| Different from the rock breaking mechanism of traditional drill bit and high pressure water jet,particle impact drilling is a new type of drilling rock breaking method,which is based on high speed hard ball particle impact rock breaking,combined with high speed hydraulic rock breaking and mechanical drill bit tooth rock breaking.with the aid of surface screening and filtering equipment,particles can be recycled,which has little influence on the specific gravity of drilling fluid,and overcomes the shortcomings of abrasive jet on serious wear of drilling equipment.When metal particles contact with bottom rock instantaneously under the action of high-speed fluid,they produce large instantaneous impact contact stress.When the instantaneous stress exceeds the ultimate compressive strength of rock,it will cause impact damage directly in the contact area,and produce tensile stress and shear stress at its boundary.Because the tensile strength and shear strength of the rock is much lower than the compressive strength,when the stress exceeds the ultimate tensile and shear strength of the rock,the dominant crack and recessive microcrack will be formed near the contact area.at the same time,the stress wave generated by the impact will propagate outward around the impact point,and the rock near the impact point will show the characteristics of plastic flow under the strong pressure.The propagation of the stress wave will cause the rock to be damaged by the tensile stress.Under the combined impact of high-frequency particles and high-speed fluid,a large amount of rock debris is generated,so as to improve the rock breaking speed of hard and abrasive-resistant strata,and has a good potential application space under the industry background that the number of deep wells and ultra-deep wells is increasing year by year.In this paper,the effects of particle volume,impact velocity,incident angle and particle mixing ratio on rock breaking by particle jet are analyzed from three aspects of theoretical analysis,numerical simulation and laboratory simulation.Based on the analysis platform of LS-DYNA,the transient dynamic analysis of particle impact rock breaking is carried out,and the relationship between the parameters of particle impact rock breaking and rock breaking effect is numerically simulated,and the standard interval of feasible particle impact rock breaking parameters is determined.Based on Newton's second law,the general equations of velocity and acceleration of particles / fluid in pipe string,nozzle and jet constant velocity core are established.The generatrix equations of cone straight nozzle,constant velocity nozzle and streamline nozzle are established.The velocity and energy conversion rate of particle / fluid in three nozzles are studied.The conclusion is that the energy conversion rate of constant velocity nozzle is higher,the pressure drop of nozzle is smaller,and the water power required is smaller.Based on this,the constant velocity nozzle is developed.Through the research method of combining the simulation calculation of mathematical model with the numerical simulation based on fluent,the correctness of particle / fluid motion equation and solution method is verified,and the relative velocity relationship between particle and fluid before particle jet impacts rock is given.Based on the dynamic spherical cavity expansion theory,the mathematical models of cavity region radius,fracture region radius,crack region radius and elastic region are established,the boundary region of particle jet coupled impact rock breaking is determined,and the calculation method of multi-particle jet coupled impact rock breaking region width is proposed.The calculation results of the model are verified and analyzed by using the research method of mathematical model calculation simulation and mutual authentication of experimental results.Based on hertz theory,the motion equation of particle impacting rock is established.The calculation method of particle impacting rock breaking volume is obtained through the relationship of maximum pressure depth,maximum impact force and erosion volume of particle impacting rock.Combined with the calculation method of water jet impacting rock breaking volume,the calculation method of particle impacting rock breaking volume is proposed finally.The relationship between different particle diameter and particle unit volume and rock breaking volume is given respectively under the same fluid velocity.Finally,the calculation results of the model are verified and analyzed by using the research methods of mathematical model calculation simulation,numerical simulation and mutual authentication of experimental results.In the process of mathematical modeling of particle jet impact depth,the research idea of taking the rock breaking depth under stable damage state as the rock breaking depth of particle jet is put forward.The evolution process of rock damage is analyzed and the damage model of rock under multiple particle impacts is given.The mathematical model of rock breaking depth after particle impacts on undamaged rock and rock breaking depth after n times impact damage is established.The relationship between rock breaking depth and impact times,particle size and impact velocity is given.Smooth particle hydrodynamics method and finite element method are used to couple particle jets to impact rock breaking depth Finally,the mathematical model calculation simulation,numerical simulation and experimental results mutual authentication research method,the model solution results were verified and analyzed.According to the process flow of particle jet impact drilling and the process parameters of impact rock breaking,the overall parameters and functional requirements of the experimental device are determined,and the particle jet coupled impact rock breaking experimental device is developed.The experimental device mainly comprises a mud pump power system,a particle circulation system,a simulated drilling system,a control and detection system and the like,can realize the real-time mixing of particles into high-pressure fluid in proportion,and can realize the process flow of particle impact drilling such as particle jet coupling impact rock breaking and particle automatic filtration.The experimental device adopts the operation mode of remote control start-stop and real-time flow control,which can realize the real-time control of jet velocity,particle mixing ratio,particle mixing speed,bit feeding speed and drilling pressure,and meet the requirements of particle jet coupling impact rock breaking experiment.Based on the self-developed experimental device of particle jet coupling impact,the experimental research on the relationship among jet velocity,particle diameter and rock breaking volume,the relationship among jet velocity,particle diameter and rock breaking depth,the experimental research on the relationship between particle volume percentage and rock breaking efficiency,the experimental research on jet angle and rock breaking efficiency,the experimental research on the contrast between particle jet coupling impact rock breaking and mechanical drill bit rock breaking drilling pressure and the penetration ability of particle jet rock breaking are carried out.The experimental results not only provide data support for the theoretical study of rock breaking volume,rock breaking velocity and rock breaking width by particle jet,but also provide the relationship among particle impact velocity,particle diameter,particle volume percentage,particle injection angle and rock breaking efficiency.The ratio relationship between particle jet rock breaking and mechanical rock breaking drilling pressure is given.The penetration capacity of particle jet coupling impact rock breaking is analyzed.The rock breaking mechanism of particle jet coupling impact is analyzed.The method of determining the particle mixing ratio is proposed according to the combination of particle impact frequency per unit rock area and the impact kinetic energy of single particle. |
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