Unconventional oil and gas (UOG) production, including hydraulic fracturing, has opened up new sources of hydrocarbon resources. Organic compounds are used in UOG for hydraulic fracturing and other production purposes. These compounds may be injected into the reservoir containing the oil and gas (typically shale) and may interact with the substrate. A portion of these compounds are returned to the surface in wastewater (flowback and produced water), along with organic substances mobilized from the shale, hypersaline formation water, and radioactive and inorganic substances. The composition of organic substances in wastewater, changes in composition during production, and the organic geochemistry of UOG production and wastewater disposal are poorly understood. We have examined the organic composition of wastewater from a number of different UOG production areas (Marcellus Shale, Permian Basin, Williston Basin, Eagle Ford Shale, California Central Valley) with 10-50 samples per area, including production time series studies. Compound classes in the wastewater include: normal and branched alkanes, aromatic hydrocarbons, some polycyclic aromatic hydrocarbons, a series of glycol ethers, phenols, amides, and heterocyclic compounds. Total dissolved organic carbon (DOC) in the wastewater can range from &lt;10 to 100s of mg/L. A typical pattern observed is very high DOC with high abundance of alkanes and aromatic hydrocarbons and glycol ethers during the flowback period (usually first 20 days after hydraulic fracturing) , followed by much lower DOC and a change to fewer alkanes and aromatic hydrocarbons during the latter stages of production. However, this general pattern may change at any time if production requires the addition of organic chemicals (e.g. to control biological growth or reduce corrosion). Identifying the composition of wastewater will assist in preparing for reuse in hydraulic fracturing or beneficial use (e.g., irrigation of crops), and in providing markers used in the event of environmental contamination from spills or leaks.

Characterization of organic matter in wastewater from unconventional oil and gas production

253rd National Meeting (2017)

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