Study On Production Mechanism Of Coal Powder In The CBM Production And Prediction Software Development

CBM production is a process of drainage gas recovery and decreasing pressurecontinuously. At the beginning of CBM production, the reservoir pressure is mainly decreasedby drainage. The drawdown pressure and fluid action during CBM production can damagecoal bed and make coal powder occur because of its poor cementation, frangibility, andcollapsibility. During transporting with fluid flow, coal powder can subside and stop in thefissure, which lower permeability of coal bed and influence the decrease of overall pressure.The coal powder in pump barrel can wear down pump barrel and plunger piston, the pumpefficiency will be reduced. In the stable production period and the production decline stage,the sedimentation of coal powder in the wellhole can seriously impact the pump efficiency forthe decrease of water yield and power. Coal powder can even bury pipe column and stuckpump. Therefore, the production of coal powder can seriously influence the whole miningbenefit, and the study on production mechanism of coal powder in the cbm production issignificant to the CBM developmentFirstly, the paper analysed the kinds of coal powder in CBM well according to the sourceof it. By using strata failure theory and the sand-production mechanism in rock mechanics,this paper discussed the failure mechanism of coal bed in CBM production, analysed theproducing mechanism of coal powder, its producing rule in each phase and influencing factorsof its production, made dynamic simulation of the damage to coal and rock causing by CBMwell perforation by using of the finite element software ANSYS/LS-DYNA, and proposedsome measures to control coal powder. Secondly, through force analysis of coal powder in thefissure of CBM well, the starting condition of coal powder was got, namely the criticalvelocity of coal powder migration. Considering the effect of production, migration, sedimentation and blocking of coal powder, the paper established the mathematical model offluid-solid coupling percolation with coal powder and the mathematical model ofcoal androck deformation during CBM well production,and provided the the dynamic models ofphysieal property parameters, auxiliary equations and definite conditions which were need inthe solution of those mathematical models. So the theoretical foundation of numericalsimulation of the coal-powder production in CBM well was provided. Thirdly, the paper usedIMPES to process the mathematical model of fluid-solid coupling percolation with coalpowder in CBM well, and got the difference equations of pressure, coal powder concentrationand water saturation. Moreover, the parameters in equations were processed and thecalculation method, MILU-ORTHOMIN was provided. Finally, according to themathematical model and solution of fluid-solid coupling seepage, the numerical simulationsoftware for the production of coal powder in CBM well was programmed in VB language.An example was calculated by using the software, and the effect of the coal-powderproduction on the seepage in CBM well was analysed according to the results. So the studyhas important consequences for improving the mining efficiency and reducing the cost ofCBM development.