Design And Rock Breaking Mechanism Of Cone Retracting Single Cone-PDC Composite Bit

The development of deep oil and gas resources is an important demand to realize our country’s energy replacement strategy.However,the high efficiency of deep oil and gas development is severely restricted by the problems of hard deep formation,poor drilling ability,low rock breaking efficiency,slow mechanical drilling rate and high drilling cost.Aiming at the above problems,this thesis designs a new type of composite bit--cone retraction single-cone PDC composite bit,which is expected to provide technical reference for drilling speed improvement in deep Wells.This thesis uses 3D modeling software to design an 8-1/2in cone retraction mono-cone PDC composite bit.Based on the theory of porous elasticity,considering the fluid-structure interaction of bottom hole rock under seepage condition,the convex bottom hole stress field was analyzed by using multi-physical finite element software.The rock breaking simulation of the composite bit was carried out by using display dynamics software.The bottom hole flow field and cuttings migration were analyzed by using computational fluid dynamics simulation software.The results show that the central rock of convex bottom hole is subjected to obvious tensile stress and its range is larger than that of conventional bottom hole.At the moment of borehole opening,the in-situ stress near the borehole is rapidly released and rebalanced in a short time.The rock near the convex bottom is in a state of rock damage or easy damage,which can effectively improve the rock breaking efficiency.When the retraction length of single-cone bit is about 20 mm,the tensile stress of core rock is the largest and the degree of damage is the highest.The larger the diameter of the single-cone bit is,the greater the tensile stress of the core rock is,and the higher the degree of damage is.The rock breaking mode of the drill bit is mainly tensile stress breaking rock,and the fluctuation of torque and transverse vibration is relatively stable,which can effectively improve the stability and service life of the drill bit.The drilling fluid creates eddy currents between the blades to remove cuttings near the cutters.An area of low pressure exists near the chute,and cuttings are discharged along both sides of the chute with the drilling fluid.