1887

Abstract

Summary

Volcanic rocks can pose significant drilling challenges, including wellbore instability and circulation losses. In the Pre-Salt section of the Santos Basin, magmatic rocks frequently intersect wells, requiring detailed lithological understanding to ensure safe and efficient drilling. This study presents a facies and compositional characterization of the basaltic volcanic sequence in well 1-BRSA-369A-RJS, the Pre-Salt discovery well. The dataset includes drilling cuttings at 3 by 3 meter intervals, sidewall core samples with thin sections, photographs, and ICP-AES data, along with wireline logs such as gamma ray, resistivity, sonic, density, photoelectric factor, neutron porosity, and caliper. Cuttings were re-described and classified into four lithofacies, correlated with four electrofacies as defined in recent studies. Samples were cleaned and analyzed using X-ray fluorescence with a Malvern Panalytical Epsilon 1 instrument and X-ray diffraction with a Bruker D2 Phaser. Geochemical and petrographic data confirm a basaltic composition, with pyroxene and plagioclase identified throughout. Log responses suggest the presence of pillow lavas and brecciated hyaloclastites. A high gamma ray zone indicates hydrothermal alteration, with enrichment in potassium feldspar and clay minerals, reduced resistivity, and uranium remobilization. Properly prepared cuttings, supported by XRF and XRD analyses, offer a powerful tool for volcanic facies identification.

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2025-11-12
2026-01-22
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References

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