A dual functional kinetic hydrate inhibitor (KHI) and compatible corrosion inhibitor (CI) package was developed to simplify production chemistry demands for operation in wet gas mode. As these two classes of chemistries are both water soluble and contain surface active components, they have a tendency for interference reducing the efficacy of each inhibitor. Their pairing in a production scenario requires both comprehensive performance testing as well as extensive secondary properties evaluation. The KHI is to serve as a traditional KHI during steady-state operations while performing as a thermodynamic hydrate inhibitor (THI) during extended shut-ins and cold well restarts. This challenge required the development of a KHI which would retain performance upon significant dilution in a thermodynamic hydrate inhibitor solvent carrier (methanol, ethanol, monoethylene glycol, etc). Performance of this new KHI would be confirmed in blind rocking cell experiments, in the presence of the matched corrosion inhibitor, targeting a hold time of more than eight days at a subcooling of 8 ºC. The CI is targeted to reduce the general corrosion rate to less than 0.1 mmpy and prevent localized attack. Due to the surfactancy of this class of chemistry, the tendency to induce and stabilize emulsions is of high concern. A robust formulation amenable to modification and potential dilution is required to address the application of chemical over a vast subsea network containing wells of varying age, existing infrastructure, production profiles, and operating conditions. This paper describes the development, qualification process, related lessons learned, and field applications of this new KHI/CI package. Introduction The oil and gas industry often relies on chemical solutions to address challenges related to flow assurance and corrosion inhibition. The transport of produced fluids containing water and acid gases such as carbon dioxide and/or hydrogen sulfide in metal pipelines afford conditions susceptible both to gas hydrate formation and corrosion. Accordingly, production chemical strategies typically must consider a compatible corrosion inhibitor and low dosage hydrate inhibitor as a unified package. Standard chemical compatibility often includes the mixing of two neat production chemicals with exposure at various temperatures to examine for hazing, phase separation, precipitation, etc. This exercise provides operators insight in the event that chemicals are accidently mixed in storage tanks or may come into contact in delivery lines. Though, the performance compatibility of a KHI and a CI presents a more challenging case.
As assets in the Southern North Sea continue to mature the tie in of new (high pressure) wells becomes more challenging. Additionally, the operators may consider centralizing their processing, increasing the complexity of the system. The wet gas then has to be transported over longer distances. Moreover, a greater emphasiss than before on the environment has created a drive to reduce production chemical usage. These factors combined have set new and challenging requirements for the chemicals that are to be applied to protect the existing facilities against hydrate formation and corrosion. Conventional offthe-shelf technologies were not able to meet the tough challenges, and required the development of a novel, and fit for purpose kinetic hydrate inhibitor (KHI) and corrosion inhibitor (CI). The minimum performance requirements for the KHI included protection against hydrate formation at conditions of 8 degrees Celcius subcooling and 200 hours of hold time. Besides the high level of subcooling and extended hold time, several secondary chemical properties were essential for successful application of the developed product. These included: solubility of the KHI and CI at elevated temperature and high salt concentrations (independent of each other and together), the chemicals are to be formulation in methanol and functionally compatible, have a minimum impact on oil in water and water in condensate separation, have low reservoir impact with produced water reinjection (PWRI), be HSSE acceptable (CEFAS sub-warning free) and comply with certified chemical cleanliness standards (SAE Class 6) to enable trouble-free umbilical application. All of these requirements were able to be met for the developed product packages. This paper describes the qualification process, lessons learned and the first successful field application of the newly developed chemistries into a recently developed reservoir block in the southern North Sea.
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.
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