Flow Assurance Issues on Mexilhão Field Operation

This paper shows the main concerns related to Flow Assurance during Mexilhão gas field operation. Mexilhão is located in Santos Basin, Brazil and flows from seven gas wells to a fixed platform through a subsea manifold. Well’s water depth average is about 470 meters and platform’s water depth is 172 meters. The tieback between the manifold and platform is 22 kilometers and there are two production pipelines of 12-inch diameter connecting them. The thermo-hydraulic profile of the production fluid enters in hydrate formation region and hydrate thermodynamic inhibitor (MEG) is injected to prevent hydrate formation. This MEG is recovered at the platform and it is reinjected in the wells. Dosing valves located at subsea manifold distributes the desirable quantity of MEG for each well. During eight years of operation, no production loss caused by hydrate blockage has been reported. This paper also shows the method of wax deposit management in Mexilhão subsea system. Although certain amount of wax had been anticipated to accumulate along pipeline, very little wax was found after pig runs. It has been observed that wax appears in platform process plant, however it does not seem to accumulate in the pipeline. Pig runs occur only for the purpose of corrosion monitoring. Another item discussed here is scale prevention, which could be performed with downhole inhibitor injection and it has not been required until today. Finally, transient simulation results which guided the operational procedure to increase gas flow rate are shown. There is no slug catcher at the platform, then, in order to avoid shut downs due to large liquid slug arrival at process plant, the procedure to increase gas flow rate must be performed carefully.