Cutting mechanics modeling for polycrystalline diamond compacts and extension to the drill bit

A single PDC mechanistic performance model has been developed based on quantitative formulations of the fundamental processes involved during rock cutting. These processes include rock shearing and failure mode, friction between the cutter and the rock, and friction between the produced chip and the rock. The interaction of these basic processes determine the magnitude of cutting forces and size of the rock chip formed.;The magnitude of the maximum cutting force to break the rock and produce a chip and the minimum cutting force resulting from sliding the rock chip are calculated with the single cutter model. The conditions at which the rock undergoes transition from brittle to ductile failure mode are established by comparing the maximum and the minimum cutting forces; furthermore, the amplitude and frequency of cutting force oscillation during the cutting process as a function of the independent variables can be quantitatively evaluated.;Single flat-faced PDC cutter experiments were conducted in Carthage marble to evaluate model predictions. Selected testing conditions of independent variables included confining pressures (0 to 5,000 psi), cutting depth (.01 to.1 in.), and back rake angle (10, 20, 30, and 40 degrees). Sharp and artificially worn cutters (wear flat areas of.01 and.031 in;The single cutter force model was implemented in a drill bit model to predict bit performance. The drill bit model predictions were evaluated with experimental data of two 8 1/2 in. diameter conventional bits drilling in Berea sandstone, Carthage marble, Mancos shale, and Pierre shale with water base and oil based drilling fluids.;Using the developed model the effect of cutting force fluctuations during brittle-hard rock drilling on the total reactive forces and moments of PDC bits was investigated. High amplitude fluctuations of the imbalance force and moment at the bit were detected, in particular, for worn bits.;In general, the results from the single PDC force model and the bit model predictions were encouraging as they were consistent with the experimental data used.