Research On The Flow Of Pulverized Coal Migration By Gas-water Two-phase In Horizontal Borehole

Due to various factors such as coal seam geological conditions,drainage methods and downhole operations,coal powder is inevitably deposited in the CBM wellbore.Excessively deposited pulverized coal may hinder the flow of gas and water.It may also cause blockage of the wellbore,card pumping and buried pumping,and affect the continuous production of CBM wells.In this dissertation,for the problem that the horizontal wellbore pulverized coal is not carried to the wellbore exit and accumulated in the wellbore during the coalbed methane well drainage process,based on the coal carrying powder theory,the Fluent software numerical simulation method is used.To study the flow law of gas-water two-phase coal-bearing powder in horizontal wellbore,we have completed three main tasks:(1)Simplified the horizontal wellbore flow pattern and optimized the numerical simulation method.Draining and depressurizing stage produces a small amount of gas,ignoring the effect of gas on the coal carrying powder.The flow of gas-water two-phase carrying coal powder is simplified as water-carrying coal powder two-phase flow;the amount of water produced during the stable production stage is small,and the effect of water on coal-carrying powder is ignored.Gas-water two-phase transport of coal powder is simplified as gas-carrying coal-powder two-phase flow;the decay phase is seen as gas-carrying coal-powder two-phase flow.Comparing the characteristics and applicability of Euler-Euleras and Euler-Lagrange numerical simulation methods,the phase-coupled discrete phase model based on EulerLagrangian numerical simulation method is selected to prepare for the next numerical simulation.(2)The numerical simulation of the flow law of coal-powder carrying water in horizontal wellbore was carried out.The effects of water production,pulverized coal mass fraction and pulverized coal particle size on the concentration of pulverized coal,the pulverized coal horizontal velocity and the pulverized coal settling velocity in the horizontal wellbore section were obtained.The results show that the particle size of pulverized coal is the main factor affecting the flow of pulverized coal to the wellbore outlet.The smaller the pulverized coal particle size is,the stronger the ability of water to carry pulverized coal.Therefore,coal pulverization is avoided as much as possible during coal bed methane drainage and pressure reduction stage to form large particle size pulverized coal,which is beneficial to solve production problems caused by pulverized coal not being carried out of the wellbore.(3)The numerical simulation of the flow law of coal-powder carried by horizontal wellbore was carried out.The influences of gas production,pulverized coal volume fraction and pulverized coal particle size on the concentration of pulverized coal,the pulverized coal horizontal velocity and the pulverized coal settling velocity in the horizontal wellbore section were obtained.The primary and secondary factors that affect the horizontal wellbore gas carrying coal powder are given.The results show that gas production is the main factor affecting gas carrying coal powder,and the greater the gas production,the more easily coal powder can be carried to the wellbore exit.Maintaining a stable gas production rate as high as possible during the stable production stage of coal bed methane can help the pulverized coal discharge out of the wellbore in a suspended manner.The results of this dissertation reveal that the flow patterns of horizontal wellbore pulverized coal in different stages of extraction are of great significance in guiding the drainage system of coalbed gas wells and reducing the cost of coalbed methane exploration.