A common concept for oil production and export comprises the use of Floating Production Storage and Offloading (FPSO) vessels. These vessels, whether purpose built or, alternatively, converted tankers receive live produced oil which is then processed on board in preparation for export. On the FPSO, gas is separated from the oil and is typically used for fuel gas, lift gas, or injection gas. There may be times when fuel gas production is forecast to reach a deficit. To address this, additional produced gas may be spiked into the oil export pipeline to the FPSO and used as a source of fuel gas.
During the front-end engineering and design (FEED) phase of a recent project, dynamic multiphase pipeline simulation showed that the oil pipeline would experience slugging across a wide range of operating conditions when fuel gas is spiked into the oil export pipeline. To mitigate slugging, a slug control valve was introduced at the outlet of the oil export pipeline. Further simulation demonstrated that using the slug control valve, slugging can be effectively mitigated.
The primary objective for the study was to recommend the simplest possible operating procedure to manage slugging in the oil export pipeline after the introduction of fuel gas spiking. In addition to avoiding slugging, the recommended slug control valve positions also needed to ensure that the pressure at the inlet of the oil export pipeline would not exceed a given threshold. Further simulation was also necessary to ensure that the slug control valve operating procedure would work irrespective of which gas is being used to spike the oil export line given that two different sources of gas with differing compositions are available. The results for only one composition will be presented here.