Abstract
In recent past, most of Brazil's oil production was generated from siliciclastic reservoirs in scenarios of deep and ultra-deep water of the Campos Basin, being much effort focused on developing technologies to guarantee production optimization. Despite the great experience acquired by Petrobras in evaluating dynamic behavior of deepwater fields, new production scenarios of heavy oil reservoirs are even more challenging due to their high oil viscosity that generates emulsion stability.
Jubarte field (siliciclastic turbidite reservoir) development features 15 heavy oil producing wells tied to P-57 floating production storage and offloading (FPSO) vessel. Each well is equipped with a 1500HP electrical submersible pump (ESP) installed in a caisson located 210 meters away from the wellhead in water depths varying from 1260 to 1360m. Over the last 3 years, since Jubarte first oil, the maturity curve of the wells has revealed a scenario where ESP has been recognized as a critical component of the subsea production system to sustain well production.
Normally adopted in projects to anticipate production during the early years, ESPs in Jubarte field have been presenting an outstanding performance, overcoming oil viscosity limitations or unpredictable multiphase flow regime with strong emulsion formation (both tied to injection of viscosity reducers and the advent of natural free water from the reservoir).
Operating ESPs installed at the seabed poses challenges in many aspects. Understanding the flow pattern (to ensure effective startup and run in optimal conditions), pump and caisson fluid dynamic behavior (to allow the pump ride through some observed inflow discontinuities) are two essential issues.
This work aims to introduce the phenomenon of flow intermittency experienced during the operation of ESPs installed in vertical caissons in Jubarte field. It also demonstrates the engineering approach and the main proposed solutions to overcome the problem of well instability. The advantages obtained through the injection of demulsifier upstream the ESP are finally presented as a key element to promote stability, allowing ESP to run properly with significant gains in production rate.
