Pore structure

Last updated
Micro CT of porous medium: Pores of the porous medium shown as purple color and impermeable porous matrix shown as green-yellow color. Open 4D micro CT.gif
Micro CT of porous medium: Pores of the porous medium shown as purple color and impermeable porous matrix shown as green-yellow color.

Pore structure is a common term employed to characterize the porosity, pore size, pore size distribution, and pore morphology (such as pore shape, surface roughness, and tortuosity of pore channels) of a porous medium. [1] [2] Pores are the openings in the surfaces impermeable porous matrix which gases, liquids, or even foreign microscopic particles can inhabit them. [3] The pore structure and fluid flow in porous media are intimately related.

Contents

With micronanoscale pore radii, complex connectivity, and significant heterogeneity, [4] the complexity of the pore structure affects the hydraulic conductivity and retention capacity of these fluids. [5] The intrinsic permeability is the attribute primarily influenced by the pore structure, and the fundamental physical factors governing fluid flow and distribution are the grain surface-to-volume ratio and grain shape. [6]

The idea that the pore space is made up of a network of channels through which fluid can flow is particularly helpful. Pore openings are the comparatively thin sections that divide the relatively large portions known as pore bodies. Other anatomical analogies include "belly" or "waist" for the broad region of a pore and "neck" or "throat" for the constrictive part. Pore bodies are the intergranular gaps with dimensions that are generally significantly smaller than those of the surrounding particles in a medium where textural pore space predominates, such as sand. On the other hand, a wormhole [7] can be regarded as a single pore if its diameter is practically constant over its length.

Such pores can have one of three types of boundaries: (1) constriction, which is a plane across the locally narrowest part of the pore space; (2) interface with another pore (such as a wormhole or crack); or (3) interface with solid. [8]

Porosity

Porosity shown as purple color(Thin section under gypsum plate of microscopic carbonate grains). Scale bar 500 micrometres. Porosity thin section GP.jpg
Porosity shown as purple color(Thin section under gypsum plate of microscopic carbonate grains). Scale bar 500 micrometres.

The proportion of empty space in a porous media is called porosity. [9] It is determined by dividing the volume of the pores or voids by the overall volume. It is expressed as a percentage or as a decimal fraction between 0 and 1. Porosity for the majority of rocks ranges from less than 1% to 40%.

Porosity influences fluid storage in geothermal systems, oil and gas fields, and aquifers, making it evident that it plays a significant role in geology. Fluid movement and transport across geological formations, as well as the link between the bulk properties of the rock and the characteristics of particular minerals, are controlled by the size and connectivity of the porous structure. [10]

Measuring porosity

The samples' total volume and pore space volume were measured in order to calculate the porosities.

Measuring pore space volume

A helium pyrometer was used to calculate the volume of the pores and relied on Boyle's Law. (P1V1=P2V2) and helium gas, which easily passes through tiny holes and is inert, to identify the solid fraction of a sample. A sample chamber with a known volume is where the core is put. Pressure is applied to a reference chamber with a known volume. The helium gas may now go from the reference chamber to the sample chamber thanks to the connection between the two rooms. The volume of the sample solid is calculated using the ratio between the starting and final pressures. The pore volume, as calculated by the helium pycnometer, is the difference between the total volume and the solid volume. [11]

Pore size and pore size distribution

Pore size

Typically, the effective radius of the pore body or neck is used to define the size of pores. [8] The position, shape, and connection of pores in solids are only a few of their numerous attributes and the most straightforward aspect of a pore to visualize is likely its size, or its extent in a single spatial dimension.

In comparison to other factors like pore shape, it is arguable that pore size has the biggest or broadest impact on the characteristics of solids. Therefore, using pore size or pore size distribution to describe and contrast various porous substances is definitely convenient and valuable. [12]

The three main pore size ranges (The current classification of pore size recommended by the International Union of Pure and Applied Chemistry) are as following: [12]

Main pore size ranges. [12]
MicroporePore width smaller than 2 nm
MesoporesPore width between 2 and 50 nm
MacroporePore width greater than 50 nm

Pore size distribution

The relative abundance of each pore size in a typical volume of soil is represented by the pore size distribution. It is represented by the function f(r), whose value is proportional to the total volume of all pores whose effective radius is within an infinitesimal range centered on r. And f(r) can be thought to have textural and structural components. [8]

Measuring pore size distribution

Mercury intrusion porosimetry [13] and gas adsorption [14] are common techniques for determining the pore size distribution of materials and power sources.

When studying the pore size distribution using the gas adsorption technique utilizing the nitrogen or argon adsorption isotherm at their boiling temperatures, it is possible to determine the pore size from the molecular level to a few hundred nm. The pressure sensor's precise constraints and the coolant's temperature stability result in a maximum observed pore size of just a little bit more than 100 nm in a realistic environment. [15]

Mercury porosimetry determines the pore size distribution and quantifies the associated incursion amount by applying pressure to the non-wetting mercury. The pore size may be readily estimated using this method and ranges from a few nm to 1000 m. The material must be robust enough to withstand the pressure since mercury intrusion requires 140 MPa of pressure for pores smaller than 10 nm. Additionally, it utilizes the idea to determine the pore size of the inkbottle neck. [15]

The relation of pore size to pore size distribution

The relationship between pore size and pore size distribution in a randomly constructed porous system, is expected to be monotone: bigger pores are connected to larger particles. The relationship between pore size and particle size is complicated by the nonrandom nature of most soils. Big pores may be found in both large and tiny particles, including clays, which promote aggregation and therefore the development of large interaggregate pores. Subdivisions of a pore size distribution in randomly structured media can express more specific characteristics of soils with more complex conceptualizations, such as the hysteresis of soil water retention. [8]

Pore morphology

The pore morphology is the shape, surface roughness, and tortuosity of pore channels representing the liquid and gaseous phases. [16]

Tortuosity of pore channels

The ratio of the length of the shortest paths between two points witing the pore space to the straight-line distance is the tortuosity, imaged by x-ray microtomography. Tortuosity via geodesic distance calculation.tif
The ratio of the length of the shortest paths between two points witing the pore space to the straight-line distance is the tortuosity, imaged by x-ray microtomography.

Tortuosity of pore channels is a unique geometric quantity that is utilized not only to measure the transport characteristics of porous system, but also to express the sinuosity and complexity of internal percolation routes. [17] [18] [19]

Toruosity is intimately connected to the transport behavior of electrical conductivity, fluid permeation, [20] molecular diffusion, and heat transfer in geoscience, impacting petrophysical parameters such as permeability, effective diffusivity, thermal conductivity, and formation resistivity factor. [18] [21]

Surface roughness

The standard definition of surface roughness for porous medium is based on the average measured vertical coordinate value in comparison to a relative surface height, such as root-mean-square roughness or arithmetic roughness. However, the lack of fractal topology consideration led to the relative surface height definition being deemed inadequate in reality. [22] [23]

The ratio of "real surface area" to "geometric smooth-surface area" was used as the second definition of surface roughness. This definition has been applied in several research to alter flow equations or measure the fluid-fluid interfacial area. [24] [25]

The fundamental idea of fractal geometry is where the third definition of surface roughness comes from, [26] in which either modifies the pore surfaces (two-dimensional) or the whole porous medium (three-dimensional) using fractal dimension adjustments, resulting in larger surface dimensions or reduced media dimensions. [27] The hurst roughness exponent, a similar definition, is occasionally used. This quantity, which spans from 0 to 1, is connected to the fractal dimension.

See also

Related Research Articles

<span class="mw-page-title-main">Aquifer</span> Underground layer of water-bearing permeable rock

An aquifer is an underground layer of water-bearing, permeable rock, rock fractures, or unconsolidated materials. Groundwater from aquifers can be extracted using a water well. Aquifers vary greatly in their characteristics. The study of water flow in aquifers and the characterization of aquifers is called hydrogeology. Related terms include aquitard, which is a bed of low permeability along an aquifer, and aquiclude, which is a solid, impermeable area underlying or overlying an aquifer, the pressure of which could create a confined aquifer. The classification of aquifers is as follows: Saturated versus unsaturated; aquifers versus aquitards; confined versus unconfined; isotropic versus anisotropic; porous, karst, or fractured; transboundary aquifer.

<span class="mw-page-title-main">Sintering</span> Process of forming and bonding material by heat or pressure

Sintering or frittage is the process of compacting and forming a solid mass of material by pressure or heat without melting it to the point of liquefaction.

Permeability in fluid mechanics and the Earth sciences is a measure of the ability of a porous material to allow fluids to pass through it.

Darcy's law is an equation that describes the flow of a fluid through a porous medium. The law was formulated by Henry Darcy based on results of experiments on the flow of water through beds of sand, forming the basis of hydrogeology, a branch of earth sciences. It is analogous to Ohm's law in electrostatics, linearly relating the volume flow rate of the fluid to the hydraulic head difference via the hydraulic conductivity.

<span class="mw-page-title-main">Porous medium</span> Material containing fluid-filled voids

In materials science, a porous medium or a porous material is a material containing pores (voids). The skeletal portion of the material is often called the "matrix" or "frame". The pores are typically filled with a fluid. The skeletal material is usually a solid, but structures like foams are often also usefully analyzed using concept of porous media.

<span class="mw-page-title-main">Proton-exchange membrane fuel cell</span> Power generation technology

Proton-exchange membrane fuel cells (PEMFC), also known as polymer electrolyte membrane (PEM) fuel cells, are a type of fuel cell being developed mainly for transport applications, as well as for stationary fuel-cell applications and portable fuel-cell applications. Their distinguishing features include lower temperature/pressure ranges and a special proton-conducting polymer electrolyte membrane. PEMFCs generate electricity and operate on the opposite principle to PEM electrolysis, which consumes electricity. They are a leading candidate to replace the aging alkaline fuel-cell technology, which was used in the Space Shuttle.

In science and engineering, hydraulic conductivity, is a property of porous materials, soils and rocks, that describes the ease with which a fluid can move through the pore space, or fractures network. It depends on the intrinsic permeability of the material, the degree of saturation, and on the density and viscosity of the fluid. Saturated hydraulic conductivity, Ksat, describes water movement through saturated media. By definition, hydraulic conductivity is the ratio of volume flux to hydraulic gradient yielding a quantitative measure of a saturated soil's ability to transmit water when subjected to a hydraulic gradient.

Poromechanics is a branch of physics and specifically continuum mechanics and acoustics that studies the behaviour of fluid-saturated porous media. A porous medium or a porous material is a solid referred to as matrix) permeated by an interconnected network of pores (voids) filled with a fluid. Usually both solid matrix and the pore network, or pore space, are assumed to be continuous, so as to form two interpenetrating continua such as in a sponge. Natural substances including rocks, soils, biological tissues including heart and cancellous bone, and man-made materials such as foams and ceramics can be considered as porous media. Porous media whose solid matrix is elastic and the fluid is viscous are called poroelastic. A poroelastic medium is characterised by its porosity, permeability as well as the properties of its constituents.

In fluid statics, capillary pressure is the pressure between two immiscible fluids in a thin tube, resulting from the interactions of forces between the fluids and solid walls of the tube. Capillary pressure can serve as both an opposing or driving force for fluid transport and is a significant property for research and industrial purposes. It is also observed in natural phenomena.

In petrophysics, Archie's law relates the in-situ electrical conductivity (C) of a porous rock to its porosity and fluid saturation of the pores:

<span class="mw-page-title-main">Tortuosity</span> Parameter for diffusion and fluid flow in porous media

Tortuosity is widely used as a critical parameter to predict transport properties of porous media, such as rocks and soils. But unlike other standard microstructural properties, the concept of tortuosity is vague with multiple definitions and various evaluation methods introduced in different contexts. Hydraulic, electrical, diffusional, and thermal tortuosities are defined to describe different transport processes in porous media, while geometrical tortuosity is introduced to characterize the morphological property of porous microstructures.

The pore space of soil contains the liquid and gas phases of soil, i.e., everything but the solid phase that contains mainly minerals of varying sizes as well as organic compounds.

Porosity or void fraction is a measure of the void spaces in a material, and is a fraction of the volume of voids over the total volume, between 0 and 1, or as a percentage between 0% and 100%. Strictly speaking, some tests measure the "accessible void", the total amount of void space accessible from the surface.

Nuclear magnetic resonance (NMR) in porous materials covers the application of using NMR as a tool to study the structure of porous media and various processes occurring in them. This technique allows the determination of characteristics such as the porosity and pore size distribution, the permeability, the water saturation, the wettability, etc.

<span class="mw-page-title-main">Separator (electricity)</span>

A separator is a permeable membrane placed between a battery's anode and cathode. The main function of a separator is to keep the two electrodes apart to prevent electrical short circuits while also allowing the transport of ionic charge carriers that are needed to close the circuit during the passage of current in an electrochemical cell.

<span class="mw-page-title-main">Freeze-casting</span>

Freeze-casting, also frequently referred to as ice-templating, or freeze alignment, is a technique that exploits the highly anisotropic solidification behavior of a solvent in a well-dispersed slurry to controllably template a directionally porous ceramic. By subjecting an aqueous slurry to a directional temperature gradient, ice crystals will nucleate on one side of the slurry and grow along the temperature gradient. The ice crystals will redistribute the suspended ceramic particles as they grow within the slurry, effectively templating the ceramic.

In fluid mechanics, fluid flow through porous media is the manner in which fluids behave when flowing through a porous medium, for example sponge or wood, or when filtering water using sand or another porous material. As commonly observed, some fluid flows through the media while some mass of the fluid is stored in the pores present in the media.

Bioclogging or biological clogging is the clogging of pore space in soil by microbial biomass; their body and their byproducts such as extracellular polymeric substance (EPS). The microbial biomass blocks the pathway of water in the pore space, forming a certain thickness of the impermeable layer in the soil, and it reduces the rate of infiltration of water remarkably.

Titanium foams exhibit high specific strength, high energy absorption, excellent corrosion resistance and biocompatibility. These materials are ideally suited for applications within the aerospace industry. An inherent resistance to corrosion allows the foam to be a desirable candidate for various filtering applications. Further, titanium's physiological inertness makes its porous form a promising candidate for biomedical implantation devices. The largest advantage in fabricating titanium foams is that the mechanical and functional properties can be adjusted through manufacturing manipulations that vary porosity and cell morphology. The high appeal of titanium foams is directly correlated to a multi-industry demand for advancement in this technology.

<span class="mw-page-title-main">Fault zone hydrogeology</span>

Fault zone hydrogeology is the study of how brittlely deformed rocks alter fluid flows in different lithological settings, such as clastic, igneous and carbonate rocks. Fluid movements, that can be quantified as permeability, can be facilitated or impeded due to the existence of a fault zone. This is because different mechanisms that deform rocks can alter porosity and permeability within a fault zone. Fluids involved in a fault system generally are groundwater and hydrocarbons.

References

  1. ↑ Tang, H. P.; Wang, J.; Qian, Ma (1 January 2015). "28 - Porous titanium structures and applications". Titanium Powder Metallurgy. Butterworth-Heinemann: 533–554. doi:10.1016/b978-0-12-800054-0.00028-9. ISBN   9780128000540.
  2. ↑ Gao, Qian-Feng; Jrad, Mohamad; Hattab, Mahdia; Fleureau, Jean-Marie; Ameur, Lamine Ighil (1 June 2020). "Pore Morphology, Porosity, and Pore Size Distribution in Kaolinitic Remolded Clays under Triaxial Loading". International Journal of Geomechanics. 20 (6): 04020057. doi:10.1061/(asce)gm.1943-5622.0001682. S2CID   216280837.
  3. ↑ "Pore size measurement :: Anton Paar Wiki". Anton Paar (in French).
  4. ↑ Dai, Quanqi; Wang, Guiwen; Zhao, Xing; Han, Zongyan; Lu, Kai; Lai, Jin; Wang, Song; Li, Dong; Li, Yafeng; Wu, Kunyu (1 August 2021). "Fractal model for permeability estimation in low-permeable porous media with variable pore sizes and unevenly adsorbed water lay". Marine and Petroleum Geology. 130: 105135. doi:10.1016/j.marpetgeo.2021.105135. ISSN   0264-8172. S2CID   236308390.
  5. ↑ Scholz, Christian; Wirner, Frank; Klatt, Michael A.; Hirneise, Daniel; Schröder-Turk, Gerd E.; Mecke, Klaus; Bechinger, Clemens (30 October 2015). "Direct relations between morphology and transport in Boolean models". Physical Review E. 92 (4): 043023. Bibcode:2015PhRvE..92d3023S. doi:10.1103/PhysRevE.92.043023. PMID   26565348.
  6. ↑ Torskaya, T.; Shabro, V.; Torres-Verdín, C.; Salazar-Tio, R.; Revil, A. (March 2014). "Grain Shape Effects on Permeability, Formation Factor, and Capillary Pressure from Pore-Scale Modeling". Transport in Porous Media. 102 (1): 71–90. doi:10.1007/s11242-013-0262-7. S2CID   53326234.
  7. ↑ Tillman, Nola Taylor; published, Ailsa Harvey (13 January 2022). "What is a Wormhole?". Space.com.
  8. 1 2 3 4 Nimmo, J.R. (2013). "Porosity and Pore Size Distribution". Reference Module in Earth Systems and Environmental Sciences: B9780124095489052659. doi:10.1016/B978-0-12-409548-9.05265-9. ISBN   9780124095489.
  9. ↑ Xiong, Yunwu; Long, Xiaoxu; Huang, Guanhua; Furman, Alex (1 December 2019). "Impact of pore structure and morphology on flow and transport characteristics in randomly repacked grains with different angularities". Soils and Foundations. 59 (6): 1992–2006. doi: 10.1016/j.sandf.2019.10.002 . S2CID   214526290.
  10. ↑ Anovitz, Lawrence M.; Cole, David R. (1 January 2015). "Characterization and Analysis of Porosity and Pore Structures". Reviews in Mineralogy and Geochemistry. 80 (1): 61–164. Bibcode:2015RvMG...80...61A. doi: 10.2138/rmg.2015.80.04 . ISSN   1529-6466.
  11. ↑ "Wisconsin Geological & Natural History Survey » Understanding porosity and density". wgnhs.wisc.edu.
  12. 1 2 3 Mays, T.J. (2007). "A new classification of pore sizes". Studies in Surface Science and Catalysis. 160: 57–62. doi:10.1016/s0167-2991(07)80009-7. ISBN   9780444520227.
  13. ↑ Pawelec, Kendell M.; White, Ashley A.; Best, Serena M. (1 January 2019). "4 - Properties and characterization of bone repair materials". Bone Repair Biomaterials (Second Edition). Woodhead Publishing: 65–102. doi:10.1016/b978-0-08-102451-5.00004-4. ISBN   9780081024515.
  14. ↑ Wypych, George (1 January 2017). "13 - ANALYTICAL TECHNIQUES USEFUL IN FOAMING". Handbook of Foaming and Blowing Agents. ChemTec Publishing. pp. 219–225. doi:10.1016/B978-1-895198-99-7.50015-5. ISBN   978-1-895198-99-7.
  15. 1 2 "Methods for Pore Size Distribution measurement :: Microtrac". www.microtrac.com.
  16. ↑ Pagliai, Marcello (2011). "Pore Morphology and Soil Functions". Encyclopedia of Agrophysics. Encyclopedia of Earth Sciences Series. Springer Netherlands: 640–645. doi:10.1007/978-90-481-3585-1_123. ISBN   978-90-481-3584-4.
  17. ↑ Clennell, M. Ben (1997). "Tortuosity: a guide through the maze". Geological Society, London, Special Publications. 122 (1): 299–344. Bibcode:1997GSLSP.122..299C. doi:10.1144/gsl.sp.1997.122.01.18. ISSN   0305-8719. S2CID   130626761.
  18. 1 2 Fu, Jinlong; Thomas, Hywel R.; Li, Chenfeng (1 January 2021). "Tortuosity of porous media: Image analysis and physical simulation". Earth-Science Reviews. 212: 103439. Bibcode:2021ESRv..21203439F. doi:10.1016/j.earscirev.2020.103439. ISSN   0012-8252. S2CID   229386129.
  19. ↑ Ghanbarian, Behzad; Hunt, Allen G.; Ewing, Robert P.; Sahimi, Muhammad (September 2013). "Tortuosity in Porous Media: A Critical Review". Soil Science Society of America Journal. 77 (5): 1461–1477. Bibcode:2013SSASJ..77.1461G. doi:10.2136/sssaj2012.0435.
  20. ↑ Fu, Jinlong; Cui, Shaoqing; Cen, Song; Li, Chenfeng (1 January 2021). "Statistical characterization and reconstruction of heterogeneous microstructures using deep neural network" (PDF). Computer Methods in Applied Mechanics and Engineering. 373: 113516. Bibcode:2021CMAME.373k3516F. doi:10.1016/j.cma.2020.113516. S2CID   228892100.
  21. ↑ Backeberg, Nils R.; Iacoviello, Francesco; Rittner, Martin; Mitchell, Thomas M.; Jones, Adrian P.; Day, Richard; Wheeler, John; Shearing, Paul R.; Vermeesch, Pieter; Striolo, Alberto (December 2017). "Quantifying the anisotropy and tortuosity of permeable pathways in clay-rich mudstones using models based on X-ray tomography". Scientific Reports. 7 (1): 14838. Bibcode:2017NatSR...714838B. doi:10.1038/s41598-017-14810-1. PMC   5665904 . PMID   29093572.
  22. ↑ Ghanbarian, Behzad; Hunt, Allen G.; Daigle, Hugh (March 2016). "Fluid flow in porous media with rough pore-solid interface: FLOW IN ROUGH-WALLED POROUS MEDIA". Water Resources Research. 52 (3): 2045–2058. doi: 10.1002/2015WR017857 . S2CID   131002491.
  23. ↑ Jiang, Hao; Guo, Bo; Brusseau, Mark L. (1 December 2020). "Characterization of the micro-scale surface roughness effect on immiscible fluids and interfacial areas in porous media using the measurements of interfacial partitioning tracer tests". Advances in Water Resources. 146: 103789. Bibcode:2020AdWR..14603789J. doi:10.1016/j.advwatres.2020.103789. ISSN   0309-1708. PMC   7727783 . PMID   33311835.
  24. ↑ Toledo, Pedro G.; Novy, Robert A.; Davis, H. Ted; Scriven, L. E. (May 1990). "Hydraulic Conductivity of Porous Media at Low Water Content". Soil Science Society of America Journal. 54 (3): 673–679. Bibcode:1990SSASJ..54..673T. doi:10.2136/sssaj1990.03615995005400030007x.
  25. ↑ Jiang, Hao; Guo, Bo; Brusseau, Mark L. (January 2020). "Pore‐Scale Modeling of Fluid‐Fluid Interfacial Area in Variably Saturated Porous Media Containing Microscale Surface Roughness". Water Resources Research. 56 (1). Bibcode:2020WRR....5625876J. doi:10.1029/2019WR025876. ISSN   0043-1397. PMC   7785087 . PMID   33408424.
  26. ↑ Mandelbro, B.B. Mandelbrot The Fractal Geometry of Nature. New York.
  27. ↑ Toledo, Pedro G.; Novy, Robert A.; Davis, H. Ted; Scriven, L. E. (May 1990). "Hydraulic Conductivity of Porous Media at Low Water Content". Soil Science Society of America Journal. 54 (3): 673–679. Bibcode:1990SSASJ..54..673T. doi:10.2136/sssaj1990.03615995005400030007x.

Further reading

This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.