PhD opportunities

Numerical modeling of percussive rock drilling: Application to drill bit design

Thesis proposal

Area of expertiseGeoscience and Geoengineering
Doctoral SchoolGťosciences, Ressources Naturelles et Environnement
SupervisorM. Ahmed ROUABHI
Co-supervisorM. Laurent Marc GERBAUD
Research unitCentre de Gťosciences
ContactGERBAUD Laurent
Starting dateOctober 1st 2022
Keywordsrock mecanics, dynamic cutting
AbstractDown-the-hole (DTH) percussion is a very effective method for drilling in hard rock. The interaction between the bit and the rock is the subject of much research study, as this is where the destructive energy of the hammer blow can be dissipated, thereby reducing the stress magnitude in the rock itself, and thus reducing the effective cut. The main variables affecting drilling efficiency can be grouped into bit design variables (size, shape and arrangement of tungsten carbides, bit flushing holes, bit head design, etc.), hammer design variables (blow impact speed and frequency, mass, length and shape of the piston), operational variables (weight on the bit and speed of rotation) and rock characteristics (strength, heterogeneity, confining, porosity...).

For 4 years, the Geosciences center has invested in the understanding of the process of rock removal under the percussive effect with two theses dedicated to this subject:
- The one of Houssam El Dannawi who showed experimentally and theoretically that the consideration of the heterogeneity of the rock was a key element in the modeling of the process of percussive drilling.
- The one of Jorge Aising who seeks to show experimentally the importance of the shape of the compression wave in the process of drilling.

The objective of this research is to improve the efficiency of the hammer action (i.e. to create a faster penetration while ensuring the durability of the components) by capitalizing on the two previous theses and by taking into account the effect of the heterogeneity of the rock, as well as its non-linear behavior, the dynamic character of the solicitations and the bit-rock interaction. It will be based mainly on:
- A numerical modeling where the candidate will propose an adaptation of the model proposed by El Dannawi with :
o A model of the evolution of the contact between the insert and the rock during the loading
o A model of rock heterogeneity.
- An experimental work where the candidate will carry out impact tests in rocks with different levels of heterogeneity while preserving an equivalent resistance at the macrostructure level.
- A numerical modeling where the candidate will propose a complete model of the drilling tool with :
o An adapted geometrical model of the tool and the rock.
o Taking into account the interaction between inserts

The expected results of the thesis are a numerical model of the interaction between the drilling bit and the rock during a dynamic impact loading (percussive drilling). This should allow to take into account the heterogeneity of the rock and to highlight the optimizing parameters of the destruction process such as the effects of the shape of the bit, the interaction distance between the impacts, the shape of the insert, ....
ProfileHow to apply
Candidates must contact the director(s) of the thesis proposal or the contact person specified. The latter will then hold auditions and select the most suitable candidate for their project.
Content of the application :
-a CV
-a letter of motivation
-transcript of marks of Master 2 (or equivalent)
-summary of the Master 2 report (or equivalent)
-Letter of recommendation from the Master 2 internship supervisor (or equivalent)
FundingConcours pour un contrat doctoral