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The light hydrocarbon composition of 209 natural gas samples and individual light hydrocarbon carbon isotopes of 53 natural gas samples from typical humic-sourced gas and sapropelic-sourced gas in the four basins of China have been determined and analyzed.Some identification parameters for humic-sourced gas and sapropelic-sourced gas are proposed or corrected.The differences of compound-specificδ13C value of individual light hydrocarbon between humic-sourced gas and sapropelic-sourced gas have been founded.The humic-sourced gas has the distribution ofδ13C benzene > -24‰,δ13C toluene >-23‰,δ13C cyclohexane >-24‰andδ13C methyl cyclohexane >-24‰,while the sapropelicsourced gas has the distribution ofδ13C benzene <-24‰,δ13C toluene <-24‰,δ13C cyclohexane <-24‰and δ13C methyl cyclohexane <-24‰.Among the components of C7 light hydrocarbon compound,such as normal heptane(nC7),methyl cyclohexane(MCH)and dimethyl cyclopentane(ΣDMCP),etc,relative contents of nC7 and MCH are influenced mainly by the source organic matter type of natural gas.Therefore,it is suggested that the gas with relative content of nC7 of more than 30%and relative content of MCH of less than 70%is sapropelic-sourced gas,while gas with relative content of nC7 of less than 35%and relative content of MCH of more than 50%is humic-sourced gas.Among components of C5-7 aliphatics, the gas with relative content of C5-7 normal alkane of more than 30%is sapropelic-sourced gas,while the gas with relative content of C5-7 normal alkane of less than 30%is humic-sourced gas.These paremeters have been suggested to identify humic-sourced gas and sapropelic-sourced gas.
The light hydrocarbon composition of 209 natural gas samples and individual light hydrocarbon hydrocarbon isotopes of 53 natural gas samples from typical humic-sourced gas and sapropelic-sourced gas in the four basins of China have been determined and analyzed. Identification criteria for humic-sourced gas and sapropelic-sourced gas are proposed or corrected. These differences of compound-specific δ13C value of individual light hydrocarbon between humic-sourced gas and sapropelic-sourced gas have been established. The humic-sourced gas has the distribution of δ13C benzene> -24 ‰ δ13C cyclohexane> -24 ‰ and δ13C methyl cyclohexane> -24 ‰, while the sapropelicsourced gas has the distribution of δ13C benzene <-24 ‰, δ13C cyclohexane <-24 ‰, δ13C cyclohexane> -24 ‰ and δ13C cyclohexane δ13C methyl cyclohexane <-24 ‰. Amm the components of C7 light hydrocarbon compound, such as normal heptane (nC7), methyl cyclohexane (MCH) and dimethyl cyclopentane (ΣDMCP), etc, relative contents of nC7 and MCH are influenced mainly by the source organic matter type of natural gas. Wherefore, it is suggested that the gas with relative content of nC7 of more than 30% and relative content of MCH of less than 70% is sapropelic-sourced gas, while gas with relative content of nC7 of less than 35% and relative content of MCH of more than 50% is humic-sourced gas. Among components of C5-7 aliphatics, the gas with relative content of C5-7 normal alkane of more than 30% is sapropelic-sourced gas, while the gas with relative content of C5-7 normal alkane of less than 30% is humic-sourced gas. These paremeters have been suggested to identify humic-sourced gas and sapropelic-sourced gas.