Preliminary study on the origin identification of natural gas by the parameters of light hydrocarbon

• DOI: 10.1007/s11430-008-5017-x
• Publication Date: 2008-07-18T14:32:57Z
• Authors: GuoYi Hu; Jian Li; Jin Li; ZhiSheng Li; Xia Luo; QingWu Sun; ChengHua Ma
• Keywords: Cyclopentanes

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-specific δ13C value of individual light hydrocarbon between humic-sourced gas and sapropelic-sourced gas have been founded. The humic-sourced gas has the distribution of δ13Cbenzene> −24‰, δ13Ctoluene >−23‰, δ13Ccyclohexane > −24‰ and δ13Cmethyl cyclohexane> −24‰, while the sapropelic-sourced gas has the distribution of δ13Cbenzene <−24‰, δ13Ctoluene< −24‰, δ13Ccyclohexane< −24‰ and δ13Cmethyl 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.