Numerical Simulation Study on the Anti-Balling Performance of PDC Drill Bits

In order to quantitatively analyze the effect of hydraulic factors on the anti-balling performance of PDC drill bits, a three-dimensional fluid volume model was established on commonly used PDC drill bits. In the model, cuttings are simulated as spherical particles that are injected into the flow field from the bottom hole. The CFD-based discrete particle modeling(DPM) is used to track the cuttings by setting the DPM boundary conditions of the drill bit body at "trap"and taking particle trapping ratio (Ra) as the evaluation parameter of balling probability.Based on numerical simulation, cutting particles movement in downhole flow field is in three-dimensional irregularform along with collision and rebound. When the particle size is less than 1.0 mm, Ra will decrease with the increase of particle sizes while it will increase with the increase of particle sizes when particle size is larger than 1.0 mm,Ra increases gradually when nozzle size increases from 8.0 mm to 16.0 mm. Compared with five-nozzle drill bit,seven-nozzle drill bit is lower in Ra, and the equal-size nozzle assembly is lower in Ra compared with non-equal-size nozzle assembly.In conclusion, raincreases linearly with the increase of nozzle size and blade width, but decreases linearly with the increase of nozzlesand blade height. The DPM based numerical simulation of the bottom hole flow field provides not only a new way for in vestigating PDC drill bit anti-balling performance, but also providing the oretical guidance for bit anti-balling design.