HR: 0800h
AN: H11B-0302    [Abstracts]
TI: A new Method to Estimate the Representative Elementary Volume (REV) for Porosity in Heterogeneous Karst Aquifers Using Geographic Information Systems
AU: * Gross, M R
EM: grossm@fiu.edu
AF: Florida International University, Department of Earth Sciences, Miami, FL 33199 United States
AU: Manda, A K
EM: amand001@fiu.edu
AF: Florida International University, Department of Earth Sciences, Miami, FL 33199 United States
AB: Karst limestones are characterized by solution-enhanced macropores and conduits that lead to exceptional heterogeneity at the aquifer scale. The interconnected network of solution cavities often results in a conduit flow regime that bypasses the less permeable rock matrix. Efforts to manage and protect karst aquifers, which are vital water resources in many parts of the world, will benefit from meaningful characterizations of the heterogeneity inherent in these formations. To this end, we propose a new method to estimate the representative elementary volume (REV) for macroporosity within karst aquifers using techniques borrowed from remote sensing and geospatial analysis. The REV represents a sampling window in which numerous measurements of a highly-variable property (e.g., porosity, hydraulic conductivity) can be averaged into a single representative value of statistical and physical significance. High-resolution borehole images are classified into binary images consisting of pixels designated as either rock matrix or pore space. A two-dimensional porosity is calculated by summing the total area occupied by pores within a rectangular sampling window placed over the binary image. Small sampling windows quantify the heterogeneous nature of porosity distribution in the aquifer, whereas large windows provide an estimate of overall porosity. Applying this procedure to imagery taken from the Biscayne aquifer of south Florida yields a macroporosity of ~40%, considerably higher than the ~28% porosity measured from recovered core samples. Geospatial analysis may provide the more reliable estimate because it incorporates large solution cavities and conduits captured by the borehole image. The REV is estimated by varying the size of sampling windows around prominent conduits and evaluating the change in porosity as a function of window size. Average porosities decrease systematically with increasing sampling size, eventually converging to a constant value and thus validating the REV concept for porosity in the Biscayne aquifer.
DE: 1829 Groundwater hydrology
DE: 1832 Groundwater transport
DE: 1857 Reservoirs (surface)
DE: 1869 Stochastic processes
DE: 1884 Water supply
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting