The Study On Raising Micro Hole Drill Bit's Rock-breaking Efficiency

Micro hole drilling technology is a well drilling technology that its bore diameter is not more than 88.9mm, it is one of the important directions of petroleum technical development. What the paper has down is integrating the domestic and foreign existing research foundation, against micro hole drilling features, to research how to improve the rock-breaking efficiency of micro hole bit, and establish the micro diameter bit's design proposal which can drill bore hole of 88.9mm, design micro hole PDC bit which is suitable for drilling in soft to medium hard strata. This will lay the foundation for enhancing micro hole rock-breaking efficiency. At first, in this paper, high-pressure mud flow eroding man-made sandstone laboratory experiment studies have been carried on under atmospheric pressure submergence condition. The experiment indicates that the broken crag volume elevates along with the jet pressure increases; the broken crag effect is best when the spray nozzle inclination angle is 30°; There are double spurts distance superiorly when the jet pressure and the spray angle are invariable, The first peak value spurts distance appears in 6~10 times of nozzle diameters place, and the second peak value spurts distance appears in 18~24 times of nozzle diameters place. Through theoretical analysis and computation, the computation model of pressure loss in the coiled tubing in micro hole well is obtained, that is, also, for the power law fluid in the annulus under disturbed flow condition, Taking the bottom of the well obtains the biggest drill bit water horsepower as the objective function, the hydraulics optimization design has been down to micro hole drilling. The drill pump's optimum capacity is 7.43L/s, the equivalent diameter of nozzle used on micro hole bit is 6.4mm. Moreover, the paper has established the simplified PDC bit three dimensional geometric model and micro hole bottom of the well flow field physical model using the PRO/E software, then uses the standard k ?εturbulent flow model and the wall surface function method to conduct the bottom of the well flow field numerical simulation research to different inclination angle single spray nozzle and multi-injection stream under drill bit static condition. Through the simulation analysis it can be known that, whenα=30°, the jet flow has the best clear crag effect; whenα=30°, the best riding position of spray nozzle on drill bit is apart from the bit's center approximately 13mm, 17mm in the bit's bottom surface; inundates flow field which forms after various injection stream attacks the bottom of the well can eliminate the rock debris of the bit's crown department flow channel, clean and cooling cogging of propeller or fan blade surface just in time. On the basis of above research, through theoretical calculation and optimization design, optimize drill bit's water power structure, develop one new highly efficient rock-breaking PDC bit that is applicable to micro hole.This article research has an important practical project significance to develop micro hole well drilling technology, and it is advantageous in raising micro hole rock-breaking efficiency and drilling speed.