A subsea production flexible flowline in Gumusut-Kakap field was found blocked in March 2021 during a routine production well-flowline switching/alignment operation. Further evaluation showed that the blockage was caused by the formation of hydrate and gel over the 1.3km length of the flexible flowline, as the live crude and water were left stagnant and untreated in the flowline over a prolonged period. This paper covers the remediation strategy and the associated challenges from a System perspective, which successfully unblocked the flowline within a relatively short period of time.

The condition of the blockage in the flexible flowline was simulated using a commercial multiphase dynamic software to ascertain the phase distribution and hence allowed the estimation of the location and length of hydrate, gel, and emulsion in the flowline which has a downward inclination of circa 50 meters height. Heating (from production well), methanol (MeOH) soaking and flowline depressurization were planned and executed. In addition to the technical methodology, the System-wide aspects were also considered for the effective and optimum execution of the remediation activities which include attempting to fulfill the production commitment, abide by the subsea hardware and flexible flowline integrity envelope, and consider the impact of the remediation operation on other operations at the Gumusut-Kakap installation.

The MeOH soaking, flowline depressurization and pressurization successfully remediated the blockage over the period of weeks. Positive results were observed at the start of the remediation when the targeted location for MeOH contact and depressurization were identified via field trial. One of the key challenges is the time factor in which to ascertain the "appropriate" waiting time for the flowline depressurization, as the remediation involved partial shut-in of the prolific production wells.

A holistic System engineering approach is critical to the successful remediation of the blockage, integrating the key technical requirements as well as the soft and non-technical aspects to deliver optimum and net positive value for the asset.

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