Study On Rock-breaking And Self-propelling Characteristic Of Self Rotating Multi-hole Jet Bit

Hydraulic jet radial horizontal well technology uses high pressure water jet to erode rock,arrange multiple horizontal wellbore in target horizon radially,improve seepage field and stress field near wellbore zone,increase single well production,and has widly application.As the core component of this technology,the jet bit has dual functions of hydraulic rock breaking and reverse jet traction,so the structure of jet drill directly determines the expected effect.At present,there are still some problems of the multi-hole jet bits,such as poor hole roundness,inadequate rock breaking and reaming capacity,large friction when hoses pass through,and limited length of horizontal wellbore extension.For self-rotating multi-hole jet bit,the size of rotating dynamic seal structure is limited due to the restriction of steering gear and borehole size,so it is difficult to realize its rotating function.In this paper,a design idea of shell self-rotating multi-hole jet drill is presented.Through the study of structural optimization design,rock breaking and self-propelling characteristics,the comprehensive performance of jet drill is improved,and technical support for radial horizontal well technology is provided.Firstly,the structural design scheme of the self-rotating multi-hole jet nozzle is put forward by combining theoretical analysis with numerical simulation.According to the design drawings,ground tests are carried out on the finished products.According to the test results,the rock breaking characteristics and self-propelling characteristics are analyzed.The main test parameters for studying rock breaking characteristics include spray distance,inlet pressure and sample strength,and the main parameters for studying self-propelling characteristics include wellbore diameter and flow rate.The results show that:(1)Two combinations of structural parameters for rotating function are given.The axial length is shortened to 36 mm and the circumferential diameter is shortened to 18 mm,which meets the restriction of steering gear and borehole size.(2)The rock breaking roundness of self-rotating multi-hole jet drill is higher than that of multi-hole jet drill and pre-rotating Counter-jet drill under certain positive and negative flow rate ratio and working condition parameters.The rock breaking efficiency of self-rotating multi-hole jet drill is higher than that of multi-hole jet drill and pre-rotating Counter-jet drill.(3)In a certain range of inlet pressure,the increase of inlet pressure of self-rotating multi-hole jet bit can significantly improve its rock-breaking ability,and the rock-breaking ability tends to be flat beyond this pressure.Under this condition,the pressure is 26 MPa.For rock samples with different compressive strength,the combination of front spray hole tension angle is the main factor affecting the quality of hole formation.(4)The main factors affecting the self-propelling force of jet bits include the inlet flow rate and the borehole diameter.Under certain conditions,the self-propelling force increases linearly with the increase of inlet flow.With the increase of pipe diameter,the self-propelling force of jet bit increases first and then decreases,and there is an optimal pipe diameter.Under this condition,the optimum diameter of the self-rotating multi-hole jet bit is 60 mm.(5)Analyzing and comparing the formulas for calculating pressure drop loss in continuous tubing under the conditions of Newtonian fluid,non-Newtonian fluid and pipe wall roughness,establishing the mean value method to predict the pipeline pressure loss in radial horizontal well system under actual working conditions,the relative error is less than 10%,which meets the engineering requirements.