Phases In Porous Media Research Articles

The relative importance of convective and conductive effects in two-phase geothermal fields

Conductive and convective transport are related in two phase porous media, provided capillary effects are negligible. This paper shows that the role of conduction will be unimportant, relative to convective effects, for sufficiently high temperatures and sufficiently high permeabilities. An approximately linear relationship holds between temperature and the logarithm of permeability, above which conduction is unimportant relative to convection.

Modeling multicomponent organic chemical transport in three-fluid-phase porous media

A two-dimensional finite-element model was developed to predict coupled transient flow and multicomponent transport of organic chemicals which can partition between nonaqueous phase liquid, water, gas and solid phases in porous media under the assumption of local chemical equilibrium. Gas-phase pressure gradients are assumed negligible and liquid flow equations are solved simultaneously using an upstream weighted solution method with time-lagged interphase mass-transfer terms and phase densities. Phase-summed component transport equations are solved serially after computation of the velocity field also by an upstream weighted finite-element method. Mass-transfer rates are evaluated from individual phase transport equations by back-substitution and corrected for mass-balance errors. A number of hypothetical one- and two-dimensional simulations were performed to evaluate the applicability of the model to predict the transport of slightly soluble and volatile organics in three-fluid-phase porous media. Results indicate that mass-transfer rate and fluid density updating have negligible effects during periods of highly transient nonaqueous liquid phase migration but become important for long-term simulations as cumulative dissolution to the water phase and volatilization to the gas phase account for longer proportions of the total mass. Due to low solubilities of environmentally important organic liquids, the efficiency of organic removal by aqueous-phase dissolution and transport can be very slow. Gas-phase diffusion can have a significant influence on the mass transport of organics with large Henry's constants.

Nonaqueous phase liquid transport and cleanup: 1. Analysis of mechanisms

Groundwater contamination by nonaqueous liquids such as organic solvents and petroleum hydrocarbons frequently occurs as a result of surface spills, tank leaks, and improper disposal practices. This first of two papers examines the physics governing the emplacement and movement of a separate phase in porous media, the role of sorption, and the conditions necessary to mobilize a separate phase. The movement of the separate phase is controlled by capillary forces, and ganglia displacement by groundwater is not possible under reasonable hydraulic gradients. In addition, because of mass transfer limitations in liquid phase dissolution, groundwater extraction at contaminated sites is shown to be ineffective in removing the nonaqueous contaminant within a reasonable time frame. Therefore other means of mobilizing the trapped second phase are needed, steam displacement is proposed and steam front propagation through contaminated porous media is evaluated. The results of laboratory experiments supporting some of these analytical results are presented in the second paper (Hunt et al., this issue).

Hydraulic continuity of residual wetting phase in porous media

This paper presents results of drainage tests in Berea sandstone, thin glass bead packs, and a two-dimensional glass capillary micromodel, obtained at vanishingly small capillary numbers, using oil and water as the two fluids. The primary objective of the present tests was to investigate the pattern of near-stationary residual wetting fluid saturations reached in Berea sandstone samples at various applied pressure differentials, using a porous plate at the exit face of the sample. Pressures ranging up to about 30 times the threshold pressure of penetration and times on the order of 5 weeks were used. The results do not indicate a lower limit of the wetting phase saturation. The lowest saturation reached is under 10% which is much lower than the “irreducible” saturations reported previously in sandstones. The near-stationary saturation reached under a certain applied pressure differential decreased abruptly when the pressure differential was increased, resulting in a lower near-stationary value after each pressure increase. The performance of the porous plate used in these tests set a limitation to the maximum pressure differential that could be used without running the risk of starting to produce also the displacing nonwetting fluid. Model experiments were performed with thin bead packs contained between two parallel glass plates in an attempt to visualize various displacement mechanisms of water from pore clusters that appear to have been completely surrounded by oil. In these experiments the islands of water which were completely surrounded by oil were displaced and produced through a continuum of oil. When oil breakthrough was prevented by the application of a capillary barrier at the exit, the displacement of water occurred close to the displacement pressure estimated for the island of beads containing the “trapped” water. Without the application of a capillary barrier, however, very much higher pressures and hundreds of pore volumes of throughput of the displacing fluid were necessary for displacement of the “trapped” water. It is believed that the mechanism of displacement of the wetting phase through a continuum of the nonwetting phase consists of transport of the wetting phase on the solid surface in the form of rivulets. Pore wedges or edges, as well as surface capillary grooves which are present on rough surfaces, have been shown to result in surface capillary transport of a wetting fluid. For example, surface capillary rise of wax was observed on ground glass surfaces.

Displacement of residual nonwetting fluid from porous media

Percolation theory of transport in random composites is used to explain the correlation between the residual saturation of nonwetting phase in porous media after displacement by a wetting phase and the capillary number, this number being a measure of the ratio of Darcy-law viscous force in the wetting liquid to interfacial tension force in curved menisci between the two phases. Statistical concepts of percolation theory give estimates of the length distribution of blobs created when the nonwetting phase loses continuity because of displacement by the wetting phase. These estimates agree with the few experimental data. Simple blob mobilization theory and experiments establish that the capillary number required to mobilize a blob is inversely proportional to its length in the direction of the Darcy-law pressure gradient; this and the predictions of percolation theory account for the observed capillary number correlation.

Percolation theory of residual phases in porous media

When one fluid displaces another by through a porous medium, the fraction of pore space occupied by trapped residual phase correlates with the ratio of viscos to capillary force in the flow. This dependence, heretofore unexplained, is derived from the mechanics of fluid blobs, the nature of pore strecture, and precolation theory. Pore space topology is shown to be as important as geometry in the statistical flow behaviour of large populations of fluid blobs in two-phase flow in porous media. Topology and geometry can each be modelled usefully by a single parameter characteristic of the pore space.

Prediction of effective thermal conductivity of two‐phase porous media by nomogram

AbstractA nomogram for the prediction of the effective thermal conductivity of two phase porous media is presented which is constructed according to the Chaudhary and Bhandari equation based upon the geometric mean of maximum and minimum thermal conductivities. A chart estimating the effective thermal conductivity values between probable limits and a nomogram determining porosity values are also included.

MECHANISMS AFFECTING DISPERSION AND MISCIBLE DISPLACEMENT

This review describes the progress made in an attempt to examine the mechanisms influencing the dispersion of solute material in another miscible phase in porous media. The medium is considered to consist of a microstructure made up of the pores and void spaces in and between the solid materials. Because the geometry of the microstructure is generally too complex to be described by a single model, it is broken into several different types of models. This requires that the important mechanisms controlling the transport be identified through experiment, so that realistic microstructure models may be developed. The microscopic results need to be combined and averaged, so that a comparison with macroscopic behavior can be attained. The theory is intimately related to experiments, since like turbulence, it is necessary to combine experimental measurement with theoretical formulations to find the values of undetermined parameters. One difficulty is that the physical structure of the media may contribute effects which are not easily included in the microscopic analysis and yet which contribute in a significant manner to the overall process. (81 refs.)