Oil and gas produced water for cattle, crops, and surface water discharge: Evaluation of chemistry, toxicity and economics

Oil and gas produced water (PW), may help alleviate regional water scarcity affecting agriculture, but is often rich in salts and organic compounds that constrain agricultural applications. The specific objective is to assess the reuse potential of conventional PW through a comprehensive assessment of chemistry, toxicity, and economics by investigating PW from 18 conventionally drilled wells from sandstone formations in the Colorado Denver-Julesburg Basin. Ammonium, total dissolved solids, boron, sodium, and chloride were all close to recommended guidelines for livestock and crop irrigation and surface water discharge. Diesel and gasoline range organics and polycyclic aromatic hydrocarbons were detected in low concentrations in evaporation ponds compared to oil water separators, suggesting volatilization or degradation of organic compounds. Radium levels were generally low, but select samples exceeded the regulatory 5 pCi/g threshold, categorizing them as Non-Exempt TENORM (Technologically Enhanced Naturally Occurring Radioactive Material) waste. EC₅₀ with Daphnia magna (D. magna) showed little to no toxicity for PW sampled in evaporation ponds in contrast to EC₅₀ values of 12 % at the oil water separator, indicating that volatile organics controlled toxicity. However, the Aryl Hydrocarbon Receptor (AhR) bioassay illustrated toxicity not captured by the EC₅₀ test. After chemical and toxicological analyses, it is clear that treatment is required, which informed our techno-economic assessment (TEA). Current PW volumes result in a treatment cost of $5.38/m³ ($1.42/barrel) by nanofiltration, but a scenario with increased volumes will result in a lower cost of $3.83/m³ ($0.60/barrel). Our chemical, toxicological, and economic assessment indicates that the PW in this study has potential to be discharged to surface water or reused for cattle and crop irrigation.