BibTex format
@inproceedings{Setiawan:2020,
author = {Setiawan, NB and Zimmerman, RW},
title = {Semi-analytical method for tracking the evolution of borehole breakouts},
year = {2020}
}
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TY - CPAPER
AB - In response to the high-stress concentration caused by excavation, rocks at the wellbore wall will collapse if the shear failure limit is exceeded. When this occurs, the shape of the wellbore enlarges from circular to roughly elliptical (breakout). The standard stress calculation method assumes a wellbore with a circular cross-section, and hence can no longer be used. Yet, knowledge of the near-wellbore stress state after the wellbore has been damage may still be required for various purposes, such as stability assessment of the open hole. In this paper, a semi-analytical solution is presented for the calculation of the stresses around a wellbore having an essentially arbitrary cross-sectional shape, in an isotropic formation. The zone of initial shear failure around a circular wellbore is calculated for a given far-field stress, using the standard solution for a circular wellbore. The rock in the failed region is then assumed to be removed, and the stress state around this new wellbore contour is then calculated using the method of conformal mapping and Kolosov-Muskhelishvili complex stress potentials. This process is iterated until a shape is obtained for which the breakout will not progress any further, at which point a stable stress state, and stable borehole shape, is reached. The method is validated against several sets of experimental data from the literature. This semi-analytical solution allows a stability assessment around the wellbore to be carried out after the breakout develops. Similarly, in an inverse manner, the method can be used to predict the in situ stress state around a damaged wellbore, if the cross-sectional hole shape can be reconstructed by methods such as electrical logging tools.
AU - Setiawan,NB
AU - Zimmerman,RW
PY - 2020///
TI - Semi-analytical method for tracking the evolution of borehole breakouts
ER -