Influence of water-based drilling fluids on the performance of the fluidic down-the-hole hammer

Abstract

Fluidic down-the-hole (DTH) hammer is a recently explored percussion drilling tool for the production of boreholes in hard rock. It has been proven efficient for exploration core drilling, geothermal drilling, and oil and gas drilling. Previous studies of this hammer have concentrated on its performance operating with clear water rather than water-based drilling fluids with additives. As the first step to filling the gap of knowledge in this area, this study was designed to explore only the performance of an SC86–H fluidic DTH hammer driven by water-based drilling fluids with various temperatures and different contents of bentonite and barite. Such performance was characterized in terms of output power, motion characteristic and operating pressure drop, and compared with that driven by water. The results showed that the output power of the SC86–H type hammer driven by drilling fluids with bentonite content <3% was better than that driven by water thanks to the lubrication effect in the fit clearance, whereas with bentonite content ≥3%, its output power was in the range or below that driven by water due to the elevation of the hydraulic losses and the frictional drag. Its operating pressure drop is only insignificantly influenced by the bentonite content. As the weighting agents in the drilling fluids, the barite particles impeded the smooth motion of the piston. However, the increased impact energy and output power can entirely offset the disadvantage mentioned above. Temperature affects the performance of the SC86–H type hammer by influencing the viscosity and density of the drilling fluids. Some optimal schemes are suggested for the rational design and application of the fluidic DTH hammer in practice. In summary, the SC86–H type hammer operated well in the drilling fluids with realistic fluid power levels. It means that the fluidic DTH hammer has good adaptation and robustness, which is favorable to practical application.