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Título

EVALUATION OF GEOCHEMICAL PARAMETERS OF EOCENE SOURCE ROCKS IN THE FOZ DO AMAZONAS BASIN, BRAZILIAN EQUATORIAL MARGIN.

Texto do resumo

The Foz do Amazonas Basin, located in the northwest of the Brazilian Equatorial Margin, encompasses parts of the states of Amapá and Pará, with a total area of 268,000 km², including the continental shelf and ultra-deep waters. It exhibits geological correlation with the Guiana-Suriname and Sierra Leone-Liberia basins due to the connection between the South American and African plates. Its formation is related to rift processes resulting from the fragmentation of Pangea. The current study aims to evaluate the geochemical parameters of Eocene source rocks, followed by computational modeling of petroleum generation. Data from 95 wells were requested from BDEP/ANP, from which the geochemical data from wells 1-APS-45B-AP and 1-BP-3-APS, corresponding to the Amapá and Travosas formations, respectively, were selected for the study.
The Total Organic Carbon (TOC) data from the Amapá Formation well range from 0.05% to 1.27%. Approximately 55% of the samples from this well have TOC (>0.5%), indicating good hydrocarbon generating potential as they are carbonate rocks, while 45% of the samples have TOC (<0.5%), indicating medium to low generation potential. S1 values (free hydrocarbons) range from 0.01 to 2.69 mg HC/g rock. S2 values (hydrocarbon source potential in Rock Eval Pyrolysis) range from 0.03 to 2.66, considered poor in all samples except one within the reasonable range between 2.5 and 5 mg HC/g rock. Tmax values are less than 435°C, indicating that the samples are immature for hydrocarbon generation, however, S2 values are very low, making the Tmax values unreliable. The IP values range from 0.05 to 0.92, with only one out of the 29 samples having an IP value lower than 0.10, a reference value. Therefore, it can be concluded that for this parameter, the samples are predominantly mature.
The TOC data for the Travosas Formation well range from poor to excellent, with values from 0.14 to 8.05. Approximately 8% of the 134 samples have values less than 0.5%, considered poor potential since they are siliciclastic rocks, while 65% are within the reference range for reasonable potential. Approximately 16% of the samples have good potential (1-2%), 6% have very good potential (2-4%), and 5% show excellent potential (>4%), with higher TOC in the deeper section of the formation. S1 and S2 values are low, indicating low hydrocarbon generation. S1 ranges from 0.01 to 0.24 mg HC/g, indicating low free hydrocarbon content. S2 ranges from 0.09 to 2.5 mg HC/g, indicating poor hydrocarbon source potential. Insoluble residue varies from 18.9 to 78.4%, suggesting carbonatic/siliciclastic deposition. Therefore, there is an increase in organic matter from the top to the base of the profiles.
The oxic paleoenvironment in the Amapá Formation led to the oxidation of organic matter in most samples, making commercial hydrocarbon generation impossible. The Travosas Formation presents poor hydrocarbon source potential and immature kerogen, ranging from type II-III to type IV.

Acknowledgments: The authors acknowledge the financial support provided by Programa de Recursos Humanos da Agência Nacional do Petróleo, Gás Natural e Biocombustíveis (PRH36-UFBA/ANP/FINEP).

Palavras Chave

Carbonate Rocks; Rock Eval Pyrolysis; Hydrocarbon Source Rocks; Amapá Formation; Travosas Formation