Afonso Flávia Priscila Souza, Lagoeiro Leonardo, Fossen Haakon, Barbosa Paola Ferreira, Pinto Celeste Bertassoni, de Souza Camila Gomes Peçanha
Department of Geology, Federal University of Paraná-UFPR, Curitiba, PR 81531-990, Brazil.
Bergen University Museum/Department of Earth Science, University of Bergen, Box 7803, N-5020 Bergen, Norway.
Microsc Microanal. 2024 Aug 21;30(4):692-702. doi: 10.1093/mam/ozae070.
Deformation bands are common constituents of porous clastic fluid reservoirs. Various techniques have been used to study deformation band structure and the associated changes in porosity and permeability. However, the use of electron backscatter diffraction technique is limited. Thus, more information is needed regarding the crystallographic relationships between detrital crystals, which can significantly impact reservoir rock quality. We employ microscopic and microstructural investigation techniques to analyze the influence of cataclastic deformation bands on pore space. Porosity measurements of the Cretaceous Ilhas Group sandstone in NE Brazil, obtained through computerized microtomography, indicate that the undeformed domains exhibit a total porosity of up to 13%. In contrast, this porosity is slightly over 1% in the deformation bands. Scanning electron microscopy analyses revealed the presence of grain fragmentation and dissolution microstructures, along with cement-filling pre-existing pores. The electron backscatter diffraction analyses indicated extensive grain fragmentation and minimal contribution from intracrystalline plasticity as a deformation mechanism. However, the c axes of quartz crystals roughly align parallel to the orientation of the deformation band. In summary, we have confirmed and quantified the internal changes in a deformation band cluster, with grain size reduction and associated compaction as the main mechanism supported by quartz cementation.
