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ORIGINAL ARTICLE
Characterization and Surfactant-Enhanced Washing Treatabilityof Drilling Fluids Stored for More than 20 Years
Luis C. Fernandez Æ Hector Zegarra ÆGustavo Baca Æ Luis G. Torres
Received: 19 April 2007 / Accepted: 3 June 2008 / Published online: 20 September 2008
� AOCS 2008
Abstract Drilling fluids represent a significant environ-
mental hazard owing to the fact that they are frequently
stored in open vessels without any treatment. The drilling
fluids studied in this work have been stored for 20–30 years
in open cesspits in the state of Tabasco (Mexico). The aim
of this work was to characterize the drilling fluids produced
in this region and to determine their treatability by means
of surfactant-enhanced washing. Two anionic and two non-
ionic surfactants (sodium lauryl ethersulfate SLES and
sodium dodecylsulfate SDS, ethoxylated nonylphenol ENP
and an unknown composition ethoxylated nonionic
Surfynol 440 respectively) were employed for surfactant-
enhanced washing assessments in the presence of a com-
mercial dispersant. Drilling fluids were contaminated with
135,400 mg of total petroleum hydrocarbons (TPH)/kg
soil, including seven polycyclic aromatic hydrocarbons
(PAHs) from 1.18 to 57.28 mg/kg. TPH removal efficien-
cies as high as 55.7% were reached when washing drilling
fluids with SDS (4%), followed by ENP 906 (1%), which
showed a TPH removal of 52.2%, and ENP itself at a lower
dose (0.1%). SLES and S440 gave removal of around
10–15% with the assessed doses.
Keywords Diesel � Drilling fluids � Mud �Surfactant-enhanced � Washing
Introduction
Drilling Fluids
Perforation processes need drilling fluids or muds. Drilling
muds are a suspension of solids (i.e., clays, barite, small
cuttings) in liquids (i.e., water or oil) or in liquid emul-
sions, with chemical additives, as required, to modify their
properties [1]. The main functions of drilling fluids or muds
are: solids suspension, pressure control, exposed rock sta-
bilization, floatability enhancement, lubrication and
cooling, among others. Drilling fluids can be oil-based,
water-based, or synthetic muds. Although water-based and
synthetic muds show risks from the environmental point of
view, oil-based muds are definitively of more concern.
Drilling fluids combine several, thousand elements and
compounds that can be harmful to nature and humans.
Depending on the material used for their preparation, they
can contain diesel or other crude fractions, clays, alkaline
chemicals, salts, surfactants, defoamers, detergents,
Gilsonite, biocides, corrosion inhibitors, drilling lubricants,
dispersants, oxygen scavengers, cutting wash, shale inhib-
itors, rheological modifiers (viscosifiers and thinning
agents), stabilizers, lignosulfonates, lignites, weighing
agents, and many more products [1].
Toxicological aspects of drill cuttings have been the
focus of discussions in recent years, but much work is still
in progress. Some biological systems have been developed
to measure toxicity in drilling muds, such as amphipod
species [2], earthworms [3], and the well-known bacterial-
Microtox system.
Many authors have reported the presence of drill cut-
tings in the terrestrial surface and in the seabed. Among
them, Carls et al. [4] and Gutleb et al. [5] described the
effects of drill cuttings presence in Texas soils (USA) and
L. C. Fernandez � H. Zegarra � G. Baca � L. G. Torres (&)
Departamento de Bioprocesos,
Unidad Profesional Interdisciplinaria en Biotecnologıa,
Instituto Politecnico Nacional, Av. Acueducto s/n. La Laguna,
Ticoman, 07340 Mexico DF, Mexico
e-mail: LTorresB@iingen.unam.mx
123
J Surfact Deterg (2008) 11:307–314
DOI 10.1007/s11743-008-1086-2
Peruvian rivers, respectively. On the other hand, Eames
et al. [6], Marsh [7], and Breuer et al. [1] investigated the
accumulation of drilling fluids in the North Sea seabed.
Treatment Processes
Several physicochemical and biological treatment pro-
cesses have been used to treat drilling fluids; thermal
desorption, low temperature distillation, thermal stripping,
incineration, solvent extraction, and evaporation [8],
besides surfactant enhanced washing [9] and supercritical
extraction [10] which are the most common physicochem-
ical processes. Biodegradation [11, 12], slurry biological
reactors [13], vermiculture [14], and phyto-remediation are
the biological processes most often employed.
Surfactant enhanced washing technology has been
widely employed for contaminated soil remediation, for
both metal and organic compounds contaminants. The
washing process in the case of contaminated soils can be
developed in situ or ex situ. This means that soils can be
directly injected with surfactant solutions; water plus co-
solvents or chelating products. On the other hand, soil can
be excavated from its original place and washed away from
its site. This process can be carried out very near from the
site in short-term operation facilities or relatively far from
the place, in more stable soil washing facilities.
Drilling Fluids from the Tabasco Exploration
and Production Zone
The aims of this work are to characterize drilling fluids
from an oil exploration and production zone in Tabasco
(Mexico) in terms of some physical-chemical parameters,
and to show the mud’s treatability by means of surfactant-
enhanced washing. Seven surfactants displaying a wide
range of molecular weights, hydrophilic-lipophilic balance
(HLB) numbers, critical micelle concentration (CMC)
values, were used; some of them ionic and some non-ionic
in nature. After the washing process of the drilling fluids,
the removal efficiencies, measured as the percent of total
petroleum hydrocarbons (TPH) removed, were correlated
against some of the surfactant features and the results of
this comparison are discussed.
Materials and Methods
Drilling Fluids Characterization
Tabasco drilling fluids were characterized in a certified
laboratory, using US EPA and ASTM methods. Among
them, leachable metals (EPA 6010A), petroleum aromatic
hydrocarbons PAHs (EPA 8310), texture, pH (ASTM
D4972-89), humidity, extractable bases, cation exchange-
able capacity CEC, electrical conductivity, total organic
carbon TOC, total nitrogen (Kjeldal), available phospho-
rus, carbonates as CO3=, nitrogen as ammonia, nitrates,
nitrites, sulfates, PO43-, Olsen phosphorus, total metals
(Al, As, Ba, Cd, Cr, Cu, Fe, Hg, Ni, Se, V, and Zn) [15],
organic Pb, and TPHs (US EPA 418).
Effect of Dispersant on Drilling Fluids Real Density
Hydropalat 44, a sodium polyacrylate manufactured by
Cognis (USA), was applied with dispersed clays, aimed at
easing the washing processes. The soil textural character-
ization test [16] was used to investigate whether six
different dispersant concentrations (0, 0.2, 0.4, 0.6, 0.8, or
1.0% w/w) are capable of maintaining the dispersion of the
drill fluid clays
Measurement of CMC for Different Surfactants
Surfactants used were Surfacpol 906, an ethoxylated no-
nylphenol (ENP) from Polaquimia, Texapon 5, sodium
lauryl ether sulphate (SLES) sold by Quimica Henkel,
sodium dodecyl sulphate (SDS) obtained from Aldrich, and
Surfynol 440 (S440) a nonionic surfactants of unknown
composition from AirProducts. See Table 5 for some
properties. Solutions containing 0.1 to 10,000 mg/l were
prepared with all surfactants. Eight dilutions of each sur-
factant were prepared and surface tension (in mN/m) was
measured in a Kruss automatic tensiometer (model K12).
The CMC value was determined by the inflection point of a
semi-logarithmic plot of surfactant dose (mg/l) versus
surface tension (mN/m).
Surfactant-Enhanced Washing of Drilling Fluids
Four surfactants were utilized in washing tests: SLES,
SDS, ENP and S440. Washing assessments were as fol-
lows: 5 g drilling fluids were placed in a 125 ml
Erlenmeyer flask, adding 40 ml of water or the surfactant
solution. Flasks were kept for 24 h at room temperature
under agitation (150 rpm). After that period, the clay and
solution were centrifuged in tubes for 10 min (10,000 rpm,
15 �C), the supernatant was discharged and drilling fluids
were evaluated for TPH. TPHs were determined by the
shaking-centrifugation extraction method of Arce-Ortega
et al. [17].
Effect of Dispersant on Surfactant-Enhanced Washing
of Drilling Fluids
Some drilling fluids surfactant enhanced washing assess-
ments were performed in the presence of 0, 0.05, 0.1, and
308 J Surfact Deterg (2008) 11:307–314
123
0.2% of the commercial dispersant Hydropalat 44 to
determine whether washing performance can be improved
by clay dispersion. Assessments were performed as previ-
ously described, except for the presence of dispersant at
different concentrations. Washing times were not changed
(i.e., 24 h).
Results and Discussion
Drilling Fluids Characterization
Drilling fluids comprised 45% sand, 34% silt, and 21%
clay; with a cation exchangeable capacity (CEC) value of
8.6 mequiv/100 g. These values classify drilling fluids as
loams (sandy loam). Exchangeable measured bases were
Na? (0.7 mequiv/100 g), K? (0.2 mequiv/100 g), Ca??
(10.6 mequiv/100 g), and Mg?? (0.5 mequiv/100 g). The
high difference between total exchangeable monovalent
ions (0.9 mequiv/100 g) and total exchangeable divalent
ions (11.1 mequiv/100 g) make the washing process of the
drilling fluids more difficult when using ionic surfactants,
as will be discussed shortly. Real or particle density
showed a value of 2.54 g/cm3. Humidity showed an aver-
age value of 33% and pH of 8 (slightly alkaline) (Table 1).
Table 2 shows some additional physical–chemical
characteristics of the drilling muds. TPH had a concen-
tration of 135,400 mg/kg (13.5%). Drilling fluid sample
and diesel standard chromatographic profiles are quite
similar, indicating the high possibility that drilling fluids
were prepared using diesel. Small differences in chroma-
tography could be due to weather process during more than
20 years.
The following total (non exchangeable) metals were
measured: (in mg/kg): Fe, 15,600; Al, 20,362; As, 31; Ba,
5,087; Cu, 123; Ni, 31; Pborganic, 4; Zn, 1,011. Some of
these metals were found in quite high concentrations.
Regarding nutrients, the following were measured (in mg/
kg): P as POlsen, 8; P�PO4, 0.27–6; Nkjeldal, 0; NNH4
, 14:
NNO2, 0.06. Finally, the amount of carbonates (CO3
=) was
19 mg/kg and total organic matter (OM) 11.0 mg/kg. All
these values are quite relevant when the biodegradation
suitability of drilling fluids is under discussion.
The 16 PAHs, considered as priority by the US EPA
(Environmental Protection Agency), were measured
(Table 3). From the seven detected PAHs, only chrysene
has been reported as carcinogenic in laboratory animals
[18]. McDonald and Portier [13] reported some PAHs
levels in three drilling fluids found in containers; naph-
thalene in a range of 13.5 to 16.8 mg/kg, 2-methyl
naphthalene between 50.1 and 213 mg/kg, acenaphthene in
Table 1 Some drilling fluids characteristics
Parameter Value Units
Sand 45 %
Silt 34 %
Clay 21 %
Classification Sandy loam –
CEC 8.6 mequiv/100 g
Na 0.7 mequiv/100 g
K 0.2 mequiv/100 g
Ca 10.6 mequiv/100 g
Mg 0.5 mequiv/100 g
Dreala 2.54 g/cm3
Humidity 33 %
pH 8 –
a Dreal is the ratio between soil mass and real soil volume (avoiding
the empty space volume)
Table 2 Muds physical–chemical characteristics
Parameter Value mg/kg, except for OM
TPH 135,400
Fe 16,550
Al 20,362
As 31
Ba 5,087
Cu 123
Ni 31
Zn 1,011
Pborg 4
P 81
NKjeldal 0.0
POlsen 6.0
PPO40.27
NNH414
NNO20.06
CO3= 19
Organic matter 11%
Table 3 PAHs considered by the US EPA as priorities, found as
drilling fluids constituents (except 2-methyl naphthalene)
Polycyclic aromatic Concentration (mg/kg)
Acenaphthene 6.45
Phenanthrene 57.28
Chrysene 1.36
Fluorene 1.18
Naphthalene 21.88
2-methyl naphthalene 12.61
Pyrene 15.46
J Surfact Deterg (2008) 11:307–314 309
123
around 10 and 29.5 mg/kg, fluorine between 12.3 and
75.7 mg/kg, phenanthrene in a range of 21.2–203.9 mg/kg,
besides anthracene values ranging from 22.8 to 217 mg/kg,
and fluoranthene in concentrations of up to 10.2 mg/kg.
Effect of Dispersant on Drilling Fluids-Real Density
Changes in real density due to the presence of a dispersant
were calculated. Real density tended to decrease over time,
which is an indication of clay sedimentation. Hence, the
changing in density value and the time needed to achieve
the minimum density value will be considered together as
an indication of the dispersant’s effects. 0.2, 0.6, and 1.0%
dispersant concentrations maintained the drilling fluids
without important density changes for 24 h: From these
assessments, changes were less important for the 0.2%
concentration (8.95 ± 6.76%) (Table 4). Based on this
finding, it was decided that the best dispersant concentra-
tion was below 0.2%. It was decided to try 0.2% and lower
dispersant doses (i.e., 0.5, 1, and 2%).
CMC Determination for Some Surfactants
The CMC is detected by the point at which surface tension
will not decrease any more, notwithstanding how much
surfactant is added, and this can be very clearly observed in
Fig. 1. The values obtained for ENP, SDS, SLES, and S440
were 100, 500, 1,000, and 5,000 mg/l, equivalent to 0.207,
1.73, 2.27, and 12.33 mol/l, respectively (Table 5). Values
reported by other authors are included for comparison
purposes. It is important to remark that it is desirable to
measure the CMC values of surfactants for each washing
assessment, since values reported in the literature were
obtained using different techniques, under different con-
ditions (temperature, ionic strength, etc.) and sometimes
using purified products (i.e., dialyzed or repeatedly pre-
cipitated). CMC measurements were carried out at
20 ± 2 �C, and no salt was added.
Drilling Fluid Washing Using the Four Surfactants
Surfactants concentrations (g/l) were fixed in function of
their CMC as follows: ENP, 0.1, 1, and 10 g/l, SLES, 0.4, 4,
and 40 g/l; SDS, 0.6, 6, and 60 g/l, and finally S440, 1, 5, and
10 g/l. All the assessments were performed in duplicate. The
standard error for this measurement was calculated, and its
value was 4.46% in average. Drilling fluid washing with only
water was performed 5 times, with an average final TPH
Table 4 Change in real densities of drill fluids as a function of the
dispersant concentration
Dispersant
concentration
(%)
D�density
(%)
Standard
deviation
(%)
Time before minimum
density is reached
(min)
0 28.41 8.04 360
0.2 8.95 6.76 1,440
0.4 7.50 0.71 120
0.6 14.49 1.95 1,440
0.8 20.24 1.43 240
1.0 14.04 6.66 1,440
Table 5 Surfactants physicochemical characteristics
Surfactant
trade name
Type Chemical name Chemical formula MW
(g/gmol)
HLB CMC (mg/l)
(this work)
MST (mN/m)
(this work)
Surfacpol 906 Non-ionic Ethoxylated nonyl phenol (ENP) HO(C2H4O)n (C6H4)C9H19 483 11 100 (45a) 29.95
Surfynol 440 Non-ionic Ethoxylated product (S440) Unknown 405.5 8 5,000 27.37
Texapon 5 Ionic Sodium lauryl ether sulphate (SLES) CH3(CH2)10CH2
(OCH2CH2)nOSO3Na
440 – 1,000 (414a) 36.96
SDS Ionic Sodium dodecyl sulphate (SDS) (C12H25SO4Na) 288 40 500 (1,586b) 32.37
MW molecular weight, HLB hydrophilic–lypophilic balance, CMC critical micelle concentration, MST minimum surface tensiona Values from Torres et al. (2003)b Value from Li-Zhong and Chiou (2001)
0
10
20
30
40
50
60
70
80
90
100
0.1
Surfactant Concentration (mg/l)
Surf
ace
tens
ion
(mN
/m)
SDSSLES
ENPS440
CMC
CMC
CMC
CMC
SDSSLES
ENPS440
SDS
SLES
ENP
S440
1 10 100 1000 10000 100000
Fig. 1 Surface tension as a function of surfactant concentration
(mg/l)
310 J Surfact Deterg (2008) 11:307–314
123
concentration of 132,359 mg/kg ± 14,144.7 mg/kg (TPH
removal efficiency of 2.24% (blank)).
All surfactants, except for SLES, the higher the surfac-
tant concentration, the higher the TPH removal. ENP
showed TPH removal from 13.38 (for 0.1 g/l) to 52.19%
(for 10 g/l). These values are not low, considering an initial
TPH concentration of 135,400 mg/kg, i.e., 18,116, and
70,665 mg TPH/kg were removed from the drilling fluids.
For SLES, even when higher doses were used, TPH
removal results were quite lower than those reported for
ENP; maximum TPH removal was 11.75% (15,909 mg
TPH/kg soil) for 4 g/l.
SDS, the ionic surfactant, showed the best removal
found in this study 55.72% (for 60 g/l),. 75,445 mg TPH/
kg; although a high SDS concentration was used (6%
solution). Lower SDS concentrations of 0.6 and 6 g/l only
removed 11,685 and 6,892 mg TPH/kg, respectively. For
S440, the removals were of 7.6% (for 1 g/l), 7.8% (for 5 g/l),
and 14.92% (for 10 g/l).
TPH removal against surfactant concentration (mg/l) in
a semi-logarithmic plot shows that the most desirable
results were obtained using ENP, since in comparison with
the rest of the surfactants, the highest TPH removal values
were achieved at lower surfactant doses. The second
interesting surfactant must be SDS, due to the highest TPH
and the third one is SLES, (Fig. 2).
As discussed in previous works [19, 20], it is very
important to emphasize that under CMC, the mechanism
responsible for drill fluids washing is an enhanced solu-
bility of the organic fraction. Below the CMC, only
monomers exist so no micelles are present to produce
solubilization. Thus, below the CMC. the roll-up mecha-
nism is remarkably efficient in removing TPH from the
clays of drilling fluids. The surfactant monomers tend to
adsorb at the clay-contaminant and clay-water interfaces,
increasing the contact angle between clay and TPHs.
Afterwards, the surfactant molecules adsorbed by the
contaminant surface induce repulsion between the head
group of the surfactant molecule and the clay particles,
promoting the separation of the contaminant from the clay
particles. All the sub-CMC calculated values for each
surfactant were fairly good (Fig. 3). With doses below or
equal to 1x CMC, removals of ca. 10% can be observed.
TPH removal results were calculated according to the
equation proposed by Chu and So [21], which correlates
the overall partition coefficient Kd (1/kg) and the [D] total
surfactant dosed to the system (mol/l):
foc=Kd ¼ ð1=bÞKow þ a=bð½D� � ½S�sorbÞ ð1Þ
where Kd is the overall partition coefficient (1/kg), a is a
constant for correlating Km and Kow (l/mol), Km is the
micelle-water partition coefficient (1/mol), Kow is the oct-
anol-water partition coefficient, b is a constant to correlate
Koc and Kow (1/kg), foc is the fractional organic carbon
content of the soil, Kow is the octanol-water partition
coefficient, and [S]sorb is the concentration of surfactant
sorbed by the soil (in mol/l).
The overall partition coefficient Kd is defined as:
Kd ¼ ½P�s=½P�w þ ½P�surf ð2Þ
where [P]s is the contaminant concentration in the soil
(mol/kg), [P]w is the contaminant concentration in the
water (mol/l), and [P]surf is the contaminant solubilized by
both monomeric and micellar forms (mol/l). The fitting of
experimental data would allow the calculation of experi-
mental values of Kow, and the constants a and b.
Data are plotted in Fig. 4. In this case, [Dsorb] is too
small as compared to [D], so it may be neglected. As
shown, data points are not represented by means of straight
lines (Eq. 1), since [D] values are in the range of 0.2–
200 M. The foc value was considered as 0.011. Chu and So
[21] proposed that the equation is constituted by two
fractions, one extends up to 1 mM values (no values cor-
respond to this segment) and the other corresponding to[1
0
10
20
30
40
50
60
10 100 1000 10000 100000
Surfactant concentration (mg/l)
TP
H r
emov
al (
%)
ENPSLESSDSS440
CMC
CMC
CMC
CMC
Fig. 2 Surfactant concentration (mg/l) vs TPH removal (%)
0
10
20
30
40
50
60
0.01 0.1 1 10 100 1000
Surfactant concentration (x CMC)
TP
H r
emov
al (
%)
ENPSLESSDSS440
Fig. 3 Surfactant concentration (9CMC) vs TPH removal (%)
J Surfact Deterg (2008) 11:307–314 311
123
to \10 mM (again, no experimental values fall in this
range). The experimental data in this work cover a wide
range of concentrations (200 to almost 200,000 mM). As
stated by Torres et al. [20], the prediction model was
developed for very low surfactant concentrations, and the
real washing processes use quite much higher concentra-
tions than those considered by the model. Nevertheless, it
is interesting to plot the obtained experimental data using
the Chu and So [21] model.
Washing TPH Removal Regarding Some Surfactant
Characteristics
The average TPH removal (for the different surfactant
concentrations) values for the four surfactants that suc-
ceeded in washing assessments were as follows: ENP
(28.0%), S440 (10.1%), SLES (9.9%), and SDS (23.1%).
As observed, it cannot be generalized whether ionic or
non-ionic surfactants show a superior development
regarding drilling fluid washing, since one surfactant
from each group reached the best TPH removal
efficiency.
For the purpose of analyzing the washing removals for
fixed concentration ranges, two average removal efficien-
cies were calculated: one for the sub-CMC region (below
and equal to 1 CMC) and one for the supra-CMC region
(above CMC). The sub-CMC average removal percentages
showed values of 13.9, 8.6, 6.8, and 7.6% for ENP, SLES,
SDS, and S440, respectively. For the supra-CMC region,
values of 35.4, 10.6, 55.7, and 11.3% were found.
Four surfactant features were considered to investigate
the relationship between removal efficiencies and the sur-
factants used, i.e., molecular weight, HLB values, CMC
(already calculated along this work), and minimum surface
tension MST (idem). The values are shown in Table 5.
When relating the total average removal for each surfactant
against surfactant properties, no good R2 values were found
at all (R2 = -0.0456, 0.3342, -0.2596, and -0.6043,
respectively). Regarding the Sub-CMC average removal, a
good correlation factor was found when comparing TPH
removal and CMC values (R2 =-0.8153), which means
that the higher the CMC, the lower the TPH washing
removal. The correlation for removal values and MW was
not bad (R2 = 0.7724), indicating that the higher the MW,
the higher the removal value. Finally, another interesting
correlation was the one found between the MST and TPH
removals (R2 = 0.7320).
When considering the supra-CMC region, a good cor-
relation was found for the pair of TPH removal-HLB
values (R2 = 0.8837), but it is interesting that, in this case,
the relationship has a positive sign, which means that the
higher the HLB value, the better the washing performance.
All these correlations suggest that surfactant characteristics
produced different effects during the washing process,
dependent on the concentration range (sub- or supra-
CMC); this has implications for the selection of commer-
cial products for drilling fluid washing operations.
Washing Drilling Fluids in the Presence of a Dispersant
Washing assessments in the presence of 0, 0.5, 1, and 2%
of Hydropalat 44 were performed in triplicate for ENP 1%.
None of the assessments with dispersant gave washing
removals higher than those measured for the non-dispersant
assessments. More experimentation (using other ENP
concentrations, and even the rest of the surfactants used
along this work) would be necessary to be more conclusive
regarding the suitability of using dispersant aid during
drilling fluids surfactant washing processes. It is important
to underline that only the dispersant effect over the wash-
ing removals was assessed and not over the contact time
required to wash efficiently drilling fluids. In the work
previously mentioned [22], the authors emphasized the use
of octyl-sulfobetaine in order to enhance drilling fluid
washing. They observed a diminution in contact times from
8 h to one half an hour.
Conclusions
ENP, SDS, SLES, and S440 yielded CMC values of 100,
500, 1,000, and 5,000 mg/l, equivalent to 0.2070, 2.272,
17.36, and 12.33 mol/l, respectively.
Best attained TPH removals were with ENP and SDS
(52.19 and 55.72% respectively). Nevertheless, ENP
achieves a similar elimination than SDS with a smaller (six
times lower) concentration. All the sub-CMC efficiencies
resulted fairly well with a reduced removal lower than
13.89% at that dose (the lowest assessed for this
0
0.001
0.002
0.003
0.004
0.005
0.006
0.007
0 1 10 100 1000
[D] (mol/l)
foc/
Kd
ENPSLESSDSS440
Fig. 4 Surfactant concentration [D] (mol/l) vs foc/Kd
312 J Surfact Deterg (2008) 11:307–314
123
surfactant). With doses below and equal to 1x CMC,
removals ca. 10% are observed.
When relating the total average removal for each sur-
factant against the surfactants properties, no good R2 values
were found. Regarding the Sub-CMC average removal, a
good correlation factor (negative value) was found when
comparing TPH removal and CMC values. When consid-
ering the supra-CMC region, a good correlation was found
for the pair TPH removal-HLB values, in this case, the
relationship has a positive sign, which means that the
higher the HLB value, the better the washing performance.
All these correlations suggest that surfactant characteristics
have different effects on the washing process depending on
the concentration range (sub- or supra-CMC), which has
implications for the selection of commercial products for
drilling fluid washing operation.
No effect of dispersant in TPH removal was observed.
More experimentation, using other ENP concentrations,
and even the rest of the surfactants used along this work,
would be necessary to be more conclusive regarding the
suitability of using dispersant during drilling fluid surfac-
tant washing processes
A surfactant enhanced washing process is a suitable
remediation process that can be used to diminish metal,
salts and/or hydrocarbon contents in these complex matri-
ces. More research is needed to optimize the process, using
mixtures of surfactants, mixtures of surfactants and salts
(i.e. NaCl, sodium metasilicate), specifically when ionic
surfactants are employed.
Acknowledgments The authors acknowledge A. Verdejo (Chem-
istry Faculty/UNAM) for allowing us to use the Kruss tensiometer
and for her invaluable support. Authors acknowledge and give thanks
for the suggestions made by D. Sabatini (University of Oklahoma) to
improve the paper.
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Author Biographies
Luis C. Fernandez has a Ph.D. degree in Oceanography from the
University of Aix-Marseille-II, France, DEA (master’s) in Oceanog-
raphy Biotechnology from the University of Aix-Marseille-II, France
(1990–1991), and a Biochemical engineering degree from the
Autonomous Metropolitan University (Universidad Autonoma
Metropolitana, UAMI). He is a Professor and Researcher at the UPIBI
IPN, Department of Bioprosses. Researcher at the Instituto Mexicano
del Petroleo (1997–2005).
J Surfact Deterg (2008) 11:307–314 313
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Hector Zegarra has a master’s degree in Biotechnology and a
Biochemical Engineering degree from the Autonomous Metropolitan
University. At the time of the research, he was a researcher at the
Instituto Mexicano del Petroleo.
Gustavo Baca has a master’s degree in Agronomy at Colegio de
Posgraduados, and an Environmental Engineering degree from the
Autonomous Metropolitan University. He participated in this work as
part of his final work degree scholarship holder at the Instituto
Mexicano del Petroleo.
Luis G. Torres has a PhD in Environmental Engineering from
UNAM, Mexico. He has experience in industrial wastewater biolog-
ical treatment, and characterization/remediation of metal and/or
petroleum-contaminated soils. Currently, he has focused his interest
on surfactant applications to environmental problems. His main
research interests are a) surfactant-enhanced biodegradation of aged
petroleum fractions in soils, b) in situ and ex situ soil washing, and c)
preparation of petroleum fractions-surfactant-water emulsions, as a
first step for fuel biotreatments (e.g. biodesulfuration) d) rheology and
mixing of sludges and suspensions applied to the solution of envi-
ronmental problems.
314 J Surfact Deterg (2008) 11:307–314
123
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