可钻式贴堵工艺中膨胀水泥机械性能参数的优选

可钻式贴堵工艺是一种适用性强、封堵可靠性高、后期处理方便的新型调整层系封堵作业技术,其常选用膨胀水泥来改善封堵效果。为了预防膨胀力挤坏可钻式贴堵管,采用有限元数值模拟方法,研究了膨胀水泥和地层的机械性能参数对贴堵管中应力的影响规律,优选了膨胀水泥的机械性能参数范围。结果表明:膨胀水泥膨胀率对贴堵管内应力的影响最大,次之是膨胀水泥的弹性模量,膨胀水泥的泊松比、地层的弹性模量和泊松比的影响较小。膨胀水泥膨胀率越大,贴堵管内的应力越大,且环空中膨胀水泥的体积越大,应力增长速率越大;随着膨胀水泥弹性模量的增大,贴堵管内的应力先增大后减小。无缺失和原套管缺失两种情况下贴堵管挤毁的可能性较小,原套管和水泥环都缺失时最可能挤毁贴堵管。优选膨胀水泥的膨胀率为0.5%,其它机械性能参数可在任意范围内变化。研究结果对可钻式贴堵工艺的成功应用具有重要的指导意义。     

非均匀地应力下套管应力的敏感性分析

套损是影响地下储气库井筒完整性的关键问题,制约着储气库长期的安全生产。为此,基于弹性力学理论,运用有限元分析方法,建立了理想固井状态下的套管-水泥环-地层组合分析模型,对受非均匀地应力时组合体各层Mises应力的分布规律进行了研究,讨论了套管应力对水泥环与地层的弹性参数变化的敏感程度。结果表明：套管内壁的应力明显高于水泥环和地层内壁的应力且沿井周呈非均匀分布;地层弹性模量对套管内壁应力的影响最为显著,套管应力随地层弹性模量的增加急剧减小;其次为水泥石弹性模量,当其与地层弹性模量相同时,套管应力达到最大。该研究成果可为优化套管完井设计和预防套管损坏提供理论参考。     

非金属密封垫片应力场的数值模拟

为研究聚四氟乙烯密封垫片的应力分布规律,根据有限元理论,建立了管法兰连接有限元模型。研究了垫片在预紧状态和工作状态下的Von Mises应力和接触应力分布,分析了管道内流体压力、螺栓预紧力和垫片材料弹性模量对其应力值和应力分布的影响。结果发现:垫片在工作状态下的Von Mises应力大于其在预紧状态;流体压力越大,垫片和Von Mises应力越大,但是其有效接触宽度越小;螺栓的预紧力越大,垫片的Von Mises应力和接触应力越大;垫片材料的弹性模量值对垫片接触应力值的影响较小。     

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。     

套管内压变化作用下水泥环界面胶结劣化试验研究

在油气井试压、储层改造等作业过程中,井筒套管内压将发生大幅变化,极易造成水泥环界面剥离,导致井筒密封完整性失效,影响建井寿命。针对上述难题,采用自主研发的水泥环密封性评价装置,开展套管内压作用下的水泥环界面胶结劣化试验,研究水泥环密封失效机理,结果表明:(1)套管内压突变和多次循环交变,都将造成水泥环密封完整性失效;(2)随着套管内压的不断增加,水泥环在径向上将突破弹性应变,产生塑性变形与残余应变,从而无法与套管变形保持一致;(3)水泥环-套管应变不连续,将导致界面剥离,气窜风险增加;(4)循环交变应力将造成水泥环微裂纹发育、孔隙结构塌陷,塑性应变不断累积,进一步削弱水泥环密封完整性。研究结果可望为水泥环完整性评价与水泥浆体系优化提供参考与指导。     

废弃井中水泥塞性能参数优化

确保废弃井中水泥塞不发生破坏是能够长期埋存地下二氧化碳的关键。在非均匀地应力条件下,废弃井中水泥塞的弹性模量、泊松比等性能参数是影响其完整性的重要因素。本文通过建立非均匀地应力条件下地层-水泥环-套管-水泥塞组合力学模型,利用有限元方法,数值模拟计算得到了不同因素下保证水泥环发生破坏的临界值:地应力组合σx=30MPa,σy=40MPa条件下,不同泊松比水泥塞所对应的临界弹性模量为:32.8、29.2、25.5、22.0、19.1GPa;20GPa和30GPa弹性模量水泥塞所对应的临界泊松比为:0.16和0.19;水泥塞弹性模量为20GPa条件下,不同泊松比水泥塞对应的临界地应力σy值分别为:51、49、46、42.5和39MPa。研究结果表明,水泥塞性能参数小于其临界值时才能确保水泥塞不发生破坏,为废弃井中水泥塞性能参数的设计提供了一定的理论指导。     

水泥套弹性模量对天然气地下储气井筒加强作用影响的研究

天然气储气井除了受到井内气压的作用,还受到周围水泥套和地层的挤压力和支撑加强作用。本文基于弹性理论建立了"井筒—水泥套—地层"组合体的计算模型,获得了组合体的应力计算公式,在此基础上,计算了不同弹性模量水泥套加强作用下的井筒应力,计算结果表明:水泥套弹性模量的增大会提高水泥套对井筒的加强作用,会降低井筒中应力沿壁厚分布的不均匀程度。     

油气水井井筒完整性研究综述

在油田开发过程中,井筒完整性对于油田钻井和后期增产措施实施大规模压裂起着至关重要的作用。本文结合试验数据,探讨井筒完整性的失效机制,分析了地质环境、井眼曲率、水泥环性能密封以及油套管腐蚀速率等多方面影响因素。结果表明,地层泥岩吸水蠕变和膨胀、产层出砂、岩层滑动、断层活动、盐岩蠕变、坍塌及地震都会造成套管损坏;井眼曲率越大套管强度也越大,对套损的损坏就越严重;利用水泥环力学性能分析,探讨密封完整性对井筒完整性的影响;同时分析油套管腐蚀的影响因素,这些因素都对保证井筒完整性起着至关重要的作用。     

新疆油田玛湖地区水泥浆体系弹塑性加量优选

体积压裂是新疆油田玛湖地区提高油气产量的主要技术手段,由于水力压裂施工过程中套管内压力循环变化,使得水泥环防应力破坏面临着巨大挑战。针对体积压裂过程中水泥环的应力破坏问题,利用全尺寸水泥环密封完整性评价装置,开展了弹性水泥浆体系不同弹塑剂JTS-1加量对水泥环完整性的影响试验,综合考虑弹塑剂JTS-1加量对水泥浆流变学影响,形成了适合新疆油田玛湖地区水力压裂工况的弹性水泥浆体系。结果表明:随着弹塑剂JTS-1加量的增大,水泥浆弹性模量降低,水泥环防应力破坏能力增大,但水泥浆黏度增大,降低了水泥浆流变性,经实验优选,推荐弹塑剂JTS-1加量为6%～8%。     

基于ANSYS的PE-HD实壁管性能与尺寸的关系

采用ANSYS逆向模拟分析高密度聚乙烯(PE-HD)实壁管的环刚度测试过程,研究了管材环刚度为6.3时其规格尺寸如直径和壁厚与原材料性能之间的关系,并分析了标准YD/T 841.2-2008的合理性。结果表明,材料的泊松比对管材最大变形量影响较小;材料的弯曲弹性模量越大,管材最大变形量越小;管材环刚度达到6.3时所需要的原材料弯曲弹性模量值与其径厚比成正比直线关系;标准YD/T 841.2-2008中关于某些壁厚的规定存在不合理性,即按照标准中规定的某些壁厚尺寸,生产PE-HD实壁管所用原材料无法达到环刚度为6.3时所需要的弯曲弹性模量值。     

A method of determining the elastic properties of diamond-like carbon films

The elastic properties of diamond-like carbon (DLC) films were measured by a simple method using DLC bridges which are free from the mechanical constraints of the substrate. The DLC films were deposited on a Si wafer by radio frequency (RF) glow discharge at a deposition pressure of 1.33 Pa. Because of the high residual compressive stress of the film, the bridge exhibited a sinusoidal displacement on removing the substrate constraint. By measuring the amplitude with a known bridge length, we could determine the strain of the film which occurred by stress relaxation. Combined with independent stress measurement using the laser reflection method, this method allows the calculation of the biaxial elastic modulus, E/(1−ν), where E is the elastic modulus and ν is Poisson's ratio of the DLC film. The biaxial elastic modulus increased from 10 to 150 GPa with increasing negative bias voltage from 100 to 550 V. By comparing the biaxial elastic modulus with the plane–strain modulus, E/(1−ν²), measured by nano-indentation, we could further determine the elastic modulus and Poisson's ratio, independently. The elastic modulus, E, ranged from 16 to 133 GPa in this range of the negative bias voltage. However, large errors were incorporated in the calculation of Poisson's ratio due to the pile up of errors in the measurements of the elastic properties and the residual compressive stress.     

Study on the Viscoelastic Poisson‘s Ratio of Solid Propellants Using Digital Image Correlation Method

Digital image correlation methods were used for further studies of the viscoelastic Poisson's ratio of solid propellants. The Poisson's ratio and the Young's relaxation modulus of solid propellants were separately determined in a single stress relaxation test. In addition, the effects of temperature, longitudinal strain, preload and storage time on the Poisson's ratio of solid propellants were discussed. The Poisson's ratio master curve and the Young's relaxation modulus master curve were constructed based on the time‐temperature equivalence principle. The obtained results showed that the Poisson's ratio of solid propellants is a monotone non‐decreasing function of time, the instantaneous Poisson's ratio increased from 0.3899 to 0.4858 and the time of the equilibrium Poisson's ratio occurred late when the temperature was varied from −30 °C to 70 °C. The Poisson's ratio increased with temperature and longitudinal strain, decreased with preload and storage time, while the amplitude Poisson's ratio increased with preload, decreases with longitudinal strain and storage time. The time of the equilibrium Poisson's ratio occurred in advance with the increase of longitudinal strain, preload and storage time.     

The dependence of the elastic properties of silica/alumina materials on the conditions used for firing

The dependence of the elastic properties of a range of powder compact samples has been measured as a function of firing variables. It was found that both Young's modulus and Poisson's ratio are particularly sensitive to the peak temperature and the time for which the peak temperature is maintained, over a range of these variables for which density is not significantly affected. The material investigated is used industrially for the manufacture of wall tiles. Firing trials conducted in an industrially operated tunnel kiln have indicated that sufficient variation in firing conditions exists, in the cross-section of the tunnel kiln, to cause significant variation in the values of Young's modulus and Poisson's ratio of bodies fired in different positions in the kiln. Microstructural examination of bodies produced to have very similar densities but vastly different values of Young's modulus and Poisson's ratio has indicated that the dependence of Young's modulus and Poisson's ratio on firing conditions can be explained by the extent of sintering within the ceramic matrix.     

On the elastic constants of amorphous carbon nitride

Elastic and thermomechanical properties of amorphous carbon nitrite thin films as a function of nitrogen concentration are reported. The films were prepared by ion beam assisted deposition with nitrogen concentrations ranging from 0 to 33 at.%. By using a combination of the thermally induced bending technique and nano-indentation measurements it was possible to calculate independent values for the Young's modulus, the Poisson's ratio, as well as the thermal expansion coefficient of the films. The hardness and elastic recovery are discussed in terms of the Young's modulus and the Poisson's ratio.     

Mechanical properties of bonded elastomer discs subjected to triaxial stress

The aim of this article was to evaluate and analyze the mechanical properties of bonded elastomer discs subjected to triaxial stress on an MTS (machine for testing samples) equipment. Saveral pulling tests were run on an Instron machine using an O-ring type of samples to evaluate the mechanical properties of testing unfilled nitrile rubber subjected to uniaxial tension. It was found from the stress–strain curve of the O-ring samples that a very small stress softening occurred when the maximum strain is less than 200%. It was also found that the stress and strain at break does not drastically vary with respect to strain rate. The initial modulus does not vary with respect to strain rate up to ε = 2 min⁻¹, and only for large values of ε does the modulus depend on the strain rate. The material used for the uniaxial tension experiments were bonded between two rigid cylindrical steel plates and the specimens were subjected to uniaxial tension on an MTS machine. It was found that the initial modulus in tension was smaller than in compression. The theoretical predicted initial modulus from Gent's equation was much larger than experimentally estimated. It was shown that the elastomer in the pancake tests was not incompressible and a value of 0.494 was determined for the effective Poisson's ratio. A mathematical equation was derived for the effective Poisson's ratio as a function of the volume fraction of voids within the testing material. © 1996 John Wiley & Sons, Inc.     

Intrinsic Mechanical Properties of 20 MAX‐Phase Compounds

The intrinsic mechanical properties of 20 MAX‐phase compounds are calculated using an ab initio method based on density functional theory. A stress versus strain approach is used to obtain the elastic coefficients and thereby obtain the bulk modulus, shear modulus, Young's modulus, and Poisson's ratio based on the Voigt–Reuss–Hill (VRH) approximation for polycrystals. The results are in good agreement with available experimental data. It is shown that there is an inverse correlation between Poisson's ratio and the Pugh ratio of shear modulus to bulk modulus in MAX phases. Our calculations also indicate that two MAX compounds, Ti₂AsC and Ti₂PC, show much higher ductility than the other compounds. It is concluded that the MAX‐phase compounds have a wide range of mechanical properties ranging from very ductile to brittle with the “A” in the MAX phase being the most important controlling element. The measured Vickers hardness in MAX compounds has no apparent correlation with any of the calculated mechanical parameters or their combinations.     

Investigation of mechanical behavior of CPC/bone specimens by finite element analysis

Calcium phosphate cement (CPC), as an important injectable biomaterial, is extensively used for bone repair in clinical application. If mechanical properties of CPC match well with that of bone tissue, it can create an appropriate mechanical environment for bone repair. In our study, the objective was to investigate the responses of bone tissue to CPC in different series of elastic modulus combinations. Finite element analysis (FEA) was applied to calculate the stress/strain on CPC-bone specimens and to further forecast the potential risky area. The predicted results indicated that CPC materials and bone tissue had different stress distribution patterns under the same loading condition. For CPC material, the Von Mises Stress peak occurred in the bone–cement joint area; while for bone tissue, the risky area was located at the bridge area among trabecular bones. The porous and loose structure of cancellous bone induced a greater Von Mises Stress in bone tissue. Quantitative analysis indicated that stress/strain distribution was directly correlated with the elastic modulus of material. When Young's modulus of bone and CPC was 1 GPa and 6.10 GPa respectively, the optimal stress matching between bone and CPC was achieved. In sum, this work confirmed that FE modeling was the ideal method for predicting fracture behavior of bone–CPC specimen both qualitatively and quantitatively.     

Numerical simulation of cement-to-formation interface debonding during hydraulic fracturing of shale gas wells

Abstract

The hydraulic fracturing process involves high pump pressure and large displacement, which increase the risk of debonding on the interface of the cement sheath and rock formation. Therefore, in this study, a three-dimensional numerical calculation model of casing-cement sheath-formation assembly was established, and the failure mechanism of the bonding surface caused by fracturing due to fluid migration was investigated. The effects of the cement sheath’s Young’s modulus and Poisson’s ratio, bonding strength, perforation azimuth angle, and non-uniform in-situ stress on the anti-debonding ability of the cement-to-formation interface were analyzed. Finally, the following conclusions were drawn: The calculation results show that the failure of the bonding surface is greatly affected by the bonding strength, and its anti-debonding ability significantly increases linearly with increasing bonding strength. Furthermore, while increasing the Young’s modulus improves the anti-debonding ability, the Poisson’s ratio of the cement sheath and the perforation azimuth angle have little effect. Under non-uniform in-situ stress, the anti-debonding ability decreases with the increase of the difference between the horizontal and vertical in-situ stress. Thus, the non-uniform in-situ stress accelerates the failure of the bonding surface.     

Mechanical properties of urea–formaldehyde foam

The mechanical behavior of urea-formaldehyde foam was studied to evaluate its potential for energy absorption applications. The apparent elastic modulus (E_f) as a function of foam density was obtained from force-deformation tests. The values of energy absorption capacity were derived from a numerical integration technique. Poisson's ratio (v) was determined by a method of uniaxial compression of cylindrical samples. An increase in foam density results in an increase in the apparent elastic modulus of the material and therefore in its energy absorption capacity. Poisson's ratio is independent of the foam density. The mechanical properties' values obtained can be incorporated in various analyses for predicting desired characteristics for energy absorption applications.     

Elastic properties of adhesive polymers. I. Polymer films by means of electronic speckle pattern interferometry

The elastic modulus and Poisson's ratio of seven different polymers frequently used as wood adhesives and/or matrix polymers in wood‐ and natural‐fibre‐reinforced composites, respectively, were determined by means of tensile tests. Specimen deformation during testing was measured by means of a mechanical extensometer and an electronic speckle pattern interferometry system, respectively. The results from both methods show an excellent correlation for the elastic modulus. The elastic moduli of the studied polymers cover a wide range from 0.47 GPa for polyurethane to 6.3 GPa for melamine–urea–formaldehyde, whereas Poisson's ratios show less variability. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3936–3939, 2007