Research On Rock Breaking Mechanism Of Micro-core Bit And Core Structure Design

Micro coring-bit is a new type of bit by setting the tooth space in the core of the bit to produce small core or large size cuttings.It is beneficial to the analysis of geological logging lithology and stratigraphic stratification,and can also improve the efficiency of rock breaking to a certain extent.The development of micro coring-bit is of great significance for improving drilling efficiency and logging quality.In recent years,the research on the design technology of the micro coring-bit and the field experiment provide some technical support for the development of the micro drill bit,but the design of the core structure of the micro coring-bit is lack of sufficient basis.Besides reasonable tooth arrangement design,optimizing the parameters of the center space structure is also an important topic for designing micro core drill.On the basis of theory,the axial loading and lateral loading of core element are simulated and analyzed in this paper,and the experiment of unit breaking is carried out on the core by different crushing methods.According to the experimental results and the design theory of the micro coring-bit,the experimental bit with adjustable core structure parameters is designed,and the full drilling experiment is carried out.The main research content of the paper is in following.1.The theoretical analysis of the working principle of the micro-core bit and the mechanism of rock breaking is carried out,and the different rock breaking methods of the micro-coring bit are deeply analyzed from the angle of rock breaking.2.The fracture experiments of different sizes of small core are carried out by different rock breaking methods,and the crushing strength of each core is obtained.The effect of different core dimensions on the rock breaking efficiency of the micro core bit is analyzed by the experimental results.3.Based on ABAQUS,the axial load and lateral loading simulation process of core unit is studied.The stress cloud map of different sections is extracted to analyze the development trend of the stress field in the core of the core.4.An experimental micro core drill which can simulate micro core PDC bit and simulate conventional PDC bit is designed and manufactured.5.Laboratory drilling experiments were carried out using micro drill bit and conventional PDC bit with equal tooth arrangement parameters.On the one hand,the micro core drilling ability of micro core drill is verified.On the other hand,the effect of micro core drill on improving drilling efficiency is tested.