Open AccessGeochemical characteristics and genesis of the Upper Paleozoic natural gas in Longdong area, Ordos Basin, NW China
Author(s) -
Qingfen Kong,
Lingyin Kong,
Jianfeng Li
Publication year - 2020
Publication title -
iop conference series. earth and environmental science
Language(s) - English
Resource type - Journals
eISSN - 1755-1307
pISSN - 1755-1315
DOI - 10.1088/1755-1315/600/1/012010
Subject(s) - natural gas , source rock , isotopes of carbon , geology , methane , paleozoic , hydrocarbon , geochemistry , maturity (psychological) , carbon fibers , kerogen , structural basin , paleontology , total organic carbon , chemistry , environmental chemistry , psychology , developmental psychology , materials science , organic chemistry , composite number , composite material
The Upper Paleozoic gases from the Longdong areas in the Ordos Basin are characterized by low contents of heavy hydrocarbon gases, the mean value of wetness as 2%, relatively heavy δ 13 C 1 (δ 13 C 1 value -28.3‰), and large variations in δ 13 C 2 + . The distribution pattern of carbon isotopic sequence of natural gas is mainly characterized by the abnormal light δ 13 C 2 + values and carbon isotopic reversal. According to the organic geochemical characteristics of natural gas and the development of gas-source rocks, the upper Paleozoic natural gas in Longdong area belongs to high mature and over-mature “coal-formed gas”. In theory, only the mixture of highly mature gas with extremely low contents of heavy hydrocarbon gases and a small amount of natural gas with higher contents and lighter carbon isotopic composition of heavy hydrocarbon gases can lead to the occurrence of abnormally light δ 13 C 2 + and the carbon isotope reversal between methane and ethane. The mixed gas is probably derived from the thermal cracking of a small amount of residual soluble organic matter in the gas-source rocks and reservoirs during the initial stage of the uplift movement at the end of Early Cretaceous. Key words: Ethane carbon isotope; Inverted sequence of carbon isotopic composition; Natural gas of high maturity; natural gas genesis; Ordos Basin.