The petroleum industry has shown great interest in the study of drilling optimization on pre-salt formations given the low rates of penetration observed so far. Rate of penetration is key to economically drill the Brazilian pre-salt carbonate rock. This work presents the results of numerical modeling through finite element method and discrete element method for single cutter drilling in carbonate rocks. The work is relevant to understand the mechanics of drill bit – rock interaction while drilling deep wells and the results were validated with experimental data obtained under simulated downhole conditions. The numerical models were carried out under different geometrical configurations, varying the cutter chamfer size and back-rake angles. The forces generated on the cutter are translated into mechanical specific energy as this parameter is often used to measure drilling efficiency. Results indicate that the chamfer size does not change significantly the mechanical specific energy values, although the cutter aggressiveness is influenced by this geometrical characteristic. Results also show there is a significant increase in drilling resistance for larger values of back-rake angle.
Drilling optimization depends on a detailed evaluation process of the cutter behavior during rock cutting. Through single cutter tests, the effects of geometrical variations in the cutter can be evaluated from the point of view of forces and energy. The possibility of assessing these phenomena numerically, through triaxial calibrations of complex models, significantly expands the spectrum of rock drilling optimization process.
The mechanical interaction between the numerical sample and the cutter is evaluated in terms of mechanical specific energy (MSE) and aggressiveness. MSE is a parameter commonly used to measure cutting efficiency and can be defined as the work done per unit volume excavated, according to Teale (1965).