Permeability (earth sciences)

About: Permeability (earth sciences) is a research topic. Over the lifetime, 15424 publications have been published within this topic receiving 288535 citations.

A numerical investigation of the hydraulic fracturing behaviour of conglomerate in Glutenite formation

Abstract: Rock formations in Glutenite reservoirs typically display highly variable lithology and permeability, low and complex porosity, and significant heterogeneity. It is difficult to predict the pathway of hydraulic fractures in such rock formations. To capture the complex hydraulic fractures in rock masses, a numerical code called Rock Failure Process Analysis (RFPA2D) is introduced. Based on the characteristics of a typical Glutenite reservoir in China, a series of 2D numerical simulations on the hydraulic fractures in a small-scale model are conducted. The initiation, propagation and associated stress evolution of the hydraulic fracture during the failure process, which cannot be observed in experimental tests, are numerically simulated. Based on the numerical results, the hydraulic fracturing path and features are illustrated and discussed in detail. The influence of the confining stress ratio, gravel sizes (indicated by the diameter variation), and gravel volume content (VC) on the hydraulic fracturing pattern in a conglomerate specimen are numerically investigated, and the breakdown pressure is quantified as a function of these variables. Five hydraulic fracturing modes are identified: termination, deflection, branching (bifurcation), penetration, and attraction. The propagation trajectory of the primary hydraulic fractures is determined by the maximum and minimum stress ratios, although the fracturing path on local scales is clearly influenced by the presence of gravels in the conglomerate, particularly when the gravels are relatively large. As the stress ratio increases, the fractures typically penetrate through the gravels completely rather than propagating around the gravels, and the breakdown pressure decreases with increasing stress ratio. Furthermore, the breakdown pressure is affected by the size and volume content of the gravel in the conglomerate: as the gravel size and volume content increase, the breakdown pressure increases.

A formulation of fully coupled thermal–hydraulic–mechanical behaviour of saturated porous media—numerical approach

Abstract: The theoretical aspects of fully coupled thermohydromechanical behaviour of saturated porous media are presented. The non-linear behaviour of soil skeleton is assumed. A new concept called ‘thermal void ratio state surface’ is introduced to include thermal effects, and the stress state level influence on volume changes. The fluid phase flows according to Darcy's law and energy transport is assumed to follow Fourier's law classically. Variation of water permeability, water and solid unit weight due to thermal effects and pore pressure changes are included. A finite element package is developed based on final matrix form obtained from discretization of integral form of field equations by finite element method and integration in time. A very good agreement between the theoretical predictions and the experimental results was obtained for the several simple problems proposed by other authors. © 1997 by John Wiley & Sons, Ltd.

A pore space model for rock permeability and bulk modulus

Abstract: A simple network model of pore space in rocks has been developed with which permeability and bulk modulus as a function of confining pressure can be calculated. Pores are modeled as straight conduits with circular, elliptic, or tapered cross sections. The interconnection of these conduits is modeled by emplacing them in regular two-dimensional hexagonal, square, or triangular networks. Flow through each conduit is modeled using Poiseuille's law. Flow through the network is calculated based upon the analogy of fluid flow in Darcy's law to current flow in Ohm's law. An estimate of the effective bulk modulus is obtained by summing the contributions of the individual pores. The effect of confining pressure on permeability and bulk modulus is determined by the solid properties and the shape of the pores. For appropriate aspect ratio distributions, the permeability and bulk modulus characteristics of the network model are similar to those found for laboratory rock samples. For rocks of moderate porosity, like sandstone, the model predicts that the bulk modulus is most affected by small, low aspect ratio pores. In contrast, for rocks like granite and tight sandstones (permeability less than 0.5 mdarcy) in which there are relatively few round pores, the bulk modulus and the permeability are both controlled by easily deformed pores. These types of responses are observed in experimental data. The success of the model in predicting these general bulk modulus and permeability responses indicates that while the models presented are too simple to represent a rock completely, the network theory approach is a promising method for modeling porous media.

Air Permeability of Waste in a Municipal Solid Waste Landfill

Abstract: The permeability of compacted municipal solid waste in a landfill with respect to air (or gas) flow was estimated using a short-term air injection test. Air was added to 134 vertical wells installed at three different depths at flow rates in the range of 0.14 –1.4 m3 min−1 and the corresponding steady state pressures were recorded. The permeability of the waste with respect to airflow (described here as the air permeability) was estimated for different anisotropy ratios ( kr ∕ kz =1 , 10, and 100) using a steady state, two-dimensional, axisymmetric analytical fluid flow model in conjunction with the measured flow and pressure data. The air permeability of landfilled municipal solid waste modeled as an isotropic medium was found to range from 1.6× 10−13 to 3.2× 10−11 m2 . The estimated air permeability results were on the low end of values previously applied to model landfill gas flow. Estimated air permeability decreased significantly with increasing waste depth. The lower permeability encountered in the ...