Remediation of Hydrate Plug in Gas Export Line – A West Africa Deep Water Case

Abstract

This paper describes a recent hydrate plug issue experienced in a 12inch gas export line of one of TOTAL E&P operated FPSOs in the deep water of West Africa. In summer 2018, due to long-term maintenance work on the dehydration unit of the FPSO's gas compression, the off- spec produced gas was injected into a remote subsea gas well injector to avoid gas flaring, in line with TOTAL's flaring policy. Methanol was continuously injected for hydrate inhibition. Unfortunately, at the end of the operation, a hydrate plug occurred in the 12-inch gas export line. Through a multi–disciplinary crisis management team, all necessary efforts and procedures were implemented to remove the plug from the line in less than 1 week. The main steps included topsides depressurisation, a subsea intervention, additional hydrate inhibitor injection (Methanol and especially MEG) and liquid flushing operations.