PhD opportunities

Rock behaviour under dynamic loading: Application to drilling in extreme environments

Thesis proposal

Area of expertiseGosciences et goingnierie
Doctoral SchoolGRNE - Gosciences, Ressources Naturelles et Environnement
SupervisorM. Hedi SELLAMI
Co-supervisorM. Laurent GERBAUD
Research unitGeosciences
ContactGERBAUD Laurent
Keywords., .
AbstractHard rock drilling is a major issue for the development of geothermal energy due to its prohibitive cost. At great depth, the rock is subjected to a strong geostatic and hydrostatic confinement which increases its resistance and modifies its behaviour. Currently, traditional rock destruction techniques (punching failure with a tricone bit or shearing failure with a PDC bit) do not effectively destroy the rock (fragile bits, limited efficiency). It is therefore necessary to use a rock cutting mechanism more efficient and better adapted to these conditions.

In shallow drilling, the use of percussion has shown its effectiveness for drilling hard and fragile rocks with a combined compression and tensile rock failure. The use of this technology in deep drilling should make it possible to increase drilling efficiency.

Although there is numerous theoretical and experimental works on the dynamic rocks cutting at atmospheric pressure, the literature is less prolix when it comes to taking into account the effect of confinement, one of the major difficulties being to develop a representative experiment.

The aim of the thesis is to propose a theoretical model of the rock failure under confinement by a dynamic loading. This will have two components:
- An experimental component where the candidate will develop and carry out impact tests under representative pressure conditions of deep drilling. One of the tasks will be to develop a non destructive rock damage measurement methodology. The tests will allow to quantify the effect of the confining pressure, the energy of impact, the shape of the insert, the rock, ... They will also make it possible to define the hypotheses for the theoretical model.
- A numerical model component where the candidate will propose a model with:
o A model of rock behaviour and a failure criterion under dynamic loading
o A model of the solicitation during the impact.

The expected results of the thesis are a numerical model of the insert-rock interaction during a dynamic loading of the impact type (percussive drilling) and an experimental set up. This should make it possible to highlight the parameters that optimize the destruction process, such as the shape of the insert, the presence of the release surface in the rock, the impact energy, preloading, ...
ProfileThe candidate must be graduated in mechanics with a strong Geomechanical / Rock Mechanics connotation. The candidate must have at the same time:
- Numerical modelling skills with, if possible, experience in the use of Comsol type software
- An interest in developing and conducting laboratory tests.
FundingConvention CIFRE