Experimental investigation on borehole breakout and its implication on stress magnitudes

H. Lin, J. Oh, I. Canbulat, H. Masoumi, Y. Zhang

Research output: Contribution to conferencePaper


Borehole breakout is a drilling induced phenomenon caused by overstress of rock around the borehole. Its depth usually aligns with the minimum principal stress direction. For this reason, it has been used to determine stress orientations and a series of researchers also argued its dimensions can be indicative of stress magnitudes. If the stress dependencies of breakout geometries are well understood, it is possible to estimate stress magnitudes based on these data. This paper investigates the influences of critical parameters on breakout dimensions, including absolute stress magnitudes, stress ratios and borehole diameter. Several experiments have been conducted on cubic (120 × 120 × 120 mm 3 ) sandstone samples with pre-drilled holes (20 mm and 30 mm) under true tri-axial loading conditions using UNSW self-designed equipment. Breakout geometries are then obtained by casting. Experimental results confirm the increasing maximum horizontal principal stress magnitudes result in larger angular span and longer breakout depth at constant minimum horizontal and vertical principal stresses. Findings of this study imply a potential on the estimation of stress magnitudes using borehole breakout.

Original languageEnglish
Publication statusPublished - 1 Jan 2018
Externally publishedYes
EventUS Rock Mechanics / Geomechanics Symposium 2018 - Seattle, United States of America
Duration: 17 Jun 201820 Jun 2018
Conference number: 52nd


ConferenceUS Rock Mechanics / Geomechanics Symposium 2018
Country/TerritoryUnited States of America

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