25th International Meeting on Organic Geochemistry IMOG 2011

P-001
Maturity assessment based on dibenzothiophenes distribution
analyzed by comprehensive two-dimensional gas
chromatography with time of flight mass spectrometry in oils
from Colombia
Raphael S. F. Silva 1 , Hélen G. M. Aguiar 2 , Mario D. Rangel 2 , Débora A. Azevedo 1 ,
Francisco R. Aquino neto 1
1 LAGOA-LADETEC, Departamento de Química Orgânica, Instituto de Química, Universidade Federal do
Rio de Janeiro, Rio de Janeiro, Brazil, 2 Petrobras/Cenpes/PDEXP/GEO, Rio de Janeiro, Brazil
(corresponding author:debora@iq.ufrj.br)
Dibenzothiophenes (DBTs) are aromatic sulphur
compounds used to maturity assessment [1]. In this
work the maturity level of ten oil samples from
Colombia was evaluated by comprehensive twodimensional
gas chromatography with time of flight
mass spectrometry (GC×GC-TOFMS). Several
studies using GCxGC have been published in the
literature [2].
The oil samples are from Upper Magdalena Valley
Basin, Colombia. The aromatic fraction of all oil
samples were analysed in a GCxGC-TOFMS System
Pegasus 4D. The column set used was a DB-5MS (30
m) as first dimension and a BPX-50 (1.3 m) as
second dimension.
The DBTs distribution of one sample is shown in
Fig.1a. Three ratios (4-/1-MDBT, 4,6-/1,4-DMDBT
and 2,4-/1,4-DMDBT) have been calculated by
GC×GC-TOFMS. The values for 4-/1-MDBT ratio
ranged from 1.16 to 2.40. The values for ratio 4,6-
/1,4-DMDBT ranged from 0.29 to 1.22. The values for
2,4-/1,4-DMDBT ratio ranged from 0.20 to 0.83.
Classical maturity biomarker parameters were
calculated for oils. Ts/(Ts+Tm) ranged from 0.40 to
0.51, C29ααα S/(S+R) from 0.47 to 0.57, C29
ββ/(αα+ββ) from 0.42 to 0.52 and TA/(TA+MA)
ranged from 0.36 to 0.51. These parameters did not
vary significantly for the samples, which show similar
levels of thermal evolution for the oils.
However, the maturity assessment based on DBT
ratios has a greater range, which allows a better
evaluation of thermal evolution. In Fig.1b is presented
a plot of the RMDBT 4/1 versus RDMDBT 4.6/1.4
ratios. The oils A, C and J were considered the most
mature, while oil H was the less mature. DBT ratios
allowed a better grouping of oils with similar maturity
level as oils E and F.
The aromatic compounds are more resistant to
biodegradation than saturated one which makes them
useful for maturity assessment. The BPX-50 column
used as second dimension provides better resolution
DBTs furnishing the peak area without coelutions.
(a)
(b)
Fig.1. (a) 3D view of the two-dimensional chromatogram of DBTs analysis for one Colombian oil
sample: dibenzothiophene (DBT), methyl-dibenzothiophenes (MDBTs), dimethyldibenzothiophenes
(DMDBTs), trimethyl-dibenzothiophenes (TMDBTs) and tetramethyldibenzothiophenes
(TeMDBTs). (b) Plot of two DBTs ratios for the oils analyzed.
References
[1] Chakhmakhchev, A. et al. (1997). Org. Geochem. 26, 483-490.
[2] Aguiar, A. et al. (2010). Fuel, 89, 2760-2768.
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