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Porosity is the ratio of pore volume to its total volume. Porosity is controlled by: rock type, pore distribution, cementation, diagenetic history and composition. Porosity is not controlled by grain size, as the volume of between-grain space is related only to the method of grain packing.
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.
A pore is not simply a void in the solid structure of soil. The various pore size categories have different characteristics and contribute different attributes to soils depending on the number and frequency of each type. A widely used classification of pore size is that of Brewer (1964): [1] [2] [3]
The fraction of water held back in the aquifer is known as specific retention. Thus it can be said that porosity is the sum of specific yield and specific retention. Specific yield of soils differ from each other in the sense that some soil types have strong molecular attraction with the water held in their pores while others have less.
Pore size varies considerably; the smallest pores (cryptopores; <0.1 μm) hold water too tightly for use by plant roots; plant-available water is held in ultramicropores, micropores and mesopores (0.1–75 μm); and macropores (>75 μm) are generally air-filled when the soil is at field capacity.
Porosity that is not considered "effective porosity" includes water bound to clay particles (known as bound water) and isolated "vuggy" porosity (vugs not connected to other pores, or dead-end pores). The effective porosity is of great importance in considering the suitability of rocks or sediments as oil or gas reservoirs, or as aquifers.
Porosimetry is an analytical technique used to determine various quantifiable aspects of a material's porous structure, such as pore diameter, total pore volume, surface area, and bulk and absolute densities. The technique involves the intrusion of a non-wetting liquid (often mercury) at high pressure into a material through the use of a ...
This measured pressure permits obtaining the pore diameter, which is calculated by using the Young-Laplace formula P= 4*γ*cos θ*/D in which D is the pore size diameter, P is the pressure measured, γ is the surface tension of the wetting liquid and θ is the contact angle of the wetting liquid with the sample. The surface tension γ is a ...