Experimental and Numerical Investigation on the Fracture Characteristics of Different PDC Cutters Penetrating Limestone

Carbonate rocks are an important oil and gas reservoir rock. Conical PDC (Polycrystalline Diamond Compact) cutter, as a special shaped PDC cutter, can significantly improve the rate of penetration (ROP) in hard formations. However, the breakage characteristics and failure mode of the conical PDC cutter penetrating carbonate rock is unclear. A series of single cutter penetration tests were carried out with the conical and conventional PDC cutters. The surface morphology of broken pit and specific energy were analyzed. The conical cutter caused brittle damage on the rock around the broken pit at the rake angle of 10 and 20 degrees. The results of the numerical model based on the cohesive element method show that the conical cutter produce the significant tensile damage on the rock at the rake angle of 10 and 20 degrees. The tensile capacity of the conical cutter is stronger than that of the conventional cutter. The research findings of this work offer insights into the breakage process and failure mode of carbonate rock by the conical cutter. 1. INTRODUCTION Carbonate rocks are an considerably important oil and gas reservoir rock (Wenzhi et al., 2014). The carbonate rocks store 70% of the oil and gas resources. Nearly 50% of proven recoverable oil and gas resources are stored in deep and ultra-deep carbonate formations worldwide (Al-Shargabi et al., 2022). Therefore, carbonate oil and gas resources have great exploration and development potential. The carbonate formations in China are concentrated at depths ranging from 5000 to 7000 meters (Ma et al., 2017). These formations consist of challenging rocks that are hard, and poorly drillable, resulting in a low rate of penetration (ROP) (Zeng et al., 2023). PDC bits dominate the global drilling market (Rostamsowlat et al., 2022). In recent years, a large number of special-shaped cutter, including conical cutter, have flooded into the drilling market (Izbinski et al., 2019). In 2010, Novatek Company invented conical PDC cutter (Durrand et al., 2010).