Dispersion in Heterogeneous Nonuniform Anisotropic Porous Media

Dispersion in Heterogeneous Nonuniform Anisotropic Porous Media
Author: Robert Albert Greenkorn
Publisher:
Total Pages: 82
Release: 1970
Genre: Dispersion
ISBN:

The objective of this project is to study the theory and measurement of dispersion during miscible flow in heterogeneous nonuniform anisotropic porous media. An understanding of the dispersion phenomenon is necessary to predict flow of miscible fluids in non-homgeneous porous media. A significant literature review of dispersion in non-homogeneous porous media was accomplished. The continuum and statistical theories of flow in porous media were studied. A series of experiments in models of unconsolidated porous media were run to study the effects of heterogeneity, nonuniformity, and anisotropy on dispersion. The non-homogeneities are defined in relation to permeability of the media and dispersion coefficients are correlated with respect to permeability. Tracer output curves from models were interpreted for dispersion. Dispersion changes significantly with permeability. When models of different permeability are connected, the dispersive effect is not reciprocal. Dispersion changes significantly with nonuniformity. Likewise there is a significant effect when models of different nonuniformity are interconnected (second-order heterogeneity). Anisotropy was included in two kinds of models (linear and radial) by packing alternate layers of beads causing flow through these layers at different angles. The usual dispersion model is not adequate for "block box" prediction of the tracer output curve for data on anisotropic shperes. The results have immediate practical applicates, especially in tracing of contaminents in surface and subsurface flow such as movement of pesticides, fertilizers, acid mine drainage, feed-lot waste, etc. through the soil.

Dispersion Phenomena of Solutes and Particles and Their Applications in Porous Media

Dispersion Phenomena of Solutes and Particles and Their Applications in Porous Media
Author: Xiaoyan Meng
Publisher:
Total Pages: 0
Release: 2019
Genre:
ISBN:

Due to the special features, nanoparticles have seen various applications from drilling and completion as well as reservoir characterization to enhanced oil recovery (EOR). Not only does dispersion dominate solute and particle transport in both aquifers and hydrocarbon reservoirs, but also it imposes a significant impact on oil recovery during either chemical flooding or miscible gas injection processes for the injected agents. Considering the inherent heterogeneity and complex flow behaviour in porous media, therefore, it is of fundamental and practical importance to accurately describe dispersion of solutes and particles (including nanoparticles) in a uniform parallel-plate fracture and a circular tube. Also, this shall serve as a solid foundation for their applications to enhance oil recovery in fractured rocks and porous media. Besides, more efforts need to be extended to study solute and particle dispersion in porous media with different degrees of heterogeneity under various flow conditions. Using the moment analysis method and Green's function, mathematical formulations have been developed to determine dynamic dispersion coefficients for passive (i.e., chemically inert) and reactive (i.e., chemically active) particles flowing in a parallelplate fracture and a circular tube with fully-developed laminar flow under different source conditions across the full-time scale. These newly developed formulations have been verified for both solute and particle transport by agreeing well with analytical solutions and the random walk particle tracking (RWPT) simulations. Subsequently, the newly developed formulations for passive particles flowing in a parallel-plate fracture have been extended to match experimental measurements, while particle dispersion coefficients are notably less than those calculated by using the extended Taylor theory. For passive solutes and particles, at early times, dispersion coefficient is not only controlled by source condition, but also negatively correlated with center-of-mass velocity. After the critical time, source effect is negligible and all dispersion coefficients approach the values obtained through the extended Taylor theory. The relationship between particle size and dispersion coefficient for passive particles varies with time where they are positively correlated if Peclet number is larger than its critical value; otherwise, they are negatively correlated. As Damköhler number increases, for reactive particles, at long times, both reaction rate and center-of-mass velocity increase in magnitude, but dispersion coefficient decreases. At early times, however, those three parameters are not sensitive to Damköhler number. Consequently, reaction at the tube walls greatly affects concentration distribution. Coupling with the RWPT and pore-network modeling simulation, it is found that particle dispersion is greatly affected by particle size in a homogeneous model; however, for a heterogeneous model, throat velocity difference caused by heterogeneity plays an important role. In a homogeneous model, dispersion coefficient of particles (i.e., 7 dp 5 10   m) is overestimated without size exclusion, while the size-exclusion effects become more important as flow rate increases. In the heterogeneous models, however, size-exclusion effects of particles can be neglected. The dispersion difference between volumetric and uniform distributions increases with particle size and heterogeneity of the pore-network model. For a homogeneous model, dispersion coefficient with uniform distribution leads to a larger value than that with volumetric distribution; however, as heterogeneity increases, dispersion coefficient with volumetric distribution shows a larger value.