THE USE OF STOCHASTIC SIMULATIONS AND GEOPHYSICAL LOGS TO CHARACTERIZE SPATIAL HETEROGENEITY IN HYDROGEOLOGIC PARAMETERS

Characterization of the spatial distribution of hydrogeologic paramete rs in an aquifer is important to understanding the hydrodynamics of a groundwater flow system. The operational procedure presented in this p aper uses core permeability and porosity data and geophysical logs to characterize hydrogeologic parameters, especially hydraulic conductivi ty (K). The procedure is illustrated with a geostatistical analysis of the permeability distribution along a 120 km cross section of the Mil k River aquifer in Alberta, Canada. Geologic and hydrogeologic data fr om aquifers come in a variety of forms, In deep, regional aquifers, th e most ubiquitous form usually is geophysical logs that are used to de termine spatial variations in the thickness, porosity, and permeabilit y as well as other rock properties of hydrostratigraphic units. Severa l methods of deriving hydraulic conductivity values from geophysical l ogs are evaluated with respect to the Milk River aquifer. Based on a s tatistical evaluation, a direct relation between porosity and permeabi lity was selected. Once the hydrogeologic data were analyzed and evalu ated, a stochastic approach using Bayesian updating with Cholesky deco mposition is used to describe the spatial heterogeneity of hydraulic c onductivity. This approach produces random-correlated fields of hydrau lic conductivity that are conditioned at specific locations by the geo physically derived hydraulic conductivity values. The conditioned, ran dom-correlated fields of hydraulic conductivity are a description of r elatively small-scale heterogeneity in the hydraulic conductivity fiel d that can be used in a numerical transport model as a detailed, spati al description of hydraulic conductivity.