Relation Between Hydraulic Conductivity and Texture in a Carbonate Aquifer: Regional Continuity

Abstract

AbstractIn the dolomite aquifer of Milwaukee County, Wisconsin, stratigraphic units deposited as mudstones have little or no visible macroporosity and, based on injection‐pressure tests, have average horizontal hydraulic conductivities of approximately 10−6 cm/sec, controlled by jointing. Coarse‐grained units (packstones and grainstones), however, have horizontal hydraulic conductivities of 10−4 cm/sec and greater, argued to be controlled by granularity, not jointing. Using this relationship between texture and hydraulic conductivity in Milwaukee County and a sedimentary facies analysis, trends in hydraulic conductivity values are predicted for five stratigraphic units over an area of approximately 3500 km2. The predictions are tested qualitatively with sets of specific capacity values within the various stratigraphic units, and quantitatively with injection‐pressure test values from five additional locations. Seven of eight qualitative and four of six quantitative predictions are judged to be successful. Therefore, trends in hydraulic conductivity, and to some extent local values, in this carbonate aquifer are predictable over areas of thousands of square kilometers without any site‐specific data on jointing.The success rate could not have been this high if hydraulic conductivity were not controlled by the granularity of the lithologic units. It is argued, therefore, that the local bulk hydraulic conductivity of this carbonate aquifer is controlled by the granular porosity, and the aquifer will generally behave as a porous medium, even at the small scale of a typical pumping test.