Peregrino field, a Statoil asset in Campos Basin approximately 85 km (53 miles) offshore from Cabo Frio/Rio de Janeiro state in Brazil, completes 4 years of production in April 2015 with the use of electrical submersible pumps as the primary artificial lift method. The oil in Peregrino is highly viscous, reaching up to 365 cP at reservoir conditions (234 bars and 82 °C), and API gravity varies between 13° and 15° API. The field development is accomplished by two drilling- capable wellhead platforms where produced fluids are transferred to a central moored floating production storage and offloading unit (FPSO) through booster pumps. There are 27 producer wells and 6 injector wells in operation. The field is producing close to 100,000 BPD of oil. In nearly 4 years of operation water cut has reached up to 95% in some of the wells and, within specific water cut range, emulsion has become a reality and a challenging factor for ESP operation.
Despite the shear effect that liquid undergoes in centrifugal pumps and sand control screens, during the field basis of design phase emulsions were not expected to be a big concern. However, some actions like downhole chemical injection were taken in case emulsions developed. Maximum viscosity considered was up to 2 times the oil viscosity at reservoir conditions and simulations showed acceptable pump behavior and production. On the other hand field experience has required simulator adjustments up to 11 times the PVT oil viscosity for water cut in the range of 30% and 60%. Empirical modifiers were obtained from controlled in-house loop tests to contemplate viscosity effects on pump head, flow and break horsepower simulations.
Due to the high emulsion viscosity, which generally leads to production loss and flow instability, the ESP performance has been severely affected. This has been observed as high differential pressure and motor electrical current fluctuations leading to possible fatigue of ESP internal components and production deferment. This paper describes the emulsion issues faced in Peregrino and the challenges to minimize their effects.
The objective of this paper is to describe the performance of the field, status and experience gained with Peregrino production regarding optimization and ESP performance.