Hydraulic Transport Simulation And Dynamic Characteristics Research Of The Pulverized Coal In Annular Drill String

Horizontal directional drilling rig is widely used in coal seam gas extraction.During the drilling process of directional drilling,the transportation technology of pulverized coal in annulus drill string is always the key factor to ensure continuous drilling.The transporting capacity directly determines the drilling efficiency.In the drilling process,to ensure the safety of drilling process,on the one hand,the influence of external parameters on the internal flow characteristics should be considered,and the pulverized coal produced in drilling can be successfully transported to the ground.On the other hand,it is necessary to ensure that the drill string itself will not be damaged during drilling.Drill string is affected by internal fluid and its dynamic characteristics will inevitably change under the condition of flow.Therefore,studying the dynamic characteristics of liquid filled pipe itself can be used as a method to predict early failure of equipment.And it is of great practical significance and engineering application value to study the flow technology of double pipe rig and the dynamic characteristics of the drill string.The main contents of this paper are as follows:(1)In this paper,domestic and foreign researches on the two-phase flow were summarized.According to the two-phase flow,a detailed analysis of the stress of particles in the two-phase flow was calculated.The physical model of two phase flow was determined,and the control equation and the turbulent motion equation of the two phase flow were derived.(2)According to the characteristics of fluid in annular pipe transporting,an software was used to simulate the fluid state in the drill string.The minimum deposition rate of fluid transmission was verified.The influence of different flow conditions on the transporting capacity was achieved.The results showed that velocity of particles increased with the increase of the transporting velocity.The rotation of the inner pipe is beneficial to the increase of particle velocity to a certain extent.The greater the viscosity of the fluid,the greater of the transporting velocity of the particles.The high viscosity transport medium would reduce the particle concentration in the tube,which was beneficial to transporting.The pressure drop of the two phase was much greater than the pressure drop of the single phase flow,and the pressure drop ratio would be reduced by the inner tube eccentricity.(3)The horizontal liquid-filled pipe model was researched.The vibration characteristics of liquid-filled pipes under different transmission speeds and different pipe parameters were tested by experiments.Based on this,an additional mass coefficient was proposed to calculate the natural frequency of the liquid filled pipe,and the accuracy of the result was verified by the comparison of the software simulation.The research not only provides the design theory for drill pipe rotating system,but also has important significance for the development and application of solid-liquid two-phase flow transportation technology.