Relationship between rock macro- and micro-properties and wellbore breakout type

This study numerically investigates the effect of material micro- and macro-parameters on the failure mechanisms and geometry of a wellbore breakout. The analysis of the borehole breakout is essential in addressing wellbore stability, well completion, and sand production problems. The three-dimensional discrete element method (DEM) was used in the simulations. The numerical tool was used in numerical model simulations of drilling through sandstone in cubic samples at the laboratory scale subjected to pre-existing far-field stresses. Besides, a series of triaxial testing simulations were performed to relate the micromechanical parameters to the macromechanical material properties. The results showed that the geometry of the breakout is affected, among the material micro-parameters, by the particle contact modulus, bond normal and shear strengths, particle crushing strength, and particle size distribution. Further, it was found that the macro-parameters including Young’s modulus, friction and dilation angles, and uniaxial compression strength (UCS) also affect the type of breakout.