The Discontinuity Stability Analysis of Sub-Seismic Modelled Fractures

Abstract Fracture modeling is a developing approach to calculate fracture porosity and permeability and has become a critical tool to help assess natural fractures and their stress state. In this study, image-log based fracture interpretation and fracture modeling methods were used to assess the stress regime, evaluate fracture network types, investigate the fractures’ effect on porosity and permeability, and analyze the stresses affecting the modelled fractures to identify which fractures are conductive, and which are sealed. Image-log based fractures are characterized looking for specific orientations from which the maximum and minimum horizontal stresses are implied. Moreover, the fractures are then modelled utilizing various petrophysical modelling approaches such as Kriging or Gaussian Random Function Simulation. After that, different fracture networks are generated to account for different scenarios, which are then upscaled using the Oda approach to produce porosity and permeability. Furthermore, fractures modelled in this study were then subject to the discontinuity stability analysis in order to analyze their present-day stress status, and identify which of these modelled fractures is critically stressed, and which is stable. Image-log based fracture interpretation orientations and trends helped shed the light on the direction and orientation of the minimum and maximum horizontal stresses. It was implied that the minimum horizontal stress is parallel to any induced fractures. In addition, the generated fracture networks were upscaled to generate fracture permeability and fracture porosity maps via the Oda upscaling method, which utilizes fracture aperture, the volume of grid cells, and the Gaussian Random Function Simulation in order to predict the results at the given fracture location. Wherever fractures are oriented parallel to the maximum horizontal stress, fracture porosity and fracture permeability maps illustrate a higher value. Finally, the discontinuity stability analysis utilized elastic parameters and principal stresses to identify which fractures are conductive. For instance, on the one hand, fractures parallel to the maximum horizontal stress were mostly critically stressed or conductive similar to the observations made with fracture porosity and fracture permeability maps. This is because the maximum stress acts to keep these fractures open. On the other hand, fracture perpendicular to it are observed to be stable. This work has furthered the understanding of fracture porosity, fracture permeability, and the stresses acting on these fractures within the area of study and has provided a computationally efficient, validated approach to modeling fracture porosity and permeability in areas with robust image log data sets. This approach is broadly applicable and can be used in conjunction with dual porosity and dual permeability modeling to create integrated geo-models to assess other areas of interest.