Effects Of Anisotropic Permeability Research Articles

Convective stability analysis of the long-term storage of carbon dioxide in deep saline aquifers

Deep saline aquifers are one of the most suitable geologic formations for carbon sequestration. The linear and global stability analysis of the time-dependent density-driven convection in deep saline aquifers is presented for long-term storage of carbon dioxide (CO 2). The convective mixing that can greatly accelerate the CO 2 dissolution into saline aquifers arises because the density of brine increases upon the dissolution of CO 2 and such a density difference may induce instability. The effects of anisotropic permeability on the stability criteria, such as the critical time for the appearance of convective phenomena and the critical wavelength of the most unstable perturbation, are investigated with linear and global stability analysis. The linear stability analysis provides a sufficient condition for instability while the global stability analysis yields a sufficient condition for stability. The results obtained from these two approaches are not exactly the same but show a consistent trend, both indicating that the anisotropic system becomes more unstable when either the vertical or horizontal permeability increases.

Natural Convection in a Cylindrical Enclosure Filled With Heat Generating Anisotropic Porous Medium

A numerical study has been made to analyze the effects of anisotropic permeability and thermal diffusivity on natural convection in a heat generating porous medium contained in a vertical cylindrical enclosure with isothermal wall and the top and bottom perfectly insulated surfaces. The results show that the anisotropies influence the flow field and heat transfer rate significantly. The non-dimensional maximum cavity temperature increases with increase in permeability ratio. For aspect ratio greater than or equal to two, the nondimensional maximum cavity temperature increases with an increase in the thermal diffusivity ratio. For aspect ratio equal to unity, there exists a critical value of thermal diffusivity ratio at which the maximum cavity temperature is a minimum. This critical value increases with an increase in the value of anisotropic permeability ratio. Based on a parametric study correlations for maximum cavity temperature and average Nusselt number are presented.

Effect of anisotropic permeability on Darcy's law

Abstract The concept of structural stability is discussed and briefly reviewed within the context of fluid flow in porous media. Then the equations for non‐Boussinesq (penetrative) convection in a porous medium with anisotropic permeability are analysed. It is shown, by deriving truly a priori estimates, that the solution exists in the natural functional framework and depends continuously on changes in the permeability. Since under appropriate circumstances the onset of thermal convection may be via Hopf bifurcation rather than stationary convection, such a priori continuous dependence estimates are of much value. Copyright © 2001 John Wiley & Sons, Ltd.

A note on squeeze film between rough anisotropic porous rectangular plates

In this paper, theoretical study of squeeze film lubrication between porous rectangular plates has been advanced by considering the simultaneous effects of anisotropic nature of the permeability and surface roughness of the plates. The effects of anisotropic permeability and roughness parameter on the performance characteristics of squeeze film are discussed. It is found that the loci of maximum load are more sensitive to the anisotropic permeability than the roughness parameter.

The effect of anisotropic permeability on free convective boundary layer flow in porous media

The effect of an anisotropic permeability on thermal boundary layer flow in porous media is studied. The convective flow is induced by a vertical, uniformly heated surface embedded in a fluid-saturated medium. A leading-order boundary layer theory is presented. It is shown that the thickness of the resulting boundary layer flow is different from that obtained in an isotropic porous medium. In general, an anisotropic permeability induces a fluid drift in the spanwise direction, the strength of which depends on the precise nature of the anisotropy. Conditions are found which determine whether or not the boundary layer flow is three-dimensional.

Effect of anisotropic permeability on the transport process during solidification of a binary mixture

Solidification of a binary mixture (NH 4Cl-H 2O) contained in a square cavity is simulated numerically. The anisotropic permeability of the mushy region is incorporated in the model by means of a specific permeability tensor and the principal permeability ratio R. Comparison of representative results with previously reported experimental data shows that the model is capable of resolving fundamental characteristics of the solidification process. Effects of the anisotropy appear to be significant. A small permeability ratio R not only promotes the growth of the secondary layer but also results in a large concentration difference between the mushy and the pure liquid regions. Due to the liquidus temperature depression by higher concentration and the earlier developed thermal convection in the upper layer, severe remelting is also found to occur. In addition, flow interaction across the macroscopic solidification front becomes stronger with increasing permeability ratio R.

Characteristics of externally pressurized porous ceramics air bearings.

In this study, basic characteristics of porous-ceramics air bearings, such as stiffness, load carrying capacity and stability, and analyzed by means of the finite element method. The validity of an FEM computer program developed in this study is examined through experimentation. The effects of anisotropic permeability, porosity and thickness of porous-ceramics materials on the stiffness and pneumatic instability are investigated. The effect of air supply area on the load carrying capacity and stiffness are also analyzed. The effect of the characteristics of porous materials on the occurrence of pneumatic instability is analyzed through the simulation of the dynamic response of bearing. Consequently, it is pointed out that the porosity and thickness of the porous-ceramic materials should be kept as small as possible in order to obtain higher stiffness and stability.

A numerical study of natural convection in a vertical, annular, porous layer

Results of a numerical study of steady, natural convection in a fluid-saturated, vertical, annular, porous layer are reported. The analysis is performed using a finite element computer program based on the Galerkin form of the finite element method. Heat transfer rates are predicted for Rayleigh numbers in the range 25 to 100 with layer aspect ratios ranging from 2 to 8 and ratios of layer height-to-inner radius of 2, 4, and 8. Representative plots of isotherms and streamlines are also presented. Effects of anisotropic permeability are evaluated in a preliminary manner. Application of the results to an insulated storage tank is illustrated.

Reservoir Limit Test on Gas Wells

Abstract During a reservoir limit test, the rate of production is held constant and the bottom-hole flowing pressure is measured. Field examples for a closed reservoir, a sealing fault, a gas-water contact and a nonsealing fault are included. The interpretation of field data is made with the aid of the observed rate of pressure decrease per unit rate of production. Graphs and equations are presented for the pressure interferences commonly found in gas reservoirs. The thousand cubic feet of gas in place proved and possibly explored during a reservoir limit test, the distance to a fault, the angle between two intersecting faults, the interference from a gas-water contact, the evaluation of the formation constants and the effect of anisotropic permeability are considered. Introduction The reservoir limit test is a transient-flow method of evaluating in- place gas, productive limits and deliverability. Background for the test is threefold: the constant (psi/bbl) pressure decline for steady flow in a closed reservoir; the pressure interferences between wells under a transient flow condition as, for example, those in the paper by Elkins; and the Laplace transformation paper by van Everdingen and Hurst. Under a transient-flow condition, the constant pressure decline mentioned before is replaced by a constant drawdown increase. The drainage radius can be evaluated in the field by noting the time of arrival, at shut-in observation wells, of a perceptible drawdown from a producing well. The pressure interferences at a producing well caused by external boundaries can be duplicated by the method of images which was first applied to oil and gas production by Muskat. Examples of Interpreted Field Data Interpretations of field data on four wells are presented. Fig. 1A is for a well in a closed reservoir. All productive limits were reached during a one-day test. Fig. 1B is for a well near a sealing fault. The 10-day test on this well shows no productive limit other than the fault. Fig 1C is for a well near a gas-water contact. The test was stopped at 1.5 days due to the interference from water. Fig. 1D is for a well near a nonsealing fault. The test was stopped at the end of the first day of production because the rate of gas flow across the nonsealing fault was equal to the rate of production from the well. Additional reserves cannot be detected after the rate of leakage becomes equal to the rate of production. Interpretation of the field data obtained during a reservoir limit test is made with the aid of certain equations developed by Jones. Coefficient of Expansion for Reservoir Gas When a well is placed on production, a pressure drawdown is propagated into the reservoir, and the drainage radius for the well increases with time. The drawdown within the drainage radius causes the in-place gas to expand. The coefficient of expansion, for a gas is defined by ............................(1) Solutions of Eq. 1 are plotted in Fig. 2 for 150F reservoirs, gas gravities from 0.6 to 1.05, and pressures from 1,000 to 15,000 psia. Similar data are available for 250 and 350F gas reservoirs. The Eg values were calculated from the compressibility factors of Brown, et al. The effective coefficient of expansion for high-pressure gas reservoirs includes the expansion of interstitial water and rock compressibility as listed in the Appendix. JPT P. 613^