Abstract
Borehole breakouts are formed by spalling of fragments in a direction parallel to the least horizontal stress. As the breakouts falling into the wellbore or being scoured by the drilling mud piece by piece, the stress concentration on the wellbore will release gradually. The wellbore is not circular or elliptical, which requires a numerical method to determine the redistributed stress around the irregular borehole. In this article, boundary element method associated with the brittle rock failure criterion is deployed to simulate the dynamic breakout of a borehole. The borehole shape is updated step by step during the time-dependent breakout. The first breakout volume is smaller than the analytical solution (Gholami et al. in J Rock Mech Geotech Eng 8:521–532, 2016). However, the total breakout volume is larger than the analytical solution because our model considers the subsequent failure of the irregular wellbore. The stress distribution around the irregular wellbore after each step of breakout is investigated and the maximum cohesive strength at which the rock will fail is figured out. These results provide new insights to understand the dynamic process of borehole breakout.
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