1 Jul 2017
1 Dec 2017 (Extended to 10 Jan 2018)
15 Jan 2018
16 Apr 2018 (Extended to 15 Jun 2018)
From 16 July 2018
By 17 September 2018
Professor of Rock Mechanics at Imperial College London, UK with expertise in Civil Engineering, Mechanical Engineering, Petroleum…
Thu-02 Nov 2018 | 16:30 – 17:00 | Summit 2
"Failure of Anisotropic Rocks such as Shales, and Implications for Borehole Stability"
In anisotropic rocks such as shale, the value of the maximum principal stress required to cause shear failure depends not only on the other two principal stresses, but also on the angle β between the maximum principal stress and the normal to the bedding plane. According to Jaeger’s plane of weakness model, for β near 0° or 90°, failure will occur at a stress determined by the failure criterion for the “intact rock”, and the failure plane will cut across the bedding planes. At intermediate angles, failure will occur along a bedding plane, at a stress determined by the strength parameters of the bedding plane. Data were analyzed from a set of triaxial (σ2=σ3) compression tests conducted on a suite of shale samples, at different confining stresses, and a range of angles β, and it was found that the data could be fit reasonably well with the four-parameter plane of weakness model (Ambrose & Zimmerman, ISRM, 2015). Based on these results, a model has been developed for the stability of boreholes drilled in shales. The fully anisotropic Lekhnitskii-Amadei solution is used to compute the stresses around the borehole wall. The Mogi-Coulomb failure criterion (Al-Ajmi & Zimmerman, IJRMMS, 2005) is used for the strength of the “intact rock”, and the plane of weakness model is used for the strength of the bedding planes. The model can be used to predict the minimum mud weight required to avoid shear failure, for arbitrary borehole orientations and anisotropy ratios (Setiawan & Zimmerman, SPE, 2018). The results show the importance of using a fully anisotropic elastic model for the stresses, and of using a true-triaxial failure criterion, in borehole stability analysis.
Robert Zimmerman obtained a BS and MS in mechanical engineering from Columbia University, and a PhD in rock mechanics from the University of California at Berkeley. He has been a lecturer at UC Berkeley, a staff scientist at Lawrence Berkeley Laboratory, and Head of the Division of Engineering Geology at KTH (Stockholm). He is Editor-in-Chief of the International Journal of Rock Mechanics and Mining Sciences, and serves on the Editorial Boards of Transport in Porous Media and the International Journal of Engineering Science. He is the author of Compressibility of Sandstones (Elsevier, 1991), Fluid Flow in Porous Media (World Scientific, 2018), and co-author, with JC Jaeger and NGW Cook, of Fundamentals of Rock Mechanics (4th ed., Wiley, 2007). In 2010 he won the Maurice A. Biot Medal for Poromechanics of the American Society of Civil Engineers. He is currently Professor of Rock Mechanics at Imperial College London, where he conducts research on rock mechanics and fractured rock hydrology, with applications to petroleum engineering, underground mining, carbon sequestration, and radioactive waste disposal.