Topological and petrophysical analyses across a fault zone containing deformation bands

Abstract

Oil reservoirs and CO₂ storage can be affected by fault damage zones with deformation bands that impact fluid flow. In this study, we analysed how a deformation band network varies in terms of frequency across the Malta Fault Damage Zone at Rio do Peixe Basin (Brazil). We used 52 sample areas moving away from the fault core to analyze the characteristics of the deformation bands network (termination, nodes proportions, and permeability) in regard to the different architectural elements of the fault zone (e.g., inner, outer, and transitional damage zone and undeformed host rock). Our results had distinct topology patterns of the deformation band network across the damage zone, and the quantitative data followed a normal distribution inside these elements but did not reflect the damage zone as a whole. The X-nodes tended to decrease moving away from the inner damage zone and became absent in the undeformed host rock, whereas the I-node increased moving away from the fault core. The topological analysis revealed similarities between the linear intensity and area frequency. The relationship between the area of deformation band branches and the sample area was inversely proportional to the equivalent pore diameter and porosity. Additionally, the deformation band connectivity decreased by one order of permeability to the branches in the deformation band. We hope that these findings stimulate further discussions on the use of topology in characterizing damage zones with deformation bands and support the modeling and simulation of CO₂ storage.