BRAZILIAN JOURNAL OF PETROLEUM AND GAS | v. 3 n. 1 | p. 029-034 | 2009 | ISSN 1982-0593
USE OF ION CHROMATOGRAPHY TO DETERMINE SIMULTANEOUSLY
HIGH CHLORIDE AND LOW IONS CONCENTRATIONS IN PRODUCED
WATER
a,b
a
Costa, E. C. T. A. 1;
a,b
Frota, T. M. P.;
a,b
Silva, D. R.
Universidade Federal do Rio Grande do Norte
b
Núcleo de Estudo em Petróleo e Gás Natural
ABSTRACT
Waters normally produced with petroleum are rich in salt, mainly chlorides, which, in contact with metal
surfaces, may induce corrosive processes. The determination of the concentration of chlorides and other
ions when the chloride content is high is very difficult due to many interfering parameters. In this study,
we report on the optimization of a new application of ion chromatography to analyze produced water
containing high concentration of chloride, which can be quantified along with the concentrations of
different ions also present in the water but in lower concentrations, such as fluoride, bromide, nitrate,
sulfate, acetate and formate. Sample preparation and conditions of elution and separation were adapted
to the nature of this kind of sample. Analytical curves were drawn for chloride and at reduced
concentrations for the other ions. Using this technique, it was possible to determine chloride and the
remaining ions simultaneously and free from interfering agents.
KEYWORDS
chloride in high concentration; ion chromatography; produced water; interfering agents; optimization
1
To whom all correspondence should be addressed.
Address: Av. Senador Salgado Filho, S/N, Lagoa Nova, CEP 59.072-970, Natal-RN, Brazil
E-mail: [email protected]
29
BRAZILIAN JOURNAL OF PETROLEUM AND GAS | v. 3 n. 1 | p. 029-034 | 2009 | ISSN 1982-0593
1. INTRODUCTION
materials (Costa et al., 2002).
Ion chromatography was originally described by
Small and coworkers in 1975 as a new technique
for the characterization of a variety of solutions
and their respective anions and cations (Small et
al., 1975). As with all chromatography techniques,
there must be precise analytical parameters to
ensure accuracy of retention times and of the
effects that these parameters may have on the
retention
times
of
each
species.
Ion
chromatography (IC) remains one of the most
powerful instrumental techniques for the
determination of inorganic anions and organic
acids in different samples (Krataa et al., 2009) such
as natural waters, snow, ice, rain, and air (Neal et
al., 2007).
Renowned and widely studied classical methods
for determining chlorides in water, such as
argentometric methods, are generally used
(Pereira, 2007). Another technique consists in
using a selective ion electrode (potentiometric
titration) but, in both techniques, some
components in the samples may cause
interference, impairing the determination of the
real concentration of different species present
(Harris, 2006). The effect of interfering agents is
even more significant in complex matrices (Hu et
al., 1999), such as the oil production waters
containing these fluids. This means that before
identifying and determining the components of the
mixture, they must be separated or removed. Since
IC is a separation technique, it can be used as an
alternative to determine chloride in samples with
high concentrations of other ions such as bromide,
iodine, sulfide, etc.
Oil production water, which is called connate
water, may exist in oil reservoirs ever since its
formation or as a mixture with underground water,
called injection water, which may be used in
secondary recovery processes. Injection water can
have a widely varied composition (Xiaoyan et al.,
2009). By examining oil produced water
specifications, one can find a limit of up to
100,000 mg.L-1 of total dissolved solids (Gabardo,
2007), that is, inorganic compounds. However, this
composition can vary as a function of a number of
factors, such as the use of fresh water captured in
production wells for injection, seawater or the oil
production water itself. The latter may contain salt
and emulsified oil and, during oil separation
processes, may receive chemical products such as
demulsifiers and anti-foaming agents. Drilling and
completion fluids can also be added (Fakhru’l-Razi
et al., 2009).
Completion fluids are used in oil production
operations to hold the reservoirs using the
hydrostatic pressure that is imposed by them,
causing a minimum of damage to the producing
formation. An inorganic salt is used in these fluids
to avoid hydration of the clay formation, which
causes swelling and subsequent damage to the
formation. These fluids generally use sodium
chloride (NaCl), potassium chloride (KCl) and
calcium chloride (CaCl 2 ) as inorganic salts and the
choice is made according to the specific weight of
the fluid to be used. These salts contain high
concentrations of chloride and are aggressive to
the environment, causing corrosion in metallic
30
In this study, IC was used as an alternative
technique to determine anions in oil production
water, a matrix considered problematic due to its
complexity. We propose to test the efficiency of IC
to determine high chloride concentrations
(> 100,000 mg.L-1).
2. MATERIALS AND METHODS
The anions were determined using the ion
chromatography technique, with detection and
suppression of conductivity, according to the
procedure 4110-C of the APHA Standard Methods
(1998) – Single-Column Ion Chromatography with
Electronic Suppression of Eluent Conductivity and
Conductimetric Detection.
Due to being considered a complex matrix, a
number of precautions were taken during the
preparation of the samples, such as prior filtration
in activated carbon filters to retain organic
materials that could damage the structure of the
analytical column and filtration with cellulose
membranes, with a 0.45 µm porosity, to retain any
suspended solids. After this cleaning stage, the
samples were diluted 100 and 500 times to fit the
concentrations to the analytical curves (Table 1).
The samples were analyzed in a DIONEX ICS-2000
BRAZILIAN JOURNAL OF PETROLEUM AND GAS | v. 3 n. 1 | p. 029-034 | 2009 | ISSN 1982-0593
Table 1. Conditions of the analytical curves obtained in the simultaneous determination of anions.
STANDARD
Fluoride
Acetate
Formate
Chloride
Bromide
Nitrate
Sulfate
P1
0.2
0.3
0.6
0.3
1.0
1.0
1.5
P2
0.4
0.7
3.0
0.6
2.0
2.0
3.0
P3
0.8
2.7
4.0
1.2
4.0
4.0
6.0
CONCENTRATION (mg.L-1)
P4
PCl1
PCl2
PCl3
2.0
3.7
5.0
3.0
100
200
500
10.0
10.0
15.0
-
PCl4
800
-
PCl5
1000
-
R2
0.99989
0.99999
0.99987
0.99998
0.99990
0.99994
0.99997
P1, P2, P3 and P4 are multi-elementary standards. PCl1, PCl2, PCl3, PCl4 and PCl5 are chloride standards in high
2
concentrations; R = linear correlation coefficient.
ion chromatograph, at the chromatographic
conditions described in Table 2. Analytical curves
were drawn for fluoride, acetate, formate,
chloride, nitrate, bromide, nitrite, sulfate and
phosphate, simultaneously, and at different
concentrations, using standards manufactured by
DIONEX, traceable to NIST (National Institute of
Standards and Technology). Five samples from a
single well were analyzed, collected on consecutive
days, each one with two different dilutions and
analyzed in triplicate.
3. RESULTS AND DISCUSSION
Seven anions have been detected and
quantified. Table 3 shows the results obtained in
the analyses performed in this study. It can be
observed that chloride and acetate were the anions
with the highest concentrations, and chloride ions
corresponded to approximately 95% of the sample
anions. Also, high concentrations of acetate may
indicate that the well from which the samples were
collected can be undergoing acid chemical cleaning
to dissolve incrusted salts (Xiaoyan, 2009), which
tend to decrease local production. Another anion
that showed a significant concentration was
bromide, a potentially interfering agent in the
determination of chloride using titrimetric
methods. Sulfate ions, in the presence of sulfatereducing bacteria (SRB), are reduced to sulfide
ions, which must be monitored due to their
potential to promote corrosion (Penna et al.,
2003). These anions also react with silver in
potentiometric titration, which may give a false
result in the determination of chloride by this
technique. This type of interference does not occur
in ion chromatography, taking into account that it
Table 2. Conditions used in the chromatographic method.
CHROMATOGRAPHIC CONDITIONS
IONPAC AS19, 4×250 mm
1.0 mL/min
10 mM KOH (0-10min), 45 mM KOH (10-30min)
25 µL
Condutivity with electrochemical suppression
30 °C
Column
Flow
Eluent
Loop
Detector
Temperature
Table 3. Results of concentration media of anion analyses by ion chromatography.
SAMPLE
1
2
3
4
5
Chloride
168,201.25
172,080.68
168,646.81
171,936.35
168,524.59
Fluoride
43.56
47.30
52.11
46.83
44.13
CONCENTRATION (mg.L-1)
Bromide
Nitrate Sulfate
1028.81
144.56
555.93
1090.25
183.10
554.36
1066.66
7079.26
679.48
1083.52
330.98
604.53
1075.56
147.34
530.41
Acetate
1930.11
2089.41
1364.88
1685.68
2045.95
Formate
23.74
21.08
18.78
21.98
21.25
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BRAZILIAN JOURNAL OF PETROLEUM AND GAS | v. 3 n. 1 | p. 029-034 | 2009 | ISSN 1982-0593
is a separation method (Weiss, 2004). It is
interesting to observe that the high chloride
concentration, surpassing values of 150,000 mg.L-1,
was determined simultaneously with anions at
lower concentrations, as fluoride and formate, as
shown in Figure 1, where the signal for the
conductivity of chloride was approximately 400 µS
whilst formate ions showed the smallest signal, less
than 0.4 µS. This is more easily observed in the
chromatogram in enhanced scale shown in
Gabardo (2007) determined anions and organic
acids in the Brazilian coast by IC, but chose to
remove chloride ions from the sample with silver
cartridges for injection in the chromatograph,
considering their interference in this technique and
quantifying them by potentiometry. In this work, all
organic and inorganic anions were determined
simultaneously by IC, with the prior dilution and
µS
4 - chloride - 9,210
600
Figure 2.
500
400
-50
0,0
10 - 21,783
6 - nitrate - 16,183
5 - bromide - 14,730
100
3 - formiate - 6,447
1 - fluoride - 4,993
2 - acetate - 5,543
200
7 - 19,483
8 - sulphate - 20,107
9 - 20,737
300
min
10,0
5,0
25,0
20,0
15,0
30,0
-0,50
0,0
10 - 21,783
9 - 20,737
1,00
7 - 19,483
2,00
3 - formiate - 6,447
3,00
1 - fluoride - 4,993
2 - acetate - 5,543
4,00
8 - sulphate - 20,107
µS
5 - bromide - 14,730
4 - chloride - 9,210
5,00
6 - nitrate - 16,183
Figure 1. Chromatogram of sample 3.
min
5,0
10,0
15,0
20,0
25,0
Figure 2. Chromatogram of sample 3 in enhanced scale.
32
30,0
BRAZILIAN JOURNAL OF PETROLEUM AND GAS | v. 3 n. 1 | p. 029-034 | 2009 | ISSN 1982-0593
removal of suspended solids and undesired organic
material, with no loss in the final result. Chloride
ions have a high affinity for the mobile phase and
elute in only 10 minutes of run, avoiding saturation
of the chromatographic column or enlargement of
peaks. In addition, no peak overlapping or
displacement of retention times, owing to the
effects of modifying the ionic force of the medium,
was observed. Although it has been already
reported that high ion concentrations may cause
these effects on retention times and the resolution
of other species (Bynum, 1981; Jenke, 1981), for
some samples considered as problematic, gradient
dilutions and elutions are commonly used to solve
these problems when determining high anion
concentrations jointly with trace anions (Weiss,
2004). The ion chromatography technique,
therefore, is able to accurately determinate
different ions at low concentrations in the
presence of chloride in high concentration without
interference.
4. CONCLUSIONS
With the procedures adopted and described in
this work for the determination of anions in
produced water, no significant interference was
observed, despite the complexity of the matrix. The
determination of high chloride concentrations by
chromatography was reproducible, without causing
the usual chromatographic disturbances, such as
peak overlapping or changes in the retention times
of components for other anions. The methodology
used was suitable to detect anions in produced
water containing high concentrations of dissolved
salts (chloride) and different ions in lower
concentrations without interferences. This new
application of ion chromatography is more efficient
then current methods like potentiometric and
titrimetric argentometric techniques.
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