Study On Coal Particle Migration In CBM Wellbore

In the drainage stage of CBM wells,there will be a large amount of coal particle entering the wellbore.The deposition of coal particle will have an adverse effect on the drainage,and my even result in blockage of the coal slime,which will lead to production suspension.In order to avoid coal particle setting and effectively remove the coal slurry and make the drainage of the CBM well proceed normally,it is necessary to conduct a detailed study on the settlement and carrying of the coal particle and the clearing and migration laws of the coal slurry in CBM wellbore.This paper starting with the study of coal particle from CBM wells,summarizes the mechanism and harm of coal particles production,and explores the basic physical characteristics and the surface properties of coal particles.Based on the understanding of the properties of coal particle,the terminal velocity of coal particle settling in water and the entrainment velocity of coal particle were measured.Through the analysis and processing of data,revised the theoretical calculation formula of terminal velocity,established the relationship between terminal velocity of coal particle settling and the critical entrainment velocity,then an empirical calculation model for pulverized coal carrying was obtained.Based on the above research results,the principles of reasonable drainage production design for CBM wells was proposed,and the drainage production design software was compiled using VB language.Based on the micro-element analysis method,established the critical start-up pressure difference model of coal slurry in undulate wellbore.According to the principle of dimensional harmony,an empirical model for the start of coal particles under conditions of solid-liquid two-phase flow was established,which incorporated experimental data.Finally,FLUENT was used to simulate the interaction between the coal slurry and flow field in wellbore under different conditions,which provided a certain reference value for formulating measures for coal slime removal.