Showing papers on "Permeability (earth sciences) published in 2003"

The role of hydromechanical coupling in fractured rock engineering

Abstract: This paper provides a review of hydromechanical (HM) couplings in fractured rock, with special emphasis on HM interactions as a result of, or directly connected with human activities. In the early 1960s, the coupling between hydraulic and mechanical processes in fractured rock started to receive wide attention. A series of events including dam failures, landslides, and injection-induced earthquakes were believed to result from HM interaction. Moreover, the advent of the computer technology in the 1970s made possible the integration of nonlinear processes such as stress–permeability coupling and rock mass failure into coupled HM analysis. Coupled HM analysis is currently being applied to many geological engineering practices. One key parameter in such analyses is a good estimate of the relationship between stress and permeability. Based on available laboratory and field data, it was found that the permeability of fractured rock masses tends to be most sensitive to stress changes at shallow depth (low stress) and in areas of low in-situ permeability. In highly permeable, fractured rock sections, fluid flow may take place in clusters of connected fractures which are locked open as a result of previous shear dislocation or partial cementation of hard mineral filling. Such locked-open fractures tend to be relatively insensitive to stress and may therefore be conductive at great depths. Because of the great variability of HM properties in fractured rock, and the difficulties in using laboratory data for deriving in-situ material properties, the HM properties of fractured rock masses are best characterized in situ.

On the use of the KozenyCarman equation to predict the hydraulic conductivity of soils

Abstract: The saturated hydraulic conductivity of a soil can be predicted using empirical relationships, capillary models, statistical models, and hydraulic radius theories. A well-known relationship between...

A new model for viscous dissipation in porous media across a range of permeability values

Abstract: In this paper a unified mathematical theory for the viscous dissipation term in the governing Brinkman equation is derived. This term has, unlike other models, the correct asymptotic behaviour in both the fully Darcy and Newtonian fluid flow limits.

Linear dynamics of double-porosity dual-permeability materials. II. Fluid transport equations.

Abstract: For the purpose of understanding the acoustic attenuation of double-porosity composites, the key macroscopic equations are those controlling the fluid transport. Two types of fluid transport are present in double-porosity dual-permeability materials: (1) a scalar transport that occurs entirely within each averaging volume and that accounts for the rate at which fluid is exchanged between porous phase 1 and porous phase 2 when there is a difference in the average fluid pressure between the two phases and (2) a vector transport that accounts for fluid flux across an averaging region when there are macroscopic fluid-pressure gradients present. The scalar transport that occurs between the two phases can produce large amounts of wave-induced attenuation. The scalar transport equation is derived using volume-averaging arguments and the frequency dependence of the transport coefficient is obtained. The dual-permeability vector Darcy law that is obtained allows for fluid flux across each phase individually and is shown to have a symmetric permeability matrix. The nature of the cross coupling between the flow in each phase is also discussed.

Assessment of the Surface Permeation Properties of Recycled Aggregate Concrete

Abstract: The water permeability, air permeability and surface permeability of recycled aggregate concrete (RAC) are compared with those of a control concrete made with natural aggregate. The study shows that the permeation properties of RAC depend on mix-design, conditions of curing and drying of samples. Relationships between permeability and other physical characteristics of concrete such as water absorption capacity and diffusivity are discussed. According to the criteria existing for ordinary concrete made with natural aggregate, RAC could be classified as being of moderate quality rather than poor quality. The testing methodology shows that some of the techniques used to measure the permeability of RAC need to be modified in order with the distinctive characteristics of this material.

The Use of Fick's Law for Modeling Trace Gas Diffusion in Porous Media

Abstract: Two models for combined gas-phase diffusion and advection in porous media, the advective-diffusive model (ADM) and the dusty-gas model (DGM), are commonly used. The ADM is based on a simple linear addition of advection calculated by Darcy's law and ordinary diffusion using Fick's law with a porosity–tortuosity–gas saturation multiplier to account for the porous medium. The DGM applies the kinetic theory of gases to the gaseous components and the porous media (or ‘dust’) to develop an approach for combined transport due to diffusion and advection that includes porous medium effect. The ADM and Fick's law are considered to be generally inferior for gas diffusion in porous media, and the more mechanistic DGM is preferred. Under trace gas diffusion conditions, Fick's law overpredicts the gas diffusion flux compared to the DGM. The difference between the two models increases as the permeability decreases. In addition, the difference decreases as the pressure increases. At atmospheric pressure, the differences are minor ( 10−13 m2) but may increase to about 2.7 for He at lower permeabilities of about 10−18 m2. A modified Klinkenberg factor is suggested to account for differences in the models.

Permeability evolution during the formation of gas hydrates in marine sediments

Abstract: [1] Fluxes of gas, energy, and fluid (water with dissolved gas) are known to control the distribution of gas hydrate and free gas in gas hydrate reservoirs, but theoretical studies have so far not focused on the effect of sediment properties (e.g., permeability) on these fluxes during the formation of gas hydrate deposits. Using a transient, one-dimensional, two-phase (gas hydrate and fluid) numerical model based on a coupled conservation approach, we examine permeability clogging during gas hydrate formation in end-member porous media and fractures initially lacking hydrate and determine the resulting changes in fluid and advective energy flux. Gas hydrate accumulates most rapidly at depth in both systems, a result consistent with borehole logging and seismic studies on the Blake Ridge. Consideration of the ratio of surface area to fluid volume explains model results that imply more rapid permeability reduction in the porous media system and more uniform hydrate formation as a function of depth in the fracture system. Depending on fluid flux, fracture aperture, or pore sizes, and other factors, the timescale for permeability clogging due to the accumulation of gas hydrate ranges from thousands to millions of years. Regenerating gas hydrate to a concentration of 10–15% of pore space in marine settings with fluid fluxes characteristic of Hydrate Ridge or Blake Ridge requires 103–105 years, meaning that hydrate deposits in these settings cannot be viewed as a naturally renewable resource. These results also imply that significant time is required to reestablish gas hydrate deposits after large-scale dissociation events associated with global-scale climate change.

Foam Mobility in Heterogeneous Porous Media

Abstract: Foamed-gas injection is a promising technique for achieving mobility control and diverting fluid to low permeability strata within heterogeneous porous media. However, the factors most important for diversion have not been stated and explored definitively. Gas mobility in the presence of foam depends critically on foam-bubble size; bubble size may vary with permeability, porosity, surfactant type and concentration, and the velocity of liquid and gas. This paper adopts a local equilibrium, scaling perspective to describe quantitatively foamed-gas mobility within heterogeneous porous media. Conventional and percolation network scaling ideas are employed. A new closed form expression for the fraction of mobile gas within a foam is derived using statistical network concepts. Additional equations indicate, for instance, that porosity plays an important role in setting gas mobility because it reflects the relative abundance of foam germination and termination sites per unit volume of porous media. Liquid velocity is also important because gas mobility is inversely proportional to this factor.

Velocity-permeability relations within hydraulic units

Abstract: Relationships between seismic velocity and permeability have been difficult to establish. I show that by grouping and sorting rocks into hydraulic units, we can establish relationships between velocity and permeability. The hydraulic units are calculated from measured porosity and permeability values. Correlation between velocity and permeability is significant within each hydraulic unit (the correlation coefficient, R2, lies in the range 0.65–0.87). This correlation is an extension of the match between porosity and permeability within a hydraulic unit. I show how the compaction and cementation history of a sediment can have effects on its physical properties such as porosity and permeability and on its seismic properties. The measured velocity data are further approximated with the Biot model. The velocity‐permeability relation and modeling results are demonstrated for a large data set of laboratory measurements. The good match between calculated and measured data demonstrates that this relation can be u...

Brittle structures and their role in controlling porosity and permeability in a complex Precambrian crystalline-rock aquifer system in the Colorado Rocky Mountain Front Range

Abstract: Expansion of the Denver metropolitan area has resulted in substantial residential development in the foothills of the Rocky Mountain Front Range. This type of suburban growth, characteristic of much of the semiarid intermountain west, often relies on groundwater from individual domestic wells and is exemplified in the Turkey Creek watershed. The watershed is underlain by complexly deformed and fractured crystalline bedrock in which groundwater resources are poorly understood, and concerns regarding groundwater mining and degradation have arisen. As part of a pilot project to establish quantitative bounds on the groundwater resource, an outcrop-based geologic characterization and numerical modeling study of the brittle structures and their controls on the flow system was initiated. Existing data suggest that groundwater storage, flow, and contaminant transport are primarily controlled by a heterogeneous array of fracture networks. Inspections of well-permit data and field observations led to a conceptual model in which three dominant lithologic groups underlying sparse surface deposits form the aquifer system—metamorphic rocks, a complex array of granitic intrusive rocks, and major brittle fault zones. Pervasive but variable jointing of each lithologic group forms the “background” permeability structure and is an important component of the bulk storage capacity. This “background” is cut by brittle fault zones of varying structural styles and by pegmatite dikes, both with much higher fracture intensities relative to “background” that likely make them spatially complex conduits. Probabilistic, discrete-fracture-network and finite-element modeling was used to estimate porosity and permeability at the outcrop scale using fracture network data collected in the field. The models were conditioned to limited aquifer test and borehole geophysical data and give insight into the relative hydraulic properties between locations and geologic controls on storage and flow. Results from this study reveal a complex aquifer system in which the upper limits on estimated hydraulic properties suggest limited storage capacity and permeability as compared with many sedimentary-rock and surficial-deposit aquifers.

A flexible wall permeameter for measurements of water and air coefficients of permeability of residual soils

Abstract: This paper describes the development of a flexible wall permeameter apparatus for measuring the water and air coefficients of permeability of residual soils. Water and air coefficients of permeabil...

Permeability evolution during progressive development of deformation bands in porous sandstones

Abstract: [1] Triaxial deformation experiments were carried out on large (0.1 m) diameter cores of a porous sandstone in order to investigate the evolution of bulk sample permeability as a function of axial strain and effective confining pressure. The log permeability of each sample evolved via three stages: (1) a linear decrease prior to sample failure associated with poroelastic compaction, (2) a transient increase associated with dynamic stress drop, and (3) a systematic quasi-static decrease associated with progressive formation of new deformation bands with increasing inelastic axial strain. A quantitative model for permeability evolution with increasing inelastic axial strain is used to analyze the permeability data in the postfailure stage. The model explicitly accounts for the observed fault zone geometry, allowing the permeability of individual deformation bands to be estimated from measured bulk parameters. In a test of the model for Clashach sandstone, the parameters vary systematically with confining pressure and define a simple constitutive rule for bulk permeability of the sample as a function of inelastic axial strain and effective confining pressure. The parameters may thus be useful in predicting fault permeability and sealing potential as a function of burial depth and fault displacement.

Mechanism controlling permeability change in clays due to changes in pore fluid

Abstract: When a water-saturated clayey soil is leached with an organic fluid such as heptane, it has been found that under some conditions the hydraulic conductivity (or the permeability) increases manyfold. While it is generally agreed that physicochemical changes (e.g., compression of double-layer thickness) and the consequent alterations to the internal fabric (e.g., shrinkage of clusters) are responsible in most cases for such an increase, the underlying mechanism is not clearly understood. Two possible mechanisms are (1) formation of a few macrocracks due to shrinkage of clusters and (2) uniform increase in intercluster porosity throughout the volume of the soil due to shrinkage of clusters. The objective of the study presented here is to examine the most plausible mechanism of permeability increase caused by leaching. With the aid of Olsen’s permeability equation based on the cluster model, Poiseuille’s law for laminar fluid flow between two parallel plates, physicochemical theories, and experimental permeability data, it is shown that the formation of macrocracks is the most plausible mechanism of permeability increase.

The effect of temperature, the nature of the pore fluid, and subyield differential stress on the permeability of phyllosilicate-rich fault gouge

Abstract: [1] Elevated temperatures and subyield deviatoric stresses were applied to oriented natural samples of clay-bearing fault gouge under pressure in order to establish their effects on the water and argon permeability under conditions closer to those found at depth in fault zones. It was found that the application of subyield differential stress normal to the fault plane resulted in a permeability reduction by a factor of ∼2. Argon permeability showed a constant rate of decrease with increasing temperature up to 150°C and limited time-dependent compaction at temperature. More substantial time-dependent compaction at elevated temperature with water pore fluid reduced the permeability by a factor of 3 over ∼6 days. When water-wet, water permeability increased with temperature up to ∼80°C, and then reduced at higher temperatures. This behavior is interpreted to be due to a combination of thermal compaction and the destabilization of structured water films coating pore throats at elevated temperatures. Increasing the pore fluid pressure did not appear to play an important role in stabilizing water films in pore throats. Based on these results, the reduction of permeability due to blocking of pore throats by structured water films is unlikely to play a role in the deeper part of fault zones. However, in the shallow crust this permeability reduction mechanism may be responsible for a significant lowering of the permeability. This has important implications for fluids that may be traveling up large faults or for the modeling of fluid flow around waste repositories, particularly when these may create temperature perturbations by their presence.

Upscaling Permeability Measurements Within Complex Heterolithic Tidal Sandstones

Abstract: We investigate numerically the effect of sample volume on the effective single-phase permeability of heterolithic tidal sandstones, using three-dimensional models reconstructed directly from large rock specimens measuring ∼45 × 30 × 15 cm. We find that both individual and averaged effective permeability values vary as a function of sample volume, which indicates that permeability data obtained from core-plugs will not be representative at the scale of a reservoir model grid-block regardless of the number of measurements taken. However, the error introduced by averaged data may be minimized using the appropriate averaging scheme for a given facies type and flow direction.

Fabric, porosity and water permeability of calcarenites from Apulia (SE Italy) used as building and ornamental stone

Abstract: The purpose of the study was to determine the properties influencing the performance of Apulian calcarenites as past and present building and ornamental stone. A comparison of qualitative fabric observations in petrographic thin sections and quantitative measurements of physical properties, including porosity, pore size distribution and permeability, is discussed. The results suggest that the mercury intrusion porosimetry data and qualitative fabric analysis related to pore size distribution are the most critical observations regarding the potential for the stone to take in and hold water and hence to weather.

Critical stress-related permeability in fractured rocks

Abstract: Abstract Conventional wisddom has always assumed that fluids prefer to flow along fractures that are orientated parallel to the maximum in-situ horizontal stress direction. These fractures have the lowest normal stresses across them and therefore provide the least resistance to flow movement. However more recent work (Barton et al. 1995) has suggested that those fractures that are orientated such that they experience a high ratio of shear to normal stress are most likely to flow. These critically stressed fractures are in a state of stress that is close to failure, allowing them to undergo a degree of shear. Even small shear displacements can cause significant dilation along a fracture surface as the two surfaces un-mate during sliding. This dilation results in a significant increase in fracture permeability, resulting in an increase in flow from these features. A review of past work reveals that this shear mechanism may be more important than previously thought. A case study from Sellafield in the UK is presented, where the critical stress technique has been successfully applied for predicting zones of enhanced permeability at the well scale. Difficulties for implementing the technique on a wider field wide scale are discussed.

Permeability change during experimental fault smearing

Abstract: [1] Smear sourced from shale or clay is thought to provide an across-fault barrier to fluid flow in sedimentary rocks. Permeability changes of this phenomenon were investigated using a triaxial testing machine. Experimental specimens consisting of interlayered siltstone (low initial permeability, ∼10−16 m2) and sandstone (high initial permeability, ∼10−13 m2) were subjected to 20, 30, and 40 MPa of effective normal stresses on a precut surface, dividing each specimen at a 30° angle to its axis, at axial shortening velocities between 0.14 and 1.41 μm s−1. Permeability was measured by the oscillation method, and permeability changes categorized in three distinct regimes that corresponded to progressively increasing rock deformation: regime 1, rapid reduction due to compaction of the siltstone layer prior to fault movement; regime 2, constant and minimum permeability while the smear developed; and regime 3, permeability recovery caused by smear thinning and loss of smear continuity. The duration of regime 2 and of smear continuity recorded provide measures of the sealing potential produced by the smear. The shale smear factor SSF, defined as (fault throw)/(thickness of low-permeability layer), shows that there may be a relation between seal potential and effective normal stress. Both factors in SSF can reach higher values when effective normal stress is 40 MPa than when that is ≥30 MPa.

Method and device for evaluating physical parameters of an underground deposit from rock cuttings sampled therein

Abstract: The invention concerns a method and a device for evaluating simultaneously and with the same equipment, physical parameters such as absolute permeability and porosity, of fragments extracted from a fragmented natural or artificial porous environment. It consists in measuring the porosity of the fragments with helium pressure tests in accordance with a protocol known per se. The enclosure (1) which contains them is communicated with a reservoir (11) of volume likewise known per se, containing helium under pressure known per se. From the equilibrium of the pressures can be deduced the value of the solid volume. The rock envelope volume and the mass of fragments are also measured. By combining those measurements, the porosity of the samples as well as the rock density is determined. Then their permeability is measured by immersing them in a viscous fluid and communicating the enclosure with the viscous fluid under specific pressure contained in a container (9) so as to compress the gas trapped in the pores of the rock, in accordance with two different protocols. By modelling the evolution of the pressure or the volume in the enclosure, and iterative adjustment, the values of the physical parameters are determined. The invention is applicable, for example, to petrophysical measurements from bore cuttings or crushed cores.