--> Post-Mortem Analysis of a Dry Well in Central Santos Basin: A Petroleum System Modeling Approach, Bender, Andre A.; Mello, Marcio; Azambuja, Nilo C.; Jesus, Carlos L.; Mio, Eduardo D., #90100 (2009)

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Post-Mortem Analysis of a Dry Well in Central Santos Basin: A Petroleum System Modeling Approach

Bender, Andre A.1
 Mello, Marcio1
 Azambuja, Nilo C.1
 Jesus, Carlos L.1
 Mio, Eduardo D.1

1HRT & Petroleum, Rio de Janeiro, Brazil.

The rate of success, that is, commercial discoveries relative to drilled wells, in the Santos Basin from 1998 to 2007 was 8.5% in average. The best rate was 20.4% in 2003. The rates mostly reflect exploration success in shallow to intermediate water depths and the time series does not show that learning was achieved during the exploration process. The geology of the area is complex and the technology discussed here does not intend to be a magic solution to all unsuccessful wells, but rather present an analysis that make clear several geological aspects of the petroleum system and, consequently, can change a drilling decision, avoid this way a dry well.

The well analyzed is located in 120 m water depths, N-NE of the Merluza Field. It is included in a gas/condensate/oil trend that extends from the southern gas fields (e.g., Tubarão Field) to the Mexilhão Field area. The geological context is of thick asymmetrical rift depocenters, overlain by salt pillows/diapirs and a salt escape zone to the west. The post-salt sequence consists of a coarse siliciclastic dominated progradational shelf. The targets of the well were Upper Cretaceous sandstones and Albian shoal carbonates (secondary target). The structures are closed, formed by salt evacuation relative to adjacent salt pillows. There are several elements of the petroleum systems that apparently indicate the presence of high probability hydrocarbon bearing structures. For example, there are large salt windows in the area that theoretically allowed in the past upward migration of hydrocarbons from the sub-salt kitchen zones to the post-rift targets. In order to explain the lack of petroleum in the structures, several explanations were examined using a petroleum system modeling approach. A complete 3D geological framework was built using public (ANP) seismic data. The results were calibrated with BHT temperature data, maturity and geochemical data of several wells from HRT database. 3D compositional basin simulation runs, with salt restoration, were performed to obtain possible kinematic histories of the structural traps and possible migration flow paths nearby the studied well. The results of this study are robust and we obtain a plausible explanation for the lack of hydrocarbons in the target structures. Additionally, the modeling technology can be part of the exploration learning process, hence, increasing the success rates in similar complex basins as
Santos Basin.

AAPG Search and Discover Article #90100©2009 AAPG International Conference and Exhibition 15-18 November 2009, Rio de Janeiro, Brazil