274-Article Text-1503-1-10-20230609.pdf

ISSN: 2716-9227 Algerian Journal of Engineering and Technology 08 (2023) 101–107 e-ISSN: 2716-9278
Algerian Journal of Engineering and
Technology
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* Corresponding author.
Tel.:+213 (0) 23 93 48 19
E-mail address: sakhitayebgr@gmail.com
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2716-9227/© 2023 The Authors. Published by University of El Oued. This is an open access article under the CC BY-NC license
(https://creativecommons.org/licenses/by-nc/4.0/). DOI: https://doi.org/10.57056/ajet.v8i1.98
Original Article
Dynamic simulation of preformed aqueous foam stability for enhanced
oil recovery application
Tayeb Sakhi a,b
*, Rachida Cheminia
, Yacine Salhia
, Abdellah Arhaliassb
a
Laboratory of Theoretical and Applied Fluid Mechanics University of Sciences and Technology Houari Boumediene, BP 32, El Allia – Bab Ezzouar
16111, Algiers, Algeria
b
Laboratory of Process Engineering – Environment – Agrifood (GEPEA-UMR CNRS 6144) C.R.T.T.-37, bd- BP 406 44602 SAINT-NAZAIRE, University
of Nantes, France.
ARTICLE INFO ABSTRACT
Article history:
Received 09 January 2023
Revised 23 April 2023
Accepted 01 May 2023
Aqueous foam is a two-phase system consisting of a continuous liquid phase and a dispersed
gas phase. Foams are widely used in a variety of industrial operations, such as the enhanced
recovery of hydrocarbons. Because of their unique properties, they can solve a variety of
reservoir heterogeneity problems, including early gas breakthrough, channeling, and even
viscous fingering. A variety of phenomena affect the stability of foams during flow, for
example, the drainage process, gas diffusion, and bubble coalescence. In this research, we used
the level-set method to simulate foam stability in various aspects, such as factors affecting
foam drainage and coalescence phenomena. According to the simulation results, the foam's
lifetime is greatly impacted by the phenomena of drainage and coalescence. Moreover, its
stability is strongly influenced by salt as well as the type of gas used to generate it.
Keywords:
Level-set method;
EOR;
Drainage;
Coalescence;
Foam stability.
1. Introduction
Enhanced oil recovery (EOR), also known as tertiary
recovery, refers to the application of developed
technologies to further increase hydrocarbon recovery
production after primary and secondary recovery [1]. Such
a recovery method involves the injection of a specific fluid
to displace oil from the injector toward the producer well
[2]. Examples of EOR injections are surfactant flooding,
polymers, microbial flooding, and steam flooding [3].
Among these techniques, foam flooding has been identified
as a great potential solution for many challenges
encountered during various phases of hydrocarbon
recovery [4, 5]. It includes channeling, defined as the gas
flow in the highly permeable zones inside the reservoir;
gravity override, which is a consequence of the high-
density difference between gas and oil, and viscous
fingering due to the large difference in viscosity between
oil and gas [6, 7] (Figures 1 and 2). Foam application
modes can be CO2 foam, steam foam, and gas-miscible
flood foam injection [8]. The injection of foam, which is
mainly composed of gas, makes it possible to mitigate
these challenges, which could significantly enhance sweep
efficiency. In addition, foam reduces gas mobility by
increasing its viscosity and/or reducing its relative
permeability [9]. It can also divert gas to unswept regions
by blocking highly permeable zones. Furthermore, it fixes
the early gas breakthrough problem. There are three foam
generation methods for foam-assisted EOR; preformed
foam is generated on the surface using a foam generator,
and co-injection foam is formed near the injector where the
solution of surfactant is co-injected with gas. Alternate
injection of surfactant and gas (surfactant alternate gas, or
SAG); the liquid containing the surfactant and the gas are

Sakhi et al / Algerian Journal of Engineering and Technology 08 (2023) 101–107 102
injected alternately in the form of "slugs." Hence, the foam
is generated in situ in the porous medium [10].
Figure 1: Illustrative schematic of different challenges leading to
poor sweep efficiency [4]
Fig 2. Comparative illustration between gas injection and foam
flooding [5]
It has been proven in many pilot studies [11, 12] and field
studies [13, 14, 15] that the application of foam in EOR
can improve the recovery of hydrocarbons. The
fundamental difficulty of foam-assisted EOR is the
stability of the foam during flow in porous media. To
obtain a higher recovery factor, it must be stable enough
during its flow. Foam stability is defined as the ability of
this foam to keep or maintain its initial properties, such as
its quality. Foam drainage, coalescence, and bubble
coarsening are the main physical phenomena that
destabilize the foam [16, 17].
The rupture of foam can have a significant impact on the
performance of foam flooding inside the reservoir.
Numerous studies have investigated the effect of salt on
foam stability, which is one of the factors limiting foam
injection in EOR applications [18,19]. Salts, in general,
increase the collapse rate, hence destabilizing the foam and
reducing its performance [20]. Masoud Hatami Laoghaire
and al [21] conducted a series of experiments to highlight
the influence of various gases and their mixtures on the
performance of foams in EOR, including bulk stability
tests, apparent foam viscosity measurements, and core
flooding testing. Their findings verified the significance of
gas types on foam stability. In the literature, a multitude of
models has been proposed to predict the behavior of foam
in porous media. These models can be classified into two
categories: population balance models to simulate the
generation, destruction, and transport of lamellae in porous
media and local equilibrium models to predict only the
reduction in mobility of gas in a steady state when it flows
in the form of foam [22].
These latter models are based on empirical formulations
calibrated from foam displacements on core samples in the
laboratory [23, 24]. The work of Wang et al. [25] focused
on the simulation of foam interface evolution in terms of
foam drainage, foam migration, and the Jamin effect,
which are crucial results in studying and evaluating foam
stability. On the other hand, their study lacked the
influence of salt on foam stability as well as the influence
of the type of gas used to generate this aqueous foam.
The purpose of the current research was to study and
evaluate the stability of aqueous foam by simulation using
the level set method and gas-liquid two-phase flow. A
successful application of fluid foam-assisted EOR requires
a thorough understanding of its fundamental performance
and flow mechanism.
2. Materials and Methods
There are different ways to represent the interface behavior
between fluids and understand the change in foam
morphology. The volume of fluid (VOF) method was
implemented for multiphase flow modeling and was
suitable to resolve sharp interfaces. This method traces the
volume of each fluid instead of the motion of particles
[26]. Another method to simulate the evolution of the foam
interface is the level set method. The level set approach
uses a signed distance function of space and time to define
the interface between two fluids (Equation 1). This sign
indicates whether point x is inside the material (Figure 3)
[27]. It is useful when it comes to modifying the foam
structure. In addition, it can handle geometric complexity
and topological changes.
Injector well Producer well Injector well
Oil-rich
zone
Foamed
gas

Fig 3. Schematic of level set function in foam interface where i
represents interface of the foam and ∅ represents level Set
function.
Equation (1)
|∅( ⃗ )| ( ⃗) ( ⃗ ⃗⃗⃗⃗) [ 28] (1)
On the interface, the density and viscosity vary as follows
(Equation 2, 3):
𝜌 = 𝜌1 + (𝜌2 − 𝜌1)∅ (2)
𝜇 = 𝜇1 + (𝜇2 − 𝜇1)∅ (3)
𝜌1, 𝜌2 are the densities of the two fluids respectively, and
𝜇1, 𝜇2 are their viscosities.
These are the Navier-Stokes equations [28]:
Equation (4)
𝜌⃗ 𝜌(⃗ ) ⃗ {⃗⃗⃗⃗⃗ [ ⃗⃗⃗ ( ⃗ ) ]} ⃗⃗⃗⃗⃗⃗
(4)
The unit matrix is I, the pressure is p, and the continuity
equation is ⃗ 𝑆𝑉 provides by converting surface
tension to volume force. Using (CSF) model [24]
Equation (5)
⃗⃗⃗⃗⃗⃗( ) ( ⃗⃗) ⃗⃗ (5)
is the surface tension and is the Dirac function.
3. Results and Discussion
3.1. Foam Drainage
Foam drainage, defined as the process of liquid draining
through networks of plateau borders, is the result of both
gravitational and capillary forces. This phenomenon has a
substantial impact on the stability of foams [29].
The geometric shape of the model is described as follows
(Figure 4) [25]: The geometric model is a square with sides
measuring 6 mm, in which hexagonal-shaped bubbles of 1
mm in radius contain the gas phase, namely nitrogen.
These bubbles are interconnected by liquid films with a
0.12 mm thickness that contains a surfactant solution. The
upper part of the model is open, while the others are walls.
Furthermore, the surface tension of this foam was 10
mN/m, and the contact angle equaled π/3.
Fig 4. Geometric model of foam drainage
The simulation results indicate that during drainage, there
was a continuous downward migration of liquid due to
gravitational, viscous, and capillary forces (Figure 5). The
upper part of this foam became increasingly dry, which
caused the liquid films to thin. Therefore, they became
weak and unstable, which caused their rupture.
Liqui
d
Gas
Gas

Fig 5. Foam drainage simulation results at different times
3.1.1. Influence of surface tension on foam stability
Surface tension is one of the most crucial factors for foam
stability [30]. To highlight the influence of surface tension
on foam stability, the structure of the foam was compared
for different values of surface tension at the same time of
foam drainage (t = 0.005 s). Thus, the results showed that
when the surface tension of this foam was equal to 10
mN/m, the drainage of liquid increased swiftly (Figure 6),
and some bubbles ruptures were observed. Nevertheless,
with a surface tension of 0.01 mN/m, the drainage of liquid
was not important and most of the bubbles kept their initial
structure. When comparing liquid film thickness between
the two cases, the lower surface tension corresponded to
more stable bubbles due to the fact that lower surface
tension may minimize the energy of the foam system,
promoting foam stability [30].
Fig 6. Simulation results of surface tension influence on foam stability

Zakari et al./ Algerian Journal of Engineering and Technology 08 (2023) 101–107 105
3.1.2. Influence of salt on foam drainage
Several studies have addressed the influence of salt (brine)
on foam stability [31,32]. In this regard, the effect of salt
on foam drainage was tested under the same conditions
mentioned before. The addition of salt to foam
significantly increased the liquid drainage, and the bubbles
also faced an important and swift rupture (Figure 7). It has
been found that salt causes a reduction in the electrostatic
repulsion in liquid film [33]. Accordingly, the two sides of
the liquid film gradually approached each other. This made
the liquid film thinner and more fragile, and consequently,
the bubbles of this foam ended up breaking.
Fig 7. simulation results of salt effect on foam lifetime
3.1.3. Influence of gases type on foam drainage
The type of used gas to form the foam was critical for
evaluating and studying its stability. Most experimental
studies of foams in porous media used either 𝑁2 nitrogen-
based foams or 𝐶𝑂2 carbon dioxide-based foams [34].
Comparative studies have shown that nitrogen-based
foams generate greater pressure gradients than CO2-based
foams [35, 36]. Indeed, 𝐶𝑂2 foams remained weaker than
𝑁2 foams, attributed to the solubility of 𝐶𝑂2 in water
which was 55 times greater than 𝑁2 [36]. This high
solubility of the gas in the liquid favored the diffusion,
the coalescence of the bubbles, and the rupture of this
foam. In this context, the stability of nitrogen, carbon
dioxide, and methane foams were simulated under the
same conditions of foam drainage at (t= 0.003s). The
results revealed that N2 foam had superior foam stability
compared to CO2 and Methane (Figure 8), which was
consistent with other research results [31, 37, 38].
Fig 8. Simulation results of the impact of gases types on foam drainage

3.2. Foam Coalescence phenomenon
When two bubbles come within a short critical distance of
each other, the thin film between the two bubbles breaks,
merging these two bubbles into one large bubble. This is
the phenomenon of coalescence. It takes place in three
stages: bubbles collision, liquid film drainage during the
collision and film rupture leading to a bigger bubble [39].
For the current study, the geometric model was a channel
of 15 mm with a pore diameter 5 mm in which there were
two bubbles of nitrogen with initial diameter of 4 mm, and
the liquid phase was surfactant solution (Figure 9).
Fig 9. Geometric model of foam coalescence
The results are as follow (Figure 10):
Fig 10. Simulation results of foam coalescence at different time
In the beginning, the two nitrogen bubbles approach
each other and then collide. After a time, the liquid film
between them gradually disappears, resulting in their union
and the appearance of a single larger bubble. The result of
this phenomenon is a growth in the size of the bubbles and
a decrease in their number until the bubbles completely
disappear [40].
4. Conclusion
In this work, the stability of aqueous foam has been
addressed in terms of foam drainage, and coalescence
phenomenon using a level-set method. The following
conclusion may be drawn.
1. The lower surface tension (σ) corresponds to a
more stable foam
2. N2-based foam are more stable foam than CO2-
based foam and CH4-based foam
3. Foam stability is strongly influenced by salt
4. The coalescence phenomenon leads to a growth
in the bubbles size and a diminution in their
number.
List of symbols
∅ : Level Set function
𝜌1: Gas density
𝜌2: Liquid density
𝜇1: Gas viscosity (Pa. s)
𝜇2: Liquid viscosity (Pa. s)
: Surface tension (N/m)
: Dirac function
⃗ : Velocity field (m/s)
t: Time (s)
P: Pressure field (Pa)

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Recommended Citation
Sakhi T, Chemini R, Salhi Y, Arhaliass A. Dynamic simulation of preformed aqueous foam stability for enhanced oil recovery
application. . Alger. J. Eng. Technol. 2023;8(1):101-107. DOI: https://doi.org/10.57056/ajet.v8i1.98
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