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

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

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

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.

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

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

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

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

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

(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

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.

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.

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.

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.

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.

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

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

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

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

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

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%

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

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

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