Laboratory Investigation Of Wellbore Breakouts As An Indicator Of In-Situ Stresses

R.Hugo Morales, Ahmed Abou-Sayed and Arfon H.Jones, Terra Tek Inc.
The 30th U.S. Symposium on Rock Mechanics (USRMS), June 19 – 22, 1989 , Morgantown, WV.


An analysis of laboratory work of borehole breakouts as an indication of magnitude and orientation of in-situ stresses is presented. Bore- holes drilled in laboratory rock specimens provided data for this investigation. Borehole spalling experiments were conducted to determine if failed borehole profiles provide a means for estimating the far-field stresses. Tests were conducted in 2.54 to 3.81 cm diameter boreholes drilled in the center of a 30.5 cm x 30.5 cm x 45.7 cm blocks of Austin Chalk and hydrostone. In two tests loads were applied after boreholes were drilled and in a third test the hole was drilled into a stressed block. Tests examined tensile and shear failure aligned with the minimum principal stress direction Zoback, et. al.[1] model predicted shear spall depth to better than 15 percent. The difference between the predicted and experimental circumferential length of the spall region ranged from 41 to 66 percent. Calculation of far-field stresses based on the spall profile yielded unreasonably large values of the far field in-situ stresses.