Design and numerical analysis of a large‐diameter air reverse circulation drill bit for reverse circulation down‐the‐hole air hammer drilling

摘要

Reverse circulation down‐the‐hole (RC‐DTH) air hammer drilling is a fast and cost‐effective method for hard rock drilling. As the air RC drill bit is the heart for RC‐DTH air hammer drilling system to form the reverse circulation, a large‐diameter RC drill bit was innovatively designed and numerically optimized with respect to the suction ability. Results show that increasing the suction‐nozzle elevation angle and deflection angle can improve the drill bit suction ability. The drill bit performance reaches its optimal state when the air flow rate was about 1.205?kg/s, thereafter it exhibits a reverse variation trend with the increase in air mass flow rate. The optimum diameter of the suction nozzles is 20?mm for the drill bit studied in this work. The RC drill bit with outer diameter of 665?mm and RC‐DTH air hammer with outer diameter of 400?mm were manufactured and a field trial was conducted. Field test results show that the penetration rate using the RC‐DTH air hammer drilling method is more than twice the conventional rotary drilling method. This drilling approach poses a great potential for the large‐diameter hard rock drilling applied in the upper portions of a well bore above the potential producing reservoir formation for land oil and gas drilling, geothermal drilling and relevant field drilling operations.