Chemical characterization in hydraulic fracturing flowback and produced water (HF-FPW) of shale gas in Sichuan of China

Abstract

Large amounts of fracturing flowback and wastewater with complex compositions are produced during hydraulic fracturing. Characterization of hydraulic fracturing flowback and produced water (HF-FPW) is an important initial step in efforts to determine a suitable treatment method for this type of wastewater. In the present study, fracturing flowback and produced water samples were obtained from well CN-F and well CN-E in the prophase and anaphase stages of the Changning shale gas mining area. Chemical characterization of inorganic and organic substances was then conducted. Metal contents were determined by inductively coupled plasma optical emission spectroscopy (ICP-OES), and all inorganic anions involved were determined by ion chromatography. The organic pollutant components were analyzed in detail by combining Fourier transform infrared spectrometer (FTIR) and gas chromatography-mass spectrometer (GC-MS). Results showed that samples contained salt (TDS = 30,000-50,000 mg/L), metals (e.g., 650 ± 50 mg/L calcium), and total organic carbon (TOC = 32-178 mg/L). The organic substances detected in all samples could be divided into six categories, alkanes, aromatics, halogenated hydrocarbons, alcohols, esters, and ketones. C 6-C 21 straight-chain alkanes and C 7-C 13 naphthenes had the highest amount of organic matter, reaching more than 48%. The organic matter contained fracturing fluid additives, such as surfactants (e.g., ethylene glycol), and nitrotrichloromethane, which is a chlorinated product of some additives. These results provide information on the chemical composition of HF-FPW in Sichuan, China, as well as a basis for subsequent processing.

Comparison of the Hydraulic Fracturing Water Cycle in China and North America: A Critical Review

“…FPW is composed of injected HF fluid, in situ formation brine, constituents leached during shale–water interactions, products of in situ transformation reactions, and hydrocarbons in the target formation (Figure S3). ,− The pH and inorganic chemical constituents of FPW produced from unconventional plays in China are similar to those in FPW in North America, − but the salinity of FPW from shale gas plays in China is generally lower (maximum reported total dissolved solids (TDS) is ∼65,000 mg/L) ,− than in the U.S. and Canada (maximum reported TDS is ∼630,000 mg/L), − ,− with the exception of the Niobrara shale play in the Denver Basin where the upper limit is approximately 30,000 mg/L (Figure F) . Geochemical and isotope data suggest that the chemical composition of FPW is controlled by the chemistry of the in situ formation brine, evaporated seawater modified by water–rock interactions derived from the target and/or several different geological strata .…”

“…104−109 Hydrocarbons including C 6 −C 21 straight-chain alkanes, C 7 − C 13 naphthenes, and chemical additives including surfactants (e.g., ethylene glycol) and nitrotrichloromethane have been reported in FPW from the Changning shale gas play in the Sichuan Basin. 88 Important indicators of organic pollutants, including aromatic hydrocarbons such as benzene, toluene, and xylene have been detected in early FPW (<7 days) from the Qaidam Basin. 110 These compounds are consistent with those detected in FPW in the U.S. and Canada.…”

Data-Driven Endpoint Selection in Data-Poor Scenarios: Bioassay Design for Shale Gas Flowback and Produced Waters

“…As shown in Figure S2, fatty alcohols, aromatics, and alkanes were the dominant pollutants among these single compounds, followed by aliphatic hydrocarbons and fatty acids. Similar to the contaminant categories in the HFList, Wang et al 21 also found abundant alcohols, aromatics, and alkanes in the SGFPW samples from China. The distribution of common physicochemical properties is presented in Figures S3−S6.…”

Prioritizing Organic Pollutants for Shale Gas Exploitation: Life Cycle Environmental Risk Assessments in China and the US

“…The uncertainty related to shale gas risks in the present study was mainly due to the life cycle inventories and the availability of data for evaluating risks, specifically organic toxicity and concentration. Previous studies have highlighted significant differences in the concentrations of organic pollutants found in flowback wastewater from shale gas sites in different regions, 60 which consequently led to considerable variations in the calculated risks. Uncertainties (±standard deviation) of LCI and associated end-of-pipe risks were analyzed through Monte Carlo simulations (SI_2 data_06).…”