Effective porosity

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

New diagrams to evaluate soil pore radius distribution and saturated hydraulic conductivity of forest soil

Abstract: Based on the widely used soil pore classification systems, soil pore ratios α, β and γ were derived. α, β, and γ represent ratios of the fine capillary porosity, coarse capillary porosity, and non-capillary porosity to the effective porosity, respectively. The parametersψm and σ of the soil water retention model developed by Kosugi were related to these pore ratios, and a simple method was suggested to estimateψm and σ from measured soil pore ratios. By analyzing the observed retention data sets of forest soils, it was shown that the soil pore ratios are effectively used to evaluate the soil pore radius distribution. A coordinate system with log(−ψm) on the abscissa and σ on the ordinate, which represents the constant α, β, and γ lines, was developed as a new diagram to evaluate the soil pore radius distribution in connection with the soil water retention characteristic. Then, the saturated hydraulic conductivityKs of forest soils was correlated with the parametersψm and σ, and with the ratios α, β, and γ using the coordinate system and the triangle diagram. Results showed thatKs is higher for the soil with a greater median and with a greater width of the pore radius distribution.Ks increases as the non-capillary pore ratio γ becomes greater and the coarse capillary pore ratio β becomes smaller. Functional relationships betweenKs and the water retention parameters, and betweenKs and the soil pore ratios were derived based on Mualem's model.

Improved estimation of mineral and fluid volumetric concentrations in thinly-bedded and invaded formations

Abstract: Calculation of mineral and fluid volumetric concentrations from well logs is one of the most important outcomes of formation evaluation. Conventional estimation methods assume a linear relationship between volumetric concentrations of solid/fluid constituents and well logs. Experience shows, however, that the relationship between neutron logs and mineral concentrations is generally non-linear. More importantly, linear estimation methods do not explicitly account for shoulder-bed and/or invasion effects on well logs nor do the account for differences in the volume of investigation of the measurements involved in the estimation. The latter deficiencies of the linear estimation method can cause appreciable errors in the calculation of porosity and hydrocarbon pore volume. We introduce a new non-linear inversion method that uses fast modeling of nuclear and resistivity logs to estimate porosity, hydrocarbon saturation, volumetric concentration of shale, and volumetric concentrations of mineral constituents in the presence of complex mineral compositions, invasion, and shoulder beds. The method assumes a multi-layer reservoir model constructed with the detection of bed boundaries from density and gamma-ray (GR) logs. Subsequently, nonlinear inversion is initialized with petrophysical properties and volumetric mineral concentrations obtained with a conventional linear estimation method combined with resistivity-saturation equations. We progressively reduce the differences between simulated and measured logs via linear iterative steps to render final estimates of porosity, fluid saturations, and volumetric concentrations of mineral constituents that honor the well logs, their volume of investigation, the process of invasion, and the assumed rock-physics model. Synthetic and field examples of application indicate that non-linear inversion is an efficient and reliable method to quantify complex mineral and fluid composition in the presence of thin beds and invasion. Comparison of results against those obtained with commercial linear estimation methods confirm the advantage of non-linear inversion in quantifying thinly-bedded carbonate formations.

A pore-size scale model for the dielectric properties of water-saturated clean rocks and soils

Abstract: The dielectric properties of water-saturated rock and soils are strongly dependent on the amount and nature of their porosity; interpretation of these geophysical data requires petrophysical models that incorporate both of these elements. The differential effective medium approximation (DEMA) is used to develop a dielectric permittivity model for clean (i.e., clay free) media that divides the pore spaces into elements corresponding to three categories of relative size scale: microscopic porosity (e.g., intergranular cracks), mesoscopic porosity (e.g., main pore volumes), and macroscopic porosity (e.g., vugs and fractures). The hierarchical size-scale structure imposed by the DEMA iterative embedding process is used to assign each pore space category its role in model construction. Use of this model demonstrates that the relationship between dielectric permittivity and porosity is significantly affected by the size scales of pores present in the rock models. A region of realizable permittivity-porosity val...

Reconsideration at field scale of the relationship between hydraulic conductivity and porosity: the case of a sandy aquifer in South Italy.

Abstract: To describe flow or transport phenomena in porous media, relations between aquifer hydraulic conductivity and effective porosity can prove useful, avoiding the need to perform expensive and time consuming measurements. The practical applications generally require the determination of this parameter at field scale, while most of the empirical and semiempirical formulas, based on grain size analysis and allowing determination of the hydraulic conductivity from the porosity, are related to the laboratory scale and thus are not representative of the aquifer volumes to which one refers. Therefore, following the grain size distribution methodology, a new experimental relation between hydraulic conductivity and effective porosity, representative of aquifer volumes at field scale, is given for a confined aquifer. The experimental values used to determine this law were obtained for both parameters using only field measurements methods. The experimental results found, also if in the strict sense valid only for the investigated aquifer, can give useful suggestions for other alluvial aquifers with analogous characteristics of grain-size distribution. Limited to the investigated range, a useful comparison with the best known empirical formulas based on grain size analysis was carried out. The experimental data allowed also investigation of the existence of a scaling behaviour for both parameters considered.