Environ Geochem Health. 2025 Nov 27;48(1):18. doi: 10.1007/s10653-025-02877-z.
ABSTRACT
The dissolution of fugitive gases in saline to hypersaline groundwater in arid regions is largely unclear. Groundwater samples from three major oil field aquifers in northern (NK), southeastern (SEK), and western Kuwait (WK) were investigated to determine the concentration, sources, evolution, and distribution of dissolved CH4. Saline NK wells demonstrated the highest concentration of CH₄ at 688 µg/L, followed by WK at 419 µg/L and SEK at 102 µg/L. Elevated CH₄ concentrations were detected in Na-Cl-SO₄ and Na-Cl type groundwater. CH₄ hotspots were located in regions with increased lineament intersections and proximity to older wells near the hydrocarbon reservoirs, exhibiting an inverse correlation with conductivity and H₂S levels. Microbes in the SEK region utilize carbon substrates, leading to reduced CH₄ levels in comparison to NK and WK. δ13CCH₄ values showed relatively depleted signatures for WK (- 51.2‰), while NK displayed enriched values alongside decreasing CH₄ levels, indicating thermogenic sources. Enriched δ13CCH₄ values in SEK (+ 9.5‰) are associated with elevated CH₄ concentrations. The δ2HCH₄ values range from – 479‰ to – 140‰, while δ2HH₂O values range from + 4 to – 36‰, indicating the presence of mixed methanogenic sources across the regions. In NK, the thermogenic methane was observed with variation in isotope signatures due to complex processes. In SEK, although reducing environments prevailed, the carbon isotope fractionation is exceeded by the hydrogen isotope due to the significant impact of microbial oxidation during the diffusive migration process. In the west of Kuwait, the isotopic signatures of methane are depleted, mainly due to the oxidation of organic matter or through Sulfate-Driven Anaerobic Oxidation of Methane (SD-AOM) and carbonate dissolution. Four primary sources of CH₄ are microbial, methyl-substrates, carbonate substrates, and mixed sources, which are identified alongside two main processes: biogenic and thermogenic.
PMID:41299129 | DOI:10.1007/s10653-025-02877-z
