Abstract

The Uinta structural and topographic basin, located in northeastern Utah, contains many of the state’s major oil and gas fields. During the production of liquid and gaseous hydrocarbons from these fields, water of varying salinities is normally co-produced.

The cumulative production of saline water from these fields, through December 1990, is approximately 1.346 billion barrels. It is produced mainly from reservoirs in the Green River and Wasatch Formations in the oil fields of Duchesne and Uintah Counties. The water/oil ratio within these two counties is increasing over time. This is due to normal encroachment of formation water into the oil and gas reservoirs and increased use of water-flood production techniques.

Four methods are used to dispose of most of the co-produced saline water. These include regulated surface discharge; reinjection back into the ground during water flood or enhanced oil-recovery projects; reinjection into salt-water disposal wells; and disposal into large, open, salt-water evaporation pits.

Uinta Basin oil well saline waters vary in total dissolved solids (salinity) and chemistry both vertically and laterally within individual formations, and throughout the basin. The six major ions (or ion-pairs) present in the saline water include sodium (plus potassium), magnesium, calcium, chloride, sulfate and bicarbonate (plus carbonate). Each of the six ions appears to vary independently throughout the basin. Areas where the saline water contains low sulfate, magnesium and calcium, and high sodium and chloride, are coincident with the basin’s major oil fields. Depending on economic factors, potentially-valuable mineral salts or saturated brines could be produced from these saline waters through the processes of solar evaporation and salt precipitation.