Direct measurement of porous media local hydrodynamical permeability using gas MRI.

The concept of hydraulic permeability is at the core of modeling single phase or multi-phase flow in heterogeneous porous media, as it is the spatial distribution of the permeability that primarily governs the behavior of fluid flow in the medium. To date, the modeling of fluid flow in porous media has been hampered by poor estimates of local permeability. Magnetic Resonance Imaging is well known for its ability to measure non-invasively the local density and flow rate of different fluids saturating porous media [1,2]. In this paper we demonstrate the first non-invasive method for the direct measurement of a single projection of the local permeability tensor of a porous medium using gas-phase MRI. The potential for three-dimensional imaging of the medium permeability is also discussed. The limitations of the method are listed and results are presented in a model porous medium as well as in a real oil reservoir rock.     

Xenon NMR measurements of permeability and tortuosity in reservoir rocks

In this work we present measurements of permeability, effective porosity and tortuosity on a variety of rock samples using NMR/MRI of thermal and laser-polarized gas. Permeability and effective porosity are measured simultaneously using MRI to monitor the inflow of laser-polarized xenon into the rock core. Tortuosity is determined from measurements of the time-dependent diffusion coefficient using thermal xenon in sealed samples. The initial results from a limited number of rocks indicate inverse correlations between tortuosity and both effective porosity and permeability. Further studies to widen the number of types of rocks studied may eventually aid in explaining the poorly understood connection between permeability and tortuosity of rock cores.     

Comparison of measurements of phase velocity in human calcaneus to Biot theory

Biot's theory for elastic propagation in porous media has previously been shown to be useful for modeling the dependence of phase velocity on porosity in bovine cancellous bone in vitro. In the present study, Biot's theory is applied to measurements of porosity-dependent phase velocity in 53 human calcanea in vitro. Porosity was measured using microcomputed tomography for some samples (n = 23) and estimated based on bone mineral densitometry for the remaining samples (n = 30). The phase velocity at 500 kHz was measured in a water tank using a through-transmission technique. Biot's theory performed well for the prediction of the dependence of sound speed on porosity. The trend was quasilinear, but both the theory and experiment show similar slight curvature. The root mean square error (RMSE) of predicted versus measured sound speed was 15.8 m/s.     

Light propagation in porous ceramics: porosity and optical property studies using tunable diode laser spectroscopy

By integrating gas in scattering media absorption spectroscopy and frequency domain photon migration a new method is developed for the study of optical porosity and optical properties of porous media, in our case ceramics. The optical porosity is defined as the ratio of the path length through the gas-filled pores and the physical path length through the whole medium. The effective refractive index of the porous ceramics is also retrieved based on the optical porosity, which is then used to evaluate the reduced scattering coefficients of the porous ceramics. The combined method provides a new way to study light propagation in porous media. A modified Looyenga model is proposed to study the relationship between the physical porosity and the effective refractive index of the porous medium, which also connects the optical and physical porosities, and provides the possibility to use the present method for porosimetry analysis.     

多孔材料内部结构的微CT扫描仪分析

本文介绍使用微CT扫描仪对样品进行扫描和图像重构的原理,以蛋糕为样品使用CT对多孔材料的内部结构进行研究,包括样品的孔隙率及其变化,水在大孔内的分布,空腔的三维重构图像和样品内部其它微细特征。结果表明, 浸水的样品在干燥后,骨架收缩,部分孔的尺寸明显增大,孔隙率增加,而没有浸水的蛋糕在干燥前后结构变化不大。文章表明,对于孔径大于几十微米的多孔性材料,使用文中的微CT扫描仪可以有效地对它们进行内部结构的研究。     

使用条件生成对抗网络生成预定导热率多孔介质

多孔介质在工程领域中的应用非常广泛,其中有效导热率和孔隙率为多孔介质材料非常重要的性质,得到一个符合需要的有效导热率和孔隙率的多孔介质材料具有重要意义.本文使用四参数随机生成方法制作了训练数据集,搭建了一个条件生成对抗网络(CGAN),使用预定的有效导热率和孔隙率作为输入,生成一个满足输入条件的多孔介质结构.特别地,由于多孔介质的孔隙结构分布对材料的有效导热率影响巨大,提出局部结构损失函数参与网络训练,使得网络更好地学习到孔隙分布与导热率之前的关系.通过使用格子Boltzmann方法验证神经网络生成的多孔介质结构的有效导热率,结果表明该方法能够快速且准确地生成预定参数的多孔介质结构.     

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.     

被孔隙介质约束的弹性杆中的导波*

为了研究导波在被孔隙介质约束的弹性杆结构中的传播规律,分析孔隙参数对导波传播特性的影响,本文建立了无限大孔隙介质包裹圆柱体的理论模型,利用孔隙介质弹性波动理论,分析了导波的频散曲线,以及圆柱半径和孔隙参数对于导波传播特性的影响。结果表明,在该结构中传播的纵向导波存在频散特性。内部圆柱半径的改变影响波导结构,从而影响导波传播。外部孔隙介质的渗透率对于导波频散的影响较小,孔隙度的改变影响孔隙介质体波波速,从而影响导波频散曲线的截止频率。同时,导波存在较小的衰减,且衰减随孔隙度增大而增大。这些结果对于后续开展无限大介质包裹弹性杆结构的超声无损评价提供了一定的理论参考。     

Tortuosity for streamlines in porous media

An analysis of tortuosity for streamlines in porous media is presented by coupling the circle and square models. It is assumed that some particles in porous media do not overlap and that fluid in porous media is incompressible. The relationship between tortuosity and porosity is attained with different configurations by using a statistical method. In addition, the tortuosity fractal dimension is expressed as a function of porosity. Those correlations do not include any empirical constant. The percolation threshold and tortuosity fractal dimension threshold of porous media are also presented as: c = 0.32, D T c = 1.07. The predicted correlations of the tortuosity and the porosity agree well with the existing experimental and simulated results.     

Porosity measurements in natural porous rocks using magnetic resonance imaging

A magnetic resonance imaging (MRI) method is presented to measure localized porosity values inside natural porous rocks for the purpose of obtaining frequency distributions of the porosity (porosity distributions). The method is applied to study six different cores, including three Berea sandstone samples, Casper sandstone, Indiana limestone, and San Andres dolomite. An image of the porosity is shown for a transverse and a longitudinal slice in order to show qualitative variations of the porosity within each core sample. The porosity distribution for the entire core has been acquired, and it is shown with a Gaussian fit to the data. In addition, for cores known to have a layered structure, a bimodal distribution is fit to the data, and the fit is used to estimate the value of the porosity for two characteristic types of layers within the core sample.     

沉降分布孔隙率多孔介质模型及数值研究

研究沉降分布孔隙率多孔介质流动和传热,根据"O"形圈理论和现场测定确定孔隙率系数,建立坐标方向孔隙率分布函数;考虑流体密度变化,并引入Brinkman-Forchheimer的扩展Darcy模型,能量方程采用界面连续条件,建立沉降分布孔隙率多孔介质流动和传热求解模型.采用差分法对模型进行离散化,应用高斯-赛德尔方法迭代求解.数值分析表明:沉降分布孔隙率条件下多孔介质内流体流动速度在壁面附近较大,中心部位较小,壁面附近孔隙率的增大使得低流速区域减小,较高流速区域增大;当孔隙率小值时,温度按线性减小;当孔隙率大值时,温度在高低温壁面附近迅速减小,在中部减小较缓,热量按导热和对流共同传递;孔隙率增大能使平均怒谢尔数增大,对流换热作用增强.     

多孔介质热导率的数值计算

通过数值模拟得出面积分形维数和孔隙率相同,而孔隙结构不同的分形多孔介质的导热特性是不相同的.说明仅仅依靠孔隙率和分形维数两个参数无法有效确定多孔介质的热物理性质,寻找新的表征孔隙结构的参数是必要的.同时也说明了前人所得出的关于多孔介质的热物性的解析表达式具有一定的局限性和不确定性.     

多孔岩芯渗透率与孔隙度的MRI研究

运用自旋回波序列,得到一系列用盐水饱和的多孔岩芯的磁共振自旋密度象,可以直观、准确地观察岩芯的结构,并对象的信号强度与渗透率和孔隙度之间的相关关系进行了分析,发现它们之间存在良好的定性关系,得到了较好的结果.     

Paramagnetic relaxation in sandstones: distinguishing T1 and T2 dependence on surface relaxation, internal gradients and dependence on echo spacing

This work provides a generalized theory of proton relaxation in inhomogeneous magnetic fields. Three asymptotic regimes of relaxation are identified depending on the shortest characteristic time scale. Numerical simulations illustrate that the relaxation characteristics in the regimes such as the T(1)/T(2) ratio and echo spacing dependence are determined by the time scales. The theoretical interpretation is validated for fluid relaxation in porous media in which field inhomogeneity is induced due to susceptibility contrast of fluids and paramagnetic sites on pore surfaces. From a set of measurements on model porous media, we conclude that when the sites are small enough, no dependence on echo spacing is observed with conventional low-field NMR spectrometers. Echo spacing dependence is observed when the paramagnetic materials become large enough or form a 'shell' around each grain such that the length scale of the region of induced magnetic gradients is large compared to the diffusion length during the time of the echo spacing. The theory can aid in interpretation of diffusion measurements in porous media as well as imaging experiments in presence of contrast agents used in MRI.     

Quantitative discrimination of water and hydrocarbons in porous media by magnetization prepared centric-scan SPRITE

MRI has considerable potential as a non-destructive probe of porous media, offering the possibility of rapid quantification of local oil and water content. This potential has not yet, however, been completely realized. In this paper, we explore a general magnetization preparation approach to the discrimination of water and oil in a model, representative, porous medium. These measurements have, as a common element, a centric scan pure phase encode readout based on the SPRITE methodology. Magnetization preparation permits facile T1, T2 and diffusion coefficient mapping as the basis for oil and water discrimination. Diffusion coefficient mapping proved to be the most robust approach to discrimination of oil and water. These methods are illustrated through static experiments and a dynamic immiscible fluid displacement experiment.     

孔隙度数值反演计算

由渗流微分方程定解问题和Peaceman方程给出了网格压力、井底压力对网格孔隙度的导数,利用三维渗流方程压强数值解计算井底压力对网格孔隙度的导数;采用共轭梯度法实现孔隙度均匀(或分块均匀)分布油藏模型的反演计算.算例表明,经过8~10次迭代后反演结果与真值的最大相对误差在0.03%以内,反演收敛于真值.     

孔隙介质包裹的充液管道结构中导波传播特性

研究孔隙介质包裹的充液管道中纵向导波传播特性,分析孔隙介质参数对频散曲线的影响。建立了孔隙介质包裹充液管道的结构模型,利用孔隙介质弹性波动理论,建立对应的频散方程,数值模拟计算得到该模型的频散曲线和时域波形,并分析了孔隙介质参数以及管壁厚度对频散曲线的影响。结果表明孔隙介质的渗透率对于导波频散的影响较小,孔隙度的改变对时域波形的位移幅度影响较大。同时,导波存在衰减,且衰减随孔隙度增大而增大。所得结论为埋地管道无损检测方面提供一定理论参考。      

随机四参数法生成多孔介质及渗流模拟

本文基于多孔介质内流动的广泛应用背景,模拟了多孔介质渗流.采用随机四参数生长法生成了多孔介质模型,并对模型中的微小固相进行了过滤处理,将随机四参数生长法生成的多孔介质结合格子玻尔兹曼方法D2Q9模型模拟了压力驱动的多孔介质中的渗流.通过将模拟结果与著名的CK理论公式的计算结果进行比较,发现在孔隙率高时误差较小(cp=0...