PDC cutter-rock interaction - experiments and modeling

Results of single PDC cutter experiments in a high pressure cell are presented and analyzed. Mechanistic models and FEM codes are developed to model the observed response. Throughout this document, `response' of a single PDC cutter test is a set of two members: MSE and (interface) friction angle.;Experiments were performed on Carthage Marble rock samples in pressurized conditions with 13 and 16 mm cutters, each with 0.010 and 0.016 inch chamfer length. Results show the cutter size effect on the response is insignificant. The chamfer length affects the response in a significant manner: in summary, larger chamfer causes higher MSE and lower friction angle. A model relating the friction angle response of a sharp cutter to its back rake angle is developed. The model parameters are measurable using drilling WOB-TOB data and rock internal friction angle. This model is extended to chamfered cutters and an equivalent back rake angle concept for chamfered cutters is developed. This model is extrapolated to cutters with wear flat. The cuttings produced in this set of tests were analyzed using a particle size analyzer machine and a general decreasing trend between MSE and mean particle size was observed. A model explaining this phenomenon using rock fracture surface energy is developed.;Experiments were performed on Torrey Buff, changing the pore and cell (borehole) pressure. Three sets of tests were performed and in all of them the cell pressure was varied from atmospheric to 500 psi. The pore pressure was: equal to cell pressure (zero differential pressure) in the first set, near atmospheric pressure in the second set, and 410 psi in the last set. A correlation of MSE versus cell and pore pressure is developed. One of the correlation parameters is calculated using friction angle and UCS. The second parameter is calculated using dilation and fluid drainage level in shear band. A model is developed based on free body diagram of the shear band attempts to quantify the dilation. The drainage level is quantified by an FEM code based on plane-strain poro-elasticity governing equations. The FEM code validity was verified by simulating Mandel's problem in poro-elasticity and comparing the results with the analytical solution.;Experiments were performed to investigate the combined effect of: depth of cut (DOC), rotary speed, cell pressure, back rake and side rake angle on the response. Fractional factorial design of experiments methodology is employed. The results show the MSE response is significantly affected by DOC and the other four parameters effect are insignificant compared to the DOC. The friction angle is affected by the following three parameters in the order of statistical significance: back rake angle, side rake angle, and DOC. A model explaining the drastic effect of DOC on MSE is developed based on cutter geometry and the concept of cutter-wall friction.