While wells reach deeper and deeper targets, understanding the cutting mechanism under confinement is not yet fully mastered. Among the numerical methods used to study this problem, the Discrete Element Method has already shown promising results, but the evolution of rock behavior with confinement is not always considered. This work proposes a calibration method based on UCS and triaxial tests to represent the evolution of rock behavior with confinement. This calibration procedure is implemented on Vosges Sandstone. The rock model failure envelope is built based on further triaxial tests and agrees with the experimental one. Secondly, linear cutting tests under confinement were implemented on the calibrated model. The results are compared to experimental ones. Their good agreement allows the validation of the proposed approach.
Understanding the destruction mechanisms in a confined environment due to high depths conditions is essential for optimizing deep drilling, not only for the gas and oil industry but also in the context of deep geothermal energy recovery or CO2 storage. With PDC drill bits accounting for 90% of the distance drilled annually, understanding the cutting mechanism is essential. The current state of the art shows that this mechanism is well understood in atmospheric conditions (Rostamsowlat, 2017), but the impact of high depths conditions (confinement, temperature, and pore pressure) is not yet fully mastered.
Different approaches are used to study this topic (experimental, numerical, and study of drilling logs); among them, numerical methods such as the Discrete Element Method (DEM) have demonstrated encouraging results (Carrapatoso et al., 2015; Helmons, 2017). Unfortunately, numerical models sometimes show a lack of representativeness concerning the evolution of the behavior of rock materials with confinement. Therefore, they are unable to reproduce the evolution of the mechanism and typically give cutting forces that differ from the ones measured in laboratories.
