Geochemical characteristics and their implication of light hydrocarbons in natural gas from the Lower Paleozoic carbonate reservoirs in the Daniudi gas field, Ordos Basin

The genetic types and source of the Lower Paleozoic natural gas in Ordos Basin China are controversial, geochemical characteristics light hydrocarbons fifth member Ordovician Majiagou Formation (O 1 m 5 ) studied by taking Daniudi field as an example, order to reveal origin source. C 5−7 dominated iso-alkanes rather than n-alkanes, methyl cyclohexane (MCH) content is mostly higher nC 7 hydrocarbons. K 2 values range from 1.06 1.16 0.33 0.81, respectively. indicate that mainly coal-derived which has been generated humic rocks Upper Carboniferous Taiyuan (C 3 t), with insignificant contribution O sapropelic rocks. pools were accumulated through downward lateral migration free phase. aromatic contents 6-7 /MCH ratios easily affected factors such water solubilization, adsorption migration, evaporation, fractionation, therefore, secondary alteration needs be considered when using these parameters identify origin.