Effect of cyclic water injection on the wettability of coal with different SiO2 nanofluid treatment time.

Coal seam water injection is proved an effective method for preventing coal and gas outburst. However, the poor wettability of coal seam has resulted in poor effect of coal seam water injection in preventing coal and gas outburst. In addition, the coal seam is in a state of injected-uninjected cycle due to multiple water injection. Therefore, it is important to study the wettability of coal seam with adding wetting agent under multiple water injection. In this paper, the effect of cyclic water injection on the wettability of coal with different SiO 2 nanofluid treatment times was investigated through contact angle tests. The results showed that increasing the treatment time of SiO 2 nanofluid would enhance the wettability of coal. In addition, the wettability of nanofluid-treated coal samples gradually got worse with the number of cycles increasing. In general, the effect of SiO 2 nanofluid on enhancing the wettability was approximately 2 to 4.5 times better than that of water. However, the difference of wetting enhancement between water and SiO 2 nanofluid became less obvious as the number of cycles increased. Even though, the nanofluid-treated coal samples showed the better wettability than water-treated coal samples after 13th cycle. Furthermore, the potential application of SiO 2 nanofluid in coal seam water injection was proposed, which had important significance for improving the effectiveness of coal seam water injection. [ABSTRACT FROM AUTHOR]