采用种子乳液聚合的方法,将功能单体2-丙烯酰胺基-2-甲基丙磺酸与苯乙烯接枝到低分子量液体聚丁二烯上,合成了一种稳定性良好的丁苯胶乳增韧剂TEL-100L胶乳。TEL-100L胶乳的结构及性能评价表明:TEL-100L胶乳具有良好的热稳定性和明显的核壳结构。水泥石的力学性能评价表明:TEL-100L胶乳可明显降低水泥石的脆度系数和弹性模量,提高水泥石的韧性及力学形变能力。对TEL-100L胶乳增韧机制的研究表明:TEL-100L胶乳不仅可以通过静电吸引作用吸附到水泥颗粒表面,而且可以通过Ca2+的桥接作用与水泥水化体系交错连接,形成致密的三维网状结构,从而提高水泥基复合材料的韧性和力学形变能力。      

Fatigue crack propagation under variable amplitude loading in PMMA and bone cement

Fatigue failure of PMMA bone cement is an important factor in the failure of cemented joint replacements. Although these devices experience widely varying loads within the body, there has been little or no study of the effects of variable amplitude loading (VAL) on fatigue damage development. Fatigue crack propagation tests were undertaken using CT specimens made from pure PMMA and Palacos R bone cement. In PMMA, constant amplitude loading tests were carried out at R- ratios ranging from 0.1 to 0.9, and VAL tests at R = 0.1 with 30% overloads every 100 cycles. Palacos R specimens were tested with and without overloads every 100 cycles and with a simplified load spectrum representing daily activities. The R- ratio had a pronounced effect on crack propagation in PMMA consistent with the effects of slow crack growth under constant load. Single overloads caused pronounced crack retardation, especially at low da/dN. In Palacos R, similar overloads had little effect, whilst individual overloads at low da/dN caused pronounced acceleration and spectrum loading retarded crack growth relative to Paris Law predictions. These results demonstrate that VAL can have dramatic effects on crack growth, which should be considered when testing bone cements.     

水泥砂浆固化粉质黏土分离式Hopkinson压杆试验与分析

为研究掺砂量（与干土的质量比）对水泥粉质黏土冲击压缩强度及能量吸收特征的影响,采用Φ 50 mm分离式Hopkinson压杆（Split Hopkinson pressure bar,SHPB）试验装置对不同掺砂量的水泥粉质黏土进行了0.4 MPa冲击气压下的冲击压缩试验。结果表明：普通水泥粉质黏土（未掺砂）动态应力-应变曲线大致分为弹性阶段、屈服硬化阶段及破坏阶段,而随着掺砂量的逐渐增加,水泥砂浆固化粉质黏土动态应力-应变曲线中屈服阶段愈加不明显,出现了理想的塑性阶段;水泥砂浆固化粉质黏土的冲击压缩强度随掺砂量的增大而先增大后减小,在掺砂量为10%时达到最大平均动强度9.56 MPa,较普通水泥土强度提高9.79%;水泥砂浆固化粉质黏土的吸收能随冲击压缩强度的增大而增大,两者具有较好的指数关系。     

防止热采井套管热破坏的预压固井技术

热力采油是开采稠油的最广泛、效益较高的方法。实践表明:注蒸汽稠油井如果用常规方法固井,那么在通常的注汽温度下,套管都因热应力而产生屈服变形。目前现场常用的防止套管热破坏方法不能从根本上解决问题。该文提出了防止热采井套管热破坏的预压固井技术,即在注水泥结束但没有凝固时,向油层套管施加内压强,使套管膨胀;水泥在套管膨胀的条件下凝固。计算表明:采用预压固井技术后,热采井在整个生产周期内,套管不但不屈服,而且还有较大的安全系数。此项技术可能成为延长热采井套管使用寿命的重要手段。     

超声波检测套管井水泥环缺陷仿真模拟

针对固井过程中由于顶替效率过低、气窜等原因造成水泥环局部缺失的现象,基于超声脉冲反射原理,运用有限元方法建立不同大小、不同方位的水泥环缺失模型,数值模拟了超声波在套管井多层介质中的传播规律。通过提取回波首波幅度、首波的接收时间,对回波进行频谱分析,对比了胶结良好和水泥环缺失两种情况下的时域特征和频域特征。在研究不同方位缺失影响时,引入了缺陷敏感频率,发现在一定激发频率下,有缺陷的位置上敏感频率会出现极大值,不同方位的缺陷有不同的敏感频率,而且区别较为显著,以此可以判断缺失方位。     

纤维增强水泥基复合材料压剪破坏的细观实验研究

对聚丙烯纤维和钢纤维增强水泥砂浆复合材料和混凝土复合材料进行了MTS 准静态单轴压缩实验和压剪加载条件下的细观力学实验研究。比较两类纤维在这两种加载条件下的作用发现: 在单轴压缩条件下, 钢纤维作用显著, 聚丙烯纤维基本没有什么作用;在压剪加载条件下, 钢纤维在材料各个变形阶段均起明显作用, 聚丙烯纤维在加载过程中起到一定的作用, 但由于含量较少对材料的极限荷载基本没有贡献。在细观实验中, 观察到了钢纤维和碎石颗粒在材料破坏过程中脱粘与断裂的作用方式。但只是在水泥砂浆试件的局部观察到了孔洞崩塌现象, 对于其促成压缩带形成的机理尚须深入的工作。