Borehole Breakout Numerical Modelling for In-Situ Stress Estimation

In-situ stress is one of the important rock properties used in different engineering disciplines; there are some techniques applied to determine in-situ stresses. One of them is borehole breakouts to estimate both orientation and magnitudes, carried out in drill holes; they are formed by induced stress exceeding compressive strength of rock around borehole wall. In this paper, estimation of in-situ horizontal stress magnitudes from borehole breakout geometries was studied in terms of depth of breakouts measured from center of borehole. The borehole cross sections were mimicked in FLAC numerical modelling software to establish a relation between ratio of breakout depth to borehole radius and stress magnitudes for given maximum horizontal stress. Then, these were compared with the field data for the back-analysis of numerical solutions. The purpose is obtaining an empirical equation of maximum horizontal stress in terms of breakout depth, borehole radius, compressive strength and minimum horizontal stress for the field studied. Keywords— Borehole Breakout, Breakout Depth, Horizontal Stresses, Numerical Analysis