Influence of riser-induced slugs on the downstream separation processes

Abstract

In Oil & Gas installations the severe slug is an undesired flow regime due to the negative impact on the production rate and facility safety. This study will evaluate the severe riser-induced slugs' influence to a typical separation process, consisting of a 3-phase gravity separator physically linked to a de-oiling hydrocyclone, based on experimental tests performed on a laboratory testing facility. Several scenarios are compared, while three PID controllers' coefficients are kept constant for all the tests: The separator pressure, water level, and hydrocyclone pressure-drop-ratio (PDR) controllers. Each respective scenario makes a comparison between uncontrolled, open-, and closed-loop anti-slug control configurations. It is concluded that both open- and closed-loop anti-slug control strategies improve the water level and PDR setpoint tracking equally well, but that the closed-loop strategy gives the best average production rate. Furthermore, it is confirmed that a PWT-efficient riser bottom pressure (Prb) anti-slug control strategy has to guarantee stabilization of the mass inflow rate to the separator (ωsep,in) for archiving acceptable hydrocyclone separation. A stable ωsep,in is observed not to be directly linked to a stable Prb.