title: Modeling fine-scale geological heterogeneity--examples of sand lenses in tills.
abstract: Sand lenses at various spatial scales are recognized to add heterogeneity to glacial sediments. They have high hydraulic conductivities relative to the surrounding till matrix and may affect the advective transport of water and contaminants in clayey till settings. Sand lenses were investigated on till outcrops producing binary images of geological cross-sections capturing the size, shape and distribution of individual features. Sand lenses occur as elongated, anisotropic geobodies that vary in size and extent. Besides, sand lenses show strong non-stationary patterns on section images that hamper subsequent simulation. Transition probability (TP) and multiple-point statistics (MPS) were employed to simulate sand lens heterogeneity. We used one cross-section to parameterize the spatial correlation and a second, parallel section as a reference: it allowed testing the quality of the simulations as a function of the amount of conditioning data under realistic conditions. The performance of the simulations was evaluated on the faithful reproduction of the specific geological structure caused by sand lenses. Multiple-point statistics offer a better reproduction of sand lens geometry. However, two-dimensional training images acquired by outcrop mapping are of limited use to generate three-dimensional realizations with MPS. One can use a technique that consists in splitting the 3D domain into a set of slices in various directions that are sequentially simulated and reassembled into a 3D block. The identification of flow paths through a network of elongated sand lenses and the impact on the equivalent permeability in tills are essential to perform solute transport modeling in the low-permeability sediments.
authors.affiliation: Technical University of Denmark, DTU Environment, Miljøvej 113, 2800 Kgs. Lyngby, Denmark. Geological Survey of Denmark and Greenland, Øster Voldgade 10, 1350 Copenhagen, Denmark. University of New South Wales, National Centre for Groundwater Research and Training, 2052 UNSW, Sydney, Australia. University of Neuchâtel, Centre for Hydrogeology and Geothermics, Rue Emile-Argand 11, 2000 Neuchâtel, Switzerland.
authors.forename: Timo Christian
authors.initials: TC
authors.lastname: Kessler
authors.forename: Alessandro
authors.initials: A
authors.lastname: Comunian
authors.forename: Fabio
authors.initials: F
authors.lastname: Oriani
authors.forename: Philippe
authors.initials: P
authors.lastname: Renard
authors.forename: Bertel
authors.initials: B
authors.lastname: Nilsson
authors.forename: Knud Erik
authors.initials: KE
authors.lastname: Klint
authors.forename: Poul Løgstrup
authors.initials: PL
authors.lastname: Bjerg
mesh_terms: D003198:Computer Simulation; D019015:Geologic Sediments; D005844:Geology / Q000379:methods*; D008962:Models, Theoretical; D012822:Silicon Dioxide
chemical_list: D012822:Silicon Dioxide