Deformation bands in carboniferous-permian sandstones of the Paraná Basin

Abstract

Deformation bands developed on Carboniferous-Permian sandstones in the eastern portion of the Paraná Basin are analyzed. Emphasis was made on their geologic evolution and possible impacts on fluid circulation within naturally fractured reservoirs. Subvertical fractures and fault zones prevail in the studied area and were generated and/or reactivated in at least three major deformation events during Permian, Jurassic-Cretaceous and Cenozoic times. Microstructuraly, two types of deformation bands can be recognized: one type characterized by grain fracturing and a second type showing gouge zone formation due to intense grain comminution. According to hydraulic properties of deformation bands and temporal relationship with hydrocarbon generation and migration, fractures within the sandstones can act as permeability barriers or conduits for fluid flow. In the studied sandstones, deformation bands with gouge zones were potential seals because grain comminution is closely related to permeability decrease. Alternatively, it is probable that marginal damaged zones should have acted as permeability pathways laterally along the gouge zones. Fractured deformation bands were conduits for fluid flow at least during a short time interval in the mesodiagenesis. Carbonate and anhydrite cementation along fractures from core samples suggest that these potential conduits were subsequently sealed still during mesodiagenesis.