井筒中煤粉运移规律的数值模拟研究

Research on the Numerical Simulation for Migration Law of Pulverized Coal in Wellbore

为了研究煤层气排采过程中煤粉在井筒中的运移规律,采用标准二维湍流分析方法建立煤粉在井筒中的运移模型,用数值模拟方法分析不同流速、不同粒径煤粉的运移规律及沉降特征。研究表明:煤粉在井筒横截面上的速度及体积百分数分布与井液类似,均为中间高,两侧低,在杆管壁面上最低。煤粉与井液组成的固液两相流初速度越大,煤粉与井液的流速就越接近,越有利于煤粉的排出。不同粒径煤粉对应不同的临界携煤粉速度,粒径越大,对应的临界携煤粉速度越大,煤粉越不容易排出。计算出井筒横截面中绝对速度小于零的煤粉占该横截面所有煤粉的百分数,即沉降百分数。并由横截面上的煤粉平均体积分数和沉降百分数得出不同粒径煤粉的临界携煤粉速度和临界携煤粉排量。计算结果为现场煤粉防控及参数优化提供参考依据。

In roder to study the migration law of pulverized coal in wellbore in the process of coalbed methane drainage,the migration model of pulverized coal in wellbore has been established by using a standarded two dimensional turbulence analysis method,so as to analyze the migration law and settlement characteristics of pulverized coal based on numerical simulation method with different flow rate and different grain sizes. Research results showed that the velocity and volume percentage distribution of pulverized coal in the cross section of wellbore are similar to that of well fluids,that is high parts in the middle,low parts on both sides,the lowest point on the wall surface of the pipe. The greater the initial velocity of solid-liquid two phase fluids mixed by pulverized coal and well fluids,the more close with the velocity of pulverized coal and well fluids,and the more conducive to the discharge of pulverized coal. Different particle sizes of pulverized coal correspond to different critical speed for carrying pulverized coal,the larger the particle size,the greater the corresponding critical speed of carrying pulverized coal,and the more difficult for discharging the pulverized coal. The percentage of pulverized coal with the absolute velocity of less than zero,accounted for all the pulverized coal in the cross section of well bore has been calculated,i. e. settlement percentage. The critical flow rate for carrying pulverized coal with different grain sizes was also obtained from average volume percentage and settlement percentage at the cross section. The calculating results provide the reference for preventing and controlling the pulverized coal and optimizing parameters at site.