25th International Meeting on Organic Geochemistry IMOG 2011

P-257
The components and carbon isotopic compositions of inorganic
hydrocarbon gases with different carbon origins synthesized in
gold tube closed-system
Jingkui Mi 1,2 , Shuichang Zhang 1,2 , Kun He 1,2
1 Research Institute of Petroleum Exploration and Development, PetroChina, Beijing, China, 2 State Key
Laboratory for Enhanced Oil Recovery, Beijing, China (corresponding author:jkmi@petrochina.com.cn)
This paper reports the components and carbon
isotope compositions effects of the abiotic
hydrocarbon gases produced by Fischer-Tropsch
synthesis under 50MPa pressure in gold tube closedsystem
in which the reactants are two kinds of CO2
with different δ 13 C values (δ 13 Cheavey-CO2=-0.5‰ 、
δ 13 Clight-CO2=-16.51‰) , a graphite(δ 13 Cgraphite=-
21.05‰) and hydrogen, with montmorillonite loading
the chloridate of iron and nickel as catalysts. The
components and carbon isotopic compositions of
synthetic alkane gases will produce great change with
the constant temperature time lasting at different
temperature. All the carbon isotope trends of synthetic
alkane gases (C1~C4) show from inverse trend, partial
reverse to normal trend with the constant temperature
time lasted from 2hr to 60hr at 400℃ in three groups
experiments in which the carbons of three different
origins are hydrogenated into inorganic hydrocarbon
gases, but the periods of the inverse trend of alkane
gases carbon isotopic holding are different. At 400℃,
the period of the inverse trend of carbon isotopic
gases holding is only 2hr when light CO2is
hydrogenated, the period of the inverse trend of
carbon isotopic gases lasting is less than 5hr if the
reactants are heavy CO2 and H2, and the period of the
inverse trend of carbon isotopic gases lasting could
maintain 20hr as the graphite is hydrogenated. The
fractionations of 24.24‰, 11.33‰, 5.02‰ and 4.22‰
among CH4, C2H6, C3H8 and C4H10 show in the
synthesis process with light CO2 and H2 as reactants,
the fractionations of 17.73‰, 5.57‰, 4.43‰ and
1.85‰ among CH4, C2H6, C3H8 and C4H10 show in the
synthesis process with heavy CO2 and H2 as
reactants, and, the fractionations of 8.22‰,
3.58‰, 3.83‰ and 4.81‰ among CH4, C2H6, C3H8
and C4H10 show in the synthesis process with
graphite and H2 as reactants, respectively. Generally,
all the maximum yield of total alkane gases occurs in
the stage the inverse trend turning to that partial
reverse of their carbon isotope in all three groups
experiment at 400℃. There is only a little ethane in
products besides methane with 2 hr constant
temperature at 700℃. With time of constant
temperature at 700℃ increasing, ethane disappear.
Moreover, the longer does constant temperature last,
the less of the amount of methane and the heavier of
carbon isotope of methane are. We suggest that the
reaction mechanisms of the carbon with different
origins affiliating inorganic gases synthesis are
different in the mantle or in meteorites. The
monatomic carbon is easier to take part in the
reaction to generate inorganic hydrocarbon gas
formation than that of gaseous carbon if the
hydrocarbon gases with inverse carbon trend of
C1~C4 are sure to be inorganic origin, and, the
gaseous carbon with enrichment 13 C is easier to enter
in to inorganic hydrocarbon gas than that with poor
13 C. The inorganic hydrocarbon gases does not yield
in the very deeper layers of the earth with high
temperature, but in a shallower layers of the earth
with relatively lower temperature in a short time,
because the heavy hydrocarbon gases would be
broken into methane with the temperature and the
time hold in a relatively high temperature increasing,
the reaction mechanism in different matter will turn
from dynamic reaction to thermal one. Methane could
also be broken into monatomic carbon and hydrogen
with temperature further increasing. This may be a
main reason that no commercial perfect inorganic
hydrocarbon gas pool is found at present.
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