Enhanced oil recovery by nonionic surfactants considering micellization, surface, and foaming properties
Enhanced oil recovery by nonionic surfactants considering micellization, surface, and foaming properties
Achinta Bera 0 1
Ajay Mandal 0 1
Hadi Belhaj 0 1
Tarkeswar Kumar 0 1
0 Department of Petroleum Engineering, Indian Institute of Technology (Indian School of Mines) , Dhanbad, Jharkhand 826004 , India
1 Petroleum Engineering Department, The Petroleum Institute , P.O. Box 2533, Abu Dhabi , United Arab Emirates
Surfactants for enhanced oil recovery are important to study due to their special characteristics like foam generation, lowering interfacial tension between oleic and aqueous phases, and wettability alteration of reservoir rock surfaces. Foam is a good mobility control agent in enhanced oil recovery for improving the mobility ratio. In the present work, the foaming behavior of three nonionic ethoxylated surfactants, namely Tergitol 15-S-7, Tergitol 15-S-9, and Tergitol 15-S-12, was studied experimentally. Among the surfactants, Tergitol 15-S-12 shows the highest foamability. The effect of NaCl concentration and synthetic seawater on foaming behavior of the surfactants was investigated by the test-tube shaking method. The critical micelle concentrations of aqueous solutions of the different nonionic surfactants were measured at 300 K. It was found that the critical micelle concentrations of all surfactants also increased with increasing ethylene oxide number. Dynamic light scattering experiments were performed to investigate the micelle sizes of the surfactants at their respective critical micelle concentrations. Core flooding experiments were carried out in sand packs using the surfactant solutions. It was found that 22% additional oil was recovered in the case of all the surfactants over secondary water flooding. Tergitol 15-S-12 exhibited the maximum additional oil recovery which is more than 26% after water injection.
Enhanced oil recovery; Ethylene oxide number; Foaming properties; Surfactant flooding; Micellization
& Achinta Bera
Surfactants play a vital role in chemical flooding for their
abilities to reduce interfacial tension (IFT) and to alter the
wettability of reservoir rock surfaces to facilitate
mobilization of trapped oil from natural reservoirs (Bera et al.
2014b; Jiang et al. 2014; Ko et al. 2014). In recent years,
surfactant flooding has become one of the most useful tools
in enhanced oil recovery (EOR) methods (Elraies et al.
2010; Flaaten et al. 2010; Kumar and Mohanty 2010;
Santanna et al. 2009; Southwick et al. 2010). Selection of
proper surfactants for EOR is an important issue in
surfactant flooding for better economic recovery. Therefore,
laboratory characterization of surfactants is one of the
major steps before implementing EOR techniques. The
main aim of the EOR process is to increase the capillary
number by reducing the IFT between water and oil
(Babadagli and Boluk 2005). As an effective candidate for
wettability alteration, surfactants also help to contribute
significantly to the production characteristics of oil during
chemical flooding (Zhang et al. 2006). Due to the
interrelationship between IFT and capillary number, interfacial
phenomena of surfactants are studied in laboratory to
screen the surfactants with respect to their activities. It has
been reported the surface activities of several surface active
agents and their mixtures play an important role in EOR
(Babadagli 2005; Babadagli and Boluk 2005;
El-Batanoney et al. 1999; Gong et al. 2005; Zhang et al. 2006).
In general, foam is defined as complex, highly
nonequilibrium dispersions of gas bubbles in a relatively small
amount of liquid generally containing surfactants (Bera et al.
2013). The main mechanism of foam stability and
foamability is the absorption of surfactants at the liquid?gas
interface. As a result, the intrinsic resistance of the lamella
and interfacial area are directly responsible for the foam
stability in the sense of thermodynamics (Huang et al. 1986).
Among the various applications of foams, their importance
in EOR process is very widespread (Aveyard et al. 1994a, b;
Exerowa and Kruglyakov 1998; Sadoc and Rivier 1999;
Shirtcliffe et al. 2003; Zochhi 1999). For surfactant flooding,
foamability and foam stability of surfactant solutions are
essential. During the last few years, the effect of solid
particles on foam formation and foam stability has been studied
intensively. It is just noted here that the effects on
foamability and foam stability of the introduction of nanoparticles
are becoming of considerable interest in current research for
application in oil fields. The common procedures of foam
preparation include shaking (Aronson 1986; Alargova et al.
2004; Binks and Tommy 2005; Dickinson et al. 2004;
Dippenaar et al. 1978; Dippenaar 1982a, b; Frye and Berg 1989;
Garrett 1979; Garrett et al. 2006), bubbling (Frye and Berg
1989; Kulkarni et al. 1977; Johansson and Pugh 1992; Pugh
2005; Vijayaraghavan et al. 2006), bubbling and shaking
(Frye and Berg 1989), bubbling and stirring (Aktas et al.
2008; Johansson and Pugh 1992; Schwarz and Grano 2005),
and sudden drop in pressure (Dickinson et al. 2004; Kostakis
et al. 2006). It was established that the particle
hydrophobicity (Aktas et al. 2008; Du et al. 2003; Horozov 2008;
Hunter et al. 2008), size (Aktas et al. 2008; Ata 2008;
Dippenaar 1982a, b; Frye and Berg 1989; Binks and Tommy
2005), and concentration (Dippenaar 1982a, b; Gonzenbach
et al. 2006; Zhang et al. 2008) affect the foam stability. For
foam flooding, the foamability and foam stability tests are
one of the major laboratory steps for the EOR method.
In EOR, different types of surfactants are used. They
have different interfacial properties for improving oil
recovery. All the components of the surfactant slug are
based on trial and error methods (Rosen 1989). For EOR
technique, it is necessary to choose the proper surfactant
with the best surface activities, i.e., ability to reduce
surface tension or IFT. There has been a considerable focus on
surfactant design in EOR methods. In most of the cases,
anionic surfactants are used because these surfactants have
several applications like emulsifiers, foam generating
agents, detergents, and effective wetting agents. Depending
on these adequate properties as well as low cost of anionic
surfactants, they are considered as potential EOR
candidates in actual reservoir cases.
In this work, foamability and foam stability of all the
nonionic surfactants have been studied by the standard
shaking method to understand their efficiencies as EOR
candidates in different brine solutions and synthetic
seawater (SSW). The critical micelle concentrations (CMCs)
of the nonionic surfactants were measured at a temperature
of 300 K, and a relationship between ethylene oxide
numbers (EONs) and CMCs of the surfactants used has
been established from the results. Dynamic light scattering
(DLS) experiments have also been performed with the
surfactant solutions at their corresponding CMCs to study
the sizes of the micelles of the surfactants. Core flooding
experiments have been performed with the surfactant
solutions. A comparison was made of the efficiencies of the
surfactants to recover additional oil.
2.1 Materials used
In this work, the surfactants Tergitol 15-S-7, Tergitol 15-S-9,
and Tergitol 15-S-12 were purchased from Sigma-Aldrich,
Germany, and the chemical name of these surfactants is
secondary alcohol ethoxylate. Their general structural
formula is: C12-14H25-29O[CH2CH2O]xH. Table 1 shows the
properties of all surfactants. The purities of the surfactants
are 99.9%. The total acid number, gravity, and viscosity of
the oil were found to be 0.038 mg KOH/g, 38.86 API, and
5.12 Pa s at 45 C, respectively. The SSW was prepared by
mixing different salts (NaCl, 23.54 g/L; KCl, 0.675 g/L;
CaCl2, 0.115 g/L; MgCl2, 5.84 g/L; Na2SO4, 3.84 g/L;
SrCl2, 0.024 g/L; KBr, 0.110 g/L; NaF, 0.090 g/L;
NaHCO3, 0.200 g/L; H3BO3, 0.030 g/L) in distilled water.
All these chemicals were procured from Merck Specialties
Pvt. Ltd., Mumbai, India, and all of the chemicals are more
than 98% pure. All the solutions and different concentrated
brines were prepared by using reverse osmosis water from a
Millipore water system (Millipore SA, 67120 Molsheim,
2.2 Measurement of surface tension and CMC
Surface tensions of surfactant solutions were measured
with a programmable tensiometer (Kruss GmbH, Germany,
model: K20 EasyDyne) using the Du Nou?y ring method at
300 K. Special attention was paid to the cleaning of the
platinum ring. The ring was cleaned with acetone and then
flame dried for each measurement. The standard deviation
was ?0.1 mN/m. For determination of CMCs of the
surfactants, the concentration versus surface tension graph
was plotted and the concentrations at the inflexion points of
the curves are considered as CMCs of the surfactants.
2.3 DLS study of the surfactants at their CMCs The surfactant solutions were prepared at their corresponding CMC values. The sizes of micelles were
Table 1 Physicochemical properties of the surfactants employed in the work
balance (HLB) value
C 9 1010, mol/cm2
measured by a laser diffraction method using a Zetasizer
version 6.00 (Malvern Instruments Ltd., Worcestershire,
UK) at 300 K. The size distribution of micelles was
obtained by the inbuilt software of the instrument. The
software uses a reflective index (RI) of 1.465 (SBO) and a
dispersant RI of 1.33 (water) during the measurement.
Drops of the surfactant solution were introduced into the
sample-containing cuvette, and the optimum volume was
indicated by the instrument.
2.4 Foamability and foam stability tests
Foamability and foam stability experiments were
conducted in a graduated measuring cylinder with 0.5wt%
surfactant solution. We used bottle shaking tests (ASTM
D-3601) to evaluate the foaming capacity of different
surfactants in the presence of salts, where the volume of
gas (air) is fixed in the container (centrifuge tube). Bottle
shaking test (ASTM D-3601) for foam generation study is a
standard method, which is reported by many authors
(Schramm and Wassmuth 1994; Tamura and Kaneko 2004;
Nadkarni 2007; Moayedi et al. 2014). For foam study, a
constant volume of the aqueous sample in a 10-mL
graduated centrifuge tube was shaken manually at a fixed
frequency for fixed time (15 min for each case) and then left
untouched on a flat surface (make necessary corrections for
volume). The foam height and liquid holdup of the
generated foam for each respective sample were recorded over
time by visual observation. A plot of time versus foam
volume indicates the foam stability. Foam stability was
measured assuming that mechanical vibrations are absent.
The foamability of the surfactant solution was measured by
taking the initially produced foam volume after constant
time shaking with different brine concentrations and SSW
at 300 K.
2.5 Apparatus and methods for surfactant flooding
for oil recovery
A schematic of the experimental setup for surfactant
flooding is shown in Fig. 1. The whole experimental setup
contains a core holder for the sand pack, different cylinders
for surfactant solution and crude oil, a pump from ISCO,
and an effluent collecting cylinder. The core holder was
fully filled with 60?70 mesh sand, and while filling the core
holder brine was used to saturate the sand pack for
measuring its porosity. Permeability was measured by brine
flooding through the sand pack. After that the sand pack
was flooded with the crude oil until water production
reaches about 1% at 400 psig. The initial water saturation
of the core was determined by mass balance. After water
flooding, a * 0.6 pore volume (PV) surfactant slug was
injected followed by * 1.25 PV water injection as chase
water flooding. The above-mentioned method has also been
described in our previous work in details (Bera et al.
3 Results and discussion
3.1 CMCs and micelle sizes of the surfactants
CMC measurement of surfactant is very important for
foamability and foam stability studies as well as their
applications in further preliminary screening of surfactants.
Before selecting a surfactant for application in oil fields, it
is necessary to characterize the surfactant initially. It is
well known that surfactants start to undergo micelle
formation at CMCs (Hoff et al. 2001). Figure 2 shows the
CMC values of the surfactants studied in this work. The
present work shows that CMCs of the surfactants (Tergitol
15-S-7, Tergitol 15-S-9, and Tergitol 15-S-12) increase
with increases in EON of the surfactants which shows a
strong similarity to another study (Wu et al. 2006). It is
found that the CMC values are 0.0031wt%, 0.0042wt%,
and 0.0051wt% for the surfactants of EON of 7, 9, and 12,
respectively. The data clearly illustrate the relationship
between EON and CMC values of the surfactants used. For
ethoxylated nonionic surfactants, the steric hindrances
between head groups of the surfactants can be expected to
increase with increasing EON. Subsequently with an
increase in EON, the head group parameter also increases
within the head group. Therefore, low EON may reduce the
head group parameter as well as the area per molecule;
therefore, the packing parameter is large which results in
bilayer aggregates (lamella). For high EON, the head group
Fig. 1 Schematic diagram of experimental setup for surfactant flooding in a sand pack
0.004 0.006 0.008
Surfactant concentration, wt%
Fig. 2 Surface tensions of the nonionic surfactants used at different
concentrations and CMC determination at 300 K
parameter and the area per molecule increase, but the
packing parameter decreases; thus, it is possible to form
cylindrical micelles. With increasing EON, the packing
parameter decreases and spherical micelles may be formed
by decreasing the aggregation number. Therefore, the
increases in head group parameter and area per molecule
for nonionic surfactants with increasing EON give rise to
an increase in CMC as the head group size increases.
Figure 2 clearly shows that the surfactants are very active
in reducing the surface tension of the liquid?air system.
Among all the nonionic surfactants, Tergitol 15-S-12
shows the lowest surface tension value at its CMC. The
surface tension values of the surfactant solutions at their
CMCs are 31, 29, and 28 mN/m for Tergitol 15-S-7,
Tergitol 15-S-9, and Tergitol 15-S-12, respectively.
It is important to consider the micelle sizes of
surfactants in oil recovery processes. Figure 3 shows the size
distributions of the micelles of the prepared surfactant
solutions at their CMC values. The z-average diameter can
be calculated in dynamic light scattering as follows (Zheng
et al. 2016; Bera et al. 2012b):
where Si is the scattered intensity from particle i and Di is
the diameter of particle i.
The sizes of the micelles are shown in Fig. 4. In the
present study, the typical micelle sizes of the surfactants
range from 0.5 lm to 10 lm which are also desired for
core flooding experiments when compared to the pore size
distribution of the sand grains in the sand pack model.
Figure 4 shows that the micelle size of Tergitol 15-S-12 is
higher than that of the other two surfactants. This is
because the ethylene oxide chain length of Tergitol
15-S12 is greater than the other two surfactants. From this
study, it can be also possible to establish a relationship
between the micelle sizes and CMCs of the surfactants.
The results show that with an increase in CMC of the
surfactant the micelle size also increases. Therefore,
Fig. 4 Sizes of micelles of the nonionic surfactants
depending on the CMCs of the surfactants their micelle
sizes can be predicted and it is possible to screen the
surfactants for further investigation for implementing in EOR
3.2 Foamability and foam stability
The foamability test is a special test of surfactants for their
selection in EOR by foam injection. In the present work,
foaming properties of nonionic surfactants were tested in
pure distilled water, NaCl solutions (2wt% and 4wt%), and
SSW. Figure 5 shows the foamability at 0.5 wt% of
different surfactants. Results indicate that Tergitol 15-S-12
generated the highest amount of foam, i.e., higher
foamability than the other nonionic surfactants used. The higher
foaming properties of Tergitol 15-S-12 may be explained on
the basis of higher EON. Nonionic surfactants like Tergitol
15-S-12, Tergitol 15-S-9, and Tergitol 15-S-7 can form
good foam below their cloud points. Nonionic surfactants
can only produce foam in good amounts when they are able
to form a well-packed adsorption monolayer at the air?
water interface. In the present case, the foaming is not high
enough for all the surfactants and the reason is the
instability of the foam films. Again, the higher foamability of
Tergitol 15-S-12 compared to other nonionic surfactants
can be explained on the basis of stability of monolayers. As
the EON of Tergitol 15-S-12 is higher than the other
nonionic surfactants, a more stable monolayer is formed and for
other cases a bilayer might be favorable. As a result,
Tergitol 15-S-12 shows higher foamability than the others
(Patrick et al. 1997; Mittal and Shah 2002). Figure 6 shows
the foaming of the Tergitol surfactants at their
corresponding CMC values after several hours of equilibrium.
Adsorption of surfactants at the air?water interface plays
an important role in the formation of foam and its stability.
The Gibbs surface adsorption equation was used to
calculate the surface excess for all the surfactants as follows
(Amaral et al. 2008; Azira et al. 2008; Tan et al. 2005;
Wang and Chen 2006):
where C is the surface excess, mmol/cm2; R is the universal
gas constant, 8.314 J mol-1 K-1; c is the surface
2wt% NaCl solution 4wt% NaCl solution
Fig. 5 Initial amount of produced foam for different surfactant
solutions in distilled water, 2wt% NaCl, 4wt% NaCl, and SSW
Fig. 6 Photograph of the foaming of the Tergitol surfactants in
distilled water after several hours of equilibrium (from left to right:
Tergitol 15-S-12, Tergitol 15-S-9, and Tergitol 15-S-7)
tension, mN m-1; T is the thermodynamic temperature, K;
and C represents the concentration of surfactant, mmol L-1
at corresponding CMC value.
The slope of the plot of logarithmic concentration of
surfactant versus surface tension gives the value of d dlncC .
On the other hand, the molecular cross-sectional area of the
polar head group (A) was calculated from the following
where NA indicates Avogadro?s number, 6.023 9 1023
mol-1; A is the molecular cross-sectional area of the polar
head group, A? 2.
Table 1 shows the calculated values of the surface
excess ?C? and molecular cross-sectional area for all the
nonionic surfactants from Eqs. (2) and (3). In our previous
work, we also determined the surface excess and molecular
cross-sectional area for several cationic, nonionic, and
anionic surfactants (Bera et al. 2013). A significant result
was found in the case of nonionic surfactant systems that as
the EON of the surfactant increases the adsorption also
increases. In the case of Tergitol 15-S-12, the surfactant
has higher EON value and its C value is greater than that of
the other surfactants (Tergitol 15-S-7 and Tergitol 15-S-9).
It is also found from Table 1 that as C values increase the
values of the molecular cross section of the polar head
group (A) of the nonionic surfactants decrease accordingly.
Surface excess is the number of moles of surfactant per unit
area at the liquid?air interface. In the solution phase, most
of the surfactants form a vertically monolayer just below
the CMC values. The area/molecule is usually determined
by the cross-sectional area of the head group. For nonionic
surfactants with ethylene oxide, the area per molecule is
generally much larger than other types of surfactants.
Therefore, with an increase in the ethylene oxide number in
the head group the area per molecule also increases. As
Tergitol 15-S-12 has the highest ethylene oxide number;
therefore, it has the lowest surface excess and the highest
area per molecule.
The foam stability of a surfactant solution can be
defined as the change in foam volume, i.e., the volume of
liquid drained from the foam, per unit time (Bera et al.
2013). The foam stability of the surfactants in distilled
water, 2wt% NaCl solution, 4wt% NaCl solution, and SSW
is depicted in Figs. 7, 8, 9, and 10, respectively. The
common way to determine the foam stability is to measure
the foam volume after production of certain amount of
foam with different time intervals. The foam structure is
related to time which quantifies the foam stability of a
certain surfactant (Kroschwitz 1994). Several factors like
drainage, disproportionation, and coalescence influence the
Fig. 8 Foam volume versus time for different surfactants in 2wt%
foam stability. Foam stability depends on dispersed
particles of colloid in the continuous phase. These dispersed
particles control the liquid drainage from the foam which
significantly accounts for the high stability of a foam.
Mainly these particles reduce the liquid drainage rate and
increase the surface viscosity of the continuous phase.
These colloid dispersions greatly affect the foam stability
(Kaptay 2004; Sethumadhavan et al. 2001).
In all solutions, Tergitol 15-S-12 shows the highest foam
stability. Foam stabilization is mainly caused by van der
Waals forces between the molecules in the foam, electrical
double layers created by dipolar surfactants (Zwitterionic
surfactant) and the Marangoni effect, which acts as a
restoring force to the lamellae. Other important factors that
Fig. 9 Foam volume versus time for different surfactants in 4wt%
Fig. 10 Foam volume versus time for different surfactants in
synthetic seawater (SSW)
control the foam stability are surface viscosity and film
elasticity. Of all the surfactants used in this study,
irrespective of other influencing factors, the main controlling
parameter is the surface viscosity. The surface viscosity of
Tergitol 15-S-12 is high due to the presence of the high
number of ethylene oxide units in the head group. The
viscous nature of the surfactant solution results in a slow
drainage of liquid through the bubble interfaces. As a
result, the foam produced by the surfactant Tergitol
15-S12 is also stable and shows higher stability than the other
surfactants. Different salts in SSW affect the foam stability;
hence, foam stability is low in the case of SSW. Some
researchers suggested two different regimes of foam decay.
One is during the initial stage immediately after foam
formation, and the other is the comparatively slow drainage
(Lunkenheimer and Malysa 2003; Carey and Stubenrauch
2009). The produced thin films in the air?water interface
indicate the foam stability. Foam stability and quality of
foam are very important in oil recovery to increase the
sweep efficiency. Therefore, laboratory study of foam
stability is a crucial step for foam flooding for EOR.
3.3 Surfactant flooding and oil recovery
Surfactants are considered to be important chemicals for
tertiary recovery by reducing IFT and changing wettability
of rock surfaces. In the present work, surfactant solutions
were injected into the sand pack after water flooding. Due
to the high porosity of the sand pack (*37%), water
flooding is able to produce high recovery (*52%).
Figure 11 shows the performances of surfactants in oil
recovery after injection of different pore volumes into the
sand pack and the variations of oil and water cuts.
Figure 11 shows that after injection of 1.15 PV water the oil
cut decreases to 5% and the water cut goes to 95%. At this
moment, the surfactant injection is started and it is found
that the water cut declines gradually and the oil cut again
increases to produce the highest recovery. The enhanced
recovery can be explained on the basis of IFT reduction or
increase in capillary number and consequent mobilization
of the oil trapped inside pore throats. As a result, the oil
saturation increases due to coalescence of oil drops and
retrapping of oil drops mobilized from the oil bank by the
surfactant slug. Figure 11 also shows that the additional of
recovery by Tergitol 15-S-12 is higher than others due to
significant interfacial surface active properties of the
surfactant. On the other hand, due to the presence of 12
Fig. 11 Oil recoveries by Tergitol surfactants in sand pack flooding
Design of surfactant
slug for flooding
Table 2 Recovery of oil by surfactant flooding of sand packs for three different systems
Permeability k, Darcy
Recovery of oil after
water flooding at 95%
water cut, %OOIP
ethylene oxide groups in Tergitol 15-S-12, the micelle size
is larger than the other two surfactants. Therefore, the
micelles formed by surfactant Tergitol 15-S-12 are more
stable than those of the other two favored by the entropy
and enthalpy of micellization. Therefore, during surfactant
flooding for Tergitol 15-S-9 and Tergitol 15-S-7 it is
difficult to form micelles in the system and they cannot reduce
the IFT as required. The oil trapped in the porous matrix
cannot be recovered easily, and residual oil saturation
remains high. As Tergitol 15-S-12 can produce a
microemulsion easily, it is also able to produce ultra-low
IFT and shows higher additional oil recovery as described
in the oil recovery section. It is also worth mentioning at
this point that the foaming property of Tergitol 15-S-12 is
better than other surfactants and as a result Tergitol
15-S12 shows higher oil recovery than the other surfactants.
Therefore, a bridge can be established from all the studies
of surfactant solutions and their influences on oil recovery
to provide an overview of the importance and significance
of this work. The additional recovery was 22.3, 24.6, and
26.9% for Tergitol 15-S-7, Tergitol 15-S-9, and Tergitol
15-S-12, respectively. The detail of the surfactant flooding
results with properties of the sand pack is given in Table 2.
Another important mechanism that plays a vital role in
oil recovery is wettability alteration by surfactants (Bera
et al. 2012a, 2015). Oil?water relative permeabilities are
highly influenced by wettability alteration during surfactant
flooding through an oil-saturated sand pack. Surfactant
flooding enhances the relative permeability of oil as the
oilwet state of the sand pack is altered to a water-wet state. As
a result, flows of oil and water through the sand pack are
changed accordingly. Water finds the path to move forward
along the pore wall with water-wet state and reaches the
center of the pores in the oil-wet state during the surfactant
flooding. Therefore, the capillary forces act along the
direction of water flooding for a water-wet surface and the
opposite for an oil-wet surface. This phenomenon also
reflects the increase in displacement efficiency by
surfactant flooding which enhances the oil recovery after water
flooding. As the sand pack is water-wet in general,
injection of the surfactant solution can recover more oil from the
oil-saturated core during surfactant flooding by alteration
of wettability toward a water-wet state. So surfactant
flooding can reduce the residual oil saturation. Therefore,
after water flooding in an oil field surfactant flooding can
significantly recover the residual oil.
Apart from the wettability alteration, in situ
microemulsion formation during surfactant flooding causes
increased oil recovery (Glinsmann 1979; Jeirani et al.
2014). During surfactant flooding, a multiphase
microemulsion system is formed by mixing the surfactant
slug with the remaining oil in the reservoir after water
flooding. As the microemulsion is formed, IFT between the
oil and surfactant slug reduces to ultra-low one which helps
to increase the capillary number followed by enhanced oil
recovery. The in situ generated microemulsion is assumed
to disseminate toward the producing well by sweeping a
significant amount of oil in the reservoir. The process
depends on the compositions present in the surfactant
solution and overall compositions of the formed
Present studies of micellization and sizes of micelles,
foamability and foam stability of different nonionic
surfactants provide a sound background for selection and
application of surfactants for EOR. Based on the results of
the work, the following conclusions can be drawn:
Tergitol 15-S-12 shows maximum foamability in
distilled water, NaCl solutions of different
concentrations, and SSW.
The present study provides useful information for
selection of surfactant systems for EOR. When the
molecular cross section of the polar head group (A)
decreases, the surface excess (C) value increases for all
the nonionic surfactants.
DLS study shows that with an increase in EON of the
surfactants the micelle sizes of the surfactants also
increase at their corresponding CMCs.
The additional recovery is more than 22%. The
surfactant with the highest EON value, Tergitol
15-S12, shows the greatest efficiency to recover more than
26% additional oil compared to straight water flooding.
Acknowledgements The first author (AB) thanks the Petroleum
Institute, Abu Dhabi, for providing the fellowship for his postdoctoral
research. The second author (AM) gratefully acknowledges the
financial support provided by Council for Scientific and Industrial
Research [22(0649)/13/EMR-II], New Delhi, to the Department of
Petroleum Engineering, Indian Institute of Technology (Indian School
of Mines), Dhanbad, India.
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