Study On Rock Breaking Efficiency And Self-propelled Capability Of A New Jet Bit For Radial Horizontal Wells

The application of high-pressure water jets to sidetrack ultra-short radius radial horizontal wells is an effective method to extract residual oil and improve crude oil recovery.At present,the radial horizontal well drilling technology used at home and abroad is a new radial horizontal well drilling technology with in-casing steering,which can rely entirely on hydraulic energy to break the rock with a jet bit and high pressure hose to drill in the formation.The key to the implementation of the new radial horizontal well technology is how to utilise the limited displacement to achieve efficient rock breaking efficiency and maximise the extensional capacity of the radial horizontal borehole.In this paper,we propose to investigate the optimal design of a new radial horizontal well jet bit and its flow field characteristics,rock-breaking borehole characteristics and extensional capacity.In this paper,based on the multi-hole jet drill bit,a new type of spin-type multi-hole jet drill bit is designed and developed,its working principle is analysed,and the rotating body,nonrotating body parts and dynamic sealing structure of the drill bit are designed.Based on the water jet dynamics,a numerical model of the hydro-jet of the spin-type multi-hole drill bit was established and CFD numerical simulation was applied to analyse and study the characteristics of the flow field inside and outside the drill bit.The results show that the internal flow field of the jet bit can be divided into four zones: forward jet zone,bottom of well overflow zone,reverse overflow zone and low-speed reverse flow zone;the optimum values of the nozzles of the drill bit are 20° for the central forward nozzle deflection angle,20° for the external nozzle deflection angle and 15° for the external nozzle tension angle.A numerical simulation model of water jet rock breaking was established,and the dynamic simulation of single nozzle hydraulic and frontend cutter tooth rock breaking was carried out by LS-Dyna,an explicit dynamic analysis software,to analyse the influence of structural and hydraulic parameters on the rock breaking effect of the jet.Based on this,a simulation study was carried out on the rock breaking process of the spin-on multi-hole jet drill bit to analyse the effect of rotational speed and other factors on the rock breaking effect,and to reveal the mechanism of rock breaking by the spin-on multihole jet drill bit.The simulation analysis shows that the width and depth of the nozzle gradually increase with the increase of diameter.The optimum nozzle diameter is 1.3mm;there is a critical value for the water jet impact velocity,and the rock will break only when this velocity is reached.Finally,a prediction model for the extension limit of the radial horizontal well drilling system was established,and the influence law of hydraulic parameters and the main structural parameters of the bit(front nozzle diameter,rear nozzle diameter,rear nozzle inclination angle and friction coefficient)on the extension limit length was analysed.It is found that the extension length of radial horizontal wells gradually decreases as the friction coefficient of the well wall increases.Reducing the angle of the rear nozzle will also increase the extended length of the bit,with a general inclination angle setting of 30°.Reducing the diameter of the front nozzle will help to increase the extended length of drilling.The research results of this paper can provide theoretical guidance for the design method of radial horizontal well jet bit structure and the prediction of self-propelled extension capacity,which has certain engineering value and theoretical significance.