Comparison of the suction-type and the normal-type DTH drill bits in reverse circulation drilling using CFD modeling

Abstract

Reverse circulation drilling is a commonly used drilling technique in mineral exploration due to its high sampling rate and cost-efficiency. The effectiveness of this drilling technique depends on the operational parameters and the utilized drill bit type. The normal-type down-the-hole (DTH) hammer bit is mainly preferred in reverse circulation drilling since it can be used either for direct circulation or reverse circulation drilling operations. A new-type drill bit named as the suction-type drill bit has been designed and developed in China to increase the efficiency of reverse circulation drilling performance. Reverse circulation drilling performance can be evaluated by the high negative pressure inside the drill bit and the suction capacity of the system. This study examines the reverse circulation drilling performances of these two types of drill bits using the Computational Fluid Dynamics (CFD) modeling. ANSYS Fluent, a CFD code, is utilized for the numerical simulations. First, three suction-type drill bits with a different number of flushing nozzles are designed and analyzed to find the optimum operational air inlet amount according to the flushing nozzle number. Then, the normal-type DTH drill bit is tested under the same operational parameters. The simulation results show that the normal-type DTH drill bit does not provide sufficient reverse circulation compared to the suction-type drill bit. The suction-type drill bit has more negative pressure inside the drill bit and suction capacity, which leads to a better reverse circulation performance.