Mechanism anlaysis of coal fines damaged to coal reservoirs and prevention countermeasures during fracturing

In order to mitigate the fine migration in coalbed methane wells after fracturing operation,both of the origin and damage of fines were analyzed.Taking the c oalbed methane wells located in southern Shizhuang Block of Qinshui Basin as an example,based on proximate analysis and X-Ray results,the wettability of coal fines wer e concluded with DLVO theory. It was demonstrated that water wetting of coal fines could explain why the flow rate of water accelerated the migration of coal fines.During t he flow back period and the dewatering period,the coal fines were much easier to release.The results also indicated that the blockage of coal fines in near wellbore area W ould do more harm to the productivity of gas wells,because the effective stress and water flow rate in the near wellbore area were higher than other areas.Measures to relie ve the injuries of fines were also proposed,including indirect fracturing to avoid the soft coal, applying cationic surfactant instead of anionic surfactant in fracturing fluid,and slower dewatering rate.