Theoretical And Experimental Study On Fluidic Hammer With High Impact Energy

As one of the green,low-carbon and recyclable renewable energy,geothermal energy is quite practical and competitive due to its large-scale storage,wide distribution,durable extraction,clean and improved environment.Compared with the hydrothermal resources,quite a number of the geothermal energy is stored as hot dry rock(HDR)geothermal resources in high temperature rock underground without or with a small amount of water.Both of China Geological Survey and Chinese Academy of Sciences have evaluated the total amount of HDR in the continental area of China(3-10 km beneath the surface).Similar results are obtained,showing that if the recoverable energy is 2% by computing,then it is equivalent to 4 000~6 000 times of total annual energy consumption during the year of 2 010 in China.Hence HDR geothermal resource seems to be one of the most promising energy resources for widely use.Drilling is the key part for the development of HDR,which has significant impact on the total capital investment and construction period of the project.The most common rock types of HDR are igneous rock or metamorphic rock,which are strong,hard,abrasive and poor drillable.The use of conventional drilling method will be ineffective and time-consuming.For example,the mean penetration rate in the drilling of ZR1 well is 1.24 m/h.And the mean penetration rate in the drilling of Japanese KAKKONDA well is about 2.21 m/h,much lower than the mean penetration rate in the drilling of oil and gas,which is more than 10 m/h.The DTH hammer drilling technology makes it possible to improve the drilling efficiency significantly in hard rock drilling of HDR.Compared with the pneumatic DTH hammer,because of the incompressibility of cycle media,hydraulic hammer is more adaptive in deep or supper deep well drilling where the confining pressure is pretty high.Additionally,both of its low energy consumption and high efficiency make the application of hydraulic hammer more extensive.However,to date the single impact energy of conventional hydraulic hammer is much lower than that of the pneumatic hammer,thus the penetration rate of a hydraulic hammer is also lower than that of the pneumatic hammer,which makes the use of hydraulic hammer low efficiency.Many domestic and foreign research institutes,drilling tools companies and drilling technology service companies have tried to develop the high-energy hydraulic DTH hammer which is more competitive in deep-well hard rock drilling,and has made some progress.However,most of the high-energy hydraulic hammers are in the research and development stage rather than the mature products that can be widely applied to commercial market.In order to improve the efficiency of HDR well drilling thereby reducing the total capital investment,the fluidic DTH hammer with high impact energy for fast drilling of HDR is proposed.A high-energy fluidic hammer drilling tool with high single impact energy,long working life and good working stability has been developed.The internal dynamic process of the fluidic hammer was studied and at the same time the theoretical calculation and numerical analysis have been implement.The work performance of the prototype was verified by bench tests and drilling tests.This study was carried out in several aspects of research content as followed below.(1)Considering the problem that the single impact energy of conventional fluidic hammer is low and the fact that premature failure of the fluidic amplifier and the cylinder caused by rapid erosion or wear usually occurs,high-energy fluidic hammer drilling tool with high single impact energy,resistance to erosion,and long working life has been designed,thus providing technical support for fast drilling of HDR.(2)Based on the computational fluid dynamics(CFD)with the technique of dynamic mesh modeling and user-defined function method,the internal dynamic process of the high-energy fluidic hammer is studied by using CFD software Fluent.By the use of visualization analysis,the variation of the separation vortex,the stopping vortex and the standing vortex of the flow field within the working chamber of the fluidic amplifier in different moments of movement of the piston was obtained.Analysis results show that: The main jet entrains fluid from both sides of the control nozzles and also when the piston moves at high velocity the fluid from the vent at the jet-deflected position and the back flow at the opposite side will be entrained,thus achieving high flow recovery which is beneficial to the high-velocity movement of the piston.(3)The relationship between the pressure recovery and the flow recovery is obtained by the numerical simulations.Results show that the pressure recovery increases with increasing of flow recovery,and the relationship between them is almost completely independent of the Reynolds number.(4)According to the results of numerical calculation results and analysis,it can be concluded that the single impact energy of the high-energy fluidic hammer is proportional to the square of the flow velocity of main jet.When the supply flow rate is constant,ignoring the interaction terms,smaller section areas of the main supply nozzle and the piston means larger impact energy.In addition,when the structure parameters of the piston remain constant,the smaller value of dimensionless coefficient Cpq which characterizes the relationship between pressure recovery and flow recovery poses larger single impact energy.In another word,the slower the pressure recovery decreases with the increase of the flow recovery,implies better performance of the fluidic amplifier and the higher energy output.Therefore,the dimensionless coefficient Cpq can be used as a basic parameter for evaluating the performance of a fluidic amplifier.(5)By using numerical simulations,the effect of different parameters of the piston on the performance of a high-energy fluidic hammer is studied.Results show that: in order to achieve better performance of the high-energy fluidic hammer,the piston diameter should be relatively small,and the diameter of piston rod and the mass of hammer need to be chosen reasonably.That is because if the diameter of the piston rod or the mass of the hammer is too large,the impact frequency of the fluidic hammer will be significantly reduced and the critical flow velocity of the fluidic amplifier will increases,thus the overall working performance will turn worse.As for the piston stroke,appropriate increase of stroke will lead to the improvement of the single impact energy.However,if the stroke is too large will lead to remarkable reduction of the impact frequency.(6)In order to optimize the simulation method,fluid resistance at the hammer was taken into account in the simulation models.Simulation results show that the axial fluid resistance caused by high movement of hammer should not be ignored,thus new hammer of low fluid resistance and high efficiency structures was designed.(7)In order to measure the performance of the high-energy fluidic hammer,bench tests for SC86 H high-energy fluidic hammer were carried out by using acoustic-wave method and non-contact measurement system.And at the same time,the measured performance parameters are compared with the numerical simulation results,showing a good agreement between them,thus verifying the accuracy of numerical results.(8)The performance of the two new-designed fluidic amplifiers and the original fluidic amplifier were tested and analyzed numerically and experimentally,which was found that the new-designed fluidic amplifiers showed better working performance compared with the original design.(9)Experimental tests on the drilling of granite blocks were performed,by which the simulation results were validated to some extent.The numerical simulation poses meaningful value for practical drilling.The maximum achieved penetration rate is 5.19 m/h,which is multiple higher than that of the conventional drilling method.Main innovative aspects in this dissertation include:(1)This paper firstly proposed a drilling method that uses high-energy fluidic hammer with a button bit to implement percussion-dominated drilling.(2)This paper firstly proposed the use of cemented carbide material to manufacture fluidic amplifier and piston.The integrated-internal-channel cylinder design was firstly proposed to improve the capacity of anti-erosion,anti-wear thereby extending working life of the fluidic hammer.(3)It is the first time to take the fluid resistance at the hammer into account in the simulation model.Hence the calculation accuracy is remarkably improved and the simulation model can precisely predict the working performance of the fluidic hammer.(4)It is the first time to propose side-offset-fed-back-loop fluidic amplifier with double vents.Good performance was achieved by the use of newly designed fluidic amplifier and the new fluidic amplifier is considered to be a new generation of fluidic amplifier for the fluidic hammer.In addition,theoretical calculation results show that the innovative designed vortex-chamber fluidic amplifier presents a even better working performance.