Permeability scale effect analyzed in high resolution in Brazilian Neoproterozoic karst aquifer

• Published in: Environmental earth sciences 2023, Vol.82 (2), p.57, Article 57
• Main Authors: Ferreira Campos Morato Filpi, Tereza Cristina, Ferreira Galvão, Paulo Henrique, da Rocha Santos, Larissa, de Vasconcelos Müller Athayde, Camila, Bahniuk Rumbelsperger, Anelize, Cury, Leonardo Fadel, Barbosa Athayde, Gustavo
• Format: Article
• Language: English
• Subjects: Aquifer permeability; Aquifers; Biogeosciences; Boreholes; Cenozoic; Channels; Computed tomography; Cores; Drilling; Earth and Environmental Science; Earth Sciences; Environmental Science and Engineering; Fractures; Geochemistry; Geology; Geophysics; Groundwater; Groundwater flow; High resolution; Hydrology/Water Resources; Karst; Logging; Original Article; Permeability; Porosity; Resolution; Scale effect; Structures; Tectonics; Terrestrial Pollution; Transmissivity
• ISSN: 1866-6280; 1866-6299
• DOI: 10.1007/s12665-022-10743-9

Quantifying the permeability in karst aquifers often is imprecise and difficult to interpret. Therefore, it is possible to notice the increase and decrease of permeability values related to the known triple porosity within the karstic system. This work analyzed small- and well-scale data from a tubular well situated in a Brazilian Neoproterozoic karst aquifer to show the scale effect and relationships between fractures/channels flow zones and regional tectonic structures of the area. At the micro-scale, 3D micro-Ct images of tubular well core samples and thin sections were used to analyze the aquifer matrix and micro-fractures. In well-scale, data from high-resolution acoustic geophysical logging, borehole video, and drilling reports helped to analyze fractures and channels. Multi-scale lineament mapping with geophysical logging aided to correlate the major tectonic structures in the area to the existing flow zones. The result showed an increase of eleven orders of magnitude in values of permeability and transmissivity from micro- to well-scale, indicating the scale effect, explained by the low permeability of the matrix and the influence of fractures and channels in flow zones in the aquifer. The groundwater flow can be linked regionally to the presence of tectonic structures associated with the anticlinal fold present in the study area, diabase dike intrusions, and the Cenozoic transcurrence. The use of high-resolution methods makes possible the distinction between matrix, fractures, and channels in the calculation of hydraulic parameters allowing a better understanding of the influence of each structure in the groundwater flow.