Assessment of fault damage zones in carbonate rocks based on numerical and sensitivity analyses

Abstract

Fault damage zones are structural geological domains that can impact a reservoir's fluid flow and geomechanical behavior during the exploration and production phases in the oil and gas industry. Several methodologies have been proposed in the literature to characterize fault damage zones considering earthquake data, geophysical methods and outcrop observations. Based on those data, statistical relationships have been proposed to predict and constrain the width of fault damage zones in the subsurface. Unfortunately, those relationships show significant data dispersion and raise uncertainties regarding the extension of damage zones. A possible explanation for such distribution is the lack of knowledge of other parameters such as lithology and associated diagenesis, depth of faulting, tectonic environment, fault propagation, fault segment linkage and deformation mechanisms. Numerical modeling has emerged as a promising alternative for understanding geological problems. However, few studies have focused on characterizing fault damage zones at depth. This study presents a novel methodology based on the finite element method (FEM) combined with elastoplastic models and fault displacement data to forecast damage zone widths around geological faults on carbonate rocks. Despite the assumptions and simplifications related to the fault shape and displacement profile, this study shows that the proposed models provide a better understanding of the deformation mechanisms that trigger damage zones. Moreover, a sensitivity study considering the proposed methodology shows that in addition to the fault displacements and the carbonate rocks' geomechanical properties, the location of measured damage zone with respect to the fault can significantly impact the assessment of damage zone widths.