DOI: 10.1007/s13367-018-0013-y
Study the effect of polymers on the stability and rheological properties of oil-in-water (O/W) Pickering emulsion muds
Praveen Kumar Jha1,*, Vikas Mahto2 and Vinod Kumar Saxena3
1School of Engineering, G D Goenka University, Gurugram, Haryana-122103, India
2Department 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 as xanthan gum, carboxymethyl cellulose (CMC), and sodium lignosulfonate have been investigated for their properties 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 filtration control properties were measured using recommended practices. Emulsion stability was analyzed using steady state shear stress-shear rate and oscillatory (dynamic) rheological measurement techniques. The emulsions 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' (elastic modulus) > G'' (loss modulus) and both are independent of changing ω (Frequency). These fluids have shown stable properties upto 70°C which shows that they can be used as drilling muds for drilling oil and gas 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]
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 lignosulfonate
The 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
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 mud systems
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 properties Rheological 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 measurements Anton 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 measurements
Oscillatory 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 properties The 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 study
One 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 rheological measurements
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 Fig. 2. (Color online) Plot of apparent viscosity vs. shear rate of
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.%).
Fig. 3. (Color online) Plot of apparent viscosity vs. shear rate of emulsion muds with increasing concentration of CMC at 30°C (oil = 20 vol.%, KCl = 3 wt.%, xanthan gum = 0.5 wt.%, and sodium lignosulfonate = 1 wt.%).
Fig. 4. (Color online) Plot of apparent viscosity vs. shear rate of 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.%).
Fig. 5. (Color online) Plot of apparent viscosity vs. shear rate of emulsion muds with increasing concentration of KCl at 30°C (oil = 20 vol.%, xanthan gum = 0.5 wt.%, CMC = 1 wt.%, and sodium lignosulfonate = 1 wt.%).
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 measurements
The 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 sodium lignosulfonate = 1 wt.%).
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- Fig. 8. (Color online) Plot of elastic and viscous moduli vs. fre-
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.%).
Fig. 9. (Color online) Plot of elastic and viscous moduli vs. fre- 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.%).
Fig. 10. (Color online) Plot of elastic and viscous moduli vs. fre- 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.%).
Fig. 11. (Color online) Plot of elastic and viscous moduli vs. fre- 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.
References
Al-Riyamy, K. and M.M. Sharma, 2004, Filtration properties of oil-in-water emulsion containing solids, SPE Drill. Complet.
19, 164-172.
Aveyard, R., B.P. Links, and J.H. Clint, 2003, Emulsions stabi- lized solely by colloidal particles, Adv. Colloid Interface Sci.
100-102, 503-546.
Benchabane, A. and K. Bekkour, 2008, Rheological properties of carboxymethyl cellulose (CMC) solutions, Colloid Polym. Sci.
286, 1173-1180.
Binks, B.P., 2002, Particles as surfactants- similarities and dif- ferences, Curr. Opin. Colloid Interface Sci. 7, 21-41.
Browning, W.C., 1955, Lignosulfonate stabilized emulsions in oil well drilling muds, J. Pet. Technol. 7, 9-15.
Bui, B., A. Saasen, J. Maxey, M.E. Ozbayoglu, S.Z. Miska, M.
Yu, and E. Takach, 2012, Viscoelastic properties of oil-based drilling muds, Annu. Trans. Nordic Rheol. Soc. 20, 33-47.
Caenn, R., H.C.H. Darley, and G.R. Gray, 2011, Composition and
Properties of Drilling and Completion Fluid, Elsevier, Waltham.
Chatterji, J. and J.K. Borchardt, 1981, Application of water-sol- uble polymers in the oil field, J. Pet. Technol. 33, 2042-2056.
Chilingarian, G.V. and P. Vorabutr, 1983, Drilling and Drilling Muds, Elsevier, Amsterdam.
Clasen, C. and W.-M. Kulicke, 2001, Determination of visco- elastic and rheo-optical material functions of water-soluble cel- lulose derivatives, Prog. Polym. Sci. 26, 1839-1919.
Cohen-Addad, S. and R. Höhler, 2014, Rheology of foams and highly concentrated emulsions, Curr. Opin. Colloid Interface Sci. 19, 536-548.
Dickinson, E., 1992, An Introduction to Food Colloids, Oxford University Press, Oxford.
Dickinson, E., 2010, Flocculation of Protein-Stabilized Oil-in- Water Emulsions, Colloids Surf. B: Biointerfaces 81, 130-140.
Dimitrova, T.D., F. Leal-Calderon, T.D. Gurkov, and B. Camp- bell, 2004, Surface forces in model oil-in-water emulsions sta- bilized by proteins, Adv. Colloid Interface Sci. 108, 73-86.
Dunstan, D.E., E.K. Hill, and Y. Wie, 2004, Direct measurement of polymer segment orientation and distortion in shear: Semi- dilute solution behaviour, Polymer 45, 1261-1266.
Garcia-Ochoa, F., V.E. Santos, J.A. Casas, and E. Gomez, 2000, Xanthan gum: Production, recovery and properties, Biotechnol.
Adv. 18, 549-579.
Hunter, T.N., R.J. Pugh, G.V. Franks, and G.J. Jameson, 2008, The role of particles in stabilizing foams end emulsions, Adv.
Colloid Interface Sci. 137, 57-81.
Jain, R. and V. Mahto, 2016, Rheological investigations of water based drilling fluid system developed using synthesised nano- composite, Korea-Aust. Rheol. J. 28, 55-65.
Jha, P.K., V. Mahto, and V.K. Saxena, 2013, Study the rheolog- ical and filtration properties of oil-in-water emulsion for its application in oil and gas well drilling, J. Pet. Eng. Technol. 3, 25-30.
Jha, P.K., V. Mahto, and V.K. Saxena, 2015, Effects of car- boxymethyl cellulose and tragacanth gum on the properties of emulsion-based drilling muds, Can. J. Chem. Eng. 93, 1577- 1587.
Krstonošić, V., L. Dokić, I. Nikolić, and M. Milanović, 2015, Influence of xanthan gum on oil-in-water emulsion character- istics stabilized by OSA starch, Food Hydrocolloids 45, 9-17.
Krynke, K.K. and J.P. Sek, 2004, Predicting viscosity of emul- sions in the broad range of inner phase concentrations, Colloids Surf. A: Physicochem. Eng. 245, 81-92.
Lacasse, M.-D., G.S. Grest, D. Levine, T.G. Mason, and D.A.
Weitz, 1996, Model for the elasticity of compressed emulsions, Phys. Rev. Lett. 76, 3348-3451.
Lummus, J.L. and J.J. Azar, 1986, Drilling Muds Optimization:
A Practical Field Approach, Penwell Books, Tulsa.
Mahto, V. and V.P. Sharma, 2009, Tragacanth gum: An effective oil well drilling mud additive, Energy Sources 27, 299-308.
Martín-Alfonso, J.E., A.A. Cuadri, M. Berta, and M. Stading, 2018, Relation between concentration and shear-extensional rheology properties of xanthan and guar gum solutions, Car- bohydr. Polym. 181, 63-70.
Milas, M., M. Rinaudo, and B. Tinland, 1985, The viscosity dependence on concentration, molecular weight and shear rate
of xanthan solutions, Polym. Bull. 14, 157-164.
Pickering, S.U., 1907, Emulsions, J. Chem. Soc. 91, 2001-2021.
Qiansheng, Y. and M. Baoguo, 2008, Development and applica- tions of solids-free oil-in-water drilling fluids, Pet. Sci. 5, 153- 158.
Ross-Murphy, S.B., 1995, Rheology of biopolymer solutions and gels, In: Dickinson, E., Ed., New Physico-Chemical Techniques for the Characterization of Complex Food Systems, Blackie, London.
Różańska, S., L. Broniarz-Press, J. Różański, P. Mitkowski, M.
Ochowiak, and S. Woziwodzki, 2012, Extensional viscosity and stability of oil-in-water emulsions with addition poly(eth- ylene oxide). Procedia Eng. 42, 733-741.
Saxena, A., A.K. Pathak, and K. Ojha, 2014, Synergistic effects of ionic characteristics of surfactants on aqueous foam stability, gel strength, and rheology in the presence of neutral polymer, Ind. Eng. Chem. Res. 53, 19184-19191.
Sharma, T., G.S. Kumar, B.H. Chon, and J.S. Sangwai, 2014, Vis-
cosity of the oil-in-water Pickering Emulsion stabilized by sur- factant-polymer and nanoparticle-surfactant-polymer system, Korea-Aust. Rheol. J. 26, 377-387.
Sharma, T., G.S. Kumar, and J.S. Sangwai, 2015, Viscoelastic properties of oil-in-water (o/w) pickering emulsion stabilized by surfactant-polymer and nanoparticle-surfactant-polymer systems, Ind. Eng. Chem. Res. 54, 1576-1584.
Smith, I.H. and G.W. Pace, 1982, Recovery of microbial poly- saccharides, J. Chem. Technol. Biotechnol. 32, 119-129.
Stancik, E.J. and G.G. Fuller, 2004, Connect the drops: Using sol- ids as adhesives for liquids, Langmuir 20, 4805-4808.
Tadros, T., 2004, Application of rheology for assessment and pre- diction of long-term physical stability of emulsions, Adv. Col- loid Interface Sci. 108-109, 227-258.
Wyatt, N.B. and M.W. Liberatore, 2010, The effect of counterion size and valency on the increase in viscosity in polyelectrolyte solutions, Soft Matter 6, 3346-3352.