Modeling PDC cutter rock interaction

Optimizing the drilling performance in high pressure high temperature (HPHT) operations is crucial to successful, economic mineral extraction, and is one of the major goals behind the Department of Energy’s (DOE) “Deep Trek” program and the primary goal of the Ultra-Deep Drilling Simulator (UDS) laboratory currently being designed and constructed at National Energy Technology Laboratory (DOE-NETL).To best leverage the valuable unique data from experiments in the UDS, a three-dimensional FLAC model of a single cutter interacting with the rock specimen (as tested in the UDS) has been developed. This cutter-rock model was developed using parameters so that various aspects of the model could be easily changed in subsequent runs.This study will present the development of the cutter-rock model and the results of the initial numerical tests investigating the effect of various geologic and drilling parameters such as: rock strength, pore pressure, stress fields and cutting depth. Also, the results of the comparison/calibration of the model with single cutter laboratory tests will be presented.Three basic initial models were run. First, two different rock types (a sandstone and a shale) with three different cutting depths are modeled to investigate the effect of rock strength and cutting depth on cutter loads. Second, The effect of various confining stress levels on the single cutter tests are analyzed by applying three different hydrostatic confinements (0 MPa, 25 MPa, and 50 MPa) to the core. Third, to incorporate the effects of fluid (both drilling mud and internal fluid) on the drilling process, pore pressure is included in the cutter/rock model. Results of these models showed that initial cutter/rock model is working properly.The calibration of the 3D numerical model with the laboratory single cutter tests was primarily accomplished by matching the average vertical and horizontal loads on the cutter between the model and the laboratory tests. A FLAC 3D model was developed to back analyze the linear cutter test data published by Glowka (1989). The model eventually calculated the cutter loads pretty close to the test results. It is found that the different failure modes in the cutter/rock model, shear (crushing) and tensile (chipping), are highly dependent on the depth of cut and the tensile strength of the rock and greatly affect the cutting loads.