DENSITY-COUPLED TRANSPORT IN HETEROGENEOUS POROUS MEDIA: OBSERVATIONS AND COMPARISON TO STOCHASTIC THEORY

PI: C. Welty, Co-PI: Tissa Illangasekare, Colorado School of Mines
Project Duration: 1/15/99- 12/31/01
Funding Source: NSF Hydrologic Science Program

Objectives

The principal objective of the research was to carry out a series of experiments to quantify the interaction between permeability heterogeneity and high solute concentrations and the effect of this interaction on macrodispersion in saturated porous media. The apparatus developed during C. Welty's 1997-98 sabbatical leave in Kassel Germany has been duplicated in the U.S. for this purpose.

The set of proposed experiments tested the hypothesis that macrodispersion in density-dependent transport can be predicted by existing stochastic theory. Although it is well known that the density of a solute plume can affect its mean motion, the effect of fluid density on fluid mixing or effective dispersion in statistically-characterized heterogeneous porous media has not been systematically documented from an observational standpoint. Qualitative experimental evidence and theoretical predictions indicate that interaction of the density gradients with degree of heterogeneity affects dispersion: the permeability heterogeneity can damp out or enhance the effects of the density gradients on solute spreading depending on the solute/solvent flow configuration.

The experiments were conducted in the laboratory to ensure isothermal conditions and to avoid unwanted geochemical reactions. Fluids of contrasting density (laboratory-grade water and NaCl solutions) were displaced through the constructed tank in a density-stratified, horizontal, stable flow configuration. This fluid displacement scenario was run for three mean pore velocities and four salt concentrations. Measurements of solute concentration made using solution samplers over time and space was compared to predictions of macrodispersion of dense, miscible fluids based on existing stochastic theory developed by the PI. The results serve to confirm previous theoretical work. Such an approach, together with ongoing numerical simulations, contributes to knowledge needed for a unified understanding of this coupled process to aid in predicting large-scale transport of dense, miscible fluids in aquifers. This knowledge base can then serve as the foundation for evaluating the effect on dispersion of additional, realistic non-ideal processes typically associated with density-coupled miscible transport, such as thermal processes and heterogeneous geochemical reactions.

Project Accomplishments

Tank construction began in January 2000. Blueprints were provided by Quentin Moore, a graduate student at Colorado School of Mines working under Tissa Illangasekare. These were modified as needed by C. Welty. Tank construction was carried out by Drexel University's machine shop from January - March 2000 under supervision of C. Welty and M. Salehin. T. Illangasekare visited Drexel in March 2000 to review progress and to assist in water supply design. Tank appurtenances were completed in April - June 2000. Acid washing and permeability testing of ten classes of pre-sieved sand was carried out by undergraduate SESEP Environmental Engineering majors Kristina Peacock and Jason Golumbfskie during June and July 2000. The tank was pressure tested in July 2000. The first packing and set of experiments were started in August 2000. From September 2000 - March 2001 initial runs were carried out by senior Doug Jerolmack, with assistance from Jason Golumbfskie, Tim McMahon, Elizabeth Loik, Jen Uhr, Paul Henry, and Casey Majewski. Hetergeneous runs were conducted in the spring of 2001 and completed by September 2001. A photo album documenting details of construction is linked here.


Related presentations and publications

Kauffman, Leon J. Dispersion of Dense, Viscous, Miscible Fluids in Heterogeneous Porous Media: Laboratory Investigation and Stochastic Two-Dimensional Mean Simulations. M.S. Thesis, Drexel University, Department of Civil and Architectural Engineering, 1996.

Welty, C., and M.M. Elsner, M., Construction of Random Fields in the Laboratory for Observations of Fluid Flow and Mass Transport, J.Hydrology, 202(1/4), 192-211, 1997.

Welty, C. "Design and Construction of a 10-m Tank Containing Porous Media Packed as a Correlated Random Field for Observations of Density-Coupled Transport", EOS Trans. AGU, 78(46), Fall Meeting Suppl., S272, 1997.

Welty, C., Kane, A.C. III and Kauffman, L. J. Stochastic Analysis of Density-Coupled Transport in Aquifers. Water Resources Research, 39(6), 1150-1167, 2003

Welty, C. "Density-Coupled Transport in Heterogeneous Aquifers", lecture presented on February 3, 2003 at "Workshop on Multiscale Modeling of Environmental Systems", Statistical and Applied Mathematical Sciences Institute (SAMSI), Feb 2 - 7, 2003, Research Triangle Park, North Carolina, http://www.samsi.info.

Jerolmack, D. J., C. Welty, and T. Illangasekare. "Fluid Density, Aquifer Heterogeneity, and Velocity Effects on Transverse Dispersivity in a Model Aquifer." Presented on December 12, 2001 at the Fall Meeting of the American Geophysical Union, San Francisco, Abstract in Eos Trans. AGU, 82(47), Fall Meeting Suppl., H32D-0346, 2001. (C)

Jerolmack, D.J. , C. Welty, and T. Illangasekare.
Fluid Density, Aquifer Heterogeneity, and Velocity Effects on Transverse Dispersivity in a Model Aquifer, in preparation.

A photo album of the 1997-99 tank construction in Germany overseen by R. Feldner, B. Krüger, C. Welty, and T. Illangasekare.

Support

This material is based upon work supported by the National Science Foundation under Grants INT 9726781 and EAR-9817823 . Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.