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.
An operator in the North Sea has successfully employed a kinetic hydrate inhibitor (KHI) for over a decade. This operator produces through two 13 mile flowlines, separated into wet gas and fluids, to a multiphase host facility. At this host facility, the two production streams recombine in a slug catcher upstream of the separation system. The wet gas line operates continuously under conditions of hydrate stability requiring the use of a KHI. As additional wells have been tied into the subsea production stream, conditions have changed necessitating advancement in KHI technology.The new production introduces formation water of considerable salinity into the production stream as well as increasing the temperature of commingled fluids in the slug catcher. As KHI polymers possess inverse solubility profiles with respect to temperature and salinity, gunking was frequently observed in the production slug catcher. The precipitated polymer, in addition to sand and organic solids in the system, caused frequent upsets and deferred production. Accordingly, a KHI polymer with improved solubility profile (cloud point) was targeted for this application. The KHI performance and compatibility with incumbent corrosion inhibitor were confirmed and optimized to a 50% reduction in treatment rate by autoclave experiments under the established qualification protocols. Solubility experiments confirmed the compatibility of the new KHI with the expected temperature and salinity parameters of the full production.This paper provides a detailed history of this 10ϩ year application, recent qualification process, and field application of this new KHI offering.
With fields getting more mature and discoveries getting smaller, operators in the North Sea are pushed to reduce development and operating costs. In order to address this challenge, they develop small fields as wet gas subsea satellites and investigate centralizing existing gas processing facilities. Both require wet gas to be transported over increasing distances. This presents an extended challenge for traditional thermodynamic hydrate inhibitor (THI) solutions as increasing subcooling equates to larger volumes being required. The application of low dosage hydrate inhibitors (LDHI) helps to unlock these new smaller fields reducing project expenditure for platform storage, transport, and pumping of hydrate inhibitor while maintain subcooling protection.A further refinement is to require the application of a kinetic hydrate inhibitor (KHI) with dual functionality. The KHI is to serve as a traditional KHI during steady-state operations while performing as a THI during extended shut-ins and cold-well restarts. This challenge required the development of a step-change polymer technology as a fit for purpose solution.The minimum performance requirements for the KHI incorporated hydrate forming conditions of 8 o C subcooling and 200 hours of hold time in blind rocking cells. Besides the high level of subcooling and extended hold time, several secondary chemical properties were essential to success. The expansion of polymer solubility (lower critical solution temperature) in 10-15% NaCl brines at temperatures up to 90 ºC for high temperature injection, polymer package formulation in a traditional thermodynamic inhibitor carrier for chemical deliverability, and extensive compatibility testing with a corrosion inhibitor were identified as key factors and rigorously examined to ensure a suitable inhibitor for the vast application. This paper describes the qualification process, related lessons learned, and successful first application of this new kinetic hydrate inhibitor offering.
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