Permeability modeling of a basin-bounding fault damage zone in the Rio do Peixe Basin, Brazil

Abstract

In permeability modeling of fault damage zones affecting porous sandstones, deformation bands are commonly considered low-permeability structures that influence fluid flow. Permeability in damage zones of such rocks exhibits and is influenced by complex networks of deformation bands separated by volumes of seemingly undeformed host rock. This study used deformation band frequency data to delimit and model the fault damage zone subdomains and fault facies in the hanging wall of the Malta Fault segment in the Rio do Peixe Basin, Brazil. We then integrate in situ permeability data collected in deformation bands and interband spaces (deformed host rock located between adjacent deformation bands) with damage zones and fault facies models to estimate the equivalent permeability perpendicular and parallel to the main fault. Our results indicated a logarithmic decrease in deformation band frequency towards the protolith with local variations controlled by minor faults in the damage zone. We identified three damage zone subdomains (inner and outer damage zones and transitional zone), totalizing roughly 200 m of width. Permeabilities of the deformation bands and interband spaces increase towards the protolith non-uniformly due to the difference in deformation intensity. The deformation bands and interband spaces in the inner and outer damage zones, which comprise fault facies representing the highest deformation intensities, exhibit permeability reductions of 1–3 orders of magnitude compared to the undeformed rocks, whereas 0–2.5 orders of magnitude reductions were observed in the transitional zone between the damage zone and the protolith. This study provides new perspectives about the permeability in deformation bands and interband spaces by different subdomains of damage zones and fault facies. This information proved is essential for modeling equivalent permeabilities along damage zones and assessing its implications to siliciclastic reservoirs affected by fault zones, where deformation bands are pervasive.