| In recent years,the development needs of deep oil and gas fields have gradually increased,and the requirements for drilling technology have also become higher.Traditional mechanical rotary drilling technology is slightly weak when drilling deep geological high-hardness rocks,and is increasingly unable to meet the needs of exploration.Laser drilling technology has attracted widespread attention due to its low cost,high efficiency,good safety,and low damage to the formation.At present,the world’s industrialized countries are racing to engage in basic theories and related technologies for laser rock breaking.Based on the systematic summary of these research results,this dissertation combines theoretical analysis and numerical simulation to study the temperature field and thermal failure of rocks under different irradiation parameters,hoping to provide a reference for further research in this field.The specific contents are as follows:(1)The model of laser heat source obeying Gaussian distribution is established.The influence of power concentration coefficient,absorption and reflection of material surface on laser,and beam offset on laser energy distribution are analyzed.The heat transfer process of laser heating steel plate and sandstone surface is analyzed by theoretical and simulation approach.Furthermore,the effects of thermal boundary conditions,thermal physical parameters and phase transformation of the sandstone on the numerical simulation results are discussed.Finally,the numerical modeling scheme is suggested to insure that the simulation results are reasonable and applicable.(2)Simulation analysis of temperature field and perforation characteristics in laser rock breaking process.The transient heat transfer model of laser rock breaking process is established based on ANSYS APDL simulation software,and the perforation process is simulated with birth and death element technology and the consideration of the sandstone solid-liquid-vapor phase transformation.The temperature field and perforation volume and shape at different time are given.The variation of specific energy and perforation depth with laser action time is analyzed.The influence of laser parameters,including laser power and spot radius,on perforation characteristics is discussed.(3)Simulation of rock fracture under thermal stresses.Based on ANSYS APDL software,the sequential thermo-mechanical coupling simulation model of laser rock breaking process is established,and the Coulomb-Mohr criterion is used as the criterion of rock strength failure.The sandstone thermal cracking behavior induced by thermal stresses is analyzed.The thermal fracture of rock under laser irradiation is obtained,and the influence of laser action time and laser power on the thermal cracking is discussed.By means of numerical simulation,the rock temperature field,perforation characteristics and rock fracture under laser irradiation are reproduced and analyzed,which provides theoretical reference and technical guidance for relevant engineering practice. |
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