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- Title
鄂尔多斯盆地中东部奥陶系马家沟组米探 1 井天然气成因与来源.
- Authors
孟强; 史江龙; 赵恒; 黄军平; 刘艳; 王镱清; 谢小敏; 徐耀辉
- Abstract
The Well Mitan-1 obtained high-yield industrial gas flow in the fourth member of the Majiagou Formation of Ordovician (O1m4) in the mid-eastern Ordos Basin, which has achieved a major breakthrough in the exploration of Ordovician subsalt natural gas. However, there are disputes on the origin of natural gas in Well Mitan-1 at present. The measured results show that the natural gas in Well Mitan-1 is mainly composed of alkane gas (95.18%), the gas drying coefficient (C1/C1-5) is 0.947, the content of H2S is 3.49%, and there is also a small amount of N2 and CO2 in non-hydrocarbon gas. The carbon isotopic compositions of methane, ethane and propane in the natural gas are −45.5‰, −26.4‰ and −24.3‰, respectively. Based on the regional geological background, the characteristics of potential source rocks and the geochemical characteristics of natural gas, it is considered that the natural gas in Well Mitan-1 is self-generated and self-accumulated oil-associated gas in Ordovician subsalt carbonate rocks. However, there are some geochemical anomalies, such as methane carbon isotope value (δ13C1) is lighter and ethane carbon isotope (δ13C2) has the characteristics of coal-type gas. Combined with the thermal simulation experiment of hydrocarbon generation and the characteristics of residual gas in rocks, it is considered that the special geochemical characteristics of Well Mitan-1 are closely related to the gypsum rocks. On the one hand, the ubiquitous gypsum-rock provides a good caprock, which makes retainment of the early-generated natural gas. On the other hand, the existence of gypsum rock promotes the generation of heavy hydrocarbon gases (C2+) and H2S. In addition, less than 5% H2S content and higher C2+ content indicate that the thermochemical sulfate reduction (TSR), if any, should not be so strong that methane is not affected by TSR. The δ13C2 may be a sensitive parameter for identifying TSR.
- Subjects
GAS wells; NATURAL gas; INDUSTRIAL gases; CARBONATE rocks; CARBON isotopes; CARBONATES; COALBED methane
- Publication
Natural Gas Geoscience, 2023, Vol 34, Issue 10, p1696
- ISSN
1672-1926
- Publication type
Article
- DOI
10.11764/j.issn.1672-1926.2023.05.011