Stress Distribution in Fractured Reservoirs: Effects of Fracture Density, Oblique Loading and Parameters of Rock and Fracture

The presence of natural fractures in fractured reservoirs plays an important role in determining the stress state that is affected by tectonic stresses and local perturbation. Fracture orientation, well stability and permeability anisotropy are all factors associated with local stress variations. Nowadays, to better understand the geomechanical behavior of reservoirs, most mechanical and hydraulic behavior modelings are coupled with stress variations. In this study, in order to investigate the correlation between fracture density (as one of the geometric properties of fracture network) and oblique loading of tectonic stress, with the variability of stress and shear strain, a discrete fracture network (DFN) was generated using the stochastic approach. Afterwards, considering the tensorial nature of the stress, the stress field under different conditions of tectonic stresses was determined using FLAC2D software as a finite-difference method. Finally, stress data were analyzed using tensor-based mathematical equations. Then, the effect of four parameters of (1) rock tensile strength, (2) rock cohesion, (3) fracture normal stiffness, and (4) fracture dilation angle on stress dispersion in loading at different angles were evaluated. The results showed that the stress perturbation and the effective variance, which indicate the dispersion of the stress distribution, have a direct relationship with the fracture density, which is defined as the number of fractures per area unit utilizing the window sampling approach. Moreover, the loading orientation is effective in total stress variability, and the effective variance is highest at loading angle of 50° and lowest at 170°. Among the parameters, it was found out that normal stiffness had the greatest effect on stress distribution, and the effects of the rock parameters were negligible. Overall, it can be said that the stress distribution and dispersion, in a dense fracture network with a normal stiffness of 500 GPa/m and a loading angle of 50°, have the maximum value.