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Norske NO9705211
SivilingeniorersForening
OSTI
OIL FIELD CHEMICALS7th international symposium
17-20 MARCH 1996Dr Holms HotelGeilo, Norway
-••> -i
Complete Chemical Analysis ofProduced Water by Modern
22
LECTURERS:
G M Graham and K S Sorbie, Hertiol Watt University, UKA Johnston, Nalco Exxon Chemicals, UK
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7th. NIF International Symposium on Oilfield Chemicals, Geilo, 17-20 March 1996
Complete Chemical Analysis of Produced Water by ModernInductively Coupled Plasma Spectroscopy (ICP)
G. M. Graham,* K. S. Sorbie,* A. Johnston* and L. S. Boak*
(* Oilfield Scale Research Group (OSRG), Heriot-Watt University; * Nalco-Exxon
Chemicals)
ABSTRACT
ICP Spectroscopy is recognised as a very effective tool for monitoring ion
compositions in many different waters. It has also been used by a number of
laboratories to determine residual levels of phosphonate (PH) scale inhibitors in
produced waters, based on the phosphorus content. Furthermore, until recently, it
had not been used effectively to monitor phosphino-polycarboxylate (PPCA)
returns; where it had been applied, large errors had frequently been observed. The
poor detection limits and accuracy obtained for PPCA inhibitors relates to the much
lower amount of phosphorus present when compared with a typical phosphonate
inhibitor. For example, 1 ppm active of the penta phosphonate DETPMP contains
approximately ~ 270 ppb phosphorus whereas 1 ppm active PPCA contains ~ 8 ppb
phosphorus, which was previously below the detection limit of commercial ICP
instruments.
However, it has been demonstrated within the OSRG that, with effective pre-
treatment, very accurate detection and assay of PPCA inhibitors can be readily
achieved. Furthermore, using modern instruments it will be demonstrated in this
paper that pre-treatment stages are no longer necessary. This significantly improves
the effectiveness of ICP detection for PPCA and other phosphorus containing
inhibitors using such instruments.
MASTER
asmeimoN OF THIS DOCUCNT B UIMTED
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INTRODUCTION
ICP Spectroscopy is recognised as a very effective tool for monitoring ion
compositions in waters originating from a variety of industrial and natural
processes. It is routinely used in many laboratories in order to determine the ionic
composition of oilfield brines. In this paper, we focus on the accurate detection of
residual concentrations of phosphorus containing chemical species where the total
phosphorus content is at the ppb level. This is of particular importance for scale
inhibitor squeeze treatments since many of the chemical species used contain
phosphorus and these species have to be accurately detected at very low
concentrations. A major advantage of ICP techniques for assaying such inhibitor
species relates to sample throughput and the robustness of the technique to many of
the solution interferences affecting many wet chemical techniques. Automated
sample introduction systems and minimal requirement for sample preparation means
that many samples can be assayed routinely on a day to day basis.
In this paper we concentrate on the ability of modern ICP - AES (Inductively
Coupled Plasma - Atomic Emission Spectroscopy) instruments to accurately
monitor phosphino-polycarboxylate (PPCA) based inhibitor species at the sub ppm
level. This is an important advance in the effective use of ICP for oilfield produced
water analysis since the accurate assay of these polymeric inhibitor species becomes
very fast and simple when compared with more time consuming wet-chemical
techniques. Furthermore, it serves to illustrate how the detection limits for
phosphorus of modern ICP-AES instruments are now significantly lower than
previously reported.
Importance of Accurate Detection of Scale Squeeze Inhibitors: The
minimum inhibitor concentration (MIC) for a given brine chemistry is the level of
scale inhibitor required to prevent scale formation to some acceptable degree in the
field. In many cases, MIC levels are often < 5 ppm and it is therefore important to
be able to accurately monitor the returning inhibitor at these low levels in order to
determine the approach of the end of the squeeze lifetime (possibly some 3-12
months after initial treatment). Alternative approaches, such as monitoring of the
scaling ions themselves, for example [Ba2+], will indicate when re-treatment is
essential, but this approach provides no lead time in order to prepare for the
operation. Furthermore, if successful computer modelling is to be carried out in
order to either optimise the conditions for future squeeze treatments or to predict the
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end of the current squeeze lifetime, accurate low concentration return analysis is
essential.1
Wet Chemical Scale Inhibitor Detection Methods: Previous work withinthe OSRG2'3 has described accurate detection and assay techniques for all of the
common inhibitor species currently used in scale control. The inhibitors examined
previously included phosphonates (PH), polyacrylates (PAA), phosphino-
polycarboxylates (PPCA), polyvinyl sulphonates (PVS) and sulphonated
polyacrylate co-polymers (VS-Co). The various analytical methods are described in
the OSRG Laboratory Procedures Manual.4 However, a major drawback to many
of the analytical methods is their sensitivity to brine composition, and the interfering
species often present in oilfield produced brines. Great care has to be undertaken in
wet chemical analytical techniques in order to ensure that sample pre-treatment
techniques allow accurate assay when using synthetic brine calibration curves. This
is often a very time consuming and laborious task. The analyst requires a good
understanding of the many possible interferences present in oilfield produced brines
and a range of techniques must be at his or her disposal.3
To illustrate this point, wet chemical phosphonate (PH) analysis by the phospho-
molybdenum blue detection technique can suffer from significant interferences in
certain produced waters. We have shown previously that large and increasing
background responses are sometimes encountered when using uv catalysed
digestion techniques. This effectively renders the analysis very poor since the true
level of background interference may be unknown and consequently lead to
misleading results which are often too high. In such brines, one possible source of
the interference is thought to result from bacterial growth within the samples
possibly due to sulphide generation.3-5 In order to combat such interferences,
alternative digestion techniques may be employed. One such approach examined
within the OSRG is to use an appropriate hot (~100°C) acid digestion technique.
Table 1 illustrates the effect on the background response for a typical PH inhibitor
when analysed colorimetrically using two different digestion techniques, in a
particularly problematic produced brine. Furthermore, Figure 1 compares the
calibration curves obtained by both techniques in this particular produced fluid and a
synthetic brine. The experimental procedures used in this example are described in
Appendix 1.
From Table 1 and Figure 1, it is evident that accurate residual detection and assay of
phosphonate species in this particular produced water would be very difficult using
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the uv-catalysed technique. Alternative techniques, which may be more time
consuming, may be required. Finally, as has been discussed in previous
publications, in wet chemical colorimetric analytical techniques, care must be taken
that the reagents themselves do not interfere with the brine.3
In a similar manner, phospho-molybdenum blue detection of PPCA inhibitors has
also been shown to suffer from significant levels of interference in a number of
produced brines3 even although very accurate detection can be achieved in a variety
of synthetic brines. In order to combat the problem of interferences present in many
oilfield produced brines, alternative detection techniques, for example the Hyamine
1622 approach,3 are often utilised in complex field produced brines. However,
such alternative techniques often respond in a similar manner to a variety of
polyelectrolytes, which may also be present at much higher concentrations in a
produced brine, possibly due to other treatment chemicals.
Requirement for Pre-Concentration of PPCA Inhibitors for Detectionby ICP'AES: As described above, ICP Spectroscopy has long been recognised
within the oilfield community as a very effective tool for monitoring ion
compositions in many different waters. It has also been used by a number of
laboratories to determine residual levels of phosphonate inhibitors in produced
waters based on the phosphorus content.3*6 Furthermore, until recently, it had not
been used effectively in order to monitor PPCA returns and, where it had been
applied, large errors have frequently been observed.6 More conventional time
consuming and sometimes unreliable wet chemical techniques are generally used.
In other words, the phosphorus content of the PPCA based inhibitors, although
very low, is not being fully exploited in terms of residual analysis.
The poor detection limits and accuracy of PPCA analysis using ICP-AES
techniques, when compared with those obtained for phosphonate inhibitors, is due
to the much lower phosphorus content. For example, 1 ppm active of DETPMP
contains ~ 270 ppb phosphorous whereas lppm active of a commonly applied
PPCA contains ~ 8 ppb phosphorus. This can be seen from the molecular
structures of the phosphonate and PPCA inhibitor species which are presented in
Figure 2. Therefore, considering manufacturers (ICP-AES) detection limits for
phosphorus, which are often quoted in the region of 40 ppb, it is not surprising that
low level PPCA analysis has previously been relatively poor when analysed directly
by ICP-AES instrumentation.
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Previous work from these laboratories, in collaboration with workers at Statoil,3
had illustrated how very effective detection and assay of phosphonate based
inhibitor species could be obtained in both synthetic and produced brines. The
accuracy of the detection and assay of such brines is demonstrated in Table 2.
However, such results are expected since several laboratories had been using ICP in
order to accurately detect residual levels of phosphonate inhibitor for many years.
In addition to the phosphonate (PH) analysis, relatively simple pre-treatment and
concentration procedures for PPCA based inhibitors were examined. This early
work showed that sample pre-treatment and concentration techniques using reverse
phase C18 (octadecylsilane, Si(CH3)3Ci8H37) chromatographic cartridges, based
strongly on procedures used routinely in PPCA wet chemical techniques, allows
very accurate PPCA analysis to be performed using conventional ICP instruments.
Table 3 presents the results obtained in this early work examining pre-treatment
techniques for PPCA analysis. Appendix 2 presents the techniques used in
previous work for the detection of PH and PPCA inhibitors using ICP
spectroscopy. These results (Tables 2 and 3) clearly demonstrate that ICP
spectroscopy is a very effective tool for monitoring both PH and PPCA based
inhibitors at threshold concentrations in both synthetic and field produced samples.
This result (obtained at the Statoil laboratories in Stavanger, Norway) lead to the
decision by both the OSRG at Heriot-Watt (Edinburgh) and Nalco/Exxon
(Aberdeen) to acquire an ICP instrument.
ICP-AES INSTRUMENT SELECTION/ASSESSMENT
With advances in ICP instrumentation, it was recognised that modern instruments
may be able to achieve significantly lower detection limits for phosphorus. Both
Nalco/Exxon and Heriot-Watt, independently assessed a number of new ICP-AES
spectrophotometers. This was performed by supplying several manufacturers with
blind samples of both PH and PPCA inhibitors in synthetic and produced brines.
For the PPCA inhibitors, samples were supplied to the instrument manufacturers in
both synthetic and produced brines. In this exercise, no pre-treatment (or
concentration) was performed. This was designed in order to test the ability of
modern instruments to detect the phosphorus content of the inhibitor at lower levels
than previously examined. Table 4 and 5 present the results obtained in the blind
samples prepared by both Heriot-Watt OSRG and Nalco-Exxon respectively, for
the PH and PPCA inhibitors. Samples were prepared for both PH and PPCA
inhibitor species in the following brines: Synthetic sea water, field produced Brent
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water, field produced Ula water and synthetic Ula water. Small volumes (< 20 ml)
of each sample were supplied to each ICP demonstrator for assay. In addition to
this, small volumes (again < 20 ml) of high and low standards were also supplied
for calibration purposes. The purpose of only supplying small volumes of sample
was to prevent the operators from calibrating in the different produced waters. This
would ensure that simple (synthetic) brines would have to be used for calibration
purposes.
Results and Discussion: Examination of Tables 4 and 5 illustrates that
acceptable assay of phosphonate based inhibitors is obtainable using either of the
instruments examined. However, in general, the results obtained were poorer than
those obtained in earlier work using an older ICP instrument (Table 2 and 3).3
However, this was not thought to be of any consequence since the instrument
operators were not provided with any information as to the origin of the samples
and the instruments would therefore have been optimised using different waters.
Analysis of the PPCA based inhibitor species in the different brines provides a
clearer indication as to the detection limits of modern ICP instruments. The main
technical result from this selection procedure was that either of the ICP instruments
examined could probably have detected the PPCA inhibitor when the machine was
fully optimised. This is because, for each instrument, a clear peak was obtained for
the high standard (20 ppm commercial PPCA - 42% active) when compared with
the background response.
EXPERIMENTAL STUDY
Since purchasing ICP-AES instruments in summer 1995, both Heriot-Watt and
Nalco/Exxon have worked closely in relation to optimisation of the ICP
instruments. Of particular interest,was the accuracy with which PPCA based
inhibitors could be detected at residual concentrations.
Analytical Line Selection and Calibration Standards: In the optimisationof an ICP -AES spectrophotometer, one of the main criteria for successful analysis
relates to the correct choice of the analytical line. For residual (ppm level) PH
analysis, where the actual concentration as P is relatively high (hundreds of ppb),
two separate analytical lines can be used for the low and high concentration regions
expected from a field return or core flood return. Neither of these lines show
significant interference from other ions commonly present in oilfield brines. In this
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respect, for phosphonate analysis in a variety of different brines, the following
analytical lines and calibration standards are now routinely used at both institutions.
Low concentration range
STD LOW 0 ppm PH (active) in appropriate synthetic brine
STD 1 5 ppm PH (active) in appropriate synthetic brine
STD 2 50 ppm PH (active) in appropriate synthetic brine
High concentration range
STD LOW 0 ppm PH (active) in appropriate synthetic brine
STD 1 50 ppm PH (active) in appropriate synthetic brine
STD 2 500 ppm PH (active) in appropriate synthetic brine
STD 3 2,500 ppm PH (active) in appropriate synthetic brine
Instrument Parameters
Make: Jobin Yvon (Instruments S.A.)
Model: JY 138 Ultrace ICP Optical Emission Spectrometer
Mode: Sequential
Analytical lines Phosphorous at 177.4 nm (Low range calibration)
Phosphorous at 214.9 nm (High range calibration)
However, for low level PPCA analysis, the 214.9 nm analytical line was shown to
be too insensitive to PPCA analysis, even at relatively high PPCA concentrations (=
50 -100 ppm PPCA). In order to combat this and to allow both high and low range
calibrations, the more sensitive analytical line is effectively measured over two
calibration ranges as described below. This is a particular advantage of ICP-AES
detection since the complete concentration range may be detected, without prior
dilution into the appropriate concentration range. For instance, the commonly
applied wet chemical Hyamine 1622 technique has a rather limited range in the
region 0 - 1 0 ppm (active) PPCA. Errors in dilution factors for unknown
concentration returns often lead to multiple analysis. By analysing directly using
ICP-AES with two calibration ranges, analytical ranges of the order 0 - 5,000 ppm
(or greater) are readily achieved.
Low concentration range
STD LOW 0 ppm PPCA (active) in appropriate synthetic brine
STD 1 5 ppm PPCA (active) in appropriate synthetic brine
STD 2 50 ppm PPCA (active) in appropriate synthetic brine
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High concentration range
STD LOW 0 ppm PPCA (active) in appropriate synthetic brine
STD 1 50 ppm PPCA (active) in appropriate synthetic brine
STD 2 500 ppm PPCA (active) in appropriate synthetic brine
STD 3 2,500 ppm PPCA (active) in appropriate synthetic brine
Instrument Parameters
Make: Jobin Yvon (Instruments S.A.)
Model: JY 138 Ultrace ICP Optical Emission Spectrometer
Mode: Sequential
Analytical lines Phosphorous at 177.4 nm (Low range calibration)
Phosphorous at 177.4 nm (High range calibration)
Instrument Set-up: Initial instrument optimisation for low level phosphorous
was performed using synthetic sea water. In order to detect the very low levels of
phosphorus present in residual PPCA samples, the procedure used differs from that
used for PH based inhibitors. For PH inhibitors, fast direct on peak analysis can be
used in order to provide very accurate assay.
However, for very low phosphorus levels, similar to those found in residual PPCA
solutions, this method proved ineffective at ppm PPCA concentrations since
background (noise) effects became significant. For PPCA assay, a gaussian type
analysis is used to capture the peak. The background correction point is then
selected close to the analytical peak at a point in the emission profile which is stable
and not affected by changes in the concentration of PPCA in the brine. Although
not fully described here, instrument optimisation to this level increases the time
taken per sample to nearly 10 minutes (some 4 times longer than required for a
single PH analysis). The procedures used are summarised in Appendix 3.
SAMPLE ANALYSIS -PPCA DETECTION IN SYNTHETIC BRINES
Synthetic Brines: This involved calibrating the ICP with ppm levels of a
commercial PPCA based inhibitor dissolved in synthetic sea water. A large number
of samples at known concentration were then successively introduced into the
instrument via an auto-sampler at varying concentrations. Table 6 shows the
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accuracy of very low level PPCA analysis in synthetic sea water by repeat analysis.
The results presented in Table 6 clearly show that ppb levels of phosphorus can be
assayed using modern ICP-AES instruments of this type.
Effect of Brine Composition: Following the success of detection of low level
PPCA analysis in synthetic sea water, the ability of the instrument to cope with very
high salinity brines was examined. In order to examine salinity effects, a high
salinity brine with a composition similar to that found in the Ula formation was
examined. This was important since very fine diameter glass nebulisers (Meinhart
nebulisers) are used in our instrument; these nebulisers must be able to cope with
high salinity oilfield brines without causing blockages. We note that the fine bore
"Meinhart" nebulisers used in these instruments do occasionally suffer from
blockages. However, with appropriate flushing between samples the problem can
be minimised and only occasional blockage occurs. The ionic composition of the
brines examined in this study are shown in Table 7. Internal calibrations using the
synthetic Ula type formation brine were then performed and repeat analysis
performed over a range of PPCA concentrations in a similar manner to that for
synthetic sea water, the results obtained are also presented in Table 6.
Synthetic Brines - Results and Discussion: Very good residual detection of
PPCA inhibitors has been achieved in both low salinity (sea water) and high salinity
(Ula formation water) brines. However, the brine salinity has been shown to
influence the results obtained quite dramatically. Pseudo calibration curves
(obtained by monitoring the intensity of the signal obtained in the different brines)
are plotted in Figure 3. This shows that a less sensitive response is obtained in the
high salinity brine. This is indicative of a suppression of the peak height caused by
the brine salinity. Calibration standards should therefore be matrix matched as close
as possible.
SAMPLE ANALYSIS - PPCA DETECTION IN PRODUCED BRINES
Following the results obtained in the synthetic brines, field produced waters were
examined. The results obtained from two produced brines will be presented in this
paper. These include one brine originating from Cormorant, a relatively low
salinity reservoir, and a second originating from Ula, a relatively high salinity
reservoir. Produced waters were collected in the normal manner from the field
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(sampled after the test separators). The samples were then filtered using analytical
grade filter paper prior to introduction into the ICP.
Cormorant Field Produced Water: When examining the accuracy of the
analysis of low concentration PPCA in this brine, instrument calibrations were
performed in synthetic sea water. A large number of samples of known
concentration were then examined following each calibration. The results of this
repeat analysis are presented in Table 8.
In addition to this, the effect of sample pre-treatment in order to reduce the levels of
dissolved organics was examined. This involved passing the produced brines
through C18 cartridges at neutral pH prior to introduction into the ICP. These
samples were then examined using synthetic sea water calibration curves. The use
of such techniques has been explained previously.3 Again, the results of this repeat
analysis are presented in Table 8. Examination of the results in Table 8 leads a
number of important results, as follows:
(i) Very accurate assay is obtained in field produced "Cormorant" water with
detection limits lower than 0.5 ppm.
(ii) Synthetic brines can readily be used for calibration purposes, with no
reduction in the accuracy obtained when using the same produced brine for
calibration purposes.
(iii) Sample pre-treatment using Cl 8 cartridges to reduce the level of dissolved
organics does not improve the accuracy of analysis.
(iv) Sample concentration techniques, as used previously to obtain very accurate
detection in field produced brines are no longer required when examining
PPCA residual
(iii) and (iv) combined implies that only minimal pre-treatment is required for
properly sampled field produced waters.
Via Field Produced Water: In more severe brines, calibration and subsequent
repeat analysis has been performed using matrix matched calibration standards. For
a sample of Ula produced water, sodium, calcium and magnesium analysis
indicated that the ionic composition of the sample obtained differed considerably
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from the synthetic Ula formation water examined above. Calibration standards
were made up in a matrix matched brine as described in Table 7 prior to analysis of
spiked samples.
Furthermore, in order to further examine the importance of matrix matching
calibration standards, the produced Ula water spiked samples were also analysed
based upon synthetic sea water and synthetic Ula water (as used previously). The
results of this examination are presented in Table 9. Clearly, very accurate analysis
is again achieved using appropriate synthetic brine standards.
Examination of the results in Table 9 shows the following:
(i) As for the lower salinity Cormorant produced water, very accurate PPCA
detection, down to - 0.5 ppm (active), is readily obtainable with minimal
sample pre-treatment using synthetic brine calibration curves.
(ii) As discussed above for synthetic brines, ionic matrix matching of calibration
standards is essential for accurate assay.
(iii) This field produced sample had a considerably lower salt concentration than
expected for 100% Ula formation brine. This meant that calibration in
synthetic Ula formation brine gave poor results. However, calibration in
synthetic sea water gave very similar (good) results to that in the matrix
matched synthetic brine. The conclusion here is that only approximate
matrix matching is required.
Blind Analysis Trial: A number of samples were prepared in a field produced
brine and analysed independently at both Heriot-Watt and Nalco/Exxon. Samples
were given to the particular analyst together with a small quantity of un-spiked brine
for determination of the brine background response. The brine used originated from
the Cormorant field operated by Shell UK from a well which had not been treated
for some considerable time due to its high water cut. It was therefore expected to
have minimal concentration of inhibitor present. The accuracy of the PPCA assay
recorded at the two institutions is presented in Table 10.
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Table 10 serves to confirm by "blind" inhibitor assay of pre-spiked samples that
very good levels of accuracy are obtainable for direct analysis of PPCA inhibitors in
produced brines using modern ICP instruments.
SUMMARY AND CONCLUSIONS
ICP spectrophotometers are widely recognised within the oilfield chemical
community as providing accurate detection tools for the major ions present in
oilfield brines. Furthermore, several laboratories have used ICP previously for the
detection of phosphonate based inhibitors in field produced brines. The results
reported in this paper re-affirm the use of ICP as a very accurate method for the
detection of PH inhibitors.
Due to the very low phosphorus content in PPCA based inhibitors, ICP had not,
until recently, been used effectively to detect residual levels of PPCA inhibitors
without extensive pretreatment. Techniques examined in this paper from previous
work in this area show that simple sample pre-treatment techniques can be applied
to oilfield brines to allow very accurate detection. Furthermore, with modern ICP-
AES instrumentation, PPCA based inhibitors can be analysed very accurately at the
sub ppm level without the requirement for sample concentration techniques. Very
accurate analysis of PPCA based inhibitor is possible at levels as low as 0.5 ppm (±
0.2 ppm) in field produced brines. In order to obtain such very low level detection
of these inhibitor species there was no sample pre-treatment used, other than
filtration to remove particulates. This is a particular advantage over more
conventional wet chemical techniques where extensive, time consuming pre-
treatment procedures may be required. This extends the range of chemical species,
present in oilfield produced brines, which may be detected using high throughput,
automated ICP based procedures.
However, ICP-AES does not address one major issue on the determination of
inhibitor returns. ICP is a laboratory based procedure which could not be deployed
on site. This means that, as with all laboratory based assay, samples have to be
transported to the laboratory. Although as described earlier, sample pre-treatment
prior to ICP analysis is minimal, this does not infer that sample re-conditioning or
sample stabilisation prior to analysis is not an issue. The OSRG have addressed
some aspects of this matter but more work is required in this area.
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REFERENCES
1. Sorbie, K.S., Yuan, M.D., Graham, G.M. and Todd, A.C.: "Appropriate
Laboratory Evaluation of Oilfield Scale Inhibitors", Presented at the
conference Advances in Solving Oilfield Scaling Problems, Organised by
IBC Ltd, Marriott Hotel, Dyce, Aberdeen, 7-8 October 1992.
2. Graham, G.M., Sorbie, K.S. and Boak, L.S.: "Development and Accurate
Assay Techniques for Poly-Vinyl Sulphonate (PVS) and Sulphonated C0-
Polymer (VS-Co) Oilfield Scale Inhibitor", Presented at the NIF 6th Int.
Symp. Oil Field Chemicals, held in Geilo, Norway, 19 - 22 March, 1995.
3 Graham G. M., Sorbie, K.S., Boak, L.S., Taylor, K. and Blilie, L.:
"Development and application of Accurate Detection and Assay Techniques
for Oilfield Scale Inhibitors in Produced Water Samples", SPE 28997,
Presented at the SPE Int. Symposium on Oilfield Chemistry, held in San
Antonio, TX. 14-17 February, 1995.
4. Graham, G.M. (Editor),: OSRG Laboratory Procedures Manual, Version 2.0,
Chapters 5 and 6, Department of Petroleum Engineering, Heriot-Watt
University, Edinburgh, UK, September 1995.
5. Kan, A.T., Varughese, K. and Tomson, M.D.: "Determination of Low
Concentrations of Phosphonates in Brines", SPE 210067, presented at the
SPE international Symposium on Oilfield chemistry, Anaheim, CA, 20-22
February 1991.
6. Taylor K.: Shell UK Exploration and Production, Aberdeen, UK,: "Round
Robin on Scale Inhibitor Analysis (conducted may 1994)" to be published.
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Appendix 1: Wet-Chemical Phosphonate Analysis
u.v. detection in Produced Formation Waters(1) Dilute the inhibitor solution to the range 0 - 4 ppm active.(2) Filter the samples under gravity using analytical grade filter paper(3) Pass approx. 30 ml of this solution through a prepared Sep Pak C18
cartridge at supplied pH, discard the initial 1-2 ml of eluent and collect theremainder
(4) Pipette 20 ml of the collected eluent into a thick walled glass(5) To this solution add 2 ml of a 20,000 ppm solution of PVS and mix with a
powder pillow of potassium persulphate (Powder Pillow 1).(6) Expose the solution to short wave u.v. (254 run) for 10 minutes.(7) Allow the solution to cool to room temperature in a water bath over 1 hour
then add 5 ml of the sulphate free mixed reagent solution* (MRS) and shakevigorously.
(8) Leave the solution for exactly 2 minutes (or exactly 5 minutes).(9) Place in an optical cell with a 2 cm path length.(10) Use a spectrophotometer to measure the absorbance at 890 nm.(11) Determine the phosphonate concentration in the particular sample using a
previously determined calibration curve.
* The mixed reagent solution, MRS, is made up as follows:(A) Nitric acid solution, (430ml of distilled water to which 70ml of concentrated
Nitric acid is diluted)(B) Ammonium molybdate solution, 4% wt/vol (4.00 diluted to 100ml with
distilled water)(C) Ascorbic acid solution, 0.1M, (1.760g diluted to 100ml with distilled water)(D) Potassium Antimonyl tartrate, lmg Sb/ml (0.2743g diluted to 100ml with
distilled water)MRS is then composed of solutions A:B:C:D mixed in the ratio 50:15:30:5.
Nitric acid detection in Produced Formation Waters(1) Dilute the inhibitor solution to the range 0 - 4 ppm active.(2) Filter the samples under gravity using analytical grade filter paper(3) Pass approx. 30 ml of this solution through a prepared Sep Pak C18
cartridge at supplied pH, discard the initial 1-2 ml of eluent and collect theremainder
(4) Pipette 20 ml of the collected eluent into 50 ml Pyrex conical flasks(5) Add 3ml of Nitric Acid soltution (20 % in distilled water) followed by 1.5 ml
of Potassium Permanganate solution (0.2 N in distilled water)(6) Boil the solutions carefully (not vigorous) in a fume cupboard over 45
minutes.(7) Allow the solution to cool to room temperature (e.g. in a water bath over 1
hour)(9) Add Ascorbic acid solution (1.76 g in 100ml distilled water) dropwise to
clarify (if required).(8) Neutralise (to pH ~ 7) with aqueous NaOH.(9) Make up to exactly 20 ml (volumetric flask)(10) Add 5 ml of the sulphate free mixed reagent solution* (MRS) and shake
vigorously.(11) Leave the solution for exactly 2 minutes.(12) Place in an optical cell with a 2 cm path length.(13) Use a spectrophotometer to measure the absorbance at 890 nm.(14) Determine the phosphonate concentration in the particular sample using a
previously determined calibration curve.
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Appendix 2: ICP Spectroscopy - Initial study, Tables 2 and 3
ICP spectrophotometer specifications:
Instrument Thermal Jarrel Ash: Atom Scan 25Laboratory Statoil
Production Chemistry Laboratories,Stavanger, Norway.
Element PhosphorusWavelength 177.499nm
Procedure for the detection of Phosphonate inhibitors in syntheticand produced brines
(1) Dilute the inhibitor solution to the appropriate concentration range (0-15ppmDequest 2060 in this case)
(2) Prepare a low and a high concentration standard (0 and 15ppm Dequest 2060in this case) in the same brine matrix
(3) Filter the samples under gravity using analytical grade filter paper(4) Pass approx. 30 ml of this solution through a prepared Sep Pak C18
cartridge at supplied pH, (pH>7) discard the initial 1-2 ml of eluent andcollect the remainder.
(5) Construct the internal calibration by analysing the prepared standards in theICP spectrophotometer at 177.499nm
(6) Determine the sample inhibitor concentration by ICP.
Note: For synthetic waters, steps 3 and 4 are omitted.
Procedure for the detection of PPCA inhibitors in synthetic andproduced brines
(1) Dilute the inhibitor solution to the appropriate concentration range (0-50ppmBellasol S40 in this case)
(2) Prepare a low and a high concentration standard (0 and 50ppm Bellasol S40in this case) in the same brine matrix
(3) Filter the samples under gravity using analytical grade filter paper(4) Pass 200 ml of these prepared samples and standard separately through
prepared Sep Pak C18 cartridges at supplied pH, (pH>7) collecting theeluent. Several cartridges should be used per sample at this stage to avoidoverloading, in this case 4 cartridges were used but this may be excessive.
(5) Adjust the pH of the eluent to pH 1.8-2.0 by dropwise addition of 10%HCl(aq)
(6) Pass this solution through a freshly prepared C18 cartridge to adsorb theinhibitor and discard the eluent.
(7) Pass 10ml distilled water through the cartridge from the same end.(8) Invert the cartridge and elute the inhibitor with 4ml 0.1N NaOH(aq) and
collect the eluent.(9) Dilute this collected eluent to exactly 5ml with distilled water
Note; the concentration factor is now 200ml - 5ml, equivalent to a concentrationfactor x40
(10) Construct the internal calibration by analysing the prepared standards in theICP spectrophotometer at 177.499nm
(11) Determine the sample inhibitor concentration by ICP.
Note: For synthetic waters, steps 3 and 4 are omitted.
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Appendix 3 ICP Spectroscopy - Current study
Phosphonate analysis in produced waters
(1) Prepare calibration standards in appropriate synthetic brine(2) Filter samples through analytical grade filter paper(3) Set up appropriate instrument parameters for PH analysis(4) Run calibration standards followed by samples directly into ICP-AES
Instrument ParametersMake: Jobin Yvon (Instruments S.A.)Model: JY 138 Ultrace ICP Optical Emission SpectrometerMode: SequentialAnalytical lines Phosphorous at 177.4 nm (Low range calibration)
Phosphorous at 214.9 nm (High range calibration)
Low concentration rangeSTD LOW 0 ppm PH (active) in appropriate synthetic brineSTD 1 5 ppm PH (active) in appropriate synthetic brineSTD 2 50 ppm PH (active) in appropriate synthetic brine
High concentration rangeSTD LOW 0 ppm PH (active) in appropriate synthetic brineSTD 1 50 ppm PH (active) in appropriate synthetic brineSTD 2 500 ppm PH (active) in appropriate synthetic brineSTD 3 2,500 ppm PH (active) in appropriate synthetic brine
PPCA analysis in produced waters
(1) Prepare calibration standards in appropriate synthetic brine(2) Filter samples through analytical grade filter paper(3) Set up appropriate instrument parameters for PPCA analysis(4) Run calibration standards followed by samples directly into ICP-AES
Instrument ParametersMake: Jobin Yvon (Instruments S.A.)Model: JY 138 Ultrace ICP Optical Emission SpectrometerMode: SequentialAnalytical lines Phosphorous at 177.4 nm (Low range calibration)
Phosphorous at 177.4 nm (High range calibration)
Low concentration rangeSTD LOW 0 ppm PPCA (active) in appropriate synthetic brineSTD 1 5 ppm PPCA (active) in appropriate synthetic brineSTD 2 50 ppm PPCA (active) in appropriate synthetic brine
High concentration rangeSTD LOW 0 ppm PPCA (active) in appropriate synthetic brineSTD 1 50 ppm PPCA (active) in appropriate synthetic brineSTD 2 500 ppm PPCA (active) in appropriate synthetic brineSTD 3 2,500 ppm PPCA (active) in appropriate synthetic brine
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Figure 1 Comparative calibration curnes obtained using theu.v. detection method with the Nitric detection methodin "difficult" field produced brine.
51
4"
0.5 1.0Absorbance 890 nm
1.5
Figure 2 Molecular Structures of the penta-phosphonate (DETPMP) andphosphino-polycarboxylate (PPCA) inhibitors examined in thissection.
H—UCH
fcoOH m OH
CHj CH—j-H
COOH
PPCA, (Mol. Wt.~ 3,600g/mol)
O
H O - P - C H 2
oCH2—P-OH
_ NCHJCH 2 NCH 2 CH 2 N
|H \ H 2 X
H O — P — O HIIO
Penta-phosphonate (DETPMP)
Figure 3 Pseudo calibration curves obtained from the signalintensity vs. [PPCA] recorded for different brines on ICP.
6000
13 5000-
100 200 300 400 500[PPCA] (active ppm)
600
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Table 1 Stability of the "u.v. digestion technique" (u.v.) compared to the"Nitric acid detection technique" (Nitric) for the detection of PH indifficult produced brines.
Absorbance (890 nm) with time
[PH]*(active) Method 2min 5min lOmin 20min
0123401234
u.v.u.v.u.v.u.v.u.v.
NitricNitricNitricNitricNitric
0.3450.4490.6130.7710.9610.1280.4220.7161.0091.282
0.6920.7600.8791.0031.1770.1440.4407321.0251.274
1.1041.1291.1921.2591.4290.1640.4650.7501..0401.256
0.1970.5120.7791.0501.243
Table 2: ICP analysis of PH, DETPMP (as Dequest 2060; 55% active) insynthetic sea water and produced waters C and D, C => BrentCharlie (ex. Shell) and D => North Alwyn (ex Total).
Known [inhibitor] ppm Determined [inhibitor] ppm 4 repeats per sampleDequest 2060 Active Dequest 2060 Active SDev %RSD
Synthetic sea water0.000.000.001.001.001.005.005.00
0.000.000.001.001.001.005.005.00
0.000.000.001.001.001.005.005.00
0.000.000.000.550.550.552.752.75
Produced0.000.000.000.550.550.552.752.75
Produced0.000.000.000.550.550.552.752.75
-0.070.21-0.020.880.901.125.024.90
Water C0.040.020.041.111.051.134.434.16
Water D0.050.000.000.730.930.874.494.60
-0.040.11-0.010.480.490.612.762.69
0.020.010.020.610.580.622.432.29
0.030.000.000.400.510.482.472.53
0.100.070.060.080.080.040.190.09
0.030.080.110.110.090.060.120.07
0.170.080.090.140.040.120.210.07
137.9032.67
234.408.678.783.723.851.91
70.84318.40307.709.788.405.412.711.59
365.00174.40701.3019.344.0014.314.651.49
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Table 3 ICP analysis of PPCA (as Bellasol S40; 42%active) in synthetic seawater and produced waters C => Brent Charlie (ex. Shell) and D =>North Alwyn (ex Total).
Known [inhibitor] ppmBellasol S40 Active
Determined [inhibitor] ppmBellasol S40 Active
4 repeats per sampleSDev %RSD
Synthetic sea water0.002.002.005.005.00
0.002.002.005.005.00
0.002.002.005.005.00
0.000.840.842.102.10
Produced0.000.840.842.102.10
Produced0.000.840.842.102.10
0.031.851.855.014.95
Water C0.032.262.245.035.04
Water D0.032.012.025.025.00
0.010.780.782.112.08
0.010.950.942.112.12
0.010.840.852.112.10
0.030.050.030.030.06
0.030.040.050.060.06
0.040.040.040.070.12
126.102.591.730.531.29
129.703.872.001.091.25
145.701.961.911.362.43
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Table 4
i.
Known[PH]ppm
0.000.701.805.3015.60
u.KnownPHJpptn
0.000.701.805.3015.60
III.
KnownPHlppm
0.000.701.805.3015.60
Nota:
Table 5
KnownPH]ppm
2.005.0010.0020.0050.00
u.KnownPHJppm
2.005.0010.0020.0050.00
Ul.
KnownPH]ppm
2.005.0010.0020.0050.00
Iota:
Spiked sample determinations during selection- OSRG prepared samples
Results delei wined by uuuument -Determine [PHI
UlaP.W.< blank
0.631.825.4715.65
Brent P.W.0.030.981.865.5015.07
ppmSAW.<bUnk
0.832.165.69
-
Results determined by instrument -Determine [PH]
Ula P.W.
--
Brent P.W.
--
--
ppmSAW.
-----
Results detenniDed by instninmt -Determine [PH] ppm
UlaP.W.
-----
Brent P.W.213.6 am
0.08< blank< blank
0.2013.61
177.4nm-0.57
< blank< blank
1.9512.63
All samples prepared as active inhi
1
2
3
SAW.
-----
Known[PPCA] ppm
0.001.302.405.2014.70
Known[PPCA] ppm
0.001.302.405.2014.70
DeterUlaP.W.
< blank< blank
1.183.4412.88
DeterUlaP.W.(Bk + 2 stds)
<Mank1.023.075.0214.10
Known!PPCA)ppm
0.001.302.405.2014.70
nine [PPCABrent P.W.
0.321.793.145.6815.89
ppmSAW.
< blank3.43972.425.1814.67
mine [PPCA] ppmBrent P.W.(Bk +1 std)
0.400.240.792.9814.17
DeterUlaP.W.UAN.
21?-0.812.153.5912.90
rilor (i.e. PPCA - 42* active. PH - 50% Active).All samples prepared in filtered brine. |"Brent - treat" refers to pre-treated samples viz - clean up and concentration • 5.All samples analysed using Phosphorous line at - 177.4 nm.Varian also examined Phosphorous line at -213.6 nm.Generally only blank and 1 standard (20ppm) used. Were 2 sub indicated a 5.2 ppm staiU S N. indicates the use of Ultra-sonic nebuliser. However this causedadditional problems due to blockages and was replaced with standard type
Spiked sample determinations during selection- Nalco/Exxon prepared samples
Results determined by instrument -Determine [PH]
Ula P.W.2.0]5.009.9019.5648.05
Brent P.W.2.245.259.84
20.0246.91
ipmSAW.
2.155.159.83
20.1348.02
Results determined by instrument -Determine [PH]
UlaP.W.
2.024.869.4818.2244.79
Brent P.W.
2.455.3910.5819.4246.67
PP»SAW.
2.165.179.9819.6247.18
tesults determined by instrument -Determine [PH]
UlaP.W.
3.036.1113.0815.0640.24
Brent P.W.213.6 nm
2.775.8310.3022.1152.35
ppmSAW.
2.48< blank10.1123.1872.70
1
2
3
Known[PPCAlppm
2.005.0010.0020.0050.00
Known[PPCAlppm
2.005.0010.0020.0050.00
Known[PPCA] ppm
2.005.0010.0020.0050.00
All samples prepared as supplied (commercial PH and PFCAll samples prepared in UD-filtered brine.All samples analysed as supplied except for * below* Samples analysed after initial visit were filteredtarooles analysed usim bv JY *ivi 'lhenno Electron assayc
Varian examined Phosphorous Hne at -213.6 am.ilank and 1 standard (20ppm) used for calibration.
DeterUlaP.W.
3.426.9311.3221.8248.00
DeterUlaP.W.
<btank< Nank13.3820.1444.81
DeterUlaP.W.
1.184.849.5619.0643.21
A).
i Phosphorous
lebuliser.
mine (PPCABrent P.W.
2.052.2610.8719.6750.87
Btme[PPCABrent P.W.
< blank< blank11.5619.6944.34
nine [PPCABrent P.W.
< blank<Uank<blank22.1952.82
meat-177.4
SAW.(Bk + 1 std)
0.105.514.986.9515.28
Brent-treat< blank
1.022.244.0513.75
mme [PPCA] ppmBrent P.W.
idardwasals
PP»SAW.
2.025.059.7145.1019.90
PP»SAW.
-<Mank< blank19.0346.67
ppmSAW.213.6 am
2.586.6111.8322.575335
nm.
SAW. (Bk +1 std)213.6nni
-5.430.773.51-7.42-3.87
0 included.
Known[PPCA]ppi
2.005.0010.0020.0050.00
177.4un-6.59-2.107.34
-13.78-4.76
SAW. (Bk +lT7.4nm
-1.31
6.6614.65
std)
•Results Obtained After WittDetermine [PPCA] ppm
UlaP.W.
2.384.9010.47
-47 JO
Brent P.W.
2.125.3610.0819.6650.61
SAW.
2.015.339.816.9550.68
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Table 6: Repeat analysis of PPCA in Synthetic Brines
(1) Synthetic seaKnown [PPCA]
active ppm0.50.5
22
5555
5050
500500
waterDeterminedactive ppm
0.6180.653
1.971.76
4.594.564.844.69
47.8647.86
500.06498.06
mean*0.64
1.87
4.57
4.77
47.86
499.06
(i) Synthetic Ula F.W.
mean of 2 readings
Known [PPCA]active ppm
0.50.50.50.5
2222
5555
50505050
500500500500
Determinedactive ppm
0.720.560.620.16
1.972.082.041.93
4.574.844.784.66
50.0449.8449.0649.06
501.24506.24506.26506.26
mean*0.36
0.39
2.02
1.99
4.70
4.72
49.94
49.06
503.74
506.26
Table 7: Compositions of the brines used in this work.
Ion
Na+
Ca2+
M g 2 +
K+
Sr2+
Ba2+
SO42-
ci-
sw(ppm)
10,890
428
1,368
460
2,960
19,766
UlaFW(ppm)
52,225
34,675
2,249
3,507
1,157
91—
153,000
Cormorant1"(ppm)
6,350
145
25
140
25
20
10,400
Matrix match (Ula)(ppm)
16,000
6,500
600
* % SW in produced cormorant sample examined >70%
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Table 8: ICP Analysis of PPCA using a Synthetic Seawater CalibrationSamples in Cormorant Produced Water,With and without C18 pre-treatment
Known [PPCA]active ppm
0.50.5
22
55
50505050
No C18 pre-treatmentDeterminedactive ppm
0.560.65
2.152.11
5.635.60
54.0057.1454.3156.10
mean*0.60
2.13
5.61
55.57
55.20
Cl 8 pre-treatmentDeterminedactive ppm
0.790.78
2.602.39
5.545.68
54.4355.9753.8958.05
mean*0.78
2.50
5.61
55.20
55.97
* mean of two readings
Note 1: Instrument drifts leads to higher concentrations recorded.This can be corrected for by incorporating standard corrections in instrument set up
Note 2: Brine contained residual phosphorous signal equivalent to - 1 ppm PPCA.This was corrected for in above results
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Table 9: ICP analysis of PPCA in produced Ula water.Calibrations in synthetic sea water, syntheticUla formation water andsynthetic Matrix matched brine (Ca, Na and Mg content determined by ICP)
(i) Synthetic SW calibrationKnown [PPCA]
active ppm00
0.50.5
22
55
5050
Determinedppm-0.100.01
0.530.50
2.062.09
5.095.30
54.5151.94
mean-0.04
0.52
2.08
5.19
53.22
(iii) Synthetic Matrix matched calibrationKnown [PPCA]
active ppm00
0.50.5
22
55
5050
Determinedppm0.100.05
0.420.54
2.041.96
5.294.85
52.5752.67
mean0.08
0.48
2.00
5.07
52.62
(ii) Synthetic Ula FW calibrationKnown [PPCA]
active ppm00
0.50.5
22
55
5050
Determinedppm-0.120.05
0.371.44
3.393.46
11.1810.96
90.3888.35
mean-0.03
0.91
3.43
11.07
89.36
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Table 10:
Unknown SampleIJ>.
1715
3414
6812
51113
2910
Analysis of spiked Cormorant samplesUsing conunercial PPCA (17% active) Calibration standards in synthetic sea waterIndependent analysis by 2 laboratories (denoted A and B) using ICP-AES
Spiked [PPCA][as supplied]
0.000.000.00
2.502.502.50
9.509.509.50
20.0020.0020.00
725.00725.00725.00
[active]
0.000.000.00
0.430.430.43
1.621.621.62
3.403.403.40
123.25123.25123.25
A[as supplied]
ppm0.660.840.7
3.092.741.89
10.3611.59.35
23.3720.6720.85
799.33837.76836.73
A[as supplied]
mean0.73
2.57
10.40
21.63
824.61
Recorded concentrationsA
[active]mean0.12
0.44
1.77
3.68
140.18
B[as supplied]
ppm0.200.000.10
1.501.30
7.808.707.20
18.90
17.20
758.60
B[as supplied]
mean0.10
1.40
7.90
18.05
758.60
B[active]mean0.02
0.24
1.34
3.07
128.96