Effective porosity

About: Effective porosity is a research topic. Over the lifetime, 1199 publications have been published within this topic receiving 26511 citations.

The Interpretation of Grain Size Distribution Curves of Clastic Sediments

Abstract: The technique of the graphical dissection of a heterogeneous distribution may be used to show that almost all grain size frequency distributions are bimodal. This consideration together with an investigation of the truncation effects due to sorting leads to the following two hypotheses concerning clastic sediments. Hypothesis I.--"All clastic sediments are essentially mixtures of three or less fundamental populations of log-normal grain sizes. The fundamental populations are: (a) "Gravel" with a median of -3.5 to -2 units and a standard deviation of 1.0 to 2.0 units. (b) "Sand" with a median of 1.5 to 4 units and a standard deviation of 0.4 to 1.0 units. (c) "Clay" with a median of 7 to 9 units and a standard deviation of 2 to 3 units." Hypothesis II.--"Sorting in clastic sediments may be recognized only by the degree of truncation of the original fundamental populations or mixtures of these populations." These two hypotheses lead to the conclusion that most clastic sediments consist of "grains" and "matrix" and the clue to effective porosity development lies in the dispersion of the "matrix."

P-wave velocity test for assessment of geotechnical properties of some rock materials

Abstract: P-wave velocity test, a non-destructive and easy method to apply in both field and laboratory conditions, has increasingly been conducted to determine the geotechnical properties of rock materials. The aim of this study is to predict the rock properties including the uniaxial compressive strength, Schmidt hardness, modulus of elasticity, water absorption and effective porosity, slake durability index, saturated and dry density of rock using P-wave velocity (Vp). For this purpose geotechnical properties of nine different rock types were determined in the laboratory and their mineralogical composition examined using thin section analysis. Utilizing the generated data, sets of empirical equations were developed between Vp and relevant quantified rock parameters. The validity of the obtained empirical equations was confirmed using statistical analysis. It is evident that rock texture and mineralogical compositions affect the geotechnical properties of rock materials. Therefore, the best relationship obtained between both E and UCS with Vp in the correlation coefficient of 0·92 and 0·95 in that order. It is concluded that Vp could be practically used for estimating the measured rock properties except dry and saturated density of rocks (r = 0·58 and 0·46 respectively).

Permeability Description by Characteristic Length, Tortuosity, Constriction and Porosity

Abstract: In this article we investigate the permeability of a porous medium as given in Darcy’s law. The permeability is described by an effective hydraulic pore radius in the porous medium, the fluctuation in local hydraulic pore radii, the length of streamlines, and the fractional volume conducting flow. The effective hydraulic pore radius is related to a characteristic hydraulic length, the fluctuation in local hydraulic radii is related to a constriction factor, the length of streamlines is characterized by a tortuosity, and the fractional volume conducting flow from inlet to outlet is described by an effective porosity. The characteristic length, the constriction factor, the tortuosity, and the effective porosity are thus intrinsic descriptors of the pore structure relative to direction. We show that the combined effect of our pore structure description fully describes the permeability of a porous medium. The theory is applied to idealized porous media, where it reproduces Darcy’s law for fluid flow derived from the Hagen–Poiseuille equation. We also apply this theory to full network models of Fontainebleau sandstone, where we show how the pore structure and permeability correlate with porosity for such natural porous media. This work establishes how the permeability can be related to porosity, in the sense of Kozeny–Carman, through fundamental and well-defined pore structure parameters: characteristic length, constriction, and tortuosity.

Evolution of porosity and diffusivity associated with chemical weathering of a basalt clast

Abstract: [1] Weathering of rocks as a result of exposure to water and the atmosphere can cause significant changes in their chemistry and porosity. In low-porosity rocks, such as basalts, changes in porosity, resulting from chemical weathering, are likely to modify the rock's effective diffusivity and permeability, affecting the rate of solute transport and thus potentially the rate of overall weathering to the extent that transport is the rate limiting step. Changes in total porosity as a result of mineral dissolution and precipitation have typically been used to calculate effective diffusion coefficients through Archie's law for reactive transport simulations of chemical weathering, but this approach fails to account for unconnected porosity that does not contribute to transport. In this study, we combine synchrotron X-ray microcomputed tomography (μCT) and laboratory and numerical diffusion experiments to examine changes in both total and effective porosity and effective diffusion coefficients across a weathering interface in a weathered basalt clast from Costa Rica. The μCT data indicate that below a critical value of ∼9%, the porosity is largely unconnected in the basalt clast. The μCT data were further used to construct a numerical pore network model to determine upscaled, effective diffusivities as a function of total porosity (ranging from 3 to 30%) for comparison with diffusivities determined in laboratory tracer experiments. By using effective porosity as the scaling parameter and accounting for critical porosity, a model is developed that accurately predicts continuum-scale effective diffusivities across the weathering interface of the basalt clast.