GWYNN, J. WALLACE, Utah Geological Survey, Salt Lake City, UT

ABSTRACT: Saline Waters Produced from Oil Fields in the Uinta and Paradox Basins, Utah

The Uinta and Paradox basins in eastern Utah contain most of the state's oil and gas fields. Saline water is normally co-produced during the production of liquid and gaseous hydrocarbons from these fields.

This study (1) characterized the chemical composition and salinity of the co-produced waters from the two basins; (2) determined the vertical and lateral changes in their salinities and chemical compositions, and the probable causes for these changes; (3) postulated flow paths and barriers for both oil and water; and (4) evaluated potential economic uses for these saline waters.

In the Uinta basin, the saline water chemistry shows a bathtub-ring pattern both in individual formations and for the basin as a whole. This pattern is characterized by a shallow basin margin zone of calcium-magnesium-bicarbonate-rich waters, an intermediate zone of variable chemistry commonly with high sulfate, and a deep central zone of potassium-sodium-chloride-rich waters. The distribution suggests that depth is the major control of water chemistry with little stratigraphic or formation control. Areas where the saline waters contain low sulfate, magnesium, and calcium, and high sodium and chloride are coincident with the basin's major oil fields.

In the Paradox basin, there is strong stratigraphic or formation control on water chemistry, particularly at the Pennsylvanian-Permian boundary. Below this boundary, the waters are highly concentrated, sodium chloride rich, and show a general increase in salinity with depth. Above this boundary, the waters are less saline and show much more variability in both chemistry and salinity. In general, the chemistry and salinity of these waters reflect host formation lithology and mode of origin (marine, mixed, or nonmarine). In addition, both salinity and chemistry change laterally within these formations and may represent the mixing of one or more water types. Ion exchange, mineral precipitation, and mixing are possible mechanisms to explain the variations in water chemistry.

AAPG Search and Discovery Article #90993©1993 AAPG Rocky Mountain Section Meeting, Salt Lake City, Utah, September 12-15, 1993.