Evaluation and flow assurance on hydrate formation during commissioning of sealed subsea wet-gas pipelines

The risk of hydrate formation may occur during commissioning of a sealed subsea wet-gas pipeline. In this paper, for such a pipeline in a sea area of China, HYSYS software was used to simulate and analyze the phase equilibrium and hydrate formation conditions, and PIPEPHASE software was used to simulate and analyze the pressure and temperature distribution of the wet gas along the subsea pipeline. Static simulation experiments were performed on the hydrate forming rate in wet gas. Based on the comparative analysis between numerical simulation results and experimental simulation results, the possibility of hydrate formation in the subsea pipeline was evaluated, and flow assurance measures were proposed to ensure the successful commissioning of the pipeline. It is shown that hydrate could theoretically generate when the wet gas is put into production between 4 and 6 MPa without inhibitor or other insulation protective measures being taken. The condensate oil contributes to inhibiting the formation of hydrate. The pressure of wet gas in the subsea pipeline fluctuates with the fluctuation of seabed, but pressure loss in the whole pipeline is little and the temperature in the pipeline drops quickly to ambient temperature. The accuracy and reliability of the numerical simulation results are confirmed by simulation experiments. Wet gas can be put into production smoothly by adopting a reasonable production plan and taking some measures, such as adding monoethylene glycol (MEG).