Study on the limestone fracturing characteristics of PDC cutters in high-temperature environments

Addressing the problems of low footage and premature failure of existing PDC bits in high-temperature geothermal wells, this study investigates the limestone fragmentation characteristics of PDC cutters under high-temperature conditions. Adopting a combined approach of experimental testing, numerical simulation, and full-scale drilling verification, the effects of key parameters-temperature, rake angle, and cutting depth-on rock-breaking characteristics. The findings reveal that: (1)The mechanical parameters of limestone, such as compressive strength and shear strength, first increase and then decrease with rising temperature, reaching a peak at 250°C, where rock-breaking difficulty is the highest; (2)Single-cutter cutting tests indicate that 350°C is the optimal rock-breaking temperature, and the specific energy of fragmentation is the lowest with the highest rock-breaking efficiency when the rake angle is 15° and the cutting depth is 2mm; (3) Simulations demonstrated that both the temperature and contact stress on the cutter face increase with penetration depth but decrease with rake angle; (4)A new Φ118mm drill bit is designed based on the research. Experimental results show that the bit operates well in high-temperature environments, with a torque increase of 5.8% and a rate of penetration improvement of 31.9% compared to conventional PDC bits. This study clarifies the optimal rock-breaking parameter combination of PDC cutters under high-temperature conditions, providing key technical support for the cutter profile optimization, structural design, and drilling parameter regulation of PDC bits for high-temperature geothermal wells.