Showing papers on "Permeability (earth sciences) published in 1987"

Reservoir Engineering in Coal Seams: Part 1-The Physical Process of Gas Storage and Movement in Coal Seams

Abstract: This is the first of two papers concerning the movement of gas in coal seams. It deals directly with the physical behavior of the coal seam as a reservoir. Coal seams show considerable differences in behavior from normal porous gas reservoirs in both the mode of gas storage and permeability characteristics. Most of the storage of gas in coal is by sorption into the coal structure, while the coal permeability is cleat-(fracture-) or joint-controlled and may vary over a wide range during production. This permeability fluctuation is not solely a phase relative permeability effect, but is rather a result of the opposing effects of effective stress increase with fluid pressure reduction and shrinkage of the coal. Reducing fluid pressure tends to close the cleats, reducing permeability, while shrinkage tends to open them.

Wettability literature survey - Part 5: The effects of wettability on relative permeability

Abstract: The wettability of a core will strongly affect its waterflood behavior and relative permeability. Wettability affects relative permeability because it is a major factor in the control of the location, flow, and distribution of fluids in a porous medium. In uniformly or fractionally wetted porous media, the water relative permeability increases and the oil relative permeability decreases as the system becomes more oil-wet. In a mixed-wettability system, the continuous oil-wet paths in the larger pores alter the relative permeability curves and allow the system to be waterflooded to a very low residual oil saturation (ROS) after the injection of many PV's of water. The most accurate relative permeability measurements are made on native-state core, where the reservoir wettability is perserved. Serious errors can result when measurements are made on cores with altered wettability, such as cleaned core or core contaminated with drilling-mud surfactants.

The microgeometry and transport properties of sedimentary rock.

Abstract: This monograph describes recent progress in modelling the transport properties of sedimentary rock. Statistical descriptions are applied to the pore-space geometry and to the transport processes involving pore fluids. Fractals are used to quantify the pore geometry at length scales shorter than grain size. Percolation theory is applied to fluid flow. The permeability can be expressed in terms of a single effective pore diameter measured from mercury injection capillary pressure. This permeability relation is valid for essentially all porous rock and for a broad class of porous media. Mercury injection provides a powerful caliper of the geometry of a percolation cluster in a pore-space and supplies new information about pore space correlations and dynamics of fluid displacements. The statistical description of fluid transport in porous media has analogues in disordered electronic and magnetic materials. Future work may make substantial use of such analogues to solve more complex problems of direct...

Numerical estimation of effective permeability in sand-shale formations

Abstract: A numerical approach is used to estimate effective permeability in sand-shale formations under steady state uniform flow conditions. Permeability is modeled as a binary, second-order stationary random function taking on two possible values Kss and Ksh in sandstone and shale, respectively. This model is realistic since experience with sandstone reservoirs has shown that randomly dispersed low-permeability shales are the single dominant heterogeneity affecting flow behavior. The cases of both spatially correlated and uncorrelated permeabilities are considered. For the case of spatially correlated permeability, an autocovariance model was fitted to data from the Assakao fluvial sandstone which outcrops in the Tassili region of the central Sahara. The turning bands method was used to simulate the spatially correlated permeabilities of blocks discretizing the flow field. Effective permeability was found to depend on the shale volume fraction, the spatial covariance structure, and the dimensionality of the flow system. Existing analytical methods for estimating effective permeability in a two-phase medium are found to be inaccurate when compared to numerical results or unapplicable to stratified environments. In addition to providing a check of analytical work, the numerical approach is found to be a useful tool for exploring the effects of reservoir heterogeneity on flow behavior in a qualitative sense.

Hydraulic conductivity of compacted clay to dilute organic chemicals.

Abstract: Four organic chemicals over a range of concentrations were permeated through compaacted specimens of kaolinite and illite-chlorite. Permeability test were performed in both rigid and flexible-wall permeameters. Soil index tests were modified for use in evaluating the effect an organic waste may have on clay. Results of the investigation showed that dilute organic chemicals (less than 80% by volume in an aqueous solution) have little effect on the hydraulic conductivity (permeability) of compacted clay. The modified index tests showed good correlation to the degree with which an organic liquid affects the hydraulic conductivity of the compacted clay.

Flow Unit Concept--Integrated Approach to Reservoir Description for Engineering Projects: ABSTRACT

Abstract: The successful application of secondary and tertiary oil recovery technology requires an accurate understanding of the internal architecture of the reservoir. Engineers have difficulty incorporating geological heterogeneity in their numerical models for simulating reservoir behavior. The concept of flow units has been developed to integrate geological and engineering data into a system for reservoir description. A flow unit is a volume of the total reservoir rock within which geological and petrophysical properties that affect fluid flow are internally consistent and predictably different from properties of other rock volumes (i.e., flow units). Flow units are defined by geological properties, such as texture, mineralogy, sedimentary structures, bedding contacts, and the nature of permeability barriers, combined with quantitative petrophysical properties, such as porosity, permeability, capillarity, and fluid saturations. Studies in the subsurface and in surface outcrops have shown that flow units do not always coincide with geologic lithofacies. The flow unit approach provides a means of uniquely subdividing reservoirs into volumes that approximate the architecture of a reservoir at a scale consistent with reservoir simulations. Thus, reservoir engineers can incorporate critical geological information into a reservoir simulation without greatly increasing the complexity of their models. This approach has advantages over more traditional methodsmore » of reservoir zonation whereby model layers are determined on the basis of vertical distributions of permeability and porosity from core analyses and wireline logs.« less

The relationship between permeability coefficients for concrete obtained using liquid and gas

Abstract: Synopsis Tests have been carried out on four concretes to measure their permeability coeficient using both water and nitrogen. In every case the gas permeability was significantly higher than the w...

Flow through Porous Media of a Shear-thinning Liquid with Yield Stress

Abstract: Darcy's law for the laminar flow of Newtonian fluids through porous media has been modified to a more general form which will describe the flow through porous media of fluids whose flow behavior can be characterized by the Herschel-Bulkley model. The model covers the flow of homogeneous fluids with a yield value and a power law flow behavior. Experiments in packed beds of sand were carried out with solutions of paraffin wax in two oils and with a crude oil from the Peace River area of Canada. The model fitted the data well. A sensitivity analysis of the fitting parameters showed that the model fit was very sensitive to errors in the flow behavior index, n, of the Herschel-Bulkley model. A comparison of the “n” values calculated from viscometer measurements and from flow measurements agreed well. A more general Reynolds number for flow through porous media, which includes a fluid yield value, was developed. The data were fitted to a Kozeny-Carman type equation using this Reynolds number. The constant in the Kozeny-Carman equation was determined for the two packed beds studied using Newtonian oils. The data could all be represented, within the experimental error, by the relationship f* = 150/Re*. Since the mean volume to surface diameter of the packing was determined by the measurement of its permeability to a Newtonian oil, assuming C' = 150, the new definition of the Reynolds number allows the direct use of the Kozeny-Carman equation with Herschel-Bulkley type fluids.

Effective and relative permeabilities of anisotropie porous media

Abstract: A model composed of a three-dimensional orthogonal network of capillary tubes was used to simulate the flow behavior in an unsaturated anisotropic soil. The anisotropy in the network's permeability was introduced by randomly selecting the radii in the three mutually orthogonal directions of the network tubes from three different lognormal probability distributions, one for each direction. These three directions were assumed to be the principal directions of anisotropy. The sample was gradually drained, with only tubes smaller than a certain diameter remaining full at each degree of saturation. Computer experiments were conducted to determine the network's effective permeability as a function of saturation. The main conclusion was that the relationship between saturation and effective permeability depends on direction. Consequently the concept of relative permeability used in unsaturated flow should be limited to isotropic media and not extended to anisotropic ones.

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.

Effects of in situ permeability on the propagation of Stoneley (tube) waves in a borehole

Abstract: We investigated the theoretical relationship between propagation characteristics of Stoneley (tube) waves in a borehole and in situ permeability by using a modified formulation of a borehole model with a formation that behaves as a Biot porous medium. We found that Stoneley‐wave attenuation and phase‐velocity dispersion increased with increasing permeability and porosity, and decreased with increasing frequency. In rocks with low to medium permeabilities (less than 100 mD), variations in formation velocity and attentuation were major contributors to variations in Stoneley‐wave properties at normal logging frequencies. However, in high‐permeability rocks (greater than 100 mD), coupling between the borehole and pore fluids associated with in situ permeability was more important than lithological changes in controlling Stoneley‐wave properties. Pore‐fluid viscosity had an effect on Stoneley‐wave propagation equal but opposite to permeability, and hence must he taken into account. We compared our theoretical ...

A Statistical Study of Reservoir Permeability: Distributions, Correlations, and Averages

Abstract: The authors propose that reservoir permeability may be statistically distributed in a variety of ways. Two hypothetical cases of reservoir layering are statistically analyzed. This analysis suggests that a restricted family of functions - all related to the normal distribution - can be used to represent permeability distributions. The log-normal distribution is one member of the family. Several sets of field data are analyzed. The analyses show that (1) permeability data are not necessarily log-normally distributed, (2) all the permeability distributions considered are closely approximated by members of the proposed family of functions, and (3) improved porosity/permeability relationships result when the permeability distribution is known.

An examination of relative permeability relations for two-phase flow in porous media

Abstract: A key parameter in modeling two-phase flow phenomena is relative permeability. It is important to understand which variables influence relative permeability, especially since so few measurements of relative permeability, especially since so few measurements of relative permeability have been made for typical contaminants at hazardous waste sites. This paper focuses on the effect of five variables on relative permeability: intrinsic permeability, pore-size distribution, viscosity ratio, interfacial tension, and wettability, by critically reviewing previously published relative permeability experiments. The wide variability in the functional relationship between relative permeability and saturation should be considered in attempts to model two-phase flow.

Permeability testing of site concrete. a review of methods and experience

Abstract: This report discusses concrete permeability to liquids, ions and gases, and describes the various coefficients and units that are used to measure these. A review is also provided of the various in situ and laboratory methods used to establish values for permeability of site concrete. A brief summary of the ease and reliability of the main groups of test methods given in the report is provided in appendix a. The test methods reviewed include: a) in situ tests (initial surface absorption test, figg method, pressure applied surface permeability, depth of carbonation, ionic diffusion by electrical measurement, drilled hole permeability test, and leak testing of whole structures); b) laboratory tests (water absorption tests, pressure induced flow tests for gases or liquids, gas diffusion, water vapour diffusion, and ionic diffusion); c) radiation attenuation, d) resistivity; e) high pressure techniques; f) transient pressure pulse and pressure decay tests; and g) osmotic pressure. Throughout the report some indication is given where possible of typical results obtained using the various test methods, and in section 6 a number of case histories are reviewed where permeability results are available from site cast concrete. (Author/TRRL)

The Effect of an Immobile Liquid Saturation on the Non-Darcy Flow Coefficient in Porous Media

Abstract: The results of an experimental research program to investigate the effects of immobile liquid saturations on the non-Darcy flow coefficient are presented. Sandstone cores of absolute permeabilities ranging from 50 to 800 md were used to investigate non-Darcy flow phenomena under multiphase conditions. Immobile liquid saturations were varied from 8 to 30% PV. The multiphase experiments were conducted with N/sub 2/ gas as the flowing phase and glycerin as the immobile liquid phase. It was found that the non-Darcy flow coefficient for the multiphase case may be estimated with a dry-core non-Darcy-flow-coefficient/permeability relationship developed for the rock in question and the effective gas permeability at a given saturation. For the immobile multiphase cases, the non-Darcy flow coefficient consistently increased with increased saturation. The experimental data obtained from this research were compared with the limited multiphase data in the literature. Where comparisons could be made, the data reported in this paper agreed favorably with the existing published data. An analysis of the experimental data revealed that a unique relationship existed between the non-Darcy flow coefficient and the effective gas permeability, porosity, liquid saturation, and effective overburden pressure at a given temperature. Correlations were developed from this analysis to predict the non-Darcymore » flow coefficient as a function of rock and fluid properties.« less

Method for determining horizontal and/or vertical permeability of a subsurface earth formation

Abstract: Pressure and flow measurements made during extraction of fluid samples from a subsurface earth formation using a borehole logging tool having a single extraction probe are analyzed to derive separate values for both horizontal and vertical formation permeability. Build-up measurements are used to derive the slope of variation of formation pressure with respect to a spherical time function, and this value is incorporated in an expression for a dimensionless variable relating pressure, flowrate, porosity, compressibility and probe radius. The resulting value of the dimensionless constant provides an index into a look-up table obtained by a new analysis of the fluid dynamics in the immediate vicinity of the probe for an anisotropic formation. The table gives values for two or more dimensionless variables from which the permeability values are derived.

The Effect of Instability on Relative Permeability Curves Obtained by the Dynamic-Displacement Method

Abstract: A study was undertaken to investigate how instability would affect the oil/water relative permeability curves obtained by the dynamic-displacement method. In this method, stable Buckey-Leverett displacement theory is used to calculate relative permeability curves from coreflood data. Thus, to obtain the true relative permeability curves by the dynamic-displacement method, the coreflood must be stable. However, the method frequently has been applied to unstable corefloods. The consequence of this application of the method has not been previously reported. The authors compared oil/water relative permeability curves from steady-state and dynamic-displacement experiments at several levels of instability. The results showed that the dynamic-displacement relative permeability curves deviated significantly from the steady-state curves as the degree of instability increased. This observation indicates the need to scale laboratory relative permeability measurements to account for instability. To obtain representative relative permeability curves for numerical modeling of a reservoir, laboratory displacement experiments should be conducted at the same degree of instability as that in the reservoir.

Permeability determination in crystalline rocks by standard geophysical logs

Abstract: The formation factor (ratio of bulk resistivity of rock to resistivity of formation fluid) obtained from the focused‐electrode log can be used to estimate the hydraulic conductivity of the unfractured granitic rock matrix (10-12-10-10m/s), using an empirical relationship developed between laboratory measurements of formation factor and permeability. The ratio of the formation factor derived from the focused‐electrode log (FF) to the formation factor derived from the density log (FB) may be used to estimate the hydraulic conductivity of fractured zones (10-9-10-6m/s), because of the following empirical relationship between the transmissivity (TH) obtained from the in situ hydrogeologic tests and the ratio of the two formation factors, namely, TH=A(FB/FF)-s, where A and s are coefficients (4.1×10-7and1.06). This empirical relationship confirms the usefulness of geophysical logs for identifying intervals of potentially high permeability in boreholes drilled in granitic rock. Estimates of hydraulic conductivi...

Cellular-automaton Fluids: A Model For Flow In Porous Media

Abstract: Numerical models of fluid flow through porous media can be developed from either microscopic or macroscopic properties. The large‐scale viewpoint is perhaps the most prevalent. Darcy’s law relates the chief macroscopic parameters of interest—flow rate, permeability, viscosity, and pressure gradient—and may be invoked to solve for any of these parameters when the others are known. In practical situations, however, this solution may not be possible. Attention is then typically focused on the estimation of permeability, and numerous numerical methods based on knowledge of the microscopic pore‐space geometry have been proposed. Because the intrinsic inhomogeneity of porous media makes the application of proper boundary conditions difficult, microscopic flow calculations have typically been achieved with idealized arrays of geometrically simple pores, throats, and cracks. I propose here an attractive alternative which can freely and accurately model fluid flow in grossly irregular geometries. This new method s...

Fines Migration, Blocking, and Clay Swelling of Potential Geothermal Sandstone Reservoirs, Denmark

Abstract: Medium-grained, moderately well-sorted sandstones of fluvio-deltaic to shallow marine origin have been investigated for fines production and for variations in porosity/permeability. Porosity and permeability change within small horizontal and vertical changes in sampling points. Also, air permeability depends on flow direction, Klinkenberg correction, and cleaning procedure. Klinkenberg-corrected permeability and brine permeability were found not to be comparable. Brine flow cause flines of kaolinite and quartz to be produced from the compacted sandstones, while uncompacted sandstones produced kaolinite, illite, and detrital minerals. Chlorites and mixed-layer clays were not produced as fines, although they were present in some samples. Reservoir damage occurred when formation brine was replaced by KCl-brine, at increase in flow velocity, and at pauses in flow. Changes in flow direction caused severe fines production, renewed bridging, and blocking by fines.

Method of estimating the travel time of noninteracting solutes through compacted soil material

Abstract: The pollutant travel time through compacted soil material (i.e., when a pollutant introduced at the top first appears at the bottom) cannot be accurately predicted from the permeability (saturated hydraulic conductivity) alone. The travel time is also dependent on the effective porosity of the material; i.e., the portion of the total porosity that contributes significantly to fluid flow. Pollutant travel time is directly proportional to effective porosity and thickness of a compacted layer and inversely proportional to permeability and hydraulic gradient. The total porosity is calculated from measurements of bulk and particle density. Pore-size distribution information is obtained from the cumulative porosity curve of the sample as measured by mercury-intrusion porosimeter. The paper also compares measured and predicted solute breakthrough times for three compacted soil materials.

Assessment of grouting efficiency in a rock mass in terms of seismic velocities

Abstract: Grouting is a geotechnical process involving, for example, injection of a cement sand and water mixture or chemical resins into the ground to improve the strength and to decrease the permeability of rocks and soils. The efficiency of grouting operations is generally assessed by carrying out permeability and loading tests. Additionally, the comparison of the seismic field velocities of a rock mass obtained before and after the grout infection operation can give a qualitative indication of the effectiveness of grouting. However, for a quantitative assessment of grouting efficiency, more complex analysis of the rock mass seismic velocity is required.

Rock fabric, permeability, and log relationships in an upward-shoaling, vuggy carbonate sequence

Abstract: Cores and logs used in the study were from a Department of Energy well in Oldham County containing a wide range of separate-vug porosity in a simple upward-shoaling carbonate sequence of early Permian (Wolfcampian) age. The authors investigated two wireline methods, one involving acoustic logs and one involving resistivity logs, and both were found to determine separate-vug porosity. Two equations relating interparticle porosity and permeability were derived using the general relationship between particle size, interparticle porosity, and permeability described earlier by Lucia as a guide to define porosity-permeability relationships. The authors report that permeabilities calculated using particle-size and interparticle porosity determined by subtracting separate-vug porosity from total porosity are more accurate than those calculated from total porosity data alone.