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- Title
The influence of pressure on hydrocarbon gas generation and carbon isotope of methane from type III kerogen.
- Authors
Chun-min HE; Jun GAN; Gang LIANG; Xing LI; Xing WANG; Hui TIAN
- Abstract
Samples from transitional source rocks of Qiongdongnan Basin were pyrolyzed under 50 MPa, 100 MPa and 150 MPa, in order to tentatively discuss the effects of pressure on hydrocarbon gas generation and carbon isotope fractionation of methane. The results presented that increasing pressure would retard the hydrocarbon gas yield when pyrolytic temperature was low (EqVRO% less than 2.69%), and when it came to wet gases, the retardation was more significant than methane. However, there would be little influence of pressure at high pyrolytic temperature (EqVRO% more than 2.77%), or even slightly promoting methane generation. Calculated kinetic parameters showed that activation energy and frequency factor increased with growing pressure, as a result of that growing pressure makes the gas in the closed gold tube expand to do more work as well as the reactant concentration enrichment. At the rate of 5 ℃/Ma, pressure increases from 50 MPa to 150 MPa, which will result in the temperature increase of about 10 ℃ for every 50 MPa in the gas window. When temperature is higher than 260 ℃, the effect of pressure is no longer obvious. The experiment results also presented that growing pressure makes methane rich in 12C1. And it could result in 3.2‰ negative shift of carbon isotope values from 50 MPa up to 150 MPa. Meanwhile, the relationships between carbon isotope values and methane conversion were not the same under different pressures, indicating that negative shift of methane carbon isotope value was not only related to the retardation of methane generation, but also related to the slight changes happened to methane generation mechanism, which resulted in the changes in the distribution of the difference of activation energy between 13C1 and 12C1.
- Subjects
CARBON isotopes; KEROGEN; METHANE; ACTIVATION energy; HYDROCARBONS; ISOTOPE shift
- Publication
Natural Gas Geoscience, 2020, Vol 31, Issue 7, p5
- ISSN
1672-1926
- Publication type
Article
- DOI
10.11764/j.issn.1672-1926.2020.05.006