Study On The Flow Law Of Fluid Carrying Coal Powder In Straight Shaft Wellbore

In this paper,to solve the problem of the coal particles accumulate the bottom of the wellbore in the coal bed methane production,the subsidence characteristics of pulverized coal particles are analyzed theoretically.The numerical simulation study on the law of transport of coal powder in the pipe annulus and the settlement of coal powder in the casing annulus is carried out.And the relationship between the velocity of coal particle settlement and the velocity of well fluid is analyzed.The main content of this article is as follows.(1)In theory,the fluid state in the pipe annulus and mechanical model of coal particle migration is analyzed.Based on this,the continuous physical model of coal powder movement is established,which can lay a theoretical foundation for the subsequent numerical simulation.Then,the advantages and disadvantages of the discrete phase model,VOF model,mixture model and euler model are analyzed.And consider the characteristics of coal dust removal process and coal dust particle subsidence process.The simulation method of different processes is optimized.(2)The simulation of the influence of particle size,liquid inflow velocity and liquid viscosity on the migration of pulverized coal in the three-dimensional model of rod and tube annulus is carried out in three dimensional models.The relationship between the velocity of liquid flow and the final velocity of pulverized coal settling is also discussed.The simulation results show that the smaller particle size can improve the ability of fluid carrying coal powder.With the increase of liquid inflow velocity,the amount of pulverized coal which is carried out of the wellbore is increasing.With the decrease of liquid viscosity,the rate of pulverized coal entrained in the annulus increases slightly.But the change is not obvious,neglecting the influence of viscosity in actual production on pulverized coal discharge.In conclusion,controlling the particle size as small as possible and increasing the velocity of liquid inflow can improve the ability of fluid to carry pulverized coal.(3)The settling velocity model of single coal particle and the final velocity model of particle settling under the interference of coal powder in the annulus are established.Based on this consideration,By using the method of simulation analysis,the theoretical results and simulation results are compared to find that the theoretical formula has certain reliability.In this paper,the law of coal movement in a straight wellbore is systematically revealed.According to the simulation results,the parameters range of particle size,inflow velocity and liquid viscosity suitable for pulverized coal discharge are given.It is of great significance to improve the production efficiency of coal bed gas and guide the large-scale commercial exploitation of coal bed gas in China.