Geological Characterization and Modeling of an Aptian Carbonate Reservoir in the Santos Basin, Brazil

Abstract

The offshore of Santos Basin, in the Brazilian Southeastern continental margin, accommodates a huge hydrocarbon province. In the early 2000’s, oil discoveries in deep and ultra-deep waters, located in the Barremian-Aptian carbonate section, brought a new economic interest to the area. In this work, we will focus on an Aptian carbonate platform, which composes one of the most prolific oil fields of this province. The work aims to present the geological context of the area and propose a workflow for the geological characterization and modeling to better understand the spatial distribution of the sedimentary facies and permo-porosity that can define preferential producing stratigraphic zones and flow paths. For this goal, the geological model represented by the structural, stratigraphic, facies and permo-porosity models will be presented. Sedimentological studies identified 5 main carbonate facies in the studied sequence: grainstones, stromatolites/shrubs, spherulitites, laminites and wackestones/mudstones. The cycles defined by facies successions allowed the interpretation of stratigraphic surfaces that can be correlated throughout the field and separate the section into 5 main zones. A stratigraphic-sedimentological forward facies model was constructed to reproduce the sedimentary stacking pattern observed from well data, based on the simulation and tests of different parameters that act in the depositional process of carbonate rocks: base level oscillations and carbonate depositional rate. The facies model is used to guide the permo-porosity distribution. The permeability distribution requires the definition of rock types, with different classes of permeability, and fracture zones. Based on 3D forward modeling, the best set of environmental conditions able to explain the pattern of carbonate deposition observed in the study area are a slow carbonate depositional rate and lake-level oscillations which were essentially induced by arid climatic conditions. In terms of reservoir quality, the better reservoir facies are stromatolites and grainstones. The higher permeabilities are a combination of the primary porosity connection, increased by dissolution and fractures. The integration of this work allows an understanding of the sedimentological processes acting in the platform, the facies and permo-porosity distribution between wells and helps in the improvement of the predictability of the production curves that can be confirmed by real production performance.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018