Natural gas genesis and sources in the Zizhou gas field, Ordos Basin, China

• Carbon isotopic compositions of alkane gases in Zizhou gas field are heavy.
• The contents of C5–7 isoalkanes and methylcyclohexanes in the gases are high.
• Gases in Zizhou gas field are typical coal-derived gas.
• The gases were generated by mature to high-mature C–P coal measures.
• Mixture of gases of different maturities caused a carbon isotopic reversal.

The Zizhou gas field is a large, tight sandstone gas field in the Ordos Basin, China. Based on the analysis of the geological background, gas components, light hydrocarbon composition, carbon and hydrogen isotope values of alkane gases, and the geochemical correlation between gases of the Zizhou gas field and analogs from other fields in the basin, we conclude that : (a) most natural gases in the Zizhou gas field are dry with a small content of wet gas; (b) the gases have similar carbon isotopic and light hydrocarbon compositions to the analogs from other fields, as well as much more positive δ13C values and high contents of C5–7i-alkanes and methylcyclohexanes, indicating typical coal-derived gas; (c) carbon isotopic reversal in some gas samples is due to mixing of coal-derived gases of different maturities; (d) the gases are sourced from mature to high-mature Carboniferous–Permian coal-measures; and (e) the gas reservoirs represent continuous accumulations.