Measurement and interpretation of corrosion inhibitor residuals in a mature offshore gas/condensate field could not be reconciled with field data leading to the identification of a potential infrastructure integrity threat that mandated understanding. The field had recently transitioned from buffered pH operation to "natural" pH operation of the monoethylene glycol (MEG) loop (alongside addition of corrosion inhibitor) due to carbonate scaling caused by formation water influx. An investigation was initiated to determine the corrosion inhibitors behavior throughout the production system with focus on demonstrating the effectiveness of the inhibitor. The investigation included extensive laboratory corrosion testing using field and synthetic fluids, residual determination in field samples using liquid-chromatography mass-spectrometry (LC-MS), field implementation and confirmation of appropriate actions. Upon completion of the investigation it was found that the intended corrosion inhibitor active components were not concentrating up in the MEG loop but were strongly partitioning to the natural gas condensate phase. This was leaving the topside facilities "under-inhibited". Obscuring this conclusion was the concentration of other benign (not corrosion inhibitor) active components present in the inhibitor formulation at very low concentrations which were giving falsely high inhibitor residuals. After changing the inhibitor injection philosophy from batch-wise to continuous, LC-MS residuals have continued to confirm the partitioning behavior in field operation without the introduction of an unmanageable secondary property concern due to the inhibitor. Further online and laboratory corrosion studies have confirmed the integrity of the production system as proof of the effectiveness of the inhibitor. These key lessons learned challenge operators and chemical vendors to consider the MEG circuit chemistry more carefully during chemical qualification to ensure that chemical behavior is understood both before field application and that it is confirmed once applied.

Control of inorganic scale deposition within the near well bore area under both natural depletion and injection water support has been a challenge to the oil industry for a number of decades. The application of scale inhibitor squeeze treatments to production wells to control the onset of inorganic scale within the near-wellbore and production tubing has been a common practice within the onshore and offshore oil and gas industry for over 30 years.The development of subsea fields require scale inhibitor squeeze treatments with extended squeeze lifetimes while limited number of flowlines to the host facility has increased the difficulty in obtaining and evaluating individual well water samples from which residual scale inhibitor concentrations are derived. Traditional analytical techniques, while robust and widely accepted, do not provide differentiation between scale inhibitors that belong to the same chemical family (i.e.: two or more phosphonates or two or more polymers).The individual analysis of phosphonate scale inhibitors in co-mingled flow backs from subsea wells is a particularly challenging application for analytical techniques in the industry. Advances in separation and mass detection techniques, however, provide new options to accurately measure the concentration of scale inhibitors in these fluids to very low detection limits. This paper will describe the analytical development of these new techniques and discuss its implication to the optimization of scale squeeze treatments in subsea, deepwater developments.

Accurate and precise analysis of scale inhibitor residuals is important to managing oilfield squeeze treatments. Phosphonate scale inhibitors are effective for the prevention and control of scale problems in oilfields. The traditional analytical technique for monitoring phosphonate scale inhibitor residuals is inductively coupled plasma optical emission spectroscopy (ICP-EOS). ICP-OES is simple and has been used for monitoring squeeze treatments for decades. However, it can only measure the total phosphorus in the system and is unable to differentiate the different forms of phosphonates in commingled samples. This paper presents a novel technique using ion chromatography and mass spectrometry (IC-MS and IC-MS/MS) for monitoring and quantifying different phosphonate scale inhibitors with high sensitivity and specificity. Ion chromatography efficiently separates phosphonate ions from other salt ions, and mass spectrometry speciates and quantitates molecular ions or fragment ions of each phosphonate. Previous work in our group (Zhang, et.al., 2014) had shown that IC-MS could be used to differentiate two phosphonates in a squeeze treatment using the characteristic molecular ions of each phosphonate. As the complexity of the squeeze treatment increases with the addition of other phosophates to the local oilfield, the development of an advanced IC-MS/MS method has been required to differentiate up to four phosphonates in a single commingled sample. This innovative technique has a detection limit of <1 ppm for each phosphonate in the mixture. The technique has been validated using both synthetic brine and field brine. Solid phase extraction cleanup work has also been performed to improve the capability of the technique in high-salinity brines. This novel analytical method will provide a powerful tool in squeeze scale management for subsea and deepwater oilfields.

Control of inorganic scale deposition within the near well bore area under both natural depletion and injection water support has been a challenge to the oil industry for a number of decades. The application of scale inhibitor squeeze treatments to production wells to control the onset of inorganic scale within the near-wellbore and production tubing has been a common practice within the onshore and offshore oil and gas industry for over 30 years. The development of subsea fields require scale inhibitor squeeze treatments with extended squeeze lifetimes while limited number of flowlines to the host facility has increased the difficulty in obtaining and evaluating individual well water samples from which residual scale inhibitor concentrations are derived. Traditional analytical techniques, while robust and widely accepted, do not provide differentiation between scale inhibitors that belong to the same chemical family (i.e.: two or more phosphonates or two or more polymers). The individual analysis of phosphonate scale inhibitors in co-mingled flow backs from subsea wells is a particularly challenging application for analytical techniques in the industry. Advances in separation and mass detection techniques, however, provide new options to accurately measure the concentration of scale inhibitors in these fluids to very low detection limits. This paper will describe the analytical development of these new techniques and discuss its implication to the optimization of scale squeeze treatments in subsea, deepwater developments.