| When drilling and exploiting oil,gas or geothermal resources in deep complex formations,traditional mechanical drilling tools are prone to severe tool damage and drilling difficulties due to hard rock,which seriously affects the cost and efficiency of long-distance drilling operations.In order to solve this problem,relevant scholars began to study alternative new rapid rock breaking methods.At present,laser rock breaking technology has the most promising development prospect.Through the non-contact damage and weakening effect of laser on rock,it can greatly increase the drilling speed and service life of mechanical tools,and improve the amount of rock breaking and efficiency.In this paper,taking granite as an example,the experiments of laser moving scanning rock breaking and laser fixed-point irradiation drilling were used to study the influence of different factors on the rock breaking effect.The fitting prediction model and the optimal parameter combination scheme of rock-breaking efficiency indicators such as rock-breaking quality,specific energy,ablation trench cross-sectional area and rock-breaking rate under the interaction of multiple factors were given.The mechanism of granite thermal cracking and surface micro-crack morphology were analyzed,and the changes of rock mineral composition and mechanical properties before and after laser irradiation were detected.The main research contents and conclusions are as follows:1.The relationship between the laser power,scanning speed,irradiation distance and the rock breaking amount,the geometric size and specific energy of ablation gully was studied by the control variable method,and the effects of rock properties and multi-track scanning mode were compared and analyzed.The results show that the amount of rock breaking and the size of ablation gully increase with the increase of laser power or the decrease of scanning speed;the increase of irradiation distance makes the ablation gully wider and shallower;excessive laser power and irradiation distance will increase of specific energy.In addition,it is concluded that the rock surface roughness has little effect on the rock-breaking efficiency,marble is difficult to be broken due to high reflectivity,and the secondary effect will be intensified if the scanning track spacing is reduced.2.The prediction models between the rock breaking mass,specific energy,ablation ditch cross-sectional area,rock breaking rate and the laser power,scanning speed,defocusing amount and scanning spacing were established by the response surface method,the trends of rock breaking efficiency under the interaction of multiple factors were analyzed,and the process parameters were optimized and verified.The optimal process parameters combination is obtained as follows: laser power = 1300 W,scanning speed = 10 mm/s,defocus = 5 mm,scanning spacing = 7 mm.3.According to the XRD analysis of rock mineral composition before and after laser irradiation,the main composition of rock was changed from cordierite,albite,muscovite and quartz to muscovite,quartz,albite and anorthite.The increase of quartz is mainly caused by the thermal decomposition of silicate,while the high heat resistance of muscovite makes it less decomposed.The results show that the composition of rock changes obviously before and after laser irradiation,and its properties weaken under the action of high temperature.4.The laser fixed-point irradiation rock breaking experiment and mechanical performance research were carried out by the hybrid Taguchi method,the rock breaking effect and crack morphology under longer irradiation time were analyzed,and the thermal cracking mechanism caused by thermal stress and the trend of rock strength under different parameters were studied.The results show that the weakening degree of rock properties increases with the increase of irradiation time,laser power and the decrease of irradiation distance,and the maximum decrease of compressive strength is 56.8%.There are 46 figures,19 tables and 71 references in this paper. |
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