Mechanical Analysis And Fragmentation Mechanism Of PDC Bits Drilling Rock

With the dramatic increase in the demand and consumption of underground mineral resources, the scarcity of resources and the supply of mineral resources and protection has become a "bottleneck" restricting the development of the national economy. Drilling is irreplaceable technical means in deep geological prospecting work, while drilling funds and materials consumed in the rock crushing is a very huge number.The crushing mechanism of hole bottom rock is one of important drilling professional basic theoretical research direction, and is the theoretical basis of design efficient, long-life rock crushing tools and develop reasonable Drill in. The study in domestic and international of rock crushing mechanism while the diamond drill drilling in hole bottom has done a lot of work, but about diamond rock fragmentation mechanism and crushing process has not yet been thoroughly mastered, still do not have a good physical model.Previous rock crushing mechanism studies, mostly based on spherical, conical or cylindrical flat bottom pressure molded into the conclusions of the stresses and deformations in the elastic half-space basis, considering the rock under the action of cutting static stress distribution, so to study the rock crushing problems. This is more appropriate for the study of rock fragmentation mechanism while table inlaid or impregnated diamond bit drilling.As the improvement of production technology of PDC and the advances of design and manufacturing technology of PDC bit, at home and abroad PDC bit has been a lot of use in oil well drilling, coal field drilling and core drilling, and PDC drill bit to adapt to the strata are more and more widely, but the theoretical research is still far behind in engineering practice. For further expand the range of applications of the PDC bits, and for the realization of the scientific design and application of PDC bits, it is necessary to clearly understand the PDC drilling rock crushing impact factors and laws, in order to effectively utilize and master them. This is the purpose of this thesis.The subject study is using a combination of the theoretical analysis and modeling, experimental research and simulation analysis, on the basis of the theoretical analysis and modeling of the rock fragmentation mechanism in previous research. Because the PDC of the PDC bit is in oblique cutting way to pressed into broken rock, the shape of the indenter is different from the spherical or conical indenter, and the cylindrical flat-bottomed indenter. Therefore, PDC drilling rock fragmentation mechanism can not simply be pressure molded into a spherical, conical or cylindrical flat bottom conclusions analysis, and need for the a specific oblique PDC shape, combined with a specific rock crushing way analysis.Through the stress analysis for the PDC pressed into cutting rock, the contact pressure between the single PDC piece and rock is detailed derivation by the use of contact mechanics theory, and the model between the role of the load and pressure with the rock depth is established. The relational model about the contact interaction of the combination of different sizes, shapes PDC piece and different geometry PDC drill is established, and the influencing factors and laws of the contact pressure is analyzed. On this basis and based on the relevant rock strength criteria, the thesis has analyzed the crack initiation and fracture plane position in front of the rock crusher, while the PDC is drilling in the rock with oblique loads, and established a theoretical model of PDC drilling rock crushing conditions.Based on the mechanical properties data of the test rock and PDC, some indoor tests of PDC pressed into cutting rock were done with the different sizes and the number of PDC. Then a PDC bit was designed, and bench test was drilling. According to the test data, the correlation between various parameters and laws were studied, and the results were compared with the theoretical research.This thesis have created a variety of different shapes and sizes PDC and the different structure of PDC bits pressed into cutting rocks geometric model by the Design Modeler of the Ansys Workbench, then used the Static Structural or Transient Structural module for finite element analysis, post-processing and analysis. Finally, the various parameters were designed and analyzed by the Design Explorer module. The chapters are as follows:The first chapter described the meaning and purpose of this thesis, and reviewed the theoretical research status and trends of rock crushing force and PDC, and elaborated the research content and methods of the thesis.The second chapter is a study on PDC stress analysis by theoretical methods, to figure out the influencing factors of the contact pressure, and the relationship between the contact pressure with the forces of the PDC composite piece.There are two contact surfaces between PDC and rock, when shaping PDC pressed into cutting rock. This thesis derived the contact pressure of the contact surface by contact mechanics theory. The relationship with the PDC pressure acting on the PDC and the depth cutting into the rock was analyzed by the limit force equilibrium condition, and this indicated that the depth of the contact pressure and the pressure into the rock is a non-linear proportional relationship. Through the force analysis of PDC bits, to draw the relationship between the pressure of drill shaft and the torque with a single PDC force and drilling machinery speed, etc.The third chapter is an analysis of PDC pressed into cutting rock crushing. According to the theory of the calculated contact pressure, the conditions of PDC pressed into the rock crushing were analyzed through the rock compressive mechanical properties. Then combination of rock strength theory, the rock crack initiation, development conditions and macro-cracking surface, while PDC pressure into cutting rock, were analyzed, and obtained the condition model of PDC drilling rock broken. So qualitative analysis of the PDC drilling rock crushing process was carried on.The contact pressure must be inevitably affect when non shaping PDC pressed into the rock, because of the shape and size variation of the contact surface between the PDC and the rock. So the contact pressure of the contact surface between a small part cutting PDC and rock was analyzed still by the relevant contact mechanics theory, and the results were compared with shaping PDC contact pressure formula. These show that the calculating form of the contact pressure between the PDC and rock was unchanged, because the form of the PDC pressed into cutting rock fragmentation unchanged, but the correlation coefficient should be related to the geometric characteristics of the PDC. Then the geometric characteristics factors influencing the contact pressure of the PDC were analyzed.The fourth chapter is about the study and the analysis of the laboratory test results, and the purpose is to verify the conclusions of the theoretical research. The mechanical properties of the test rock and PDC were trials test by pilot plant, and the test data may as the data foundation of micro-drill test and numerical analysis.Several physical models of some shaping and non-Shaping PDC pressed into cutting rock were designed, and micro-drilling tests were trialed. According to the results of various tests, the factors of impact of the PDC drilling rock crushing effect were analyzed. According to the conclusions of the preliminary research, a PDC bit was designed and manufactured, and bench test was trialed, and the test parameters and effects were analyzed.Chapter V, on the basis of theoretical and experimental research, numerical analysis of the PDC pressed into cutting rock was executed. Several simulation geometry models were designed. The first model was a single shaping PDC pressed into cutting rock, and the second model was a single non-shaping PDC pressed into cutting rock, and the third model was combination of PDC constituted by two or six PDC, which pressed into cutting rock. The geometry factors of cutting angle and torsion angle etc. were considered in the simulation analysis process. The correlation between the various parameters was analyzed by the Design Explorer of ANSYS. The nephogram of the stress and deformation and curve of the various parameters correlation showed that the size effect of the PDC to the contact pressure and deformation on the rock have a greater impaction, and the theoretical curves and numerical analysis curve is more in line with, this also showed that the theoretical analysis is definite.Chapter VI is the concluding chapters, which summarizes the relevant conclusions of the full text, and analyzes and outlooks the questions and requires to continue in-depth this research.In short, through theoretical derivation modeling, test analysis and the numerical analysis, the mechanism of the PDC pressed into cutting rock crushing achieved certain results.