Deformation Experiments on Bowland and Posidonia Shale - Creep behavior at in situ pc - T conditions
Abstract
We conducted constant stress deformation experiments at elevated confining pressures, pc = 50 - 115 MPa, and temperatures, T = 75 - 150 °C, on Posidonia (GER) and Bowland (UK) shale, which exhibit varying petrophysical and mechanical properties, to unravel their long - term creep properties at simulated reservoir conditions. Recorded creep curves exhibit either only a primary (decelerating) or additionally a secondary (quasi steady state) and a tertiary (accelerating) creep phase during deformation and strongly depend on applied pc - T conditions and sample composition. At high temperature and axial differential stress and low confining pressure, creep strain is enhanced and a transition from primary towards secondary and tertiary creep behavior is observable. Compared to creep strain recorded during deformation of either carbonate - or quartz - rich Bowland shale, creep strain of Posidonia shale, which is rich in weak constituents (clay, mica, organic content) is enhanced. Performed electron microscopy on polished thin sections prepared from deformed samples revealed that creep strain is mainly accommodated by deformation of weak minerals and local pore space reduction. Additionally, micro crack growth during secondary creep was observed. We used an empirical correlation between creep strain and time based on a power law to describe the decelerating creep phase, also accounting for the influence of confining pressure, temperature and axial differential stress. The obtained results also suggest a correlation between primary creep strain and mechanical properties determined from short - term constant strain rate experiments.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMMR41D0070H
- Keywords:
-
- 3902 Creep and deformation;
- MINERAL PHYSICS;
- 3909 Elasticity and anelasticity;
- MINERAL PHYSICS;
- 3924 High-pressure behavior;
- MINERAL PHYSICS;
- 3954 X-ray;
- neutron;
- and electron spectroscopy and diffraction;
- MINERAL PHYSICS