Abstract
Rock cutting leads to a combination of brittle and ductile failure, and each failure mode has a different effect on drilling efficiency and the morphology of cuttings produced while drilling. A commercial, two-dimensional Discrete Element Method (DEM) code was used to investigate the link between cuttings morphology and downhole conditions using a single polycrystalline diamond compact (PDC) cutter. The methods described here differ significantly from previous studies in that grain-level forces were spatially averaged to determine the rate of energy dissipation within the rock volume during the entire cutting process. Stress-space methods and plasticity theory were then used to calculate the total energy lost due to brittle and ductile failure modes separately. Results indicate a direct and quantifiable relationship between confining stress, down-hole pressure, drilling efficiency and a transition from chip-like to ribbon-like cuttings morphologies.
