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Stress relaxation tests on an outcrop shale

Abstract

Numerous observations have shown that shale formations may creep in and close the annulus between rock and casing in deep wells, thus effectively sealing off the well sections in a natural way. This movement of the rock is partly controlled by strain and partly by stress, and parts of the rock may be in a post-peak state while other parts are in a pre-peak state. The effect of pre-peak versus post-peak conditions on creep characteristics was studied in a set of stress relaxation tests on Pierre II shale. It was found that the stress relaxation process can be described with great precision both by a logarithmic function and a power-law function. However, only the power-law function fulfills the expected asymptotic behavior for infinite time. Temperature fluctuations can be accurately accounted for by an Arrhenius-type factor. The shear stress relaxation appears to be insensitive to pore pressure alterations. There is an indication that the relaxation rate is slightly higher when the rock is in a strain hardening state than in a strain softening state. No significant effect of exposure to NaOH was seen on the relaxation process.

Category

Academic chapter

Language

English

Author(s)

Affiliation

  • SINTEF Industry / Applied Geoscience
  • Norwegian University of Science and Technology

Year

2022

Publisher

American Rock Mechanics Association (ARMA)

Book

56th U.S. Rock Mechanics/Geomechanics Symposium

ISBN

9780979497575

View this publication at Norwegian Research Information Repository