Estimation of porosity and hydraulic conductivity from X-ray CT-measured solute breakthrough

Abstract

AbstractHeterogeneities are common in natural porous media and are present on different scales. Use of X-ray computed tomography (CT) may provide a tool for quantifying smallscale heterogeneities in porosity and hydraulic conductivity in porous media. Porosity and saturated hydraulic conductivity distributions were estimated using CT for a series of undisturbed soil core samples taken from a field site. CT measurements were collected during breakthrough experiments using an iodide tracer. Techniques were developed to estimate porosity and hydraulic conductivity from solute breakthrough data. Results were compared with bulk sample measurements. CT-measured porosity compared well with laboratory-measured porosity. Hydraulic conductivity estimated from CT methods slightly overestimated laboratory-measured values. These techniques provide a method to quantify the spatially variable porosity and hydraulic conductivity on a millimetre scale rather than on a core-averaged scale. Chemical transport through the soil was predicted using a finite element method for each core using the CT-measured soil properties. Comparisons between measured and predicted chemical transport suggest that small-scale heterogeneities cause departures between measured and simulated solute breakthrough curves, and that a smaller grid size may be needed to improve the simulation.