Wellbore stability analysis in fractured formation using DEM-DFN method: A case study on one of the wellbores in Persian Gulf

Wellbore instability in fractured formations is one of the most challenging issues in drilling engineering. In order to determine an efficient drilling methodology, it is necessary to investigate main factors which can affect the wellbore instability mechanisms. Injection rate, viscosity and density of drilling fluids are the main drastic and controllable parameter which can affect the shear and tension failure in wellbores. In this study, numerical modeling of a wellbore in Persian Gulf was carried out, using Distinct Element Method (DEM). Representation of natural fracture system in numerical simulation was conducted by Discrete Fracture Network (DFN) method. The results of numerical modeling and parametric study showed that with increase flow rates from 20 to 200 barrels per hour, the shear displacement also increased. Similarly, increase in viscosity from 1 to 1000 cP caused increase in fracture shearing and therefore instability around wellbore. By increase the viscosity and rate of drilling fluid, the shear and tensile failures increase and due to its effect on the hydraulic opening of the discontinuities, a decrease in fluid pore pressure was observed. In this study, normalized yield zone criteria were used to model validation and finally the results of wellbore stability analysis compared with field data.