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Abstract: The Distribution of Hydraulic Conductivity within the Dolomite Aquifer of Southern Wisconsin and its Relation to System Sedimentology


The Devonian/Silurian dolomite aquifer of eastern Wisconsin consists of interbedded mudstones and coarser facies on the western flank of the Michigan Basin. Hydraulically, the units are inter-bedded high and low conductivity aquifers and aquitards which have been subsequently fractured. In southeastern WI, the system behaves as a dual porosity medium where horizontal motion is dominantly porous medium flow and vertical exchange between high conductivity strata is controlled by fractures within lower conductivity aquitards.

Despite lithification, dolomitization and structural deformation, the horizontal hydraulic conductivities (Kh) of these units is still most strongly correlated to the original environment of deposition. Differences of two to three orders of magnitude exist between coarse and fine-grained facies and persist for 100s of kilometers parallel to strike. In all the facies observed, there is also an exponential increase of Kh with an increase in scale of measurement from rock volumes of 1E-04 to 1E+03 cubic meters. This scaling effect is directly linked to depositional facies.

The vertical anisotropy (Kh/Kv) of units within the system also varies with sedimentary facies. Here, however, fine-grained units have values closer to unity, suggesting dominance by vertical fractures.

AAPG Search and Discovery Article #90939©1997 AAPG Eastern Section and TSOP, Lexington, Kentucky