New Prediction Method for ROP Potential of Shaped PDC Cutters

Summary Mechanical specific energy (MSE) is normally used to evaluate the rock-cutting efficiency of shaped polycrystalline diamond compact (PDC) cutters. The lower the MSE, the higher rock-breaking efficiency the cutters and the bits will have, and by default, it is considered that a higher rate of penetration (ROP) can be obtained while drilling. To validate this conclusion, and also to investigate the relationship between the rock-cutting efficiency of a single cutter and the ROP performance of a drill bit, the single-cutter rock-cutting test and the drill bit rock-breaking test were conducted using five types of shaped cutters. The results show that MSE is an effective indicator for evaluating the rock-cutting efficiency of both shaped cutters and their bits. However, MSE cannot be used to predict the ROP performance of shaped cutter PDC bits. And this discrepancy between MSE indication and ROP performance is enlarged today due to the wide applications of enhanced drilling parameters, where the MSE of all shaped cutter bits has reached a similar range of constant values, while the ROP still varies for different bit designs and different drilling energy inputs. To address the limitation of MSE in predicting ROP potentials of shaped cutters, two new evaluation indicators were derived in this work: the penetration ability (K) and the shearing ability (C), based on the findings that the effective contact area of shaped cutters formed at given drilling conditions determines the ROP performance of the drill bit deployed with these cutters. The prediction results of these two new indicators agreed well with actual ROP performances of shaped cutter bits in the laboratory tests. Through the newly developed indicators, the correlation between the single-cutter rock-cutting test results and the ROP performances of drill bits is established. Therefore, the ROP potentials of shaped cutters can be evaluated just using the single-cutter rock-cutting test, without the need for the drill bit tests and field trials, which greatly saves the research and development time and cost.