Abstract
This paper describes numerical analyses of laboratory thick-walled cylinder (TWC) tests used to study the stability of vertical wellbores in hard clays. The TWC experiments were designed to simulate the drilling process by reducing the internal cavity pressure although maintaining the external radial stress and measuring internal changes in volume within the model wellbore. Radial deformations of the cavity (borehole squeezing) attributable to plastic deformations of the clay represent a critical condition for the design of wells drilled through ductile formations (i.e., very hard soils and poorly lithified rocks). The current analyses simulate coupled flow and deformation in the TWC soil specimens using a finite element (FE) program and the MIT-E3 model to represent the effective stress-strain-strength properties of the reference clay, resedimented Boston blue clay (RBBC). The model is freshly calibrated using results of laboratory triaxial element tests performed at the same stress levels as the TWC experiments (). The numerical simulations are compared with data from experiments performed at different levels of confining stress, rates of depressurization, and wall thickness. The numerical model provides good estimates of the instability measured in the TWC tests and provides an accurate estimate of the undrained shear strength controlling cavity deformations. These validations provide confidence in the application of the model for estimating behavior of prototype (i.e., vertical and deviated) wellbores in similar hard clay formations.
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Acknowledgments
This research was sponsored by BP America, in Houston, and by the BP-MIT Major Projects Program. The authors are grateful to Dr. Stephen Willson for his technical advice and support. The authors would also like to thank their colleagues, Dr. John Germaine and Dr. Naeem Abdulhadi, who carried out the TWC tests and associated element tests.
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Published In
Journal of Geotechnical and Geoenvironmental Engineering
Volume 143 • Issue 2 • February 2017
Copyright
© 2016 American Society of Civil Engineers.
History
Received: Jul 16, 2015
Accepted: May 27, 2016
Published online: Aug 17, 2016
Discussion open until: Jan 17, 2017
Published in print: Feb 1, 2017
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