Research On Hydraulic Rock Breaking Capacity And Self-propelled Ability Of The Radial Jet Drilling Technology

Radial jet drilling(RJD)technology is an effective method to enhanced oil recovery by drilling through the near wellbore damage zone,and increasing the drainage radius greatly.It totally depends on the hydraulic rock breaking technology which is one of the key technologies.High pressure flexible hose which is hard to feed in is used as the operation pipe.It is really necessary to research the hydraulic rock breaking capacity and self-propelled ability of the RJD technology to continuously drill round radial hole.The effect of confining pressure on the velocity attenuation of high pressure water jet was studied by numerical and experimental method for the confining pressure environment at the bottom of the well.Results show that the traditional method to generate confining pressure by controlling the outlet valve may be not suitable to research the high pressure water jet that happens at the bottom of oil wells.Based on the numerical results,and given that the water has the same physical property before and after the nozzle at the bottom of oil wells,the confining pressure may have no influence on the energy conversion efficiency of high pressure water jet.As the “core” of radial jet drilling(RJD)technology,the energy conversion efficiency of the multi-orifices nozzle was researched,and the nozzle discharge coefficient was derived.The effect of flow rate and number of the orifices on the nozzle discharge coefficient was studied by experiment.Results show that the nozzle discharge coefficient of multi-orifices nozzle depends on the discharge coefficient and weight ratio of each type orifice;most of the energy loss of each orifice was caused by local resistance loss;the local resistance coefficient would slightly decrease with flow rate while greatly increase with the orifices due to the complicated flow.For the purpose of improving the efficiency of rock-breaking,a rotating multi-orifice nozzle was designed.The structure parameters of multi-orifice nozzle were designed by fluid mechanics and mechanical theory.The rock breaking efficiency of the rotating nozzle and traditional nozzle with the same experimental condition was compared.It turns out the rotating multi-orifice nozzle works better.Based on the physical model of the multi-orifices nozzle and fluid mechanics,a convenient model to calculate the self-propelled force was developed.The proposed model was validated by means of experiment and numerical simulation.The effects of the number,angle,and diameter of the orifices were investigated.Results show that the forward orifices exert a negative effect on the self-propelled ability,whereas their angles present a positive effect.With an optimal angle,the backward orifices primarily generate the self-propelled force.The large diameter of orifices may decrease the self-propelled ability under laboratory conditions.A new method to feed in the high pressure hose by using the drag force generated by the high velocity flow in the narrow gap was proposed.It is validated by numerical and experimental ways.The effects of the length,height,eccentricity and flow rate of the narrow gap on the drag force were investigated.Results show that the method can generate considerable drag force easily which is comparative with the self-propelled force generated by the nozzle.The velocity and length of the narrow gap can greatly increase the drag force.The effect of the eccentricity can be neglected.The smaller height of the narrow gap is recommended.Research results presented in this paper can provide theoretical guidance for the improvement of the rock breaking capcity and the self-propelled ability of the radial jet drilling technology.