Journal
CHEMOSPHERE
Volume 306, Issue -, Pages -Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.chemosphere.2022.135594
Keywords
Hydraulic fracturing; Strontium isotope; Groundwater contamination; Geochemical modeling; Hydrochemistry
Categories
Funding
- National Natural Science Foundation of China [42072286, 41761144059]
- Special Funds for Basic Scientific Research of Central Colleges [300102299301, 300102291507]
- Fok Ying Tong Education Foundation [161098]
- National Ten Thousand Talent Program [W03070125]
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In this study, the sources of strontium and its isotopic composition in hydraulic fracturing flowback fluid were identified, and it was determined that 87Sr/86Sr can be used as a sensitive indicator for groundwater pollution. A modeling approach was used to assess the sensitivity of 87Sr/86Sr in indicating contamination, and it was found that even a small amount (0.89%) of fracturing flowback fluid can be identified using this method.
Hydraulic fracturing technology has made unconventional oil and gas development economically viable; however, it can lead to potential environmental issues such as groundwater pollution. Strontium isotope (87Sr/86Sr) is considered as a sensitive tracer to indicate potential groundwater contamination. In this study, strontium (Sr) and 87Sr/86Sr sources of hydraulic fracturing flowback fluid are identified with 87 flowback fluid samples and 5 borehole core samples. High Sr concentrations and 87Sr/86Sr values were found in fracturing flowback fluid. The hydrogeochemistry evidence shows high Sr and 87Sr/86Sr in fracturing flowback fluid mainly comes from formation water with high ion concentrations, while Sr and 87Sr/86Sr of formation water develop in diagenesis and long term water-rock interaction (e.g., feldspar dissolution and clay mineral transformations) under the high temperature and pressure. A complete evaluation system was executed to assess the sensitivity of 87Sr/86Sr indicating potential pollution on groundwater. The mixing curves which 87Sr/86Sr combined with Sr and Cl were also established by mixing models to indicate groundwater pollution. The modeling results show mineral dissolution/precipitation and cation exchange have little impact on 87Sr/86Sr in the mixing process between fracturing flowback fluid and groundwater, which 87Sr/86Sr can identify contamination when only 0.89% of fracturing flowback fluid mixes with groundwater. Finally, the potential contamination pathways are discussed. It is highly unlikely fracturing flowback fluid contaminates groundwater and soil through upward migration, whereas leakage is a more prevalent pollution pathway.
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