This paper presents the results of numerical modeling through finite element method and discrete element method for single cutter drilling in carbonate samples. This work is relevant to understand the mechanics of drill bit – rock interaction while drilling deep wells and the results behavior were validated with experimental data raised under simulated downhole conditions. Triaxial confining tests were carried out in cylindrical samples of the same carbonate rock used in the cutting experiments. The results were used to create a virtual rock to be utilized by both the discrete and finite element methods. 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, MSE as this parameter is often used to measure drilling efficiency. Results indicate that the chamfer size does not change significantly the MSE 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.
The drilling optimization depends on a detailed evaluation process of the cutter behavior during the 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 among 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). The aggressiveness, in a single cutter scenario, can be defined as the slope of the cutting force to normal force (Akbari et al., 2014a) and, conventionally, the more aggressive the cutter, the higher the penetration rate achieved. In numerical modeling of single cutter test, keeping constant the depth of cut and the rate of penetration among simulations, the aggressiveness can be used as a sensitivity parameter in analyses regarding the cutting efficiency.