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Petroleum
journal homepage: http://www.keaipublishing.com/en/journals/petroleum
Preparation of an environmentally friendly emulsion-type lubricant based
on crude rice bran wax
Zhengqiang Xiong
∗
, Fan Fu, Xiaodong Li, Yanning Li
Beijing Institute of Exploration Engineering, Beijing, 100083, China
HIGHLIGHTS
•Crude rice bran wax oil - in - water emulsion (named CRBWE) was first fabricated by agent-in-water method.
•CRBWE is nontoxic and biodegradable.
•CRBWE exhibited good lubricity.
•CRBWE has promising application as environmental friendly lubricant to reduce torque and drag in petroleum drilling.
ARTICLE INFO
Keywords:
Emulsion-type lubricant
Crude rice bran wax
Lubricity
Biodegradable
Water-based drilling fluids
ABSTRACT
In this study, crude rice bran wax oil - in - water emulsion (named CRBWE) was prepared by agent-in-water
method. The critical factors influencing the sample preparation process were optimized. For instance, the op-
timum hydrophile-lipophile balance value of compound emulsifier was 12.33–13.40, the content of compound
emulsifier was 10 wt%, the emulsification temperature was 70 °C–80 °C, the agitation speed was 200 rpm, and
the emulsification time was 30–45 min. The performances as a lubricant of drilling fluid were also evaluated
with respect to lubricity, rheology and filtration loss of CRBWE. The results showed that CRBWE had good
lubricity and didn't affect the rheological properties of drilling fluid. For example, when it was added into
bentonite dispersion at room temperature with the fraction of 1 wt%, the coefficient of friction of bentonite
dispersion dramatically decreased to 0.077, and the coefficient of friction reduced rate was greater than 80%.
Overall, these findings indicated that CRBWE would have promising applications as environmental friendly
lubricant of drilling fluids to reduce torque and drag in petroleum and natural gas drilling.
1. Introduction
As drilling in directional and extended-reach wells continues to gain
popularity, high torque and drag become increasingly critical issues.
This is particularly factual for water-based drilling fluids, which gen-
erally gives rise to high coefficients of friction between drillstrings or
drillstrings and wellbore wall [1]. One of the most commonly used
methods for reducing torque and drag is the addition of a lubricant to
the water-based drilling fluids [2]. Lubricants for drilling fluids can be
divided into two categories: solid lubricants and liquid lubricants in-
cluding emulsion-type and oil–based type. In addition, increasingly
strict environmental constraints have changed the choice of chemistries
utilized for water-based drilling fluids in recent years. So far, the
available and environmentally friendly lubricants for drilling fluids
mainly include vegetable oils [3,4], fatty acid esters [5], polyethers [6],
olefins [7] and paraffin [8].
Rice bran wax is a natural plant wax derived from rice bran, which
is an important byproduct of rice bran oil industry of about 0.5–0.6
million metric tons per year in China [9]. The chemical constituents of
rice bran wax are mainly mixtures of saturated esters of long chain fatty
acids (C
22
and C
24
) and long chain aliphatic alcohols (C
24
to C
40
), with
C
24
and C
30
being the predominant fatty acid and fatty alcohol, re-
spectively [10,11]. More specifically, Vali et al. [10] reported that
crude rice bran wax contains wax esters, rice bran oil, aliphatic alde-
hydes, fatty alcohols, free fatty acid. The purified rice bran wax is edible
and can serve as a substitute for carnauba wax in most applications due
to its relatively high melting point. It is used in candles, polishes, fruit &
vegetable coatings, food, pharmaceuticals, cosmetics and other in-
dustrial preparations [12,13]. Owing to the presence of fatty acid esters
and rice bran oil, crude rice bran wax can be used as raw material for
https://doi.org/10.1016/j.petlm.2018.09.002
Received 6 November 2017; Received in revised form 29 July 2018; Accepted 6 September 2018
Peer review under responsibility of Southwest Petroleum University.
∗
Corresponding author.
E-mail address: xiongzq1012@126.com (Z. Xiong).
Petroleum 5 (2019) 77–84
2405-6561/ Copyright © 2019 Southwest Petroleum University. Production and hosting by Elsevier B. V. This is an open access article under the CC BY-NC-ND
license (http://creativecommons.org/licenses/BY-NC-ND/4.0/).
T
preparing a lubricant. However, the research on the application of
crude rice bran wax (abbreviated as CRBW) to prepare lubricant for
drilling fluids is rarely reported.
The objective of this paper is to prepare an environmentally friendly
emulsion-type lubricant (named CRBWE) and evaluate its performance
in the water-based drilling fluids. The CRBWE was prepared by agent-
in-water method. Different factors influencing the preparation of
CRBWE were studied, i.e. hydrophile-lipophile balance value (HLB
value), emulsifier dosages, emulsification temperature and emulsifica-
tion time. Moreover, the performance of CRBWE was evaluated in terms
of emulsion stability, droplet size and lubricity. In comparison, three
kinds of commercial lubricant for drilling fluids were used as control
group.
2. Materials and methods
2.1. Materials
The CRBW (Industrial Grade) was collected from Xingtai Wax
Industry Co. (Hebei, China). Fatty acid methyl ester (Industrial Grade)
was a mixture of esters of C18 to C22 fatty acid, purchased from
Huayang Oil Co. (Shandong, China). Emulsifier A (C.P.) was a sorbitan
fatty acid ester and emulsifier B (C.P.) was a polyoxyethylene sorbitan
fatty acid esters, which were purchased from Beijing Reagent Co.
(Beijing, China). Sodium bentonite was obtained Xiazijie Bentonite Co.
(Xinjiang, China). Oil-based lubricant (Lubricant-3) was mainly com-
posed of white oil, sulfonated soybean oil and emulsifier, obtained from
Chengtong Drilling Materials Plant (Beijing, China). Lubricant-1 and
Lubricant-2 were the paraffin emulsion, and supplied by Continental
Shelf Petroleum Engineering Technology Co. (Shandong, China) and
Shengli Chemical Co. (Shandong, China), respectively.
2.2. Preparation of CRBWE by agent-in-water method
A typical preparation of CRBWE was as follows: first, the oil phase
was prepared by mixing CRBW (20 g) with fatty acid methyl ester (20 g)
at 75 °C. Then, the emulsifier A (7.5 g) and emulsifier B (2.5 g) were
dissolved in tap water (50 g) at 70 °C to obtain the aqueous phase. After
that, the above oil phase was generally added to the aqueous phase and
the mixed solution was stirred at 70 °C using a digital electric mixer (JJ-
1A, Changzhou, China) for 30 min and the final product was prepared.
2.3. Emulsion stability
Emulsion was first transferred into a stoppered and graduated glass
tube. Then the stability behavior of the emulsion was observed for one
week. The stability of emulsions to creaming [14] was assessed as fol-
lows:
= ×
( )
RH
H100%
E
T
(1)
Where R, H
E
and H
T
represented the fraction of emulsion phase, the
height of emulsion phase and the total height of emulsion system (in-
cluding the height of emulsion phase and the height of the separated
water), respectively.
2.4. Droplet size measurements
Emulsion droplet size and size distribution were measured by LA-
950V2 type laser particle size analyzer (HORIBA, λ = 650 nm). The
rate of circulation, agitation speed and ultrasonic power were
1735 rpm, 2890 L/min and 30 W, respectively. Before the measure-
ment, the sample was prepared by diluting the CRBWE nearly 100 times
with distilled water.
2.5. Preparation of bentonite dispersion
The bentonite dispersion was prepared by adding 5 g sodium ben-
tonite to 100 mL distilled water and stirred at about 10,000 rpm for
20 min using a frequency conversion homogenizer (GJSS-B12K,
Qingdao, China). The bentonite dispersion was aged for 24 h at room
temperature in order to pre-hydrate the bentonite dispersion fully.
2.6. Rheological measurements
Rheological properties were characterized by a ZNN-D6S type ro-
tating viscometer (Qingdao, China). The bentonite dispersion was
stirred at 10,000 rpm for 5 min using a frequency conversion homo-
genizer (GJSS-B12K, Qingdao, China), and then CRBWE or lubricant
was added under stirring for 5 min. The apparent viscosity, plastic
viscosity and yield point were calculated from 300 to 600 rpm readings
using following formulas from API recommended practice of standard
procedure for field testing drilling fluids [15]:
Apparent viscosity (AV) = 0.5Φ600 (mPa s) (2)
Plastic viscosity (PV) = Φ600-Φ300 (mPa s) (3)
Yield point (YP) = 0.511(Φ300-PV) (Pa) (4)
In order to evaluate the resistance to temperature of CRBWE, the
bentonite dispersion with CRBWE was rolled for 16 h at desired tem-
perature (the temperature of bentonite dispersion was the same as the
desired temperature of rolling furnace) by using a hot rolling furnace,
and then the rheological properties are also determined by a rotating
viscometer after cooling to room temperature.
Filtration loss of drilling fluid was measured by using ZNS type filter
press (Qingdao, China) under a pressure of 689.5 kPa (100 psi) and
room temperature for 30 min.
2.7. Lubricity measurements
Lubricating properties were evaluated by lubricity/EP tester (OFI
Testing Equipment Inc., USA) at room temperature. Briefly, a steel test
block that simulates the wall of borehole is pressed against the test ring
by a torque arm. The torque is measured by the intensity of current that
is required to turn the ring at a constant rpm when immersed in the
drilling fluid that is tested. One hundred and fifty inch-pounds of torque
had been applied to the test block running at 60 rpm. After 5 min torque
reading was recorded. The lower the torque value, the better the lu-
bricating properties. The coefficient of friction and coefficient of fric-
tion reduced rate were calculated as follows:
= × ×ft
t%
100
34 100
0
(5)
= ×ff f
f%100
1 2
1
(6)
Where: fwas the coefficient of friction without dimension. twas the
torque reading of drilling fluid without dimension. t
0
was the torque
reading of distilled water without dimension.
f
was the coefficient of
friction reduced rate, %. f
1
was the coefficient of friction of drilling fluid
with dimension. f
2
was the coefficient of friction of drilling fluid with
sample, which is dimensionless.
3. Results and discussion
3.1. Physicochemical properties analysis of CRBW
Physicochemical testing methods were adopted for the determina-
tion of the following properties of CRBW: melting point (GB/T8026-
2014), acid value (GB/T5530-2005) and saponification value (GB/
T5534-2008), and the results are shown in Table 1.
Z. Xiong, et al. Petroleum 5 (2019) 77–84
78
3.2. Effect of hydrophile-lipophile balance value on performance of CRBWE
In this paper, fatty acid methyl ester was employed as dissolvent to
decrease viscosity of CRBWE. Because if the formulation of CRBWE
doesn't contain fatty acid methyl ester, CRBWE prepared will be a pasty
liquid that can't be poured. In addition, emulsifier A and emulsifier B
were utilized as compound emulsifiers to emulsify CRBW and fatty acid
methyl ester. The mass ratios of emulsifier A and emulsifier B were
adjusted to satisfy the proper HLB values for optimum emulsification
conditions. The mixed HLB values were calculated by the following
equation:
= × + ×C C W C W% %
mix A A B B
(7)
where C
A
,C
B
and C
mix
are the HLB values of emulsifier A, emulsifier B,
and the compound emulsifiers, and W
A
% and W
B
% are the mass
percentages of emulsifier A and emulsifier B in the compound emulsi-
fiers, respectively. All the HLB values used were obtained at 25 °C.
The mixed HLB value of compound emulsifiers was varied from 9.65
to 14.47, and the results are shown in Fig. 1. When the mixed HLB value
rises from 9.65 to 14.47, the fraction of emulsion phase (R) gradually
increases and reaches the plateau, while it sharply decreases when
mixed HLB is more than 13.40. Therefore, the mixed HLB values be-
tween 12.33 and 13.40 are chosen to emulsify the CRBW and fatty acid
methyl ester. In the further study of emulsion, the mixed HLB value of
compound emulsifiers is determined at 12.33, and the equivalent mass
ratio of emulsifier A and emulsifier B is 3:1.
3.3. Effect of compound emulsifier concentrations on performance of
CRBWE
The influence of compound emulsifier concentrations on the per-
formance of CRBWE was studied. According to Fig. 2, as the con-
centration of compound emulsifier (the compound emulsifier con-
centrations is the mass ratio of emulsifier A and emulsifier B to CRBWE)
increases from 6 wt% to 12 wt%, interfacial tension decreases sig-
nificantly, so the fraction of emulsion phase improves and then keeps
steady. Emulsion stability is also often estimated by the average size of
the droplets, so the droplet size of CRBWE was also measured (Fig. 3).
Fig. 3 (a) depicts the particle size distribution of emulsion with different
addition of compound emulsifier. The droplet size distribution of
CRBWE narrows with the increasing dosage of emulsifier from 6 wt% to
10 wt%. However, when the concentration of compound emulsifier is
12 wt%, the droplet size distribution of CRBWE broadens. Accordingly,
the average diameter of CRBWE decreases from 36.35 μm to 14.03 μm
as the dosage of emulsifier improves from 6 wt% to 10 wt% in Fig. 3 (b).
It indicates that the average diameter of CRBWE decreases with the
increase in emulsifier concentration because of the increase in inter-
facial area and the decrease in interfacial tension. However, the average
diameter of CRBWE increases with the improvement of emulsifier
concentration. It could be attributed to the aggravation of Brownian
motion and the increasing number of micelles [16], resulting in the
Table 1
Physicochemical properties of crude rice bran wax.
Test Observed values
Melting point 53.5 °C
Acid value 12.4
Saponification value 148.3 mg/g
Fig. 1. Emulsion stability as a function of mixed HLB value for CRBWE with
20 wt% CRBW, 20 wt% fatty acid methyl ester, 10 wt% compound emulsifier
and 50 wt% water prepared at emulsification temperature of 70 °C, agitation
speed of 300 rpm, and emulsification time of 30 min.
Fig. 2. Emulsion stability as a function of compound emulsifier concentrations
for CRBWE with 20 wt% CRBW, 20 wt% fatty acid methyl ester and mixed HLB
value of 12.33 prepared at emulsification temperature of 70 °C, agitation speed
of 300 rpm, and emulsification time of 30 min.
Fig. 3. Effect of compound emulsifier concentrations on droplet size of CRBWE:
(a) particle size distribution; (b) average diameter.
Z. Xiong, et al. Petroleum 5 (2019) 77–84
79
increase of droplet size of CRBWE.
In order to investigate the effects of CRBWE on lubricating property
of water-based drilling fluids, CRBWE was added into bentonite dis-
persion at different concentrations (0.5, 1.0, 1.5, 2.0, and 2.5 wt%,
respectively, i.e. 0.5 wt% means 0.5 g of CRBWE is introduced into
100 g of bentonite dispersion at 0.5 g/100 g) and the results are dis-
played in Fig. 4. As observed in Fig. 4, the coefficient of friction (f) of
bentonite dispersion with CRBWE goes down remarkably with the in-
creasing concentrations of CRBWE and the compound emulsifier con-
centration as well. More specifically, when the concentration of CRBWE
in bentonite dispersion is 1.0 wt%, fof bentonite dispersion is 0.149,
0.121, 0.089 and 0.106, respectively as the dosage of compound
emulsifier is from 6 wt% to 12wt%. When the concentration of CRBWE
is higher than 1.0 wt%, fof bentonite dispersion fluctuates within a
narrow range. The experimental results illustrate that CRBWE has a
great effect on reducing friction. It could be interpreted that CRBWE is
fully emulsified into fine droplet and then easily adsorbed onto the
metal surface to improve lubrication of bentonite dispersion. Moreover,
when the metal surface is saturated for the fine oil droplet, fof ben-
tonite dispersion hardly changes.
Through the section of study, the concentration of compound
emulsifier is determined at 10 wt%. Furthermore, according to Fig. 4,
the concentration of CRBWE in bentonite dispersion is determined at
1.0 wt% in the further study of lubricity.
3.4. Effect of emulsification temperature on performance of CRBWE
The emulsification temperature was varied from 60 °C to 100 °C to
evaluate the performance of CRBWE, and the results are depicted in
Figs. 5–7. From Fig. 5 we can see that the fraction of emulsion phase
improves and then keeps steady with the increase of emulsification
temperature. This may be due to the influence of melting point of
CRBW that is 53.5 °C on emulsification of CRBW. When the emulsifi-
cation temperature is 60 °C, CRBW hasn't been fully emulsified and
results in the inferior emulsion stability. In addition, Fig. 6 describes the
particle size distribution of CRBWE with different emulsification tem-
perature. When the emulsification temperature is enhanced from 60 °C
to 80 °C, the particle size distribution of CRBWE concentrates and
average diameter decreases from 32.69 μm to 14.24 μm. However,
when the emulsification temperature exceeds 80 °C, the particle size
distribution of CRBWE broadens and average diameter rises. It could be
explained that the evaporation of water and molecular motion accel-
erate with further increase of emulsification temperature.
The effects of CRBWE with different emulsification temperature on
Fig. 4. Effect of compound emulsifier concentrations on lubricity of CRBWE.
Fig. 5. Emulsion stability as a function of emulsification temperature for
CRBWE with 20 wt% CRBW, 20 wt% fatty acid methyl ester, 10 wt% compound
emulsifier, 50 wt% water and mixed HLB value of 12.33 prepared at agitation
speed of 300 rpm and emulsification time of 30 min.
Fig. 6. Effect of emulsification temperature on droplet size of CRBWE: (a)
particle size distribution; (b) average diameter.
Fig. 7. Effect of emulsification temperature on lubricity of CRBWE.
Z. Xiong, et al. Petroleum 5 (2019) 77–84
80
lubricity of water-based drilling fluids was evaluated by adding 1.0 wt%
CRBWE into bentonite dispersions and the experimental results are
shown in Fig. 7.fof bentonite dispersions shows descending trend with
the increasing emulsification temperature. More specifically, when the
emulsification temperature is 70 °C, the value of fis 0.089. When the
emulsification temperature is 80 °C, the value of fis 0.090. The decrease
in fat temperatures higher than 80 °C could be explained as follows: the
evaporation rate of water accelerates at high temperature and leads to
the increase in proportion of oil phase. In addition, the prepared
CRBWE is paste and can't flow when the emulsification temperature
exceeds 80 °C. Thus, the optimum emulsification temperature chosen is
70 °C–80 °C.
3.5. Effect of agitation speed on performance of CRBWE
Figs. 8–10 show the variations of performance of CRBWE with dif-
ferent agitation speed. As observed in Fig. 8, the fraction of emulsion
phase increases and then keeps steady with the increasing agitation
speed. From Fig. 9, it can be seen that the particle size distribution of
CRBWE concentrates and average diameter of CRBWE falls with the
increase of agitation speed. It could be explained that CRBW and fatty
acid methyl ester are sheared into fine oil drops as the agitation speed
grows, brings about the decrease of droplet size.
As shown in Fig. 10,fas the agitation speed increases from 100 rpm
to 200 rpm, reaches a peak value at the agitation speed of 200 rpm, and
fluctuates within a narrow range between 0.082 and 0.098. The reason
is possible that CRBWE is primarily absorbed onto metal surface when
its average diameter is about 15 μm.
Overall, taking into account the lubricity of CRBWE, the optimum
agitation speed chosen is 200 rpm.
3.6. Effect of emulsification time on performance of CRBWE
Five different emulsification times from 15 min to 75 min were
evaluated to study the effect of emulsification time on performance of
CRBWE, and the results are shown in Figs. 11–13.Fig. 11 depicts the
emulsion stability of CRBWE with different emulsification time. Rin-
creases and then keeps steady as the emulsification time extends. As
observed in Fig. 12(a), the particle size distribution of CRBWE con-
centrates during 15 min and 45 min but broadens with increasing
emulsification time thereafter. The average diameter of CRBWE drops
during 45 min but increases again in 60 min as shown in Fig. 12(b). For
instance, when the emulsification time is 45 min, the average diameter
is minimal and is 14.59 μm. It could be contributed to the fact that
CRBW is enough emulsified to be fine droplet with the extension of
emulsification time. However, when the emulsification time exceeds
45 min, the collision probability between fine emulsion particles in-
creases, which results in the enlarging of emulsion particle size.
The variations in fare illustrated in Fig. 13. From Fig. 13, the
coefficient of friction of bentonite dispersion with CRBWE decreases as
the emulsification time increases from 15 min to 45 min reaches a peak
value at the emulsification time of 45 min, and increases thereafter.
More specifically, when the emulsification time is 45 min, the value of f
is 0.074. This may be due to the influence of emulsion particle size on
adsorbing onto metal surface. Thus, the optimum emulsification time
chosen is 30 min–45 min.
3.7. Microstructure of CRBWE
For comparison, the emulsion droplet size and size distribution of
Fig. 8. Emulsion stability as a function of agitation speed for CRBWE with
20 wt% CRBW, 20 wt% fatty acid methyl ester, 10 wt% compound emulsifier,
50 wt% water and mixed HLB value of 12.33 prepared at emulsification tem-
perature of 70 °C and emulsification time of 30 min.
Fig. 9. Effect of agitation speed on droplet size of CRBWE: (a) particle size
distribution; (b) average diameter.
Fig. 10. Effect of agitation speed on lubricity of CRBWE.
Z. Xiong, et al. Petroleum 5 (2019) 77–84
81
CRBWE was observed by using Olympus BX60 model metallurgical
microscope. Owing to the high viscosity of CRBWE, emulsion droplets
were bonded each other, and the emulsion droplet size distribution
could not be accurately observed under optical microscope. Therefore,
before the measurement, the sample was prepared by diluting the
CRBWE 100 times with distilled water. Experimental results showed
emulsion droplet had better dispersibility in water, and the particle size
ranging from 5 to 16 μm dominated (see Fig. 14). Moreover, an ob-
servation result was basically identical with the test result (the average
diameter was 14.03 μm) based on laser particle size analyzer.
3.8. Performance of bentonite dispersion containing CRBWE
In order to investigate the influences of CRBWE on rheological
properties and lubricity of water-based drilling fluids, the CRBWE was
added to bentonite dispersion. As the depth of borehole increases, the
temperature in borehole increases as well. Therefore, the effect of
temperature on performance of bentonite dispersion containing CRBWE
was taken into account with the aging temperature varying from 80 °C
to 120 °C. After high temperature aging for 16 h and cooling to room
temperature, the performance of bentonite dispersion containing
CRBWE was determined and the results are shown in Figs. 15 and 16.
Hereinto, CRBWE was obtained under the optimum formula and con-
dition.
In Fig. 15 (a), AV of bentonite dispersion with CRBWE goes up
slowly with the increasing concentrations of CRBWE, but grows more
evident with the increase of aging temperature. It also can be seen that
when the aging temperature is below 100 °C, AV of bentonite dispersion
increases slightly with the increasing fraction of CRBWE. However,
when the aging temperature is 120 °C and the fraction of CRBWE is 2 wt
%, the value of AV has increased from 13 mPa s to 21 mPa s. It could be
interpreted that CRBW and fatty acid methyl ester hydrolyze rapidly
with the increase of temperature which results in the increase of car-
boxyl and hydroxyl. Carboxyl which is strongly hydrated group can be
absorbed easily onto the bentonite particles by electrostatic adsorption
and hydroxyl can be absorbed easily onto the bentonite particles by
hydrogen bonds, which bring about the forming of network structure.
The network structure can wrap free water and decrease the distances
among organic compounds, bentonite particles and water molecules,
which results in the increasing of particle–particle friction. Conse-
quently, the AV of bentonite dispersion with the same amount of
CRBWE increases with the increase of aging temperature [17].
The variations in filtration loss are illustrated in Fig. 15 (b). The
filtration loss of bentonite dispersion with CRBWE increases slightly at
room temperature with the increasing concentrations of CRBWE, while
drops with the increase of CRBWE concentration after aging at high
Fig. 11. Emulsion stability as a function of emulsification time for CRBWE with
20 wt% CRBW, 20 wt% fatty acid methyl ester, 10 wt% compound emulsifier,
50 wt% water and mixed HLB value of 12.33 prepared at emulsification tem-
perature of 70 °C and agitation speed of 200 rpm.
Fig. 12. Effect of emulsification time on droplet size of CRBWE: (a) particle size
distribution; (b) average diameter.
Fig. 13. Effect of emulsification time on lubricity of CRBWE.
Fig. 14. Optical microscope image of CRBWE at 100× magnifications.
Z. Xiong, et al. Petroleum 5 (2019) 77–84
82
temperature. As the fraction of CRBWE increases, the decrease in fil-
tration loss at temperatures higher than 80 °C could be explained as
follows: The formation of network structure and the improvement of
the electrostatic stability of bentonite particles are beneficial to main-
tain fine particles to form compact filter cake and reduce filtration loss
[17].
According to Fig. 16, the coefficient of friction decreases with the
increasing concentrations of CRBWE, while increases with the in-
creasing of aging temperature. More specifically, when the fraction of
CRBWE is 2 wt% after high temperature rolling at 120 °C, the value of f
is 0.14 and the Δfis 70.7%. It could be explained that CRBW hydrolyzes
rapidly with the increase of temperature, which results in the reduction
of carbon chain length. The higher the temperature the hydrolysis ve-
locity faster. Therefore, the lubricity of bentonite dispersion lowers
with the hydrolysis of CRBW and fatty acid methyl ester.
Through the section of study, it could be stated that CRBWE has the
better resistance to temperature in improving the filtration and lu-
bricity. However, CRBWE will increase the viscosity of bentonite dis-
persion at high temperature.
3.9. Comparison of lubricity between paraffin emulsions, oil based lubricant
and CRBWE
A comparison of the lubricating performance between Lubricant-1,
Lubricant-2, Lubricant-3 and CRBWE was conducted and the results are
demonstrated in Fig. 17. Hereinto, CRBWE was prepared by the op-
timum formula and technology. Those products were added into ben-
tonite dispersion with different concentrations. As observed in Fig. 17,
the coefficient of friction decreases as the fraction of lubricant in-
creases. However, when the fraction of lubricant is more than 1 wt%, f
fluctuates within a narrow range. For example, when the fraction of
Lubricant-1, Lubricant-2, Lubricant-3 and CRBWE is 1.0 wt%, the value
of fis 0.147, 0.152, 0.062 and 0.077, respectively. It can be concluded
that the lubricity of CRBWE is close to oil-based lubricant (Lubricant-3),
but better than other paraffin emulsion lubricant.
4. Conclusions
(1) In this paper, a novel emulsion-type lubricant CRBWE based on
crude rice bran wax and fatty acid methyl ester is prepared for the
first time. The critical synthesis conditions are established, that is,
12.33 to 13.40 for HLB value of compound emulsifier, 10 wt% for
dosage of compound emulsifier, 70 °C–80 °C for emulsification
temperature, 200 rpm for agitation speed, and 30 min–45 min for
emulsification time.
(2) The CRBWE obtained at the optimal preparation conditions has
excellent emulsion stability, water dispersibility, small emulsion
particle size, good lubricity and high temperature resistance.
Furthermore, it is nontoxic and biodegradable, which has high
environmental protection effect. In comparison with other paraffin
emulsion lubricant, the CRBWE has better lubricity.
(3) The experimental results show that CRBWE is a potential lubricant
for reducing torque and drag in petroleum and natural gas drilling.
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Fig. 15. Effect of temperature on bentonite dispersion with CRBWE: (a) ap-
parent viscosity; (b) filtration loss.
Fig. 16. Effect of temperature on lubricity of CRBWE.
Fig. 17. Comparison of lubricating performance between different lubricants.
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