Deep Water Reservoir Management: the Brazilian Experience

Abstract

Abstract Exploratory activities in the Campos Basin began in 1968, and in 1974 was made the first discovery, the Garoupa Field, at a water depth of 120 m. Advancing to deep waters, large Tertiary reservoirs were found, including the fields of Albacora (250–900 m, 1984), Marlim (600–1,100 m, 1985) and South Marlim (900–2,600 m, 1987). After that, other seven giant oilfields were discovered in Tertiary and Upper Cretaceous reservoirs, including the last one, Roncador Field, discovered in 1996. The exploratory success in the Campos Basin was strongly influenced by the systematic use of 3-D seismics. The excellent seismic data quality plays a very important role in the exploratory and development phases of the complex deep water reservoirs. Reliable seismic processing and interpretation is the key to reservoir mapping, substantially reducing costs and risks. Reservoir studies are conducted by multidisciplinary teams combining geologists, geophysicists, and drilling, production and reservoir engineers. Usually, an early production system (pilot "mini-project") is set up to obtain information on reservoir and operational data. The overall project is divided into phases, which allow the development of appropriate technologies, risk reduction and investment distribution over time. Introduction Campos Basin, off the southeastern cost of Brazil, covers about 100,000 km2, extending roughly from the coast to the 3,400 m isobath (Fig. 1). To the north, it is separated from the Espirito Santo Basin by the Vitoria High, and to the south, it is separated from the Santos Basin by the Cabo Frio High. The first seismic surveys started in 1968 and the first exploration target was Albian and Neocomian carbonates. Only in 1979, Cretaceous and Tertiary turbidites became important targets. Today, Tertiary and Cretaceous turbidites represent nearly 90% of the total reserves of the basin. After 30 years of exploration, the Campos Basin accounts for 88% of the total Brazilian reserves, and 71% of the oil production. Since the first discovery in 1974 (Garoupa Field, water depth of 120m), the deep water portion of the basin has showing a strong potential to be prolific. In 1984 the Albacora Field was discovered in water depths between 250 and 900 m; in 1988 the Marlim Field (600 to 1,100 m); in 1987 the South Marlim Field (900 to 2,600 m). After that, other seven giant oilfields were discovered, including the Roncador Field, discovered in 1996. The size of the discoveries in deep water Campos Basin encouraged PETROBRAS to go ahead with investments in technology for deep-water production. Today almost 76% of the company's proved reserves, and 79% of the total reserves lie in waters deeper than 400 m (Fig. 2). The total Brazilian reserves are presently estimated in 16.9 billion barrels of equivalent oil, and the proved reserves are estimated in 8.5 bi llion barrels. The next table shows the reserves of the main fields located in water depths between 250 and 2,600 m. The greatest oil in place volume is in South Marlim (10 billion barrels) immediately followed by Roncador (9.2 billion barrels). The largest proved oil reserve is in Marlim Field (2,2 billion barrels) and the most important production comes today from Albacora and Marlim (170,000 and 190,000 bbl/d, respectively).