Multiscale characterization of surfactant-enhanced coal rock pore-fracture imbibition

To further explore the effect of the surfactant on strengthening the wetting of micropore fractures, coal particles and coal pillars with different numbers of fractures were selected to prepare anionic surfactant sodium dodecyl sulfate (SDS) and cationic surfactant cetyltrimethylammonium bromide (CTAB) solution for coal sample imbibition experiments. A modified Langmuir model is used for fitting and analyzing the water absorption data.The results show that the influence of surfactant on the percolation effect is diverse at different scales of the fracture, and the absorbed volume of water of coal particles is reduced to 23 %-50 % of the original. In addition, the variation range of water absorption of coal pillars with few fractures is within 1 %, and the water absorption of coal pillars with more fractures is about 33 % higher than the original value. Through the microscope test, we found that the surfactant hardly blocks the channel where the opening of the pore and fracture is large, as the fissure opening decreases, the plugging gets worse. Plugging induced by the adsorption of surfactants and coal fracture surfaces potentially hinder water imbibition in coal. The findings provide more sufficient theoretical guidance for the research and development of efficient and clean surfactants in the future.