Characterization of Fault Damage Zones and Associated Fracture Networks and Their Influence on Fluid Flow in the Tight Carbonate Reservoir

Abstract

Abstract In the tight carbonate reservoir located in onshore Mexico, fault damage zones and associated fracture networks represent major permeability structure and greatly affect fluid flow. In this study, we present a method for characterizing and modeling fault damage zones and fracture networks. The main objectives are to use fault damage zone and fracture network models to predict fluid-flow pathways in the reservoir and to understand their impact on well production performance. Appropriate geometric attributes are used for unsupervised seismic facies classification with the aim of delineating fault damage zones. The utility of the facies approach lies in its capacity for classifying the fault system with distinct classes based on the degree of fracturing. The three-dimensional fault damage zones are extracted and modeled from the seismic facies volume. A natural fracture network model in the target formation is deterministically built by meshing fracture lineaments that are automatically tracked along depth slices of the edge-enhanced curvature attribute. The fracture network model provides fracture characters in terms of fracture orientation, length, density and connectivity. Local fracture network models at individual wells can be built using fracture connectivity analysis technique. The fault damage zone model delineates fault zone architecture and spatial variability. Our results show that the main fracture sets parallel or subparallel to the fault zone strikes regionally. Fractures distribute surrounding fault damage zones with enhanced fracture density. A good correlation between the fault damage zones and the lost circulation is observed. Based on the production data, fault damage zones can act as fluid conduits. In some instances, fault damage zones can create flow barriers. Conditioned with well data, the conductivity of the fault damage zones and related local fracture networks is calibrated. Using the local fracture network model, the fluid flow pathways and fracture vertical connectivity are determined. With borehole breakouts and drilling induced fractures, the identified maximum horizontal stress orientation is in the NNE direction. Our results show that the conductive properties of fault damage zones and fractures could be affected by the stress state and in situ stress orientations. This explains the fact that the wells located in the fault damage zones and fractures with the orientations preferable for extension tendency or slip tendency have high productivity. The continuous fault damage zone model and the discrete fracture network model can be used to capture 3-D complexity of fluid flow in fault damage zones, improve the prediction of flow pathways and help the lateral or horizontal well design.