Offshore Production Units for Pre-Salt Projects

Abstract

Petrobras and partners have been developing Brazilian Santos Basin Pre-Salt ultra-deepwater areas through the use of Floating Production Storage and Offloading Units (FPSOs), equipped with topside facilities designed to receive produced fluids and process them to generate end streams to export and injection. The large hydrocarbon volumes in Santos Basin Pre-Salt areas, which have been successively confirmed by the results of exploratory and productions wells, have encouraged Petrobras and partners to choose an aggressive development strategy over a more conventional one. Based on this decision, FPSOs were chosen, mainly due to crude oil storage capability thus not requiring the construction of long-length oil pipelines, and also because of other characteristics that allow a short term completion with economic advantages. Therefore, the topside process plant conceptual design had to deal with uncertainties in the reservoir fluid compositions and production profiles. This means a wide range of CO2 and H2S contents, oil API gravity, flow rates and arriving fluid pressures and temperatures, in order to guarantee an adequate nominal capacity and turndown, and also the proper performance within the established design cases. The main purpose of the topside facilities is to gather and treat the produced fluids to be sent ashore. The treated oil is routed to cargo tanks, the produced water is treated and discharged overboard, an dthe bulk treated gas stream is exported through a gas pipeline network, which allows to send the stream to three different gas processing sites onshore. The separated CO2-rich stream is injected back to the reservoir. Besides the production units specially designed for Santos Basin Pre-Salt features, some Pre-Salt reservoirs from Campos Basin have been also being produced, by connecting new wells to existing production units. The main approaches regarding these units and its production in Campos Basin Pre-Salt are also part of the scope of this paper. As a result of these different strategies and due to the daily efforts to overcome the forementioned challenges, more than six hundred thousand barrels per day of crude oil, as a monthly average, have been produced in Brazilian Pre-Salt areas, after only eight years since the early developments of the area.