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.

Effect of Cracking on Drying Permeability and Diffusivity of Concrete

Abstract: The increase of overall drying permeability and diffusivity of concrete due to cracking is determined experimentally and formulated mathematically. The test specimens are C-shaped beams deformed by a tie rod and reinforced on the tensile face so that uniformly spaced cracks are produced. The difference in the loss of weight for various drying periods between cracked and uncracked specimens is measured and used to quantify the effect on permeability and diffusivity. The overall drying diffusivity and permeability in the cracking direction, which is theoretically proportional to the crack width cubed and inversely proportional to the crack spacing, is found to increase about 2.25 times for crack width 0.1 mm and crack spacing 70 mm. Although appreciable, this value is two orders of magnitude less than the theoretical upper bound predicted on the basis of viscous flow calulation if it is assumed that the cracks are of constant thickness, have planar walls, and are continuous. It is concluded that even though the major cracks are seen to be continuous on the specimen surface, they must be discontinuous in the specimen interior, perhaps being interconnected by much narrower necks with a width about 10 times smaller. This fact is of interest for deducing fracture process zone models from visual observations of cracks on the specimen surface. Although approximate, the presently derived formula for the increase of diffusivity and permeability is directly usable in finite element programs for drying or wetting of concrete.

Porosity and Permeability in Bioturbated Sediments

Abstract: Owing to the textural contrast that commonly exists between matrix and trace fossils, biogenic flow media are common in the rock record. Broadly speaking, the permeability contrast between the matrix and the trace-fossil-affected zones constitutes the most important parameter for characterizing biogenically influenced flow media. Biogenic permeability is separated into two categories: (1) highly contrasting permeability fields (dual-permeability networks) and (2) comparably diffuse and lowly contrasting permeability fields (dual-porosity networks). Dual-permeability flow media normally display poor reservoir characteristics in that only the permeable conduits (i.e., trace fossils) effectively transmit fluids, and resources may be absent in the tighter matrix. Also, a large number of tortuous, tubular flow paths constitute the flow medium. Dual porosity may also reduce the resource quality of a sedimentary rock by introducing nearly unpredictable heterogeneities and often presenting a gradient of permeability fields between the burrowed and matrix end-members. The assessment of bulk permeability, which in practical terms is the upscaled permeability from trace-fossil versus matrix-scale to bed- and bedset scales, is in need of research and refinement. At the present, a few studies have shown that the bulk permeability of strata containing isolated burrows dominantly follows the harmonic mean of burrow/matrix permeabilities. As burrow connectivity increases, the geometric and the arithmetic means of permeability can be applied. A gradation exists between the three methods that we are not yet able to characterize. Recent research has shown that the geometric and harmonic means can be applied to media that are > 20% bioturbated. Factors other than connectivity influence bulk permeability, including burrow diameter and burrow architecture. The influence of these parameters is not yet quantified.

Mechanical compaction, microstructures and permeability evolution in sandstones

Abstract: We present an overview of experimental results that we obtained in the last decade on the permeability evolution with stress and the analysis of stress-induced damage in sandstones. The goal of these studies was to get a fundamental knowledge on the interplay between deformation at the microscale level, fluid flow processes and the macroscopic rock properties. In a first part we present experimental data on the effect of stress on permeability, with emphasis on the influence of stress path and failure mode. In a second part, results from a microstructural study on the mechanics of deformation in Berea sandstone are shown. Although both studies have not been done on the same rock, some general conclusions are drawn on the influence of mechanical deformation on permeability with implications for field studies.