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.

Permeability and degassing of dome lavas undergoing rapid decompression: An experimental determination

Abstract: The gas permeability of volcanic rocks may influence various eruptive processes. The transition from a quiescent degassing dome to rock failure (fragmentation) may, for example, be controlled by the rock’s permeability, in as much as it affects the speed by which a gas overpressure in vesicles is reduced in response to decompression. Using a modified shock-tube-based fragmentation bomb (Alidibirov and Dingwell 1996a,b; Spieler et al. 2003a), we have measured unsteady-state permeability at a high initial pressure differential. Following sudden decompression above the rock cylinder, pressurized gas flows through the sample. Two pressure transducers record the pressure signals above and below the sample. A transient 1D filtration code has been developed to calculate permeability using the experimental decay curve of the lower pressure transducer. Additionally an analytical steady-state method to achieve permeability is presented as an alternative to swiftly predict the sample permeability in a sufficiently precise manner. Over 100 permeability measurements have been performed on samples covering a wide range of porosity. The results show a general positive relationship between porosity and permeability with a high data scatter. Our preferred interpretation of the results is a combination of two different, but overlapping effects. We propose that at low porosities, gas escape occurs predominantly through microcracks or elongated micropores and therefore could be described by simplified forms of Kozeny–Carman relations (Carman 1956) and fracture flow models. At higher porosities, the influence of vesicles becomes progressively stronger as they form an increasingly connected network. Therefore, a model based on the percolation theory of fully penetrable spheres is used, as a first approximation, to describe the permeability-porosity trend. In the data acquired to date it is evident, that in addition to the porosity control, the sample’s bubble size, shape and distribution strongly influence the permeability. This leads to a range of permeability values up to 2.5 orders of magnitude at a given porosity.

Permeability and Effective Stress: GEOLOGIC NOTES

Abstract: Permeability of the Berea Sandstone was measured as a function of both confining pressure and pore pressure. As expected, permeability decreased with increased confining pressure and increased with increasing pore pressure. However, pore pressure had a significantly larger effect on permeability than did confining pressure. This behavior can be explained if the matrix through which the pore fluid flows has a higher compressibility than the granular framework which supports externally applied stresses.

Strength, porosity, and permeability development during hydrostatic and shear loading of synthetic quartz-clay fault gouge

Abstract: [1] The strength and permeability of fault zones must be quantified in order to accurately predict crustal strength and subsurface fluid migration To this end, we performed experiments on mixtures of fine-grained quartz and kaolinite incremented at 10 wt% intervals between the two end-member components (analogues for natural fault gouge) in order to establish their strength and fluid flow properties during hydrostatic and shear loading Hydrostatically compacted samples exhibited permeability reduction on increasing effective pressures from 5 MPa to 50 MPa, with the rate of reduction displaying strong dependency on the synthetic fault gouge composition The permeability decreases continuously with increasing kaolinite content Porosity exhibits a distinct minimum that evolves with increasing effective pressure according to the relative compaction of the quartz and kaolinite end-members Porosity evolution with increasing clay content is predicted satisfactorily by a simple ideal packing model At the highest effective pressure (50 MPa), permeability reduced log-linearly over 4 orders of magnitude with increasing clay content Mechanically, sheared gouge samples showed a continuous reduction in frictional strength with increasing clay fraction Permeability decreased further on shear loading after initial hydrostatic compaction to 50 MPa This was most evident for the pure quartz end-member, with two orders of magnitude additional reduction, whereas the clay-rich samples were reduced only tenfold, mostly before a shear strain of 5 Variation of permeability with both clay content and shear deformation may be adequately described by previously published empirical predictors for fault zone permeability Clay content has the largest effect on permeability, and shear deformation affects permeability of quartz-rich gouges more than clay-rich gouges