Prevention of hydrate plugging by kinetic inhibitor in subsea flowline considering the system availability of offshore gas platform

[Display omitted] •Methodology was proposed to prevent hydrate plugging in subsea flowline using KHI.•System availability was analyzed to predict shutdown frequency of offshore gas platform.•This approach provides the guideline of KHI injection according to the system downtime. This paper presents a new methodology to apply a kinetic hydrate inhibitor (KHI) to prevent hydrate plugging considering the system availability of the topside system in an offshore gas platform. The proposed methodology comprises three steps: the system availability analysis by Monte Carlo simulation, subsea multiphase flow simulation to evaluate the risk of hydrate plugging, and application of KHI to prevent hydrate plugging. The topside system availability and its longest downtime were estimated to be 99.3% and 47h, respectively. As a result of the multiphase flow simulation, the temperature in the flowline decreases from 40°C to 5°C during the system downtime, creating the condition for hydrate formation. Thus, polyvinylcaprolactam (PVCap) was used to delay hydrate plugging for a period longer than the cooldown time. As a result, the injection rate of 0.75wt% of PVCap was required 0.6 times per year to prevent hydrate plugging, while 30wt% of mono ethylene glycol (MEG) was required under the same hydrate formation condition. This approach provides the guideline for KHI injection according to the system downtime and flowing performance in subsea gas flowline as a risk management strategy to mitigate operation risks in the offshore gas platform.