Research On Preparation And Performance Of C_f Reinforced ZrB₂-SiC Ceramics For Hot-melt Drill Bit Shells

The hot-melt drilling technology uses a special hot-melt drill bit to generate high temperature and transfer it to the surrounding rock and soil to melt it,and then squeeze the molten material out of the bottom of the hole by self-weight or counterweight pressure to achieve the drilling effect.During the upflowed process of the melt,the pores or fissures of the formation can be filled to form a hard and stable vitreous pore wall,which replaces the role of the casing.Thus,it can effectively deal with the problems of deep drilling such as high temperature formation,hard formation drilling,hole wall stability,and drilling fluid loss.However,during the actual indoor and field tests,it was found that the shell material of the hot melt drill bit has problems such as inability to withstand high temperature,easy oxidation and wear at high temperature,and its service life is not long;resistance heating pyrolytic graphite has a slow heating rate and a lower temperature limit(?1300?)is not enough to melt hard and dense rocks such as granite.Throughout the development history of hot-melt drilling technology at home and abroad,the shell material of hot-melt drill bits is one of the key factors restricting the development and application of this technology.To solve the problems encountered by the hot melt drill bit shell,it is necessary to improve and test the hot melt drill bit.This article conducts hot-melt tests on hard and dense granite.It is necessary to re-select heating elements and shell materials,prepare multiple sets of shell materials for performance optimization and mechanism analysis,determine the material formula that meets the indicators,and finally build a test device indoors for hot melt Stone test to verify the actual effect of the optimized shell material.Therefore,this article has carried out the selection of thermal elements and shell materials for hot melt drills,the heat transfer simulation of shell materials,the preparation and characterization of shell materials,the performance optimization and mechanism analysis of shell materials,and the construction of hot melt rock test equipment.Research work such as the drilling test of hot melt rock,and the conclusions are as follows:(1)Selection of thermal element and shell material of hot melt drillSince the temperature of resistance heating is not enough to melt granite,combined with working temperature,high temperature performance and processing difficulty,etc.,summarize and compare the characteristics of various metal heating materials and non-metal heating materials,and select electric heating silicon molybdenum rods and induction heating high-strength graphite The combination.Refer to the previous test data to determine the index of the shell material,the pressure is above 6MPa,the temperature resistance is above 1500?,and the processing cost is less than 1,000 RMB.According to the mechanical properties,oxidation resistance and processing cost,a variety of high-temperature resistant materials were analyzed,and ZrB₂-SiC ceramics(abbreviated as ZS)with excellent comprehensive properties were determined as the shell material for the hot melt rock test.(2)Numerical simulation of shell material of hot melt drill bitThe heat transfer effect of the shell needs to consider the thermal conductivity,heat capacity,density and other properties of the material.The heat transfer process of determining the hot melt rock process is heating element-shell inner wall-shell outer wall-rock in sequence.One of the key factors affecting heat transfer is the heat transfer effect of the shell.The mathematical model of the hot melt rock test is established,and the distribution law and heat transfer mechanism of the influence of ZrB₂-SiC ceramics on the temperature field of the hot melt rock are analyzed.The temperature is transferred from the heating element to the rock through the shell,and the overall trend is decreasing.The overall heat transfer of the shell material is greater than that of granite,and the decline is slower than that of granite.The heat transfer effect of the shell is intuitively expressed through the temperature of the outer wall of the shell.The heating element is 1600?,and the outer wall of the shell must reach at least 1500?to meet the requirements.The calculation found that the temperature of ZrB₂-SiC ceramic transferred to the rock after 10mm is 1557?.A control group was added to evaluate the influence of different shells and shell thicknesses on the heat transfer effect.The heat transfer effect of ZrB₂-SiC ceramics is better than that of the control group,and the thickness limit is 30mm.(3)Preparation of ZrB₂-SiC-C_f composite materialThe addition of carbon fiber can effectively improve the oxidation resistance,mechanical properties and thermal shock resistance of ZrB₂-SiC ceramics.First,the ZrB₂-SiC mixed powder is mixed by ball milling,and then the C_f and ZrB₂-SiC mixed powder are mixed with magnetic stirring to avoid the damage of Cf due to ball milling,and the ZrB₂-SiC-C_f mixed powder is obtained.In an Ar atmosphere,with the process parameters of holding for 1 hour at 2000?,the ZSC_f composite material(abbreviated as ZSC_f)of carbon fiber with different volume fractions was prepared by the hot-pressing sintering process.The density of ZSC_f composite material is more than 99%,and C_f is evenly dispersed in the composite material without agglomeration.(4)Perform performance test on ZSCf composite material and study its strengthening mechanism.The mechanical properties of ZSCf composites with different volume fractions of C_f were tested for bending strength and Vickers hardness,thermal shock resistance test for three thermal cycles of air cooling at 1600?and oxidation resistance test for 0.5h high temperature oxidation at 1600?.It is concluded that ZSC_f6 with a Cf volume fraction of 6%has the best mechanical properties and thermal shock resistance.It is analyzed that the mechanical properties and thermal shock resistance are strengthened by mechanisms such as fiber toughening and crack deflection,and the increases are 46.7%and 39.2%,respectively.In terms of oxidation resistance,the higher the C_f volume fraction,the better the oxidation resistance of ZSC_f,and the increase of ZSC_f20 is 73.5%.Through the barrier and deflection mechanism of Cf to oxygen,the effect of reducing the cavity in the oxide layer and forming a local reducing environment can effectively improve the oxidation resistance of the ZSC_f composite material.The theoretical working time is 360h,which is far beyond the shell material of the same thickness used in the past.Sacrificing the oxidation resistance of the part,choose ZSC_f6 with the best comprehensive performance as the shell material.The bending strength reaches443MPa,the Vickers hardness reaches 1520 kgf/mm²,the fracture toughness reaches 5.18 MPa·m^1/2,and the performance drops 10%after three thermal cycles.,Its performance meets the requirements of the use of hot-melt drill shell materials.(5)Construction of hot melt rock test equipment.Compare the melt effect of resistance heating silicon molybdenum rod and induction heating high-strength graphite.Resistance-heated hot melt rock has poor effect,slow heating rate and other defects.Induction heating is fast,reaching 1500?in 8 minutes,and the effect of hot-melting granite is obvious.Therefore,the medium frequency induction heating high-strength graphite was selected for the hot melt rock test.Determine the feasibility of the hot melt test through experiments,optimize the test plan,adjust the temperature,weight on bit and other process parameters of the hot melt rock,optimize the bit configuration,calculate the reasonable size,calculate the theoretical upper limit of the hot melt test,and organize the test rocks.Sub-analysis.In the end,the process parameters were determined as power of 20k W,WOB 2T,and working temperature of 1600?.Both the rock and the graphite column are wrapped with thermal insulation wool,and the truncated graphite column has the best hot melting effect.The test device has a limit depth of 167mm for hot-melted granite.The test rocks are granite,plagioclase and basalt.(6)Determine the actual effect of ZSC_f6 as a shell material through the hot melt rock test.The ZSC_f6 composite material is selected as the shell material,SiC and Al₂O₃ are used as the control group,and the shell is not used as the reference.The test rock selected three types of granite,plagioclase,and basalt according to the deep stratum and the different SiO₂ content.The test process parameters are power 20k W,hot melt temperature 1600?,WOB 2T,and melting depth 50mm.Discuss and analyze the difference of the drilling speed of different shells in three kinds of rocks through the test data,and the influence of different SiO₂ content on the drilling speed.After the test,the graphite column was cut to observe and analyze the adhesion of the shell to graphite and rock.The drilling speed of using ZSC_f6 shell in basalt and plagioclase is nearly 1.5 times that of granite,mainly because of the higher melting temperature of granite and the presence of part of SiO₂ in the form of quartz.The use of ZSC_f6 shell is higher than SiC and Al₂O₃ in drilling speed and anti-adhesiveness in three kinds of rocks.ZSC_f6 shell maintains integrity and reusability.Through the hot molten rock test,it can be known that the ZSC_f6 composite material fully meets the needs of hot-melt bit shell materials.