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1.
Understanding the role of shuttle vibrations in pore fluid distribution is an essential task in the exploration of plant growth
in root modules aboard space flights. Results from experimental investigations are reported in this paper on the distribution
of immiscible fluid phases in glass beads under vibrations. Hexadecane, a petroleum compound immiscible with and lighter than
water, was used in the experiments. The higher freezing point of Hexadecane (18 °C) allowed the solidification of the entrapped
blobs in the presence of water in porous media, so that their size distribution can be obtained. van Genuchten function, commonly
used to express moisture retention curves, is found to be an adequate fit for blob size distribution at residual saturation.
The effect of vibrations on the fate (mobilization, stranding, or breakup) of a solitary ganglion in porous media was studied
using a network model. A mobility criterion considering viscous, gravity, and capillary forces was developed to determine
the fate of a solitary ganglion in a porous medium. It is concluded that the effect of vibrations is to increase the likelihood
of breakup and mobilization of blobs entrapped in porous media at residual saturation. The pore fluid distributions after
vibrations are less uniform than those before vibrations. 相似文献
2.
In this article, we derive a simple expression for the tortuosity of porous media as a function of porosity and of a single
parameter characterizing the shape of the porous medium components. Following its value, a very large range of porous materials
is described, from non-tortuous to high tortuosity ones with percolation limits. The proposed relation is compared with a
widely used expression derived from percolation theory, and its predictive power is demonstrated through comparison with numerical
simulations of diffusion phenomena. Application to the tortuosity of hydrated polymeric membranes is shown. 相似文献
3.
Transport in Porous Media - Permeability of fractured media plays an important role in many hydrogeologic applications. In this study, we propose an approach to quantify the equivalent permeability... 相似文献
4.
The tortuosity ( τ), defined in the present context as the ratio of the free diffusion coefficient to the restricted diffusion coefficient of a contained fluid, is an important but difficult to measure characteristic of a porous medium, particularly when it is partially saturated with water. We develop and apply methodology, based on nuclear magnetic resonance (NMR) pulsed field gradient techniques, to measure τ for various sandstone rock cores as a function of residual water fraction. The NMR methodology requires the use of bipolar pulsed field gradient stimulated echo pulse sequences to avoid systematic errors due to magnetic susceptibility differences and D 2O as a stationary immiscible water phase; this was selected as it provides no 1H NMR signal. Tortuosity of the free pore space was successfully measured using liquid ethane as a probe fluid for three different sandstones over the full accessible range of residual water saturation. Generally, the tortuosity was observed to increase with residual water (D 2O) content; however, significant variations were observed between the different sandstones. 相似文献
6.
The dispersion process in particulate porous media at low saturation levels takes place over the surface elements of constituent particles and, as we have found previously by comparison with experiments, can be accurately described by superfast nonlinear diffusion partial differential equations. To enhance the predictive power of the mathematical model in practical applications, one requires the knowledge of the effective surface permeability of the particle-in-contact ensemble, which can be directly related with the macroscopic permeability of the particulate media. We have shown previously that permeability of a single particulate element can be accurately determined through the solution of the Laplace–Beltrami Dirichlet boundary value problem. Here, we demonstrate how that methodology can be applied to study permeability of a randomly packed ensemble of interconnected particles. Using surface finite element techniques, we examine numerical solutions to the Laplace–Beltrami problem set in the multiply-connected domains of interconnected particles. We are able to directly estimate tortuosity effects of the surface flows in the particle ensemble setting. 相似文献
8.
In the past decades, there was considerable controversy over the Lucas–Washburn (LW) equation widely applied in capillary
imbibition kinetics. Many experimental results showed that the time exponent of the LW equation is less than 0.5. Based on
the tortuous capillary model and fractal geometry, the effect of tortuosity on the capillary imbibition in wetting porous
media is discussed in this article. The average height growth of wetting liquid in porous media driven by capillary force
following the [`( L)] s( t) ~ t1/2DT{\overline L _{\rm {s}}(t)\sim t^{1/{2D_{\rm {T}}}}} law is obtained (here D
T is the fractal dimension for tortuosity, which represents the heterogeneity of flow in porous media). The LW law turns out
to be the special case when the straight capillary tube ( D
T = 1) is assumed. The predictions by the present model for the time exponent for capillary imbibition in porous media are
compared with available experimental data, and the present model can reproduce approximately the global trend of variation
of the time exponent with porosity changing. 相似文献
9.
Nuclear Magnetic Resonance (NMR) is an increasingly popular well-logging tool in petroleum industry because it is the only tool that attempts to estimate formation permeability. In this paper, spatially correlated porous media are generated. Permeabilities of these media are computed by the lattice Boltzmann method. NMR relaxation responses are simulated by a random walk technique and formation factors are computed by solving a Laplacian equation. The testing of commonly used NMR permeability correlations shows that three conditions should be met for the validity of these correlations. The surface relaxivity should not vary significantly. The formation factor should depend only on porosity. And the characteristic pore body radius should be proportional to the characteristic throat radius. The correlations are improved by including surface relaxivity and formation factor. 相似文献
10.
In this article, we propose an approach to obtain the equivalent permeability of the fluid-filled inclusions embedded into
a porous host in which a fluid flow obeys Darcy’s law. The approach consists in the comparison of the solutions for one-particle
problem describing the flow inside the inclusion, firstly, by the Stokes equations and then by using Darcy’s law. The results
obtained for spheres (3D) and circles (2D) demonstrate that the inclusion equivalent permeability is a function of its radius
and, additionally, depends on the host permeability. Based on this definition of inclusion permeability and using effective
medium method, we have calculated the effective permeability of the double-porosity medium composed of the permeable matrix
(with small scale pores) and large scale secondary spherical pores. 相似文献
11.
The presence of interfaces in fluid/solid biphasic media is known to strongly influence their behavior both in terms of solid deformation and fluids flow. Mathematical models have traditionally represented these interfaces as lines of no-thickness and whose behavior is given in terms of effective permeabilities whose physical meaning is often disconnected to the microscopic nature of the interface. This article aims to reconcile macroscopic and microscopic interface representations by investigating how the nature of microscopic flows and pressures in the interface can be used to explain its macroscopic behavior. By invoking a proper thickness average operation, we derive an closed form expression that relates the effective interfaces permeabilities to its microscopic properties. In particular, we find that the effective interface permeabilities are strongly influenced by three factors: the ratio of bulk and interface permeabilities, the fluid viscosity, and the physical thickness of the interface. 相似文献
12.
Transport in Porous Media - Permeability and formation factor are important properties of a porous medium that only depend on pore space geometry, and it has been proposed that these transport... 相似文献
14.
Pore network analysis is used to investigate the effects of microscopic parameters of the pore structure such as pore geometry, pore-size distribution, pore space topology and fractal roughness porosity on resistivity index curves of strongly water-wet porous media. The pore structure is represented by a three-dimensional network of lamellar capillary tubes with fractal roughness features along their pore-walls. Oil-water drainage (conventional porous plate method) is simulated with a bond percolation-and-fractal roughness model without trapping of wetting fluid. The resistivity index, saturation exponent and capillary pressure are expressed as approximate functions of the pore network parameters by adopting some simplifying assumptions and using effective medium approximation, universal scaling laws of percolation theory and fractal geometry. Some new phenomenological models of resistivity index curves of porous media are derived. Finally, the eventual changes of resistivity index caused by the permanent entrapment of wetting fluid in the pore network are also studied.Resistivity index and saturation exponent are decreasing functions of the degree of correlation between pore volume and pore size as well as the width of the pore size distribution, whereas they are independent on the mean pore size. At low water saturations, the saturation exponent decreases or increases for pore systems of low or high fractal roughness porosity respectively, and obtains finite values only when the wetting fluid is not trapped in the pore network. The dependence of saturation exponent on water saturation weakens for strong correlation between pore volume and pore size, high network connectivity, medium pore-wall roughness porosity and medium width of the pore size distribution. The resistivity index can be described succesfully by generalized 3-parameter power functions of water saturation where the parameter values are related closely with the geometrical, topological and fractal properties of the pore structure. 相似文献
15.
多孔介质的渗流特性是油气藏工程、地下水资源利用、高放废物深地质处置等实际工程领域的热门研究问题.基于分形理论及多孔介质由一束面积大小不等的椭圆形毛细管组成的假设,本文建立了流体在分形多孔介质中渗流时的绝对渗透率及相对渗透率的分形渗透率模型.结果表明,绝对渗透率是最大和最小孔隙面积、分形维数、形状因子ε的函数,且当ε =1时,本文模型可以简化成Yu与Cheng模型;而非饱和多孔介质的相对渗透率与饱和度和多孔介质微结构参数有关.将本文提出的渗透率分形模型预测与实验测量数据及其他模型结果进行对比,显示它们整体吻合很好. 相似文献
16.
Gaseous flow regimes through tight porous media are described by rigorous application of a unified Hagen–Poiseuille-type equation.
Proper implementation is accomplished based on the realization of the preferential flow paths in porous media as a bundle
of tortuous capillary tubes. Improved formulations and methodology presented here are shown to provide accurate and meaningful
correlations of data considering the effect of the characteristic parameters of porous media including intrinsic permeability,
porosity, and tortuosity on the apparent gas permeability, rarefaction coefficient, and Klinkenberg gas slippage factor. 相似文献
17.
Hysteresis phenomena in multi-phase flow in porous media has been recognized by many researchers and widely believed to have significant effects on the flow. In an attempt to account for these effects, a theoretical model for history-dependent relative permeabilities is considered. This model is incorporated into 1-D two-phase nondiffusive flow system and the corresponding flow is predicted. Flow history is observed to have a notable impact on the saturation profile and fluids breakthrough. 相似文献
18.
Results from stochastic reconstruction of porous solids and from a direct comparison of calculated and experimental effective
transport properties are presented. Eight porous solids of different microstructures were selected to evaluate the performance
of two reconstruction methods based on simulated annealing. The common method was constrained by the two-point probability
function and the lineal-path function for the void phase, whilst the constraints of our new method were further supplemented
by the lineal-path function for the solid phase and by two adjustable parameters. The new method was capable of reproducing
the void and solid phases as large clusters spanning the entire replicas. Non-percolating clusters formed minor volume fractions
of both phases. Although the common method reproduced the microstructures quite well, their pore space connectivity was significantly
poorer. Therefore, effective permeability, effective ordinary diffusivity, and effective Knudsen diffusivity calculated for
the replicas obtained using the new method were always much greater than the same quantities related to the common reconstruction
method. For most of the porous solids, values of the effective properties calculated on the basis of the new reconstruction
method better matched their experimental counterparts than the corresponding values derived from the microstructures reproduced
using the common reconstruction method. 相似文献
19.
CO2 injection is one of the most promising techniques to enhance oil recovery. However, an unfavorable mobility ratio, reservoir heterogeneity and gravity segregation can reduce the macroscopic sweep efficiency. In situ foaming of injected CO2 is the method that has the most potential for improving sweep efficiency based on controlling CO2 mobility. This study investigates the foaming behavior of N,N,N′-trimethyl-N′-tallow-1,3-diaminopropane (DTTM) surfactant with CO2 in a transparent porous microflow model with natural rock pore structures. It focuses on the effect of the salinity induced non-Newtonian behavior of DTTM solution on foam propagation. The performance of foams stabilized by 0.5 wt% DTTM solution over the viscosity range from 0.71 (at 5 wt% NaCl) to 41 cp (at 20 wt% NaCl) was compared with conventional polymer-enhanced foams whose liquid phase contained a commonly used foaming surfactant, C15–18 Internal Olefin Sulfonate (C15–18 IOS) and a hydrolyzed polyacrylamide. Such comparisons have also provided insight into the respective impacts of liquid phase viscosification by worm-like surfactant micelles and polymer on foam texture associated with its rheological characteristics. It was found that at low aqueous phase viscosity (injection liquid viscosity of 0.71 cp) the maximum achievable viscosity of DDTM foam was around 1000 cp, which was 80 times IOS stabilized foam. The interfacial tension of DTTM was higher than that of IOS, resulting coarser foam texture and higher individual lamella resistance. An increase in DTTM solution viscosity by a factor of 33 decreased foam generation and viscosity for gas injection. This was not observed for the simultaneous injection of gas and DTTM solution. Overall, the effect of liquid phase viscosity on transient foam behavior during gas injection is similar for both DTTM and IOS regardless of the difference in the nature of viscosifying agents (WLM vs 3330 s polymer). An increase in gas injection pressure without liquid injection delayed foam propagation and reduced the magnitude of foam viscosity. The results from this study indicated that DTTM surfactant is an important alternative to commercially available polymers that have been used to enhance foam performance in porous media. This particular surfactant type also overcomes several disadvantages of polymers such as limited temperature and salinity tolerance, shear degradation, and filtering in low permeability formations.
相似文献
20.
Low pressure gas percolation characteristic in ultra-low permeability porous media is investigated in this article through core flow experiments. The results show that the wall-slip layer covers more than 10% of the average porous channel radius on account of minimum pore size when the permeability is below 0.1 × 10 ?3μ m 2 order, and seepage behavior is contrasted to that in mid-high permeability pore media. When the gas pressure is not high enough, the flow regime turns into transitional flow instead of slip flow, and nonlinear relationship between the measured gas permeability and the reciprocal of average pressure exists. The gas measuring permeability experiment would be influenced by the non-linear relationship. If Klinkenberg-corrected method is applied to speculate the equivalent liquid permeability, the extrapolated value will become less or minus. Simultaneously, actual gas flow velocity at the outlet is beyond the calculated value with Klinkenberg formula. A new gas seepage model based on the general slip boundary condition is derived from the homogenization technique in this article. At last the flow model is examined to be suitable for representing the gas flow behavior in ultra-low permeability media and estimating the absolute permeability from single-point, steady-states measurements. 相似文献
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