Percussive rotary drilling is recognized as the mostefficient method for hard rock drilling. Despite clearadvantages over conventional rotary methods, there arestill some uncertainties associated with percussivedrilling. For geothermal applications, drilling accountsfor a large portion of the total cost. Specifically, thewear of drill bits when drilling in hard rock is apredominant cost factor and drilling parameters areoften based on the experience of the field operator.Within the framework of the H2020 project GEOFIT,numerical simulations of percussive drilling areperformed in order to evaluate the rock drilling processand gain insight about the trade-off between wear andRate of Penetration (ROP). In the simulations, the rockmaterial was represented by the Bonded DiscreteElement Method (BDEM), the drill bit by the FiniteElement Method (FEM), the drilling fluid by theParticle Finite Element Method (PFEM) and theabrasive wear on the surface of the drill bit wasrepresented by Archard’s wear law. The drillingsimulations were conducted for two rock materials; asedimentary rock material corresponding to what wasfound when drilling at the GEOFIT pilot site in AranIslands, Ireland, and a harder reference rock similar togranite. The results show that, at a drill bit impact forceof 10 kN, the ROP in the sedimentary rock was 6.3times faster than for granite. When increasing theimpact force to 40 and 50 kN, however, the ROP for thesedimentary rock is only 1.9 and 1.6 times faster,respectively. Furthermore, the wear rate decreased withincreased impact force when drilling in the granite rock.For the sedimentary rock, however, the loadingresulting in the best trade-off between abrasive wearand ROP was the second highest loading of 40 kN,which suggests that an increase in impact energy mayincrease the rate of penetration but may not beeconomically motivated.

GEOFIT