Study the effect of polymers on the stability and ...

© 2018 The Korean Society of Rheology and Springer 127

Korea-Australia Rheology Journal, 30(2), 127-136 (May 2018)DOI: 10.1007/s13367-018-0013-y

www.springer.com/13367

pISSN 1226-119X eISSN 2093-7660

Study the effect of polymers on the stability and rheological properties of

oil-in-water (O/W) Pickering emulsion muds

Praveen Kumar Jha1,*, Vikas Mahto

2 and Vinod Kumar Saxena

3

1School of Engineering, G D Goenka University, Gurugram, Haryana-122103, India2Department of Petroleum Engineering, IIT(ISM), Dhanbad, Jharkhand-826004, India

3Department of Fuel and Mineral Engineering, IIT(ISM), Dhanbad, Jharkhand-826004, India

(Received August 22, 2017; final revision received February 23, 2018; accepted March 31, 2018)

A new type of oil-in-water (O/W) Pickering emulsion systems, which were prepared by polymers such asxanthan gum, carboxymethyl cellulose (CMC), and sodium lignosulfonate have been investigated for theirproperties as multifunctional emulsion muds with respect to rheological control and filtration control prop-erties. Diesel oil was used as dispersed phase and KCl-brine as continuous phase in the developed emul-sions. Initially, rheological parameters like apparent viscosity, plastic viscosity, gel strength, and filtrationcontrol properties were measured using recommended practices. Emulsion stability was analyzed usingsteady state shear stress-shear rate and oscillatory (dynamic) rheological measurement techniques. Theemulsions were found to exhibit shear-thinning (pseudoplastic) behavior. Experiments conducted for oscil-latory rheological measurements have shown that emulsions are stable as per the stability criteria G' (elasticmodulus) > G'' (loss modulus) and both are independent of changing ω (Frequency). These fluids haveshown stable properties upto 70°C which shows that they can be used as drilling muds for drilling oil andgas wells.

Keywords: Pickering emulsion, emulsion mud, depleted reservoir, elastic modulus, loss modulus

1. Introduction

An emulsion can be defined as a heterogeneous mixture

that consists of droplets of dispersed liquid phase in a con-

tinuous immiscible liquid phase. The immiscibility causes

an interfacial tension (IFT) at the contact area between

two liquid phases. An emulsion is stabilized using surfac-

tants (emulsifiers), surface-active polymers, solid particles

or natural polymers such as polysaccharides (Aveyard et

al., 2003; Binks, 2002). Development of stable emulsion

is important in many industries like food industry, paint

industry, cosmetic industry, pharmaceutical industry, and

emulsion mud industry. Later is the type drilling mud sys-

tem with low density suitable for low pressure and depleted

fractured reservoirs. Enhanced rheological and lubricating

properties, low filtrate loss to the formation, and mini-

mized balling of drill bits as compared to conventional

water-based muds (WBMs) are some of the advantages of

emulsion muds. Furthermore, these types of muds have

lower cost and are more environment friendly as com-

pared to oil-based muds (OBMs) (Jha et al., 2013; 2015;

Qiansheng and Baoguo, 2008). Emulsion muds prepared

using conventional emulsifiers are not suitable for their

application in high pressure high temperature (HPHT)

conditions because of significant impairment in viscoelas-

tic properties which destabilizes the oil-water interface. It

has been experimentally examined that stable emulsions

can also be formulated using dispersed solid particles.

Such emulsions are referred to as ‘Pickering emulsions’

(Pickering, 1907; Sharma et al., 2014; 2015). Pickering

emulsions exhibit long-term stability against emulsion

breakdown processes such as coalescence, sedimentation,

flocculation, and phase inversion. The reason behind their

long-term stability is the adsorption of the small size solid

particles at the oil-water interface held together by attrac-

tive inter-particle forces providing a steric barrier for the

prevention of breakdown processes. The strength of the

barrier depends on the difficulty of removing solid parti-

cles from the oil-water interface. Moreover, presence of

colloidal particles around the oil-water interface also changes

the rheological properties of the emulsion systems (Dick-

inson, 2010).

Xanthan gum is a natural polymer and an important

industrial biopolymer. The viscosity of emulsions contain-

ing xanthan gum remains constant over a varied range of

salt concentrations. It has the ability to stabilize emulsions

(Krstonošić et al., 2015). It also has cross-linking and

shear-thinning (pseudoplastic) features that make it an

effective additive for drilling muds (Caenn et al., 2011;

Chatterji and Borchardt, 1981; Garcia-Ochoa et al., 2000;

Jain and Mahto, 2016). In emulsion muds, it works as vis-

cosity modifier and emulsifier. Its temperature limitation

is up to 121°C (Lummus and Azar, 1986). Carboxymethyl

cellulose (CMC) is an anionic polymer with a variety of

different uses in numerous industries. In drilling muds, it

is primarily used as filtrate loss reducer but it also works*Corresponding author; E-mail: [email protected]

Praveen Kumar Jha, Vikas Mahto and Vinod Kumar Saxena

128 Korea-Australia Rheology J., 30(2), 2018

as viscosity modifier in freshwater and saline based drill-

ing muds in which salt content does not exceed 50,000

mg/L. It also maintains adequate flow properties at in situ

conditions. It is usually available in a high and low vis-

cosity grades. Either grade works as an effective filtrate

loss reducer. It is a long chain molecule that can be

polymerized to different molecular weights. CMC suspen-

sions are shear-thinning, impart high apparent viscosities

at very low shear rates, and maintain adequate flow prop-

erties at in situ conditions (Benchabane and Bekkour,

2008). Lignosulfonates are water soluble, hetero-disperse

polymers used in the drilling muds to control filtrate loss.

Lignosulfonates also work emulsion stabilizer by lowering

down IFT because the lignosulfonate molecule is adsorbed

at the oil-water interface, establishing a semi-rigid film

(Browning, 1955).

The long-term physical stability of Pickering emulsions

can be studied using rheological measurement techniques.

It has been observed that emulsions display viscoelastic

properties. The origin of the elasticity is due to the inter-

facial energy of the emulsion droplets. It has been hypoth-

esized that the thinning of the continuous film separating

the two dispersed emulsion droplets is considerably inhib-

ited if the film has viscoelastic properties which arises due

to the adsorption of particle network at oil-water interface.

The consistency of an emulsion and so the emulsion muds

can be controlled by optimizing the phase volume of the

dispersed droplets, their size distribution and by the addi-

tion of various viscosity modifiers such as polymers and

finely divided inert solids. Usually drilling muds are

thixotropic fluids and exhibit viscoelastic behavior. Vis-

coelastic properties of drilling muds are important to eval-

uate their parameters of such as gel strength, hydraulic

modeling, and solid suspension. In case of emulsion muds,

stability is an important parameter which is required to be

controlled to achieve optimum performance during drill-

ing operations (Bui et al., 2012).

Tadros (2004) observed that rheological measurement

techniques such as steady state shear stress-shear rate rhe-

ology, constant stress rheology and oscillatory (dynamic)

rheology can be used to investigate the long term physical

stability of emulsions by examining their several break-

down processes. The stability of foams and emulsions can

be evaluated by measuring the drainage versus time under

static condition but rheological measurement techniques

(steady state shear stress-shear rate rheology and oscilla-

tory rheology) can also be used as an important tool to

investigate the long term physical stability (Cohen-Addad

and Höhler, 2014).

The scope of the work reported herein was therefore to

investigate the development of O/W Pickering emulsion

muds stabilized by polymers without using any surfactant

as emulsifier. Three different polymers were used for this

work like xanthan gum, low viscosity CMC, and sodium

lignosulfonate. Recommended measurements were used

to estimate the rheological and filtration control properties

of developed emulsion systems by varying concentrations

of oil and additives. The effect of particulate matter to

fluid ratio and the O/W ratio on emulsion stability was

assessed. The stability of emulsion muds was character-

ized using steady state shear stress-shear rate and oscilla-

tory rheological measurement techniques which were

subsequently used to examine the physical stability of

emulsion systems.

2. Experimental Details

2.1. Materials used: Diesel oil, KCl, NaOH, xanthan

gum, CMC, and sodium lignosulfonateThe diesel oil was obtained from local distributor of

Indian Oil Corp. Ltd., Dhanbad, India. Potassium chloride

(KCl) and sodium hydroxide (NaOH) were purchased

from Merck, Mumbai, India. Xanthan gum was obtained

from Otto Kemi, Mumbai, India. Low viscosity CMC was

Table 1. Composition of O/W Pickering emulsion muds.

O/W Pickering

emulsion muds

Oil

(vol.%)

KCl

(wt.%)

Xanthan gum

(wt.%)

CMC

(wt.%)

Sodium lignosulfonate

(wt.%)pH

Filtercake thickness

(mm)

A1 10 3 0.5 1 1 9.49 1

A2 20 3 0.5 1 1 9.68 0.9

A3 40 3 0.5 1 1 8.73 0.7

A4 20 3 0.3 1 1 10.53 0.5

A5 20 3 0.4 1 1 8.60 0.6

A6 20 3 0.5 2 1 10.11 0.8

A7 20 3 0.5 3 1 9.68 0.9

A8 20 3 0.5 1 2 10.72 1

A9 20 3 0.5 1 3 9.67 1.1

A10 20 4 0.5 1 1 9.91 0.8

A11 20 5 0.5 1 1 9.45 0.9

Study the effect of polymers on the stability and rheological properties of oil-in-water (O/W) Pickering emulsion muds

Korea-Australia Rheology J., 30(2), 2018 129

purchased from RFCL Limited (RANKEM), New Delhi,

India. Sodium lignosulfonate was purchased from Triveni

Chemicals, Vapi, India. All the materials were used as

received without further treatment. Water used as contin-

uous phase in this work was distilled water.

2.2. Formulation of O/W Pickering emulsion mudsystems

Pickering emulsion mud was prepared of 500 ml vol-

ume. Initially, a brine solution was prepared using 3 wt.%

KCl in distilled water by mixing it for 2 min at 12000 rpm

in Hamilton Beach mixer. Then one pellet of NaOH was

mixed to maintain the pH of the fluids above 8. The pH

of the drilling muds should be maintained in the range of

8-11. It helps in the control of corrosion, effective use of

thinners, and calcium stability (Caenn et al., 2011). After

this, 1 wt.% of CMC was added in the brine solution and

mixed for 5 min at 15000 rpm. Once all the CMC was

mixed properly, 0.5 wt.% of xanthan gum was added and

mixed. Then 1 wt.% sodium lignosulfonate was added and

mixed. Finally, 20 vol.% of diesel oil was added in the

polymeric mixture and the emulsion system was homo-

geneously mixed at 18000 rpm for 10 min. Different com-

positions of emulsions were prepared in the same manner

by varying concentrations of diesel oil, xanthan gum,

CMC, sodium lignosulfonate, and KCl as shown in Table 1.

3. Physical Measurements

3.1. Rheological and filtration control propertiesRheological and filtration control properties of emulsion

systems were analyzed using recommended procedures at

room temperature. The drilling muds are monitored for

their rheological properties and fluid consistency in the

field. For this investigation, Fann V-G viscometer is used.

The viscosity of the fluid is proportional to the shear stress

experienced by fluid. The rheological properties such vis-

cosity (apparent, plastic) and yield point were calculated

from 600 rpm and 300 rpm dial readings using following

mathematical relationships (Mahto and Sharma, 2009):

Apparant Viscosty (µa) = θ600/2 (cP), (1)

Plastic viscosity (µp) = θ600 − θ300 (cP), (2)

Yield point (yp) = θ300 − µp (lb/100ft2), (3)

where θ600 = Dial reading at 600 rpm and θ300 = Dial read-

ing at 300 rpm.

Initial gel strength (10 s) as well as final gel strength (10

min) was measured by rotating the cylinder at 3 rpm. The

gel strengths are measured by observing maximum deflec-

tion of dial at 3 rpm before the gel breaks (Caenn et al.,

2011).

Filtration control properties were measured with the

help of Fann filter press; Series 300 at 100 psi pressure at

ambient temperature. In this process filtrate volumes dis-

charged in 30 min is measured. The cake thickness plays

a major in the efficiency of a drilling mud. So, the filter

cake thickness is measured to the nearest 1/32 in (1 mm)

after washing off the excess mud in a gentle stream of tap

water. Filter cake thicknesses of the developed emulsion

muds have been tabulated in Table 2.

3.2. Steady state shear stress - shear rate measurementsAnton Paar rheometer (Model: Rheo Lab QC) was used

to examine the steady state shear stress - shear rate mea-

surements at 30°C with log vs. log coordinate system using

viscosity vs. shear rate as parameters of the axis. In this

process, the fluid sample was put in a measuring cup and

the cup was fixed to dynamic EC motor drive with mea-

suring system. The temperature is provided by a hot water

bath connected externally to the motor drive.

3.3. Oscillatory rheological measurementsOscillatory rheological measurements were conducted in

the linear viscoelastic region (LVR) using Bohlin-Gemini

II Rheometer, a product of Malvern Instruments Ltd.,

U.K. All the measurements were done at 40°C tempera-

ture. It performs the following tests: Creep, viscometry

(controlled stress (CS), controlled rate (CR), and con-

trolled deformation (CD)), CD oscillation, CS oscillation,

stress relaxation, and time temperature superposition with

advanced data processing. It can work in the temperature

range of 40°C to 300°C. It has measuring geometry like

parallel plates, cone and plate, and cup and bob. The par-

allel plates measuring geometry was used for the oscilla-

tory rheological measurements.

4. Results and Discussion

4.1. Rheological and filtration control propertiesThe properties of drilling muds depend on several fac-

tors, which may be the volume fraction of the particles,

size distribution of the suspended particles, and the type of

polymers added in the development of the mud (Chiling-

arian and Vorabutr, 1983). Table 2 shows the rheological

and filtration control properties of developed emulsions by

varying concentration of oil, KCl, and polymeric addi-

tives. It can be observed that increasing the concentration

of oil from 10 vol.%-40 vol.% increased the rheological

properties of emulsion muds. The viscosity emulsions

increase with volume fraction of dispersed phase (oil) as

the crowding of droplets increases. The emulsion droplets

behave as fine rigid particles that increase the rheological

properties (Dimitrova et al., 2004; Hunter et al., 2008;

Krynke and Sek, 2004). A drilling mud with higher yield

point to plastic viscosity ratio is preferred. Higher yield

point/plastic viscosity ratio is a measure of shear-thinning

(pseudoplastic) behavior of a drilling mud which is a



desirable property as it becomes to gel when circulation is

stopped so that drilled cuttings can be suspended and

breaks up quickly to a thin fluid when agitated by resump-

tion of drilling. Observations reveal that the gum also

worked as viscosity enhancer for the emulsion systems.

Rheological properties increased with increasing concen-

tration of the gum. This property of xanthan gum is due to

the intermolecular interaction which increases the macro-

molecule dimensions and molecular weight (Smith and

Pace, 1982). With salt addition, local charge inversion, and

subsequent chain expansion between polymer molecules

increase the viscosity (Milas et al., 1985). Likewise, it can

be seen that apparent viscosity increased with increasing

concentration of CMC from 1-3 wt.%. The rise in the

apparent viscosity is due to the increase in the intermo-

lecular interactions between the CMC molecules (Wyatt

and Liberatore, 2010). Sodium lignosulfonate did not

show any significant effect on the rheological properties

as it mainly stabilized the emulsions and reduced the fil-

trate loss.

Studies have shown that emulsion muds have ability to

reduce the filtration loss to the formation. Lower filtrate

volume is due to the capability of emulsion droplets to

provide thin filter cake on the wall of the well while drill-

ing. Emulsion droplets work as rigid particles which form

thin filtercake that can reduce the amount of filtrate loss to

the formation. Emulsion droplets with smaller sizes are

more rigid and less deformed than larger droplets. Exter-

nal additives like surfactants and polymers are added which

stabilize the emulsion. Hence, the control of filtercake

thickness and their properties play an important role for

the successful drilling operation (Al-Riyamy and Sharma,

2004). The results from experiments conducted on filtrate

loss studies have shown significant reduction in filtrate

loss with increasing concentration of diesel oil. It can be

observed from Table 3 that increasing the concentration of

diesel oil as dispersed phase from 10 vol.%-40 vol.%

decreased the total filtrate volume significantly. Apart from

enhancing rheological properties, CMC also reduced the

filtrate loss as can be observed from Table 3. This may be

due to the anionic nature of CMC where adsorption and

flocculation occur as a result of hydrogen bonding between

hydroxyl groups on the polymer and solid surfaces. This

results in the formation of thin filtercake which reduces

the filtrate loss to the formation. Likewise, sodium ligno-

sulfonate is also anionic in nature and molecular structure

contains hydroxyl groups. So, adsorption and flocculation

may occur as a result of hydrogen bonding between

hydroxyl groups of the polymer and solid surfaces which

finally reduced the total filtrate loss.

Table 2. Rheological and filtration properties.

O/W Pickering

emulsion muds

Apparent

viscosity

[cP]

Plastic

viscosity

[cP]

10 s Gel

Strength

[lb/100ft2]

10 min Gel

Strength

[lb/100ft2]

Yield point

[lb/100ft2]

Yield point/

plastic viscosity

ratio

30 min

Filtrate loss

[ml]

A1 25 12 11 20 26 2.17 48

A2 37.5 15 14 25 45 3 20

A3 75 20 27 45 110 5.5 8.5

A4 20 8 6 8 24 3 21

A5 30 10 7 14 22 2.2 20

A6 42.5 19 16 28 49 2.58 14

A7 46 22 16 30 48 2.19 9

A8 38 16 15 25 44 2.75 14

A9 38 16 15 27 44 2.75 10

A10 39 16 15 25 46 2.89 20

A11 40 18 15 25 44 2.45 20.5

Table 3. Rheological and filtration properties of some favorable muds after 24 h aging at 70°C.

O/W Pickering

emulsion muds

Apparent

viscosity

[cP]

Plastic

viscosity

[cP]

10 s Gel

Strength

[lb/100ft2]

10 min Gel

Strength

[lb/100ft2]

Yield point

[lb/100ft2]

Yield point/

plastic viscosity

ratio

30 min

Filtrate loss

[ml]

A7 47.5 25 17 30 45 1.8 9.5

A8 39 16 16 26 46 2.89 14

A9 40 18 17 26 44 2.45 10



4.2. Aging studyOne of the issues related to of emulsion muds is their

stability at high temperature conditions. The properties of

additives used in conventional WBMs degrade at higher

temperature and drilling muds become unsuitable for drill-

ing operations. The properties of drilling fluids should be

same at different temperature conditions. Comparing the

results of Table 2 and Table 3, it can be seen that prop-

erties of developed emulsion muds are nearly same but

there is some increase in the apparent and plastic viscosity.

From Table 1, it is observed that the mud systems that

have shown increase in the viscosity, have highest poly-

meric concentrations (A7 = 3 wt.% CMC; A8 = 2 wt.%

sodium lignosulfonate; A9 = 3wt.% sodium lignosulfon-

ate). Likewise, xanthan gum (0.5 wt.%) is also in the high-

est concentration in these emulsion systems. The increase

in apparent and plastic viscosity may be due to the uncoil-

ing of the coiled structures of the polymers at high tem-

perature (70°C). As a result, they became linear and swollen

which finally increased the viscosity of the continuous

phase. The rheological and filtration control properties of

some favorable drilling muds have been found stable after

24 h aging at 70°C as shown in Table 3. This shows that

polymers worked as perfect stabilizer for the O/W Pick-

ering emulsion muds.

4.3. Steady state shear stress-shear rate rheologicalmeasurements

Steady state shear stress-shear rate rheological measure-

ment technique is a convenient method to assess emulsion

breakdown processes. Emulsions which are weakly floc-

culated show strong shear-thinning behavior. They also

exhibit thixotropy (viscosity reduction with time) and the

change in thixotropy with time may be used as an indi-

cation of the strength of the weak flocculation. This

behavior may occur due to rearrangement of microstruc-

ture in emulsion flow and/or breakdown of flocs. In case

of drilling fluids, which follow power-law model, the val-

ues of ‘n’ and ‘k’ can be predicted by the use of following

mathematical relationships (Caenn et al., 2011):

n = 3.32 log (θ600/θ300) (5)

k = θ600/(1022)n (6)

The values of ‘n’ obtained using above relationship of

the emulsion systems have been shown in Table 4. It is

clear from the data that muds are showing shear-thinning

(pseudoplastic) behavior. As concentrations of oil and

polymeric additives were increased, the value of ‘n’

decreased which shows the shear-thinning behavior. The

results obtained from the Table 4 also show that ‘k’ values

increased with increasing concentrations of oil and addi-

tives. The value of flow consistency index (k) in Eq. (6)

indicates the thickness of the drilling fluid. An increase in

the value of ‘k’ indicates the increase in the overall hole

cleaning effectiveness of the fluid (Saxena et al., 2014).

Figure 1 provides the log/log plot showing the effect of

diesel oil concentration upon the functional relationship

between viscosity and shear rate. It can be observed from

the graph, shear-thinning behavior increased with increas-

ing concentration of oil from 10 vol.%-40 vol.%. Shear-

thinning behavior in emulsions is the indication of pres-

ence of weak attractive forces between the emulsion drop-

lets which finally give rise to the formation of elastic gel

like network (Dickinson, 1992).

The polymeric additives (xanthan gum, CMC, and sodium

lignosulfonate) have shown shear-thinning behavior with

their increasing concentrations. Figure 2 shows the effect

of xanthan gum on the shear-thinning behavior of emul-

sion muds in the concentration range of 0.3 wt.% to 0.5

wt.%. It can be observed that fluids have shown almost

same behavior at 0.3 wt.% and 0.4 wt.% polymer con-

centrations. As concentration increased from 0.4 wt.% to

Table 4. Power-law parameters obtained using Eqs. (5) and (6).

O/W Pickering

emulsion muds‘n’ ‘k’

A1 0.395 3.328

A2 0.321 8.116

A3 0.206 35.885

A4 0.321 4.329

A5 0.264 9.630

A6 0.365 6.778

A7 0.395 5.958

A8 0.341 7.156

A9 0.341 7.156

A10 0.331 7.870

A11 0.368 6.250

Fig. 1. (Color online) Plot of apparent viscosity vs. shear rate of

emulsion muds with increasing concentration of oil at 30°C

(KCl = 3 wt.%, xanthan gum = 0.5 wt.%, CMC = 1 wt.%, and

sodium lignosulfonate = 1 wt.%).



0.5 wt.%, pseudoplasticity increased and the recommended

concentration of xanthan gum was found to be 0.5 wt.%.

This jump in the shear-thinning behavior is due to linear

alignment of the coiled polymeric structure of gum with

increasing shear rate which increased the viscosity of the

emulsion mud. Hence, it was investigated that 0.5 wt.% is

the critical concentration of xanthan gum. The jump here

indicates the increase in pseudoplasticity of the mixture

with increase in the shear rate at 0.5 wt.% xanthan gum

concentration. This increase in the pseudoplasticity is due

to the fact that at this higher concentration of the gum, the

extent of linear alignment is higher. Martín-Alfonso et al.

(2018) also reported the influence of gum on the rheolog-

ical properties of the solutions. Figure 3 gives the graph-

ical overview of effect of CMC concentration on the

functional relationship between viscosity and shear rate. In

case of CMC, pseudoplasticity of the mud systems did not

change significantly with increasing concentration because

it mainly worked as filtration control agent and had little

effect on the rheological properties of the developed sys-

tems. Figure 4 shows the shear-thinning behavior of emul-

sion systems with increasing concentration of sodium

lignosulfonate. It can be observed that 3 wt.% of sodium

lignosulfonate is the critical concentration that has shown

increase in the shear-thinning behavior. KCl also induced

shear-thinning behavior with its increasing concentration

as can be observed from Fig. 5. The increase in the shear-

thinning behavior with increasing concentration of KCl is


emulsion muds with increasing concentration of xanthan gum at

30°C (oil = 20 vol.%, KCl = 3 wt.%, CMC = 1 wt.%, and sodium

lignosulfonate = 1 wt.%).


emulsion muds with increasing concentration of CMC at 30°C

(oil = 20 vol.%, KCl = 3 wt.%, xanthan gum = 0.5 wt.%, and



emulsion muds with increasing concentration of sodium ligno-

sulfonate at 30°C (oil = 20 vol.%, KCl = 3 wt.%, xanthan

gum = 0.5 wt.%, and CMC = 1 wt.%).


emulsion muds with increasing concentration of KCl at 30°C

(oil = 20 vol.%, xanthan gum = 0.5 wt.%, CMC = 1 wt.%, and




due to local charge inversion and chain expansion of the

polymers that increased the viscosity (Milas et al., 1985).

In case of emulsion systems, measurements like viscosity

vs. shear rate are investigated to provide the measure of

colloidal interactions among droplets. The reason of shear-

thinning behavior is the presence of free polymers in the

water which form shear-thinning solutions. This behavior

caused by polymers is admitted to the fact that the disen-

tanglement of the polymer coils occurs in the solution or

the orientation of polymer coils increases in the direction

of fluid flow (Clasen and Kulicke, 2001). In drilling muds,

this behavior is a desirable property as it provides better

hole cleaning during drilling operations.

4.4. Oscillatory rheological measurementsThe viscoelastic responses of emulsions can be assessed

by undertaking dynamic oscillatory measurement. These

are most commonly used method to obtain information

about the flocculation in emulsions. For viscoelastic sys-

tems, the stress and strain are out of the phase. The phase

angle shift (δ) can be measured as the time shift (∆t)

between the amplitudes of the oscillatory stress (τ0) and

strain (у0):

δ = ω∆t. (7)

From the phase angle shift and amplitudes various vis-

coelastic parameters may be obtained. These include com-

plex modulus (G*), elastic modulus (G'), loss modulus

(G''), and tan δ. The relationship between these parame-

ters is shown as follows:

G* = τ0/у0, (8)

G' = G*cos δ, (9)

G'' = G* sin δ. (10)

These data was subsequently used to obtained elastic

modulus and loss modulus of the emulsion systems. The

presence of network structure is indicated by measure-

ments which show G' > G'' and both are independent of ω.

Weak emulsions are characterized by G'' > G' and both

show significant dependency upon ω (Ross-Murphy, 1995).

On the other side weak gels are characterized by G' > G''

and both parameters show little dependency upon ω. An

emulsion is considered stable when G' > G'' and both

parameters are independent of ω. This behavior is readily

demonstrated in Fig. 6. As can be observed from the fig-

ure that at 10 vol.% oil concentration, G' > G'' but both G'

and G'' are dependent upon ω which shows the properties

of a weak gel. As the concentration of oil increased, G' >

G'' and both G´ and G'' became independent of changing

ω. This shows that oil resulted in the formation of more

elastic network structure. The origin of this elasticity is

due to the interfacial energy of the droplets. At low vol-

ume fractions of oil, IFT provides spherical size of drop-

lets. However, at higher volume fractions, the droplets get

deformed due to force caused by volumetric constraints.

This deformation (strain) resulted in the storage of energy

(Dunstan et al., 2004). The degree of the formation net-

work structure can be inferred from oscillatory rheological

measurements because more developed network structure

demonstrates an elastic response to shear. For viscoelastic

systems δ takes some value in the range of 0° to 90°. Fig-

ure 7 shows how δ varies with varying ω. At 10 vol.% oil

concentration, δ is showing more complex behavior with

changing frequency. On the other side, when concentra-

tion of oil was increased from 10 vol.%-40 vol.%, δ was

found to be less than 15° with varying ω which shows that

system tends to exhibit elastic response to shear. So, it

shows that network structure so as the emulsion stability

was achieved well by increasing concentration of dis-

Fig. 6. (Color online) Plot of elastic and viscous moduli vs. fre-

quency of emulsion muds with increasing concentration of oil at

40°C (KCl = 3 wt.%, xanthan gum = 0.5 wt.%, CMC = 1 wt.%,

and sodium lignosulfonate = 1 wt.%).

Fig. 7. (Color online) Plot of phase angle (δ) vs. frequency (ω)

of emulsion muds with increasing concentration of oil at 40°C

(KCl = 3 wt.%, xanthan gum = 0.5 wt.%, CMC = 1 wt.%, and




persed phase (oil).

Figures 8-10 show the effect of concentrations of xan-

than gum, CMC, and sodium lignosulfonate on G' and G''

with changing ω respectively. It is clear from the plots that

both G' and G'' became independent of ω with increasing

concentrations of polymers which resulted in the stabili-

zation of emulsion systems as per the stability criteria

(Lacasse et al., 2004). The reason behind increased visco-

elasticity is inter-twisting among the polymers. In case of

emulsions such rheological behavior arises because an

elastic network is created among the dispersed phase drop-

lets. Emulsion stabilizers such as polymers get adhered to

the dispersed phase droplets through sharing of colloidal

particles thus providing excellent stabilization (Dimitrova

et al., 2004; Różańska et al., 2012; Stancik and Fuller,

2004).

The data in Fig. 11 demonstrate that high salt (KCl) con-

centration may lead to weakly associated emulsions. It is

suggested that higher concentrations of salts shield the

electrostatic repulsions to such an extent so that aggrega-


quency of emulsion muds with increasing concentration of xan-

than gum at 40°C (oil = 20 vol.%, KCl = 3 wt.%, CMC = 1

wt.%, and sodium lignosulfonate = 1 wt.%).


quency of emulsion muds with increasing concentration of CMC

at 40°C (oil = 20 vol.%, KCl = 3 wt.%, xanthan gum = 0.5 wt.%,

and sodium lignosulfonate = 1 wt.%).


quency of emulsion muds with increasing concentration of

sodium lignosulfonate at 40°C (oil = 20 vol.%, KCl = 3 wt.%,

xanthan gum = 0.5 wt.%, and CMC = 1 wt.%).


quency of emulsion muds with increasing concentration of KCl

at 40°C (oil = 20 vol.%, xanthan gum = 0.5 wt.%, CMC = 1

wt.%, and sodium lignosulfonate = 1 wt.%).

Fig. 12. (Color online) Photographs of emulsion muds taken

after the settled time for 30 days (1: oil = 10 vol.%; 2: oil = 20

vol.%; 3: oil = 40 vol.%; 4: xanthan gum = 0.3 wt.%; 5: CMC

= 2 wt.%; 6: CMC = 3 wt.%; 7: Na-lignosulfonate = 2 wt.%; 8:

Na-lignosulfonate = 3 wt.%).



tion of polymers takes place which may suppress the sta-

bilizing roles of polymers. It can also be observed from

Fig. 12 that little settling has been observed in the emul-

sion developed using 10 vol.% oil which has shown the

properties of a weak gel as also characterized by oscilla-

tory rheological measurements. There is no significant

change on the long-term stability of other emulsion muds

even after settled for 30 days.

5. Conclusions

Diesel oil improved the rheological properties of O/W

Pickering emulsion muds. It also controlled filtration con-

trol properties significantly. Xanthan gum worked as vis-

cosity modifier for the emulsion systems. CMC, and

sodium lignosulfonate worked as filtrate loss reducers.

The stabilization of emulsions was achieved well with the

help of these polymers without using any surfactant

(emulsifier). Steady state shear stress-shear rate rheologi-

cal measurement techniques have shown that emulsions

exhibit shear-thinning (pseudoplastic) behavior. The rhe-

ological characterization done by oscillatory rheological

measurements has shown that the developed emulsions

form an elastic network which provides them with long

term stability. The developed emulsion systems have shown

stable rheological and filtration control properties upto

70°C which ensure their suitability for drilling oil and gas

reservoirs.

Acknowledgements

Authors gratefully acknowledge financial support and

necessary laboratory facilities provided by IIT (ISM),

Dhanbad (India) and G D Goenka University, Gurugram

(India) to carry out this research work.

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