离散元数值法在煤层井壁稳定中的应用

本文针对煤层气水平井井壁稳定问题,采用UDEC离散元法,建立了严重节理化的煤层井眼模型,对沁水盆地3号煤层水平井围岩失稳坍塌的过程进行了模拟,发现钻井液密度、井眼尺寸、节理密度对井壁稳定性有一定的影响。研究结果表明离散元数值法的有效性,并为研究裂隙煤岩井壁稳定问题提供了潜在的研究方向,提出相应的稳定井壁的对策。     

椭圆井眼井壁稳定性研究

钻头破碎岩石形成井眼后,钻井液代替了破碎后的岩石对井壁起到了支撑作用,在一定程度上维持着井壁的稳定。长期以来针对井壁稳定性的研究都是基于理想的圆形井眼,而对非圆形井眼井壁稳定性的研究很少;然而,在实际情况中井壁受钻柱的碰磨、井内介质的冲刷、地层应力以及岩石本身的力学性质等因素的影响而表现为非圆形的井眼,因此有必要分析非圆形井眼井壁稳定性情况。通过建立数值仿真模型分析了井壁在最大主应力方向和最小主应力方向受损后的井眼应力情况,结果表明:基于圆形井眼计算出的泥浆密度窗口要大于基于受损井眼所得出的密度窗口,所以,如果基于圆形井眼的计算结果去调节泥浆密度是不理想的,应该根据实际井眼的计算结果来做相应的调节。     

椭圆井眼围岩弹塑性应力和变形研究

针对由井眼崩落造成的椭圆形井眼的井壁稳定问题,基于岩石力学、弹塑性力学等相关理论,通过建立不同椭圆度井眼的有限元计算模型,采用Mohr-coulomb塑性准则作为其本构模型,在利用圆形井眼稳定性理论对有限元计算模型验证的基础上,获得了不同椭圆度井眼的围岩应力和应变,从而得出了椭圆度与井壁应力与应变的关系。结果表明,随着椭圆度的增大,塑性区变大,即高应力区向远处岩层深入,且椭圆形井眼在最小地应力方向应力更加集中。     

伊朗雅达油田S1水平井钻井液技术

伊朗雅达油田地层岩性复杂,泥页岩易发生水敏性垮塌;部分地层含盐膏易导致钻井液流变性变差;下部碳酸盐地层裂缝发育易发生井漏;水平井施工过程中井壁稳定、井眼净化及润滑防卡难度大。通过使用KCl-聚合物钻井液体系,顺利完钻,施工中井壁稳定,井眼净化效果好,满足了水平井钻井施工的要求。     

页岩油水平井钻井液密度计算

泌页2HF井是河南油田一口非常规页岩油水平井,斜井段、长水平段泥页岩发育,易垮塌,井壁不稳定,钻井液密度的准确预测,对于平衡地层坍塌压力、稳定井眼和安全钻井至关重要。通过建立地层坍塌压力计算模型,利用测井资料计算岩石力学参数及地层坍塌压力,为制定合理的钻井液密度提供依据。现场结果表明,该理论和方法对于泌页2HF井钻井设计和施工具有指导意义。     

气体钻井地层流体冻结技术研究

气体钻井中往往遇到地层出水的复杂情况,当地层出水量达到5m3/h以上时,地层出水后水与岩屑粘结在一起,在钻杆上形成泥包,容易引起井眼缩小、循环阻力增大,严重时发生卡钻、井壁失稳等复杂情况,导致无法继续实施气体钻井的施工,必须转化为常规钻井方式或泡沫钻井方式。目前气体钻井期间所应用的地层出水封堵技术主要分为物理封堵和化学堵水,然而其封堵效果均比较有限,文章通过理论研究并运用有限元模型进行地层流体冻结技术研究,以便能从根本上解决气体钻井出水后引起的井壁稳定及防卡问题。     

井壁附近瞬态温度的数值计算方法

在石油钻井开采等过程中研究热量在地层中的传播具有很重要的意义。特别是在进行井漏机理研究中,利用它可以分析温度对井眼破裂压力、裂缝重启压力以及裂缝延伸压力的影响。本文使用有限差分法近似地求得近井壁地层的温度分布。利用此方法,可以求得任意时刻井壁温度随井深的分布,任意时刻、任意井深处井壁温度的径向分布,任意点温度随时间的变化,从而进一步了解温度在石油工程上的影响。     

雷家地区全油基钻井液技术

在裂缝性页岩钻井过程中,如果出现井壁失稳现象,单纯提高钻井液密度重新使井眼达到稳定状态,会造成如压差卡钻、降低钻进速度等一系列工程问题,更严重的是如已揭开油气层,会对油气层造成严重的伤害。针对辽河油田雷家地区井壁失稳现象突出的问题,利用自主研发的处理剂形成了一套全油基钻井液体系,通过页岩膨胀率、滚动回收率、砂床实验以及三轴压缩实验等方法对全油基钻井液的抑制性、封堵性及保持页岩强度能力进行了评价。结果表明:自主研发的全油基钻井液体系能够有效抑制页岩水化膨胀,封堵地层微裂缝,对页岩强度有很好的保持能力。在高28井施工过程中,全油基钻井液性能稳定,井壁稳定,符合现场施工要求。     

页岩井壁失稳机理分析及钻井液对策研究

页岩气开发主要以大位移井、水平井为主,由于页岩地层裂缝与层理发育、水敏性强,在长水平段钻井过程中极易发生页岩脱落掉块、垮塌和缩径等井壁失稳问题,同时还存在携岩困难、摩阻大及井眼轨迹难以控制等一系列难题。在对页岩岩性评价和页岩井壁失稳机理分析的基础上,探索出了适合于页岩气开发,保持井眼稳定的页岩气钻井技术,该技术一方面主要是对页岩表面微裂缝进行有效的封堵,另一方面主要是对页岩表面易分散和膨胀性黏土矿物进行有效抑制。     

裂缝孔隙度评价模型分析

裂缝孔隙度是裂缝有效性评价的重要指标之一,其能否准确计算直接关系到裂缝有效性的评价质量,而裂缝孔隙度评价模型的选择是计算的关键。在前人的大量研究基础上,总结出三种裂缝孔隙度评价模型:常规电阻率模型;重构声波时差曲线模型;光电吸收模型。本人综合评价认为:井壁光滑的情况下可使用特征曲线重构模型和光电吸收截面模型,但电流电阻率模型效果最好。     

Drucker-Prager-Cap modelling of boron carbide powder for coupled electrical-thermal-mechanical finite element simulation of spark plasma sintering

The coupled electrical-thermal-mechanical finite element method in the continuum scale has been widely used to investigate the spark plasma sintering process. An accurate constitutive model of powder material is pivotal for precise continuum finite element simulation. In this study, the Drucker-Prager-Cap model, which is highly accurate in describing the densification behaviour of powder material, was adopted to numerically analyse the spark plasma sintering process of boron carbide powder. First, the parameters of the model were defined to be dependent on temperature and density for higher accuracy; they were determined by minimising the discrepancy between the simulated and experimental results. Based on a spark plasma sintering experiment with a cylindrical sample, the parameters of the Drucker-Prager-Cap model were identified at 1500 °C, 1600 °C, 1700 °C, 1800 °C, and 1900 °C. A coupled electrical-thermal-mechanical finite element simulation with the model was performed for spark plasma sintering of boron carbide powder at 1750 °C and 1850 °C. The temperature, stress, and relative density were investigated numerically. By comparing the model results with the temperature and relative density measured in the experiment, the continuum finite element method with the Drucker-Prager-Cap model was validated.     

Modeling granular material blending in a rotating drum using a finite element method and advection‐diffusion equation multiscale model

A multiscale model is presented for predicting the magnitude and rate of powder blending in a rotating drum blender. The model combines particle diffusion coefficient correlations from the literature with advective flow field information from blender finite element method simulations. The multiscale model predictions for overall mixing and local concentration variance closely match results from discrete element method (DEM) simulations for a rotating drum, but take only hours to compute as opposed to taking days of computation time for the DEM simulations. Parametric studies were performed using the multiscale model to investigate the influence of various parameters on mixing behavior. The multiscale model is expected to be more amenable to predicting mixing in complex geometries and scale more efficiently to industrial‐scale blenders than DEM simulations or analytical solutions. © 2018 American Institute of Chemical Engineers AIChE J, 64: 3277–3292, 2018     

边坡稳定性分析的Fuzzy数学模型

用模糊数学（ＦｕｚｚｙＭａｔｈｍａｔｉｃｓ）理论分析裂隙岩质边坡稳定性问题，根据模糊测度原理，针对实际边坡工作问题，建立了具有实际工程意义的模糊测度模型，并给出了具体的数值方法，使该模型可以更方便地用于分析矿山边坡稳定问题。     

Study of cold powder compaction by using the discrete element method

The discrete element method (DEM), based on a soft-sphere approach, is commonly used to simulate powder compaction. With these simulations a new macroscopic constitutive relation can be formulated. It is able to de-scribe accurately the constitutive material of powders during the cold compaction process. However, the force-law used in the classical DEM formulation does not reproduce correctly the stress evolution during the high density compaction of powder. To overcome this limitation at a relative density of about 0.85, the high density model is used. This contact model can reproduce incompressibility effects in granular media by implementing the local solid fraction into the DEM software, using Voronoi cells. The first DEM simulations using the open-source YADE software show a fairly good agreement with the multi-particle finite element simulations and experimental results.     

基于有限元的聚酰亚胺多孔板振动应力仿真研究

针对卫星运输和发射过程中容易因振动而导致伸杆末端感应式磁力仪三轴传感器安装接口板应力集中的现象,采用ANSYS Workbench有限元,研究聚酰亚胺接口板正弦振动应力与安装孔的数目、孔的直径和安装圆半径之间的变化关系。采用回归分析方法建立应力优化模型,最后得到接口板安装孔的最优参数。研究工作为聚酰亚胺在强振环境下的航天工程应用提供了设计依据。     

内压作用下钢骨架增强塑料管静力分析

采用截面折算方法,推导了复合管应力解析计算公式;建立了分离式三维有限元分析模型,对钢骨架增强塑料复合管的应力、变形分布进行了数值模拟分析,得到复合管网状应力分布规律。通过静液压爆破实验证实了所提出的理论计算公式和有限元数值模拟结果的可靠性,可用于管道在应力和承载力等方面的工程设计。     

脉冲鼓泡流化床压力波动特性的模拟

在分析脉冲气流作用下均匀鼓泡流化床的波动结构和波动机理的基础上,建立了反映其压力波动特性的二维离散单元模型。根据脉冲鼓泡流化床的特点,提出了模型离散单元的划分方法,确定了系统的模型参数。采用直接数值积分的方法,对床层的压力波动进行了模拟研究,计算与实验结果基本上一致。     

Investigation of combination of finite element formulation and element type on the accuracy of 3D modeling of polymeric fluid flow in an extrusion die

The aim of this work is to investigate the effect of finite element formulation and element type on the accuracy of 3D modeling of generalized Newtonian fluid flow in complex domains. Computer models based on three finite element solution schemes (mixed, continuous, and discrete penalty), and two element types (hexahedral and tetrahedral) in a 3D framework were developed. The well‐known Carreau model was used to reflect the rheological behavior of the fluid. To determine the validity of the developed computer simulations, the flow of two high‐density polyethylene (HDPE) melts with different viscosities through an extrusion die was simulated and compared with experimentally measured data. Comparison showed that the three methods produced nearly the same results with the hexahedral elements. However, continuous penalty method using tetrahedral elements demonstrated an extreme discrepancy from the experimental data. Discrete penalty method was unable to predict secondary variable (pressure) accurately using tetrahedral elements. The best results were obtained by the use of mixed method in conjunction with tetrahedral elements. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Development of a discrete element model with moving realistic geometry to simulate particle motion in a Mi-Pro granulator

This paper presents the implementation of a methodology incorporating a 3D CAD geometry into a 3D discrete element method (DEM) code; discussing some of the issues which were experienced. The 3D CAD model was discretised into a finite element mesh and the finite wall method was employed for contact detection between the elements and the spherical particles. The geometry was based on a lab scale Mi-Pro granulator. Simulations were performed to represent dry particle motion in this piece of equipment. The model was validated by high speed photography of the particle motion at the surface of the Mi-Pro's clear bowl walls. The results indicated that the particle motion was dominated by the high speed impeller and that a roping regime exists. The results from this work give a greater insight into the particle motion and can be used to understand the complex interactions which occur within this equipment.     

受压容器开口补强的优化设计

将有限元应力分析方法与设计方法相结合 ,提出了基于受压容器口补强的极限分析理论和优化设计思想 ,采用有限元前处理程序 ,自动生成常见球罐和柱罐的优化力学模型 ,并在屏幕上或用汇图仪绘制出罐体的三维图形。建立起受压容器开口补强优化设计的教学模型。根据此问题的特殊性 ,采用改进后的 0 .6 1 8法进行优化计算 ,优化过程中将模型划分成可变域和不可变域两部分 ,利用计算机的顺序文件存贮不变域单元刚度阵 ,提高了有限元重分析的计算效率