Vibration induced impact damage can significantly reduce PDC bit/cutter life in hard/abrasive and interbedded formations. To develop a more stable fixed cutter bit for these difficult lithologies, an R&D initiative was launched to investigate new cutter designs and experiment with their count/placement to improve drilling efficiency and mitigate vibration. The research yielded an innovative cutting structure and a conical shaped polycrystalline diamond element (CDE) with an ultra-thick synthetic diamond layer. The element is positioned at bit center with the conical tip pointing vertically down towards the rock. The location of the conical element combined with the optimized placement of the conventional PDC cutters allows an uncut rock column to develop. The stress relieved rock column is continuously crushed by the centrally positioned conical element. This enables the bit to deliver faster ROP and reduce the potential for vibration. The conical element has undergone extensive laboratory testing to evaluate its potential to improve ROP. Using a single cutter test apparatus, engineers measured the element抯 ability to fracture rock at varying depths-of-cut. They determined the new CDE exhibits up to a 70% increase in cutting efficiency compared to standard PDC cutters. An existing PDC bit was modified to include the new CDE at bit center. A Mi616 type bit was fitted with CDE and run in North Dakota and Utah through a highly mixed sequence of formations, where the objective was to increase ROP and to reach KOP in one run. The bit improved ROP over a longer interval drilled compared to benchmark PDCs used in offsets. Subsequent field testing has substantiated the CDE抯 potential and how it can be used to improve PDC bit performance.
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