Print this pageUncertainty Analysis Applied to Petroleum System Mass Balance in Deepwater Santos — Is It from Overcharged System?
A complete 3D petroleum system modeling was carried out in deep water area in Santos Basin aiming to understand maturation, generation and migration mechanism and to assess the inherent risk associated. The uncertainty related with scarce data from source rock richness and distribution in these deep water areas requires a probabilistic approach in order to test the petroleum system charge and to analyze the impact of overcharging in the total cumulated volumes in the model. A reference simulation scenario was built encompassing three source rock levels: The lowest interval, related to Barremian/Buracica sequence (Talc-Stevensitic sequence), with thickness ranging from 20 to 190 m, HI from 60 to 550 mgHC/gTOC and TOC from 0.58 to 5.5 %; The intermediate level comprising distal facies of the Itapema Formation deposited during Neo-Barremian to Eo-Aptian (Jiquiá local stage), characterized by radioactive and organic rich dark shales having more than110 m thick (1-RJS-625 well) and represented in the model with thickness ranging from 15 to 190 m, HI from 66 to 825 mgHC/gTOC and TOC from 0.44 to 5.5 %; and , finally, the uppermost source rock comprising distal shales interbedded with carbonates from Barra Velha Formation (Eo-Aptian sequence deposited during the SAG phase) with thickness ranging from 6 to 120 m, HI ranging from 11 to 200 mgHC/gTOC) and TOC from 0.05 to 2.0 %. This reference model expelled 258.1 Bbbls and the expected cumulated volumes in reservoirs reaches 67.9 Bbbls, realizing petroleum system efficiency of about 26.3%. A second model was modeled, representing the best in class generation scenario where thickness, TOC and HI richness from Early Aptian and Alagoas source rock were improved about 50%. It encompass about of 372.4 Bbbls of expelled hydrocarbons and 77.0 Bbbls of expected trapped hydrocarbons, achieving petroleum system efficiency of about 20.67%. It points to an overcharged petroleum system, where the available reservoir space is apparently full filled. A stochastic risk approach was carried out, considering TOC and HI from Jiquiá and Alagoas as main uncertainties and comprising about full 3D simulations. The results confirm that hydrocarbon generation and reservoirs charge is not the decisive factor in the petroleum exploration success in this area.
AAPG Search and Discover Article #90100©2009 AAPG International Conference and Exhibition 15-18 November 2009, Rio de Janeiro, Brazil