25th International Meeting on Organic Geochemistry IMOG 2011

P-319
The study of C1-C3 gas generation behavior of kerogen by
closed-system thermal simulation and Py-GC
Yuhong Liao, Xunyong Zhu, Ansong Geng, Yinhua Pan
Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, China (corresponding
author:liaoyh@gig.ac.cn)
In closed thermal simulation system, the C1 directly
generated by kerogen was mixed with C1 generated
by oil cracking. It is hard to eliminate the actual gas
generation behavior of kerogen. In this research,
kerogen was heated at two rates, 20ºC/h and 2 ºC /h
in a closed system from 350 ºC to 600 ºC. The
volume of C1, C2 and C3 was measured and weight
normalized. Conversions of C1, C2 and C3 were
calculated based on gas generated (conversion in
Fig. 1(a)). Then the reacted kerogens were
pyrolyzated by Py-GC at 800 ºC for 10s to study the
residual C1, C2 and C3 potential of kerogen. The real
conversion rates of C1, C2 and C3 of kerogen were
calculated based on residual rates of conversion
(conversion in Fig. 1(b)). The thermal maturities of
kerogen were calculated based on Easy Ro
(Sweeney et al., 2000). The conversions measured
were plotted against calculated Ro.
The Py-GC results indicated that more than 90% of
C1, C2 and C3 potentials of kerogen were
progressively consumed up before Ro% reach 1.3.
While weight-normalized volume of C1, C2 and C3
generated in closed system simulation suggest that
the generation of C1, C2 and C3 extends to much
higher maturity range. The generation of C1 doesn‘t
reach its end though Ro% reaches 3.0. So there
exists dramatically difference in gas generation
behavior between closed system and open system
thermal simulation. It is due to significant
hydrocarbon secondary cracking in closed system
thermal simulation. Kerogen first releases
hydrocarbons with higher molecule weight during
thermal maturation, then these hydrocarbons crack
into smaller ones step by step and the final products
are methane and pyrobitumen. Thus the generation of
methane can last very broad maturity range. In open
system thermal simulation, the alkyl side chains are
released from structure of kerogen as volatile
molecules and blown away, and there is no
secondary cracking of hydrocarbons during kerogen
thermal maturation. Most C1 can only be generated
by the primary cracking.
The experimental results also indicate that the
distribution of activation energy (E) based on closed
system pyrolysi are much higher than the distribution
of activation energy at identical frequency factor (A =
1.0E+14). The average activation energy of C1
generation is 62.53 kcal/mol in closed system
pyrolysis, while average activation energy of C1
generation is 52.75 kcal/mol. In open system
pyrolysis, average activation energy of C2 generation
is 52.33 kcal/mol, and average activation energy of
C3 generation is 49.78 kcal/mol. Average activation
energy of C3 is much lower than C1. It indicated that
C3 alkyl side chains are much easier to be broken
apart from kerogen structure. It is consistent with
common accepted rules of hydrocarbon generation.
Fig. 1 (a) Conversion of C1, C2 and C3 in closed system
simulation based on volume of gas generated; (b) Real
conversion of C1, C2 and C3 of kerogen based on residual
rate of conversion measured by Py-GC
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