Date: Thursday, Feb 5th
Presenter: Dr. Dorthe Wildenschild, Professor, Environmental Engineering, OSU CBEE, Associate Dean, OSU Graduate School
X-ray tomography is a technique that allows for three-dimensional observation and measurement of variables internal to an otherwise opaque object. Detail resolution ranges from 100s of microns for cm-sized samples, 1-5 microns for mm-sized objects, and 100s of nm for micron-sized objects. Contrast depends on density and atomic number of the imaged object and creative use of contrast agents can thus help delineate otherwise difficult to identify features. The technique has advanced to the point where detailed probing and quantitative analysis of processes and mechanisms at the pore-scale is possible.
Among the variables of relevance to reaction and transport in subsurface porous media that can be measured are pore/fracture space characteristics such as pore size distribution, pore area/volume and reactive surface area. In terms of flow path characterization, information about pore networks such as geometry, connectivity, and tortuosity can be measured with increasing detail. For multi-phase systems, we can measure fluid-fluid interfacial area and curvatures and characterize the wettability state of a porous medium. Pores and multi-phase fluid bodies can be classified as connected vs. disconnected, and morphological and topological measures such as Betti and Euler numbers can be measured.
Changes to the pore structure in response to reactive processes such as precipitation and dissolution can be quantified, and reaction kinetics derived from imaging at multiple time steps during the transformation. For relatively simple porous media, microbial biofilms can be imaged and characterized in three dimensions to provide biofilm volume, spatial distribution, biofilm response to changes in environmental conditions, etc.
This presentation will provide an overview over the current state of imaging of earth science materials using x-ray tomography, and a discussion of use of contrast agents, technique limitations, and new potential advances.
Dorthe Wildenschild is a Professor in the School of Chemical, Biological and Environmental Engineering at Oregon State University. Research in her group focuses on physics, chemistry, and microbiology of relevance to flow and transport in porous mediagenerally applied to the subsurface environment and, in many cases, involving multiphase flow phenomena. She received MS and PhD degrees in Civil and Environmental Engineering from the Danish Technical University (DTU) in 1992 and 1996 and has been at OSU since 2002.