Showing papers on "Permeability (earth sciences) published in 1974"

Atmospheric pressure effects on 222Rn transport across the Earth-air interface

Abstract: The effect of large-scale atmospheric pressure changes on the 222Rn flux across the soil-air interface is investigated. Field data collected during 1972 and 1973 show that pressure changes of 1–2% associated with the passage of frontal systems produce changes in the 222Rn flux from 20 to 60%, depending upon the rate of change of pressure and its duration. A simple model of molecular diffusion combined with pressure-induced transport in the soil has been confirmed by laboratory experiments using a vertical column of 226Ra-bearing sand. On the basis of this model, pressure changes of 10–20 mbar occurring over a period of 1–2 days produce Darcy velocities of the order of 10−4 cm s−1 near the surface of a soil having a permeability of 10−8 cm2. The corresponding variations in the 222Rn flux predicted by the model are in agreement with those observed from valley alluvium in central New Mexico.

Quantitative analysis of mass and energy balance in non-ideal models of the renal counterflow system.

Abstract: A modified Newton-Raphson method for solving finite difference equations for the renal counterflow system is described. The method has proved generally stable and efficient, and has given significant computational results for a variety of models: calculations on single solute models of the coupled vasa recta nephron counterflow system have shown that for large water and solute permeabilities of the exchanging membranes, behavior of the non-ideal system approaches that of the previously described ideal central core model. Concentration by salt and urea mixing in two solute models has been analyzed and previous conclusions from central core models have been found to remain valid in non-ideal systems. The numerical solutions have set some order of magnitude bounds on permeability requirements for concentration in different types of non-ideal systems. Finally, from the detailed concentration profiles it has been possible to relate the rate of free energy creation and dissipation from transmembrane transport of solutes and water to the net rate of free energy efflux from the counterflow system, and so to compute in a given model the fraction of power used for solute concentration.

Diffusion of Fluids Through Porous Media with Implications in Petroleum Geology

Abstract: Diffusion measurements made for helium through porous cores including caprocks show that the effective diffusivity decreases with decreased permeability of the rock for gas-phase diffusion and for helium dissolved in water. A similar correlation is obtained of decreased diffusivity for increased threshold-displacement pressure for nitrogen displacing water from the rock. These correlations verify that parameters which indicate constrictions in the interstices of the rock also restrict diffusion.

Flow through a Porous Wall with Convective Acceleration

Abstract: This paper deals with the flow in very porous media when the convective acceleration of the flow cannot be neglected. The governing equations are taken to be a generalized Darcy's law which takes the convection term into account in the porous region and Euler's equation in the pure fluid region. Two types of flow are investigated in detail: One is a one-dimensional flow streaming into or out of a plane porous wall with a tangential component of velocity to the surface and the other is a two-dimensional stagnation point flow through a porous wall. It is found that vorticity is created when the flow crosses the surface of the wall obliquely. It is also shown that there may be the case in which the usual Darcy's law is inaccurate to describe the flow even when the permeability of the porous medium is very small.

Permeability of Cohesionless Soils

Abstract: The permeability coefficient, K , of a porous matrix in Darcy's equation of hydraulic conductivity depends mainly on the properties of the solid matrix, e.g., porosity, tortuosity, particle size composition, and shape of grains. The main objective of the present experimental work is to bring out the effects of the uniformity coefficient, U , and the grain effective diameter, D 10, on the permeability of the porous matrix. This experiment modifies the standard permeability equation to take into account the grain effective diameter. Based on the results, it is clear that K increases with increasing of the grain effective diameter, uniformity coefficient, and void ratio.

Relative Permeability and the Gross Pore Structure of Wood

Abstract: Water-saturated, longitudinal core samples of nine hardwoods and three softwoods were measured for specific permeability and also for relative permeability to water and nitrogen gas. Constant flow rates were achieved for specific permeability. Relative permeability curve shapes were influenced more by the pore structure of wood than by its specific permeability. It appears that softwoods could be drained much lower in degree of saturation than hardwoods. In imbibition-type measurements, the softwoods were higher in saturation but lower in relative permeability than the hardwoods.

Pulse Tests and Other Early Transient Pressure Analyses for In-Situ Estimation of Vertical Permeability

Abstract: The formation vertical permeability is often the dominant reservoir parameter in the performance of water and/or gas coning into a well, gravity drainage of high relief reservoirs, and interlayer cross-flow in secondary recovery projects. The advantages of either a pulse test or analyzing the early transient pressure response of a constant rate test compared to previous techniques are simplicity of interpretation, short duration of test, and minimum interference from conditions some distance away from the test well. The pulse test has a further advantage over the constant rate test, because the rate does not have to be kept constant during the short flow period. The vertical permeability pulse test has been used to estimate the vertical permeability of a low permeability zone in the Fahud field, Oman.

Effects on highway subdrainage of gradation and direction of flow within a densely graded base course material

Abstract: Because of the relatively high content of fine-grained particles, densely graded base course aggregates will not readily drain once saturated with water. An investigation of permeability and its effect on drainage of densely graded base course material specified by the Maryland State Highway Administration was conducted using a prototype permeameter. The experimental permeameter provided values of permeability of a compacted sample both in the vertical and horizontal direction without removing or disturbing the compacted specimen. The horizontal permeability was found to be only slightly greater than the vertical permeability. Experimental permeability data was applied to an example of lateral drainage from the midpoint of a roadway to a shoulder drain under conditions proposed by the Army Corps of Engineers for base course drainage. The direction of flow in the base course material was found to have little effect on the drainage characteristics; fines content is the more significant factor in determining the rate of highway subdrainage.

Study of possible mechanisms of gas transfer through polymer films

Abstract: A study was made of the effect of pressure and temperature on the permeability of polyethylene and fluoroplastic specimens of different porosites in relation to helium, argon, nitrogen and carbon tetrachloride. Results of investigation are interpreted on the basis of Knudsen-Poiseuille rules and activated diffusion law. A ratio was derived which describes the superimpositions of these rules and enables porosity to be determined also average radius and number capillaries per unit area established. It was shown that heat treatment of a porous specimen reduces the radius and number of capillaries and therefore gas permeability. The difference of temperature relations of gas permeability factors in activated diffusion, capillary flow or the superimposition of these transfer effects was indicated.

Consolidation and rebound processes in one-dimensional porous columns

Abstract: The present paper analyzes the consolidation and rebound processes of one-dimensional porous columns as they relate to petroleum production operations. Darcy's law and its implication for a mobile matrix are discussed. The specific problem considered is the shrinkage or expansion of a porous system to a single step function change in pressure at the base of the column, which may be considered to be either semi-infinite or finite. The theory presented herein includes general forms of formation permeability and pressure and couples the movement of solid particles and liquid. The effect of the movement of solid particles on the flow of liquid is demonstrated. It is shown that in regions where the consolidation or expansion process is dominant the additional flow of liquid due to the movement of the solid particles can be of the same order of magnitude as the flow of liquid given by Darcy's law. The differences between consolidation and expansion processes are examined. One aspect of consolidation or rebound that has resulted in considerable confusion is the choice of a coordinate system (moving or stationary) to develop the mathematical model. This aspect is also examined in detail. Even though a nonlinear equation results, analytical solutions exist for a class of problems. Examples are presented. The nonlinear equation has also been solved numerically, and the solutions obtained have been correlated with constant property solutions through a transformation that has been used to describe the flow of gases through porous media as well as the transmission of heat by conduction.

Earth formation permeability determining technique using synthetic resistivity parameters

Abstract: A pad mounted well logging measuring device provides a determination of permeable and impermeable zones in a subsurface earth formation.

Le perméamètre autoforeur

Abstract: A usual method for measuring the coefficients of permeability and consolidation of fine grained soils in situ is by means of permeameters installed by driving or pushing into the soil. The disadvan...

Discharge and Travel Time for Ground-Water Conduits

Abstract: A system of mathematical and graphical procedures gives solution for the steady-flow discharge and travel time for nonuniform confined ground-water conduits in which any or all of the following characteristics vary from point to point: permeability, porosity, and cross-sectional area. The methods use solutions of mathematical models based on the Darcy equation and the equation of continuity. Modified procedures give relatively simple solutions with some loss in accuracy.

Influence of properties of filtering liquids on the permeability of disperse systems

Abstract: A method is proposed for determining the filtration characteristics of finely dispersed systems (clayey soils) through a calculation of their adsorption and rheological properties.