Luke Griffiths

Position and contact

Position: PhD Student (3rd year)

Office: 403, 5 Rue René Descartes

Email: luke.griffiths@unistra.fr

Lab: Laboratoire de Déformation des Roches

Twitter: @Luke_Gri

Research Interests

Geothermal energy

Rock physics

Thermal stressing in rock

Fracture mechanics

Developpement of tools for (geo)science

Publications

Griffiths, L., Heap, M. J., Baud, P., & Schmittbuhl, J. (2017). Quantification of microcrack characteristics and implications for stiffness and strength of granite. International Journal of Rock Mechanics and Mining Sciences, 100, 138–150, doi.org/10.1016/j.ijrmms.2017.10.013

Griffiths, L., M. J. Heap, T. Xu, C. Chen, and P. Baud (2017), The influence of pore geometry and orientation on the strength and stiffness of porous rock, Journal of Structural Geology, 96, 149–160, doi:10.1016/j.jsg.2017.02.006.

Griffiths, L., M. J. Heap, F. Wang, D. Daval, H. A. Gilg, P. Baud, J. Schmittbuhl, and A. Genter (2016), Geothermal implications for fracture-filling hydrothermal precipitation, Geothermics, 64, 235–245, doi:10.1016/j.geothermics.2016.06.006. [PDF]

Griffiths, L., T. D. Blanchard, J. A. Edgar, and M. S. Shahraeeni (2015), Trace Warping vs. Impedance Warping in 4D Seismic Inversion, in 77th EAGE Conference and Exhibition 2015, doi: 10.3997/2214-4609.201413090. [PDF]

Conference presentations

Combining active and passive acoustic methods to monitor thermal microcracking in the laboratory (talk), Luke Griffiths, Olivier Lengliné, Michael J. Heap, Patrick Baud and Jean Schmittbuhl, 12th EURO-conference on Rock Physics & Geomechanics, Ma'ale HaHamisha, Israel.

The Influence of Temperature on the Seismic Velocity of Granite (talk), Luke Griffiths, Olivier Lengliné, Michael J. Heap, Patrick Baud and Jean Schmittbuhl, 5th European Geothermal Workshop, Karlsruhe, Germany.

Shape matters: pore geometry and orientation influences the strength and stiffness of porous rocks (talk), Luke Griffiths, Michael Heap, Tao Xu, Chong-Feng Chen, and Patrick Baud, EGU General Assembly 23-28 April 2017, Vienna, Austria.

Bridging the gap between micro- and lab-scale measurements using automated micrograph analysis for constrained micromechanical modelling (poster), Luke Griffiths, Michael Heap, Patrick Baud, and Jean Schmittbuhl, EGU General Assembly 23-28 April 2017, Vienna, Austria.

In-situ changes in the elastic wave velocity of rock with increasing temperature using high-resolution coda wave interferometry (poster), Luke Griffiths, Michael Heap, Olivier Lengliné, Jean Schmittbuhl, and Patrick Baud, EGU General Assembly 23-28 April 2017, Vienna, Austria.

Experimentally reproducing the thermal breakdown of rock on the Earth's surface through diurnal variations in temperature (poster), L. Griffiths, M.C. Eppes*, M.J. Heap, R. Keanini, P. Baud, AGU Fall Meeting 2016, 12-16 December, 2016, San Francisco.

A new setup for studying thermal microcracking through acoustic emission monitoring (talk), European Geothermal Congress 2016, 19-23 October 2016, Strasbourg.

Barite precipitation: consequences on fracture permeability and injectivity at the geothermal sites of the Upper Rhine Graben (poster), European Geothermal Congress 2016, 19-23 October 2016, Strasbourg.

A new setup for studying thermal microcracking through acoustic emission monitoring (poster), EGU 2016, 23–28 April 2016, Vienna, Austria.

Geothermal implications for fracture-filling hydrothermal precipitation (talk), European Geothermal Workshop 2015, 19-20 October 2015, Strasbourg.

Time-dependent permeability anisotropy in the Buntsandstein sandstone at the Soultz-sous-Forêts geothermal site (talk), 2nd Bochum Workshop on "Geothermal Reservoir Monitoring and Characterization", 15 September 2015, Bochum.

Permeability anisotropy and fracture healing in sedimentary formations in a hydro-geothermal context (talk), 11th EURO-conference on Rock Physics and Geomechanics 2015, 6–11 September 2015, Ambleside, Lake District.

Awards

Zero-fee grant to attend 12th EURO-conference on Rock Physics and Geomechanics 2017.

Outstanding Student Poster and PICO (OSPP) Award, EGU General Assembly 2016.

Early Career Scientist's Travel Award, EGU General Assembly 2016.

Zero-fee grant to attend 11th EURO-conference on Rock Physics and Geomechanics 2015.

Student Travel Grant, EAGE Conference & Exhibition 2015.

Sponsored by the EAGE with the support of Saudi Aramco to attend the EAGE Borehole Geophysics Workshop II 2013 and participate in the short course entitled "Borehole Seismic: Fundamentals".

Teaching

Programming in C practicals for 1st year EOST students, 2015/2016.

Lecture in M2 course Physique des roches appliquée aux réservoirs et aux risques (applied Rock Physics) on the effect of mineral precipitation on fracture permeability, October 2015.

Interactive 2D sliding wing crack model (Ashby and Sammis, 1990)

This will be part of a series of interactive plots looking at various aspects rock mechanics, any comments are most welcome!

The Ashby and Sammis, 1990 2D sliding wing crack model "describes the evolution of damage with strain and from it a criteria for failure can be established". It is often applied to the mechanical failure of rock.

The input parameters are the initial crack damage parameter D0 of the rock, the minimum principal stress σ3, the friction coefficient μ along cracks, and KI/πc, which is the fracture toughness divided by π times the crack half-length. D0 is a function of the crack length, the crack orientation (45° here) with regards to the direction of the maximum principal stress σ1, and the crack surface density.

Below I have provided an interactive chart I made (JavaScript, D3) which allows the user to plot the results from the Ashby and Sammis, 1990 2D sliding wing crack model and compare with their mechanical data. The graph shows the dependacy of axial stress on damage. The onset of dilatancy is where crack propagation begins. This can be considered as the stress at which an acceleration in the number acoustic emissions is observed. As the maximum principal stress σ1 increases, cracks continue to propagate until they nucleate at the peak stress, which is considered to be the failure stress.

The input parameters may be inferred through fitting both the modelled peak stress and the stress at the onset of dilatancy to values provided by uniaxial and triaxial mechanical tests. Inferred parameters for various rocks are given in Baud et al., 2014.

Things to watch out for: 

  • There is a trade-off between the friction coefficient μ and the KI/πc constant for uniaxial tests.
  • Avoid high values of D0 where the curve has no peak. For the model, the rock is "already broken".