Measurement of porous media component content and heterogeneity using gamma ray tomography

Abstract

Abstract. Tomographic images of porous media are complex distributions of linear attenuation coefficients that reflect the combined effects of scanning spatial resolution, photon statistical measurement errors, and true material densities. We address how the true voxel-scale attenuation distribution and measurement errors are convoluted to yield measured density frequency distributions. A deconvolution algorithm is demonstrated that uses the measured density frequency distributions and known photon statistical errors to quantify average cross-section volume contents of pure components and a mixedcomponent phase. The mixed-component phase represents regions where components are intertwined or varied in spaces smaller than the scanning resolution. This approach is applied to a complex core of the Culebra Dolomite Member of the Rustler Formation collected at the Waste Isolation Pilot Plant, near Carlsbad, New Mexico. The methodology provides a quantitative measure of the volume content of gypsum, dolomite, and mixedcomponents, and heterogeneity in the sample. This research demonstrates how porous media compositions can be quantified by applying a statistical approach to tomographic measurements obtained from gamma ray computerized tomography (gamma CT). More importantly, the relationship between the density frequency distribution and the component volume content and heterogeneity in a sample can be determined. These procedures are general in nature and may also be applied to X ray and synchrotron images, subject to the limitations of the specific machine and porous media system. Tomography Measurements

Methods for colloid transport visualization in pore networks

“…The opacity of most natural media precludes use of light‐based visualization methods and presence of iron oxide may confound use of MRI. With requisite optimization of detection limits, sensitivity, as well as spatial and temporal resolution, imaging techniques based on X‐ray [ Thieme et al , 2003; DiCarlo et al , 2006; Li et al , 2006], γ ‐ray [ Hsieh et al , 1998], or positron emission [ Khalili et al , 1998] may in the future enable imaging of colloid concentrations or even individual colloids in intact soil cores.…”