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).

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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.

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