Evaluation of a Naturally-derived Deflocculant (Terminalia Chebula) in Bentonite Dispersions

Document Type: Research Paper

Authors

Department of Petroleum Engineering, Petroleum University of Technology, Ahwaz, Iran

Abstract

The unwanted addition of salt to drilling causes flocculation which has an adverse effect on mud rheological properties. To treat the flocculated mud chemical, deflocculants are commonly used; however, their disadvantages such as negative environmental effects, lower tolerance to contamination, and toxicity motivated scientists to search for effective additives. Using plant derived additives instead of commercial additives could help resolve the mentioned weaknesses, because they are nontoxic, cheap, easily accessible, and act multi-functional. In this paper the effect of black myrobalan rheological properties of flocculated bentonite mud was investigated and its performance was compared with chrome lignosulfonate (CLS). Rheological and filtration tests were conducted and properties such as plastic viscosity, yield point, gel strength, thixotropy, and apparent viscosity were calculated. It was perceived that by increasing black myrobalan concentration to 0.6 wt.%, rheological parameters and filtration loss decreased by 50% and 66.3% respectively, but they increased at higher concentrations, which indicated that black myrobalan acted as a deflocculant up to 0.6 wt.%. The deflocculation behavior of black myrobalan at low concentrations is attributed to ellagitannic acid and tannic acid. The comparison of the enactment of black myrobalan with chrome lignosulfonate showed that black myrobalan had a stronger decreasing effect on the rheological parameters and filtration compared to CLS.

Keywords


Evaluation of a Naturally-derived Deflocculant (Terminalia Chebula) in
Bentonite Dispersions
Jalal Neshat and Seyed Reza Shadizadeh*
Department of Petroleum Engineering, Petroleum University of Technology, Ahwaz, Iran
Received: July 17, 2015; revised: November 02, 2015; accepted: December 05, 2015
Abstract
The unwanted addition of salt to drilling causes flocculation which has an adverse effect on mud
rheological properties. To treat the flocculated mud chemical, deflocculants are commonly used;
however, their disadvantages such as negative environmental effects, lower tolerance to
contamination, and toxicity motivated scientists to search for effective additives. Using plant derived
additives instead of commercial additives could help resolve the mentioned weaknesses, because they
are nontoxic, cheap, easily accessible, and act multi-functional. In this paper the effect of black
myrobalan rheological properties of flocculated bentonite mud was investigated and its performance
was compared with chrome lignosulfonate (CLS). Rheological and filtration tests were conducted and
properties such as plastic viscosity, yield point, gel strength, thixotropy, and apparent viscosity were
calculated. It was perceived that by increasing black myrobalan concentration to 0.6 wt.%, rheological
parameters and filtration loss decreased by 50% and 66.3% respectively, but they increased at higher
concentrations, which indicated that black myrobalan acted as a deflocculant up to 0.6 wt.%. The
deflocculation behavior of black myrobalan at low concentrations is attributed to ellagitannic acid and
tannic acid. The comparison of the enactment of black myrobalan with chrome lignosulfonate showed
that black myrobalan had a stronger decreasing effect on the rheological parameters and filtration
compared to CLS.
Keywords: Flocculation, Black Myrobalan, Bentonite Mud, Deflocculant, Chrome Lignosulfonate.
1. Introduction
Drilling operation is the most significant stage in the development of oilfields and drilling fluid is the
essential constituent of rotary drilling. It performs functions such as carrying cuttings from the hole
and permit their separation at the surface, cooling and lubricating the drill bit and drill string,
balancing formation pressure to prevent blowout, stabilizing the wellbore, and forming a thin, lowpermeable
filter cake (Benyounes et al., 2010; El-Sukkary et al., 2014). Drilling fluids typically are
classified into three major groups, namely pneumatic, oil-based, and water-based. Oil-based drilling
fluids have excellent properties such as stability, lubricity, and temperature stability. Though, the
excessive use of oil-based drilling fluids harms the environment and it is important to develop more
environmentally-friendly drilling fluids; hence water-based drilling fluids are more acceptable than
other types (Meng et al., 2012). They do not damage the environment, and they are easy to construct,
* Corresponding Author:
Email: shadizadeh@put.ac.ir
22 Iranian Journal of Oil & Gas Science and Technology, Vol. 5 (2016), No. 2
cost-effective to maintain, and proficient to overcome most drilling problems (Amoco Drilling Fluids
Manual, 1994).
The simplest water-based mud is a mixture of water and bentonite, which is called bentonite–treated
mud. It is usually utilized in drilling trouble-free shallow wells. Bentonite is added in order to provide
viscosity to improve cutting carrying capability, suspension, lubricity, and reduce filtration loss.
Viscosity or resistance to flow is provided by the large flat shape of the sheets, but it is the
electrostatic charges on the sheets, which make bentonite unique (AVA Drilling Fluids Manual, 2004;
Azar, 2007).
One of the major problems related to bentonite mud is flocculation. Flocculation occurs when clay
platelets are electrically attracted to each other. One of main sources of flocculation is salt, which may
originate from make-up water, salt stringers, massive salt sections, salt water flows, and commercial
sources (Baker Hughes, 2006). When the Na+ ion content is raised to 1%, the water becomes more
positively charged than the ionized covering cloud that protects the clay platelet. The positive Al3+
edge joins the oxygen face, and the drift of edge to face is speeded up. The viscosity rises
dramatically, and water loss becomes intense, when the clay flocculates edge to face in a “House of
Cards structure,” (Lyons, 2010). A common way to overcome this problem is to use deflocculants or
thinners. Some of known chemicals are lignosulfonate, tannin, and lignite (Skalle, 2010).
There are good reasons, including economics, environmental protection, toxicity, etc. to improve
drilling fluid performance and management. Drilling mud may represent 5% to 15% of drilling costs,
but may cause 100% of drilling problems. Furthermore, increasing environmental concerns have
limited the use of some of the most effective drilling fluids and additives and the industry is dedicated
to replace them to low toxic, less harmful and less pure mud additives which are acceptable according
to current environmental norms (Amanullah, 2007; Bloys et al., 1994).
Therefore, many researchers have tried to improve mud properties through replacing different
commercial additives by environmentally-friendly additives. Yousif et al. (2011) assessed typical
properties of lignite from Lakhra coal mines in Pakistan as a drilling mud thinner. They found that it
was capable of increasing plastic viscosity, reduced yield point and gel strength, and satisfied its
effectiveness as mud thinner and mud weight tolerance. Meng et al. (2012) studied the influence of
carbon ash on the properties of bentonite dispersion and realized that by the addition of carbon ash,
filtration loss and filter cake thickness increased dramatically, whereas the density decreased slightly.
They also observed that increasing carbon ash concentration could result in high yield point and the
ratio of yield point to plastic viscosity but low variation in viscosity. First time Narayana (2013)
investigated the ability of black myrobalan in reducing the viscosity of the bentonite dispersion. He
observed that among all the tannin-bearing materials, Myrobalan powder caused the greatest reduction
in viscosity. Mehta and Jatkar (2013) showed that the addition of myrobalan powder changed the pH
of the bentonite mud in a manner similar to its effect on viscosity. El-Sukkary et al. (2014) assessed
several vanillin-modified polyoxyethylene surfactants in water-based drilling fluid and perceived that
AV and YP increased, and hence they can be used as rheological modifiers. Muds formulated with
some of these surfactants showed lower filtrate loss than blank mud, while these classes of additives
were not stable against temperature. Moslemizadeh and Shadizadeh (2015) investigated the effect of
Henna extract as a new additive on swelling of sodium bentonite in aqueous solution. They found that
Henna extract had deflocculating characteristics at low concentrations up to 0.2 wt.% and indicated
good inhibition properties to sodium bentonite swelling at about 3 wt.%. Shirmardi and Shadizadeh
(2015) studied the effect of Sedr leaf extract (Ziziphys Spina Christi) on drilling fluid properties and
observed that Sedr extract is capable of reducing shale and sodium bentonite swelling at 3% in WBM.
It acted as a filtration control agent without affecting the rheological properties of drilling fluid. They
J. Neshat and S. R. Shadizadeh/ Evaluation of a Naturally-derived Deflocculant … 23
proposed that inhibition characteristics of Sedr extract could be due to the wettability alteration of
clay platelets.
This paper describes the results from the evaluation of black myrobalan as a new non-toxic and
biodegradable additive in water-based mud for the development of environmentally-friendly and
efficient water-based mud.
2. Materials and Methods
2.1. Materials
a. Bentonite
Bentonite is a type of clay consisting mainly of a hydrous silicate of aluminum. It is formed by
weathering volcanic tuff and ash and consists mainly of montmorillonite [(Al, Mg)2(Si,Al)4O10Cax on
H2O] and contains varying amounts of other minerals like quartz (SiO2) and calcium and sodium
feldspar [(CaAl2Si2O8),(NaAl3Si2O8)]. Bentonite is categorized into two types: Na-bentonite, which
has a high swelling capacity, and Ca-bentonite, which is a non-swelling clay and forms colloidal very
quickly in water (Abu-Jdayil, 2011). By comparing the specifications of bentonite X with API
standard (Table 1), it was found that bentonite used in this study is in agreement with API standard.
The particle size distribution of bentonite X was measured by Zetasizer model Zen 3600 (Malvern
Instruments Ltd, UK) and the result is represented in Figure 1. According to this figure, bentonite X
has a normal particle size distribution around 1500 nm. X-ray diffraction (XRD) was performed (by
normal scan between 5° and 80° with a phase and time step of 0.02° and 0.5 second respectively) by
Panalytical diffractometer model PW-1710 in order to characterize the chemical composition of
bentonite X. The XRD pattern of bentonite X in Figure 2 shows that it mostly contains
montmorillonite and quartz. The physical and chemical analyses of this bentonite are given in Table 2.
Table 1
Specifications of bentonite X (Amoco production company, 1994).
Test for Specification (22.5 lb./bbl.
bentonite)
Bentonite X API standard
θ600
YP/PV (lbf/100 ft2.cp)
41
3.1
>30
≤3
Vf (cc/30 min)
Yield (bbl./ton)
Moisture (wt.%)
+200 mesh (wt.%)
10.9
100
10
0.3
≤15
>91
≤10
≤4
24 Iranian Journal of Oil & Gas Science and Technology, Vol. 5 (2016), No. 2
Figure 1
Particle size distribution of API bentonite (Z-Average=672.2 d.nm).
Table 2
Chemical and physical analyses of bentonite X.
Component Mass percentage (wt.%) Standard Error
SiO2
Al2O3
69.3
15.4
0.2
0.2
Na2O
MgO
CaO
Fe2O3
K2O
P2O5
3.9
2.8
2.4
2.4
1.2
0.1
0.09
0.08
0.07
0.07
0.05
0.04
Density (gr/cc)
Swelling volume (cc)
pH
4.2
12
9
--------
--------
--------
The bentonite used in this study was supplied by Doreen Kashan (D.K., Tehran, Iran) company.
J. Neshat and S. R. Shadizadeh/ Evaluation of a Naturally-derived Deflocculant … 25
Figure 2
XRD pattern of API bentonite representing different minerals (number show phasing angles for minerals).
b. Black myrobalan (Terminalia Chebula)
Black myrobalan or Terminalia Chebula is a moderate tree which belongs to the family combretaceae.
Its drupe is about 1 inch to 2 inch in size and has five lines or ribs on the outer shell (Figure 3). It
grows in India, Myanmar, Bangladesh, Egypt, Turkey, and China. It is used in tanning the leather, in
dyeing industry, in the basic aniline dyes as a mordant. In addition to the main uses, it has been used
for centuries in the manufacture of writing inks (Mehta and Jatkar, 2013). It is also extensively used in
traditional medicine as antimicrobial and is also employed to cure infectious diseases. Black
myrobalan contains the triterpenes arjun glucoside 1, arjungenin, and the chebulisides 1&2. Other
constituents are tannins up to 30%, chebulic acid 3% to 5%, chebulinic acid 30%, tannic acid 20% to
40% (Surya Prakash et al., 2012; Bag et al., 2013). Gas chromatography-mass spectrometry (GC-MS)
analysis was performed by Perkin-Elmer GC Clarus 500 system interfaced to mass spectrometer
equipped with an Elite-5MS (30mx250μm) composed of 5% Phenyl and 95% dimethylpolysiloxane.
(Figure 4) revealed 1,2,3 Benzentriol, Levonoglucosenone, and n-Hexadecanoic acid (palmitic acid)
as the frequent components in black myrobalan composition (Amala and Jeyaraj, 2014). Physical
properties of black myrobalan are summarized in Table 3.
0
50
100
150
200
250
300
350
400
450
5 15 25 35 45 55 65 75
Intensity (Counts/sec)
2θ (°)
M7
G
11
M
19
Mi
61
M
34
Q
26
Q
39
F
21
Q
36
I
8
I
Q
27
Ca
42
M : Montmorillonite
I : Illite
G : Gypsum
F : Feldspar
Q : Quartz
Ca : Calcite
Mi : Mica
26 Iranian Journal of Oil & Gas Science and Technology, Vol. 5 (2016), No. 2
Figure 3
Terminalia chebula leaf, fruit, and extract (Rathinamoorthy and Thilagavathi, 2014).
Table 3
Black myrobalan extract properties.
The hydroalcoholic extract of black myrobalan in this study was purchased from Adonis Gol Daru
(A.G.D.) Pharmacy Company (Tehran, Iran). Properties of black myrobalan are given in Table 3.
c. Chrome lignosulfonate (CLS)
Lignosulfonates are the strongly anionic by-product of the sulfite process. They are used in water
based drilling fluids to deflocculate a clay dispersion which results in a cost effective reduction in
fluid loss and cake thickness (AVA Drilling Fluids Manual, 2004). Chrome is added to lignosulfonate
to assist with rheology stabilization (ASME Shale Shaker Committee, 2005). This additive was
provided by Pars Drilling Fluid (PDF) Company (Tehran, Iran).
Property Description
Type of Extract
Appearance
Hydroalcoholic
Brown
CMC
Major component
Nature
1.2 wt.%
1,2,3 Benzentriol
Acidic
J. Neshat and S. R. Shadizadeh/ Evaluation of a Naturally-derived Deflocculant … 27
Figure 4
Structure and mass spectrum of major phytochemicals identified by GC-MS in Terminalia Chebula extract. (1).
1, 2, 3 Benzentriol; (2). Levonoglucosenone; (3). n-Hexadecanoic acid (palmitic acid)(Amala and Jeyaraj, 2014)
28 Iranian Journal of Oil & Gas Science and Technology, Vol. 5 (2016), No. 2
2.1. Experimental methods
a. Preparation of flocculated bentonite sample
A standard bentonite dispersion was prepared by the addition of 20 lb./bbl. (5.4 wt.%) bentonite to
350 cc distilled water and stirring at 6000 rpm. After 5 minutes, the mixing cup was removed from the
mixer and the sides were scraped to dislodge any bentonite adhering to the cup. The mixer was
replaced and stirring continued for an additional 10 min (for a total mixing time of 15 min). Then, the
bentonite sample aged for 24 hours to hydrate fully (API RP-13I, 2009). Prior to flocculating the mud,
it was stirred at 6000 rpm for 5 minutes to be homogenized. In order to increase additives solubility
and clay stabilization, the pH of bentonite dispersion was increased to 9.5 by the addition of 1M KOH
solution. Then, a 2 wt.% NaCl solution was added to the dispersed bentonite sample and mixed for 10
minutes. Predetermined contents (0.2, 0.6, 1.2, 2, and 3 wt.%) of black myrobalan or CLS were then
added to the solution and mixed at 6000 rpm for an extra 10 minutes.
b. Characterization of bentonite mud
Fann V-G meter model 35 was used to measure the rheological properties of mud at high shear rates.
Brookfield DVII+ viscometer was also utilized to quantify the rheological behavior at low shear rates
and at room temperature. API filtration loss of mud was determined by Baroid API filter press
(Houston, Texas) at 100 psi (689.28 kPa) and 64 °F (17.8 °C). The pH value was measured by Kent
EIL7045/46 digital pH meter. All the tests were carried out based on API-RP 13I. All the tests were
carried out based on API-RP13I standard.
3. A review on rheological models
Rheological models are mathematical equations used to predict fluid behavior across a wide range of
shear rates (Rabia, 2002). Three models used in this paper are explained as below:
3.1. Bingham plastic model
In the early 1900’s, E.C. Bingham recognized that some fluids exhibit a plastic behavior and are
distinguished from Newtonian fluids in a way that they require a yield stress to start flowing. These
fluids are called to show a Bingham plastic behavior and are characterized by (Baker Hughes, 2006):
.      (1)
where τ0 (lbf/100 ft2) is yield point; μp (cP) is plastic viscosity and γ (1/s) stands for shear rate.
According to this model, the rheological parameters are calculated by Equations 2-6:

0.5(2)
(3)

100(4)
 

100.
(5)
!" 2(6)
J. Neshat and S. R. Shadizadeh/ Evaluation of a Naturally-derived Deflocculant … 29
where, θ3, θ6, θ600, and θ300 are dial readings at 3, 6, 600, and 300 rpm respectively (Meng et al.,
2012).
The primary problem of the Bingham plastic model is inability to accurately describe the rheological
behavior of drilling fluids at low shear rates and yield point (Meng et al., 2012; Baker Hughes, 2006).
3.2. Herschel-Bulkely model
The Herschel-Bulkely (Yield-Power Law) is another model describes the rheological behavior of
drilling muds more accurately than other models (Rabia, 2002).
This model is described by:
$.     % (7)
where τ (lbf/100ft2) is the shear stress and τy (lbf/100ft2) represents the yield stress of the fluid; K
lbf.sn/100ft2) is the flow consistency index (and n represents the flow behavior index. Herschel-
Bulkely (YPL) model reduces to the Bingham plastic model when n=1 and reduces to the Power Law
model when τ0=0 (Hassiba and Amani, 2012; Rabia, 2002).
3.3. Robertson-Stiff model
Robertson and Stiff (1976) proposed a three-parameter model to describe the rheological behavior of
drilling fluids and cement slurries. Like the Herschel Bulkely model, it has been found to provide very
close approximations for pressure losses in the circulating system in most drilling situations (Kök et
al., 2000; Baker Hughes, 2006). In this model, shear stress is related to shear rate as given below:

&';)
&'(8)
́0;+
&'(9)
where, A, B, and C are constants determined by regression analysis. This model includes the
Newtonian (C=0 and B=1), power law (C=0 and B≤1), and Bingham plastic (C≥0 and B=0) models as
specials cases (Kök et al., 2000). Rheograms of all of the models which were explained before are
shown in Figure 5.
Shear rate and shear stress values (for V-G with a bob radius of 1.7245 cm) are also calculated
according to:
""1.0678 ./
100 (10)
" 1.7034 .234(11)
""1.7034 .234
4. Results & discussion
4.1. Rheological characterization of bentonite dispersion
a. High shear rates
The full flow curves of the flocculated bentonite mud in the presence of different concentrations of
black myrobalan are represented in Figure 6. As could be seen in this figure, the addition of 2 wt.%
NaCl solution increases the shear stress. By increasing black myrobalan concentration to 0.2 wt.%,
shear stress decreases, and the further addition of black myrobalan extract up to 3 wt.% causes a slight
30 Iranian Journal of Oil & Gas Science and Technology, Vol. 5 (2016), No. 2
increase in resistance to flow. According to Figure 7, some of active constituents of black myrobalan
such as chebulic acid and 1-6 pentagalloyl glucose deprotonate in alkaline mud and become
negatively charged. These deprotonated groups are physically adsorbed on the positively charged
edges of clay platelets and neutralize them. The large size of these active constituents leads to
establishing a repulsive force between the negative charges on clay surfaces and deprotonated groups.
Thus a lower shear stress is needed to generate a known shear rate. A slight increase in shear stress at
higher concentrations is due to the aggregation of black myrobalan molecules, which increases the
solid concentration in the mud and consequently improves the flow resistance of mud.
Figure 5
Rheograms of different rheological models (Skalle, 2010).
Figure 6
Rheological behavior of bentonite mud containing different concentration of Black Myrobalan.
0
5
10
15
20
25
30
35
40
45
50
0 200 400 600 800 1000 1200
Shear stress (lbf/100 ft2)
Shear rate (1/s)
0%
0.20%
0.60%
1.20%
2%
3%
mud+2% NaCl
J. Neshat and S. R. Shadizadeh/ Evaluation of a Naturally-derived Deflocculant … 31
Figure 7
Mechanism of clay deflocculation by Black Myrobalan.
Figure 8 displays the effect of different concentrations of black myrobalan on fitting the rheograms of
the experimental data with different rheological models. As illustrated in this figure, Herschel-
Bulkely and Robertson-Stiff models are more accurate than Bingham plastic in describing bentonite
dispersion including black myrobalan. By increasing black myrobalan extract to 0.6 wt.% rheograms
tend to match Herschel-Bulkely model with a lower yield stress and higher slope compared to blank
mud.
Parameters resulted from the regression analysis of different rheological models are given in Table 4.
0
5
10
15
20
25
30
35
40
45
50
0 200 400 600 800 1000 1200
τ(lbf/100 ft2) Shear rate (
1/s)
0%
BP
HB
rs
Experimental
32 Iranian Journal of Oil & Gas Science and Technology, Vol. 5 (2016), No. 2
Figure 8
Fitting experimental data to different rheological models for different concentrations of Black Myrobalan
extract.
0
5
10
15
20
25
30
35
0 200 400 600 800 1000 1200
τ (lbf/100 ft2)
Shear rate (1/s)
0.6 %
BP
HB
rs
Experimental
0
5
10
15
20
25
30
35
0 200 400 600 800 1000 1200
τ(lbf/100 ft2)
Shear rate (1/s)
1.2 %
BP
HB
rs
Experimental
0
5
10
15
20
25
30
35
40
0 200 400 600 800 1000 1200
τ (lbf/100 ft2)
Shear rate (1/s)
3 %
BP
HB
rs
Experimental
J. Neshat and S. R. Shadizadeh/ Evaluation of a Naturally-derived Deflocculant … 33
Table 4
Parameters of rheological models for bentonite mud containing different concentrations of black myrobalan
(HB: Herschel-Bulkely, RS: Robertson-Stiff, BP: Bingham plastic).
Black myrobalan concentration (wt.%) Rheological model Parameters R2 RMSE
0
HB
K=0.5749
n=0.5408
τy=23.14
0.9999 1.389
RS
A=7.025
C=96.8
B=0.2719
0.9989 0.3793
BP τ0=30.63
μp=0.0167
0.9827 16.54
0.2
HB
K=0.1808
n=0.7092
τy=5.253
0.9999
1.306
RS
A=0.3859
C=86.51
B=0.6204
0.9998 2.705
BP τ0=9.577
μp=0.02
0.9946 10.99
0.6
HB
K=2584
n=0.6727
τy=4.817
0.999
0.4146
BP τ0=10.45
μp=0.0213
0.9879 17.6
RS
A=0.6368
C=37.7
B=0.5626
0.9991 5.435
1.2
HB
K=0.2581
n=0.6791
τy=3.492
0.9999
2.131
BP τ0=9.126
μp=0.022
0.9929 14.31
RS
A=0.4231
C=44.29
B=0.6206
1 1.14
2
HB
K=0.1813
n=0.7206
τy=6.426
0.9995
0.3002
BP τ0=10.93
μp=0.0218
0.993 13.67
RS
A=0.4968
C=79.42
B=0.5995
0.9996 0.3313
3
HB
K=0.175
n=0.7333
τy=6.539
0.9998 2.786
BP τ0=11.01
μp=0.0233
0.9953 12.02
RS
A=0.3903
C=100.6
B=0.639
0.9993 0.3313
34 Iranian Journal of Oil & Gas Science and Technology, Vol. 5 (2016), No. 2
AV reveals the flowability of drilling fluids and is related to the rate of penetration. PV is caused by
the friction between the suspended particles and influenced by the viscosity of the base liquid (Meng
et al., 2012).
Figure 9 shows the effect of black myrobalan on the rheological parameters. As it is shown in Figure
9, by increasing black myrobalan concentration to 0.6 wt.%, AV decreases from 22.5 cP to 14 cP, and
it then increases to 16.25 cP at 3 wt.%. Plastic viscosity increases slightly from 7 cP to 10.5 cP at 3
wt.%. Yield point decreases from 13 lbf/100 ft2 to 9 lbf/100 ft2 at 0.6 wt.%, and it increases again to 12
lbf/100 ft2 at 2 wt.%; lastly, it decreases slightly to 11.5 lbf/100 ft2 at 3 wt.%. LSRV varies with the
same trend as yield point and decreases from 22.5 cP to 4 cP at 1.2%; it increases to 6 lbf/100 ft2 at
2% with slightly decreasing to 5 lbf/100 ft2 at 3%.
Figure 9
Rheological parameters of bentonite mud containing different concentrations of black myrobalan.
The gel strength is a measurement of the shear stress necessary to initiate the flow of a fluid which has
been quiescent for a period of time (Annis & Smith, 1996). Thixotropy of the mud is the difference
between the low readings after 10 sec and 10 min (El-Sukkary et al., 2013). The effect of black
myrobalan on 10 sec and 10 min gel strength and the thixotropy of bentonite mud are illustrated in
Figure 10. As can be seen, by increasing black myrobalan concentration to 1.2 wt.%, 10 min gel
strength decreases by 44%, and 10 sec gel strength decreases by 70%, while thixotropy increases by
83%; however, their variation at higher concentrations of black myrobalan are trivial. According to
Figures 9 and 10, it can be understood that increasing black myrobalan concentration to 0.6 wt.%
decreases the rheological parameters of flocculated bentonite mud to minimum but increases them at
higher concentrations. On the other hand, black myrobalan acts as a deflocculant in the range of 0.2
wt.% to 1.2 wt.%.
0
5
10
15
20
25
30
0 1 2 3 4
Viscosity (cp)/Yield point (lbf/100 ft2)
Black myrobalan extract oncentration (wt.%)
AV
PV
LSRV
YP
J. Neshat and S. R. Shadizadeh/ Evaluation of a Naturally-derived Deflocculant … 35
Figure 10
Variation of gel strength and thixotropy of bentonite mud containing different concentrations of black
myrobalan.
The effect of black myrobalan on the rheological parameters of flocculated mud is compared with
CLS in Figure 11. As can be observed, bentonite muds including 0.2 wt.% to 0.4 wt.% black
myrobalan were found to have rheological parameters lower than the mud with the same content of
CLS.
Figure 11
Comparison of rheological parameters of bentonite suspension comprising black myrobalan and CLS.
0
5
10
15
20
25
0 0.2 0.6 1.2 2 3
Gel strength (lbf/100 ft2)
Black myrobalan concentration (wt. %)
g.s 10" g.s 10' thixotropy
0
5
10
15
20
25
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 Viscosity (
cp)/Yield point (
lbf/100 ft2)
Black myrobalan CLS concentration (wt. %)
AV
PV
LSRV
YP
36 Iranian Journal of Oil & Gas Science and Technology, Vol. 5 (2016), No. 2
The gel strength of mud containing black myrobalan is compared with CLS in Figure 12. It is clear
that gel strength and thixotropy values for CLS and black myrobalan are almost identical for a given
concentration. The summary of the variation of rheological parameters of bentonite mud is given in
Table 5.
Figure 12
Comparison of gel strength values of bentonite mud containing different concentrations of black myrobalan by
CLS.
Table 5
Rheological parameters data for bentonite mud containing different concentrations of black myrobalan or
chrome lignosulfonate.
Concentration
(wt.%)
AV(cP) PV (cP)
G.S. 10”
(lbf/100 ft2)
G.S. 10’(lbf/100
ft2)
YP (lbf/100 ft2)
B C B C B C B C B C
0 22.25 22.25 7 7 20 20 21.5 21.5 13 13
0.2 14 15.5 9 9.2 6.5 7 13 11.5 10 12
0.6 14 12.5 9 9 6 4 12 11.5 9 7
1.2 15 12.75 10 9.5 6 4 12 7 10 6.5
*B: black myrobalan and C: Chrome Lignosulfonate.
Parameters of Herschel-Bulkely model for bentonite mud including black myrobalan and CLS are
represented in Figure 13. As indicated in Figure 13-a, increasing black myrobalan and CLS
concentration to 3 wt.% causes yield stress to decrease from 23.14 lbf/100 ft2 to 3.5 lbf/100 ft2 and
2.85 lbf/100ft2 respectively, and the value of yield stress for CLS is somewhat higher. According to
Figure13-b, increasing black myrobalan or CLS concentration causes flow behavior index (n) to
increase but decreases consistency index (K); however, they become steady at concentrations more
0
5
10
15
20
25
0 0.2 0.6 1.2
Gel strength (lbf/100 ft2)
Black myrobalan or CLS concentration (wt. %)
g.s 10" g.s 10'
g.s 10"_CLS g.s 10'_CLS
J. Neshat and S. R. Shadizadeh/ Evaluation of a Naturally-derived Deflocculant … 37
than 0.6 wt.%. It is also clear that the values of K and n of black myrobalan are respectively lower and
higher than those of CLS at concentrations lower than 0.5 wt.%, which shows that the degree of
deflocculation for the mud containing black myrobalan is higher than the one having CLS.
RYP shows the capability of drilling fluids to carry the cuttings (Meng et al., 2012). A high RYP
indicates that it is a shear thinning mud which is desirable for suspending the cuttings when
circulation is stopped, and it breaks up quickly to a thin fluid when it is agitated by the continuation of
drilling (Mahto and Jain, 2013).
Figure 13
Parameters of Herschel-Bulkely model for bentonite mud including different concentrations of black myrobalan
and CLS. (upper) yield stress (lower) consistency index and flow behavior index.
Figure 14 displays the variation of the RYP of bentonite mud against black myrobalan and CLS
concentration. As their concentrations increase to 1.2%, RYP decreases gradually from 1.85lbf/100
ft2.cP to 1lbf/100 ft2.cP and 0.68 lbf/100 ft2.cP respectively; thus the drilling fluid capacity of bentonite
mud to carry drilling cuttings is reduced, while the value of RYP of black myrobalan is higher than
that of CLS, which is an indication of higher capacity of bentonite containing black myrobalan to
carry the cuttings.
0
5
10
15
20
25
0 0.5 1 1.5
τy (lbf/100 ft2)
Deflocculant concentration (wt.%)
BM
CLS
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
0 0.5 1 1.5
K (lbf.sn/100 ft2)/ n
Deflocculant concentration (wt.%)
n_BM
K_BM
K_CLS
n_CLS
38 Iranian Journal of Oil & Gas Science and Technology, Vol. 5 (2016), No. 2
Figure 14
Effect of black myrobalan and CLS on RYP and RLVP of bentonite mud.
b. Low shear rates
Apparent viscosity of bentonite mud containing different concentrations of black myrobalan extract is
shown in Figure 15. By increasing black myrobalan concentration to 3 wt.%, apparent viscosity
decreases. The flow curve of bentonite mud comprising different concentrations of black myrobalan
at low shear rates is also illustrated in Figure 16. It is obvious that increasing black myrobalan
concentration to 0.2 wt.% causes shear rate to decrease suddenly, and by the further addition of black
myrobalan shear stress changes insignificantly.
Figure 15
Apparent viscosity of bentonite suspension containing different concentrations of black myrobalan extract.
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
0 0.2 0.4 0.6 0.8 1 1.2 1.4
RYP/RLVP (lbf/100ft2.cP)
Black myrobalan/CLS concentration (wt. %)
RYP_BM
RYP_CLS
0
2000
4000
6000
8000
10000
12000
14000
16000
18000
1 10 100 1000
Apparent viscosity (cP) Shear rate (
1/s)
0%
0.20%
0.60%
1.20%
2%
3%
J. Neshat and S. R. Shadizadeh/ Evaluation of a Naturally-derived Deflocculant … 39
Figure 16
Rheological behavior of bentonite suspension comprising different concentrations of black myrobalan extract at
low shear rates.
c. Filtration characteristics of bentonite mud
The profile of filtration volume of bentonite mud containing different concentrations of black
myrobalan against time is shown in Figure 17. As expected, filtration volume is proportional to square
root of time; by increasing black myrobalan concentration to 0.2 wt.%, filtration profile drops
meaningfully and becomes unchanged at higher concentrations.
Figure 17
Comparing filtration profile of bentonite mud containing black myrobalan by CLS.
0
20
40
60
80
100
120
140
0 50 100 150 200 250 300
Apparent viscosity (cP)
Shear rate (1/s)
0%
0.20%
0.60%
1.20%
2%
3%
0
5
10
15
20
25
30
35
0 5 10 15 20 25 30 35 40
Vf(cc)
Time (min)
Blank mud
0.2_CLS
0.6_CLS
1.2%_CLS
0.2_BM
0.6%_BM
1.2%_BM
40 Iranian Journal of Oil & Gas Science and Technology, Vol. 5 (2016), No. 2
The filtration profile of mud containing black myrobalan is compared with CLS in Figure 18. The
results show that mud containing black myrobalan has lower filtration than the one having CLS,
which indicates that, in bentonite mud containing black myrobalan, clay platelets are dispersed highly
and decrease the filtration volume more than CLS.
Figure 18
Filtration loss of bentonite dispersion comprising with different concentrations of black myrobalan/CLS.
4.2. Effect of black myrobalan on pH of bentonite mud
Figure 19 illustrates the pH of black myrobalan solution and bentonite dispersion at different
concentrations of black myrobalan. As can be seen, the pH of bentonite dispersion decreases from 9 to
6.7 by increasing black myrobalan concentration to 3 wt.%. The pH of black myrobalan solution
decreases to 4.4 at 1.2 wt.% and becomes steady for higher concentrations. The acidic pH of black
myrobalan solution is due to the presence of components such as tannic acid, gallic acid, ellagic acid,
etc. in its composition.
Figure 19
Variation of pH of bentonite dispersion by addition of black myrobalan
7
12
17
22
27
32
37
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6
API filtration loss (ml)
Black myrobalan extract concentration (wt. %)
B.M
CLS
3
4
5
6
7
8
9
10
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
pH
Black myrobalan extract concentration (wt. %)
Bentonite dispersion
BM solution
J. Neshat and S. R. Shadizadeh/ Evaluation of a Naturally-derived Deflocculant … 41
4.3. Effect of black myrobalan on the electrical conductivity of bentonite dispersion
Figure 20 demonstrates the electrical conductivity of bentonite dispersion containing different
concentrations of black myrobalan. As shown, increasing black myrobalan concentration to 1.2 wt.%
causes conductivity to increase to 319 μs/m, and it then becomes stable near this value for higher
concentrations.
Figure 20
Effect of black myrobalan on electrical conductivity of bentonite dispersion.
5. Economic and environmental justification of utilization of black myrobalan
In present time, countries like India and China are the main sources of black myrobalan (Terminalia
Chebula) and export it to Iran with an average cost of $2.6 per kilogram, while purchasing chrome
lignosulfonate costs $5.5-6 per kilogram. According to geographical condition and climate of Iran,
local planting of the black myrobalan rather than importing causes black myrobalan to be more
available than chrome lignosulfonate. Other advantages such as non-toxicity, high solubility in water,
and anti-corrosion characteristics suggest it for a potential replacement for chrome lignosulfonate.
This extract is totally biodegradable and does not have any environmental problems, which makes it
applicable in offshore drilling.
6. Conclusions
1. The addition of NaCl to bentonite mud enhances shear stress in the rheogram of mud
significantly, which is due to the flocculation of clay platelets.
2. Herschel-Bulkely and Robertson-Stiff models predict the rheology of bentonite mud
comprising black myrobalan with high accuracy.
3. The addition of black myrobalan to flocculated bentonite mud up to 0.6 wt.% decreases the
AV; 10 sec and 10 min gel strength; LSRV; and RYP, but it increases PV.
4. Rheological parameters of mud comprising black myrobalan are lower than those of the mud
having CLS at the same concentration up to 0.4 wt.%. Values of 10 sec and 10 min gel
strength are the same for both black myrobalan and CLS in this range of concentration. It
150
200
250
300
350
400
0 0.5 1 1.5 2 2.5 3 3.5
Conductivity (μs/m)
Black myrobalan extract concentration (wt. %)
42 Iranian Journal of Oil & Gas Science and Technology, Vol. 5 (2016), No. 2
could be realized that the deflocculation effect of black myrobalan is due to the neutralization
of positive charges on the edges of clay platelets by deprotonated hydroxyl groups. Since the
edge surface area of clay platelet is relatively a small proportion of the total area, this effects
occurs at low concentrations of black myrobalan.
5. The gel strengths of mud for both black myrobalan and CLS are almost identical at the same
concentration
6. The addition of black myrobalan and CLS to flocculated bentonite mud caused consistency
index to decrease, but increased flow behavior index, which is an indication of the
deflocculation of mud. At concentrations lower than 0.5 wt.%, consistency index and flow
index of the mud having black myrobalan are lower and higher respectively compared to
those of the mud having CLS. They also decrease the yield stress of Herschel-Bulkely model.
7. Increasing black myrobalan concentration to 0.6 wt.% decreases the apparent viscosity of
mud at low shear rates; however, its effect at higher concentrations is insignificant.
8. Aging mud including black myrobalan for 24 hours caused the apparent viscosity and shear
stress of bentonite mud to unexpectedly decrease.
9. Black myrobalan decreases the filtration volume of flocculated mud at concentrations lower
than 1.2 wt.%, which is because of the deflocculation of clay platelets and plugging the pores
by these platelets. Comparing the filtration of black myrobalan with that of CLS showed that
black myrobalan decreases the filtration volume of mud more than CLS at the same
concentration.
10. A comprehensive study of the performance of black myrobalan showed that black myrobalan
is a more efficient deflocculant compared to CLS at concentrations less than 0.4 wt.%.
11. The addition of black myrobalan increases electrical conductivity up to 1.2 wt.%, and it then
levels off.
12. The addition of black myrobalan decreases the pH of mud due to the presence of components
such as tannic acid, gallic acid, ellagitannic acid, etc.
13. CLS is harmful to the environment because of the existence of chrome in its composition and
is prohibited by environmental protection organizations, while black myrobalan is a plantbased
and nontoxic material, which makes it a potential replacement for CLS.
Acknowledgments
The authors would like to thanks the laboratory technicians of Petroleum University of Technology
for providing equipment and materials.
Nomenclature
AV : Average viscosity
BM : Black myrobalan
CLS : Chrome lignosulfonate
G.S. : Gel strength
K : Consistency index [lbf.sn/100ft2]
LSRV : Low shear rate viscosity
PV : Plastic viscosity
RLVP : Ratio of low shear rate viscosity and plastic viscosity
J. Neshat and S. R. Shadizadeh/ Evaluation of a Naturally-derived Deflocculant … 43
RYP : Ratio of yield point and plastic viscosity
SR : Shear rate
SS : Shear stress
Vf : Filtration volume [cc]
YP : Yield point
YPL : Yield Power law
Greeks
     : Shear rate [s-1]
μp : Plastic Viscosity [cP]
τ : Shear stress [lbf/100 ft2]
τ0 : Minimum shear stress [lbf/100ft2]
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ASME Shale Shaker Committee, Drilling Fluids Processing Handbook, p. 596, Elsevier, 2005.
Recommended Practice for Laboratory Testing of Drilling Fluids, 8th Edition, p. 33, API/ANSI, 2009.
Amala, V.E., Jeyaraj, D.M., Comparative Evaluation of Phytochemicals Present in the Methanolic
Extract of Terminalia Chebula Retz., Terminalia Bellirica Roxb., and Phyloanthus Emblica L.,
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Choo, K. Y., Bai, K., Effects of Bentonite Concentration and Solution pH on the Rheological
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El-Sukkary, M. M. A., Ghuiba, F. M., Sayed, G. H., Abdou, M. I., Badr, E. A., Tawfik, S. M., &
Negm, N. A., Evaluation of Some Vanillin-modified Polyoxyethylene Surfactants as Additives
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Technology, Ahwaz, 175 p. 2015.
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Drilling Fluid Properties, M.Sc. Thesis, Petroleum University of Technology, Ahwaz, 120 p.
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Rathinamoorthy, R., Thilagavathi, G., Characterization of In-vitro Evaluation of Terminalia Chebula
Extract for Antimicrobial Potential, International Journal of Pharmacy and Pharmaceutical
Sciences, Vol. 6, No. 2, p. 932-938,2014.
SuryaPrakash, D.V., Sreesatya, N., Avanigadda, S., & Vangalapati, M., Pharmacological Review on
Terminalia Chebula, International Journal of Research in Pharmaceutical and Biomedical
Sciences, Vol. 3, No. 2, p. 679-683, 2012.
Singh, D., Choi, S. M., Zo, S. M., Painuli, R. M., Kwon, S. W., Han, S. S., Effect of Extracts of
Terminalia Chebula on Proliferation of Keratinocytes and Fibroblasts Cells: an Alternative
Approach for Wound Healing, Evidence-based Complementary and Alternative Medicine, p. 1-
13,2014.
Skalle, P., Drilling Fluid Engineering, 2nd Edition, p. 18 & 25, Ventus Publishing ApS., 2010.
Yousif, M. et al., Characteristic Properties of Lakhra Lignite to Be Used as Drilling Mud Additive, in
SPE/PAPG Annual Technical Conference, SPE Paper No. 156211, Islamabad, Pakistan, 2011.

Abu-Jdayil, B., Rheology of Sodium and Calcium Bentonite–water Dispersions: Effect of Electrolytes
and Aging Time, International Journal of Mineral Processing, Vol. 98, No.3, p. 208-213, 2011.
Drilling Fluids Manual, Rev. 6, p. 21& 274, Amoco Production Company, 1994.
Amanullah, M., Screening and Evaluation of Some Environmentally-friendly Mud Additives to Use
in Water-based Drilling Muds, SPE 98054, SPE E&P Environmental and Safety Conference,
Texas, U.S.A., 5-7 March, 2007.
Azar, J.J., Drilling Engineering., p. 46, Penn Well Corporation, 2007.
Drilling Fluids Manual, p. 101 & 169, AVA Company, 2004.
ASME Shale Shaker Committee, Drilling Fluids Processing Handbook, p. 596, Elsevier, 2005.
Recommended Practice for Laboratory Testing of Drilling Fluids, 8th Edition, p. 33, API/ANSI, 2009.
Amala, V.E., Jeyaraj, D.M., Comparative Evaluation of Phytochemicals Present in the Methanolic
Extract of Terminalia Chebula Retz., Terminalia Bellirica Roxb., and Phyloanthus Emblica L.,
Fruit Extracts Using GC-MS Analysis, International Journal of Pharma and BioSciences, Vol. 5,
No. 4, p. 927-934, 2014.
Drilling Fluids Reference Manual, Revised Edition, p. 19-486, Baker Hughes, 2006.
Benyounes, K., Mellak, A., and Benchabane, A., The Effect of Carboxymethylcellulose and Xanthan
on the Rheology of Bentonite Suspensions, Energy Sources, Part A: Recovery, Utilization, and
Environmental Effects, Vol. 32, No. 17, p. 1634-1643, 2010.
Bloys, B., Davis, N., Smolen, B., Bailey, L., Houwen, O., Reid, P., Montrouge, F., Designing and
Managing Drilling Fluid, Oilfield Review, Vol. 6, No. 2, p. 33-43, 1994.
Choo, K. Y., Bai, K., Effects of Bentonite Concentration and Solution pH on the Rheological
Properties and Long-term Stabilities of Bentonite Suspensions, Applied Clay Science, Vol. 108,
p. 182-190, 2015.
El-Sukkary, M. M. A., Ghuiba, F. M., Sayed, G. H., Abdou, M. I., Badr, E. A., Tawfik, S. M., &
Negm, N. A., Evaluation of Some Vanillin-modified Polyoxyethylene Surfactants as Additives
for Water Based Mud, Egyptian Journal of Petroleum, Vol. 23, No. 1, p. 7-14, 2014.
Hassiba, K. J., & Amani, M., The Effect of Salinity on the Rheological Properties of Water-based
Mud under High Pressure and High Temperatures for Drilling Offshore and Deep Wells, EarthKök, M. V., A Rheological Characterization and Parametric Analysis of a Bentonite Sample, Energy
Sources, Part A: Recovery, Utilization, and Environmental Effects, Vol. 33, No. 4, p. 344-348,
2011.
Kök, M. V., Batmaz, T., & Gücüyener, I. H., Rheological Behavior of Bentonite Suspensions,
Petroleum Science and Technology, Vol. 18, No. 5-6, p. 519-536, 2000.
Lyons, W., Working Guide to Drilling Equipment and Operations: First Edition, 617 p. Gulf
Professional Publishing., 2010.
Meng, X., Zhang, Y., Zhou, F., & Chu, P. K., Effects of Carbon Ash on Rheological Properties of
Water-based Drilling Fluids, Journal of Petroleum Science and Engineering, Vol. 100, p. 1-8,
2012.
Mahto, V., Jain, R., Effect of Fly Ash On the Rheological and Filtration Properties of Water-based
Drilling Fluids, International Journal of Research in Engineering and Technology, Vol. 2, No. 8,
p. 50-156, 2013.
Mehta, D. N., Jatkar, S. K., pH Control of Rotary Drilling Fluids, Journal of the Indian Institute of
Science, Vol. 18, p. 101-107, 2013.
Narayana, P.Y., Rotary Drilling Mud. Part I, The Effect of Tannin on the Viscosity, Journal of Indian
Institute of Science, Vol. 21, pp. 169-178, 2013.
Moslemizadeh, A., Shadizadeh, S. R., Experimental Investigation of Effect of Plant Additive (Henna)
on Shale Swelling: Used in Water-based Drilling Fluids, M.Sc. Thesis, Petroleum University of
Technology, Ahwaz, 175 p. 2015.
Shirmardi Dezaki, A., Shadizadeh, S. R., Experimental Investigation of Effect of Sedr Leaf Extract on
Drilling Fluid Properties, M.Sc. Thesis, Petroleum University of Technology, Ahwaz, 120 p.
2015.
Rabia, H., Well Engineering & Construction, p. 242 & 245, Entrac Consulting Limited, 2002.
Rathinamoorthy, R., Thilagavathi, G., Characterization of In-vitro Evaluation of Terminalia Chebula
Extract for Antimicrobial Potential, International Journal of Pharmacy and Pharmaceutical
Sciences, Vol. 6, No. 2, p. 932-938,2014.
SuryaPrakash, D.V., Sreesatya, N., Avanigadda, S., & Vangalapati, M., Pharmacological Review on
Terminalia Chebula, International Journal of Research in Pharmaceutical and Biomedical
Sciences, Vol. 3, No. 2, p. 679-683, 2012.
Singh, D., Choi, S. M., Zo, S. M., Painuli, R. M., Kwon, S. W., Han, S. S., Effect of Extracts of
Terminalia Chebula on Proliferation of Keratinocytes and Fibroblasts Cells: an Alternative
Approach for Wound Healing, Evidence-based Complementary and Alternative Medicine, p. 1-
13,2014.
Skalle, P., Drilling Fluid Engineering, 2nd Edition, p. 18 & 25, Ventus Publishing ApS., 2010.
Yousif, M. et al., Characteristic Properties of Lakhra Lignite to Be Used as Drilling Mud Additive, in
SPE/PAPG Annual Technical Conference, SPE Paper No. 156211, Islamabad, Pakistan, 2011.