DEVELOPMENTS IN THE LABORATORY EVALUATION OF CORROSION INHIBITORS: A REVIEW

Adelina J. Son, Ph.D Champion Technologies

P.O. Box 450499 Houston, Texas 77245-0499

ABSTRACT Numerous laboratory methods have been developed to evaluate the concentration of various corrosion inhibitors in oil and gas production fluids. The laboratory evaluation, often referred to as residual analysis, provides quick monitoring of the adequacy of treatment levels of corrosion inhibitors in different applications, time of dispersion or travel through fluids as well as efficiency of the inhibitor. The review will discuss procedures, varying from the simple wet techniques to the sophisticated and expensive instrumental procedures, from bulk analysis to specie-specific techniques. Establishing mass balance using analytical techniques with batch samples of corrosion inhibitors as standards can be tricky. Factors such as partitioning, chemical reactions with other chemical species, adsorption onto solids, solubility changes, etc. must be understood and considered in the calculations. The utility and applicability of the methods will be compared with respect to cost and ease of setup, range of applications, selectivity, accuracy, detection limit, reproducibility and limitations. The review will include analysis of the industry needs and challenges facing the researchers developing new procedures. Keywords: analysis of corrosion inhibitors, review of methods, determination of imidazolines, quaternary amines, phosphonates in production waters, spectroscopy, solid phase extraction, chromatography, surface analysis

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INTRODUCTION This review is a compilation from the open literature and covers the most useful laboratory and field methodologies pertaining to the measurement of corrosion inhibitors in oilfield-related samples. To the analysts, who are new to the field of corrosion inhibitor analysis, the review can serve as an introduction and a guide to the subject. To the experienced chemists, it points out the current limitations and may inspire some needed innovations. The review is concentrated on the phase of the oilfield industry that uses the most corrosion inhibitors, i.e. production and transportation of produced fluids. However, the methods reviewed are also applicable to the drilling and refining areas. Some reference to the chemistry of the sample involved is presented to understand rationale behind the choice of methods and allow improvements to be put in place, as the analyst sees fit. A few methods for characterization of phosphonates are included because phosphonates are components in some corrosion inhibitor formulations. Why is accurate determination of the concentration of corrosion inhibitors important?

1. Residual corrosion inhibitor analysis confirms adequate inhibitor transport and protection in operations related to drilling, production, plant processing, transmission through pipelines and refining.

2. Effectiveness of the inhibition programs is generally monitored by corrosion probes, coupons and increases in the iron content of the water1,2. In the absence of an effective monitoring program, residual inhibitor analysis guides adjustment of treatment levels to prevent corrosion problems and expensive hardware replacements. For example, a tubing failure occurred in an offshore production system in Northern North Sea. Residual analysis showed the absence of inhibitor. The cause was poor location of the inhibitor injection nozzle3.

3. In some locations, corrosion control programs are linked to set inhibitor concentrations. The operator mandates constant monitoring and adjustment of the inhibitor concentration to the predefined value. Such practice has resulted in lower cost of treatment and generally less hardware and maintenance problems.

4. Government regulations set allowable chemical discharge levels for oilfield chemicals due to concern over adverse biological effects. Accurate determination of residual inhibitor concentrations in water and solids for disposal is required to ensure that they are within safe levels for discharge, particularly in environmentally sensitive areas (North Sea, Gulf of Mexico, etc.). In the U.S., monitoring is a responsibility of the Materials Management Service (MMS). In the North Sea, regulations are defined by the Oslo and Paris Commission (OSPAR) Harmonized Mandatory Control Scheme (HMCS). Chemical usage and discharge are regulated according to the hazard quotients calculated by the Chemical Hazard Assessment and Risk Management (CHARM) model. Chemical companies are required to submit an estimation of fraction released to the Centre of Environment, Fisheries and Aquaculture Science (CEFAS), Burnham-on-Crouch, England as part of the HMCS submissions. Theoretical calculations are often not backed by actual data due to lack of suitable analytical techniques to assay the discharges4.

5. Multiphase systems, where condensation of water and/or hydrocarbon occurs, are difficult to treat. Conventional treatment is based on the gas volumes where what is really needed is treatment based on the liquid phase volumes5. Corrosion inhibitor measurements can complement multiphase modeling for systems where condensation occurs for improved corrosion control.

Corrosion inhibitors in the oilfield industry are usually complex mixtures, which present difficulties in analyzing for concentrations of the inhibitors in oilfield waters. The film-forming components of the corrosion inhibitors are mixed with surfactants and solvents to control

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dispersion, flow properties and prevent emulsion problems6. Some of the components of corrosion inhibitors are shown in Figure 1. Many corrosion inhibitors are formulated with 2 or more of these components: quaternary amines, amides, imidazolines, phosphate esters and surfactants7,8. Quaternary ammonium compounds (quats) are of particular interest because they function as surfactants, corrosion inhibitors and biocides in the petroleum and gas production industry. Many of the published residual techniques were developed for quats and are now routinely applied in analysis of samples. The corrosion inhibitor concentration is calculated based on the quat content. In addition to the complex chemical environment, partitioning of the components to the different phases and adsorption on the metal occur. This results in low concentrations of the chemical specie(s) in the monitored phase. In developing analytical methods, it is important to understand not only the chemistry of the inhibitor and the chemical environment but also physical properties such as solubility and partitioning behavior. The aqueous phase is the more commonly monitored phase. The active ingredients of water-soluble or water dispersible corrosion inhibitors partition to the water which tends to migrate toward the oil/water interface. The location of the sampling point can be critical, particularly if the objective is to be able to relate corrosion inhibitor concentrations to corrosion protection. Current analytical techniques can monitor one or more of the components. The utility of a procedure depends on the accuracy, speed, sensitivity, selectivity and precision of the method9. This is a lofty demand considering that many treating chemicals are combination of corrosion inhibitors, emulsion breakers, scale inhibitors and other surface-active agents. The requirements to qualify as a good method are serious challenges to chemists who need to work with difficult and constantly changing matrix interferences in oilfield samples. The accuracy of any analytical investigation is also dependent on the sample integrity. Acidizing of field samples is commonly done to prevent formation of insoluble iron compounds and other solids and potential loss of corrosion inhibitors through adsorption. Matrix matching eliminates or minimizes interferences present in the sample. The practice can be critical when employing certain spectroscopic techniques. The choice of analytical technique depends on many factors. Ideally, the analysis is carried out as close to the lease or treatment facilities as possible. The burden and the challenge, then fall on the district laboratories for decision on what method to use, based on the number of samples, the technical experience of personnel and available equipment. Most district laboratories use titration and UV-Visible spectroscopic methods, which use simple low cost equipment. Procedures, which are more sophisticated, have been reported and are useful for problem solving associated with large and critical accounts and to meet government and environmental regulations. Some require expensive equipment and well-trained personnel who are typically available only in the companys main analytical laboratories.

VISIBLE SPECTROSCOPY Analytical techniques, which are based on development of colors (methyl orange, bromophenol blue, bromocresol purple), are run routinely in many laboratories because they are easy and inexpensive to set-up and can be run by personnel with minimal training. In the oilfield industry, they are commonly referred to as Dye Transfer methods. In general, these methods lack specificity, sensitivity and are prone to interferences, including matrix interference. Common interferents are polar organic compounds from crude oil and other chemicals, some of which exist in higher concentrations relative to the corrosion inhibitor. With training and

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experience, many analysts are able to overcome the difficulties and report accurate and precise data. The use of chloroform with the bromocresol purple and methyl orange extraction techniques presents safety concerns for the analysts. Toluene, used with the bromophenol blue extraction method, is a less toxic solvent. Dye transfer methods are based on the reaction of cationic surface-active agents with the basic form of many dyes to form salts or complexes10. Skadhauge and Fogh11,12 discovered the reaction of quats with bromocresol purple forming a blue complex and led to the development of an analytical method for quantitative analysis of quaternary ammonium compounds. In the procedure, the inhibitor/dye complexes, are extracted with solvents and monitored by Visible Spectrophotometry at 620 nm to read the absorbance. The bromocresol purple complex formation has been used extensively in the oilfield for determination of quaternary ammonium compounds in corrosion inhibitors9,13,14,15. Figure 2 shows spectra for bromocresol purple complexes for a set of corrosion inhibitor standards. The linear range achieved in the analysis depends on the corrosion inhibitor blend. Fortenberry et. al.16 utilized the methyl orange dye transfer method to analyze field brine samples. Limitations with this dye-extraction technique included interferences from other treating chemicals present in the brine sample and adsorption of the quaternary amine/dye complex onto the glass container. Lower than expected concentrations were measured, based on treating rates. This was attributed to loss of the quat to clays, scales and iron precipitates and partitioning processes. Another dye extraction method uses bromophenol blue as complexing agent17,18. The complex is non-polar and can be extracted from the aqueous phase (brine) using toluene. Absorbance of the blue complex is read at 600 nm. In all the dye extraction techniques, matrix interference is a big problem. Matrix matching by preparing the standards in clean untreated brines similar to the sample matrix minimizes this problem. Synthetic brines of the same composition maybe substituted if there is difficulty in obtaining sufficient volumes of untreated field brines. In situations where synthetic brines of similar composition are not available, matching the chloride content of the water used to prepare the standards with the chloride content of the sample(s) improves accuracy. Error is reduced, but not completely eliminated14. A brief description of the procedures is found in Appendix A. Another acceptable analysis is the phosphomolybdenum blue method for phosphates, phosphonates and phosphate esters19,20. Phosphonates and phosphate esters are used as scale and corrosion inhibitors and are known to form synergistic mixtures with other components of corrosion inhibitor formulations7,8. The procedure involves: a) digestion of the sample with sodium or potassium persulfate to convert all the P-containing compounds to orthophosphates, b) treatment with molybdate solution which converts the orthophosphates to a yellow complex of phosphomolybdic acid (PO3Mo12O36)21, c) reduction with ascorbic acid or stannous chloride to the blue complex, and d) analysis at 650 700 nm. In the field labs, Hach kits are used quite extensively due to the convenience of having pre-weighed reagents. Kan et. al.20 modified the classic colorimetric technique for phosphonate with the use of a pressure cooker for the persulfate digestion. Methyl isobutyl ketone (MIBK)/cyclohexane solvent extracts the phosphomolybdate complex before reducing with stannous chloride to the phosphomolybdenum blue complex. The modification resulted in detection limits of 0.1 mg/L and improved accuracy. The MIBK/cyclohexane solvent eliminated the common interferences to the orthophosphate determination.

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STATIC ULTRAVIOLET SPECTROSCOPY

Izawa22 used ultraviolet spectroscopy to characterize surface-active agents and published the wavelength of maximum absorption of cationic surfactants including alkylpyridinium halides (max = 259.5 nm) and alkylbenzyldimethylammonium chloride (max = 263 nm), two commonly used components of water-soluble corrosion inhibitors. Fortenberry et. al. 16 used UV absorbance at 260 - 280 nm to analyze brines from six pipelines from various areas in the U.S. treated with water-based corrosion inhibitors. The same samples were analyzed using the methyl orange extraction method. Relative to the dye extraction technique, UV spectroscopy was found to be more accurate, sample preparation was much simpler and interferences were overcome using the spectra subtraction feature of the UV spectrometer software. The UV calibration curve was linear over a much wider range of concentration (350 ppm) compared to the dye extraction method (50 ppm). UV spectroscopy was employed for monitoring residual corrosion inhibitors in a pipeline and also for a number of leases in Alberta, Canada. The presence of other treating chemicals and the high salinity (some close to saturation with inorganic salts) of the brines, which changed with time, challenged the skills of the analytical chemists14. The chemists realized that solubility and partitioning characteristics of the corrosion inhibitor change with the salinity of the water and remedial measures were put in place. This included multiple and frequent sampling, information on the production volumes (oil and water), calibration curves with matched matrices and standards bracketing. A dynamic chart for each location showed the trend and indicated when adjustment of inhibitor level was necessary. Lab data in the running chart were corrected for partitioning. A description of the procedure is found in Appendix B. STATIC FLUORESCENCE SPECTROSCOPY

Quaternary amines fluoresce and are easily detected in low concentrations2. Fluorescence is a more selective technique, requiring the use of two wavelengths (excitation and emission). It is more sensitive compared to the UV method. The fluorescence method is equally simple to set up but with improved accuracy over UV analysis. For quats, the procedures consist or separating the oil phase from the brine, filtration of the brine phase, dilution as needed and reading the fluorescence intensity with 325 nm as excitation wavelength and 400 nm as emission wavelength9. Analysis for imidazolines or amidoimidazolines by fluorescence spectroscopy, involves complexation with fluorescamine and detection using excitation wavelength of 275-280 nm and emission wavelength of 460 - 490 nm. Depending on the type of imidazoline and sample matrix, the author found that using 390 5 nm for excitation gave sharper and more intense fluorescence signals. The procedure is described in Appendix B and Figure 323.

AUTOMATED FLUORESCENCE SPECTROSCOPY

In 1977, Gatlin et. al.2 used fluorescence as a field method to continuously monitor inhibitor residual in water flood projects. The inhibitors were Inhibitor A, which was a quaternary ammonium compound, and Inhibitor B, which was a combination of quaternary ammonium compound and an organic liquid oxygen scavenger. The fluorescing component was the quaternary ammonium compound. They used 315 - 335 nm excitation wavelength and 380 - 410 nm emission wavelength. In-line monitoring provided an instantaneous recording of chemical residual, used to control corrosion inhibitor injection. Dependence of emission intensity on pH

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and temperature was observed and addressed, but did not affect the accuracy of the analysis. Concentration of two ppm of inhibitor was detected continuously in the flow system. The test procedure consisted of setting up the flow system, standardizing the fluorescence spectrometer and then initiating the flow. The chemical pump, downstream from the sampling point, injected inhibitor when the corrosion inhibitor level fell below the preset level. The flow system consisted of two turbine/centrifugal injection pumps (capacity of 20,000 22,000 barrels/day). A 30-ft. tubing was run upstream of one of the pumps to the flow cell of the fluorescence spectrometer. The fluid exited from the flow cell to a disposal pit. Son and Chakravarty9 discussed the successful use of an automated fluorescence spectrometer in the field. The spectrometer was equipped with an auto-sampler and was programmed to serve the districts need to analyze a high number of samples in the field using technical personnel with no training in corrosion inhibitor determination. Part of the instrument setup entailed generation of calibration curves for each of the corrosion inhibitors used in the different locations. After the initial set-up, a chemist checked the calibration curves and performed maintenance on the system on a regular basis. The fluorescence spectrometer was programmed to do sample pickup, dilution of sample, mixing, delivery to fluorescence cell, rinsing, analysis and calculation. The field personnel collected the sample, filtered the sample when turbidity was observed, poured the sample to a test tube in the auto-sampler, chose the calibration curve and pushed a button. Within minutes, the results were obtained and any treatment adjustment was made. Dye extraction methods and static spectroscopy methods monitor one component of the corrosion inhibitor. It is well documented that the individual components partition between the oil and aqueous phases. In the field, as soon as the corrosion inhibitor is injected into the system, the inhibitor partitions to the different phases. Gough24 observed that higher molecular weight quats are very much depleted relative to the lower molecular weight quats in field brine samples. Higher molecular weight quats either partitioned to the oil phase or have been lost to the metal surfaces25. This phenomenon is demonstrated in Figure 4. It can be seen from the two emission spectra (before and after partitioning to brine and condensate phases) that the concentrations of the partitioned standards are lower relative to the non-partitioned standards. The emission wavelength used in the analysis was 460 nm and the excitation wavelength was 390 nm. The use of partitioned standards is highly recommended14,17 for a closer simulation of how much corrosion inhibitor is actually in the aqueous phase that is providing the protection to the system being treated and monitored.

THIN LAYER CHROMATOGRAPHY

Buck, et.al.5,26 used thin layer chromatography (TLC) because the simplicity of the method and inexpensive instrumentation make it suitable for field analysis. Silica gel layer was chosen as adsorption medium because it readily separated non-polar diluent oils from the more polar nitrogen-based corrosion inhibitors. The field procedure is patented26. Buck et. al. used a thin layer of adsorbent (silica gel) mechanically bound to a 20 cm2 or smaller glass support. A weakly absorbent material, such as kieselguhr, was coated near one edge of the plate where the sample of formation fluid can be applied. A sample of produced fluid was applied 2-4 cm from one edge of the plate. Standards were applied on both sides of the sample (horizontally aligned). Solvent was dried off and then the plate was placed in a container that can be closed, with the sample application edge closest

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to the bottom of the container. An eluting solvent was added to the container just below the sample zone. The plate was exposed to the solvent vapor and was allowed to equilibrate. The sample plate was suspended, not touching the solvent during the solvent equilibration phase. After equilibration, the plate was lowered into the solvent. The solvent traveled up the plate via capillary action. After a predetermined time for the solvent to travel beyond the sample and standard spots, the plate was removed, dried and sprayed with a suitable visualization agent. The sample spot size and intensity was compared to the standards. When the inhibitor concentration read below the standards, it was an indication that additional inhibitor needed to be added to the production system. TLC can also be used to identify, qualitatively, unknown corrosion inhibitors in a sample. In TLC, as the solvent passed through the sample zone, the components compete for the adsorption sites on the layer with the solvent, and those that are less strongly adsorbed to the layer than the solvent are carried further up the vertical plate, while those more strongly adsorbed are retained closer to the original spot point. Hence, the components of the sample become spatially separated on the adsorbent. When separation is complete, derivatization reagents can be sprayed onto the adsorbent and each derivative viewed with both visible and UV light. In the method development studies, 224 corrosion inhibitors were chosen by Buck et. al.5 to represent a range of polarity and compound types. The solvents and derivatizing reagents were identified for each corrosion inhibitor type. TLC was found to be sensitive up to 1 ppm. Detection limit was found to be dependent on the compound of interest, matrix interference and the ability to load sufficient material on the adsorbent layer5.

FOURIER TRANSFORM INFRARED (FTIR) SPECTROSCOPY

Martin, Valone and Haltmar used FTIR and 13C NMR (nuclear magnetic resonance) spectroscopy to accurately determine residual corrosion inhibitor concentrations in inhibited diesel solutions27. 13C NMR is the reference method for FTIR analysis. FTIR is a rapid and precise technique for determining inhibitor concentration and has the advantage of providing information on the composition or decomposition of inhibitors. The inhibitor was a reaction product of an amine with a dimer-trimer acid and blended with an ethoxylated surfactant in an aromatic solvent. The reaction product, as used in the diesel solutions, was a mixture of imidazoline and amide. Peaks in the FTIR spectrum, 1740 cm-1 and 1550 cm-1 for the ester and amide functionalities, were used for the analysis. These peaks were unique to the inhibitor and not found in the diesel. For both 13C NMR and FTIR techniques, the ester peak was easily characterized. Initially, it was assumed, that all amine functionality in the corrosion inhibitor was in the amide form. The solutions were divided into two portions. Half was kept at ambient temperature while the other half was heated at 240oF for 24 hours to simulate downhole temperatures. The heated imidazoline solutions partially hydrolyzed to the amide form, converting to a mixture of secondary and tertiary amides. Using the 1550 cm-1 peak for analysis, the heated samples gave consistently lower concentrations relative to the calculated starting concentration. FTIR does not have the sensitivity to measure ppm levels of corrosion inhibitors. The detection limit for the inhibitor/diesel solution was approximately 10-20%27. Reverse-phase solubility was observed. Martin and Valone investigated the utility of FTIR and 13C NMR techniques for a quality assurance program 28,29. In the FTIR method, the weight ratios of the amine to acid for 28

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neutralized imidazoline formulations gave a linear correlation with a correlation coefficient of 0.92. The FTIR method is useful for hydrocarbon-based systems but generally not applicable to aqueous samples. In the oilfield industry, FTIR is used for quick identification of unknown inhibitors and not for residual analysis. It continues to be a popular quality control method, particularly in the manufacture of imidazolines and amides.

HPLC/ULTRAVIOLET SPECTROSCOPY/FLUORESCENCE

High performance liquid chromatography (HPLC) is a separation technique. It is suitable for analysis of corrosion inhibitors, which are mixtures of different components. In an HPLC analysis, the components separate by differences in polarity. The separation occurs as a flowing mobile phase passes through the column. The flow of the mobile phase can be gradient or isocratic. In gradient flow, two or more solvents are mixed in a programmed manner to effect the best separation of the components in a mixture. In addition to variable composition, the flowrate can vary during the analysis. In isocratic flow, the mobile phase is premixed (constant composition) and the flowrate is kept constant. During method development, conditions are optimized (flowrate, type and temperature of column, mobile phase composition and pH) to get the best separation and peak shapes. The basic parts of the HPLC system are the pump, injector, column and detector. The pump delivers a programmed flow of solvent. The injector introduces the sample into the flowing mobile phase. The column has a finely divided packing, which slows the rate of travel of different chemicals according to their affinity for the packing. The chemical is qualitatively defined by the time of arrival at the detector. In 1993, Cossar and Carlile introduced a new method for determination of quaternary pyridinium salts13. They used gradient flow, mixing acetonitrile and a pH 5 aqueous acetate buffer and flowing through a C-18 Bondapak column (15 cm x 3.9 cm) to separate the components. UV absorbance at 280 nm was utilized to monitor the major components of corrosion inhibitors. HPLC was shown to overcome the interference problem with the dye transfer method. Linear response was obtained for 1 1000 ppm range. The computer-controlled operation allowed identical treatment of the samples. The time versus absorbance trace for any number of samples could be directly compared, even if they were acquired on different days. With the HPLC method, Cossar and Carlisle showed that every corrosion inhibitor formulation has its own fingerprint of characteristic peaks. The authors found that 25-minute runs produced acceptable confidence for greater than 95% of field water samples analyzed. At a flowrate of 2 mL/minute, all the quaternary amines were eluted in 12 minutes. A column wash and column equilibration for 13 minutes prepared for the next sample injection. The area under the peak was directly proportional to the amount of inhibitor in the sample. Standard concentrations were made to bracket the recommended treating rate. Hence, sample from a pipeline being treated at 300 ppm is analyzed using 100, 300, 500 ppm standards prepared in distilled water. For the two pyridine quats in the study, the authors found detection limits of 0.3 and 3 ppm. In contrast, the dye transfer method had detection limits of 5 and 10 ppm for the same samples. McKerrell and Lynes30 developed a HPLC method to analyze nitrogen-containing corrosion inhibitors in a mixed hydrocarbon/glycol solvent. The method was used to analyze two corrosion inhibitors. Inhibitor A was imidazoline in triethylene glycol. Inhibitor B consisted of a

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mixture of fatty acid, alkylamine salts, polyol ester and fatty acid ester in an aromatic solvent. The inhibitors were used in oil pipeline fluids to provide protection to the well risers and to the pipeline in the Far North Liquids and Associated Gas Systems (FLAGS) pipeline at St. Fergus in Scotland. Samples were taken at the slug catcher and consisted of the production brine, condensate, diesel oil, triethylene glycol, Inhibitor A and Inhibitor B. The samples were dispersed in a methanol/dichloroethane solution. Separation of the two inhibitors was done using a mobile phase of water, methanol, dichloroethane and acetic acid. The dichloroethane produced sharpened peak shapes, improved retention time reproducibility and promoted column regeneration. Acetic acid (0.1% v/v) was found to be the key to successful and reproducible regeneration of the ODS 2 column. For detection, McKerrell and Lynes derivatized the inhibitors with fluorescamine. Detection limits were 0.02% (200 ppm) for the imidazoline (Inhibitor A) and 0.1% (1000 ppm) for Inhibitor B. Automation of the HPLC allowed unattended analysis around the clock. Son and Chakravarty9 used isocratic flow of premixed mobile phase components (55% sodium heptanesulfonic acid, buffered at pH 2 2.5 and 45% acetonitrile) to separate quaternary amines. Using a Spherisorb C-18 column (25 cm x 4.6 mm), the quats were detected using both UV and fluorescence, installed in series. At 1.25 mL/minute, flow, the analysis time was 30 minutes. Peaks of interest eluted within 10 minutes and the other components eluted later. A column wash and regeneration followed. The UV monitoring wavelength was 270 nm while for fluorescence measurements, excitation wavelength was 320 nm and the emission wavelength was 400 nm. The column was maintained at 40C, which promoted lower viscosity of the mobile phase and lower column pressures. The simplicity, improved signal to noise ratio and lower pump maintenance, are desirable features for running the method in small district laboratories. The investigation9 showed that HPLC/fluorescence was less sensitive to common interferents such as dodecylbenzene sulfonic acid (DDBSA) and salinity of the production water. Matherly, et. al.15 analyzed imidazoline and amine-based corrosion inhibitors in production fluids from the North Slope, Alaska using HPLC/fluorescence. Solid phase extraction (SPE) was used to process the samples. The method was used for analyzing corrosion inhibitors in both aqueous and crude oil samples, as well as solids from corrosion coupons and production pipes. For crude oil samples, the SPE (silica gel columns) trapped the desired corrosion inhibitor species and allowed crude oil and non-polar solvents to pass through. After column clean-up with o-xylene and methanol, complexation of the trapped chemical with fluorescamine and extraction of the complex with methanol was accomplished, using a secondary pump circulating at 10 mL/minute at pressures less than 500 psi. The corrosion inhibitor/fluorescamine complex was eluted with methanol and then injected into the chromatograph. The complexation, with the fluorescamine/methanol solution circulated through the SEP column, was complete in 30 minutes. On injection of the inhibitor/fluorescamine complex in methanol into the HPLC column, the peaks of interest eluted within 3-7 minutes for imidazolines and 9-20 minutes for amines. A standard calibration curve was generated using corrosion inhibitor batches. Standards were processed the same way as the samples. Brine samples were processed using C-18 bonded silica gel and washing with D. I. Water. The HPLC procedure used by Matherly et. al. employed isocratic solvent flow at 2 mL/min, excitation wavelength of 278 nm and emission wavelength of 476 nm. The detection limit for imidazolines, amides and amines was 0.2 mg/L or ppm.

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With data from the HPLC/fluorescence method on concentrations of imidazoline and amido-amines in both oilfield water and crude oil samples, they were able to estimate the lifetime of the corrosion inhibitor treatments in the well and hence, to estimate when the next well treatment was needed. Analytical data corresponded very well with the data from the corrosion probes placed on similar wells. Matherly, et. al. extended the use of the technique to determine corrosion inhibitors that filmed on metal surfaces or that were adsorbed on solids. The pipes and solid samples were substituted for the SPE column and the inhibitor extracted using recirculation of fluorescamine/methanol solution. With the component separation feature of HPLC, the corrosion inhibitor concentration can be determined several times (based on each component) from the same sample run, providing an internal check on the accuracy of the analysis (assuming components have similar partitioning characteristics). HPLC methods are laboratory procedures that are suitable to district or plant laboratories due to easy set-up and ease of automation. Unattended 24-hour analysis has been setup in many applications.

GAS CHROMATOGRAPHY /MASS SPECTROMETRY

In 1995, Gough, Haslegrave and Hedges3 compared Fast Atom Bombardment Mass Spectrometry (FAB-MS), Gas Chromatography-Mass Spectrometry (GC-MS) and Liquid Chromatography with diode array detection (LC-DAD) for the analysis of quaternary ammonium compounds. They preferred the superiority of the GC-MS for its sensitivity (

were eluted from the SPE cartridge with n-hexane/THF (95/5) solution, then the eluting solvent was evaporated using a stream of nitrogen or a vacuum pump. The concentrated amine sample was then reacted with trifluoroacetic acid (TFAA) in THF or n-hexane and analyzed by GC/FID, GC/NPD and GC/MS. Derivatization with TFAA prevented nonlinear adsorption effects. Adsorption causes the formation of strong tailing peaks in a chromatogram. Standards were prepared with an internal standard of dicyclohexylamine in n-hexane and derivatized the same way. The GC was equipped with a split/splitless injector, a flame-ionization detector (FID) and a nitrogen-phosphorus detector (NPD), both operated at 320C. Helium was the carrier gas. The fused silica capillary column had a film thickness of 0.25 um of DB-5. The splitter allowed the simultaneous detection using FID and NPD. This technique is applicable to refinery samples. The GC/FID/NPD (without the MS detector) equipment can be found in many refinery facilities.

ELECTROSPRAY IONIZATION MASS SPECTROMETRY (ES-MS)

The number of publications on ES-MS in the oilfield industry demonstrates the high level of interest and the success of research scientists in extending the use of this technique to more chemical products and to lower concentrations. Extensive development work has keyed on detection, qualitatively and quantitatively of quaternary ammonium compounds and imidazolines. The extensive use of quats and imidazolines in corrosion inhibitor formulations is due to their proven strong adsorption to surfaces. They coat metal and metal oxide surfaces acting as a barrier to water and other corrodents. Imidazolines are sufficiently strong Lewis bases to displace water from the Lewis acid sites of the oxide surfaces32. Moreover, their strong adsorption properties carry over to solids in the production system phases (crude oil and brine) as well as to the analytical determination, i.e. to the surfaces encountered in the various processing steps. The imidazoline is preferentially oil soluble, sparingly soluble in the water and tends to accumulate at the oil/surface interface. A mechanism that makes imidazoline inhibit corrosion is that water droplets roll off the imidazoline-coated surfaces leaving them completely oil-wet32. Many corrosion inhibitor formulations include additives to make imidazolines partition more to the brine. In addition to GC/MS, Gough, Mothershaw and Byrne also used LC/Electrospray Mass Spectrometry (ES-MS) to analyze oilfield chemicals24. Quats are permanently positively charged molecules and are very responsive to electrospray ionization. Detection is in the sub-ppm levels. With soft ionization, the individual quat molecules have little or no fragmentation. With the LC column separating the individual quat components of corrosion inhibitors, quantitative analysis of the individual components can be obtained in a single analysis. This information is very useful for troubleshooting. ES-MS is easy to automate and interface with LC and has superseded traditional soft ionization techniques such as Fast Atom Bombardment (FAB) and Chemical Ionization (CI). With such a sensitive analytical tool, the authors were able to observe that quat molecules partitioned to the water phase >98%. Only 1% of the C18 quat partitioned to the oil phase. Partitioning occurs on injection of the corrosion inhibitor to the production fluid. The dominant mechanism that controls redistribution of quaternary ammonium actives in field systems appeared to be surface adsorption. The longer and more linear the quat, the higher the extent of surface adsorption.

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Gough, et. al.33 extended the use of ES-MS to various quat corrosion inhibitors, imidazoline corrosion inhibitors, emulsion breaker intermediates (alkylphenol, linear alcohol, alkylamine ethoxylates and phenol/formaldehyde resins), chelants and phosphonate scale inhibitors. For emulsion breakers, the ES-MS clearly showed the oligomeric series of ethoxylated alkylphenols with 3-9 moles of ethylene oxide (EO) for a product made with four moles EO. For this work, Gough et. al. analyzed a combination of benzalkonium chloride coco quat (5%), DETA imidazoline (35%) and an EB package (5%) and 55% solvent. Two types of imidazolines were analyzed TOFA (tall oil fatty acid)-DETA (diethylenetriamine) and a palm oil-aminoethylethanolamine imidazoline. With this technique, the presence of both amides and imidazolines, common in industrial imidazolines, was clearly shown. This is advantageous when troubleshooting problems in the field. The ratio of amides to imidazolines in a formulation can affect solubility and partitioning of the imidazoline in a formulation and hence, the performance in particular applications. In the manufacture of industrial imidazoline, the quality control of imidazolines usually includes specifications for amide to imidazoline ratios. The ES-MS technique is superior to the classical infrared technique for this particular quality control test. With the ES-MS developments, changes in the molecular composition of inhibitor formulations as the product is distributed throughout oilfield systems can now be monitored. Solid phase extraction (SPE) was used as part of the sample preparation process by McCormack et. al.34. LC/ electrospray ionization multistage mass spectrometry (LC/ESI-MSn) allowed the determination of individual imidazolines (2-alkyl-1-ethylalkylamide-2- imidazolines and 2-alkyl-1-ethylamine-2-imidazolines) in crude oils with detection levels

region where they separate and are detected. Various mass spectrometers will differ in equipment design for ion formation and detection. Langley35 also published an LC-ESI-MS work on imidazoline and quaternary ammonium salt. Collective information on different corrosion inhibitor components is providing the industry with more insight into the detailed molecular composition of corrosion inhibitors and improved understanding of performance. Grigson et. al.4 used electrospray ionization tandem mass spectrometry (ESI-MS/MS) to study the composition of proprietary oilfield chemicals such as corrosion inhibitors and demulsifiers and measure their residues in produced waters and marine sediments collected near two oil production platforms (Thistle and Magnus) in the North Sea. ESI/MS work has generated much useful and needed information for the industry on corrosion inhibitors and other products. The soft ionization technique, as pointed out earlier, produces molecular ions with little or no fragmentation patterns. Background ions from the instrument or the solvent, and additional peaks from the samples themselves sometimes presented difficulty in analysis of complex mixtures. Grigson used tandem MS to get additional specificity to analyze complex samples such the marine sediments. In ESI/MS/MS, the parent ions of the quats and the imidazolines were subjected to a collision-induced dissociation (CID) with argon. The daughter ions were then analyzed by mass analysis. Grigson combined selective ion recording (SIR) with the ESI/MS and improved the sensitivity of detection to parts per trillion levels with low coefficient of variations (0.65 1.09%). To process marine sediments, freeze-drying, followed by methanol extraction for quaternary ammonium salts and dichloromethane extraction for imidazolines, both using an ultrasonic bath, gave >90% recoveries. SPE procedures to remove salts from the sample and to concentrate the analyte were developed and resulted in good recoveries for imidazolines and benzalkonium quaternary ammonium salts. Octadecyl (C-18) bonded silica cartridges were found adequate. Grigsons work to analyze for quaternary amines and imidazolines in produced water samples and marine sediments assisted in the validation of the CHARM predictions of concentrations of oilfield chemical residues in produced water samples4. Phosphate esters are also used in corrosion inhibitor blends33,36. Field brine samples from a lease treated with a blend of phosphate ester, imidazoline and amides were analyzed using LC/ESI-MS. Selective ion chromatograms of corrosion inhibitor standards are shown in Figure 5. Three components are shown phosphate ester, imidazoline and amide, identified by their masses and fragmentation patterns. Calibration curves for the phosphate ester and imidazoline were generated. The amide peak was not used, because when the field water samples were analyzed, the amide peak was missing, indicative of the loss of the amide through partitioning and adsorption processes. Calibration curves were for corrosion inhibitor concentrations of < 1 ppm to 50 ppm and were linear with excellent correlation coefficients for both the phosphate and the imidazoline components (Figure 6). Field samples were analyzed to contain 1.1 to 1.4 ppm of corrosion inhibitor, using either calibration curve37. For accuracy and precision, field samples with concentrations lower than 1 ppm should be pre-concentrated through solid phase extraction or even through simple evaporative techniques.

13

NUCLEAR MAGNETIC RESONANCE (NMR) SPECTROSCOPY

NMR spectroscopy is a powerful tool in the structural determination of organic compounds. Compared to other spectroscopic techniques where the spectral response varies with the chemical compound, in NMR spectroscopy, the spectral response (intensity vs. number of species producing the signal) is independent of the compound. With this technique, absorption coefficients are the same for the different organic substances, as long as the same nuclei are analyzed. A widely used material, cocoamidopropyl betaine, is used in the oilfield industry as a component of corrosion inhibitors and foamers. The compound gives specific signals in 1H (proton) and 13C-NMR. The signal position at 3.3 ppm is a very specific one and usually no other chemical group appears in this part of the spectrum. Interferences are usually identified with signals in other areas of the spectrum38. As in other quantitative analytical techniques, the signal intensity related to an internal standard corresponds to the concentration. For cocobetaines, Gerhards, et. al.38 found 0.5% (500 ppm) solutions can be directly identified with either proton or carbon 13 NMR. For lower concentrations, specific pre-concentration steps should be considered. The betaine-specific signal has the advantage of an eight-fold degeneracy, increasing the intensity of the signal by this factor. In proton NMR, the signal most suited for the quantification of betaines is produced by an overlap of the signals of the hydrogens in the two methyl groups attached to the quaternary nitrogen and of the signal of the two hydrogens in the methylene group in the alpha position of the amide structure. This signal appears at 3.3 ppm38. In NMR spectroscopy, it is necessary to add an internal standard to the sample, which produces a signal in a spectral region, which is free of signals from sample molecules. For the analysis of betaines, Gerhards used sodium trimethylsilyl propionate (TSP) which produces a strong signal that is not split by coupling effects (i.e., a single peak is observed at 0 ppm chemical shift). NMR has the added advantage that it produces other structural information that allows the detection of unusual components in the betaine test solution. NMR spectroscopy for betaines is relatively quick (30 minutes or less) and hence, may be applied to quality control operations. However, NMR spectroscopy, similar to LC/ESI-MS, requires expensive instrumentation and special training for chemist operators. Even when utilized in quality control operations, the instrument needs to be kept in a specially designed and well-maintained laboratory. Carbon 13 NMR and FTIR spectrometers were used to study hydrolysis of imidazolines to amides27, 28,39 in corrosion inhibitor formulations and to determine substitution of materials in the formulation and addition of correct ratios of ingredients. Both techniques showed that the imidazoline/amide molar ratios decreased more than 20-fold within 20 days of inhibitor synthesis. Substitution of different dimer-trimer acid in the corrosion inhibitor and addition of correct ratios of ingredients were easily detected. From the Valone 13C NMR study, the peaks of interest were the dimer-trimer acid at approximately 180 ppm, the amide at approximately 174 ppm, the ester at approximately 173 ppm and the imidazoline at about 167 ppm. Due to signal to noise problems, only the peak heights could be measured, rather than the preferred method of peak area integration. The latter gives more accurate results since the peaks are not single sharp peaks but rather closely spaced multiplets. To improve the accuracy, an internal reference standard, Trimethylsilane (TMS) of known concentration was added to each sample. TMS is used as a reference for chemical shifts.

14

The investigations by Valone et. al. 27, 28,39 showed that Carbon 13 NMR and Fourier Transform Infrared (FTIR) spectroscopic techniques complement each other in the qualitative and quantitative analysis of corrosion inhibitors. McMahon36 used 31P NMR to monitor the mechanism involved in the use of sodium alkylethoxyphosphate (NaAEP) as a corrosion inhibitor in a crude oil pipeline. The NaAEP had phosphate monoester and diester components and a small amount of phosphoric acid. It was demonstrated that the phosphate ester was preferentially water-soluble in an oil/water system with tendency to migrate to the oil/water interface. The application of NMR for analysis of corrosion inhibitors in both aqueous and oil samples is demonstrated in Figures 7 940. In Figure 7, the top spectrum is for a crude oil dissolved in deuterated chloroform and the lower spectrum is the crude oil treated with an imidazoline-containing product. The crude oil 1H spectrum was clean in the chemical shift range of 3.5 to 6.8 ppm. The additive is evident in the bottom spectrum. Figure 8 is the enlarged spectra of the crude with the imidazoline-containing product. The regions are identified, with the imidazoline, amide and amine peaks close to 3 ppm. Figure 9 is a spectrum of a produced brine with 0.5% (v/v) corrosion inhibitor blend containing imidazoline and phosphate ester. 1H data was collected at 750 MHz using a PRESAT (pre-saturation) experiment to suppress the water signal. The water signal suppression is through selective excitation of water protons resulting in significantly reduced intensity. Methanol and acetate salts, common in corrosion inhibitor formulations, give quite distinct signals as in Figure 9. The integrated ratio of the (CH2)n and the terminal CH3 (see region labeled Aliphatic) peaks can be used to identify the fatty acid used to produce the imidazoline. From preliminary data, it is estimated that the detection limit would be around 100 ppm for the additive. Data was collected using 64 acquisitions. Increasing the number of acquisitions will improve the signal to noise ratio and allow lower concentrations to be determined.

ION CHROMATOGRAPHY Ion chromatography (IC) is a separation technique for chemical compounds in either anionic or cationic forms, in aqueous samples. IC is similar to HPLC, using a gradient pump to push the buffer through the column. The ions separate in the column by a difference in polarity and on elution are monitored by the detector of choice. Different columns are used for cations and for anions. In the oilfield industry, its application has expanded to analysis of anions (chlorides, fluorides, nitrates, sulfates, etc.) in water samples, organic acids, scale inhibitors (phosphonates) and cations such as quats. For environmental discharge samples, ICP is able to determine low levels of organic acids. A conductivity detector is widely used for monitoring the concentrations of the ionic species in a sample. With the introduction of mass detectors to replace the conductivity cells, the technique will see an explosion of applications. The mass detector has the advantage of both qualitative and quantitative identification of the unknown samples. Aminotrimethylenephosphonic acid (ATMP) is used as a component of scale and corrosion formulations. Commercial ATMP usually contain ATMP, hydroxymethylenephosphonic acid (HMPA), n-methylaminodimethylenephosphonic acid (n-MADMP), phosphate and phosphite. In 1985, Pacholec, et. al.41 published the first report on identification and quantification of ATMP phosphonates by ion chromatography. Using two detectors - conductivity and a post column reaction with Fe(III) followed by UV/Vis detection at 330 nm, they were able to separate and

15

quantify all components in ATMP. The detection limits for the components ranged from 0.4 to 2.0 ppm. Figure 10 is an overlay of ion chromatograms of two scale/corrosion inhibitor formulations from a scale problem troubleshooting project42. The lack of performance in the product was attributed to a decrease in Component A. Spectra were generated using a conductivity detector and hence, the individual phosphonate components were not identified in the same experiment. With a mass detector, the components would have been identified by their molecular weights.

INDUCTIVELY COUPLED PLASMA SPECTROSCOPY For corrosion control programs in the oilfield industry, inductively coupled plasma spectroscopy (ICP) is an important analytical technique. In developing treatment programs, scale predictions, troubleshooting, problem-solving, and produced water composition is needed. ICP, for its, simplicity, speed, accuracy, precision and multi-range capability is preferred over atomic absorption, UV-Visible and titration techniques. In addition to cations, ICP is also used for analysis of sulfur (for sulfates) and phosphorus (for phosphonates and phosphates) in water samples. ICP involves very simple sample preparation filtration and dilution with acid and deionized water to the linear range for a particular analyte. The equipment is easily automated, which is almost a requirement for the number of water samples that have to be analyzed in the laboratories on any given day. One drawback is that the ICP spectrometer is a laboratory equipment, not field equipment. In laboratory development experiments and performance evaluations, it is often the case that not enough field brine can be sampled from the production system. The brine composition is established using ICP spectrometry and the required volume of synthetic brines of similar composition is easily prepared to do the particular testing. In scale squeeze projects, ICP is used by many laboratories to determine residuals where the concentrations are in the low ppm to ppb levels. Graham et. al.43 effectively monitored ppb levels of phosphonate and phosphino-polycarboxylate (PPCA) scale inhibitors in oilfield waters using ICP. The difficulty associated with low levels of scale inhibitors (ppm to ppb) was overcome with the choice of the right analytical line (177.499 nm P line) and matching the matrix of the standards with the produced brine. Concentrations

GEL PERMEATION CHROMATOGRAPHY

Most of the components used in corrosion inhibitor formulations are small molecules. However, polymeric molecules, such as the emulsion breakers and acid corrosion inhibitors, are also routinely used in the industry. Gel permeation chromatography (GPC), also known as size exclusion chromatography (SEC), is for characterization of high molecular weight compounds, such as emulsion breakers, water clarifiers and flow improvers, rather than identification and quantification. GPC was used to analyze for conversion products of acid corrosion inhibitors, including surface films formed on N80, J55 and 1026 stainless steel coupons, exposed to 15% HCl for up to 6 hr at 65C (121F)45. The inhibitors included 1-octyne-3-ol and a commercial formulation containing 4-ethyl-1-octyn-3-ol, a nonionic ethoxylated surfactant and a reaction product of acetophenone, formaldehyde and an amine with and without inhibitor aids (formic acid or potassium iodide). The inhibitor aids are used to improve adherence of the protective film. By GPC, the film formed from the corrosion inhibitors was found to be polymeric ketones from 400-2000 molecular weight.

CAPILLARY ELECTROPHORESIS/DAD

Amines are widely used as corrosion inhibitors in refineries. GC and HPLC are widely used for analysis of aliphatic and cyclic amines. Another applicable technique applicable is capillary electrophoresis (CE)46. In CE, application of an electric field separate amines as cationic species and are detected indirectly using low pH electrolyte systems containing UV-absorbing additives.

SURFACE ANALYSIS TECHNIQUES

The focus of this review is on determination of corrosion inhibitors and related oilfield chemicals in solution. However, surface analysis techniques are often used with solution techniques to characterize performance of corrosion inhibitors. A few are briefly described here, more to direct researchers to some potential tools that can complement difficult problem-solving, and definitely to aid in the development of better and greener inhibitors. The demands of new regulations make it mandatory to develop improved performance, reasonably-priced and environmentally-friendly chemicals. Where the corrosion inhibitor concentration is measured in solutions and protection is related to a set of minimum dissolved concentration, surface analysis measures how much corrosion inhibitor comes out of solution. These techniques measure the thickness of the coating that is deposited on the metal. Surface analysis techniques, such as X-ray Photoelectron Spectroscopy (XPS) and Time of Flight Secondary Ion Mass Spectrometry (ToFSIMS), were used after electrochemical testing to determine the surface composition and chemical state of the quaternary amine inhibitor. There was no evidence of chemical reaction of the quaternary ammonium compound with the steel surface. Adsorbed quaternary amine inhibitor was observed and measured at different concentrations. The lowest concentration detected for the amine quat was 20 ppm25. XPS and ToFSIMS surface analysis were used to monitor the adequacy of coverage, and hence, corrosion protection. It was concluded that adsorption of the quat was due to a simple ionic interaction of the quat with the steel surface. Longer chain quats were preferentially absorbed. Another surface analysis technique is surface-enhanced Raman spectroscopy (SERS)47. The strength of adsorption of quaternary compounds was found dependent on the steel used.

17

Transmission Mossbauer Spectroscopy, complemented by FTIR, was used to study the effects of corrosion inhibitors on the corrosion of steel surfaces48. Actually detected were various forms of iron oxides, -FeOOH and superpara-magnetic (SPM) -FeOOH. In the presence of nitrite corrosion inhibitors, the corrosion product formed on mild steel showed non-stoichiometric magnetite (Fe3-xO4) along with oxyhydroxides. Phosphate inhibitors showed the presence of ferrous phosphate. It was noted that sodium hexametaphoshate inhibited corrosion by hydrolysis and subsequent formation of the barrier film. The protection mechanism of phosphate was by iron phosphate formation, along with oxyhydroxides. Electronic impedance spectroscopy is widely used in the evaluation of oilfield corrosion inhibitors. However, the technique evaluates performance, rather than concentration and is outside of the scope of the intended review. Papavinasam49 et. al.s paper discusses the various performance methodologies for corrosion inhibitors in oil and gas pipelines.

DISCUSSION Exploration for oil and gas is more challenging than ever. The search has taken the oil companies to more remote, undeveloped areas on land and into deep waters. The challenge to operators include low temperatures, high pressures, sweet and sour gases, miles of umbilical tubing to bring chemical treatments where they are needed, long pipelines to transport production fluids to processing plants, and more rigid state and federal regulations. Cost of hardware (tubulars, pipelines, pumps, etc.) constitute a significant percentage of production operations. Preservation of hardware integrity is closely linked to good corrosion control. When corrosion problems occur that require replacement of tubulars, the cost of replacements plus lost production during downtime is significant. There are many monitoring techniques (electrochemical, ultrasonic, radioactive tracers, coupons, etc.) available, some of which are very expensive, but there is no guarantee of 100% protection year round. Residual corrosion monitoring provides added assurance of protection. With remote sampling areas, the transport of samples can be problematic and can result in loss of sample integrity. Low maintenance and low cost of production operations can be promoted by not only preventing corrosion but also through early detection of the initiation of a corrosion problem. Usually, catching the problem early results in a quick and more effective solution, preventing need for tubular or pipe replacements. Residual analysis on location is definitely an advantage. A challenge to the operator, and chemical and service providers is to provide simple, fast and accurate analysis in the platforms or sampling stations. Automation with rugged, inexpensive equipment circumvents the lack of trained technical personnel. The analyzer must be able to operate under uncontrolled environment and unstable, sometimes teetering or swaying remote production facilities. Some development work to impart ruggedness to the automated fluorescence method, successfully employed as a field method in a lease in North America9 is needed. Development of a robotic version of the dye transfer methods with improved accuracy and precision will appeal to, and help small district labs and field personnel. With the demands for more cost effective chemicals, lower chemical treatments per barrel of produced fluids and more restrictive environmental policies made into laws, lower and lower residual concentrations, (low ppms to ppb) need to be determined. A challenge to the industry is to develop more sensitive analytical methods. Elimination of matrix interference and development of easy and quick sample preparation will continue to challenge the analytical chemists and need to be continuously addressed. Development of more reasonably priced analytical instruments would promote acquisition and use in district laboratories.

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Extensive research is underway to address the demands for greener chemicals. New chemicals are designed and synthesized every day. New chemistries for corrosion inhibitors may need new or drastically improved analytical techniques. LC/ESI/MS and NMR spectroscopy are excellent for qualitative identification but will need more development work to analyze low concentrations (parts per billion or lower). The tandem MS technique, capable of parts per billion sensitivity, needs more development work. The second MS module makes the instrument more expensive and beyond the reach of most district laboratories.

SUMMARY AND CONCLUSIONS Spectroscopic techniques (UV/Visible) provide specificity, low detection limits and portable analytical solutions for the analysis of oilfield chemicals. These techniques may sometimes be hindered by interferences. In some situations, advanced analytical techniques such as fluorescence spectroscopy, can be applied with improved accuracy. When needed, analytes can be chemically modified through derivatization procedures to provide the necessary detection mechanism. For complex mixtures, often encountered with oilfield samples, hyphenated techniques using separation techniques are needed and required for analytical accuracy. Examples are thin layer chromatography (TLC) and high performance liquid chromatography (HPLC). The chromatographic techniques can be coupled with various detection methods: UV, Visible, Fluorescence, Mass Spectrometry, etc. FTIR, a workhorse for organic chemicals analysis has the advantage of sensitivity and specificity. It is applicable for hydrocarbon-based matrices but is not applicable for direct analysis of aqueous-based systems. NMR offers the capability of analysis of aqueous systems but may lack the required detection limits. Existing analytical methods for determination of residual corrosion inhibitors are discussed and compared in the paper to give the analyst a choice of methods depending on the number of samples, the technical ability of personnel and laboratory instrumentation available. The sensitivity, ease and cost of set-up are compared (Table 1) for the different methods. Challenges in the industry that need to be addressed with more research and developments have also been discussed.

ACKNOWLEDGEMENTS

The author wishes to thank Claire Conboy, Nellie Chu, George Cunningham, Kathy Eddlemon, Henry Fisher, Danielle McGowen, Sabrina Miller, Mark Nace and Rupi Prasad for their invaluable help in the preparation of the manuscript and Champion Technologies for permission to publish the paper.

REFERENCES

1. Joosten, M., Buck, E., Kolts, J., Erickson, D. and Mai, M., Paper No. 9, Corrosion 92. 2. Gatlin, L. W., Hudman, J. D. and Williams, D. C., Oilfield Subsurface Injection of Water,

ASTM STP 641, C.C. Wright, Dennis Cross, A. G. Ostroff and J. R. Stanford, Eds., ASTM, 1977, pp. 57-68.

3. Gough, M.A., Haslegrave, J. A. and Hedges, W. M., 6th International Oilfield Chemicals Symposium, Geilo, Norway, 1995.

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4. Grigson, S. J. W., Wilkinson, A., Johnson, P., Moffat, C. F. and McIntosh, A. D., Rapid Communications in Mass Spectrometry 14, 2210-2219 (2000).

5. Buck, E., Allen, M., Sudbury, B. and Skjellerudsveen, B., Paper No. 99, Corrosion 93. 6. Son, A. J., Proceedings, NACE Northern Area Western Conference, Saskatoon,

Saskatchewan (March 2000). 7. Naraghi, A., U.S. Pat. 5,611,991, March 1997. 8. Naraghi, A. and Grahmann, N., U.S. Pat. 5,611,992, March 1997. 9. Son, A. J. and Chakravarty, J., Paper No. 344, Corrosion 96. 10. Rosen, M. J. and Goldsmith, H. A., Systematic Analysis of Surface-Active Agents, 2nd

Edition, Wiley-Interscience (1972), pp. 459-463. 11. Skadhauge, K. and Fogh, J., Acta Path. Microb. Scan., 32, 290 (1952). 12. Fogh, J., Paul, O., Rasmussen, H and Skadhauge, K., Analytical Chemistry, 26, No. 2

(1954), pp. 392-395. 13. Cossar, J. and Carlile, J., Paper No. 98, Corrosion 93. 14. Son, A. J., Paper No. 04373, Corrosion 2004. 15. Matherly, R., Jiao, J., Blumer, D. and Ryman, J., Paper No. 543, Corrosion 95. 16. Fortenberry, C., Jr., Grahmann, N., Miller, C., and Son, A., SPE 26607, 68th Annual

Technical Conference and Exhibition of the Society of Petroleum Engineers, Houston, Texas, Oct. 1993.

17. Son, A. J. and Muckleroy, B. S., Materials Performance, Sept. 1997, pp. 38-47. 18. Siggia, S. and Hanna, J., Quantitative Organic Analysis via Functional Groups, 4th

Edition, John Wiley & Sons (1979), pp. 690-693. 19. Clesceri, L.S., Greenberg, A. E. and Trussell, R. R., Standard Methods for the

Examination of Water and Wastewater, American Health Association, Washington, D.C. (1989), pp. 4-139 to 4-147.

20. Kan, A. T., Varughesse, K., and Tomson, M. B., SPE 21006, Feb. 1991 (Anaheim, California).

21. Javier, A., Crouch, S. and Malmstadt, H., Analytical Chemistry 40, No. 13 (1968), pp. 1922 1925.

22. Izawa, Y., J. of Japan Oil Chemist Society, Vol. 11 (1962), pp. 627-630. 23. Guilbault, G., Editor, Practical Fluorescence, Marcel Dekker, Inc. (1990) pp. 265-269.

24. Gough, M. A., Mathershaw, R. A. and Byrne, N. E., Paper No. 33, Corrosion98. 25. Palmer, J. W., Piercey, A. R., Hibbert, S., Mitchell, R., Swift, A. J., Turgoose, S., Paper No.

40, Corrosion 95. 26. Buck, E. and Sudbury, J., U.S. Pat. 5,152,177 (Oct. 1992). 27. Martin, J. and Valone, F., Paper No. 232, Corrosion 84. 28. Martin, J., Valone, F. W. and Haltmar, W. C., Paper No. 378, Corrosion 85 (Boston). 29. Martin, J. and Valone, F., Paper No. 233, Corrosion 84. 30. McKerrell, E. H. and Lynes, A., Chemicals in the Oil Industry International Symposium, 3rd

Royal Society Special Publication No. 67 (1988), pp. 212 -222. 31. Kusch, P., Knupp, G., Hergarten, M., Kozupa, M. and Majchrzak, M., J. of

Chromatography A, Vol. 1113, Issues 1-2, (April 2006), pp. 198-205. 32. McMahon, A. J., Colloids and Surfaces 59 (1991) pp. 187-208. 33. Gough, M.A., Langley, G. J., Hedges, W. M. and Byrne, N.E., 8th International

Oil Field Chemical Symposium, March 1997, Geilo, Norway. 34. McCormack, P. Jones and Rowland, S. J., Rapid Communications in Mass

Spectrometry 2002, 16: 705-712 35. Langley, G. J., Chemicals in the Oil Industry (Special Publication, Royal Society

of Chemistry), V 211, 190-197 (1998). 36. McMahon, A. J., Proceedings of the 7th European Symposium on Corrosion Inhibitors

(7SEIC) Ann. Univ. Ferrara, N.S., Sez. V, Suppl. N9, 1990. 37. Chu, N., Internal Report, Champion Technologies, Nov. 2005. 38. Gerhards, R., Jussofie, I., Kaseborn, D., Keune, S. and Schulz, R., Tenside Surfactants

Determination, 33 (1996), 1, pp. 8-14.

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39. Martin, J. A. and Valone, F.W., Paper 232, Corrosion 84 (New Orleans). 40. Conboy, C., Unpublished Report, Champion Technologies, Sept. 2006. 41. Pacholec, F., Rossi, D., Ray, L. and Vazopolos, S., Organic Analytical Chem., Vol.3, No.

12 (1985). 42. Son, A. J. and Sitz. C., Proceedings, International Symposium for Ion Chromatography,

San Diego, California (2003). 43. Graham, G., Sorbie, K., Johnston, A. and Buck, L., 7th NIF International Symposium on

Oilfield Chemicals, Geilo, Norway (March 1996). 44. Riggs, O. L., Jr., Hutchison, M. and Gant, P.L., Material Protection, V.5, No. 11

(Nov. 1966), pp. 27-29. 45. Frenier, W. W. and Iob, A., Paper No. 150, Corrosion 88 (St. Louis).

46. Pereira, E. A., and Tavares, M. F. M., J. of Chromatography A, Vol. 1051, Issues 1-2, pp. 303 308 (Oct. 2004).

47. Oblonsky, L., Divine, T. and Chestnut, G., Corrosion, Volume 51, No. 12, pp. 891-900 (Dec. 1995).

48. Ramesh Kumar, A. V., Nigam, R. K., Monga, S. S. and Mathur, G. N., Anti-Corrosion Methods and Materials, Vol. 49, No.2, pp. 111-117 (2002).

49. Papavinasam, S., Revie, R. W., Attard, M., Demoz, A. and Michaelian, K., Corrosion, Vol. 59, No. 10, pp. 897 912 (2003).

APPENDIX A DYE EXTRACTION METHODS6,9-17

Sample Preparation and Standards Preparation are similar for the different dye extraction methods and consist of the following: 1. Separate the oil phase from the brine phase. 2. Acidify, as needed, using hydrochloric acid or nitric acid to pH 2. 3. Filter the aqueous sample (Whatman #2 filter paper, 0.45-micron filter, etc.) to remove

any suspended solids. 4. Obtain untreated brine from the lease or prepare synthetic brine similar to the sample

matrix. Acidify and filter, if needed. Standards Preparation1. Prepare 1% solution of water-soluble or water-dispersible corrosion inhibitor in the clean

untreated or synthetic brine. If not completely clear, treat with methanol. 2. Prepare 3 5 standards with the concentrations bracketing the expected sample(s)

concentration(s) in the clean brine. Note: standards are prepared from a sample of the corrosion inhibitor, preferably from the same batch used to treat the system in the field. Turn on the spectrometer while the standards are being prepared. Complexation with Bromocresol Purple 1. Prepare 3 phosphate buffers, pH 5.7, 4.2 and 9.7 (Buffers A, B and C). 2. Process standards and samples according to the following extraction procedures. 3. To a known volume of standard (or sample) in a separatory funnel, add bromocresol

purple, Buffer A and chloroform. Shake well. 4. Separate the chloroform (bottom) layer and add Buffer B and shake well. 5. Separate the chloroform (bottom) layer and add Buffer C. Mix well. 6. Extract the chloroform layer a third time, add ethanol and mix well. 7. Read and record absorbance at 590-600 nm.

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8. Generate the calibration curve (standard concentration vs. absorbance) and calculate concentration of the corrosion inhibitor in the sample(s). Correct for any dilution of the sample(s).

Complexation with Bromophenol Blue 1. To a known volume of standard or sample in a separatory funnel, add sodium carbonate

solution. Shake well. 2. Add bromophenol blue solution. Shake well. 3. Add toluene and shake well. 4. Extract the top toluene layer and measure absorbance of standards and samples at 580-

600 nm. 5. Generate the calibration curve (standard concentration vs. absorbance) and calculate

concentrations of corrosion inhibitor in the samples from the calibration curve. Correct for any dilution.

Complexation with Methyl Orange 1. To a known volume of standard or sample in a separatory funnel, add borax buffer

solution, adjust pH to 8-9. 2. Add methyl orange and shake well. 3. Add chloroform and extract the inhibitor/methyl orange complex with chloroform (bottom

layer). 4. Measure absorbance of methyl orange complex in the chloroform at 425 nm. 5. Generate calibration curve (concentration vs. absorbance and calculate concentration(s)

of inhibitor in the brine sample(s) by comparison to calibration curve (absorbance vs. concentration of standards). Correct for any dilution.

APPENDIX B STATIC ULTRAVIOLET AND FLUORESCENCE SPECTROSCOPY METHODS FOR

CORROSION INHIBITORS IN OILFIELD WATERS2,9,14

Sample(s) Preparation and Standards Preparation are the same as given in Appendix A. Turn on the spectrometer while preparing the standards and the sample(s). Static Ultraviolet Spectroscopy 1. Read absorbance of the standards at desired wavelength, single or range (for quats, 270

nm, 260-280nm) and generate the calibration curve. 2. Read absorbance of the sample and compare to the calibration curve to determine

concentration. Dilute the sample, as needed. Correct concentration results using the dilution factor.

Static Fluorescence Method 1. To monitor the quat component, set excitation wavelength at 325 nm and emission

wavelength at 400 nm. The fluorescence intensities of standards and samples are read directly.

2. To monitor the imidazoline or amine components, they need to be complexed with fluorescamine. While the fluorescence spectrometer is warming up, add fluorescamine solution to standards and samples. Mix well.

3. Allow color development for 15-30 minutes. Use the same time for both standards and samples.

4. Set the excitation wavelength at 275-280 nm and the emission wavelength at 460 480 nm. Read the fluorescence intensities of the standards and generate calibration curve. Read the fluorescence intensities of the samples. Calculate sample(s) concentration from

22

the calibration curve (concentration vs. fluorescence intensity. Correct for dilution, as needed.

Both UV and fluorescence methods can be easily automated by adding an auto-sampler and building the automation into the program that comes with the spectrometer. Automated Fluorescence Spectrometry as a Field Method 1. Turn on fluorescence spectrometer lamp and stabilize for 30 minutes. 2. Load the undiluted field samples into the carousel. Acidify and filter sample, if turbidity

is detected, before loading sample into the carousel. 3. Load the proper calibration curve (each corrosion inhibitor has a different calibration

curve, set-up by a chemist initially and rechecked at monthly intervals). 4. When oil or emulsion is visually detected, a methanol sample is run before and after the

brine sample. 5. Equipment goes through the following steps: sample pickup, dilution, mixing, delivery to

fluorescence cell, rinsing and analysis. 6. Deionized water is inserted after every 10 samples to check the lamp intensity and

methanol wash every 15th sample to prevent problems from oil, solids and emulsions. 7. Check calibration curves at programmed intervals by running a few standards and

comparison to the stored calibration curves.

APPENDIX C

SPE/HPLC/FLOURESCENCE FOR ANALYSIS OF CORROSION INHIBITORS IN CRUDE OIL15

1. Prepare a series of standards in o-xylene. Pipet a known volume of each standard into a silica gel cartridge.

2. Wash cartridge with o-xylene and methanol until clear solution comes out. 3. With a recirculating pump, circulate a fixed volume of fluorescamine solution in methanol

through the cartridge for 30 minutes. Make up to volume with methanol and mix well. 4. Inject solution of fluorescamine complex to HPLC. Read fluorescence intensity using

excitation wavelength of 278 nm and emission wavelength of 476 nm. 5. Generate calibration curve of concentration vs. fluorescence intensity. 6. Analyze crude oil samples as above, calculating the inhibitor concentration by

comparison with the calibration curve. 7. For aqueous samples, a C-18 cartridge is used. Washing is done with D.I. water, followed

by the fluorescamine complexation and extraction with methanol. Note: solids and corrosion inhibitor on the surface of the pipe may be analyzed by putting the solid or pipe in a small beaker, cover with enough fluorescamine solution and circulate, using recirculation pump, for 30 minutes.

APPENDIX D NMR SPECTROSCOPY PROCEDURE FOR BETAINES28

1. Weigh 40 mg of betaine sample. Add 1 g of 0.75% propyl-deuterated NaTSP in D2O into

NMR tube. The deuterated water acts as lock substance in the NMR experiment. The deuterated propyl group prevents additional signals in the high field part of the 1H-NMR spectrum observed from ordinary propyl groups which could interfere with signals in that spectral region.

2. Record spectrum. 3. Check spectrum for unexpected signals to identify unusual components.

23

4. Integrate the signal intensities of the betaine-specific signal at 3.3 ppm and the TSP signal.

5. Calculation of Betaine Concentration: % Betaine = mTSP /mBET* IBET/ITSP * MBET/MTSP* nHTSP/nHBET* 100 Where m = weighed mass I = intensity M = average molecular weight n = number of hydrogens producing the betaine specific signal and in the

trimethylsiloxy group of TSP

Table 1. Comparison of Analytical Procedures for Analysis of Corrosion Inhibitors

Method Analyzed Component

Detection Limit

Automation Relative Ease/Cost of Set-up

Methyl Orange Complexation

Quats* 1 ppm No Easy/Low

Bromocresol Purple Complexation

Quats < 1 ppm No Easy/Low

Bromophenol Blue Complexation

Quats

Figure 1. Typical Components of Corrosion Inhibitors

H2C N

CH3

CH3

R

HNCORN

NCORHH

21

Coco Quat where R = C8 C18 Diamide, where R = predominantly C18

N N

RNCORH2

N N

RNH2

2

Amidoimidazoline, where R = predominantly C18 Imidazoline, where R = predominantly C18

R(OCH2CH2)xO P

O

OHOH

(Mono)- Phosphate Ester, P

O

O

O

OH

R(OCH2CH2)x

R(OCH2CH2)x where R = alkyl group

(Di)- Phosphate Ester, where R = alkyl group

Figure 2. Absorbance Spectra of Bromocresol Purple/Quaternary Amine Complexes

FIGURE 2. Absorbance Spectra of Bromocresol Purple Complexes of Corrosion Inhibitor Standards

Wavelength (nm)200 400 600

Abs

orba

nce

(AU

)

0

0.2

0.4

0.6

0.8

1

1.2

25

Figure 3. Reaction of Fluorescamine with Primary Amines

O

O

R N H 2+

C O O H

NRO

O HO

Fluorescamine Primary Amine Pyrrolidine Figure 4. Emission Spectra of Corrosion Inhibitor, Before and After Partitioning

26

min6 8 10 12 14

Norm.

0

25000

50000

75000

100000

125000

150000

175000

MSD1 TIC, MS File (F:\DATA\2005912\NC591202.D) API-ES, Pos, SIM, Frag: 70 (TT), "MSD Positiv e"

13.

960

MSD1 TIC, MS File (F:\DATA\2005912\NC591203.D) API-ES, Pos, SIM, Frag: 70 (TT), "MSD Positiv e"

13.

952

MSD1 TIC, MS File (F:\DATA\2005912\NC591204.D) API-ES, Pos, SIM, Frag: 70 (TT), "MSD Positiv e"

13.

951

MSD1 TIC, MS File (F:\DATA\2005912\NC591205.D) API-ES, Pos, SIM, Frag: 70 (TT), "MSD Positiv e"

13.

957

MSD1 TIC, MS File (F:\DATA\2005912\NC591206.D) API-ES, Pos, SIM, Frag: 70 (TT), "MSD Positiv e"

7.7

38

13.

951

MSD1 TIC, MS File (F:\DATA\2005912\NC591207.D) API-ES, Pos, SIM, Frag: 70 (TT), "MSD Positiv e"

7.7

46

13.

616

Figure 5. Selective Ion Chromatograms of Corrosion Inhibitor Standards

Phosphate Ester

Amide

Imide

Figure 6. Calibration Curves for Corrosion Inhibitor Components (LC/ES/MS)

Amount[ng/ul]0 20

Area

0

100000

200000

300000

400000

123

4

5

6

Amidoimidazoline, MSD1 TIC

Correlation: 0.99757

Rel. Res%(1): 634.370

Area = 10199.0006*Amt -8176.4925

Amount[ng/ul]0 20

Area

0

200000

400000

600000

800000

1000000

123

4

5

6

Phosphate Ester, MSD1 TIC

Correlation: 0.99923

Rel. Res%(1): -19.290

Area = 22136.0228*Amt +12786.805

27

Figure 7. Crude Oil with ProductContaining Amidoimidazoline

AliphaticAminesAmidesAcids

Ethersvinylaromatic

Res

idua

l wat

er

-(C

H2C

H2O

)-

MeO

H

Ace

tate

NaT

SP

Figure 8. Crude Oil Sample with Additive

TMS

28

AliphaticAminesAmidesAcids

Ethersvinylaromatic

Res

idua

l wat

er

-(CH

2CH

2O)-

MeO

H

Acet

ate

NaT

SP

Figure 9. Corrosion Inhibitor in Produced Brine

Poor Performer

Figure 10. IC Chromatograms of Good and Poor Performing Scale Inhibitors

A B

29

logo: number: 07618paper: Paper No.copyright: 2007 by NACE International. Requests for permission to publish this manuscript in any form, in part or in whole must be in writing to NACE International, Copyright Division, 1440 South creek Drive, Houston, Texas 777084. The material presented and the views expressed in this paper are solely those of the author(s) and are not necessarily endorsed by the Association. Printed in the U.S.A.cp: Copyright