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An Acad Bras Cienc (2022) 94(Suppl. 3): e20211433 DOI 10.1590/0001-3765202220211433
Anais da Academia Brasileira de Ciências | Annals of the Brazilian Academy of Sciences
Printed ISSN 0001-3765 I Online ISSN 1678-2690
www.scielo.br/aabc | www.fb.com/aabcjournal
An Acad Bras Cienc (2022) 94(Suppl. 3)
Running title: OIL
GEOCHEMICAL
INTERPRETATION AFTER
RECOVERY
Academy Section: ENGINEERING
SCIENCES
e20211433
94
(Suppl. 3)
94(Suppl. 3)
DOI
10.1590/0001-3765202220211433
ENGINEERING SCIENCES
Implications of microbial enhanced oil
recovery and waterfl ooding for geochemical
interpretation of recovered oils
LUCIANA G.P. SODRÉ, LAERCIO L. MARTINS, LORRAINE LOUISE G.C. DE ARAUJO,
DANIELLE M.M. FRANCO, BONIEK G. VAZ, WANDERSON ROMÃO, VALÉRIA M.
MERZEL & GEORGIANA F. DA CRUZ
Abstract: Biosurfactants and waterfl ooding have been widely reported thus far for
enhancing oil production. Nevertheless, there is a lack of literature to explore enhanced
oil recovered methods effects on its chemical composition. The aim of this work is
to investigate the effects of a biosurfactant produced by Bacillus safensis and brine
injection on the recovered petroleum composition, and their implications for geochemical
interpretation. Original and oils recovered from displacement tests were analyzed
by gas chromatography and ultra-high-resolution mass spectrometry, emphasizing
saturated and aromatic biomarkers and basic and acidic polar compounds. Geochemical
parameters based on some saturated compounds were subtly affected by the recovery
methods, showing their reliable applicability in geochemical studies. Contrarily,
parameters based on some aromatic compounds were more affected by biosurfactant
fl ooding, mostly the low molecular weight compounds. Thus, these aromatic parameters
should be applied with caution after such methods. The distribution of basic and acidic
polar compounds can also be modifi ed affecting the geochemical interpretation. In the
case of the basic ones, the biosurfactant greatly infl uenced the N class species with
favorable loss of lower aromaticity compounds. In addition to water solubilization, the
compositional changes described in this study can be related to fractionation due to
adsorption on reservoir rocks.
Key words: Biomarkers, biosurfactant, MEOR, oil recovery, petroleomics.
IN TRODUCTION
Water injection (waterfl ooding) and thermal or
miscible enhanced oil recovery (EOR) methods
are the most worldwide recovery techniques
for enhancing oil production (Suleimanov
et al. 2020). Further, there are several studies
of microbial enhanced oil recovery (MEOR)
applications at laboratories and pilot-scale
tests (Safdel et al. 2017, She et al. 2019).
The MEOR methods can use biosurfactants,
which are amphiphilic molecules, aimed at oil
displacement by physicochemical forces. In this
case, a chemical interaction occurs among the
injected fl uids, the reservoir fl uids, and reservoir
rocks. Its main mechanism is the decreasing of
immiscible fl uids interfacial tensions (Kryachko
2018). Despite their benefits, waterflooding
and the enhanced oil recovery methods have
some misgivings regarding the compositional
modification of geochemical analytes by the
injected products, which can affect the quality
of geological samples and thus compromise
their interpretation (Leitenmüller & Rupprecht
2019).
In addition, knowledge of the characteristics
of the oil produced is vital to the primary
LUCIANA G.P. SODRÉ et al. OIL GEOCHEMICAL INTERPRETATION AFTER RECOVERY
An Acad Bras Cienc (2022) 94(Suppl. 3) e20211433 2 | 19
processing step which has the purpose of
separating the gas under controlled operating
conditions and removing water, salts, and other
impurities making the oil suitable for transfer to
the refinery. For refining efficiency, it is essential
that know the type of oil that will enter your
distillation tower as load, given that fuel quality
is obtained by mixing certain hydrocarbons.
Furthermore, the analysis of polar compounds
is extremely important for the management
of refining processes and for determining the
economic value of oil (Adiko & Mingasov 2020,
Marshall & Rodgers 2004). These uncertainties
emphasized the importance of a preview
chemical characterization, including non-polar
and polar oil compounds produced after any
recovery method.
There are few studies in the literature
that describe the effects of waterflooding
on the properties of the recovered oil. They
have proposed that waterflooding may be
responsible for removing lighter and water-
soluble compounds from the oil, decreasing
its API gravity (Li & Zhang 2010, Chang et al.
2016). Following these lines, water washing is
the primary cause of composition changes in
the water-flooded oil (de Hemptinne et al. 2001).
Nonetheless, studies concerning the effects of
MEOR method on the produced oil composition,
mainly polar fraction, are not reported (Nikolova
& Gutierrez 2020). This absence of studies
can be related to the difficulty of analysis by
conventional analytical techniques since
the recovered oils are typically rich in polar
compounds (Auflem et al. 2001, Speight 2006).
For Hughey et al. (2002), GC-MS simplifies
identification by using characteristic patterns
of mass fragmentation, in conjunction with
retention time, but still suffers from limitations.
To overcome that, it is recommended to use
high-resolution techniques, however, still little
is used to analyze oils after additional recovery
processes.
Gas chromatography with a flame ionization
detector (GC-FID) has been applied to assess
n-alkanes and isoprenoids in petroleum (Head
et al. 2010, Martins et al. 2017). At the same time,
GC coupled to mass spectrometry allows the
detection of specific saturated biomarkers, such
as terpanes and steranes (Peters & Moldowan
1991, Gürgey 1998, Peters et al. 2005) and
aromatic compounds (Heckmann et al. 2011). The
detection and distribution of these compounds
can be applied in geochemical studies regarding
oil-oil and oil-source rock correlations, source
rock, and oil maturity, organic matter source,
and depositional environment, biodegradation,
among others (Peters et al. 2005, Larter et al.
2006).
In addition, high-resolution mass
spectrometry, such as Fourier Transform Ion
Cyclotron Mass Spectrometry (FT-ICR MS), has
emerged as an impressive tool that enables
petroleum chemical composition analysis at
the molecular level, mainly of the heteroatomic
polar compounds, such as naphthenic acids and
other nitrogen-containing compounds (Rodgers
et al. 2005, Oldenburg et al. 2011, Niyonsaba et al.
2019). FT-ICR MS has been also widely applied in
geochemical investigations (Hughey et al. 2002,
Shi et al. 2010, Vaz et al. 2013, Oldenburg et al.
2014, Poetz et al. 2014, Ziegs et al. 2018). Once each
oil compound has a different molecular formula
(CcHhNnOoSs) with an exact molar mass, it is
possible to solve and identify at the same time
each one of the thousands of compounds in a
complex mixture, with sufficiently high power
of mass resolution and precision. Hence, it
can separate and select polar oil components
depending on their heteroatom class (NnOoSs),
number of unsaturation, i.e., double bond
equivalent (DBE), and carbon number (CN)
(Marshall & Rodgers 2008).
LUCIANA G.P. SODRÉ et al. OIL GEOCHEMICAL INTERPRETATION AFTER RECOVERY
An Acad Bras Cienc (2022) 94(Suppl. 3) e20211433 3 | 19
In this context, the purpose of this study is to
investigate the potential effects of biosurfactant
flooding and waterflooding on the chemical
composition of the recovered oils obtained
in a previous study (de Araujo et al. 2019),
with emphasis on the possible impact on the
geochemical interpretation based on saturated
and aromatic biomarkers, and mainly basic and
acidic polar compounds, once for the latter,
there are almost no reports in the literature of
their analysis after waterflooding, and as far as
known, none after the biosurfactant injection,
as proposed here.
MATERIALS AND METHODS
Core flooding experiment and oil samples
characterization
The core flooding experiments were performed
by oil displacement with 3 wt% NaCl brine. In
the MEOR recovery experiment, a 125.0 mg.L-
1 biosurfactant solution (equal to 1.3 CMC)
was injected at intervals with NaCl brine, as
described in more detail by de Araujo et al. 2019.
The applied biosurfactant was isolated from
the mangrove-derived strain Bacillus safensis
CCMA-560 based on the procedure previously
described by Domingos et al. 2015.
For improving reading comprehension, the
crude oil used by de Araujo et al. 2019 is called
in the current study as Control Oil, and the oils
recovered after the displacement tests as Oil
I and Oil II, respectively, to waterflooding and
biosurfactant flooding. Control Oil, Oil I, and
Oil II were assessed using gas chromatography
with flame ionization detector (GC-FID) and by
electrospray ionization in positive-ion mode
ESI(+) FT-ICR mass spectrometry.
Control Oil, Oil I, and Oil II samples were
fractionated on a classical liquid chromatography
from which saturated hydrocarbons, aromatics,
and polar compounds were obtained using
n-hexane, n-hexane:dichloromethane (DCM)
(8:2,v/v), and DCM:methanol (MeOH; 9:1,v/v),
respectively (details in Martins et al. 2014).
The saturated and aromatic fractions were
characterized using gas chromatography-mass
spectrometry (GC-MS).
Gas chromatography with flame ionization
detector (GC-FID)
GC-FID analysis of the total oil samples was
performed according to Martins et al. 2017,
with an Agilent 6890N GC-FID system with
synthetic air, H2, and N2 as flame gases, an HP-5
capillary column (30 m x 0.32 mm x 0.25 μm),
and 5α-androstane (0.02 mg.mL-1) applied as the
internal standard for n-alkane quantification.
n-Alkanes, pristane (Pr), and phytane (Ph) were
identified based on the chromatographic profile
of reference samples and their retention time.
Gas chromatography-mass spectrometry (GC-
MS)
GC-MS analysis of saturated and aromatic
fractions was performed in Martins et al. 2017,
with an Agilent Technologies 6890N GC with a
DB-5 column (30 m x 0.25 mm x 0.25 μm) coupled
to an Agilent 5973 MSD mass selective detector.
Linear scanning (Scan) analysis in the range of
50-550 Daltons and selective ion monitoring
(SIM) were used as the analysis model. The
compounds were identified based on literature
data, the chromatographic profile of reference
samples, and mass spectra.
The saturated biomarkers tricyclic terpanes
(TT), 25-norhopane (NH), trisnorneohopane
(Ts), trisnorhopane (Tm), regular hopanes
(H) and gammacerane (G) were investigated
monitoring m/z 191, while diasteranes (Dia)
and regular steranes (RS) were investigated
monitoring m/z 217 (Peters & Moldowan 1991).
The aromatic biomarkers dimethylnaphthalene
(DMN), trimethylnaphthalene (TMN),
LUCIANA G.P. SODRÉ et al. OIL GEOCHEMICAL INTERPRETATION AFTER RECOVERY
An Acad Bras Cienc (2022) 94(Suppl. 3) e20211433 4 | 19
phenanthrene (Phe), methylphenanthrene
(MPhe), methyldibenzothiophene (MDBT), and
triaromatic steroids (TAS) were investigated
monitoring m/z 156, 170, 178, 192, and 198,
respectively (Heckmann et al. 2011).
Fourier transform ion cyclotron resonance
mass spectrometry (FT-ICR MS)
Oils analyses were carried out in a Solarix 9.4T
ESI(+) FT-ICR mass spectrometer and in a 7T
SolariX 2xR ESI(-) FT-ICR mass spectrometer
(Bruker Daltonics, Bremmen, Germany; based
on Pinto et al. 2017 and Souza et al. 2018). The
chemical profile of the oil sample was analyzed
in a positive [ESI(+)] and negative [ESI(-)] modes.
In positive mode, about 1 mg of the
oil samples were dissolved in a solution of
toluene:methanol (0.67 mg.mL-1 ), and straightly
infused in the ESI sources at a flow rate of
10 µL.min-1.The instrument was externally
calibrated with L-arginine (200-1500 m/z) and
settings were: capillary voltage of 3.9 kV; transfer
capillary temperature of 220 °C and 2.5 L.min-1
of drying flow. In negative mode, about 1 mg of
the oil samples were dissolved in a solution of
toluene:methanol (0.5 mg.mL-1), and straightly
infused in the ESI sources at a flow rate of 240
µL.h-1. The instrument was externally calibrated
with sodium trifluoroacetate (NaTFA) and
settings were: capillary voltage of 4.5 kV; transfer
capillary temperature of 200 °C and 4.0 L.min-1
of drying flow.
For ESI(+) mode, a 0.04 s of ion accumulation
time was used, with the mass spectra range of
m/z 200-1500, accuracy lower than 3 ppm, and
resolving power was about 400 000. For ESI(-)
mode, a 0.010 s of ion accumulation time was
used, with the mass spectra range of m/z 129-
2000, accuracy lower than 1 ppm, and resolving
power was about 770 000. For both methods,
was colleted 200 scans.
The mass spectra were internally calibrated
with homologous series of neutral [ESI(-)] and
basic [ESI(+)] compounds of nitrogen ions
(CcHhNn), using the Compass Data Analysis
software (Bruker Daltonics, Bremmen, Germany),
and an algorithm elaborated for petroleum
signal processing (Composer software, Sierra
Analytics, Pasadena, CA, US) providing the DBE
versus CN and Van Krevelen plots. M/z values
measurements set the elemental composition of
the oil samples, and the class diagrams and DBE
distribution were built in Excel spreadsheets.
RESULTS AND DISCUSSION
n-Alkanes and isoprenoids by GC-FID
Figure 1a shows the chromatographic profiles
(fingerprint) obtained by GC-FID analyses of
the Control Oil, and the recovered oils from
the waterflooding (Oil I) and MEOR (Oil II)
techniques. It can be observed n-alkanes with
medium to high molecular weight (n-C13 to
n-C33) in all chromatograms, as well as the
high abundance of the isoprenoids pristane
(Pr) and phytane (Ph). Furthermore, there is a
pronounced hump (UCM - unresolved complex
mixture) in the GC chromatograms, which
contains compounds not readily resolved by
conventional gas chromatography, such as NSO
compounds, and compasses many recalcitrant
products of biodegradation (Head et al. 2010).
In order to further evaluate the modifications
of the hydrocarbon composition in the oil
samples after the flooding experiments, it
was calculated the total concentration of
n-alkanes (sum of n-C13 to n-C33; Fig. 1a) and
the concentration of individual n-alkanes, in
addition to the pristane and phytane (Fig. 1b) for
the Control Oil and the recovered oils. Moreover,
some parameters used in geochemical studies
were determined based on these hydrocarbon
compounds, including Pr/n-C17, Ph/n-C18, Pr/
LUCIANA G.P. SODRÉ et al. OIL GEOCHEMICAL INTERPRETATION AFTER RECOVERY
An Acad Bras Cienc (2022) 94(Suppl. 3) e20211433 5 | 19
Ph, Σn-C21- /Σn-C22+, PCI (Preferential Carbon
Index; Fig. 2; Appendix A - Supplementary
Material Table SI).
In contrast to the Control Oil, Oil I and Oil
II present a reduction in the total concentration
of n-alkanes (sum of n-C13 to n-C33; Fig. 1a),
which is expected due to the effects of their
adsorption on the rock. Additionally, it is possible
to verify that the n-alkanes with medium to
high molecular mass (n-C13 to n-C33) and the
isoprenoids Pr and Ph were partially removed
from the oil sample throw both recovery tests,
as shown by their lower concentrations to the
Oils I and II than the Control Oil (Fig. 1b).
However, it is possible to verify that the
individual concentration of these n-alkanes and
isoprenoids remained greater when using the
MEOR recovery method (range of 0.008 to 0.213
mg per 100 mg of oil; Oil II in Fig. 1b), implying
a better recovery of saturated hydrocarbons by
this enhanced method after the waterflooding.
That result suggests that biosurfactants play
an important role in mobilizing hydrophobic
molecules by reducing their interfacial tension
with brine (de Araujo et al. 2019).
The solubility of the lower molecular weight
hydrocarbons (n-C13 to n-C22) in water is more
pronounced during the waterflooding process
Figure 1. (a) Chromatographic
profiles gained by GC-FID
analyzes of the three oil
samples, presenting the total
concentration of n-alkanes
in mg per 100 mg of oil. (b)
The individual concentration
of n-alkanes and isoprenoids
pristane (Pr) and phytane (Ph).
LUCIANA G.P. SODRÉ et al. OIL GEOCHEMICAL INTERPRETATION AFTER RECOVERY
An Acad Bras Cienc (2022) 94(Suppl. 3) e20211433 6 | 19
(Oil I in Fig. 1b) in accordance with Zhu et al.
2003, which presented a reduction in the relative
abundance of nonpolar components of low
molecular weight and a rise in the abundance of
long-chain n-alkanes after the primary recovery
process. The solubility of these medium
molecular weight compounds when using the
aqueous solution recovery method can be
compared to the water washing process in the
reservoir (Li & Zhang 2010, de Hemptinne et al.
2001). Hence, water washing reveals itself as a
potential process for changes in oil composition
for water injection experiments. The results also
agree with a previous study by Bailey & Krouse
1973, which reported that low molecular weight
compounds are preferably removed from the oil
during contact with water.
Contrary to that observed for n-alkanes,
especially of low molecular weight, the
isoprenoids are less soluble in water (solubility
of Pr is 1.0x10-8 mg.L-1 , and Ph is 1.7x10-5 mg.L-
1 at 25 °C) and, therefore, the n-alkanes are
preferably removed on the isoprenoids by water
washing. Price 1976 and Xu et al. 2012 observed
that the Pr/n-C17, Ph/n-C18, and Pr/Ph ratios
were slightly altered when water was used as a
method of oil recovery. However, in the current
study, there were no significant changes for
these ratios for Oil I and Oil II compared to
the Control Oil (Fig. 2). The preferential carbon
index (PCI) also remained relatively constant,
resulting in no odd/even carbon preference in
both oil recovery processes (Fig. 2). However,
the ratio Σn-C21-/Σn-C22+ for Oil II is higher than
for Oil I, contrarily the observation in a series of
waterflooded wells made by Chang et al. 2016,
indicating a later decrease caused by the water
washing. Such behavior could be explained if the
oil/water interfacial tension is sufficiently high;
the biosurfactant could have good interfacial
activity for mobilizing the lighter hydrocarbons
while the heavier molecular components remain
trapped in porous media (Zhu & Lei 2015).
The results on n-alkanes and isoprenoids
agree with a previous water washing study
by Lafargue & Le Thiez 1996, which reported
that aliphatic hydrocarbons composition over
C15+, including the isoprenoids, shows a little
variability. However, aromatic and sulfur-
containing compounds varied significantly.
Saturated and aromatic biomarkers by GC-MS
Gas chromatography coupled to mass
spectrometry was used since it is a more specific
technique than the GC-FID to detect complex
molecules such as biomarkers from the terpanes
Figure 2. Star diagram of
geochemical parameters
obtained by the GC-FID
analyses showed no
significant variations,
except for the Σn-C21-/Σn-
C22+ ratio.
LUCIANA G.P. SODRÉ et al. OIL GEOCHEMICAL INTERPRETATION AFTER RECOVERY
An Acad Bras Cienc (2022) 94(Suppl. 3) e20211433 7 | 19
and steranes families (Peters et al. 2005). As
shown in Fig. 3a (and Appendix A - Table SII),
brine and biosurfactant injections only slightly
affected the geochemical parameters based
on saturated biomarkers. These parameters
encompass essential geochemical proxies
(Peters & Moldowan 1991) to distinguish
depositional environments of source rocks and
to assess oil biodegradation, such as 25NH/
C30H, C23TT/C30H, G/C30H, C31R/C30H, C22/
C21 TT, C24/C23 TT, C26/C25 TT, C35/C34S, C28/
C29 RS, Dia27/C27, RS/C30H, and homohopane
index (HI) in addition to parameters for thermal
maturity evaluation, such as Ts/(Ts + Tm), C31 S/
(S + R), C29 S/(S + R), C29 ββ/(ββ + αα) (Peters &
Moldowan 1991).
The ratios C24/C23TT, C28/C29RS, and C35/
C34S are more pronounced while the ratio C26/
C25 TT decreased for Oil I. This random behavior
is associated with the differences in the low
water solubility and adsorption in the rocks for
these compounds. Chang et al. 2016 consider
that although the values of the C22/C21TT and
C24/C23TT ratios are nearly constant, C26/C25TT
can decrease in oils recovered with water.
Herein it is also highlighted that the
biosurfactant flooding would lead to relatively
more constant or slightly affected saturated
biomarker ratio values, comparing Oil I and II to
the Control Oil. Oil II exhibits an action over the
rate Dia27/C27, and additional experiments are
required to a plausible explication.
Geochemical parameters based on aromatic
biomarkers (Fig. 3b; Appendix A -Table SIII) were
more affected by the recovery techniques than
the parameters based on n-alkanes, isoprenoids,
Figure 3. (a) Geochemical
parameters based on the
saturated biomarkers
compounds, (b) and
based on aromatic
biomarkers.
LUCIANA G.P. SODRÉ et al. OIL GEOCHEMICAL INTERPRETATION AFTER RECOVERY
An Acad Bras Cienc (2022) 94(Suppl. 3) e20211433 8 | 19
and saturated biomarkers, in agreement with
their higher solubility of aromatic than aliphatic
hydrocarbons in water and with previous
work (Chang et al. 2018). As observed in Fig.
1a the concentration of n-C18 decreased for
recovered oils when compared with Control Oil
consequently, an increase of the Phe/n-C18 ratio
was expected, nonetheless, this ratio exhibits an
increase in Oil I and decrease in Oil II, indicating
an effect of biosurfactant on a lesser recovery of
phenanthrene.
The 1-MPhe/Phe ratio is slightly higher in
Oil I, and the Phe/ΣMPhe ratio decrease in the
same oil, relative to the Control Oil, which is
consistent with the observed by Kuo 1994, that
noticed an increase in the methylphenanthrene
indices when the oil is recovered with water.
The biosurfactant flooding cause an increased
in the Phe/ΣMPhe ratio indicating that
methylphenanthrenes were less recovered than
phenanthrene.
The MDBT/Phe ratio values increased
systematically for Oils I and II when compared
to Control Oil (Fig. 3b). These results imply a
preferred recovery of methyldibenzothiophenes
(MDBT) than phenanthrene (Phe) in agreement
with the water washing effect since a lower
abundance of low molecular mass fractions
is reported, in addition to an increase in
high molecular mass polycyclic aromatic
hydrocarbons (Chang et al. 2016, Zhu et al. 2003).
Nevertheless, the results show a
variation in the relative concentration of the
methylphenanthrenes isomers. The high value
of the MPI ratio of Oil II while MPI-1 and MPI-2
values are higher for Oil I, which indicates an
increase in 1-MPhe and 9-MPhe. That follows
according to Bonilla & Engel 1988, who argue that
the relative abundance of 2-MPhe and 3-MPhe
decreases with the increase of migration, and
consequent adsorption of these minerals from
the rock, which makes the 1-MPhe and 9-MPhe
more abundant in the reservoir.
The parameters DBR, DNR-1, and TNR-1
based on dimethyl and trimethylnaphthalene
isomers show a substantial reduction after the
waterflooding and MEOR. These results point to
the influence of adsorption on the distribution
of naphthalene isomers during the recovering
experiments with brine or aqueous biosurfactant
solution, in line with the more solubility
of naphthalenes in aqueous solution than
phenanthrenes (Chang et al. 2016). Furthermore,
the decrease in the DNR-1 and TNR-1 ratios for
oils recovered with an aqueous solution are
consistent with some of the results of Chang et
al. 2016, who also verified a reduction in these
ratios values after the waterflooding process for
two of their samples under study.
Regarding triaromatic steroids, it is possible
to verify that the values of the TAS-1 ratio are
practically unchanged for Oil I. Indeed, Chang
et al. 2016 argues that the parameters based
on triaromatic steroids remain relatively
constant due to the subtle distinction in water
solubility among their isomers. Contrary to
that, the values of the TAS-2 ratio showed more
considerable variation among the oils, showing
a decrease for recovered oils, especially when
the biosurfactant was injected. That could be
explained by the higher adsorption of C26 TAS
20S by rock compared to C28 TAS 20S, since
Trindade & Brassell 1992 report that triaromatic
steroids have more significant interaction with
rock minerals.
As a result, the parameters based
on dimethyl and trimethylnaphthalene,
phenanthrene, methylphenanthrene,
methyldibenzothiophenes, and triaromatic
steroids should be used with caution after brine
and biosurfactant injection into the reservoir,
specially the DBR and DNR-1 ratio.
LUCIANA G.P. SODRÉ et al. OIL GEOCHEMICAL INTERPRETATION AFTER RECOVERY
An Acad Bras Cienc (2022) 94(Suppl. 3) e20211433 9 | 19
Basic polar compounds by ES(+) FT-ICR MS
The oil samples were assessed by ESI(+) FT-ICR
MS to investigate changes in the basic polar
compounds. The heteroatom class distribution
(NnOoSs) of the Control Oil and the recovered
oils are shown in Fig. 4a (exhibiting all classes
above 1% of the relative abundances). The N
class was most abundant in the Control and
recovered oils (89, 85, and 59%, respectively),
likely encompassing pyridine, quinoline,
acridine compounds, and their derivatives (Qian
et al. 2001, Terra et al. 2015), followed by the N2
(4, 3, and 9%, respectively) and NS (7, 5, and 8%,
respectively) classes.
Oil I presents a more similar heteroatom class
distribution with Control Oil, while Oil II contrasts
(Fig. 4). During the core flooding experiments,
may occur preferential adsorption and apparent
solubility of petroleum components in water (Liu
et al. 2004). In this sense, it was possible to notice
a slight decrease in the relative abundance of
species of N, N2, and NS classes in Oil I, while
Oil II is enriched with compounds of N2 and NS
classes, in addition to the detection of N4O4, NO,
NOS, and O2S classes above 1% likely due to the
significant decrease in the relative abundance
of the N class. These changes in the composition
of the polar compounds after the biosurfactant
flooding indicate that the biosurfactant affects
the recovery of basic polar compounds from the
oil in a particular way.
Regarding the N class, it can be observed
in its DBE distribution in Fig. 5a a reduction
in the relative abundance in compounds with
DBEs between 5 and 14 in the recovered oils in
relation to the Control Oil. These compounds
slightly decreased in Oil I, whereas Oil II showed
more pronounced reductions, with compounds
with DBE up to 10 most affected by the MEOR
recovery experiments (Oil II). Concerning the
N2 class (Fig. 5b), Oil II also presents the most
distinctive profile, showing the higher relative
abundance of compounds with DBE between 7
and 25. Although the increased relative lot of N2
compounds for Oil II should be related to the
decreasing in the relative abundance of its N
compounds, it is also clear that some reductions
are related to low DBE compounds ranging
from 7 to 10. The DBE distribution of NS class
Figure 4. (a) Heteroatom class distributions for Control Oil, Oil I, and Oil II. (b) Ternary diagram used in geochemical
studies of maturity assessment illustrating the effect of MEOR (Oil II) on the polar nitrogen compounds of the
Control Oil. (c) Star diagram showing the DBE ratios for the N (DBE 4-13/DBE 14-23), N2 (DBE 8-16/DBE 17-24), and
NS (DBE 6-13/DBE 14-21) classes in the Control Oil and the recovered Oils I and II.
LUCIANA G.P. SODRÉ et al. OIL GEOCHEMICAL INTERPRETATION AFTER RECOVERY
An Acad Bras Cienc (2022) 94(Suppl. 3) e20211433 10 | 19
for Oil I (Fig. 5c) shows a more similar profile
as the Control Oil, although with lower relative
abundance. However, the DBE distribution for
Oil II shows an increase in aromaticity, with
greater relative abundance to compounds with
high DBE values (DBE 14 to 21), also presenting
the decrease in the relative abundance of lower
DBE compounds (mainly with DBE 6 and 7).
The data here suggests there are some
intermolecular interactions or side-reactions
of N species with the biosurfactant molecule,
trapping these complexes in the porous media.
The molecular structures of N class species
encompassing pyridines, naphthenic pyridines,
quinolines, and their derivatives (Terra et al. 2015)
could act as nitrogen nucleophile (Solomons
et al. 2016) in a reaction with the applied
biosurfactant. This biosurfactant belongs to low
molecular mass biosurfactants group and it is a
surfactin analog, formed by a cyclic lipopeptide
composed of a hydroxyl fatty acid chain (de
Araujo et al. 2019). Further evidence is needed to
confirm this hypothesis.
A ternary diagram (Fig. 4b) usually used to
evaluate oil and bitumen maturities (Oldenburg
et al. 2014) was plotted, using the relative
abundance of the compounds from N class
with DBE 7, 10, and 12, being likely quinolines,
benzoquinolines, and the most robustness
aromatic core structural indenoquinolines or
azopyrenes, respectively. This plot is based on
that N heteroatom compounds become more
aromatic (greater predominance of higher
DBE compounds) with increasing thermal
maturation (Oldenburg et al. 2014, Poetz et al.
2014). It can be observed in the ternary diagram
that there is a more significant alteration in the
distribution of compounds in N class in Oil II,
which affects the assessment of maturity. Oil
II presents a higher abundance of compounds
with DBE 10 and 12 and lower DBE 7 than the
other oil samples, showing that the lighter and
less aromatic compounds, such as quinolines,
were more affected.
To further investigate the decrease in the
relative abundance of the low aromaticity
polar compounds of the N, N2, and NS classes
(Fig. 4c) the following ratios were determined
based on the sum of the relative abundance of
compounds with lower DBE over the sum of the
relative lot of compounds with higher DBE: DBE
4-13/DBE 14-23 for N class; DBE 8-16/DBE 17-24 for
N2 class; DBE 6-13/DBE 14-21. As can be observed
in Fig. 4c, only Oil II shows a significant decrease
of the lower DBE compounds, which points to
the preferential loss of the lower aromaticity
Figure 5. DBE distribution of the N (a), N2 (b), and NS
(c) classes in the Control Oil and the recovered Oils I
(from waterflooding) and II (from MEOR).
LUCIANA G.P. SODRÉ et al. OIL GEOCHEMICAL INTERPRETATION AFTER RECOVERY
An Acad Bras Cienc (2022) 94(Suppl. 3) e20211433 11 | 19
compounds during the MEOR recovery
experiment, possibly by water solubilization
or rock adsorption. Oil I is more similar to the
Control Oil, concerning the nitrogen abundance
(Fig. 4a) and its distribution (Fig. 4c). The N
compounds with DBE higher than 15 remained
primarily unchanged in all oil samples, being
more resistant to the oil recovery processes
using aqueous solutions and likely less affected
by the effects of geochromatography. Moreover,
there is a similarity in the DBE range (4 to 20)
for the Control and Oil I. However, Oil II shows
a clear, distinct trend concerning the others
concerning the amount of unsaturation of the
molecule, indicating a broader range for the
heteroatom classes (DBE 5 to 24).
The effects on the basic polar compounds
due to the application of MEOR are highlighted
in the DBE versus CN plots of the N, N2, and NS
classes for Oil II (Appendix A - Fig. S1) (Marshall
& Rodgers 2008), which have a distinct profile
from the Control Oil, as already observed in Fig.
4c and 5. These results corroborate an increase
in the relative abundance of basic polar
compounds with higher molecular mass and
higher aromaticity for the oil recovered with the
aqueous biosurfactant solution. Additionally,
Fig. S2 (Appendix A) shows the Van Krevelen type
diagrams for Nx (N and N2) of the Control and
recovered oils, using the H/C and N/C ratios (Kim
et al. 2003, Corilo et al. 2010). It can be observed
the same tendency of Oil II to distinguish from
the others, since it presents a subtly altered
range of the H/C and N/C ratios, suggesting an
increase in the number of heteroatoms of these
classes (higher N/C) and more unsaturated
compounds (lower H/C). In general, the Control
Oil and Oil I show an unsaturation content of
1 to 1.9 and heteroatoms content of 0.015 to
0.08, respectively, with a higher intensity of 1.5
and 0.03. Oil II shows an unsaturation content
of 0.8 to 1.9 and heteroatom content of 0.015
to 0.11, with a higher intensity of 1.6 and 0.03,
respectively.
Acidic polar compounds by ES(-) FT-ICR MS
The oil samples were assessed also by ESI(-) FT-
ICR MS to investigate changes in the acidic polar
compounds. The heteroatom class distribution
(NnOoSs) of the Control Oil and the recovered
oils are shown in Fig. 6a (exhibiting all classes
above 1% of the relative abundances). The N class
has the highest abundance of all oils, reflecting
mainly to the low molecular weight alkylated
carbazoles, benzo- and dibenzocarbazoles,
with less than three alkyl carbon substituents
(Oldenburg et al. 2014). The O class has the
second greatest abundance, which encompasses
likely components with a hydroxyl functional
group able to be deprotonated (Oldenburg et
al. 2014), mostly related to phenolic compounds
(Shi et al. 2010). The O class occurrence is
generally reported in source rocks and crude
oils (Vaz et al. 2013, Poetz et al. 2014, Cui et al.
2014, Pereira et al. 2013, Mahlstedt et al. 2016,
Oldenburg et al. 2017, Wan et al. 2017, Rocha et
al. 2017). The O2 class is also in high abundance,
mainly composed of naphthenic carboxylic
acids (Larter et al. 1997, Kim et al. 2005).
According to Fig. 6a Control Oil and Oil II,
obtained after MEOR, have more similarities in
their heteroatom class distribution, with similar
high abundance for the N, O, NO2, and O3S
classes. However, Oil I show an increase in N
and O classes’ relative abundances, while there
is a decrease in NO2 and O3S classes, beyond
the suppression of NO2S and O3S2 classes. For
cases of nitrogenous compounds reduction
in recovered oils (I and II), this suggests that
these compounds and their analogs may be
preferentially adsorbed by a rock or carried out
by the injected solutions (Larter et al. 1997).
The changes in the composition of acidic
polar compounds also affect the geochemical
LUCIANA G.P. SODRÉ et al. OIL GEOCHEMICAL INTERPRETATION AFTER RECOVERY
An Acad Bras Cienc (2022) 94(Suppl. 3) e20211433 12 | 19
assessment of the recovered oils using the
ESI(-) FT-ICR MS data. In this way, Fig. 6b
presents a triangular diagram based on the N
class distribution commonly used to assess
thermal maturity of oils (Oldenburg et al. 2014),
using the distribution of carbazoles (DBE 9),
benzocarbazoles (DBE 12), and dibenzocarbazoles
(DBE 15). It can be seen that all three samples
are in the 0.74 and 0.84% vitrinite reflectance
equivalent (%Re) range compared with
Oldenburg et al. 2014 results, which indicate
oils in the oil window. However, there was a
subtle change in the maturity assessment of the
recovered oils, with both classified with a slightly
lower maturity level than the Control oil due to
the higher proportion of N-compounds with DBE
9 and 12 than 15. This behavior can also be seen
in Fig. 7a showing that there was a significant
increase in the relative abundance of N class
for oils I and II mainly regarding carbazoles (DBE
9) benzocarbazoles (DBE 12) when compared to
Control oil.
Fig. 7b shows the DBE distribution of O
class species ranging from 4 to 17, and it is also
observed an increase in the relative abundance
of low DBE compounds for the recovered oils
compared with the Control oil, mainly those with
DBE 4, 5, and 6. This is more pronouncedly even
in oil I, when compared to Control Oil.
The Fig. 8a-b shows the carbon number
distributions for O class compounds with DBE 4
and DBE 5, typically ranges from 13 to 67 (Martins
et al. 2021), with greater relative abundance of
species with 27 and 28 carbon atoms. These
compounds have been commonly reported in
studies of crude oils, and rock extracts by ESI(-)
FT-ICR MS, and the ones with DBE 5 are mostly
methyl- and dimethyl-isoprenoidyl phenols
(Zhang et al. 2011, Martins et al. 2021), although
some works have interpreted them as sterol-
like compounds (Oldenburg et al. 2014, Rocha
Figure 6. (a) Distribution of heteroatom classes, (b) triangular, and (c) star plots illustrating the maturity and
biodegradation assessment, respectively, for the oil samples.
LUCIANA G.P. SODRÉ et al. OIL GEOCHEMICAL INTERPRETATION AFTER RECOVERY
An Acad Bras Cienc (2022) 94(Suppl. 3) e20211433 13 | 19
et al. 2017). It is then perceived for oils I and II a
significant relative decrease in medium to high
molecular weight compounds (carbon number
22 to 50) in DBEs 4 and 5 and this occurs mainly
in oil recovered with biosurfactant. That could
be strongly related to the water washing process
that occurs when injecting solutions into the
reservoir in order to recover the oils, with the
consequent solubilization of these aromatic
compounds in the water. It is worth mentioning
the water washing may be the dominant process
for changes in oil composition in experiments
carried out with aqueous solutions (Chang et al.
2016, de Hemptinne et al. 2001).
Regarding the O2 class (Fig. 7c), the DBE
distribution ranges from 1 to 20. It was verified
that all the samples have a predominance of
DBE 1 compounds (acyclic acids), which are
mostly reported as fatty acids (Rocha et al. 2019,
Martins et al. 2021). However, a markedly high
relative abundance of DBE 1 compounds was
verified in Oils I and II. Fig 8c shows the carbon
number distributions for O2 class compounds
with DBE 1, ranging from 12 to 50. Fatty acids
(DBE 1) that dominate the O2 compounds
typically range from carbon number 12 to 48
(Martins et al. 2021). By the plot, it is possible
to identify a predominance of compounds with
carbon number 16 and 18. The abundant O2
compounds with DBE 1 and 16 carbon atoms
likely correspond to hexadecanoic acid (VIII-a;
C16H32O2) (Shi et al. 2010, Liu et al. 2015, Han et al.
2018a). It is noticed once again that oils I and II
have a different trend than Control Oil. There is
an increase in the relative abundances of low
DBE compounds (mainly DBE 1 to 7; Fig. 7c).
The presented changes on the O and O2
classes also affect the geochemical assessment
based on them. A star diagram was plotted
(Fig. 6c) using biodegradation ratios calculated
based on the DBE distribution of these classes
(prioritizing the most abundant above; according
to Vaz et al. 2013, Larter et al. 1997, Kim et al. 2005).
O Class DBE 4, for example, slightly affected the
monoaromatic index 2 (MA2; DBE 4/7; Larter
et al. 1997). The biodegradation trends can be
observed, in which DBE 4 (monoaromatic core
compounds) is the most abundant (case of the
oil I) to non-/slightly biodegraded oil samples
(Martins et al. 2017). For the O2 Class, the high
abundance of DBE 1 compounds in the recovered
oils (oils I and II) affects more significantly the
A/C ratio (acyclic/cyclic acids ratio), modified
A/C ratio, and more subtly, the SA index. Only
the modified SA index does not change since it
is not based on DBE 1 compounds. In general,
an A/C ratio higher than 1, as presented for oils
I and II, corresponds to a non-biodegraded oil
(Kim et al. 2005). This follows in agreement with
Figure 7. DBE distribution of (a) N, (b) O, and (c) O2
classes for the oil samples.
LUCIANA G.P. SODRÉ et al. OIL GEOCHEMICAL INTERPRETATION AFTER RECOVERY
An Acad Bras Cienc (2022) 94(Suppl. 3) e20211433 14 | 19
previous studies that applied ESI(-) FT-ICR MS
(Hughey et al. 2002, Cui et al. 2014, Mahlstedt
et al. 2016, Wan et al. 2017, Rocha et al. 2017),
which indicate a predominance of N species in
non-biodegraded crude oils (Fig. 6a). However,
the Control Oil has an A/C ratio of 0.81, being
classified as light to moderately biodegraded oil.
Therefore, as with thermal maturity, the applied
recovery methods can affect the biodegradation
assessment by ESI(-) FT-ICR MS analyses.
In addition, it is already known from previous
studies that FT-ICR MS is able to distinguish
crude oils from different origins (Hughey et al.
2002, Wan et al. 2017, Rocha et al. 2017). This
is possible because both the distribution of
heteroatomic compounds and their relative
abundance vary according to the geological
origins of the oils (Rocha et al. 2017). Thus, to
extend the geochemical characterization of the
oils, a paleoenvironmental assessment of the
three oil samples (I, II, and Control Oil) was carried
out, applying the ratios established by Rocha
et al. 2018 (Fig. 9), based on the distribution of
DBE for the O and O2 classes, which are among
the most abundant classes here. The results
indicate changes in the paleoenvironment
evaluation among the samples, with oils I and II
being classified as a marine while the control oil
is classified as lacustrine (Fig. 10). This indicates
that the applied recovery methods can affect
this geochemical assessment.
Moreover, according to Rocha et al. 2018,
the distributions of elementary classes can be
used to distinguish lacustrine oils from marine
ones. The first significant difference between
these two depositional environment conditions
Figure 8. Carbon number distributions of the (a) O
Class DBE 4, (b) O Class DBE 5, and (c) O2 Class DBE 1.
Figure 9. Depositional environment assessment
of oil samples (I, II, and Control Oil) based on the
distribution of O1 polar compounds investigated by
negative ESI FT-ICR MS.
LUCIANA G.P. SODRÉ et al. OIL GEOCHEMICAL INTERPRETATION AFTER RECOVERY
An Acad Bras Cienc (2022) 94(Suppl. 3) e20211433 15 | 19
is related to the Nx and Oz classes, which
dominate the fraction of acidic compounds in
all samples. Lacustrine oils tend to be enriched
with Nx compounds, while marine oils can be
distinguished by their more abundance for
Ox compounds. The NxOz compounds show a
similar distribution in oil samples, regardless of
the deposition environments of the generating
rocks (Rocha et al. 2018). Thus, the oil samples
in the current study were assessed in a ternary
diagram (Fig. 10) using the relative amounts of
the three major elementary classes: Nx, Oz, and
NxOz. The results suggest subtle differences in
the distribution of the three oil samples’ polar
compounds, however, all the samples are more
enriched in Nx compounds, indicating lacustrine
depositional paleoenvironment of the source
rocks of the Control Oil. So, these results
demonstrate that the paleoenvironmental
assessment by ESI (-) FT-ICR MS analyses can
also be affected using the applied recovery
methods.
CONCLUSION
Waterflooding and biosurfactant flooding only
subtly affect the geochemical parameters
based on saturated hydrocarbons. Accordingly,
the parameters Pr/n-C17, Ph/n-C18, Pr/Ph,
PCI (preferential carbon index), and Σn-C21-/
Σn-C22+ based on n-alkanes and isoprenoids,
and several parameters based on tricyclic
terpanes, hopanes, gammacerane, diasteranes,
and steranes can be reliably applied for
geochemical interpretation after brine and
biosurfactant injection into the reservoir. In
addition, the injection of biosurfactant revealed
a more significant recovery of n-alkanes and
isoprenoids than the waterflooding technique
highlighting its potential applicability.
On the other hand, geochemical
parameters based on aromatic hydrocarbons
are affected by biosurfactant flooding and
the know effects due to the application of
waterflooding. As a result, the parameters
based on dimethyl and trimethylnaphthalene,
phenanthrene, methylphenanthrene,
methyldibenzothiophenes, and triaromatic
steroids should be used with caution after brine
and biosurfactant injection into the reservoir,
especially the DBR and DNR-1 ratios.
The distribution of basic polar compounds
can also be modified by the waterflooding
and MEOR methods affecting the geochemical
interpretation. Nitrogen compounds and their
analogs may be preferentially carried out
by the injected water, with favorable loss of
compounds with lower aromaticity, especially
after biosurfactant injection. Likewise, analysis
of polar compounds by ESI (-) FT-ICR MS
showed that recovery methods can also affect
geochemical assessment, such as thermal
maturity, biodegradation, and depositional
paleoenvironment, based on acidic species,
since Oils I and II proved to be different from
Control Oil, in general. Further investigation is
Figure 10. Ternary diagram for the most abundant
elemental classes assigned on the negative ESI FTICR-
MS results: Nx, Oz, and NxOz, for the oil samples (I, II,
and Control Oil).
LUCIANA G.P. SODRÉ et al. OIL GEOCHEMICAL INTERPRETATION AFTER RECOVERY
An Acad Bras Cienc (2022) 94(Suppl. 3) e20211433 16 | 19
still required to comprehensively understand
and verify the additional effects of the
biosurfactant in the aromatic polar compounds.
So, the study of changes in the chemical
composition of petroleum after secondary
(waterflooding) and advanced (MEOR) recovery
processes, through the analysis of saturated,
aromatic, and polar compounds, showed that a
chemical investigation of the oils recovered with
aqueous solutions is fundamental to properly
qualify these oils, since the recovery processes
used in this study proved to be able to influence
the chemical composition of the oil, especially
at the level of geochemical interpretation when
the acidic species of the oils were analyzed in
depth. Waterflooding is undoubtedly considered
one of the most dominant processes for changes
in the chemical composition of petroleum, as
demonstrated in this work.
Acknowledgments
The authors are grateful to Laísa R. Brasil for the
recovered oils from the porous media experiments, and
to PETROBRAS for the crude oil donations. This work was
performed with financial support provided by Programa
de Formação de Recursos Humanos- Agência Nacional
do Petróleo (PRH20-ANP), Brazil; by Fundação de Amparo
à Pesquisa do Estado do Rio de Janeiro (FAPERJ - Proc.
E-26/210.760/2019 and Proc. E-26/210.163/2021), Brazil;
and by Coordenação de Aperfeiçoamento de Pessoal de
Nível Superior (CAPES - Finance Code 001), Brazil.
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SUPPLEMENTARY MATERIAL
Appendix A: Tables SI-SIII.
Figures S1-S2.
How to cite
SODRÉ LGP, MARTINS LL, DE ARAUJO LLGC, FRANCO DMM, VAZ BG, ROMÃO
W, MERZEL VM & DA CRUZ GF. 2022. Implications of microbial enhanced
oil recovery and waterflooding for geochemical interpretation of
recovered oils. An Acad Bras Cienc 94: e20211433. DOI 10.1590/0001-
3765202220211433.
Manuscript received on October 25, 2021;
accepted for publication on February 1, 2022
LUCIANA G.P. SODRÉ1
https://orcid.org/0000-0002-6307-6307
LAERCIO L. MARTINS1
https://orcid.org/0000-0001-6216-990X
LORRAINE LOUISE G.C. DE ARAUJO1,2
https://orcid.org/0000-0003-0661-3759
DANIELLE M.M. FRANCO3
https://orcid.org/0000-0002-3691-4328
BONIEK G. VAZ3
https://orcid.org/0000-0003-1197-4284
WANDERSON ROMÃO4
https://orcid.org/0000-0002-2254-6683
VALÉRIA M. MERZEL5
https://orcid.org/0000-0001-8817-4758
GEORGIANA F. DA CRUZ1
https://orcid.org/0000-0003-2116-2837
1Universidade Estadual do Norte Fluminense Darcy Ribeiro
(UENF), Laboratório de Engenharia e Exploração de
Petróleo (LENEP), Rodovia Amaral Peixoto, Km 163, Avenida
Brennand, Imboassica, 27925-535 Macaé, RJ, Brazil
2Universidade Federal do Rio de Janeiro (UFRJ), Instituto
de Química, Avenida Athos da Silveira Ramos, 149,
Ilha do Fundão, 21941-909 Rio de Janeiro, RJ, Brazil
3Universidade Federal de Goiás (UFG), Instituto de
Química, Avenida Esperança, Chácaras de Recreio
Samambaia, 74690-900 Goiânia, GO, Brazil
4Universidade Federal do Espírito Santo (UFES), Avenida
Fernando Ferrari, 514, Goiabeiras, 29075-910 Vitória, ES, Brazil
5Universidade Estadual de Campinas (UNICAMP), Centro
Pluridisciplinar de Pesquisas Químicas, Biológicas e
Agrícolas (CPQBA), Avenida Alexandre Cazellato, 999,
Paulínia/Betel, 13148-218 São Paulo, SP, Brazil
Correspondence to: Georgiana Feitosa da Cruz
E-mail: georgiana@lenep.uenf.br
Author contributions
Sodré LGP: experimental work, conceptualization, writing and
editing. Martins LL: treatment concerning the results from FT-
ICR MS. De Araujo LLGC: core flooding experiment and treatment
concerning the results from core flooding experiment. Franco
DMM: made oils analyses in 7T SolariX 2xR ESI(-) FT-ICR mass
spectrometer (Bruker Daltonics, Bremmen, Germany). Vaz BG:
suport and discussion from FT-ICR MS analysis obtained in a 7T
SolariX 2xR ESI(-) FT-ICR mass spectrometer. Romão W: suport
and discussion from FT-ICR MS analysis obtained in a Solarix
9.4T ESI(+) FT-ICR mass spectrometer. Merzel VM: isolated and
supplied the biosurfactant for the core flooding experimente.
Da Cruz GF: conceptualization, writing, discussion, review and
supervision.
