Relation Between the Mechanical Specific Energy, Cuttings Morphology, and PDC Cutter Geometry

This paper discusses a series of experiments performed on Carthage Marble Limestone rock samples in a high pressure single PDC cutter testing facility. The tests were performed at 450 psi confining pressure conditions and four different cutters were used. Two different cutter diameter sizes of 13 mm and 16 mm, each with two different chamfer sizes of 0.010 inch and 0.016 inch were tested. Effect of the cutter geometry on the MSE of the cutting action and grain size distribution are discussed in this paper. The experimental results show that, in the tested range, the difference between the MSE when the two different cutter sizes are considered is insignificant. On the other hand, the results show that a change in the chamfer length from 0.010 inch to 0.016 inch can significantly increase the required MSE (as much as 20%). The cuttings produced at each test were gathered and tested in a particle size testing facility and the results were analyzed to determine which drilling parameters can be best correlated to the particle size distribution of the cuttings. The results show that the minimum particle size of the cuttings has a relatively strong dependency on the MSE of each test. The minimum particle size decreases as the MSE of the cutting increases and this is closely related to the extra energy required to regrind and crush the rock as a consequence of decreased drilling efficiency. In fact, the MSE can be estimated by the rock fracture surface energy and the grain size distribution.