The Discovery and Appraisal History of Two Supergiant Oil Fields, Offshore Brazil

Abstract

ABSTRACT From the beginning, exploration in the Campos Basin has faced the limitations in production technology imposed by the water depth. Structural, stratigraphic, and seismic evidences nonetheless indicated that the deep-water region of the basin as highly attractive. The discovery of the Marlim and Albacora super giant fields in water depths ranging from 250 m to 2,000 m proved that prognostic correct and triggered the search for technological solutions which would make production feasible in such frontier regions. Estimated volumes of oil in place for the Marlim Complex (which encompasses the Marlim Field and some adjacent proved and potential areas) and the Albacora Field are 14.1 and 4.5 billion barrels, respectively. In the Albacora Field, hydrocarbon is accumulated in turbidite reservoirs ranging in age from Albian to Miocene, while in the Marlim Complex accumulation occurs mainly in Oligocene turbidites. The drilling of the wildcat wells responsible for the discovery of these fields was based on wide-open 2-D seismic grids. To optimize delineation efforts and lend support to field development, 3-D seismic surveys were shot over both hydrocarbon accumulations. The amplitude maps derived from 3-D data proved a powerful tool in mapping both external geometry as well as variations in the properties of turbidite reservoirs containing these accumulations. The highly positive results provided by 3-D seismic data led to the shooting of a large exploratory 3-D survey covering the deepwater region southwest of the Marlim Field. Another exploratory 3-D seismic survey has already been programmed to cover the deepwater region north of the Albacora Field. The next important step in the exploration of the Marlim and Albacora fields will be the search. for oil in deeper stratigraphic targets. INTRODUCTION Brazil has one of the world's largest sedimentary areas (Fig. 1), covering over five million square kilometers (1,900,000 mi2) of national territory, both on and offshore. Offshore sedimentary areas total 800,000 km2 (308,880 mi2) down to a water depth of 200 m (656 ft). Considering the continental slope down to the 2,000 m (6,562 ft) isobath, offshore sedimentary areas exceed 1,000,000 km2 (386,100 mi2 Offshore areas hold 72% of Brazilian reserves (438,779,000 m3 or 2.760 billion barrels) and account for 70% of domestic production (653,500 barrels per day). This production corresponds to 47% of national consumption. It is in the offshore areas, mainly in deep-water regions, that PETROBRAS places its greatest expectations as to the future discovery of important hydrocarbon sources (Fig. 2).1 The Campos Basin, located off the coast of the state of Rio de Janeiro (Fig. 1), is by far the most prolific of Brazil's sedimentary basins. It contains 69% of national reserves, and its present average production of 410,000 BOPD represents 89% of national output. Figure 3 shows the geographic distribution of Campos Basin oil fields, along with a bathymetric map. Down to the depth of 3,200 m (10.500 ft), the basin covers an area of 100,000 km2 (38,610 mi2).