Three-dimensional hydro-mechanical model of borehole in fractured rock mass using discrete element method

Borehole stability, in heavily fractured rock mass has been a significant issue in deep earth resources exploration and extraction. In this study, a three-dimensional model using 3DEC is developed to simulate a borehole drilled in fractured rock mass. A model with overbalanced drilling conditions is simulated in this study. In doing so, different depths of a borehole, MB-1 borehole, in Northern Perth basin was simulated. The developed model was validated against log measurements of Caliper log and strength of rock is found as a governing factor in controlling the stability. Then, hydro mechanical modelling was carried out and it was observed that high mud flow rates and high pore pressure increased the instability around borehole. Furthermore, a parametric study was performed to investigate the influence of viscosity and fluid flow on the stability. Shear displacement linearly increase with an increase in flow rate while fluid pressure decreases due to increase in fractures aperture with an increase in flow rate. Similarly, increase in viscosity caused increase in fracture shearing and therefore instability around borehole.