Elsigood, Bobby;
Brantut, Nicolas;
Meredith, Philip G;
Healy, David;
Mitchell, Thomas M;
Aben, Frans M;
(2023)
Stress-Induced Anisotropic Poroelasticity in Westerly Granite.
Journal of Geophysical Research: Solid Earth
, 128
(11)
, Article e2023JB026909. 10.1029/2023jb026909.
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Abstract
We measured poroelastic properties of cracked granite under triaxial conditions, at elevated confining pressure and a range of differential stresses. Skempton's coefficients and undrained Young's modulus and Poisson's ratio were determined directly by recording in situ fluid pressure during rapid cycles of axial and radial stress. Drained properties were measured both statically and dynamically at ultrasonic frequencies. At a given confining pressure, increasing differential stress leads to the development of elastically transverse isotropy, with symmetry axis aligned with the compression axis. Skempton's coefficients are also anisotropic, with larger changes in pore pressure in response to radial stress (coefficient Bx) than to axial stress steps (Bz). The anisotropy in the Skempton coefficients increases with increasing differential stress, with Bz decreasing and Bx slightly increasing. The evolution of static moduli and the Skempton coefficients is well approximated by Gassmann's equation using dry moduli obtained from ultrasonic measurements. Simplified predictions of the Skempton coefficients based on crack density tensors inverted from dynamic data also shows acceptable agreement with direct observations. Perfect quantitative agreement is not reached, due to the imprecision of our dynamic measurements, model simplifications, and inherent differences between static moduli obtained using stress steps of several MPa stress and dynamic ultrasonic stress oscillations.
| Type: | Article |
|---|---|
| Title: | Stress-Induced Anisotropic Poroelasticity in Westerly Granite |
| Open access status: | An open access version is available from UCL Discovery |
| DOI: | 10.1029/2023jb026909 |
| Publisher version: | https://doi.org/10.1029/2023JB026909 |
| Language: | English |
| Additional information: | © 2023. The Authors. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Earth Sciences |
| URI: | https://discovery-pp.ucl.ac.uk/id/eprint/10180811 |
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