Safe and Successful Gas Hydrate Plug Remediation in Vega Asset – Norwegian Gas Condensate Subsea Production System

Abstract

Gas hydrate plugs formed in subsea flowlines create complex challenges in plug remediation operations and can result in significant operational expenditures. In Vega, a Norwegian gas condensate subsea asset, a hydrate blockage was identified in a 12" ID flowline in June 2020. This work chronicles a series of operational activities in the detection of the hydrate blockage, modeling assessment, and safe and successful plug remediation efforts. Under the assumption that multiple plugs were present in the flowline, gas pockets could have formed in between the plugs, creating intermediate high-pressure regions. The two-sided depressurization of the flowline below hydrate equilibrium pressure (10 bara at 5°C) established successful pressure communication from both ends of the flowline. The field data interpretation showed the release of gas pockets and the corresponding pressure spikes during plug dissociation. The operational experiences from hydrate plug detection and melting, as well as modeling activities, provide valuable input for future hydrate remediation operations. The collective team effort in recording and analyzing all the instances addresses three main concerns of paramount significance in the oil and gas industry, which include the safety of personnel, equipment, and the environment.

Influence of Varying Underinhibition on Methanol in Gas Hydrate Agglomeration

“…Successful (or full) inhibition is achieved when THIs completely suppress hydrate formation . However, an insufficient amount of THI can lead to a higher hydrate plugging risk, and one can say that the systems are underinhibited. , Several field cases have been reported on hydrate plugging due to underinhibition. − Hemmingsen et al showed that the plugging potential of a three-phase system (comprising synthetic condensate Exxsol D60, gas, and water) with MEG reaches its maximum at a THI concentration of 10–15 wt %. In underinhibited systems, as water gets converted to hydrates, the THI concentration increases higher than the original concentration present in the system, leading to self-inhibition. , Based on the changes in THI concentration and changes in subcooling, the hydrate morphology in an underinhibited system was categorized into four zones: hard plugs (0–5 wt % THI), soft plugs with a high degree of agglomeration (5–20 wt % THI), and gel-like plugs and transportable hydrate slurry (20–50 wt %). , …”