| As a green energy,hot dry rock achieves more and more attention due to its vast reserves and strategic significance.However,the exploitation of hot dry rock is difficult because of its complicated stratigraphic conditions and poor drillability,which results in a lower penetration rate and higher cost.In order to solve this problem,a novel drilling method based on fluidic hammer with high impact energy was proposed in this paper.Compared with normal drilling methods,the high-energy fluidic hammer is more applicable to hot dry rock due to its advantages of higher penetration rate,more straight hole,less spare parts,longer service life.Moreover,this technique can be used in deep well drilling without the limitation of backpressure in borehole,which can be a potential solution to hard rock drilling in deep or ultra-deep well.Due to the high pressure and impact energy of this fluidic hammer,the work was mainly focuses on the ability and stability of the key structures like fluidic amplifier,buffer mechanism,cylinder,and piston.The contents of research and main conclusions were presented as follows:(1)In this paper,dual-jet nozzle,rotary guide vane nozzle with chamber and slot-rotary guide vane nozzle were proposed to be applied to the DTH hammer bit.Numerical method based on Fluent was conducted to study the flow field in borehole and the effects on cuttings migration and rock fragmentation were also discussed.The results show that the dual-jet nozzle and rotary guide vane nozzle with chamber were not suitable for the DTH hammer bit under lower pressure conditions.The lot-rotary guide vane nozzle formed a pressure filed with both high pressure zone and low pressure zone which can help removing cuttings and reduce the rock strength.(2)The effects of piston length and diameter on energy transfer for different rocks were studied with constant mass and impact speed of piston.The strength analysis was also made to investigate the optimal structure of a piston.The results showed that: 1)The energy absorbed by rock increases with the decrease of the piston diameter;2)When the piston length is the optimal value,the rock can achieve the most impact energy,otherwise the energy absorbed by rock may decrease;3)The higher the drillability grade of rock and the impact velocity,the less the influence of hammer structure on rock breakage.4)The maximum stress always appears at the end of the bit and stress concentration will be found on the edge of relatively small area.The design of hammer should take the allowable strength of bit into account.(3)To learn the relationship between the flatness of impinging face and energy efficiency,numerical method was conducted and some conclusions were made as follows: 1)The flatness of impinging surface of piston or bit can result in vibration in radial direction which causes the energy loss by friction between the hammer and wall;2)The bump height and positon,piston-rod diameter,and fit clearance between rod and chamber were all key factors to the energy transfer;3)The higher speed of the piston rod,the less effect the flatness was.It can be inferred that the flatness of impinging face can make a less effect on the energy loss for the fluidic hammer with high-impact energy than the normal drilling method.(4)Considering the potential effects of heavy impact on the sealing,especially for the upper parts in the fluidic hammer,relative research was conducted and the results are conducted as follows: 1)The separated gap between the sealing surfaces of sealed cap and fluidic amplifier is a key factor which caused the failure of sealing rings under high-pressure fluid environment;2)The negative correlation between the value of gap and the amount of superposed disk springs was presented.3)With no more than three disk springs,the sealing rings may be destroyed as the gap is over 0.187 mm.When the amount of disk spring is four,the gap may reach 0.086 mm and the sealing rings may fail after longtime work.In order to ensure that the sealing rings work safely,the amount of disk springs should be no less than five so that the value of gap can reduce to below 0.049 mm.(5)Buffering mechanisms,consists of disk spring,cushion chamber,or joint for collision,were proposed in this paper.Both ANSYS/LSDYNA and Fluent and were used to research the buffered performance.The results show that: Although all the three buffering mechanisms can significantly decrease the impact load and preserve the hydraulic amplifier from destroying,considering a long-term work,the buffering mechanism based on joint for collision seems more suitable for fluidic hammer with high energy.Innovation of the article:(1)Three buffering mechanics respectively consist by disk spring,cushion chamber and joint for collision are proposed for decrease the impact from piston-rod with high velocity.(2)To improve the energy transmission,the piston structure was investigated by ANSYS/LSDYNA.The effects of parameters of the piston structure and its swing were discussed.(3)The relationship between high energy impact and sealing in DTH hammer under high pressure condition was first studied.The relationship between the amount of separation and the working state of seals was established and the reasonable arrangement of disc spring was put forward.(4)Slot-rotary guide vane nozzle was first proposed to be applied to the DTH hammer bit. |
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