| With the continuous exploration and development of Songliao volcanic rock stratum by domestic and foreign scholars,it is found that the stratum rock has strong abrasiveness,poor drillability,slow mechanical drilling speed,long drilling cycle and other problems,so the rock breaking efficiency is relatively low.PDC bit is widely used in this area because of its high wear resistance and high hardness.At present,the research on Songliao volcanic rock stratum at home and abroad is mainly focused on the application effect evaluation,while the research on the rock breaking mechanism is less,so the targeted research on the rock breaking mechanism of PDC bit cutting teeth in this stratum can not be ignored,which is of great significance to improve the rock breaking efficiency of this stratum.Based on the study of the rock characteristics of the volcanic rock stratum,it is considered that the low rock breaking efficiency is mainly due to the high in-situ stress conditions,multiinterbedded stratum with cross-bedded,and the high bottom hole temperature.Based on the above three characteristics,this paper studies the rock breaking mechanism of PDC cutter in Songliao volcanic rock stratum,clarifies the relationship between cutting teeth and rock,finds that the vibration impact load can improve the rock breaking efficiency of cutting soft hard interbeded rock,reveals the influence of cutting parameters and bottom hole temperature on rock breaking specific work,and the influence of cutting parameters on cutting teeth temperature.The specific research results are as follows:(1)This paper analyzes the resultant force of rock in the process of PDC cutter breaking,and deduces the solution process of cutting force.Based on the analysis of rock stress under the deep in-situ stress field,the stress components satisfying the rock stress distribution at the bottom of vertical well section and inclined well section are obtained.Based on the typical rock mechanics parameters of Songliao volcanic rock stratum,a PDC cutter breaking rock model is established to simulate the stress distribution in the vertical and inclined well sections.The peak value of the stress in the inclined section is slightly larger than that in the vertical section.By comparing the influence of side rake angle and back rake angle on the specific work of rock breaking,the proper side rake angle and back rake angle are found,which is conducive to the improvement of rock breaking efficiency.(2)The idea of soft hard interbeded rock model is put forward,the process of PDC cutter breaking soft hard interbeded rock is simulated,and the indoor experiment of cutting interbeded rock was done.The error of obtained cutting force between numerical simulation and indoor experiment is very small,which verifies the reliability of simulation.It can be seen from the comparison of cutting forces of homogeneous rock and soft hard interbeded rock that the existence of soft hard interbeded interface increases the cutting difficulty,and the cutting force fluctuates greatly.(3)Comparison and analysis are made on the cutting forces of cutting soft hard interbeded rock with various dip angle of bedding and bedding thickness under in-situ stress field or non in-situ stress field,and the influence of vibration and impact load on rock breaking efficiency of soft hard interbeded rock is analyzed.The cutting force of soft hard interbeded rock under the vibration impact and non vibration impact is compared.The influence of different vibration frequency and impact amplitude on the specific work of rock breaking is compared.The conclusion that PDC cutter under vibration impact load can improve the rock breaking efficiency is given.(4)This paper analyzes the thermal theory of rock breaking process of PDC cutter,and establishes the coupled model of temperature and displacement of PDC cutter breaking rock under in-situ stress field.It is found that the highest temperature occurs in the contact area between cutting teeth and debris.Different side rake angle,back rake angle,cutting speed and cutting depth can have a certain impact on the temperature of cutting teeth.The influence of different cutting parameters on specific work of rock breaking under different bottom hole temperature is analyzed. |
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