Borehole Breakouts in St. Meinrad Sandstone under Hydrostatic to Highly Anisotropic Far-field Stresses

Wellbore instability often leads to failure in the form of breakouts, which are a major concern in the petroleum industry because they interfere with production and facilitate unwanted sanding. We report on two sets of experiments in which a high-porosity quartz sandstone was subjected to conditions inducing breakouts around boreholes. As in other quartz-rich sandstones, breakouts are not “dog eared” but rather tabular, long and very narrow. They resemble compaction bands that have been partially emptied. The apparent creation of compaction bands initiated by the borehole stress concentration constitutes an added concern, since such bands have diminished porosity and can impede the free flow of fluids through the sandstone.