Abstract

An evaluation of 748 chemical analyses of spring, water-well, and oil-and gas-well water samples was made to determine the vertical and lateral variations of salinity and chemistry within the Paradox Basin of Utah. Water salinity and chemistry show the most variance in the vertical direction. Total dissolved solids (TDS), sodium and chloride contents generally increase with depth, while calcium, magnesium, sulfate, and bicarbonate contents decrease. Waters are similar both in salinity and chemistry at similar elevations within formations belonging to the same geologic period.

The contact between the Pennsylvanian and Permian formations is the major divide for vertical changes in water salinity and chemistry. Above the contact, waters are meteoric, generally low in total dissolved solids (TDS) and sodium chloride, and belong to an open, dynamic hydrologic system. Below the boundary, waters are high in TDS and sodium chloride. I propose that these waters belong to a relatively closed and static hydrologic system.

High-salinity and high-sodium chloride brines occur at the lowest sample elevations within the basin, and are coincident with many oil and gas reservoirs. Chemical data are of great value in hydrocarbon exploration, development, production, and brine disposal programs.