| PDC bit is an important downhole rock breaking tool in oil and gas drilling engineering.Its rock breaking efficiency will directly affect the final drilling cost.When drilling in complex and difficult formations,the cutting teeth of PDC bits will be difficult to penetrate rocks due to rapid wear,and produce obvious compaction effect and slip phenomenon.This will lead to a sharp decline in the working performance of the bit,and ultimately make the bit lost drilling capacity.In order to solve this problem,an axially inclined PDC bit tool is proposed in this paper.The bit tool has a unique "axially inclined" structure,which can make the cutting teeth produce alternating trajectory cutting motion,This cutting method can enhance the rock penetration ability of cutting teeth,thus improving the rock breaking efficiency of drills.In this paper,the following research work is carried out for the axially inclined PDC bit tool:1.A kind of drill bit and its matching tool which can realize the rock breaking characteristic of alternating trajectory cutting is put forward,and the structure characteristics and working principle of the tool are analyzed;2.Geometry suitable for the axially inclined PDC bit tool is established.Kinematics analysis is carried out on the basis of geometry theory.The influence law of inclination angle and transmission ratio on the movement track of cutting teeth and bottom hole coverage is obtained;3.The influence of rock strength,penetration depth,tooth diameter,forward inclination angle and wear height on total cutting force and specific work of fragmentation under single-tooth cutting condition is studied.Based on this,the mechanical model of single-tooth cutting is established;4.The influence of cross angle on total cutting force and breaking specific work under cross cutting condition is studied.The rock breaking effect under single-tooth cutting and cross cutting conditions is compared.Based on this,the mechanical model of cutting teeth under cross cutting condition is obtained.Finally,the working load model of axially inclined PDC bit tool is established;5.Laboratory experiments were carried out to study the effects of different inclination angles and transmission ratios on bit drilling rate and torque.The technical advancement of the tool was verified by comparing with conventional drilling mode.6.A digital simulation software is developed for calculating the working load and bottom hole topography of the drill bit through the theoretical results of the preceding paper.A design theory for the axially inclined PDC bit tool is also proposed.The ?152.4mm bit tool product is designed under the guidance of the design theory,and its performance is analyzed by the digital simulation software.The research results of this paper improve the rock breaking theory of cross cutting,and have a certain reference value for the design and development of new drills,especially those with cross cutting characteristics.At the same time,it has important guiding significance for the engineering application of axially inclined PDC bit tools and the improvement of rock breaking efficiency in hard-to-drill formations. |
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