--> Application of Petroleum Geology Techniques to an Environmental Study of Groundwater Resources in Southwestern Indiana, by W. M. Mitchell and Z. Smidchens; #90986 (1994).

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Abstract: Application of Petroleum Geology Techniques to an Environmental Study of Groundwater Resources in Southwestern Indiana

William M. Mitchell, Zinta Smidchens

The Indiana Geological Survey, in cooperation with the Indiana Division of Oil and Gas, is currently engaged in a study of the Mississippian and Pennsylvanian rocks of southwestern Indiana to identify the 3,000 ppm and 10,000 ppm total dissolved solids (TDS) boundaries. These boundaries are used to define aquifers as Underground Sources of Drinking Water (USDW) that are protected by law from contamination.

The majority of data was derived by calculating TDS using resistivity and density/porosity readings from geophysical logs of 2,200 wells. Elevations of the 3,000 ppm and 10,000 ppm boundaries were interpolated on the basis of these calculations.

Five core holes (449 to 609 feet deep) were drilled for this study, and resistivity and density/porosity logs were run. Thirteen selected zones in these core holes were isolated with packers, and formation waters were recovered. TDS values of the samples were measured by two different laboratory techniques and were compared to calculated TDS values. All zones tested had salinity values less than 10,000 ppm, and 50 percent of the samples had salinity values approaching the calculated values.

This study demonstrated that the boundaries delineated by the first occurrence of 3,000 ppm and 10,000 ppm TDS form generally basinward-dipping surfaces; however, they are much more irregular than anticipated and are characterized by numerous localized salinity anomalies. The 10,000 pm TDS surface appears to be deeper than expected and reversals in salinity gradients are relatively common. Salinity anomalies and reversals can be indicators of fluid upwelling or of the introduction of surface water.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994