CHARACTERIZATION OF FLOW AND SOLUTE TRANSPORT IN THREE-DIMENSIONAL HETEROGENEOUS POROUS MEDIA USING MAGNETIC RESONANCE IMAGING

1H magnetic resonance imaging (MRI) was used to obtain sequential images of water doped with a paramagnetic tracer as it flowed through a three-dimensional (3D) flowcell (25.5 × 9 × 8.5 cm3) packed with spatially correlated heterogeneous distribution of 1cm3 blocks, each containing one of five different sand fractions. Tracer concentration breakthrough curves (BTCs) were obtained from MRI signal intensity profiles at each voxel (0.1875 × 0.1875 × 0.225 cm3). Voxel scale BTCs were averaged over 0.25 cm, 1 cm, and vertical cross section, and compared with numerical simulations using a finite difference code (STOMP). Root-mean-squared error (RMSE) between measured and simulated BTCs decreased over increasing average scales. Five set of hydraulic conductivity (K) values based on literature and measured values were tested. Considerable differences between measured and predicted BTCs were observed at 0.25 cm and 1 cm scale. The difference can be attributed to: (i) reduction in local effective conductivity caused by the mixing of the coarse and fine sands, and (ii) variability between the experimentally packed and numerical heterogeneous permeability field. Mean arrival time, apparent velocities, and apparent dispersivity were determined from measured BTCs using method of moments for two heterogeneous permeability field with different longitudinal correlation length. Results showed that effective apparent dispersivity increased at a higher rate over distance in the permeability field with a shorter correlation length.