Performance Of High-energy Down-the-hole Fluidic Hammer Driven By Different Drilling Fluids

As a hydraulic percussion drilling tool,down-the-hole(DTH)fluidic hammer was born in the 1970s and was independently developed by China.The cost-effective DTH fluidic hammer has successfully been used for oil and gas drilling,mineral and geothermal drilling over the past several years.Decades of research and development enabled DTH fluidic hammer to provide a high rate of penetration(ROP),lower well deviation,and lower bit wear in hard rock formations.Despite these advantages,the current DTH fluidic hammer suffers from limitations due to the requirement for clean water to avoid wear and damage to the steel fluidic oscillator.The heart in DTH fluidic hammer is the fluidic oscillator based on the Coanda effect.A high-energy DTH fluidic hammer with hydraulic-damping-device and full tungsten carbide fluidic oscillator was proposed in the study.Striking features of this DTH fluidic hammer tool include extended life expectancy and capability to withstand drilling fluids solids content.It is observed that the hydraulic-damping-device design is effective in protecting the fragile fluidic oscillator from damage.The DTH fluidic hammer was considered to be one of the technologies with potential to reduce deep hard rock drilling cost because of the existing industrial air and water hammers in hard rock drilling applications and ease of incorporation of hammers into existing drilling systems.As noted above,however,no detailed study has previously been performed to thoroughly investigate DTH fluidic hammer performance in drilling mud environments,and,no study has been performed to evaluate the effectiveness of next-generation technologies,such as the high-energy DTH fluidic hammer with full carbide fluidic oscillator and hydraulic-damping-device.Large scale testing under simulated drilling conditions offered an economical alternative to high-day-rate field testing as well as providing clear performance comparison of different power levels,mud density,mud viscosity,additive composition,and mass concentration.The following conclusions are obtained in the study:(1)The hydraulic-damping-device could effectively brake the backward movement of the impact body to a stop without interrupting the supply jet to normally switch to the other side attachment wall.In this situation,the fluidic oscillator is maintained as intact without any damage due to the impact energy.The required damping length(RDL)can remain relatively stable over a more extended range of supply flow rate(Q_s).Higher full stroke length and larger mass of impact body resulted in a longer RDL,but this increment was not a one to one ratio.Thus,the impact feedback is optional for a normal switch in the output-fed fluidic oscillator for a fluidic hammer.(2)The analysis results show that the operation of the fluidic oscillator is affected by the supply flow rate and load characteristics significantly.Although the oscillation frequency of output-fed bistable type fluidic oscillators depends on the load characteristic and then varies more or less in direct proportion with the Q_s.When the partial stroke disappears,it also operates under constant Strouhal number.(3)The performance of the DTH fluidic hammer driven by water-based drilling fluid was in the range of the water or better at lower bentonite content.However,at higher bentonite content(?3%),the performance was in the lower range or below that of the water.Therefore,utilization of bentonite contributes to improving the lubricating effect and miniaturization of the frictional drag between the fit clearance.However,the viscosity of the drilling fluid also increases with the rise of the bentonite content,which caused the increase of hydraulic losses in the flow channel and the frictional drag on the impact body.The?p is only insignificantly influenced by the bentonite content of the drilling fluids.(4)The results also showed that with the addition of barite,the operational smoothness and impact frequency decreases slightly in the range of testing.However,the improvement of impact velocity,impact energy,and output power can entirely offset the disadvantage mentioned above.The fit clearance between the piston and sleeve must be large enough not to ensure the operational smoothness,yet should not so large such that the leakage losses between the clearance reduce the driving force of the impact body.In practice,the high motion rate of the piston,and the abrasive nature of the cuttings or barite will enlarge the fit clearance even though the tungsten carbide is tough and abrasion-resistant.Thus,it is not necessary to enlarge the clearance if the barite does not seriously affect the smoothness of the impact body.The temperature of the drilling fluids affects the performance of the DTH fluidic hammer by influencing the viscosity and density,rather than the thermal expansion and mechanical stresses in the components of the DTH fluidic hammer in the range of contents tested.(5)The performance of the DTH fluidic hammer has been shown to depend on the polymer concentration,molecular weight,and flexibility of macromolecular chains.The results show that the velocity decay rate and half-width spreading coefficient decrease with the increase of polymer concentration based on the measurements of the mean velocity as a function of radial and axial position.It is shown that,compared with a classical(Newtonian)turbulent jet,the effect of the polymers is to reduce the spreading rate,centreline velocity decay,Reynolds stresses and viscous dissipation rate.Thus,the increment of polymer concentration prevents the formation of entrainment.When the polymer concentration is higher than a certain value,the polymer drilling fluid will not be able to drive the DTH fluidic hammer.For different flexible polymers,the performance of hydraulic hammer driven by flexible polymers is worse with the same polymer mass concentration and molecular weight.Alternative products with similar properties to the flexible polymers should be selected to replaced these polymers.(6)The oil phase in oil-based drilling fluid can not lubricate the movement of the impact body in the DTH fluidic hammer.Oil-based drilling fluid without solid additives will depress the output performance of fluidic hammer due to its low density.The bentonite additive in oil-based drilling fluid can lubricate the matching structure in the DTH fluidic hammer.Oil-based drilling fluid with barite can elevate the output performance of DTH fluidic hammer by increasing the pressure drop.The motion stability and impact frequency of the impact body can be decreased by the barite particles.