Geochemical Characteristics and Genesis of Oil-Derived Gas in the Jingbian Gas Field, Ordos Basin, China

• Published in: Energy & fuels 2017-10, Vol.31 (10), p.10432-10441
• Main Authors: Han, Wenxue, Tao, Shizhen, Hou, Lianhua, Yao, Jingli
• Format: Article
• Language: English
• ISSN: 0887-0624; 1520-5029
• DOI: 10.1021/acs.energyfuels.7b01179

The source rocks of natural gas of the Jingbian gas field in Ordos Basin, China, are unclear, and the origin of oil-derived gas is controversial. On the basis of a series of experiments on source rock evaluation, including total organic carbon, Rock-Eval pyrolysis, carbon isotope composition of kerogen, chloroform bitumen A, maceral compositions, and gas chromatograms, we evaluated the hydrocarbon generation potential of the possible source rocks. We also conducted the components and stable carbon isotopes of natural gas and compared geochemical characteristics of natural gas and source rock-adsorbed gas. The results indicate that source rocks from the Lower Permian Taiyuan Formation have some hydrocarbon-generating capability but far less than its proximate Carboniferous and Permian coal measures. Oil-derived gas originated from Lower Permian Taiyuan Formation limestone was expulsed to the Majiagou Formation by coal-derived gas generated from the Carboniferous and Permian coal measures, as indicated by source rock evaluation, adsorbed gas, and geochemical characteristics of gas collected from the limestone-developed area. The former two gases mixed in the Majiagou Formation above the gypsum–salt bed, which corresponds to the geochemical characteristics of gas from the above gypsum–salt bed. Source rocks from the Majiagou Formation above the gypsum–salt bed experienced much more weathering, leaching, and oxidation compared to those under the gypsum–salt bed, suggesting that the latter are comparatively better than the former. As a result of the barrier of the gypsum–salt bed, source rocks of the Majiagou Formation under the gypsum–salt bed can generate a self-stored natural gas reservoir, as indicated by adsorbed gas and geochemical characteristics of gas from under the gypsum–salt bed. Natural gas of the Jingbian gas field is mainly from the Carboniferous and Permian coal measures, with limited oil-derived gas from the Taiyuan Formation.