This paper presents the work done to address the severe instabilities of a subsea multiphase pump installed at the riser base to boost the production of a deep-water West Africa field. Moreover, the actions performed to further optimize its operation are discussed.
The analysis and troubleshooting of the behaviour of the subsea multiphase pump and production network was facilitated by Eni digital oilfield system, which makes the data available to all the relevant specialist regardless of their geographical collocation. The real time data archive and the capability to seamlessly correlate different variables available within the digital system environment were leveraged to quickly perform specific engineering analyses. For example, it is possible to compare the operating conditions with the design data and to feed the thermo-fluid dynamic simulators.
In particular, one of the root causes of the encountered instability issues was the ratio of the production coming from two different reservoirs and commingled at the inlet of the boosting system. In fact, the mix temperature was higher than expected and higher than the pump maximum operating temperature, thus leading to automatic pump shut-downs. Once identified, this phenomenon was prevented by optimizing the mix from different wells and changing the setpoint of the temperature alarm after a requalification of the pumps and manifold materials. A further cause of frequent pump trips was due to hydrodynamic slugging of the production network and its interaction with the pump recirculation system, which were identified and partially prevented with a fine tuning of the pump control system. Also, the presence of spurious erroneous readings from the multiphase flow meter installed at the pump outlet, due to the presence of scales, was the cause of pump trips. Lab analyses confirmed the risk of scales precipitation at specific water ratios between the two reservoirs. An acid job helped reinstating the meter reliability and the overall system stability. Finally, switching from flow-control mode to torque-control mode further reduced the pump trips.
The work of a multidisciplinary, committed team together with the availability of the digital oilfield system for real-time and historical data allowed to successfully overcome and solve these issues leading to smooth operations. A series of operational lessons learned were also collected for other similar projects.
