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Showing papers on "Effective porosity published in 1999"


Journal ArticleDOI
TL;DR: In this paper, the authors define changes in effective porosity and hydraulic conductivity that result from the redistribution of stresses and strains in disturbed rock masses, based on pre-disturbance porosities and conductivities, knowledge of the number of joint sets, and the indices of Rock Quality Designation (RQD) and Rock Mass Rating.

95 citations


Journal ArticleDOI
Luc Lebbe1
TL;DR: In this paper, a series of borehole resistivity measurements and a resistivity-salinity relation was found under the shore with semi-diurnal tides at the French-Belgian border.

71 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of the pore size distribution index (PSI) was used to improve the predictive capability of the modified Kozeny-Carman equation, and the results showed that the improvement came through a better Ks 5 B1f n e estimation of large values of Ks.
Abstract: tating a large number of samples. For this reason indirect methods have held promise as an alternative to making Effective porosity, defined here as the difference between satiated direct measurements. A further advantage of indirect total porosity and water-filled porosity at a matric potential of 33 kPa, has been shown to be a good predictor for saturated hydraulic methods is that they allow researchers to obtain an conductivity (Ks) using a modified Kozeny-Carman equation. This estimate of the variability of saturated conductivities equation is of the form of a coefficient (B ) multiplied by effective based on the variability of an easily measured predictor porosity raised to a power (n ). The purpose of this study was to variable (Ahuja et al., 1989). improve the predictive capability of the modified Kozeny-Carman A number of relationships have been developed that equation by including information from moisture release curves (soil can be used to calculate Ks with easily measured soil water content vs. matric potential relation). We fitted the Brooks- properties. Some are purely empirical and are often Corey (B-C) equation parameters (pore size distribution index and related to soil texture (Rawls et al., 1992; Puckett et al., air entry potential) to moisture release data from a large database 1985). Other relationships use physically based equa(.500 samples). Values of Ks were also available from the same tions. Ahuja et al. (1984, 1989) showed that a modified source. Inclusion of the pore size distribution index into the KozenyCarman equation improved the Ks estimation over using only effective Kozeny-Carman equation porosity, but only slightly. The improvement came through a better Ks 5 B1f n e [1] estimation of large values of Ks. We also fit a relationship for the coefficient (B) of the Kozeny-Carman equation as a function of the was applicable to a wide range of soils from the Southern two B-C parameters with a constant value of n 5 2.5 for the exponent. Region of the USA, Hawaii, and Arizona. Here fe is Overall the use of Brooks-Corey parameters from moisture retention the effective porosity calculated as saturated water condata improved estimates of Ks over using effective porosity (fe) alone. tent (us) minus the water content at 33 kPa matric potenThere is still considerable error in predicting individual Ks values, tial, and B

65 citations


Journal ArticleDOI
TL;DR: In this paper, it is shown that the porosity of a round wire mesh screen is related to the loss coefficient, and that porosity increases with the angle between the wind and the surface.

45 citations


Journal ArticleDOI
TL;DR: In this paper, the authors used the Kozeny Equation to estimate the porosity of the upper part of the Arnager Greensand from microscopic images, and compared the petrophysical properties, porosity and permeability obtained from image analysis.
Abstract: Arnager Greensand consists of unconsolidated, poorly sorted fine-grained, glauconitic quartz sand, often silty or clayey, with a few horizons of cemented coarse-grained sand. Samples from the upper part of the Arnager Greensand were used for this study to estimate permeability from microscopic images. Backscattered Scanning Electron Microscope images from polished thin-sections were acquired for image analysis with the software PIPPIN®. Differences in grey levels owing to density differences allowed us to estimate porosity, clay and particle content. The images were simplified into two phases, pores and particles, and the specific surface of the solid phase was calculated. We used the Kozeny Equation to calculate the permeability. The petrophysical properties, porosity and permeability obtained from image analysis were compared to results using laboratory methods. The 150x magnification of the image can not resolve the microporosity within the clay fraction, so we suggest that the imaged porosity at 150x magnification is close to the effective porosity for permeability assessment. The Heporosity, however, represents the total porosity of the Arnager Greensand. For permeability estimation, a local permeability was calculated for each image. For calculation of the plug scale permeability, we compare three different averaging methods: arithmetic, harmonic, and geometric mean. In every case the calculated permeability overestimates the measured permeability. Only the lowest calculated local permeabilities corresponds to the measured permeabilities, suggesting that the overall permeability for these samples is governed by the least permeable parts.

33 citations


Journal ArticleDOI
TL;DR: Three-dimensional numerical modeling is used to characterize ground water flow and contaminant transport at the Shoal nuclear test site in north-central Nevada, and the effect of porosity in radioactive decay is crucial and has not been adequately addressed in the literature.
Abstract: Three-dimensional numerical modeling is used to characterize ground water flow and contaminant transport at the Shoal nuclear test site in north-central Nevada. The fractured rock aquifer at the site is modeled using an equivalent porous medium approach. Field data are used to characterize the fracture system into classes: large, medium, and no/small fracture zones. Hydraulic conductivities are assigned based on discrete interval measurements. Contaminants from the Shoal test are assumed to all be located within the cavity. Several challenging issues are addressed in this study. Radionuclides are apportioned between surface deposits and volume deposits in nuclear melt glass, based on their volatility and previous observations. Surface-deposited radionuclides are released hydraulically after equilibration of the cavity with the surrounding ground water system, and as a function of ground water flow through the higher-porosity cavity into the low-porosity surrounding aquifer. Processes that are modeled include the release functions, retardation, radioactive decay, prompt injection, and ingrowth of daughter products. Prompt injection of radionuclides away from the cavity is found to increase the arrival of mass at the control plane but is not found to significantly impact calculated concentrations due to increased spreading. Behavior of the other radionuclides is affected by the slow chemical release and retardation behavior. The transport calculations are sensitive to many flow and transport parameters. Most important are the heterogeneity of the flow field and effective porosity. The effect of porosity in radioactive decay is crucial and has not been adequately addressed in the literature. For reactive solutes, retardation and the glass dissolution rate are also critical.

29 citations


Journal ArticleDOI
TL;DR: In this paper, a 0.15-0.3 m thick clay membrane has been tested at Rodbyhavn on the Danish island of Lolland and the results showed that at a natural water content of w=40-45% it is possible to establish a homogeneous membrane with hydraulic conductivity k <5×10 -12 m s -1 giving an extremely low transport by advection.

20 citations


Journal ArticleDOI
TL;DR: In this paper, the elastic moduli and acoustic velocities of shaley sandstones strongly depend on the amount of clay as well as on its position among sand grains in the sand grains.
Abstract: The elastic moduli (and acoustic velocities) of shaley sandstones strongly depend on the amount of clay as well as on its position among sand grains In many cases clay may fill pores without noticeably affecting the stiffness of the rock Such clays are non-load-bearing Here, the stiffness of the rock is determined primarily by the load-bearing quartz frame We examine several data sets and show that in this case a simple unique relation exists between the acoustic velocity and the porosity of the load-bearing frame of the rock This porosity can be calculated as the sum of the effective porosity (total porosity minus microporosity inside clay) and the volumetric fraction of clay in the rock Also, it is the sum of the total porosity and the volumetric fraction of solid clay particles in the rock

17 citations


ReportDOI
TL;DR: In this article, the authors describe an approach to estimate hydraulic and transport properties in fractured-rock aquifers, and demonstrate the approach at a sedimentary fractured rock site in the Newark Basin, N.J. The approach has three components: characterization of the hydrogeologic framework of ground-water flow within the rock-fracture network, estimation of hydraulic properties (hydraulic conductivity and storage coefficient) within that framework, and estimation of transport properties (effective porosity and dispersivity).
Abstract: Investigations of the transport and fate of contaminants in fractured-rock aquifers require knowledge of aquifer hydraulic and transport characteristics to improve prediction of the rate and direction of movement of contaminated ground water. This report describes an approach to estimating hydraulic and transport properties in fractured-rock aquifers; demonstrates the approach at a sedimentary fractured-rock site in the Newark Basin, N.J.; and provides values for hydraulic and transport properties at the site. The approach has three components: (1) characterization of the hydrogeologic framework of ground-water flow within the rock-fracture network, (2) estimation of the distribution of hydraulic properties (hydraulic conductivity and storage coefficient) within that framework, and (3) estimation of transport properties (effective porosity and dispersivity). The approach includes alternatives with increasingly complex data-collection and analysis techniques.

10 citations



Journal ArticleDOI
TL;DR: In this article, a methodology is developed to predict the distributed hydraulic conductivity field based on the original undisturbed parameters of hydraulic conductivities, Rock Mass Rating (RMR), Rock Quality Designation (RQD), and additionally the induced strains.
Abstract: Changes in the hydraulic conductivity field, resulting from the redistribution of stresses in fractured rock masses, are difficult to characterize due to complex nature of the coupled hydromechanical processes. A methodology is developed to predict the distributed hydraulic conductivity field based on the original undisturbed parameters of hydraulic conductivity, Rock Mass Rating (RMR), Rock Quality Designation (RQD), and additionally the induced strains. The most obvious advantage of the methodology is that these required parameters are minimal and are readily available in practice. The incorporation of RMR and RQD, both of which have been applied to design in rock engineering for decades, enables the stress-dependent hydraulic conductivity field to be represented for a whole spectrum of rock masses. Knowledge of the RQD, together with the original hydraulic conductivity, is applied to determine the effective porosity for the fractured media. When RQD approaches zero, the rock mass is highly fractured, and fracture permeability will be relatively high. When RQD approaches 100, the degree of fracturing is minimal, and secondary porosity and secondary permeability will be low. These values bound the possible ranges in hydraulic behaviour of the secondary porosity within the system. RMR may also be applied to determine the scale effect of elastic modulus. As RMR approaches 100, the ‘softening’ effect of fractures is a minimum and results in the smallest strain-induced change in the hydraulic conductivity because the induced strain is uniformly distributed between fractures and matrix. When RMR approaches zero, the laboratory modulus must be reduced significantly in order to represent the rock mass. This results in the largest possible change in the hydraulic conductivity because the induced strain is applied entirely to the fracture system. These values of RMR bound the possible ranges in mechanical behaviour of the system. The mechanical system is coupled with the hydraulic system by two empirical parameters, RQD and RMR. The methodology has been applied to a circular underground excavation and to qualitatively explain the in situ experimental results of the macropermeability test in the drift at Stripa. Copyright © 1999 John Wiley & Sons, Ltd.

Proceedings ArticleDOI
01 Jan 1999
TL;DR: In this paper, a Magnetic Resonance Imaging Log (MRIL) was run in two cored wells in Obaiyed field in Egypt to determine the variation in rock permeability to better design well completion program and select best perforation intervals.
Abstract: Permeability is a key factor in well completion in many reservoirs all over the world. The dependency of permeability on the accurate determination of reservoir total and effective porosity, irreducible and movable fluids and the correct correlation between the pore throat and the pore body made it a real challenge. The capability of the Nuclear Magnetic Resonance to provide effective and total porosity, capillary bound fluids and movable fluids provides means for better estimation of rock permeability. Magnetic Resonance Imaging Log (MRIL) was run in two cored wells in Obaiyed field in Egypt to determine the variation in rock permeability to better design well completion program and select best perforation intervals. Obaiyed field is a gas sandstone reservoir with low porosity ranging between 5 to 10 porosity units. Obtaining a reliable permeability in this reservoir faced two challenges; the first due to the reservoir heterogeneity while the second due to the drilling mud. The reservoir rock is heterogeneous and varies from very fine, fine to coarse-grained sandstone. The coarse grained sands represent the high permeability zones, which are imbedded within the fine-grained sand. The key issue in this reservoir is to determine the locations of these high permeability zones within the fine-grained sand beds for well stimulation planning. The determination of the T2 cut-off for both the fine and the coarse grained sands, which vary with depth due to the reservoir heterogeneity, generated a great challenge in determining the formation permeability. A function depending on an average of the T2 distribution is developed to provide the segregation. The wells in Obaiyed field are drilled with oil base mud with very long relaxation time T1 that even exceeds the gas relaxation time. This property of the oil base mud, if it is not taken into account in logging and interpretation, makes it difficult to obtain a reliable porosity since the NMR will under-polarize the invading OBM as well as the residual formation gas. The time domain analysis technique (TDA) was used to overcome this problem. In this paper, our experiences in such complex situation is discussed, core analysis is provided, core to log calibration in two wells is presented and recommendations for future applications in Obayied and other similar fields are suggested.

Proceedings ArticleDOI
06 Sep 1999
TL;DR: A combined geophysical survey has been conducted at the test site Nauen near Berlin, prospecting a shallow aquifer in fluvial sediments bordered by glacial till as mentioned in this paper.
Abstract: A combined geophysical survey has been conducted at the test site Nauen near Berlin, prospecting a shallow aquifer in fluvial sediments bordered by glacial till. Some of the geophysical results have been reported earlier [1]. Comprehensive investigations of geoelectric sections and depth-soundings as well as georadar profiles were interpreted to describe subsurface conditions. The structure of the dipping glacial till is well recognisable up to a depth of 13 m. The sandy sediments above represent the aquifer with the water table at a depth of about 2 m. The radar velocities and resistivities from Block-Inversion of geoelectric sections have been used to derive hydrological parameters. The aquifer is accordingly determined to have a porosity around 24 % and a water content of 5 % in the vadose zone. At the main profile, five SNMR soundings have been carried out in order to compare the results with those from conventional geophysical methods. Inversion results show mobile water contents of less than 20 % in the first few meters of the vadose zone, increasing rapidly to 30 %. This means an aquifer with an effective porosity of at least 30 % plus adhesive water content. Decreasing water contents below 15-18 m relate to the glacial till which has low permeability and less mobile water. Increasing water contents in larger depth again to values above 30 % indicates another aquifer which is not verified with other methods yet. The decay times within the aquifer are generally about 150-250 ms and correspond in average to medium sands [2]. However, in detail they are somewhat ambiguous.

Proceedings ArticleDOI
01 Jan 1999
TL;DR: In this paper, a neural network was used to reconcile the differences between density log effective porosity and plug core total porosity values in a shaly, laminated Cretaceous sandstone.
Abstract: Well logs and cores are used to define formation thickness, porosity, and water saturation. These data are required to design well completions and to prepare workover and reservoir management plans. The presence of shale (clay) in the pay zone complicates log interpretation. This paper presents a methodology utilizing a neural network to reconcile the differences between density log effective porosity and plug core total porosity values in a shaly, laminated Cretaceous sandstone. Core plug measurements are typically taken in the better pay intervals and generally do not include the shale laminations evident in core photographs. Log measurements do include the heterogeneity that is evident in core photographs, but the log measurements represent an average of a 6-to-36-in. section that does not reflect the small scale variability. A multivariable correlating technique was used to associate gamma ray, density, and shallow and deep resistivity logs with core plug porosity measurements. Core water saturation values were used to tune a shaly sand water saturation model. The S W model was used to choose between plug core porosity, density log porosity, or neural network porosity as the preferred measurement to use with induction log resistivity to estimate water saturation. The porosity and water saturation values were then used to construct bulk volume oil and bulk volume water logs that were combined to identify productive zones. A case history format is used to explain the approach developed to correlate the four dependent variables measured by the logs with the core porosity and water saturation measurements. The subject field is an 80-well Gallup pool located on the southwest flank of the San Juan Basin of northwest New Mexico. The high clay content of the Muddy Formation in the Powder River Basin is known for contributing to errors in water saturation estimates. If modern logs capable of resolving thin beds are not available, this methodology can be applied to the Muddy, the Gallup and other Cretaceous reservoirs in the Rockies that contain thin shale laminations.

Journal ArticleDOI
TL;DR: In this article, a dual-porosity model is developed to study processes of in situ leaching, which involves two overlaying continua at the macroscopic level: a permeable fracture system that determines the flow field of leach solution and a relatively impermeable matrix system, and their ratios in addition to the concentration of reagent and the ore grade.
Abstract: A dual-porosity model is developed to study processes of in situ leaching. The model involves two overlaying continua at the macroscopic level: a permeable fracture system that determines the flow field of leach solution and a relatively impermeable matrix system that determines the leaching kinetics. The most obvious advantage of the model is that parameters it requires are minimal and easily available in practice. These parameters include the in situ hydraulic conductivity, longitudinal and transverse dispersivities, the lumped rate constant, and an empirical rock mass classification index, RQD (Rock Quality Designation). The simulation of in situ leaching processes is linked to RQD through the effective porosity of fractured media. The incorporation of RQD enables the simulation of in situ leaching processes to be carried out for a whole spectrum of ore deposits. When RQD approaches 0, it represents that the ore deposit may be a porous medium with a high effective porosity. This may reduce the double-porosity model to a single porosity model. When RQD approaches 100, it represents that the ore deposit may be considered as impermeable and unleachable. These values bound the possible ranges in behavior of the system. Based on the double-porosity model, the relation between particle size and leachability is developed, and the effects of double porosities on the concentration of a dissolved mineral are investigated. It is demonstrated through model results that the recovery rate of a valuable mineral is mainly determined by the effective porosity of the fracture pore system, the porosity of the rock matrix system, and their ratios in addition to the concentration of reagent and the ore grade.

Journal ArticleDOI
TL;DR: In this article, the migration behavior of Se in this compacted bentonite has been studied and the retardation factor obtained, which is at least one order of magnitude lower than the one obtained by means of batch sorption experiments due to a lower availability of sorption sites when increasing the compaction degree.
Abstract: Migration experiments were carried out in compacted Ca-bentonite as a complement of the FEBEX [Full-Scale Engineered Barriers Experiment in Crystalline Host Rock] project large scale tests. Through diffusion and permeation experiments with triated water were used to perform a deep characterization of the clay diffusion parameters (diffusion coefficient, effective porosity and permeability). In through diffusion experiments, a variation of tracer concentration in both reservoirs was allowed. Since in these experimental conditions an analytical solution of the diffusion problem does not exist, an analytical approximation was used and the results compared with a numerical model which takes into account the presence of the sintered steel filters confining the clay plug. The migration behavior of Se in this compacted bentonite has been studied and the retardation factor obtained. The calculated Kd is at least one order of magnitude lower than the one obtained by means of batch sorption experiments due to a lower availability of sorption sites when increasing the compaction degree.

01 Jan 1999
TL;DR: In this article, a simple one dimensional model of fluid flow and dissolution reaction has been elaborated to understand the changes in porosity in the carbonate rocks and how porosity changes during replacement of the original saturated solution by a cold undersaturated fluid.
Abstract: To appreciate the changes in porosity in the carbonate rocks a simple, one dimensional model of fluid flow and dissolution reaction has been elaborated. The results indicate how porosity changes evolve during replacement of the original saturated solution by a cold undersaturated fluid injected into the carbonate aquifer. Such modeling, with hydraulic feedback via porosity - permeability relationship, could be potentially used to recognize the sites of unfavorable development of porosity.