Stratigraphy and petrophysical properties of the volcanic rocks of Serra Geral Group: A case study in the Antas River Valley region, Rio Grande do Sul, Brazil

Author(s)

Meucci, Marcelo Canals ; de Lima, Evandro Fernandes ; May Rossetti, Lucas de Magalhaes ; Pasqualon, Natalia Gauer ; Mohr, Ingrid Muller ; Brose, Gabriel Calzia

• Document type: Journal article
• Source: Journal of South American Earth Sciences; v. 154, p. 14-pg., 2025-03-01.

Abstract

Interest in volcanic rocks, including those found within sedimentary sequences, has grown significantly in recent years driven by their potential as unconventional reservoirs for hydrocarbon production and CO2 storage. The investigation of the petrophysical properties of volcanic rocks aim to better understand their capacity and efficiency for fluid storage-such as water, hydrocarbons, or CO2-and the conditions that enable fluid migration within these lithotypes. However, the diversity of morphologies and lithofacies in volcanic successions creates complex permeable-porous structures, making it challenging to analyze and model these reservoirs. For a complete understanding, it is necessary to combine the study of petrophysical properties with detailed stratigraphic analysis. For this paper, the research was conducted through the study of 5 columnar sections, located in the Antas River Valley region, part of Paran & aacute;-Etendeka Igneous Province in southern Brazil. The stratigraphic framework was integrated with petrographic techniques and laboratory measurements of porosity, permeability and density for volcanic samples of Vale do Sol and Palmas Formations (Serra Geral Group). The data obtained indicate that the petrophysical properties are highly controlled by lava internal structures and secondary processes. The highest porosities were found in the brecciated tops of rubbly lava flows (26.32%) and vesicular dacites (23.62%), mainly associated with vesicles, whereas interclast porosity types occur in autobreccias. Despite some high porosity values, the overall permeability is low (<1mD), however, this does not take into account the degree of fracturing observed in the field. The low porosity and permeability values are mainly associated with high presence of secondary minerals precipitated in the pores. These results demonstrate that the volcanic rocks in the Serra Geral Group have a complex pore system, due to primary and secondary processes, from magma ascension and emplacement on the surface to dissolution and precipitation of secondary minerals. Understanding the petrophysical properties and their association with lava morphologies is key for modelling volcanic reservoirs and quantifying the capacity of these lithotypes to store fluids, whether for hydrocarbon prospection or for geological CO2 storage. (AU)

• FAPESP's process: 19/22084-8 - The Paraná Magmatic Province: petrogenesis, chronology and environmental impact of Cretaceous tholeiitic, alkaline and silicic magmatism in the Brazilian Platform
• Grantee: Valdecir de Assis Janasi
• Support Opportunities: Research Projects - Thematic Grants
• FAPESP's process: 23/00150-4 - Analysis of social support networks in situations of fetal loss
• Grantee: Julie Higuti Fukushima
• Support Opportunities: Scholarships in Brazil - Scientific Initiation