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Crustal structure and CO (sub 2) occurrences in the Brazilian basins

Andre Ferraz, Luiz Gamboa, Eugenio Vaz dos Santos Neto and Rui Baptista
Crustal structure and CO (sub 2) occurrences in the Brazilian basins
Interpretation (Tulsa) (November 2019) 7 (4): SL37-SL45

Abstract

CO (sub 2) occurrences are common in hydrocarbon reservoirs in different geologic and geotectonic environments. In most of the Brazilian sedimentary basins, carbon dioxide occurs in minimal amounts. However, more recent deepwater exploration in the Santos Basin discovered significant concentrations of CO (sub 2) in some petroleum fields geographically dispersed. Adjacent fields within a very similar geologic context can hold a few percent to 80% of CO (sub 2) creating great scientific challenges for understanding the origin of CO (sub 2) and the identification of the main controls that govern its erratic distribution. That is the case of the Tupi (Lula) field, which has low CO (sub 2) content, and the neighbor Jupiter field, with an abnormal 80% of CO (sub 2) in the gas cap. The origin of this CO (sub 2) from earth's mantle was already proved by isotopic analyses of noble gases. We have developed some hypotheses to explain this mantle sourced carbon dioxide in hydrocarbon reservoirs of the Santos Basin, namely, regional crustal thinning, deep-seated faults, high fault density, igneous intrusions, among others. The CO (sub 2) is abundant in the mantle, and the continental crust can act as a seal that inhibits these fluids from flowing toward the earth's surface. The highly stretched continental crust in the Santos Basin allows CO (sub 2) -rich mantle material to intrude the upper levels of the continental crust in some locations. Fault systems associated with these magmatic intrusions can direct the carbon dioxide into the upper sedimentary section in a trajectory toward the surface. Understanding the crustal structure of a sedimentary basin is an important step in the exploratory process for the assessment of CO (sub 2) risk. The integration of geophysical (grav-mag) and geochemical data prove great efficacy in identifying the origin of CO (sub 2) and the most important controls on its distribution in the Santos Basin. Such results strongly suggest this approach as a valuable tool for derisking new exploration projects.


ISSN: 2324-8858
EISSN: 2324-8866
Serial Title: Interpretation (Tulsa)
Serial Volume: 7
Serial Issue: 4
Title: Crustal structure and CO (sub 2) occurrences in the Brazilian basins
Affiliation: Universidade Federal Fluminense, Niteroi, Brazil
Pages: SL37-SL45
Published: 201911
Text Language: English
Publisher: Society of Exploration Geophysicists, Tulsa, OK, United States
References: 35
Accession Number: 2020-011784
Categories: Economic geology, geology of energy sourcesApplied geophysics
Document Type: Serial
Bibliographic Level: Analytic
Annotation: Part of a special section on Waste water and CO2 injection, edited by Marfurt, K.
Illustration Description: illus. incl. sketch map
Secondary Affiliation: University of Lisboa, PRT, Portugal
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2020, American Geosciences Institute.
Update Code: 2020
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