Journal of Petroleum Science and Engineering 139 (2016) 264–275

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The novel approach for the enhancement of rheological propertiesof water-based drilling fluids by using multi-walled carbon nanotube,nanosilica and glass beads

A.R. Ismail a,n, A. Aftab b, Z.H. Ibupoto c, N. Zolkifile d

a Faculty of Chemical and Energy Engineering, Universiti Teknologi, Malaysiab Petroleum and Natural Gas Engineering Department, Mehran UETSZAB, Pakistanc Department of Chemistry, Sindh University, Pakistand Scomi Oiltools, Malaysia

a r t i c l e i n f o

Article history:Received 20 November 2015Received in revised form14 January 2016Accepted 29 January 2016Available online 9 February 2016

Keywords:LubricityCoefficient of frictionFiltrate volumeNanoparticlesMicronmaterials

x.doi.org/10.1016/j.petrol.2016.01.03605/& 2016 Elsevier B.V. All rights reserved.

esponding author.ail address: razak@utm.my (A.R. Ismail).

a b s t r a c t

Nano and micron materials are investigated in water-based drilling fluid (WBDF) to improve its rheo-logical behaviour. Due to the environmental and certain operational concerns, the use of oil-baseddrilling fluid (OBDF) and synthetic based drilling fluid (SBDF) is restricted that caused the industryseeking for new ways to enhance rheological properties of WBDF. This study was based on investigatingthe applicability of multi-walled carbon nanotube (MWCNT), nanosilica and glass beads (GBs) as primaryadditives for enhancing the filtrate volume, lubricity and other rheological properties of WBDF. Thisstudy focused on the effect of different concentrations such as 0.001 ppb, 0.002 ppb, 0.01 ppb, 0.02 ppb,0.1 ppb, and 0.2 ppb of each MWCNT and nanosilica over the rheological performance of WBDF. Effect ofGBs of different sizes such as (90–150 μm) and (250–425 μm) was investigated at different concentra-tions of 2 ppb, 4 ppb, 6 ppb, 8 ppb, 10 ppb, and 12 ppb over rheological performance of WBDF. Resultsrevealed that coefficient of friction (CoF) for drilling fluid without nanoparticles and GBs was 0.238.0.01 ppb of MWCNT and nanosilica provided 44% and 38% CoF reduction. 4 ppb of GBs (90–150 μm)provided 28% CoF reduction. MWCNT showed 4.5 ml of filtrate volume and 2/32 inch of mud cakethickness. Thus, MWCNT can be a better choice as a drilling fluids additive for WBDF.

& 2016 Elsevier B.V. All rights reserved.

1. Introduction

Enhanced formulation and engineering design of drilling fluidssystem are key to reach target depth of hydrocarbon reservoir.Drilling fluids showed complex behaviour of rheological propertiesunder various drilling conditions (Livescu, 2012; Majidi et al.,2010; Baba Hamed and Belhadri, 2009). Mainly three types ofdrilling fluids such as OBDF, SBDF and WBDF are used to drill oiland gas wells. Among these drilling fluids WBDF is widely usedand considered inexpensive and environmentally friendly (Chris-tiansen, 1991; Mao et al., 2015; Rodrigues et al., 2006; Sade-ghalvaad and Sabbaghi, 2015; Tehrani et al., 2009). But it has beenalso reported that macro, micro and polymer additives basedWBDF can raise the problems of unstable rheological properties athigh pressure, high temperature (HPHT) down hole conditions(Abdo and Haneef, 2013; Abdo et al., 2014; Mao et al., 2015). WBDF

is typically a combination of fresh water and drilling fluids ad-ditives such as water activity salts, viscosifiers, filtrate reducersand hydrate resistant polymers.

Addition of potassium chloride (KCl) in WBDF is frequently wellaccepted and commonly adopted by oil and gas industry to controlrheological properties and better hydration-resistance particularlyin shale (Khodja et al., 2010). During drilling through water sen-sitive clays, KCl muds hold drill cuttings together. But a great dealof research has been conducted by Brien apos and Chenevert(1973), Chang and Leong (2014), and Clark et al. (1976) that highconcentration of KCl in WBDF caused the problems of accretion.Moreover, it has been also identified that high concentration of KClraised flocculation in rheological properties of drilling fluid andincreased the cutting disposal cost (Chesser, 1987). Therefore,lower concentration of KCl has been recommended with polymersto achieve desired rheological properties.

Polymers are used to improve the rheological performance ofthe drilling fluids. Various polymers such as poly anionic cellu-lose (Fritz and Jarrett, 2012; Joel et al., 2012; Van Oort, 2003),

Nomenclature

API American Petroleum InstituteAV apparent viscosityFW fresh waterCMC carboxy methyl celluloseFL fluid lossGBs glass beadsGS gel strengthHPHT high pressure high temperatureKCl potassium chloridePV plastic viscosityMWCNT multi-walled carbon nanotubeNaOH sodium hydroxide or caustic sodaOBDF oil-based drilling fluidPAC poly anionic cellulosePHPA poly hydrolytic polyacrylamideRPM rotation per minuteSBDF synthetic-based drilling fluidWBDF water-based drilling fluidYP yield point

Units

cc cubic centimetercp centipoiseft feetg grammPa s milli Pascal's secondnm nanometerppb pound per barrelppg pound per gallonPa s Pascal's secondΦ dial readingμm micrometer

Units conversion

= 0.4788 Pa s1lb

100 ft2

1 cp¼1 mPa s=1 ppb 1 g

350 cc

A.R. Ismail et al. / Journal of Petroleum Science and Engineering 139 (2016) 264–275 265

Xanthan gum (Van Oort, 2003), and carboxy methyl cellulose(CMC) (Sehly et al., 2015) have been reported to improve therheological properties of drilling fluids. Polymers are heat in-sulators in nature and cannot be applied at extreme downholeconditions (Jeon and Baek, 2010; Mao et al., 2015). Moreover,these macro-size polymers cannot seal the nanopore throats ofthe wellbore. Therefore, oil and gas researchers are focusing touse physical small and enhanced heat transfer drilling fluidsadditives for better progress of drilling fluids rheology (Ama-nullah et al., 2011; Amanullah and Al-Tahini, 2009; Hoelscheret al., 2012; Zakaria et al., 2012).

Nanoparticles have enhanced the performance drilling fluidsbecause of its distinctive type such as highly enhanced physico-chemical, electrical, thermal, and hydrodynamic properties(Amanullah et al., 2011). Multifunctional applications of nano-particles attract a variety of industries for instance biomedicaltechnology, electronics, coating industry and material composite(Saidur et al., 2011). Similarly, successive efforts are also taken bythe petroleum institutions to develop advanced material for nanosensing or nanorobots to collect the underground reservoir valu-able data for the investigation of reservoir performance and deli-verability (Hoelscher et al., 2012). Materials added in drilling fluidsranging in size between 1 and 100 nm are called nanoparticles(Amanullah and Al-Tahini, 2009; Hoelscher et al., 2012; Zakariaet al., 2012). Nanoparticles compared to their bulk phase materialsoffer many potential applications to oil and gas industry (Ama-nullah et al., 2011). Various applications of nanoparticles in drillingfluids have been reported in the literature such as controlling themud filtrate volume (Contreras et al., 2014; Srivatsa and Ziaja,2011; Barry et al., 2015), minimizing differential pipe sticking(Javeri et al., 2011), drilling and production at HPHT conditions(Nguyen et al., 2012; Singh et al., 2010; William et al., 2014) andenhancing shale stability (Hoelscher et al., 2012; Li et al., 2012;Riley et al., 2012).

More recently nanocomposites have been introduced as analternative to polymers and clays to improve rheological proper-ties of the drilling fluids (Jain and Mahto, 2015; Mao et al., 2015;

Sadeghalvaad and Sabbaghi, 2015). It has been identified that theapplicability of the nanocomposites is novel in drilling fluids withbetter effects over rheological performance of drilling fluids. Inthis study, nanoparticles such as MWCNT, nanosilica and micro-nmaterial such as GBs (90–150 μm) and GBs (250–425 μm) areused in WBDF to examine their effects over the rheologicalperformance.

2. Methodology

The methodology discussed in this paper was based on thelaboratory work. All the drilling fluid testing work was carried outas per recommended practice API RP 13B-1 for investigating WBDF.The experimental design is given in Fig. 1.

2.1. Material selection

MWCNT (21 nm), nanosilica (12 nm), GBs (90–150 μm), GBs(250–425 μm) and Tween 80 surfactant were purchased. Drillingfluids additives potassium chloride (KCl), flowzan, caustics soda(NaOH), poly anionic cellulose (PAC), partial hydrolytic poly-acrylamide (PHPA) and barite were provided by a drilling fluidservice company.

2.2. Formulation of basic water-based drilling fluid

350 cc of basic WBDF was prepared by adding fresh water (FW),KCl, NaOH, flowzan, PAC, PHPA and barite. The formulation wasdesigned to achieve mud weight of 12 ppg. 290 ml of freshwaterwas added with 39 g of KCl and stirred for 3 min. After 3 min,0.13 g of NaOH was added into the solution and stirred for another2 min. Then, 0.43 g of flowzan was added into the solution andstirred for 5 min. 1.3 g of PAC was added into the solution andstirred for another 5 min. Later, PHPA with 3.9 g was added intothe solution and stirred for 10 min. Lastly, 180 g of barite was ad-ded and stirred for another 30 min.

Addition of MWCNTs and nanosilica with different concentration ( 0.001,0.002, 0.01, 0.02, 0.1 and 0.2 ppb) into base mud

Determination of rheological properties such as yield point, plasticviscosity, API filtrate volume, and Lubricity

Addition of glass beads with different size (90-150 µm and 250-425 µm) anddifferent concentration (2, 4, 6, 8, 10 and 12 ppb) into base mud

Proceed

Start

End

No

Yes

Formulating drilling fluid

Result analysis

Fig. 1. Experimental design.

A.R. Ismail et al. / Journal of Petroleum Science and Engineering 139 (2016) 264–275266

2.3. Preparation of homogeneous colloidal dispersion ofnanoparticles

MWCNT was dispersed into 40 ml of distilled water and 5 ml ofTween 80. The mixture was placed in ultrasonication machine for25 min. Then, dispersed mixture was added in WBDF after barite.Mixture of drilling fluids was mixed for 10 min. However, nano-silica was dispersed in distilled water without Tween 80 and ad-ded in WBDF after barite.

2.4. Rheological properties

Flow properties of drilling fluids such as plastic viscosity (PV),yield point (YP), 10-seconds gel strength (10 s GS), and 10-min gelstrength (10 min GS) were determined by using rheometer asshown in Fig. 2(b). Filtrate volume was determined by low pres-sure filtrate volume tester as shown in Fig. 2(a). Total 26 drillingfluids were investigated for rheological performance. Experi-mental work was repeated three times over 26 drilling fluids for

certainty. Experimental condition for the measurement of rheo-logical properties, lubricity and API filtrate volume is given in Ta-ble 1. PV and YP were calculated by the following equation:

Φ Φ= − ( )PV 600 300 1

Φ= − ( )YP PV300 2

whereas Φ = Dial600 reading at 600 RPM, and Φ = Dial300 readingat 300 RPM.

2.4.1. LubricityThe lubricity test was conducted by measuring the CoF using

extreme pressure/ lubricity tester model 212 as shown in Fig. 3.This test is based on metal to metal study which is a similar casebetween drill string and wellbore. Lubricity was calculated byusing Eqs. (3)–(6):

= ( )CoFTorque reading

100 3

Fig. 2. (a) API filter press and (b) rheometer.

Table 1Experimental conditions for the measurement of rheological properties, lubricityand API filtrate volume.

Drilling fluid systems Operating conditions

(a) WBDFþMWCNT at Rheological properties and lubricity weredetermined at ambient conditions

0.001 ppb, 0.002 ppb, 0.01 ppb,0.02 ppb, 0.1 ppb, and 0.2 ppb

(b) WBDFþNanosilica at Filtrate loss volume was determined at APIconditions (100 psi and ambient temperature)

0.001 ppb, 0.002 ppb, 0.01 ppb,0.02 ppb, 0.1 ppb, and 0.2 ppb

(c) WBDF þ GBs (90–150 μm)at 2 ppb, 4 ppb, 6 ppb, 8 ppb,10 ppb, 12 ppb, and 14 ppb

(d) WBDFþ GBs (250–425 μm)at 2 ppb, 4 ppb, 6 ppb, 8 ppb,10 ppb, 12 ppb, and 14 ppb

Fig. 3. Lubricity tester.

A.R. Ismail et al. / Journal of Petroleum Science and Engineering 139 (2016) 264–275 267

with instrument set at 60 RPM and pressure of 100 lbs, which are

= −( )

inch lbs torque wrench readinginch torque shaft lever arm

100150

1.5 4

= ( )( )

CFMeter reading for water standard

meter reading obtained in water calibration 5

= ( )( )( )CoF

Meter reading for water CF100 6

whereas, CoF¼coefficient of friction, and CF¼coefficient factor.

3. Results and discussion

3.1. Effect of particle concentration on plastic viscosity

PV was enhanced by using MWCNT and nanosilica. It wasmaintained between operating values 20–29 cp (20–29 mPa s)(Guo et al., 2006; Jain et al., 2015). Fig. 4(a) showed the effects ofnanoparticles at different concentrations in WBDF to the PV. Therewas a decrease in PV value when a small concentration of nano-particles which is 0.001 ppb is added into the drilling fluid.However after 0.01 ppb concentration of nanoparticles, the PVprovides the increasing trend. MWCNT and nanosilica exhibitedthe same trend after 0.1 ppb. MWCNT decreased the PV because itmay improve volume of suspended material in the drilling fluid.Moreover, the presence of nanoparticles gives less effect to thewater based drilling fluid by increasing the friction between thesuspended particles in the drilling fluid. It may be that the con-centration of nanoparticles such as MWCNT and nanosilica is sosmall compared to the basic drilling fluid's additives to give

Fig. 4. (a) Plastic viscosity at different concentrations of nanoparticle and(b) plastic viscosity at different concentrations of glass beads.

Fig. 5. (a) Effect on yield point at different concentrations of MWCNT and nano-silica and (b) effect on yield point at different concentrations of glass beads.

A.R. Ismail et al. / Journal of Petroleum Science and Engineering 139 (2016) 264–275268

significant impact over the PV. Low PV helps in drilling rapidlybecause of low viscosity of drilling fluid exiting at the bit. Beha-viour of micron GBs was different than that of nanoparticles. PV ofmicron GBs based drilling fluids increases with the increase of itsconcentration (Fig. 4(b)). Recently, Jain et al. (2015) and Mao et al.(2015) used nanocomposite in WBDF and found that targeted PVwas achieved after 0.3 ppb of the nanocomposite. However, thepresent study attained target PV of 21 cp and 20 cp (21 mPa s and20 mPa s) at lower concentration of 0.01 ppb of nanosilica andMWCNT.

3.2. Effect of particle concentration on yield point

YP is the ability of a drilling fluid to lift the cuttings fromdownhole towards surface. Normally, high YP is required to con-duct better flow of drilling fluids throughout the circulation sys-tem such as from downhole towards surface. Inappropriate YP canaffect the equivalent circulation transition point between laminarand turbulent flows, and efficiency of cutting transport. YP im-proved with addition of the nanoparticle. It increases after0.01 ppb of nanoparticles as shown in Fig. 5(a). It may be thatsolids start to accumulate when increasing the concentration ofnanoparticle. Moreover, YP increased after 8 ppb of GBs (Fig. 5(b)).However, high concentration of GBs in drilling fluids can desta-bilize the PV. More recently, Jain et al. (2015) and Mao et al. (2015)found acceptable YP after adding 0.3 ppb of the nanocomposite.

Nonetheless, the present results showed 39 lb

100 ft2or (16 Pa s) of YP at

lower concentration 0.1 ppb of MWCNT and nanosilca.

3.3. Effect of particle concentration on API Filtration Loss

Low filtrate volume by enhancing the composition, thicknessand deposition of the mud cake is the requirement of qualitydrilling fluids. Conventional mud filtrate additives such as PAC,CMC and PHPA are in macrosizes and cannot plug the nanoporethroat of wall of the wellbore (Al-Bazali et al., 2005; Mao et al.,2015). Filtrate volume was controlled by using nano-based drillingfluids. MWCTNs and nanosilica showed minimum filtrate volumeas shown in Fig. 6(a) and (b). However, 5 ml was found at 4 ppb of90–150 μm GBs as shown in Fig. 7(a) and 5.2 ml at 4 ppb of 250–425 μm GBs as shown in Fig. 7(b). Among primary drilling fluidsadditives, MWCNT found better material for prevention of filtrateloss; it may be due to its high surface area and nanotube structure.These nanoparticles attached to the drilling fluid material andformed thin and impermeable mud cake. Sadeghalvaad and Sab-baghi (2015) found 19 ml of filtrate volume by using 14 ppb ofTiO2/clay composite. Mao et al. (2015) reported 14 ml of filtratevolume at 0.1 ppb of hydrophobic silica nanoparticles composite.However, the present study reported 4.8 ml of filtrate volume byadding 0.01 ppb of nanosilica (Fig. 6(a)). Moreover, filtrate volume

Fig. 6. (a) Effect of nanosilica on FL of WBDF and (b) effect of MWCNT on FL ofWBDF. Fig. 7. (a) Effect of glass beads (90–150 μm) on FL of WBDF and (b) effect of glass

beads (250–425 μm) on FL of WBDF.

Fig. 8. Error bar chart for filtrate volume of MWCNT and nanosilica based drillingfluids.

A.R. Ismail et al. / Journal of Petroleum Science and Engineering 139 (2016) 264–275 269

was obtained as 4.5 ml by using 0.01 ppb of MWCNT (Fig. 6(b)).Error bar chart representing nanosilica and MWCNT based drillingfluids showed that measurements are precise for the filtrate vo-lume of the drilling fluids at different concentrations of nano-particles as shown in Fig. 8.

3.4. Effect of particle concentration on mud cake thickness

Mud cake thickness was less affected by adding nanoparticles(Fig. 9(a)). As proved the presence of MWCNT reduced the mudfiltrate volume because it may disperse in the drilling fluid and thenanotube structure may prevent the movement of barite particlesfrom passing through the filtrate paper. The mud cake has thin andsmooth surface texture because nanoparticles have good strengthand dispersion property. It may form a bridge within the particleand gives a homogeneous system which further reduces the por-osity of mud cake. Low porosity of the mud cake prevents mudinfiltration thus giving lower fluid loss volume. It proves that na-noparticles act as the filter between the drilling fluid particles andhelp to make bridging faster. Fig. 9(b) showed the mud cakethickness for the different concentrations of GBs. The trendshowed that the mud cake thickness increased when the GBs

concentration was increased. For small size of GBs (90–150 μm),the mud cake thickness was increased slowly after addition ofconcentration of GBs. But the size of the mud cake slightly in-creased for bigger size of GBs (250–425 μm). The value of mud

Fig. 9. (a) Effect of nanosilica and MWCNT on thickness of mud cake and (b) effectof coarse and fine glass beads on thickness of mud cake.

Fig. 10. (a) 10-s gel strength for nano silica and MWCNT and (b) 10-min gelstrength for nano silica and MWCNT.

A.R. Ismail et al. / Journal of Petroleum Science and Engineering 139 (2016) 264–275270

cake for both size of GBs was higher than controlled sample butstill within the acceptable range. Moreover, the larger size of GBshas resulted in forming a very thick mud cake.

3.5. Effect of particle concentration on gel strength

Small amount of nanoparticles provided better effect to the GS.Fig. 10(a) showed the effect of different concentrations of nano-particles to the 10-s GS. For nanosilica, the trend was flat within its0.001–0.2 ppb concentration. This phenomenon was in contrastfor MWCNT because the trend shows the increasing behaviour ofGS. Fig. 10(b) showed the effect of different concentrations of na-noparticles to the 10-min GS. Flat type pattern was obtained; itmay be that 10 min GS does not show much effect at higherconcentration of nanoparticles. Basic drilling fluid without nano-particles provided high value which was 8 lb

100 ft2or (3.8 Pa s). 10 s GS

was increased after 0.001 ppb of MWCNT and showed similartrend until 0.2 ppb of MWCNT. It may be increased in the attrac-tive forces between particles thus resulting in higher GS. Better GSprovided lower circulation pressure to restart the drilling opera-tion. The effect of different concentrations of GBs to the 10-s and10-min GS is given in Fig. 11(a) and (b), respectively. As shown inFig. 11(a), the 10-s GS for both sizes of GBs gradually decreasedwith addition of 2 ppb of GBs until 6 ppb. However, after 6 ppb itslightly increased until 12 ppb. The trends were investigated for10 min GS of GBs drilling fluids with addition of different con-centrations. 10-min GS was increased with addition of 4 ppb GBs

(Fig. 11(b)). However, it was still in the range of typical value of 10-min GS for WBDF which is −6 8 lb

100 ft2or (3–4 Pa s) (Guo et al., 2006).

This may occur due to increase in solids content and the suspen-sion capacity of drilling fluid that could not afford the higherconcentration of GBs. Moreover, 10-s GS lay within typical range ofGS that is −1.8 6.2 lb

100 ft2or (0.9–3 Pa s) (Jain et al., 2015).

3.6. Effect of particle concentration on lubricity

Lubricating medium for the drill string while drilling thewellbore is one of functions of drilling fluid (Aston et al., 1998). CoFdescribes the ratio of the force of friction between two bodies andthe force pressing them together. Fig. 12(a) shows that CoF slightlydecreased after small concentration of nanoparticles was addedinto the drilling fluid. The MWCNT yielded the lower CoF com-pared to nanosilica. It may be MWCNT has a cylindrical shape andporous nanotubes that make the surface area higher compared tonanosilica. Nanosilica has amorphous nature. Torque reductionreached 38% and 44% with the addition of nanosilica and MWCNTto the WBDF. Torque reduction was achieved about 28% by usingfiner GBs. Coarse GBs tend to crush during rotation and give theangular shapes and resulted in higher values of CoF compared tofiner GBs Fig. 12(b). Finer GBs develop an optimum standoff dis-tance and form a slippery layer between the borehole and drill

Fig. 11. (a) 10-s gel strength for fine and coarse glass beads at different con-centration and (b) 10-min gel strength for fine and coarse glass beads at differentconcentration.

Fig. 12. (a) Effect of nanoparticles concentration on CoF and (b) effect of fine andcoarse glass beads on CoF.

Table 2Absolute and relative CoF reductions for nanoparticle based drilling were de-termined at ambient pressure and temperature. Surface finish and roughness weremetal-to-metal and 1 μm. Chemistry of each drilling fluids was FW 81%, KCl 11%,NaOH 0.03%, Flowzan 0.12%, PAC 0.36%, PHPA 0.84%, and Barite 50% with differenttypes of nanoparticle.

Concentration ofnanoparticles, ppb

Nanosilica drilling fluids MWCNT drilling fluids

AbsoluteCoFreduction

Relative Cofreduction (%)

AbsoluteCoFreduction

Relative CoFreduction (%)

0 0.238 0 0.238 00.001 0.187 21 0.177 250.002 0.153 35 0.146 380.01 0.146 38 0.132 440.02 0.169 29 0.156 340.1 0.185 22 0.171 280.2 0.201 15 0.185 22

A.R. Ismail et al. / Journal of Petroleum Science and Engineering 139 (2016) 264–275 271

string and reduce the CoF. Absolute and relative CoF reduction atdifferent concentrations of fine and coarse GBs are provided inTable 3. CoF of the MWCNT was between 0.1 and 0.18. It was be-tween 0.1 and 0.2 for nanosilica. Chemistry of reported fluids,operating conditions, surface roughness, absolute and relative CoFreduction values at different concentrations of nanosilica andMWCNT in drilling are given in Table 2. However, developed for-mulations provided high lubricity than basic drilling fluid butshowed lower lubricity than nanocomposite based muds reportedby Mao et al. (2015) and Jain et al. (2015). It may be that the use ofbarite (50%) in the reported drilling fluids increased the surfaceroughness. Hence lubricity was reduced. This study presented theeffects of four different primary additives such as MWCNT, nano-silica, GBs (90–150 μm) and GBs (250–425 μm) over CoFs at am-bient conditions, constant basic drilling fluid chemistry and sur-face roughness of 1 μm. However, downhole temperature, surfaceroughness, and chemistry of drilling fluids could have very sig-nificant impact over the behaviour of CoF found at laboratory scale(Livescu and Craig, 2014). Mao et al. (2015) found that lubricity ofWBDF improved at HPHT conditions after adding nanosilica/polyacrylamide nanocomposite. Ettefaghi et al. (2013) found thatthermal conductivity of base fluid improved by adding MWCNT,thus lubricity of the base fluid was also increased. Therefore, it isexpected that enhanced heat transfer quality of nanomaterials

such as MWCNT and nanosilica can improve the rheologicalproperties in particular lubricity at high temperature conditions.

More recently, studies primarily focused on effect of nano-

Table 3Absolute and relative CoF reduction for micron glass beads based drilling weredetermined at ambient pressure and temperature. Surface finish and roughnesswere metal-to-metal and 1 μm. Chemistry of each drilling fluids was FW 81%, KCl11%, NaOH 0.03%, Flowzan 0.12%, PAC 0.36%, PHPA 0.84%, and Barite 50% withdifferent types of GBs.

Concentration ofglass beads, ppb

Glass beads (90–150 μm)drilling fluids

Glass beads (250–425 μm)drilling fluids

AbsoluteCoFreduction

Relative CoFreduction(%)

Absolute CoFreduction

Relative CoFreduction (%)

0 0.238 0 0.238 02 0.211 11 0.235 14 0.169 28 0.206 136 0.180 24 0.227 48 0.206 13 0.230 310 0.208 12 0.234 112 0.215 9 0.236 0.8

A.R. Ismail et al. / Journal of Petroleum Science and Engineering 139 (2016) 264–275272

particle and nanocomposite based drilling fluids over lubricity atlow temperature conditions (Kania et al., 2015). Little attention has

Table 4Relationship between rheological properties and CoFs of reported drilling fluids.

Drilling fluids system Relationship betweenrheological propertiesand CoF

Correlationcoefficient

Strength ofrelationship

MWCNT PV and CoF 0.77928 StrongYP and CoF 0.426466 MediumGS-10 s and CoF �0.06234 NoneGS-10 min and CoF 0.207181 WeakAPI FL and CoF 0.610553 Strong

Nanosilica PV and CoF 0.379583 MediumYP and CoF 0.374732 MediumGS-10 s and CoF 0.781852 StrongGS-10 min and CoF 0.203438 WeakAPI FL and CoF 0.452964 Medium

Glass beads (90–150 μm) PV and CoF �0.42121 MediumYP and CoF 0.432124 MediumGS-10 s and CoF 0.497869 MediumGS-10 min and CoF 0.869752 StrongAPI FL and CoF 0.038329 None

Glass beads (250–425 μm) PV and CoF �0.07865 NoneYP and CoF 0.452392 MediumGS-10 s and CoF 0.362994 MediumGS-10 min and CoF 0.6843 StrongAPI FL and CoF 0.329358 Medium

been paid to the effect of lubricants in drilling fluids at hightemperature. However, some scientists (Livescu and Craig, 2014;

Table 5Commonly used scale to identify the strength of correlation coefficient (Hall, 2012).

Negative values Positive values Strength of relationship

�0.3 to �0.1 0.1–0.3 Weak�0.5 to �0.3 0.3–0.5 Medium�1.0 to �0.5 0.5–1.0 Strong

0 to �0.1 0–0.1 No correlation

Livescu et al., 2014; Castro et al., 2015) investigated novel drillingfluids lubricants (currently in field) with the linear friction testerat high temperature conditions. Researchers found that lubricity of

drilling fluids was improved to 40–60% at variable field conditionssuch as high temperatures, chemistry of base fluids, and surfaceroughnesses by using novel lubricants (Livescu and Craig, 2014;Livescu et al., 2014; Castro et al., 2015).

3.7. Relationship of rheological properties of drilling fluids andcoefficient of friction

Relationship of rheological properties of drilling fluids and theirCoF was determined by using Pearson's correlation. It is explainedin the correlation that positive coefficient is between 0 and 1.0; if xincreases so does y. Negative coefficient is between 0 and �1.0; ifx increases, y decreases (Hall, 2012). Behaviour of rheologicalproperties of reported drilling fluids showed weak, medium,strong, and none in relation with their CoFs. Drilling fluids for-mulations showed positive relationship between most of therheological properties and their CoFs. Rheological properties ofreported drilling fluids were stable at ambient conditions. Morerecently, Abduo et al. and Ismail et al. (2014) found that rheolo-gical performance of WBDF could improve at HPHT conditions byadding small concentration of nanomaterial in particular MWCNT.Behaviour of rheological properties such as PV, YP , FL and CoF wasfound stable at HPHT conditions by using nanosilica/poly-acrylamide nanocomposite based drilling fluids (Mao et al., 2015).Therefore, it is expected that rheological performance will bestable at HPHT conditions by using reported nanoparticles such asMWCNT and nanosilica based drilling fluids. It was found thatincrease in the rheological properties does increase the CoF.However, negative relationship was found between both PV andCoF of GBs (90–150 μm) and GBs (250–425 μm) drilling fluids asshown in Table 4. Relationship between rheological properties ofthe prepared drilling fluids and their CoF is reported in Table 4.Pearson's correlation condition applied for better understandingthe strength of the relationship between CoF and rheologicalproperties is provided in Table 5. Moreover, results of presentstudy were compared with most recent studies. It was found in thecurrent study that small concentration of nanoparticles has bettereffect over rheological performance of WBDF compared to themost recent studies as shown in Table 6.

4. Conclusion

Experimental work was conducted in conventional WBDF. Na-nosilica and MWCNT can be used as rheological modifiers forWBDF. Rheological properties such as PV, YP, GS, API FL and mudcake thickness were improved by adding the nanoparticles. Onlysmall concentration of MWCNT and nanosilica was required inorder to improve the drilling fluid performance which is about0.01 g because of the superior behaviour of particles. However, incase of GBs the better performance of drilling fluids was gained byusing 4 ppb concentration of glass beads. Mud cake thickness ofMWCNT and nanosilica was slightly changed from the defaultvalues. However, mud cake thickness of glass beads based drillingfluids showed large values compared to nanoparticle based dril-ling fluids. CoF was minimized by using MWCNT and nanosilica.However, GBs showed less effect over CoF reduction. Moreover, thepresent nanoparticle and micron material based drilling fluidscould be investigated at high temperature or bottom hole tem-perature to insight effects of these conditions over its rheology.Ongoing work with some novel nanoparticles or nano-microncomposite with improving results will be presented in future.

Table 6Comparison of present study data with the most recent literature on water-based drilling fluids containing nanoparticles.

Rheologicalproperties

Mao et al. (2015), nanoparticle WBDF Jain et al. (2015), nanoparticle WBDF Jain et al. (2015), nanoparticle WBDF Sadeghalvaad and Sabbaghi (2015),nanoparticle WBDF

Present study results, nanoparticle WBDF,Micronmaterial WBDF

PV 16 mPa s at 0.3 g of polymer based silica nanoparticlescomposite

20 mPa s at 0.3 g of thenanocomposite

20 mPa s at 0.3 g of polyacrylamide/clay composite

22 mPa s at 7 g of TiO2/claycomposite

22 mPa s at 0.2 g of nanosilica

22 mPa s at 0.2 g of MWCNT30 mPa s at 12 g of GBs (90–150 μm)29 mPa s at 12 g of GBs (250–425 μm)

YP 5.5 mPa s at 0.3 g of the composite 9 Pa s at 0.3 g of the composite 13.5 Pa s at 0.3 g of the composite Not reported 18.9 mPa s at 0.2 g of nanosilica18.6 Pa s at 0.2 g of MWCNT18.9 Pa s at 12 g of GBs (90–150 μm)18.9 Pa s at 12 g of GBs (250–425 μm)

10 s GS Not reported 3.5 Pa s at 0.3 g of the composite 3 Pa s at 0.3 g of the composite Not reported 3.3 Pa s and at 0.2 g of nanosilica3.8 Pa s at 0.2 g of MWCNT3.3 Pa s at 12 g of GBs (90–150 μm)3.3 Pa s at 12 g of GBs (250–450 μm)

10 min GS Not reported 5.5 Pa s at 0.3 g of the composite 5 Pa s at 0.3 g of the composite Not reported 2.8 Pa s and at 0.2 g of nanosilica3.3 Pa s at 0.2 g of MWCNT2.8 Pa s at 12 g of GBs (90–150 μm)2.3 Pa s at 12 g of GBs (250–425 μm)

API FL 11.6 ml was found at 0.3 g of the composite 7.8 ml of API FL was found at 0.3 g ofthe composite

11 ml of API FL was found at 0.3 g ofthe composite

19 ml at 14 g of the composite 4.8 ml of API FL was found at 0.01 g ofnanosilica4.6 ml of API FL was found at 0.01 g ofMWCNT5.1 ml was found at 4 g of GBs (90–150 μm)5.2 ml was found at 4 g of GBs (250–425 μm)

CoF CoF was not reported at 0.3 g but it was found 0.057 at0.5 g of the composite

Not reported Not reported Not reported CoF reduction was 38% at 0.01 g of nanosilica

CoF reduction was 44% at 0.01 g of MWCNTCoF reduction was 28% at 4 g of GBs (90–150 μm)CoF reduction was 13% at 4 g of GBs (250–425 μm)

A.R.Ism

ailet

al./Journal

ofPetroleum

Scienceand

Engineering139

(2016)264

–275273

A.R. Ismail et al. / Journal of Petroleum Science and Engineering 139 (2016) 264–275274

Acknowledgements

The authors wish to thank the Ministry of Higher Education, Ma-laysia and Universiti Teknologi Malaysia for funding this project underFundamental Research Grant Scheme (vote R.J130000.7842.4F437 andvote R.J130000.7842.4F551) and Research University Grant (vote Q.J130000.2542.08H72). We are also grateful to Higher EducationCommission (HEC), Islamabad, Pakistan and Mehran UET SZAB,Khairpur Mir's Campus, Sindh Pakistan, for providing opportunity toexplore new area of research in the field of petroleum engineering. Wethank Nusrat Kamal and Radzuan for their guidance. Wewish to thankJannah and Hasanah who helped in experimental work.

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Further reading

Darley, H.C., Gray, G.R., 1991. Composition and Properties of Drilling and Comple-tion Fluids, fifth ed. Gulf Publishing Co, Houston 401-5. ⟨https://www.elsevier.com/books/composition-and-properties-of-drilling-and-completion-fluids/unknown/978-0-12-383858-2⟩.

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