Journal
JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH
Volume 123, Issue 6, Pages 4751-4764Publisher
AMER GEOPHYSICAL UNION
DOI: 10.1029/2018JB015636
Keywords
limestone; permeability; anisotropy; deformation; compaction
Categories
Funding
- UK Natural Environment Research Council [NE/K009656/1]
- NERC [NE/K009656/1] Funding Source: UKRI
Ask authors/readers for more resources
We performed triaxial deformation experiments in Purbeck limestone (13.8% average porosity) across the brittle-ductile transition and monitored the evolution of permeability and wave velocities as a function of strain. In the brittle regime, the rock yields in dilation. In the ductile regime, the rock first yields in compaction and then undergoes net dilation at some critical level of strain. The permeability increases after failure in the brittle regime and decreases with increasing compaction in the ductile regime. The wave velocities decrease with increasing strain, and the material becomes transversely isotropic. At axial strains of the order of 5%, the anisotropy parameters (from Thomsen, 1986) are around epsilon approximate to-0.2 and approximate to decrease with increasing axial strain beyond the yield point-0.3. Under hydrostatic conditions, the rock also yields in compaction. The hydrostatic yield point is not marked by any significant drop or increase in wave velocity during loading, but wave velocities decrease (and therefore crack density increases) significantly upon unloading. In all our tests, the permeability change is proportional to the initial porosity change until the point of net dilation is reached. The strain at that point also acts as a scaling factor for the relative drop in P and S wave velocities during deformation. All our experimental data point to a disconnection between the evolution of permeability, porosity, and wave velocities during deformation in the ductile regime: permeability is controlled by a fraction of the micropore network, while wave velocities are mostly influenced by microcracks that do not contribute significantly to either the total rock porosity or fluid flow properties.
Authors
I am an author on this paper
Click your name to claim this paper and add it to your profile.
Reviews
Recommended
No Data Available