Reservoir Geophysics in Brazilian Pre-Salt Oilfields
Authors: Johann Paulo Roberto , Martini Alvaro Favinha , Maul Alexandre , Nunes Joao Paulo Pereira 
Published: April 2012

This paper focuses on the impact that reservoir geophysics has had on theproduction development of the Brazilian marine carbonate pre-salt fieldsstarting from the first oil discovery in 2005 to 2011. The evolution of threemain knowledge areas of reservoir geophysics technology will be detailed, namely: acquisition, processing and interpretation, all oriented towardsreservoir characterization and monitoring. Seismic acquisition technology hasexperienced an increase in " information density" (seismic traces per squarekilometer). In the seismic processing domain, the improvement of seismicalgorithms and methodologies has allowed for better seismic data quality, resolution and imaging. In particular, the algorithms/techniques of 3-Dmultiple suppression and 3-D depth migration have significantly evolved in recent years. In the seismicinterpretation area, geological contextoriented seismic attributesalgorithms/methodologies have made possible better reservoir characterizationin the deep and ultra deep-water Brazilian offshore basins.

Introduction

Petrobras is one of the world's leading companies in deep and ultra-deep waterexploration and production. The company currently operates approximately 25% ofthe ultra-deep water production facilities in the world, enjoying globalrecognition for its vast and unmatched expertise in this area. Within thiscontext, which still poses enormous scientific and technological challenges, wesaw the discovery of the microbial carbonate rocks province of the Brazilianpre-salt play, which is already averaging a daily production in excess of100,000 b/d and which can potentially double or even triple the presentBrazilian reserves level of 15 billion barrels, representing, at this moment, areserves-to-production ratio of at least 18 years.

The Brazilian microbial carbonate reservoirs province which is presently beingput in production offers rare opportunities for the Brazilian technologicaldevelopment and for national and international companies that are involved inthematic areas, especially in subsurface sciences and technologies such asgeophysics, geology and reservoir engineering.

Given the magnitude of the occurrence of these oil reservoirs - ranging fromthe Santos sedimentary basin, at the south, extending north through the Camposbasin to reach the Espirito Santo basin, about 200 km wide by 800 km long, comprising an area of approximately 149,000 km2 (Figure 1) - substantialfinancial investments will be required to allow exploitation of these deposits, especially with the drilling of wells and the installation of productionfacilities at ultra-deep water environment and buried reservoir rocks, morethan 5,000 m below sea level.

The scientific and technological opportunities are immense, starting with theimprovement of the geological knowledge of these microbial carbonate rocks, their reservoir characteristics and their fluids types. This knowledge will beimproved over the years by the drilling of new wells, collection of coresamples, performance of geophysical logging and formation testing in thesewells in addition to long-duration production tests (LDT), and analysis of thedata obtained from the pilot and final production systems.

Particularly in the area of reservoir geophysics, opportunities are associatedwith improved geophysical characterization of these microbial carbonatereservoirs, which are located at depths greater than 5,000 m below sea level, and their future potential geophysical monitoring, after the onset of secondaryrecovery projects such as water and/or gas injections.

The discovery and production of this province of microbial carbonate reservoirsin the Brazilian pre-salt is impacting the Brazilian oil industry as a whole, including both, large and small companies, and also international ones which, directly or indirectly, work in Brazil.

Not only the industry will have to respond, but also research centers anduniversities throughout the country will need to be strategically integratedtogether with the Brazilian government to promote the necessary industrialrevolution that will materialize the production of these findings.