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2-D and 3-D Representations of Outcrop Heterogeneity from Lidar Imagery for Groundwater Modeling

Nichols, Elizabeth M.1; Weissmann, Gary 1; Wawrzyniec, Timothy 1; Frechette, Jedediah 1; Scuderi, Louis A.1
1 Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM.

Development of models that preserve the influence of heterogeneity at varying scales is vital for modeling petroleum movement in reservoirs and solute dispersion in groundwater systems. Varying velocities in a flow field are caused, in part, by material heterogeneity. In order to characterize heterogeneity at the 2-3m scale, a series of high-resolution (millimeter-scale) terrestrial lidar scans were taken of sediments located in braided stream exposures west of Albuquerque, New Mexico, and of fluvial sediments near the Hanford Site in Washington. At both sites, multiple scans of the same outcrop were projected onto a 2D plane. Mean and standard deviation were calculated from the projected multiple points in the 2D grid. The mean and standard deviation results were processed through a series of filters to enhance textural information and distinguish between sand and gravel. The resulting binary image was converted to a text array of numerical color values, one representing each lithology (e.g. sand, gravel). Each lithology was assigned a reasonable hydraulic conductivity value. Because of limitations related to 2D flow models, we are evaluating the influence of 3D heterogeneity in the Albuquerque sediments by scraping the outcrop to reveal succesive slices at ~2 cm intervals. We are developing a 3D volume by scanning each successive slice, compiling the 3D point cloud data, and interpolating lidar reflection intensity values into a regular 3D grid. Lithofacies will be segmented from this grid. Groundwater flow and solute transport time were simulated using a finite-difference model (MODFLOW) and a particle tracking code (RWHet), respectively. 2D simulations show that flow and solute transport are focused by cross-bedding into the coarser-grained units, and we expect results from the 3D simulations show similar trends. Thus, the majority of the flow may be focused into a smaller volume of the material making up a reservoir or aquifer. This indicates that at the small scale, petroleum bypass may be significant even with minimal contrast in permeability between various sedimentologic materials. These solute transport simulations result in non-Fickian distribution of velocity across the simulation caused by heterogeneity. We expect to use results from these studies to allow prediction of non-Fickian transport parameters for upscaling in similar heterogeneous media.


AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009