| With the exploration and development of oil and gas resources to the deep hard strata,the drill ability of rock deteriorated.A series of problems have been emerged,such as the poor rock drill ability,the low efficiency and the short life of the existing conventional PDC bits and so on.These results directly lead to the extension of drilling cycle and the increase of drilling cost,which cannot meet the development requirement of the efficiency of drilling.PDC cutting tooth is the basic cutting unit of drill bit,the difference of its structure shape directly influences the rock-breaking efficiency and service life of the drill bit.Therefore,it is of great significance to design the cutting teeth with different structure for different strata,and provides a new way for realizing the speed increase and efficiency of hard formation drilling.At present,conventional planar teeth are difficult to eat into rock under the condition of the deep hard strata,the low efficiency and the short life of the existing conventional PDC bits make the shape of PDC cutting teeth gradually shifted to non-plane.Based on these,this paper carried out the research of the new non-planar cutting tooth structure design and rock breaking mechanism under the condition of the deep hard strata.The main research contents and results are as follows:(1)Based on the research status of PDC cutting tooth structure design,rock breaking mechanism simulation analysis,rock breaking experiment analysis and the field application,a new non-planar tooth for deep hard strata was proposed,and its properties are comprehensively studied through the combination of theory,simulation and experiment.(2)Based on the analysis of the rock performance and the force analysis of PDC cutting teeth,the process of single tooth cutting to rock breaking was studied.Obtained the indexes for determining the performance of PDC cutting teeth:?The cutting performance of the cutting gear is represented by the average size of the cutting load in three directions of axis,cutting and diameter;?The variance of the cutting load in the axial,cutting,and radial direction of the cutter is represented by the cutting stability of the three directions;? The average value of the fractured rock is characterized by the high and low rock efficiency,and the fluctuation amplitude and variance of the curve indicate the stability of its efficiency.(3)After comparing the fracture mechanism,the load and rock breaking specific work in three directions of the cutting teeth used in engineering,the results showed:The rock breaking efficiency and life of non-planar cutting teeth were significantly higher than that of conventional planar cutting teeth.Then the design of a new type of non-planar cutting tooth applied to hard strata was proposed:the structure characteristics and working principle of this new type of tooth fused with the ridge type cutting teeth and the stepped teeth.(4)Using the combination analogy,three new type of cutting teeth with the advantages of ridge shape and ladder shape are designed,they are:"One ridged double ladder"Cutter,"Double ridges double ladders" Cutter and"Three ridges three ladders" Cutter.Make the comparative analysis on average load value,load fluctuation and rock breaking specific work of these three new cutting teeth in three directions.Then make the conclusion,The No.3 new tooth:"Three ridges three ladders" Cutter had the highest rock breaking efficiency and the most stable cutting process,and the teeth were the least likely to be damaged by impact load and had the longest life.(5)A comparative study was carried out on the single tooth experiment of "Three ridges three ladders" cutting tooth and a conventional planar cutting tooth.The results showed that:the cutting load of the new non-planar cutting tooth is only 1/2 of the conventional teeth,and the radial and axial loads are only 1/3 and 1/9 of the conventional teeth than the conventional planar cutting tooth.The variance of the load on the three direction of the new non-planar cutting tooth is only 1/4,1/2,1/10 of the conventional tooth,so the tri-axial stationarity of new non-planar cutting tooth is better.In addition to that,the new non-planar cutting tooth has less a rock breaking specific energy than the conventional tooth,so the cutting efficiency of it is higher(6)The finite element model of a full-bit with the new non-planar cutting tooth and a conventional PDC bit are established,and comparative analyzed the rock breaking simulation.The results showed that:The stress level of the new non-planar cutting tooth bit is lower than that of the conventional tooth bit,and it was easier to break the rock in hard strata.The new non-planar tooth bit had less influence on the rock around the borehole and it was more conducive to ensuring the stability of the wellbore.The acceleration of the new non-planar tooth bit was less than that of the conventional bit,and this new kind of bit had higher rock breaking efficiency. |
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