Research On Reverse Jet PDC Bit

At present,the problem of low drilling speed in unconventional exploration areas such as horizontal wells is becoming more and more prominent,one of the reasons is that the bottom hole pressure is too high,resulting in cuttings can not be recycled out of the bottom hole in time.The “chip hold down effect” of the cuttings is caused by the excessive pressure of the bottom hole.Meanwhile,it will cause the repeated fracture of the rock.Therefore,the method of reducing the bottom hole pressure can effectively eliminate “chip hold down effect” and improve the ROP.The reverse jet PDC bit is based on the jet pump technology,five reverse jet nozzles and reverse channel is designed in the internal structure,which can form a local negative pressure region at the bottom of the well.This paper analyzes the basic characteristics of the reverse jet bit to reduce the bottom hole pressure by changing the hydraulic parameters,such as nozzle diameter,the size of junk slot,throat diameter,flow ratio and area ratio,as well as external factors such as inlet velocity,rotational speed,which combined CFD numerical simulation with the analysis method of jet pump.The design of cutting structure includes crown,tooth arrangement,etc.The finite element analysis of the whole design shows that the strength of the result meets the requirements.The design size of the chip removal groove of the reverse jet bit is very small,which is not contribute to pass through the cuttings bed in horizontal well when pulling out is started.The cuttings clearing drill pipe which can effectively remove cuttings bed is designed to eliminate the negative influence of cuttings bed on reverse jet drill bit in horizontal well.The cuttings cleaning drill pipe is arranged on the drill pipe with four-blade spiral structure.The design parameters of the cuttings removal drill pipe is designed by the theoretical analysis of the ejection angle and the spiral angle of the screw structure.The DPM discrete phase simulation method is used to monitor the velocity and turbulence intensity of cuttings under the action of cuttings cleaning drill pipe.The regularity of removing of cuttings bed is analyzed by changing the spiral structure length,spiral angle,rotating speed and the number of blades in DPM.In this paper,the reverse jet drill bit and cuttings cleaning drill pipe are designed,and their working regularity are researched by using numerical simulation method,which indicates the practical engineering value for the design of the new drill bit.