25th International Meeting on Organic Geochemistry IMOG 2011

P-373
Geochemistry of coalbed methane and co-production water of
Fuxin basin, Northeast China
Shaobo Liu, Yan Song, Xiaokang Gao
Research Institute of Petroleum Exploration and Development (RIPED), PetroChina, Beijing, China
(corresponding author:lsb@petrochina.com.cn)
Coalbed methane have been commercially produced
in Liujia block, Fuxin basin, Northeast China. Gas
composition, �D and � 3 C of coalbed methane;
chemical composition, �D and � 8 O of production
water were analyzed in this study.
TDS (total dissolved solids)of production water is
low (1601 to 2384 mg/l) and exclusively NaHCO3
type. �D (-85.3 to -78.9 per mil), � 8 O (-10.9 to -9.9
per mil), TDS of production water have a narrow
range.
The isotopic values of water from production wells,
mine, river plot below the global meteoric water line
(GMWL) on a line near but above the values of
present-day water. The results indicates that all the
water comes from meteoric water and has the similar
distillation.
�D (-258.8 to -230.41 per mil) and � 3 C (-52.7 to -44.7
per mil) of coalbed methane plot on the thermogenic
area of Whiticar‘s CD diagram (Fig.1). High C1/C2+
ratio (above 3000) and �DCH4-DH2O diagram show that
CO2-reduction secondary biogenic gas mixed with
thermogenic gas. � 3 C (-22.6 to -18.6 per mil) of
coalbed dioxide indicates that the mixing amount of
biogenic gas is low.
Three stages of coalbed methane accumulation is put
forward: (1) In early Cretaceous, the original low
mature (Ro=0.5 to 0.61%) thermogenic gas
accumulated in the Fuxin group coal; (2) The basin is
uplift and the sedimentary rock is eroded in late
Cretaceous; (3) Diabase intrudes the coal-bearing
strata in Tertiary and highly permeable contact zone
is developed. Thermogenic gas from the contact
metamorphic coal and deep strata, secondary
biogenic gas from meteoric water along the contact
zone, mixed with original low mature thermogenic
gas.
� 13 C-CH4(‰ vs.PDB)
-120
-100
-80
-60
-40
-20
Fuxin Powder River
II
IV
IV
0
-450 -400 -350 -300 -250 -200 -150 -100 -50 0
III
I
�D-CH4(‰ vs.SMOW)
Fig.1 Whiticar‘s CD diagram methane
showing compositional fields for gases of various
origins (Whiticar, 1999).
①-thermogenic gas;②-bacteria methyl type
fermentation gas;③-bacteria carbonate reduction
gas;④-mixed and transition gas. Data of Powder
River from Flores et al.(2008) are used for
comparison.
References
[1] Flores R M, Rice C A, Stricker G D, Warden A,
Ellis M S. Methanogenic pathways of coal-bed
gas in the Powder River Basin, United States:
The geologic factor [J]. <strong>International</strong> Journal of
Coal Geology, 2008,76: 52–75
[2] Whiticar M J. Carbon and hydrogen isotope
systematics of bacterial formation and oxidation
of methane [J]. Chemical Geology, 1999, 161:
291–314.
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