Effective porosity

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

Formation Resistivity and Water Saturation

Abstract: This chapter discusses that the sedimentary formations are capable of transmitting an electric current only by means of the interstitial and adsorbed water they contain. They would be non-conductive if they were entirely dry. The electrical resistivity of a fluid-saturated rock is its ability to impede the flow of electric current through that rock. Dry rocks exhibit infinite resistivity. The resistivity of reservoir rocks is a function of salinity of formation water, effective porosity, and quantity of hydrocarbons trapped in the pore space. Relationships among these quantities indicate that the resistivity decreases with increasing porosity and increases with increasing petroleum content. Resistivity measurements are also dependent upon pore geometry, formation stress, and composition of rock, interstitial fluids, and temperature. Resistivity is, therefore, a valuable tool for evaluating the producibility of a formation.

An analysis of the pressure transient testing of a man-made fractured geothermal reservoir *

Abstract: Pressure-transient testing of a hydraulically fractured geothermal reservoir in low-permeability crystalline basement rock has involved constant rate injection and pressure buildup tests under a wide range of field conditions for a number of fractured regions. Following conventional reservoir analysis methods, data are treated in terms of a transient diffusion equation that relates fluid flow and pressure levels in the main fracture system, associated joints, and the matrix permeability. Pressure-flow data are compared to type curve solutions of the diffusion equation for various flow geometries. The following points are considered in detail: (1) the limits on the fracture geometry, aperture and diffusing areas as determined from the diffusion parameters; (2) the parameters (flow impedance, diffusivity) of the flow-through systems are related to those governing the pressure inflation of the main fractures; (3) the relationship of the rock properties to the reservoir compressibility, effective porosity and permeability are discussed. In particular, laboratory experiments show that the flow properties of all sizes of cracks from large single fractures to the microstructure are pressure dependent if the fluid pressure is near the confining stress; and (4) the competition of flow into the various types of porosity (main fractures, joints, and microstructure) and the effectmore » on the interpretation of type curves are discussed.« less

Porous Medium Typology Influence on the Scaling Laws of Confined Aquifer Characteristic Parameters

Abstract: An accurate measurement campaign, carried out on a confined porous aquifer, expressly reproduced in laboratory, allowed the determining of hydraulic conductivity values by performing a series of slug tests. This was done for four porous medium configurations with different granulometric compositions. At the scale considered, intermediate between those of the laboratory and the field, the scalar behaviors of the hydraulic conductivity and the effective porosity was verified, determining the respective scaling laws. Moreover, assuming the effective porosity as scale parameter, the scaling laws of the hydraulic conductivity were determined for the different injection volumes of the slug test, determining a new relationship, valid for coarse-grained porous media. The results obtained allow the influence that the differences among the characteristics of the porous media considered exerted on the scaling laws obtained to be highlighted. Finally, a comparison was made with the results obtained in a previous investigation carried out at the field scale.

Effective porosity implies effective bulk density in sorbing solute transport.

Abstract: The concept of an effective porosity is widely used in solute transport modeling to account for the presence of a fraction of the medium that effectively does not influence solute migration, apart from taking up space. This non-participating volume or ineffective porosity plays the same role as the gas phase in single-phase liquid unsaturated transport: it increases pore velocity, which is useful towards reproducing observed solute travel times. The prevalent use of the effective porosity concept is reflected by its prominent inclusion in popular texts, e.g., de Marsily (1986), Fetter (1988, 1993) and Zheng and Bennett (2002). The purpose of this commentary is to point out that proper application of the concept for sorbing solutes requires more than simply reducing porosity while leaving other material properties unchanged. More specifically, effective porosity implies the corresponding need for an effective bulk density in a conventional single-porosity model. The reason is that the designated non-participating volume is composed of both solid and fluid phases, both of which must be neglected for consistency. Said another way, if solute does not enter the ineffective porosity then it also cannot contact the adjoining solid. Conceptually neglecting the fluid portion of the non-participating volume leads to a lower (effective) porosity. Likewise, discarding the solid portion of the non-participating volume inherently leads to a lower or effective bulk density. In the author's experience, practitioners virtually never adjust bulk density when adopting the effective porosity approach.