25th International Meeting on Organic Geochemistry IMOG 2011

P-006
Chemical and geochemical characterization of heavily
biodegraded oils from Colombia by comprehensive twodimensional
gas chromatography coupled to time-of-flight mass
spectrometry (GCXGC-TOFMS)
Renata Filgueiras 1 , Ricardo Pereira 1 , Raphael Salles 1 , Leonardo Mogollón 2 , Débora
Azevedo 1
1 Universaidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil, 2 Ecopetrol, Piedecuesta, Colombia
(corresponding author:renata_filgueiras@yahoo.com.br)
Biodegradation of crude oil in subsurface petroleum
reservoirs is an important alteration process with
major economic consequences. Geochemical
parameters using biomarkers are important to
characterization of oil-oil and oil-rock source
correlations. 1 In this way, the correct identification of
biomarkers is important to knowledge concerning
origin and migration of oil, even in biodegraded
samples. Comprehensive two-dimensional gas
chromatography coupled with time-of-flight mass
spectrometry (GC×GC-TOFMS) is an appropriate
technique for the elucidation of molecular composition
of complex petrochemical samples, such as
biodegraded oils. 2 This work provides the first study
concerning biomarker geochemical characterization of
heavily biodegraded oils from Colombia by GCxGC-
TOFMS, aiming the separation, identification and
quantification of biomarkers to determine geochemical
ratios.
Saturated fractions of four heavily biodegraded oil
samples from Colombia, named oils #1, #4, #5 and
#6, were analyzed on a GCxGC-TOFMS Leco
Pegasus 4D. The column set used was a HP-5MS (30
m) as first dimension and a BPX-50 (1.5 m) as
second dimension. The compounds were tentatively
identified by the use of ChromaTOF 4.0 Software.
The geochemical parameters calculated for all
samples are given in table 1. The samples have
distinct characteristics mainly concerning
biodegradation, which can influence parameters
related to thermal evolution and origin. Tri and
tetracyclic terpanes, esteranes, hopanes,
bisnorhopanes (BNH), trisnorhopanes (TNH), 25norhopanes
(C26-C34), norgammacerane,
secohopanes and n-alkanes were detected in
samples #4, #5 and #6. The detection of these
compounds is characteristic of a mixture of nonbiodegraded
and biodegraded oils. On the other
hand, the same compounds were identified in the
sample #2, except n-alkanes, esteranes and
homohopanes (C31-C35), characterizing heavily
biodegraded oil. This distinction is based on the
increasing 25-norhopane/C30-hopane ratios
(25NH/H30), which have high values between 1.36
and 6.04 (Table 1).
Table 1. Some geochemical correlations showing
source parameters of samples.
Parameter Oil 2 Oil 4 Oil 5 Oil 6
25NH/H30 6.04 2.14 2.38 1.36
Hop/St nd 0.9 0.99 1.08
H30/C27 ααα nd 1.55 0.97 1.87
C27 (%)
C28 (%)
C29 (%)
nd
nd
nd
49.0
34.4
16.6
41.8
27.7
30.5
42.6
33.7
23.6
Tr23/H30 7.77 8.66 3.89 5.91
Te24/H30 nd 0.80 0.64 0.53
Tr25/Tr26 0,64 0.74 1.05 1.74
H35/H34 nd 1.39 1.49 1.57
nd = not detected.
Hopane/Sterane ratios between 0.97 and 1.87 are
indicative of marine organic matter deposition with
contribution of algae and plankton. The predominance
of C27 steranes indicates major contribution of marine
phytoplankton. 5
For all samples the low concentration of tricyclic
terpanes C19 and C20, when compared to C23, is
also indicative of marine oils. The detection of
tetracyclic poliprenoids, C30 sterane, 28,30-BNH and
25,28,30-TNH are indicative of oils samples probably
derived of anoxic marine depositional environment. 2
The higher sensibility and chromatographic
resolution allowed a better characterization of oil
fractions. In addition, geochemical parameters were
calculated, demonstrating the applicability of GCxGC-
TOFMS in biomarker ratios. So, the use of GCxGC-
TOFMS in geochemical analysis can easily support oil
exploration.
References
[1] Peters, K.E. et al. (2005). The Biomarker Guide,
2 nd Edition, Cambridge University Press: New
York, 1155 pp.
[2] Aguiar et al. (2011).Energy & Fuels, in press.
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