Organic Substances in Wastewater from Continuous Oil and Gas Production in the Permian Basin

In 2019 the Permian Basin (4.2 million barrels of oil per day) passed the Ghawar Field in Saudi Arabia to become the world's largest producing onshore oil field. Along with oil and gas, the Permian Basin produces between 9 and 15 million barrels of wastewater per day. The wastewater contains a host of chemical substances, including high levels of salt, organic substances, metals, and radioactive materials, posing problems of safe disposal and challenges for cleanup and reuse. Here, we discuss the organic composition of wastewater from the Permian Basin and soil from sites where improper disposal of this wastewater occurred.

Wastewater was collected at sites across the Permian Basin. Dissolved organic carbon (DOC) concentrations ranged from 30-350 mg/L in produced water sampled at least a week after hydraulic fracturing in the wells, consistent with DOC values of produced water in other shale plays (e.g. Eagle-Ford and Marcellus). Extractable hydrocarbons in wastewater collected directly from the wellhead, determined by liquid/liquid extraction in dichloromethane and analyzed by gas chromatography/mass spectrometry, were found to be dominated by straight and branched alkanes (C₁₀-C₃₈). However, wastewater from the separator tank contained mostly chemicals used in production (e.g. a series of glycol ethers, and phenols) as observed elsewhere in produced water from continuous shale plays. Of interest was the presence of 2-iodophenol, probably produced by the reaction of high levels of iodine in formation water with phenol used as a production chemical.

Most wastewater from oil and gas production is disposed of properly, or treated for reuse, but we investigated sites in southeastern New Mexico on Federal (BLM) land where suspected illegal dumping of >4,000 barrels of wastewater occurred. The dump sites had high conductivity and chemistry consistent with produced water in the Permian Basin. Organic substances present in the surface soil consisted mostly of straight and branched alkanes >C₂₀, suggesting that the lower molecular weight alkanes had been lost to volatilization. Below 5 cm in the soil, the extractable hydrocarbons consisted of more oxygenated organic compounds that appear more mobile in the environment.