نوع مقاله : مقاله پژوهشی
گروه ژئومکانیک نفت، دانشکده مهندسی معدن، دانشگاه تهران
Borehole breakouts can be modelled by the propagation of cracks in the vicinity of wellbores. Coalescence of these cracks with a series of formed sub-parallel cracks leads to a breakout. Using fracture mechanics principles, the propagation of cracks in the vicinity of wellbores resulting in the final formation of breakouts is investigated. An indirect BEM with higher order elements has been used to numerically simulate cracks propagation. Various configurations of cracks placement around a wellbore are analyzed. Numerical results showed that the ratio of stresses normal to wellbores’ axis has a significant effect on breakouts final shape. For a given lower normal stress, higher stress ratios lead to wider breakouts, eventually leading to wellbore instability. Furthermore, for a given higher normal stress, higher stress ratios tend to form deeper breakouts with a limited width increase. Hydrostatic stress field can be completely stable or unstable depending on a threshold stress value.