Interaction and linkage of basin-boundary fault segments control deformation bands distribution and damage zone permeability

Abstract

Analyzing the factors that affect the fault damage zone parameters and the impact of deformation on host rock permeability is fundamental for predicting the fluid flow behavior in subsurface reservoirs. This study combines 3D seismic data with field-based structural and petrophysical analyses to determine the influence of a basin-boundary fault geometry on (1) the damage zone thickness, (2) the spatial distribution of deformation bands, and (3) the damage zone permeability. Seismic interpretation and outcrop investigation on the Portalegre Fault, NE Brazil, revealed complexity in the boundary fault geometry and subsidiary structures. The boundary fault exhibits significant local variation in its strike (from N45°E up to N85°), while minor faults and deformation bands establish cross-cutting relationships with NW–SE-oriented structures, displacing NE–SW- and E–W-oriented structures. By analyzing deformation bands frequency, we identified the presence of three subsequent fault damage zones, totaling approximately 275 m in width. The first damage zone was developed near the basin-bounding Portalegre Fault, and secondary rift faults developed the other two damage zones during breaching and segment overlap. We observed that the permeability distribution recorded successive increases and decreases as we moved away from one fault and approached another. This structural and petrophysical complexity led us to interpret this fault damage zone as a linking damage zone. These observed patterns contrast with the structural and petrophysical behavior of a wall damage zone, wherein the frequency of subseismic structures decreases and permeability increases with distance from the fault. Thus, our study highlights the effect of fault tip interaction and linkage on the distribution of deformation bands and permeability, clarifying aspects related to structural heterogeneities of siliciclastic reservoirs affected by faults.