In the pursuit of greater productivity, Petrobras has been using increasingly ESP (Electric Submersible Pump) on its wells, especially on heavy oil fields, in which the gaslift method is not as effective as that system. However, since the ESP MTTF (Mean Time to Failure) is not greater than two and a half years, major offshore operators have been looking for new technologies that can reduce intervention time and costs. Deepwater Pumping Modules (MoBo) are an excellent alternative for that. The system consists of an ESP installed on a caisson located on the sea bed. This module allows not only for faster interventions when compared to conventional ESP (inside the well), but also admit ESP workover without interrupting production (by using gas-lift as a contingence).
On the other hand, Pumping Modules (MoBo) have inherent constructive characteristics that may lead to a great extent of liquid-gas separation. The geometry of those systems has a downward annular flow that can contribute not only for instabilities such as severe slugs, but also to an excessive gas fraction at pump intake, causing the phenomenon known as gas-lock.
This study intends to characterize the fluid-dynamic behavior of Pumping Modules through the use of a multiphase transient approach. This model has been developed using a 1-D multiphase transient software and it has been validated through an extensive comparison with real field data. To accomplish that, data were collected from online instrumentation and production tests to be used as validation parameters. Finally, due to the highly tri-dimensional characteristics of the flow, a validation against a substantially more refined 3-D model has been run.
After model validation, a study was conducted in order to map possible operational conditions, determining whether the system would be stable or not under certain boundary conditions. That study has helped Petrobras to predict possible unsuitable behavior prior to new installations, as well as to define optimum operational conditions of wells during their production life. As a conclusion, the validated model shows to be a useful tool for flow assurance studies in those scenarios.