Showing papers on "Permeability (earth sciences) published in 1990"

Biofilm growth and the related changes in the physical properties of a porous medium: 1. Experimental investigation

Abstract: An experimental investigation was conducted to quantify the permeability reduction caused by enhanced biological growth in a porous medium. Studies were conducted using sand-packed column reactors for which variations in piezometric head, substrate concentration, and biomass measured as organic carbon were monitored in space and time. Methanol was used as a growth substrate. Permeability reductions by factors of order 10−3 were observed. The data show that a limit on permeability reduction exists, having a magnitude of 5 × 10−4 in the present study. The limit on permeability reduction and the existence of high densities of bacteria in substrate depleted zones are explained with an open pore model. Permeability reduction was observed to correlate well with biomass density for values less than about 0.4 mg/cm3, and exhibited independence at higher densities.

Three-phase relative permeability of Berea sandstone

Abstract: Reservoir engineering calculations frequently require consideration of coexisting oil, water, and gas phases. Such three-phase flow occurs when oil is displaced by simultaneous gas/water flow as in CO{sub 2}, water-alternating-gas flooding, steam-flooding, or other enhanced recovery processes. For this reason, reservoir simulators generally include three-phase relative permeability prediction methods. This paper presents two- and three-phase relative permeabilities measured on a water-wet fired Berea sandstone core with a fully automated steady-state method to investigate prediction methods experimentally.

Biofilm growth and the related changes in the physical properties of a porous medium: 2. Permeability

Abstract: Growth of a biofilm in a porous medium reduces the total volume and the average size of the pores. The change in the pore size distributions is easily quantified when certain geometric assumptions are made. Existing models of permeability or of relative permeability can be manipulated to yield estimates of the resulting reduction in permeability as a function of biofilm thickness. The associated reductions in porosity and specific surface can be estimated as well. Based on a sphere model of the medium, the Kozeny-Carman permeability model predicts physically realistic results for this problem. Using a cut-and-random-rejoin-type model of the medium, the permeability model of Childs and Collis-George yields qualitatively reasonable results for this problem, as does a generalization of the relative permeability model of Mualem. Permeability models of Kozeny-Carman and of Millington and Quirk lead to unrealistic results for a cut-and-random-rejoin-type medium. The Childs and Collis-George and the Mualem models predict that the permeability reduction for a given volume of biomass is greatest when the porous medium has uniform pore sizes.

Sand-bentonite liners: predicting permeability from laboratory tests

Abstract: Soil–bentonite mixes are frequently used as impervious blankets in waste disposal projects. Numerous results of laboratory permeability tests are presented for sands containing up to 33% bentonite....

Mercury intrusion and permeability of Louiseville clay

Abstract: Several theories have been proposed to correlate the permeability (hydraulic conductivity) with the pore-size distribution of soils, and it seemed interesting to determine if these theories could b...

Elements of Soil Mechanics

Abstract: Classification and identification properties of the soil soil water, permeability and flow shear strength of soils elements of stress analysis stability of slopes lateral earth pressure earth retaining strutures bearing capacity of soils foundation, settlement soil compression rate of foundation settlement compaction and soil mechanics aspects of highway designs soil suction and partial saturation critical state theory site investigation and ground improvement.

Macroscopic parameters from simulations of pore scale flow

Abstract: We simulate two-phase flow in a porous medium, which is represented by random, isotropic two- and three-dimensional networks containing up to 80 000 interconnected pore spaces. The simulations are sufficiently large that macroscopic properties of the flow may be determined. For unstable viscous floods, we show that the displacements are compact with a fractal interface between the fluids. The fractal dimension is found as a function of viscosity ratio. For invasion percolation, where the displacement is controlled by capillary forces, and for viscous fingering, we calculate relative permeabilities in an averaged two-phase Darcy equation, which we show are functions of mean saturation. The relative permeabilities also depend on flow rate, which means that the two-phase Darcy equation is nonlinear, even with microscopic linear Poiseuille flow.

Stability of an acid front moving through porous rock

Abstract: As an acid flows through porous rock, it etches the rock and so increases the permeability. This propagating reaction front suffers an instability, rather like the viscous fingering instability, in which the acid prefers to follow high-permeability channels which it has already etched. We have examined the linear stability, obtaining analytic results for small and large wavenumbers and for small variations of the permeability, and obtaining numerical results in other cases.

Gas permeability changes in rock salt during deformation.

Abstract: Abstract Gas permeability and porosity measurements have been made during hydrostatic and triaxial quasi-static, stress-rate controlled compression tests. The permeability and porosity of the as-received samples decrease significantly as a result of hydrostatic loading. These changes are largely irreversible, and are believed to “heal” or return the rock to a condition comparable to its undisturbed state. The permeability can increase more than 5 orders of magnitude over the initial (healed) state as the samples are deformed during deviatoric loading. The gas permeability and porosity changes are consistent with a flow model based on the equivalent channel concept. A model of microcrack initiation and growth based on the frictional sliding crack suggests the flow paths initially develop along grain boundaries and then along axial intragranular tensile cracks. Post-test visual observations support the model predictions.

The Averaging Process in Permeability Estimation From Well-Test Data

Abstract: Permeability estimates from the pressure derivative or the slope of the semilog plot usually are considered to be averages of some large ill-defined reservoir volume. This paper presents results of a study of the averaging process, including identification of the region of the reservoir that influences permeability estimates, and a specification of the relative contribution of the permeability of various regions to the estimate of average permeability. The diffusion equation for the pressure response of a well situated in an infinite reservoir where permeability is an arbitrary function of position was solved for the case of small variations from a mean value. Permeability estimates from the slope of the plot of pressure vs. the logarithm of drawdown time are shown to be weighted averages of the permeabilities within an inner and outer radius of investigation.

Lessons learned from compacted clay liner

Abstract: A highly plastic clay liner was compacted in the field with full‐sized equipment to an average of more than 100% of standard Proctor maximum dry density. The average field permeabilities of two sections of the liner, as measured with four sealed double‐ring infiltrometers and a 16×16ft(4.88×4.88m) pan lysimeter, were 3×10-5 and 10×10-5cm/s. Laboratory permeability tests were conducted on samples compacted in the laboratory by three procedures, only one of which gave a reasonable prediction of the permeability of the liner. The high permeability of the liner was caused by the failure to achieve the two “basic” compaction objectives that govern the permeability of compacted clays. The basic objectives (destruction of soil clods and bonding between lifts) and 17 other key factors that influence the permeability of compacted clays explain the performance of the liner and provide a basis for understanding how to construct liners to avoid such high permeabilities.

Thermal effects of compaction‐driven groundwater flow from overthrust belts

Abstract: The thermal consequences of compaction-driven groundwater flow resulting from overthrusting are studied with a two-dimensional numerical model. The model represents a foreland basin 5 km deep and 400 km wide and is used to estimate quantitatively the magnitude, direction, and thermal consequences of fluid expulsion. Model simulations in which the permeability structure is homogeneous lead to maximum Darcy velocities of the order of 1 cm/yr; temperature in the foreland increases by less than 5°C. A sensitivity analysis reveals that temperature in the foreland may be increased an additional 2°C by increasing porosity, speed of thrusting, or heat flow. However, if the area underneath the thrust sheet is not effectively sealed, fluid escapes upward and thermal perturbations in the foreland are negligible. Models with basal and midlevel aquifers produce maximum Darcy velocities of the order of 4 cm/yr, but temperature in the foreland again increases by less than 5°C. Models in which hot fluids at depth are channeled directly upward through a high-permeability pathway can produce temperature perturbations as high as 50°C, over limited areas. Modeling results suggest that the expulsion of pore fluids from orogenic zones through the process of sediment compaction is likely to produce significant thermal perturbations in adjacent forelands only over areas that are spatially restricted, or spatially and temporally restricted.

Minipermeameter-Based Study of Permeability Trends in Channel Sand Bodies (1)

Abstract: Permeability is the single most important factor influencing fluid flow in reservoirs. To map the distribution of this property in three dimensions, we did outcrop studies with a minipermeameter. Ribbon-like distributary channel sand bodies exposed along the Yorkshire coast of England were selected as study objects. Results show a close connection between depositional facies and permeability in the ribbon channels, as witnessed by the five facies-related permeability classes. Semivariogram analyses and correlation of permeability profiles indicate that permeability measurements tend to be unrelated at distances exceeding 2-3 m. Thus, the detailed permeability patterns seen in these distributary channel sand bodies in well bores may be significantly different from the perm ability distributions in the vicinity of the well. The short permeability correlation length implies that at the macroscale or facies level, flow units are expected to be strongly lenticular. Models of the spatial flow-unit distribution in this sand body type should mimic such a pattern. By using a scaling-up procedure, the complex macroscale pattern could be used to generate models of the gross permeability distribution in ribbon-like channel sand bodies at less refined averaging scales. In the active fills of ribbon-like channel sand bodies, the classical upward decrease in permeability was rarely seen. The zones with highest permeability were mostly present in the central to uppermost parts of these sand bodies. These trends, along with the lensoid shape of the permeability class zones, should be maintained in detailed modelings and simulations of this type of reservoir sand body. Clay content, grain size, and stratification type seem to be the factors most strongly influencing permeability in the investigated sand bodies.

Permeability estimation from velocity anisotropy in fractured rock

Abstract: Cracks in a rock mass subjected to a uniaxial stress will be preferentially closed depending on the angle between the fracture normal vectors and the direction of the applied stress. If the prestress fracture orientation distribution is isotropic, the effective elastic properties of such a material after application of the stress are then transversely isotropic due to the overall alignment of the cracks still open. Velocity measurements in multiple directions are used to invert for the probability density function describing orientations of crack normals in such a rock. This is accomplished by expanding the crack orientation distribution function into generalized spherical harmonics. The coefficients in this expansion are functions of the crack density and the crack aspect ratio distribution. The information on fracture distribution obtained from the velocity inversion allows an estimation of the anisotropic permeability of the fractured rock system. Permeability estimates are based on the number of cracks open of each aspect ratio, and the contribution of a given crack is weighted by the cosine of the angle between the crack and the direction of the applied pressure gradient. This approach yields a prediction of permeability as a function of the angle from the uniaxial stress axis. The inversion for crack orientation is applied to ultrasonic velocity measurements on Barre granite, and permeability predictions for this sample are presented. The inversion results are good and reproduce velocity measurements well, and the permeability predictions show some of the expected trends. Initial comparisons of the predictions with available permeability data, however, show deviations, suggesting that further information on partial crack closure and connectivity of cracks should be included into the permeability model.

In Situ Measurements of Soil Physical Properties by Acoustical Techniques

Abstract: Knowledge of porosity, air permeability, pore structure, and surface layering of soils is desirable in agricultural research. The conventional techniques are invasive, typically requiring sample extraction. When monitoring seasonal changes, the conventional methods disrupt considerable proportions of the test plot surface. The sample area used in conventional measurements may be too small to represent the variations in the test plot. Here, the feasibility of acoustical techniques for monitoring surface air porosity (total porosity minus volumetric water content), air permeability, and pore structure and the variation of these properties to depths of several centimeters below the surface is demonstrated. Test soil plots prepared using three soil materials, masonry sand, a Grenada silt loam (fine-silty, mixed, thermic Glossic Fragiudalf) and a Catalpa silty clay (fine, montmorillonitic, thermic Fluvaquentic Hapludoll), were considered. Variation in water content and compaction of each soil material were considered. Both acoustic reflection and transmission measurements were made in the audio-frequency range. The soils are modeled as air-filled, rigid-framed porous media. The acoustic-reflection measurements involve analysis of propagation data from a small loudspeaker and two vertically separated microphones. The acoustic-transmission measurement requires a specially designed probe microphone. Analysis of the acoustic-reflection data yields qualitative indications of the relative air permeability of the soils. The transmission measurement yields information about the changes in air permeability with depth. Quantitative information on surface porosity, air permeability, tortuosity, and layering is presented by fitting theoretical predictions based on the soil model to the measured sound reflection and transmission data. The acoustically determined air porosity for the soils considered is within 10% of the values determined by gravimetric techniques. (H. Hess and K. Attenborough on leave from the Dep. of Engineering Mechanics, The Open Univ., Walton Hall, Milton Keynes MK7 6AA, England.)

Method and apparatus for testing subsurface formations

Abstract: A method and apparatus for testing subsurface formations, particularly a formation having a permeability less than about 10 millidarcies is disclosed. The test is made by use of a down hole test tool designed in such a way as to control the decompression of the fluid as it enters the tool. The formation characteristics are determined by analyzing the pressure versus time plot resulting from the test. Such characteristics as flow rate of liquid phase mud through the mud cake, formation permeability, formation pressure, invasion diameter, and the extent of supercharging, can be determined. The entire test takes no longer than a few minutes, versus hours and sometimes days for more conventional techniques and test tools.

The impact of synthetic leachate on the hydraulic conductivity of a smectitic till underlying a landfill near Saskatoon, Saskatchewan

Abstract: The impact of leachate on the hydraulic conductivity, k, of a glacial till used in the contraction of a liner for a landfill near Saskatoon, Saskatchewan, is evaluated. Low-gradient triaxial permeability testing of the water-moulded till over a 7-month period with six pore volumes of test leachate at a hydraulic gradient of approximately 100 gave a hydraulic conductivity of 3.0 × 10−9 cm/s, compared with 6.0 × 10−9 cm/s for the water-permeated sample at the same gradient. The k was also evaluated at gradients of 20 and 50 during water permeation and found to be 8.0 × 10−9 and 6.8 × 10−9 cm/s, respectively. The slight decrease in k with increase in gradient was attributed to a decrease in void ratio, resulting from a net increase in applied effective stress at the outflow end of the specimen. An assessment of the clay mineral composition of the till at the end of permeability testing did not show collapse of the smectite peak. Instead, the leachate appeared to have actually enhanced the smectite peak relat...

Thermoelasticity and the formation of black smokers

Abstract: Darcy's Law flow in a permeable medium, consisting of uniform parallel evenly spaced fractures, is used to elucidate how thermoelastic effects may modify the permeability and flow in fracture-controlled hydrothermal systems. Some simple permeability models are then used to investigate whether black smoker venting can result from focussing of low velocity porous flow into fractures at shallow depths (≃ 100 m.). The models indicate that: (a) thermoelastic processes may be important in controlling the temporal evolution of hydrothermal upflow zones; (b) permeability structure, not just the bulk value of the permeability, may be critical for the formation of black smokers; (c) a small zone extending to a depth of ≃ 100 m containing a few fractures a factor of 2 or more wider than average may be sufficient to focus upflow into discrete vents provided thermoelastic and chemical effects seal parts of the upper crust.

Geological/Stochastic Mapping of Heterogeneity in a Carbonate Reservoir

Abstract: Two major problems in estimating interwell porosity and permeability patterns are estimating permeability profiles in uncored wells and interpolating wellbore information between wells. This paper reports on a technique combining core analysis, rock fabrics, and wireline logs used to estimate permeability values at 1-ft intervals in 32 wells in Section 15 of the Dune field. Stochastic geologic interpolation was generated with a geostatistical method known as conditional simulation. Simulation of water-flooding showed that the stochastic realizations with a low degree of continuity gave the most realistic results. Infill drilling to achieve an average well spacing of 2.5 acres increased recovery by 27 to 32%.

Gas migration in discrete fracture networks

Abstract: A mathematical model is presented for the upward pulsating gas-water displacement, from a gas source at a constant production rate or pressure at the bottom boundary to a constant pressure boundary at the top boundary. The study shows a complicated flow phenomenon caused by the unequal advance of the gas in fractures of different permeability or different inclinations. The results show that the gas breakthrough at the surface is governed by the high permeability fractures. At a constant rate of gas production the breakthrough is associated with a gas pressure drop at the bottom gas boundary. As a result, downward back flow takes place until the gas pressure builds up and reinitiates the upward displacement. It is concluded that calculations with average properties of the fracture permeability, for example, using the continuum approach, will underestimate the breakthrough time of the gas at the surface. Under constant pressure boundary conditions at the top of the cavern the average permeability will overestimate the amount of gas carried out by the fracture network. Under constant flow rate boundary conditions at the top of the cavern (i.e., bottom of the flow domain), calculations with average fracture permeability will overestimate the pressure in the cavern. The problem is of practical interest for low-level radioactive waste repositories located in hard rock below the sea bottom.