Experimental Investigations of the Effect of the Pore Pressure on the MSE and Drilling Strength of a PDC Bit

Abstract

Abstract Experiments to investigate the effect of the pore pressure on a single PDC cutter forces were performed on Sandstone core samples. The experiments were performed in a high pressure single PDC cutter testing facility which is designed to perform one round of cut on the rock sample with a single PDC cutter. The cell confining pressure and the pore pressure were controlled and other operating conditions such as the depth of the cut and rotary speed were kept relatively constant. The results can be applied to equip PDC bit simulators with better bit performance prediction by considering the effect of the formation pore pressure in the model. Such knowledge improves the drilling optimization analysis by providing more accurate predictive guidelines. The methods used and the lessons learned in these experimental investigations can be modified and utilized in more advanced similar types of investigations. These experimental data were used in production of well-fitting correlations of logarithmic nature relating the MSE to the differential pressure and the confining pressure. The correlation demonstrates that the pore pressure has the same type of effect that the confining pressure has on the MSE but weakend by a coefficient. The same type of behavior, but to an even lower extent, was observed when the drilling strength was considered. Two rock and operational parameters dependent constants exist in the correlation; a detailed discussion on the physical meaning and methods to obtain those constants is included. This study adds up to the rock mechanics knowledge of the PDC bit cutting action by proposing a quantitative means to account for the effect of the pore pressure. The results can not only be used to enhance the accuracy of any type of PDC bit simulator; but also, to test or validate rock failure models that consider the pore pressure.