Showing papers on "Permeability (earth sciences) published in 1982"

Porous media equivalents for networks of discontinuous fractures

Abstract: The theory of flow through fractured rock and homogeneous anisotropic porous media is used to determine when a fractured rock behaves as a continuum. A fractured rock can be said to behave like an equivalent porous medium when (1) there is an insignificant change in the value of the equivalent permeability with a small addition or subtraction to the test volume and (2) an equivalent permeability tensor exists which predicts the correct flux when the direction of a constant gradient is changed. Field studies of fracture geometry are reviewed and a realistic, two-dimensional fracture system model is developed. The shape, size, orientation, and location of fractures in an impermeable matrix are random variables in the model. These variables are randomly distributed according to field data currently available in the literature. The fracture system models are subjected to simulated flow tests. The results of the flow tests are plotted as permeability ‘ellipses.’ The size and shape of these permeability ellipses show that fractured rock does not always behave as a homogeneous, anisotropic porous medium with a symmetric permeability tensor. Fracture systems behave more like porous media when (1) fracture density is increased, (2) apertures are constant rather than distributed, (3) orientations are distributed rather than constant, and (4) larger sample sizes are tested. Preliminary results indicate the use of this new tool, when perfected, will greatly enhance our ability to analyze field data on fractured rock systems. The tool can be used to distinguish between fractured systems which can be treated as porous media and fractured systems which must be treated as a collection of discrete fracture flow paths.

Characterization of drained and undrained response of thermally loaded repository rocks

Abstract: The fluid pressure and mechanical response of a potential repository rock to heating is shown to be characterized by the isothermal parameters of the classic stress-strain theory for a porous medium, in combination with some nonisothermal parameters describing the fluid, solid, and pore volume expansivities. The isothermal coefficients are described in terms of easily interpretable parameters by noting that the fluid response can be formulated within the limits of drained and undrained behavior. The low permeability-high thermal conductivity environment generally considered to be ideal for nuclear waste storage would appear to favor an undrained response, at least within the isolated pores and cracks of a fractured rock medium. Several cases are presented that provide a qualitatively correct demonstration of the effects of heating in this environment. These include fluid pressure increases in excess of temperature-induced increases in in situ stress, elastic strain and the potential for inelastic crack propagation, and porosity-permeability augmentation. If the rocks are dry, or of a high permeability such that fluid flow takes place at constant fluid pressure, similar rock material alterations are possible. This follows from the fact that when the temperature is raised to some high value, say 80° or 90°C, and then decreased to its ambient value, the final volume of a polycrystalline substance will generally be greater than the initial one. Hence the effect of temperature is irreversible because of the differential thermal expansion of the composite mineral grains and the generation of new grain boundaries. The increase in porosity during such a heating episode is calculable and empirically related to increases in permeability.

Hydraulic fracturing propping agent

Abstract: A high strength propping agent for use in hydraulic fracturing of subterranean formations comprising solid, spherical particles having an alumina content of between 40 and 60%, a density of less than 3.0 gm/cc and an ambient temperature permeability of 100,000 or more millidarcies at 10,000 psi.

Steady-State Measurements of Relative Permeability for Polymer/Oil Systems

Abstract: Means for increasing tertiary oil recoveries from previously waterflooded viscous oil reservoirs are receiving added attention today as a result of industry-wide efforts to improve U.S. oil producing rates and reserves. Injection of a bank of polymer solution that precedes injection of a miscible slug (e.g., a micellar fluid) can reduce reservoir permeability contrasts and result in improvement of the sweep efficiency of the process. To evaluate the potential magnitude of improved recovery and economics of prior polymer slug injection, there is a need for basic polymer/oil relative permeability data for use in performance evaluation calculations. The observation in these studies was that the presence of polymers in the water phase had a significant and consistent effect, lowering water relative permeability over the entire water saturation range. 15 refs.

Empirical equations for estimating two-phase relative permeability in consolidated rock

Abstract: The permeability of a porous rock to a saturating fluid is determined by the geometry of the rock pore system and not by the physical properties of the fluid. This general statement assumes the absence of a chemical reaction between the rock and fluid, and a single homogeneous fluid phase. If more than one fluid is present, permeability to any fluid depends not only on the geometry of the rock pore system but also on the fraction and distribution of each fluid phase, the interfacial tensions, the saturation history, and possibly other factors. Although direct prediction of relative permeability from theoretical considerations is a worthwhile objective, the most successful techniques for making these predictions are essentially empirical. Rather than attempting a theoretical solution to the problem, the authors have used an empirical approach. In their study a rather extensive set of relative permeability data was compiled, and conventional stepwise linear regression analysis techniques were used, to develop prediction equations from the laboratory data. This procedure is designed to produce a satisfactory fit of the data with a minimum of terms in the equation; it is not intended to provide the best possible data fit.

Effects of pressure and partial water saturation on gas permeability in tight sands: experimental results

Abstract: Effective permeability to gas with various degrees of brine saturation has been measured in the laboratory for several very tight sandstones from the Spirit River formation of Alberta, Canada. Gas permeability as low as 20x10/sup -9/ darcy was measured successfully with a pulse-decay permeameter with nitrogen as the mobile fluid. Results show that gas permeability depends very strongly on the degree of saturation, with 40% saturation causing permeability to decrease an order of magnitude relative to the dry rock. Therefore, accurate knowledge of in-situ saturations is crucial before natural-gas production rates can be estimated in these formations. 9 refs.

Permeability, percolation and statistical crack mechanics

Abstract: The permeability of sands and soils seems to be adequately described by Darcy's law, but the permeability of rocks is complicated by a number of factors related to the probability of crack intersections. During the last few years a statistical theory of fragmentation has been developed, which has been successful in explaining the observed behaviour of rocks. In this paper, a theory of permeability is developed which draws on the concepts employed in previous work. The permeability involves three factors, the average fluid flux per crack, the number of cracks per unit area, and the fraction of cracks that are not isolated. Probabilistic ideas are used in connection with the hydrodynamic theory of flow through a single crack to develop an integral expression for permeability. The result has the form of Darcy's law for anisotropic media. Although the current work is motivated by the need to develop optimized oil-shale retorts, it is believed that the theory can be applied to a variety of other problems. For the covering abstract of the symposium see TRIS 452576. (Author/TRRL)

Permeability reduction in subterranean reservoirs

Abstract: A method for selectively reducing the permeability of the higher permeability zones of a subterranean reservoir having heterogeneous permeability, such permeability reduction occurring a substantial distance away from a well in which there is injected into the reservoir an aqueous solution or solutions of a water-soluble polymer, a material capable under certain conditions of at least partially cross-linking the polymer to form a gelatinous precipitate, and a water-soluble alkaline material in an amount sufficient to maintain the pH of the polymer-containing composition above about 9 until the composition has passed a substantial distance through the reservoir.

Tight Gas Sands-Permeability, Pore Structure, and Clay

Abstract: Gas permeability has been measured on a suite of cores from the Spirit River tight gas sand of western Alberta and on two samples from the Cotton Valley formation of east Texas. Using nitrogen as the mobile fluid, we have measured permeability as a function of partial water saturation at in-situ levels of pore pressure and confining pressure. Samples from both locations show strong dependence of permeability (k) on effective pressure and on the degree of water or brine saturation. The validity of Darcy's law in the microdarcy range has been verified in a dry Spirit River sample. Extensive thin-section, x-ray diffraction, and scanning electron microscope (SEM) studies have been conducted. The primary clays in Spirit River and Cotton Valley cores are chlorite and illite. In one sample we measured k vs. saturation first with distilled water and then with a 2% KCl brine solution and saw no significant change in permeability behavior. By observing the effects of pressure, partial saturation, and salinity on permeability in these samples, we can deduce several important characteristics of the pore structure and can evaluate the relative importance of clay content.

On the relationship between formation resistivity factor and porosity

Abstract: A theory on the relationship between formation resistivity factor and porosity is presented. This theory considers that, from the standpoint of the flow of electric current within a porous medium saturated with a conducting fluid, the pore space can be divided into flowing and stagnant regions. This assumption leads to a general expression, and formulas currently used in practice are special cases of this expression. The validity of the new expression is established by the use of data corresponding to sandstones and packings and suspensions of particles. For the case of natural rocks, the theory confirms Darcy's equation and gives an interpretation of the physical significance of the so-called cementation exponent.

Permeability of fractured rock: effect of fracture size and data uncertainties

Abstract: Equations are derived for equivalent Darcy permeability of a fracture system that consists of nonextensive fractures having arbitrary orientations with respect to the rock block considered. It is shown that in the case of nonextensive fractures, one cannot proceed to the limiting process where the volume of the bounding rock block can be reduced to an arbitrarily small value. Therefore, the dimensions of the block along with the dimensions of the fractures appear in the equations for the nine components of permeability. This leads to a situation where the equivalent permeability matrix is not only nonsymmetric, but also it does not follow the tensorial rules of axis rotation. This leads to the conclusion that, in the case of nonextensive fractures, the equivalent permeability cannot be defined as a characteristic intrinsic property of the medium as is possible in the case of porous medium or in a fractured medium that has extensive fractures. To analyze the effect of uncertainties in the field data on the estimation of equivalent permeability, a 'second-order' statistical analysis is proposed. The method is quite general and can be used to analyze the propagation of parameter uncertainties in models. A numerical example using preliminary fracture data frommore » the Columbia River basalt in Washington State is presented. The mean and standard deviation of the equivalent permeability of a 5 X 5 m block is estimated. Assuming that each component of the equivalent permeability has log normal distribution, the probability of their assuming values different from the mean is found to be significant. This points out the uncertainty that would be inherent in the flow simulation, if the mean value of permeability is used.« less

Use of swelling clays to reduce permeability and its potential application to nuclear waste repository sealing

Abstract: The injection of swelling-clay slurries into joints or faults at a deep-burial nuclear waste disposal site may result in significant permeability reductions for the effective containment of radioactive wastes. In an experiment conducted to illustrate the permeability change accompanying clay swelling, a coarse stone with interconnected pore spaces was injected with a clay-electrolyte slurry, modelling the pressure-grouting of a fractured repository rock. Subsequently, solutions with lower electrolyte concentrations were driven through the clay-filled stone, corresponding to migration of lower salinity ground-waters through the clay-grouted fracture. The initial injection procedure reduced the permeability of the stone from 1-10 darcies to 700 nanodarcies; the changes in solution composition decreased permeability by more than 2 additional orders of magnitude to 3 nanodarcies. For application at a nuclear waste repository, the electrolyte concentration of the injected clay slurry should be made higher than that of the ground-water in the host rock. Subsequent interaction of the ground-water with the clays would initiate swelling and create the additional, post-injection permeability reductions that may be important in preventing the escape of buried radioactive wastes. The measured permeability of the clay filling is considerably lower than that of cement tested for borehole plugging. Clays also have the advantage over cement and chemical grouts in that they are geologically stable at relatively low temperatures and have a high capacity for radionuclide adsorption.

Vadose Zone Permeability Tests: Summary

Abstract: Solutions to determine saturated hydraulic above a water table by means of constant head borehole infiltration tests are summarized and critiqued. Analytical solutions are available for open and partly cased boreholes and deep and shallow water table conditions. The formulas are based on various simplifying assumptions pertaining to soil properties and boundary conditions. None of the solutions account for capillary effects. For identical test conditions values of hydraulic conductivity calculated from these formulas may differ by as much as a few hundred percent.

Vadose Zone Permeability Tests: Steady State Results

Abstract: Free surface and saturated-unsaturated flow models are applied to the problem of constant head borehole infiltrat1on tests for determining saturated hydraulic conductivity above a water table. The free surface model follows the same general approach employed to develop analytical solutions, but this model does not suffer from some of the many simplifying assumptions regarding boundary conditions. Nonetheless, the results of steady state simulations with the free surface model agree rather well with the analytical solutions. The free surface approach provides a distorted view of the infiltration process. Saturated-unsaturated models used to simulate quasi-steady state conditions indicated that only a small volume of soil in the vicinity of the borehole is completely saturated with water. Based on saturated-unsaturated simulations in four different homogeneous, isotropic soils, an empirical solution is developed for deep water table conditions to estimate saturated hydraulic conductivity with improved accuracy. Due to the effects of borehole geometry unsaturated soil characteristics, water table depth, heterogeneity, and anisotropy, it is extremely difficult to develop a completely general formula.

Physical properties of rocks; porosity, permeability, distribution coefficients, and dispersivity

Abstract: Accompanying the increased emphasis on using the "solid earth" as a repository for waste as well as a source of fluids is the increased need for prediction of effects of these planned stresses on porous media. To fully describe the state of a fluid in a porous media it is necessary to specify: a) the pressure of the fluid, b) the composition of the fluid and e) the energy contained in the fluid. To describe and thus predict the flow and compositional variation of a fluid in porous media in time and space it is necessary to specify: a) the distribution of parameters affecting flow in the space of interest, b) initial conditions of pressure, composition and temperature or enthalpy, c) sources and sinks affecting flow and chemical variation in time and space, and d) boundary conditions. Presented in this paper are tabulations of data on porosity and permeability factors pertinent to flow; and distribution coefficients and dispersivity factors pertinent to chemical variation. Reported porosities vary from 0.000 to 87.3%, permeabilities range from "too low to measure" to 8.1 cm/sec. Because of the uncertainties of factors affecting laboratory determined dispersivities and distribution coefficients, only field based values are reported for these parameters.

Vadose zone permeability tests: unsteady flow.

Abstract: Saturated-unsaturated flow models are used to simulate transient conditions in four soils during constant head borehole infiltration tests in the vadose zone. Infiltration rate varies directly with saturated hydraulic conductivity and is also influenced by unsaturated soil properties, antecedent moisture conditions, anisotropy and borehole conditions. The method recommended by the U.S. Bureau of Reclamation to determine when to terminate a test may lead to overestimating saturated hydraulic conductivity. Simple graphical procedures are developed to overcome field problems associated with large water volume requirements or long time required to reach steady state by using early time date to estimate the steady infiltration rate.

The influence of permeability on compressional wave velocity in marine sediments

Abstract: To investigate the effect of permeability on the propagation of seismo-acoustic waves through marine sediments, a theoretical model based on Biot's equations is established which relates the compressional wave velocity measured at a fixed frequency to computed velocities at zero and infinite frequencies in terms of sediment porosity and permeability. The model is examined experimentally in a standard soil mechanics consolidation test (itself dependent, among other things, on sediment porosity and permeability) which has been modified to include measurements of compressional wave velocity at l MHz and shear-wave velocity at 5 kHz. This test allows the elastic modulus of the sediment frame to be assessed under different load conditions simultaneous with the velocity determinations. From a number of tests on different samples, five samples are chosen to typify the range of sediment sizes. The results show that the difference between the measured velocity at l MHz and the model-derived velocity at zero frequency increases with increasing particle size (from clays to fine sand), with decreasing porosity, and with increasing permeability. For sediments coarser than fine sand, the simple model breaks down, possibly because of the dominance of scattering/diffraction effects at the high frequency of the experiment. Within this limitation themore » model seems satisfactory to offer a capability of predicting the permeability of a sea floor sediment to an order of magnitude by the in situ measurement of seismic velocities over a wide range of frequencies; the prediction process requires a good in situ determination of sediment porosity such as that offered by electrical formation factor measurements.« less

Theoretical and experimental determination of matrix diffusion and related solute transport properties of fractured tuffs from the Nevada Test Site

Abstract: Theoretical and experimental studies of the chemical and physical factors which affect molecular diffusion of dissolved substances from fractures into a tuffaceous rock matrix have been made on rocks from G-Tunnel and Yucca Mountain at the Nevada Test Site (NTS). A variety of groundwater tracers, which may be useful in field tests at the NTS, have also been developed and tested. Although a number of physical/chemical processes may cause nonconvective transport of dissolved species from fractures into the tuff matrix, molecular diffusion seems to be the most important process. Molecular diffusion in these rocks is controlled by the composition of the groundwater through multicomponent effects and several rock properties. The porosities of the samples studied ranged from about 0.1 to 0.4. The constrictivity-tortuosity parameter ranged from 0.1 and 0.3 and effective matrix-diffusion coefficients were measured to be between 2 to 17. x 10{sup -7} c,{sup 2}/s for sodium halides and sodium pentafluorobenzoate. Total porosity was found to be the principle factor accounting for the variation in effective diffusion coefficients. The constrictivity-tortuosity factor was found to have a fair correlation (r = 0.75) with the median pore diameters measured by mercury intrusion. Measurements of bulk-rock electrical impedance changes with frequency indicate that the constrictivity factor has a maximum value of 0.8 to 1, but may be smaller. If the larger values are correct, then the diffusion paths in tuff are more tortuous than in granular media. Computation of the full diffusion-coefficient matrix for various tracers in J-13 well water from the NTS indicates coupling of the diffusion fluxes of all ionic species. These effects are being incorporated into a numerical model of multicomponent-matrix diffusion.

A New Method To Measure Directional Permeability

Abstract: The problem of measuring directional permeability by applying Darcy's Law has been unresolved for some time. This study shows that for 2-dimensional cases of anisotropy, 3 measurements must be made on a laboratory sample to calculate the maximum and minimum permeability from the data. These are (1) angle B, which shows the direction of flow with respect to the direction of maximum permeability, (2) angle A, which shows the direction of flow with respect to the direction of the driving force gradient, and (3) the R11 element of the resistivity tensor that appears in a special form of Darcy's Law.

Permeability of Grout Seals Surrounding Thermoplastic Well Casing

Abstract: An experimental test program was conducted to measure the longitudinal permeability of a grouted thermoplastic water well casing system. A neat cement grout, with and without calcium chloride or bentonite admixtures, was placed in the annulus of a simulated well. Test pressure and specimen configuration was shown to influence the measured coefficient of permeability. A neat grout with a water/cement ratio of 2.0 had a much higher permeability coefficient than the same grout with a water/cement ratio of 0.46. Once the bond line between the grout and casing was broken, the permeability of the system was generally higher than for the initial test. Specimens with a bell coupling included had a slightly higher permeability than specimens with straight pieces of casing. The effect on permeability of the admixtures in the grout was not conclusive. However, the addition of a bentonite slurry to the test water was observed to decrease the permeability coefficient when tested under low pressure. The permeability coefficient of the basic neat grout casing system ranged from 20 – 100 × 10 −5 cm/sec at low test pressure. It was concluded that the casing has an impact on the longitudinal permeability of the system since the coefficients of permeability measured were significantly higher than other published values. However, the coefficients of permeability measured were in the range of soils with low permeability such as silts.

An investigation of the permeability of Yorkshire Chalk under differing pore water and confining pressure conditions

Abstract: The pores and pore throats of chalk form a very complicated network of channels through which fluid flow takes place. Due to the nonrigid character of the rock fabric, variations in pore water and confining pressures can cause significant changes to the intrinsic porosity and permeability of the rock. This paper describes the results of permeability tests at a series of high confining pressures and low pore water pressures performed on chalk from East Yorkshire, England. It has been found that permeability variations are more sensitive to changes in the pore water pressure than to changes in the confining pressure. Scanning electron microscope studies have indicated that pressure solution phenomena and grain deformation are responsible for permanent changes in porosity and permeability induced during the tests. The possibility of such changes occurring in production reservoirs is highly relevant to the choice of exploitation strategy.

A theoretical study of pore water pressures developed in hydraulic fill in mine stopes

Abstract: The use of the model is demonstrated by analyses in which fill levels, water levels and the pore water pressures developed in the voids of the fill material are predicted. The effects on these features of various parameters, such as rate of pouring of the fill, fill permeability and drain location and performance, have been investigated.-from Authors

Fractured shale gas reservoir performance study--An offset well interference field test

Abstract: Gas production characteristics of naturally fractured Devonian shale have been quantified through a three-well interference test using an established producing well and two offsets placed on the primary and secondary regional fracture trends relative to the producer. Three individual shale zones were tested simultaneously by buildup, drawdown, and pulse tests to investigate reservoir gas flow characteristics, natural fracture properties, and gas storage and release mechanisms. Test results show severe permeability anisotropy, indicating elliptical drainage pattern with an 8:1 axis ratio. Essentially all gas is stored in a sorbed state in the shale matrix and is transported toward the wells through the native fracture system.