GEOSCIENCES CHALLENGERS TO DEVELOP AND PRODUCE PRE-SALT FIELDS, OFFSHORE SE BRAZIL

According to the Petrobras ́ Strategic Plan 2020, in the next 10 years, Petrobras ́ oil production will reach 5,4 Kboe/d, twice today’s production, and almost triple today ́s Brazilian gas production (from 384 Kboe/d to 1,109 Kboe/d). A significant part of this production increment will come from the Pre-Salt Oil Province, which typically presents important volumes of associated gas. The gas-associated Lula oil field, one of the largest fields of the Pre-Salt Province, has a high GOR (> 200 m3/m3), reinforcing the importance of these province for the future of Brazilian gas production. After successfully testing two wells, PETROBRAS, as the operator of Block BMS-11 (Santos Basin), and partners BG and PETROGAL, announced Tupi discovery in the Pre-salt province of Santos Basin by November 2007. An extended well test program (EWT) was initiated to acquire reservoir dynamic information from May 2009 up to the end of 2010. The official commerciality declaration of this area, now named as Lula field (including Lula and Cernambi areas) was informed to the National Petroleum Agency of Brazil in December 2010, after drilling and testing additional wells and analyzing the EWT data. Since 2010, a production pilot is in progress in Lula field, anticipating more robust reservoir information for the definitive production systems. This strategy, frequently used by PETROBRAS production development projects, consists of development in phases: EWT, Production Pilot, and Definitive System. Pre-Salt reservoirs are lacustrine carbonates, mostly microbialites, deposited during the Sagand Rift-Phase (Aptian), and coquinas of the Rift-Phase (Barremian), formed during the South Atlantic Gondwana break-out. They are located at more then five km depth below sea level, at ultra deep water (around 2,2 km), and under a two km thick layer of evaporites. The main geoscience reservoir challenges to develop these areas are related to (1) geological model: understanding the origin and characterize the rock-system itself, (2) describing and representing reservoir rock heterogeneities, (3) imaging seismically reservoir rocks and fluids, (4) and the definition of the production strategy: analyzing the impact of heterogeneities for different production strategies, including placing the wells at optimum locations according to each production strategy (predicted water flood at some areas or WAG at other areas). To overcome these difficulties, Petrobras set up a large R&D program internally and with Brazilians and international universities, research centers and service companies. The major geosciences research trends, mainly related to reservoir geology and geophysics, actually on development to accomplish these challengers, are discussed on this paper.