A Particle Resistance Model for Flow through Porous Media

A particle model for resistance of flow in isotropic porous media is developed based on the fractal geometry theory and on the drag force flowing around sphere. The proposed model is expressed as a function of porosity, fluid property, particle size, fluid velocity （or Reynolds number） and fractal characters D f of particles in porous media. The model predictions are in good agreement with the experimental data. The validity of the proposed model is thus verified.     

应用粒子图像测试技术测量球床多孔介质单相流动的流场

多孔介质在生产生活以及科技发展中的应用十分广泛, 随着能源、化工、冶金和原子能等领域技术的发展, 以及近代工农业生产技术的进步, 大量多孔介质的传热传质问题逐渐出现, 进一步促进了多孔介质学科的形成和发展, 使其成为当今科学技术中令人瞩目的研究热点之一. 通过实验获得准确的实验图像和数据, 并使用相应软件对实验所得数据和流体流动图像进行深度分析, 这样既有真实可靠的实际数据, 又有直观的理论的支持, 使对多孔介质的研究更为完善. 实验结合粒子图像测试技术和折射率匹配技术对叉排排列玻璃球多孔介质填充床内的流体流动转变过程进行流场测试, 并提取数据, 采用Tecplot软件对提取数据进行处理, 得出流体流动机理的转变过程. 实验固相为由直径25 mm水晶玻璃球叉排堆积而成的填充床, 液相为65%苯甲醇和35% 无水乙醇配制的匹配液. 液相与固相的折射率都为1.477, 成功消除由于折射率不匹配引起的激光光线偏折. 实验得到雷诺数为 4.7 ≤ Re ≤ 1000时球床内流场图, 对比不同雷诺数时流场和流线变化得出: 随着雷诺数的增加, 流线变得越来越紊乱; 当雷诺数在220以上时, 球床内漩涡在尺寸变化上出现突跃, 在位置和形态变化表现出随机特征, 预示进入了稳定的湍流.     

XFEM modeling of hydraulic fracture in porous rocks with natural fractures

Hydraulic fracture (HF) in porous rocks is a complex multi-physics coupling process which involves fluid flow, diffusion and solid deformation. In this paper, the extended finite element method (XFEM) coupling with Biot theory is developed to study the HF in permeable rocks with natural fractures (NFs). In the recent XFEM based computational HF models, the fluid flow in fractures and interstitials of the porous media are mostly solved separately, which brings difficulties in dealing with complex fracture morphology. In our new model the fluid flow is solved in a unified framework by considering the fractures as a kind of special porous media and introducing Poiseuille-type flow inside them instead of Darcy-type flow. The most advantage is that it is very convenient to deal with fluid flow inside the complex fracture network, which is important in shale gas extraction. The weak formulation for the new coupled model is derived based on virtual work principle, which includes the XFEM formulation for multiple fractures and fractures intersection in porous media and finite element formulation for the unified fluid flow. Then the plane strain Kristianovic-Geertsma-de Klerk (KGD) model and the fluid flow inside the fracture network are simulated to validate the accuracy and applicability of this method. The numerical results show that large injection rate, low rock permeability and isotropic in-situ stresses tend to lead to a more uniform and productive fracture network.     

A Micro-Mechanism Model for Porous Media

Based on the tortuous-expanding path/channel model, a micro-mechanism model for porous media is developed. The proposed model is expressed as a function of tortuosity, porosity, resistance coefficient, and fluid properties. Every parameter in the proposed model has clear physical meaning. The results show that the model predictions are in good agreement with those from the existing experimental data.     

A fractal streaming current model for charged microscale porous media

An analytical expression for the streaming current in fractal porous media is developed based on the capillary model and the fractal theory for porous media. The proposed fractal model is expressed as a function of the space charge density at the solid–liquid interface, the fluid flow rate, the Debye–Huckel parameter, the minimum and maximum pore/capillary radii and fractal dimensions for porous media. The results are compared with available experimental data and good agreement is found between them. In addition, factors influencing the streaming current in porous media are also analyzed.     

二维多孔热密封材料的有效导热系数模拟

本文对于二维多孔热密封材料的有效导热系数模拟提出一种简单有效的方法,它可以模拟介于固相连续和固相不连续之间的任何形式的孔隙分布结构,通过类比多孔渗流模型得出一种相关系数,再根据热阻串并联的关系计算四种可计算模型的有效导热系数,通过相关系数得到具体模型的有效导热系数。本文的模拟方法可以控制孔隙率、孔径、孔隙分布、温度等影响有效导热系数的重要参数,考虑了辐射的影响,而且模拟简单,计算快速,模拟结果与文献中实验的结果相比较能很好的吻合,验证了本文方法的正确性。     

气体动理学格式模拟多孔介质流动的可行性

将气体动理学格式（GKS）拓展到模拟多孔介质内的低速渗流,并检验在孔隙尺度上模拟不可压缩低速流动的可行性与有效性.结果表明：GKS具有二阶空间精度,能够较精确地计算多孔介质的渗透率;相比于单松弛格子玻尔兹曼方法,GKS能够精确实现壁面无滑移边界条件,从而正确反映渗透率与黏性无关的特性;对于Berea砂岩切片结构中的复杂流动,模拟结果与实验吻合较好,能较精确地计算渗透率.给出GKS模拟达西渗流的马赫数选取准则,为研究多孔介质流动提供新的工具.     

多孔介质两相流的局部守恒有限元分析

用局部守恒有限元法研究多孔介质两相渗流问题.详细阐述局部守恒有限元法的基本原理,推导两相渗流问题的局部守恒有限元计算格式并编制相应的计算程序.通过一维Buckley-Leverett两相渗流算例验证该方法的正确性.应用局部守恒有限元法和混合有限元法分别对2个模型进行分析对比.计算结果表明局部守恒有限元法具有良好的鲁棒性及适用性,相较于混合有限元法,处理过程简单,计算时间缩短,为标准有限元法应用于复杂渗流问题提供了一种途径.     

变形双重介质分形油藏非达西流动分析

考虑与实际生产相符的介质的双重特性和分形特征,并考虑介质的变形,引入双重分形介质渗透率模数,建立应力敏感地层双重分形介质系统的流动方程.采用Douglas-Jones预估-校正法获得无限大地层定产量生产时变形双重分形介质模型的数值解和无限大地层定压生产时分形介质双孔模型的数值解,作出了典型的压力曲线图版.     

A difference-fractal model for the permeability of fibrous porous media

In this Letter, a difference-fractal model for the permeability of viscous flow through fibrous porous media is proposed. Since fractal objects have well-defined geometric properties, and are discrete and discontinuous, we apply the difference approach to developing the fractal model. The model of non-dimensional permeability is expressed as a function of porosity and fractal dimension. To verify the validity of the proposed model, the predicted permeability values are compared with those of experimental measurements. A good agreement between the prediction of the fractal model and the existing experimental data from the literature is found.     

单一微孔隙中油水相对渗透率特性研究

孔隙渗流是多孔介质渗流的微观基础。本文对孔隙中的两相流应用分相模型,结合达西渗流定律,提出了适用于油水两相的相对渗透率模型,得到相对渗透率与孔隙度无关、相对渗透率只是微孔隙中相态分布的几何尺度以及流体饱和度的函数等结论。设计了微流动实验装置,以去离子水和白油的乳化液为两相流体,在不同含油率下研究了微孔隙中油水两相的渗流特性,并与相应条件下的模型计算结果进行对比。结果表明,对于低渗透尺度等级的微孔隙,实验与计算结果吻合较好,对于高渗透尺度等级的微孔隙,实验与计算结果存在偏差。在某些条件下,油与水的相对渗透率之和存在大于1的情形。     

Time-domain calculations of sound interactions with outdoor ground surfaces

A time-domain formulation for sound propagation in rigid-frame porous media, including waveform attenuation and dispersion, is developed. The new formulation is based on inversion of the relaxation functions from a previous model [Wilson DK, Ostashev VE, Collier SL. J Acoust Soc Am 2004;116:1889-92], thereby casting the convolution integrals in a form amenable to numerical implementation. Numerical techniques are developed that accurately implement the relaxational equations and transparently reduce to previous results in low- and high-frequency limits. The techniques are demonstrated on calculations of outdoor sound propagation involving hills, barriers, and ground surfaces with various material properties. We also compare the relaxation formulation to a widely applied phenomenological model developed by Zwikker and Kosten. The two models can be made equivalent if the resistance constant, structure constant, and compression modulus in the ZK model are allowed to be weakly frequency dependent. But if the ZK parameters are taken to be constant, as is typically the case, the relaxation model provides more accurate calculations of attenuation by acoustically soft porous materials such as snow, gravel, and forest litter.     

超声波对多孔介质中两相流动的影响

近年来，超声技术已被应用于采油工程中，在油井解堵，水井增注等方面发挥了重要的作用。     

考虑弥散效应的多孔介质中超绝热燃烧的数值模拟

研究多孔介质内往复流动下的超绝热燃烧。一维模型包括气体输运、多孔介质固体的辐射、导热和气固两相间的对流换热。通过数值计算研究超绝热燃烧的形成、以及弥散效应、当量比和多孔介质材料本身对超绝热燃烧特性的影响。计算结果的有效性通过实验进行了验证并取得了相同的趋势。结果表明,组分弥散效应对气体温度分布和反应热影响很小;同一工况下,不考虑气体混合物的热弥散效应,会导致过高的气体温度计算值。同时,计算结果表明小孔径的多孔介质更有利于贫可燃极限的扩展,对30 ppi的多孔介质燃烧器,得到了当量比为0．092的可燃极限。     

用格子玻尔兹曼方法研究流动-反应耦合的非线性渗流问题

根据格子玻尔兹曼计算技术以及相应渗流理论，对多孔介质内流动-反应(矿物介质的溶解等)耦合这一非线性渗流问题进行了数值研究，计算结果与解析解基本符合.数字图像重构技术反映的结果表明流体流动和反应之间可以发生强烈的耦合和反耦合作用，同时可以形成条带结构这一自组织现象，与实验和其他理论分析结果符合也很好. 关键词： 非线性渗流 耦合反应 数值模型     

裂缝性介质多尺度深度学习模型

结合人工神经网络建立裂缝介质多尺度深度学习流动模型.基于一套粗网格和一套细网格,通过在粗网格上训练数据,多尺度神经网络能够以较少的自由度训练出准确的神经网络.并在粗网格上通过求解局部流动问题获得多尺度基函数,结合神经网络进一步得到精细网格的解.基于离散裂缝的流动方程可视为多层网络,网络层数依赖于求解时间步数.阐述裂缝介质多尺度机器学习数值计算格式的建立,介绍如何使用多尺度算法构建离散裂缝模型的多尺度基函数,并采用超样本技术进一步提高计算准确性.数值结果表明,多尺度有限元算法与机器学习结合是一种有效的流体流动模拟算法.     

Validity of the permeability Carman-Kozeny equation: A volume averaging approach

A volume averaging approach is used to estimate the porous media permeability. Contrary to traditional methods that rely on solving the Navier-Stokes equations for laminar flow, this approach has the advantage that it does not require the specification of some physical conditions and parameters (pressure drop and viscosity). Numerical results on synthetic models of porous media showed that (i) the local porous medium configuration has an important effect on the permeability value, and (ii) the Carman-Kozeny equation cannot describe the permeability behavior as a function of porosity and characteristic lengths. In turn, our results indicate that simple empirical equations, commonly used in practice, are unable to describe the permeability functionalities over a broad range of porous media configurations.     

Modelling of chemical vapour deposition for optical fibre manufacture

A study of numerical modelling has been carried out for chemical vapour deposition processes with applications to manufacture of optical fibres. Temperature distributions and thermophoretic particle deposition have been calculated for the modified chemical vapour deposition (MCVD) and the outside vapour deposition (OVD) processes. A two torch formulation and a heat flux boundary condition are used for MCVD and the present model is shown to be capable of predicting tube wall temperatures and deposition profiles correctly. The present results are in agreement with experimental data. For OVD modelling, nonorthogonal body-fitted coordinates have been utilized to solve a conjugate problem including the jet flow and heat conduction through a two-layered cylinder that consists of an original target and the deposited porous layers. Surface temperatures and efficiencies of particle deposition have been obtained.     

Modelling two-phase flow in porous media at the pore scale using the volume-of-fluid method

We present a stable numerical scheme for modelling multiphase flow in porous media, where the characteristic size of the flow domain is of the order of microns to millimetres. The numerical method is developed for efficient modelling of multiphase flow in porous media with complex interface motion and irregular solid boundaries. The Navier–Stokes equations are discretised using a finite volume approach, while the volume-of-fluid method is used to capture the location of interfaces. Capillary forces are computed using a semi-sharp surface force model, in which the transition area for capillary pressure is effectively limited to one grid block. This new formulation along with two new filtering methods, developed for correcting capillary forces, permits simulations at very low capillary numbers and avoids non-physical velocities. Capillary forces are implemented using a semi-implicit formulation, which allows larger time step sizes at low capillary numbers. We verify the accuracy and stability of the numerical method on several test cases, which indicate the potential of the method to predict multiphase flow processes.     

致密油藏液测应力敏感性计算模型

综合成藏地质学、岩石力学和渗流力学,建立准确可靠的致密油藏考虑边界层、临界喉道和孔喉分布的液测应力敏感性计算模型.由于大庆油田致密油藏孔喉分布范围比长庆油田更窄,导致大庆油田应力敏感性更强,因此大庆油田产能更低.本文从微观角度定量表征了真实油藏中应力敏感性的作用机理.