Induced Shear Failure by Temperature Reduction at Uni-axial Strain Conditions
T. Voake, A. Nermoen, R.I. Korsnes and I.L. Fabricius
Event name: IOR 2017 - 19th European Symposium on Improved Oil Recovery
Session: Poster Introductions 1
Publication date: 24 April 2017
Info: Extended abstract, PDF ( 1.15Mb )
Price: € 20
This study improvises uniaxial strain condition during cooling by keeping constant overburden, and adjusting radial stress at cooler temperatures in order to re-establish the same radial dimensions prior to cooling. The amount of radial stress reduction by thermal contraction could be sufficient to trigger shear failure. Experiments are performed on Mons chalk and Kansas chalk so the role of induration can be assessed. Calcite thermal expansion is highly anisotropic. Weakening caused by temperature fluctuation could give insight to what gives chalk its strength, cementation, or repulsive electrostatic forces. For each chalk type, shear failure line is determined. The samples are heated to 90oC and loaded to 70% of the axial stress required to induce shear failure. Then the temperature is reduced by 60°C. The change in confining pressure necessary to restore zero radial strain is estimated. The two chalks show different behaviour. Mons demonstrates this cooling would induce shear failure, but has no significant effect on its strength. Kansas, is able to restore uniaxial strain conditions without shear failure. The strength of the Kansas sample was unaffected, however the change in confining pressure needed to restore the uniaxial strain condition decreased with each additional cycle, indicating changing elastic properties.