Identifying the Causes and Sources of Harmful Gases in Tunnel Construction

Strategic Insights -

Research conducted by researchers at Southwest Petroleum University in Chengdu, People's Republic of China, has highlighted the importance of understanding the causes, sources, and migration processes of harmful shallow underground gases in tunnel construction. The research, published in the journal Frontiers in Earth Science, focuses on the Tingzikou Irrigation Area Water Diversion Project, where the issue of harmful shallow underground gases in the tunnel has become increasingly prominent.

Key Takeaways:

  • The study applied an integrated approach of carbon isotope composition to analyze the geochemical characteristics of shallow natural gas components from a high-gas water diversion tunnel in the Tingzikou Irrigati Area.
  • The results revealed that the methane content is the most abundant, at up to 45.16%, while carbon oxides are in the range of 0.02%-0.1%.
  • The study concluded that the shallow natural gas originates from the shallow oil and gas source rock layers of the Ziliujing Formation at the Ziliujing anticline, making it a 'self-generated and self-stored' gas.
  • The research highlighted the importance of identifying the causes and sources of harmful gases to prevent possible catastrophic impacts and mitigation during tunnel construction.
  • The study provided further evidence of the source of shallow natural gas in the area by comparing isotopic values from different strata and data from the Sichuan Basin fault system.

Statistics:

  • The methane content in the gas samples ranges from 40.12% to 45.16%.
  • The carbon dioxide content in the gas samples ranges from 0.02% to 0.1%.
  • The heavier hydrocarbons (C2+) account for 2.27% of the gas samples.
  • The dryness coefficient is 0.96, indicating relatively low thermal maturity.
  • The average d13C1 value (a measure of the isotope composition of the carbon in the gas sample) is -28.80, which is similar to the ethane isotope values of the J1l and J1m strata in the central Sichuan Basin.

Sources:

  • "Sources of shallow natural gases in the Longgang marine gas field, NE Sichuan Basin: an example from the water conveyance tunnel." Frontiers in Earth Science, 2025,13.
  • http://www.frontiersin.org/earth_science (Frontiers Media S.A.)
  • https://doi.org/10.3389/feart.2025.1573369