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Experimental Study of Nanoparticle-Surfactant-

Stabilized foam for potential drilling application:

IFT, Foamability and Stability

Shariar Ghosi†, Ezat KazemZadeh†*, Mohammad Soleimani‡

† Petroleum Engineering Group, Science and Research Branch, Islamic Azad University, Tehran,

Iran

‡ Research Institute of Petroleum Industry, Tehran, Iran

* Corresponding author: Ezat kazemzadeh

Postal address: Iran, Tehran, The end of Shahid Satari Highway, University Square, After Shohaye

Hesarak, Islamic Azad University - P.O Box: 775/14515

Email address: kazemzadehe@ripi.ir

Phone number: ***********

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Keywords: foam drilling, surfactant, nanoparticle, IFT, foamability, foam stability.

Abstract

Today underbalanced drilling has attracted much attention to itself. Among low density drilling

fluids, foam has better ability to carry drilling cuttings, and to suspense them while drilling is

stopped. Of foam properties, which has important role in controlling bottomhole pressure and

carrying cutting, are foam stability and foamability. Mixture of nanoparticle and surfactant was

used to stabilize foam. Nanoparticles could not solely generate foam. With adsorption of cationic

surfactant molecules on nanoparticles, they change from complete hydrophilicity to partial

hydrophobicity, and make nanoparticles as a surface active material.

The surface tension of nanoparticle-surfactant mixture was measured in domain of surfactant

concentration, nanoparticle concentration, salinity and pH. Measurement revealed that surface

tension experienced a minimum which is related to maximum adsorption of surfactant on

nanoparticles. Also, surface tension decreased with an increase in nanoparticles and a decrease in

salinity.

Nanoparticle-surfactant stabilized foam was prepared through Ross-Miles method, and

foamability and foam stability was investigated. With respect to reduction in the surface tension,

the domain of surfactant concentration divided into two characteristic section, namely, high

adsorption and low adsorption, respectively related to high IFT reduction and low IFT reduction.

It was found out that foamability has the most resistance in high adsorption region.

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In high adsorption region (about 1 CMC), due to reaching to the maximum hydrophobicity,

nanoparticles act as a surface active material and obtain the more stability than surfactant stabilized

foam and nanoparticle-surfactant stabilized foam at low adsorption region.

1. Introduction

Underbalanced drilling is a developing application in many oil fields, especially on the Norwegian

continental shelf, have started to show signs of aging. To have a successful underbalanced drilling,

bottomhole pressure control is necessary and pressure gradient in whole drilling column should be

the same. Foam as a low density drilling fluid can satisfy these conditions. Also foam has important

role in carrying cutting.

Aqueous foam is dispersion of gas phase in continuous water phase. For making foam, surface

active material is needed. Traditionally, surfactant used as a surface active. It was found out that

surfactant molecule tend to lie down in at gas-liquid interfacial instead of being in liquid bulk.

Foam is made by absorption of surfactant to gas-liquid interfacial and reducing interfacial tension.

However surfactant-stabilized foam has some potential weaknesses such as high surfactant

retention in porous media and unstable foam properties under reservoirs hard conditions; like high

temperature and salinity (1).

Over a century Pickering and Ramsden discovered colloidal particle with appropriate wettability

can behave as an emulsion stabilizer (2-3) but only in recent years, with the development of

nanotechnology, it has provided an alternative of using of nanoparticle as foam stabilizer. There

are many research efforts related to particle and nanoparticle-stabilized gas foam (4-5). Alargova

(6) demonstrate micro none spherical particles in the absence of amphiphilic material are

appropriate foam stabilizer. In comparison between SDS surfactant and these particles, later has

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more foam stability and first has more foam ability. Which is correct for nanoparticle instead of

the micro rod too (7). Nanoparticles usually are very hydrophilic and prefer to stay in liquid bulk

rather than lying down at interfacial. So for having a good surface active agent, we need to use

nanoparticles with appropriate hydrophobicity or modify surface properties of nanoparticle. The

latter way is considered in many articles for using nanoparticle as a surface active agent. The

optimum particle hydrophobicity has been achieved by appropriate chemical synthesis or surface

modification (8-10). Using Janus particles (11-12), using appropriate coating (13) and adding

oppositely charged surfactant with nanoparticle (14). The later method has been applied in many

research (15-18). It has been shown that mixture of nanoparticle and surfactant has many

advantage over using surfactant alone to generate foam.

For nanoparticle present in carbon dioxide water mixture, contact angle θ can determine the foam

type. Foam could be distribution of gas bubble in water (if θ<90°) or water’s drop in gas (if θ>90°)

depending on contact angle of nanoparticle at the interface. Mechanisms of stabilization for

nanoparticle stabilized foam is very different. It includes high nanoparticle attachment energy

rather than surfactants (4 and 10), Particle arrangement in film Drainage [5], Growing aggregate

and cork formation [19] and maximum capillary pressure of coalescence [20].

In this work, it was investigated Interfacial properties of nanoparticle-surfactant mixture. Foam

properties, includes stability and foamability, was analyzed based on this IFT behavior and the

complexity of synergistic effect between nanoparticles and surfactant molecules would be

understood clearly.

2. Experiments

2.1. Materials

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Cationic surfactant cetyl trimethyl ammonium bromide (CH3(CH2)15N(Br)(CH3)3>99%) was

purchased from SIGMA ALDRICH and used as received. Salts, namely, NaCl, CaCl2 and

Na2(SO4);also, was purchased from from SIGMA ALDRICH. Silica nanoparticles as a solid

powder (20 nm >98%) were supplied by Nano Pasargard Novin. Ultrapure water with resistance

of less than one micro Siemens (mho) was produced in the laboratory and used in the tests.

2.2. Foaming dispersions preparation

A certain mass of deionized water was weighted in a 100 ml beaker and silica nanoparticles were

added to it. Mixing was achieved at high speed for 15 minutes by magnetic homogenizer. The

predetermined mass of surfactant was added to it and high speed mixing was conducted again in

the same period of time.

2.3. IFT measurement

This experiment was conducted using Sigma 700 IFT meter through ring method. The mixture,

which prepared as described in section 2.2., was put in the apparatus. After a specific number of

measurement, IFT was averaged and reported here.

2.3.1. Box-Behnken Design

IFT experiment design was proceed through Box-Behnken mthod. Variables, which included

surfactant concentration, nanoparticle concentration, pH and salinity, was fixed on three level, 1,

0 and -1, which are upper, medium and low limit values, respectively. Table 1 shows the

parameters and related levels.

2.4. Foaming and foam stability

Ross-Miles test was utilized to prepare foams. According to this method, after opening the valve

of a buret, the certain volume of foaming dispersion flows through the buret, from fixed height

above a beaker. It pours down continuously on the same foaming dispersion, which is in the beaker.

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The foam volume was measured after closing the valve of the buret and exactly after falling the

last drop, and it was considered as a criterion for foam ability. Also the foam volume was

monitored for every five minute, and the foam decay diagram was plotted versus time to investigate

foam stability.

3. Results and discussion

3.1. IFT

These experiments were designed using Box-Behken method. Table 2 shows IFT results.

3.1.1. Effect of surfactant concentration

Figure 1 shows that, in absent of nanoparticle, with increasing surfactant concentration before

critical micelle concentration, which equals to 0.038 wt%, IFT decrease. After this point due to

micelle formation, IFT almost is constant.

In presence of nanoparticles, surfactant is not the only foam agent, in other word nanoparticles is

also responsible for reduction in interfacial tension. Adsorption of surfactant on nanoparticles

make them partial hydrophobic; therefore, nanoparticle tend to come on the interface and stay

there firmly. As shown in figure 2, IFT experienced a minimum in the domain of surfactant

concentration.

Nanoparticle hydrophobicity change due to adsorption of surfactant on nanoparticles. Before 1

CMC, surfactant adsorption, which occurs because of vanderwals electrostatic forces, increases as

surfactant concentration decreases. Therefore nanoparticles has a synergistic effect on IFT

reduction besides of surfactant molecules. The synergistic effect continued until 1 CMC, and IFT

reached a minimum equals to 17 dyne/cm. After the minimum, an increase in surfactant

concentration leads to the adsorption of a second layer of surfactant molecules, through chain-

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chain interaction, on nanoparticle surface and reduces particle hydrophobicity and increases

interfacial tension. Figure 3 shows synergistic effect of nanoparticle-surfactant mixture.

3.1.2. Effect of nanoparticle concentration

Figure 4 shows increasing nanoparticle concentration result in IFT reduction. With increasing

nanoparticle concentration, more nanoparticles come to interface; therefore, IFT reduces.

3.1.3. Effect of pH

With comparison between test 5 and 6, 7 and 8, 13 and 15, 14 and 16, 17 and 19, and 18 and 20,

it was found that an increase in pH has negative and small effect on the interfacial tension of

mixtures. Hence, repulsion between nanoparticles is directly related to their charge density and

charge density increases with increasing pH; therefore, an increase in pH causes a reduction in

nanoparticle aggregation. Aggregation in large scale prevent nanoparticles from acting as surface

active materials and destabilize foams generated by them. But, the effect of pH variation in low

enough against other variables such as nanoparticle concentration, surfactant concentration and

salinity, as descried in the Figure 5.

3.1.4. Salinity effect

As shown in figure 6, increasing salinity result in decreasing interfacial tension of mixtures. An

increase in salinity increases aggregation intensively. Because salt ions are very smaller than

nanoparticles and surfactants; therefore has more activity. Thus these ions neutralize nanoparticles

and surfactant molecules effectively. In one hand, surfactant head group charge is lowered, and in

other hand zeta potential of nanoparticles is decreased. The twofold reason result in a significant

increase in IFT.

3.2. Foamability

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Table 3 shows values of foamability in the domain of surfactant concentration, nanoparticle

concentration and salinity.

As seen in figure 7, foam ability in all samples with a mixture of nanoparticles and surfactant is

lower than the foam stabilized only by the surfactant. On one hand adsorption of surfactant on the

surface of nanoparticle reduces amount of free surfactant, on the other hand small amount of

energy to bring hydrophobized nanoparticles to interface causes most of nanoparticles do not

become surface activate so they do not participate in foam formation. Therefore, coming

nanoparticle to interface would not help to compensate reduction of free surfactants and result in

less foam formation.

3.2.1. Effect of salinity

Figure 8 shows that in the low adsorption region (0.5 and 1.5 CMC), where IFT reduction is lower

than other regions, salinity can have more destructive effect on foamability. In this region, a little

amount of surfactant molecules adsorbed on nanoparticles and neutralize nanoparticle partially. In

other hand salt ions effectively neutralize nanoparticles; therefore, nanoparticle aggregation are

expedited and foamability reduce drastically. As salinity increase, this effect can be observed more

intensive.

In high adsorption region (1 CMC), where IFT reduction reach to the most value, destructive effect

of salinity on foamability are abated to the minimum. In this region, nanoparticle completely

surrounded by a monolayer of surfactant, and therefore, salt ions cannot reduce the ability of

nanoparticle to be a foam agent.

3.2.2. Effect of nanoparticle concentration

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As seen in the figure 9, with increasing nanoparticle concentration results in increasing

foamability. In other words, as nanoparticle concentration increase, resistance against salinity

rises. In 4000 ppm salinity, only foams was stabilized that their foam agent contain nanoparticles.

3.3. Foam stability

In foam decay diagram, foam is more stable as foam decay slope approaches to zero. As shown in

figure 10, nanoparticle-surfactant-stabilized foam at high adsorption region has more stability than

both surfactant stabilized foam and nanoparticle-surfactant-stabilized foam at low adsorption

region. Nanoparticle-surfactant-stabilized foam at low adsorption region has less stability than that

of in high adsorption region. This is because of reduction in surfactant, which occur in result of

surfactant adsorption on nanoparticles, and lack of participation of nanoparticles in the interface.

3.4. Analyzing foamability and foam stability based on IFT

One may expect foam ability and foam stability are improved as IFT decrease. As shown in the

figure 11, it seems to foam stability has the same behavior as IFT behavior do. However foam

ability behave in the opposite way. The reason of IFT reduction in nanoparticle-surfactant mixture

is the presence of modified nanoparticle in the interface, which prevent from gas diffusion into

liquid film, disproportionation and coalescence of bubbles. Therefore foam stability increases.

This is an adverse factor for foamability. Because free surfactant molecules reduce with adsorption

of surfactant molecules on nanoparticles; therefore, foamability was lowered.

As shown in the figure 11, in where that the most IFT reduction occurs, there is the most foam

stability and the lowest foam ability. It should be noted that at this point, foamability has the most

resistance against salinity.

4. Conclusion

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Nanoparticles could not make foam solely. Adsorption of oppositely charged surfactant molecules

on nanoparticles causes wetting characteristic modification of nanoparticles, in way that complete

hydrophilic nanoparticle change to a partial hydrophobic nanoparticle; therefore, they can place at

the interface and act like a surface active material. This causes that modified nanoparticles create

a reduction in the interfacial tension. Thus, the interfacial tension of nanoparticle-surfactant

mixture were measured in the domain of nanoparticle concentration, surfactant concentration, pH

and the salinity. In other hand foamability and foam stability was conducted through Ross-Miles

method and the related result analyzed based on IFT measurement. The conclusion are underlined

in the following sentences.

1. Surfactant molecules are not the only IFT reduction agents. As surfactant adsorption

increases, nanoparticles have more significant effect on IFT reduction. The most IFT

reduction was observed at about 1 CMC of surfactant concentration.

2. With respect to amount of IFT reduction, surfactant domain was divided into two

characteristic regions, namely, high adsorption and low adsorption, which are related to

high IFT reduction and low IFT reduction respectively. It was revealed that in high

adsorption region, foam had the most resistance against salinity. As it was expected, in

low adsorption region, salinity had the most destructive effect on foamability and foam

stability.

3. IFT was reduced as nanoparticle concentration increased. Also pH had a negative and small

effect on IFT. Because a decrease in pH result in a decrease in zeta potential and an increase

in nanoparticle aggregation.

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4. Foamability in all sample of nanoparticle-surfactant mixture was lower than that of

surfactant stabilized foam with the same surfactant concentration. This is related to

reduction of free surfactant molecules by adsorption of surfactant on nanoparticles.

5. It was found out that nanoparticle-surfactant-stabilized foam at high adsorption region has

more stability than both surfactant stabilized foam and nanoparticle-surfactant-stabilized

foam at low adsorption region.

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Figure 1. IFT variation in domain of surfactant concentration.

Figure 2. IFT variation in domain of surfactant. Blue points) surfactant solution. Red points)

nanoparticle-surfactant mixture.

Figure 3. Contour plot and IFT versus nanoparticle concentration and surfactant concentration.

Figure 4. Surface plot of IFT versus a) salinity and nanoparticle concentration b) pH and

nanoparticle concentration.

Figure 5. Contour plot of IFT versus a) pH and surfactant concentration b) pH and nanoparticle

concentration.

Figure 6. a) Surface plot of IFT versus salinity and nanoparticle concentration. b) Contour plot of

IFT versus salinity and nanoparticle concentration.

Figure 7. Foamabilty of surfactant stabilize foam and nanoparticle-surfactant stabilized foam.

Figure 8. Contour plot of foamability versus surfactant concentration and salinity.

Figure 9. Contour plot of foamability versus nanoparticle concentration and salinity.

Figure 10. Foamability of different foams.

Figure 11. Comparison between IFT, Foam stability and Foam ability in the domain of surfactant

concentration.

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Figure 1.

30

35

40

45

50

55

60

65

70

75

0 0.01 0.02 0.03 0.04 0.05 0.06

IFT

(dyne/

cm)

surfactant concentration (CMC)

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Figure 2.

0

10

20

30

40

50

60

70

80

0 0.5 1 1.5 2

IFT

(dyne/

cm)

surfactant concentration (CMC)

15

Figure 3.

16

Figure 4.

17

Figure 5.

18

Figure 6.

19

Figure 7.

15

17

19

21

23

25

27

29

31

33

0.4 0.6 0.8 1 1.2 1.4 1.6

foam

volu

me

(cm

3)

surfactant concentration (CMC)

Surfactant

0.01 wt% nano

0.10 wt% nano

20

Figure 8.

21

Figure 9.

22

Figure 10.

Figure 12. Foamability of different foams.

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Figure 11.

15

25

35

45

55

65

75

85

95

105

115

0.4 0.6 0.8 1 1.2 1.4 1.6

Surfactant concentration (CMC)

IFT (dyne/cm)

foam stability (min)

Foam ability

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Table 1. Variables and their value in Box-Behnken design.

variable unit Upper limit Lower limit

Surfactant concentration CMC 1.5 0.5

Nanoparticle concentration Wt% 0.01 0.1

salinity ppm 2000 4000

pH - 5 9

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Table 2. IFT measurement in domain of pH, salinity, surfactant and nanoparticle concentration

Experiment

number Surfactant

concentration

(CMC)

Nanoparticle

concentration

(wt%)

pH Salinity

(wt%) IFT (dyne/cm)

1 0.5 0.01 7 3000 50.7

2 1.5 0.01 7 3000 42.6

3 0.5 0.1 7 3000 39.2

4 1.5 0.1 7 3000 27.2

5 1 0.055 5 2000 25.1

6 1 0.055 9 2000 24.4

7 1 0.055 5 4000 27.3

8 1 0.055 9 4000 26.6

9 0.5 0.055 7 2000 43

10 1.5 0.055 7 2000 32.5

11 0.5 0.055 7 4000 46

12 1.5 0.055 7 4000 35.5

13 1 0.01 5 3000 34.1

14 1 0.1 5 3000 19.7

15 1 0.01 9 3000 33.8

16 1 0.1 9 3000 18.6

17 0.5 0.055 5 3000 44.8

18 1.5 0.055 5 3000 34.2

19 0.5 0.055 9 3000 44.2

20 1.5 0.055 9 3000 33.7

21 1 0.01 7 2000 32.4

22 1 0.1 7 2000 17.9

23 1 0.01 7 4000 35.4

24 1 0.1 7 4000 20.9

25 1 0.055 7 3000 25.6

26 1 0.055 7 3000 25.5

27 1 0.055 7 3000 25.6

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Table 3. Foamability measurement in domain of salinity, surfactant and nanoparticle concentration

Experiment

number

Surfactant

concentration

(CMC)

Salinity (ppm) Nanoparticle

concentration

(wt%)

Foamability (cm3)

1 0.5 0 0 26

2 1 0 0 31

3 1.5 0 0 31

4 0.5 0 0.01 19

5 1 0 0.01 28

6 1.5 0 0.01 29

7 0.5 0 0.055 25

8 1 0 0.055 26

9 1.5 0 0.055 30

10 0.5 0 0.1 24

11 1 0 0.1 23

12 1.5 0 0.1 30

13 0.5 2000 0.01 7

14 1 2000 0.01 19

15 1.5 2000 0.01 16

16 0.5 2000 0.055 14

17 1 2000 0.055 17

18 1.5 2000 0.055 20

19 0.5 2000 0.1 16

20 1 2000 0.1 20

21 1.5 2000 0.1 21

22 0.5 4000 0.01 0

23 1 4000 0.01 9

24 1.5 4000 0.01 8

25 0.5 4000 0.055 6

26 1 4000 0.055 13

27 1.5 4000 0.055 11

28 0.5 4000 0.1 10

29 1 4000 0.1 16

30 1.5 4000 0.1 14

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