MAPPING HYDROGEOCHEMISTRY OF THE DENVER-JULESBURG BASIN

Since 2011, more than 2900 oil and gas wells have been drilled and hydraulically fractured in Denver-Julesburg (DJ) Basin, with each of these wells using an average of 810,000 gallons of water for drilling and fracturing. 100% of these wells are located in high or extreme water stress areas, creating concern within communities about increased freshwater withdrawals for oil and gas purposes. The objective of this study is to identify aquifers with a total dissolved solids (TDS) content exceeding 10,000 parts per million (ppm), (the EPA classification for Underground Sources of Drinking Water), and evaluate them as potential alternatives to freshwater for industry use. This research has generated a database of groundwater quality data within the basin and mapped geospatial water quality data. Data was taken from the National Carbon Sequestration Database (NATCARB), a database containing national brine information. For this study, 1,206 data entries were collected, of these, 497 met criteria for further analysis; which included depth information, complete entries for major ion concentrations, TDS greater than 10,000 ppm, pH between 4.5 to 9.5, and charge balance less than 5%. Four geological units with more than 44 database entries were identified: “D” Sandstone, Muddy “J” Sandstone, Plainview Formation, and Lyons Sandstone. The dominant cation of all brine samples is sodium (Na⁺). Dominant anions were either chloride (Cl^-) or sulfate (SO₄^2-). For example, 99% of samples in Lyons have a dominant cation of sodium, 35% of samples have a dominant anion of chloride, and 6.5% of samples have a dominant anion of sulfate. Histograms of water quality parameters indicated high skewness within data distributions. Median TDS for each unit are: 16,472 parts per million (ppm) in the D Sandstone; 14,959 ppm in the J Sandstone; 26,583 ppm in the Plainview; and 29,512 ppm in the Lyons. According to results, all geological formations analyzed have similar water chemistry, and TDS increases with depth and age.