Chandler, MR;
Mecklenburgh, J;
Rutter, E;
Lee, P;
(2019)
Fluid injection experiments in shale at elevated confining pressures: determination of flaw sizes from mechanical experiments.
Journal of Geophysical Research: Solid Earth
, 124
(6)
pp. 5500-5520.
10.1029/2018JB017207.
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Abstract
Triaxial experiments and direct fluid injection experiments have been conducted at confining pressures up to 100 MPa on Mancos shale, Whitby mudstone, Penrhyn slate and Pennant sandstone. Experiments were conducted with sample axes lying both parallel and perpendicular to layering in the materials. During triaxial failure Penrhyn slate was stronger for samples with cleavage parallel to maximum principal stress, but the two orientations in the shales displayed similar failure stresses. Initial flaw sizes of around 40 µm were calculated from the triaxial data using the wing-crack model, with the shales having shorter initial flaws than the non-shales. During direct fluid injection, breakdown was rapid, with no discernible gap between fracture initiation and breakdown. Breakdown pressure increased linearly with confining pressure, but was less sensitive to confining pressure than expected from existing models. A fracture mechanics based model is proposed to determine the initial flaw size responsible for breakdown in injection experiments. Flaw sizes determined in this way agree reasonably with those determined from the triaxial data in the non-shales at low confining pressures. As confining pressure rises, a threshold is reached, above which the fluid injection experiments suggest a lower initial flaw length of around 10 µm. This threshold is interpreted as being due to the partial closure of flaws. In the shales an initial flaw length of around 10 µm was determined at all confining pressures, agreeing reasonably with those determined through the triaxial experiments.
| Type: | Article |
|---|---|
| Title: | Fluid injection experiments in shale at elevated confining pressures: determination of flaw sizes from mechanical experiments |
| Open access status: | An open access version is available from UCL Discovery |
| DOI: | 10.1029/2018JB017207 |
| Publisher version: | https://doi.org/10.1029/2018JB017207 |
| Language: | English |
| Additional information: | © 2019. The Authors. This is an open access article under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/), which permits use, distribution and reproduction in any medium, provided the original work is properly cited. |
| Keywords: | shale, fracture, rock deformation, fracture mechanics, cracks, flaw sizes |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Mechanical Engineering |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10075370 |
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