The discovery of a giant oil accumulation in ultradeep waters off Brazil’s southeast coast is opening a new frontier for exploration and production. This pre-salt play, founded on the Tupi discovery in the Santos basin, contains potential recoverable reserves of 795 million m3 to 1.3 billion m3 [5 to 8 billion bbl] of oil equivalent.
Just one of several structures found beneath a thick layer of salt, the Tupi structure is pushing technological boundaries as E&P teams seek to define its geographic limits.
(Image)Presalt versus subsalt. Both types of salt are capable of forming traps and seals for migrating hydrocarbons. Presalt wells target reservoirs beneath the layer of autochthonous salt. Subsalt wells target reservoirs beneath themobile allochthonous salt canopy. Postsalt wells target formations above the salt.
From a geologic perspective, this play is a product of interminably slow tectonic and depositional processes involving continental rifting, seafloor spreading, and sedimentation. These processes were associated with the split between South America and Africa during the Cretaceous breakup of Gondwana. The depositional processes created source, reservoir, and seal layers necessary to successfully produce an active petroleum system.
From a technological perspective, the viability of the presalt play is a result of operator experience gained through overcoming the challenges of constructing wells in deep and ultradeep waters off the coast of Brazil. Just as important are improvements to seismic imaging, which allow geophysicists to identify potential structures masked beneath layered evaporites that may be as thick as 2,000 m [6,560 ft].
Expertise and techniques developed to exploit deepwater fields of the Campos basin have been adapted to wells in the Santos basin. Exploration models from the Santos basin presalt play, in turn, have led to significant discoveries in neighboring basins. This article discusses the geology and history of Brazil’s presalt play and describes challenges associated with exploration and production of presalt carbonate reservoirs.
Beasley CJ, Fiduk JC, Bize E, Boyd A, Zerilli, Dribus JR, Moreira JLP and Pinto ACC: “Brazil’s Presalt Play,” Oilfield Review 22, no. 3 (Autumn 2010): 28–37.