Experimental study on effect of H₂S aqueous solution on permeability of low-rank coal

In order to study the effect of H₂S solution to the permeability of low-rank coal, we select low-rank coal sample from Wucaiwan Coal Mine（ＷＣＷ） of eastern Junggar Basin coalfield and Shaerhu Coal Mine（ＳＥＨ） of Tuha coalfield. The porosity and permeability at the parallel and vertical stratifications were compared before and after the acidizing experiments using various methods including the tests of porosity and permeability, Nuclear magnetic resonance（ＮＭＲ） and scanning electron microscopy （ＳＥＭ）. The results show that H₂S solution can react with the minerals in pores and fractures, lead to the increase of porosity, the change of pore size distribution, the enhancement of connectivity between pores and fractures. At the same time, some materials such as coal powder and clay minerals transport out through fractures with H₂S solution, resulting in improving the permeability of coal. The larger initial porosity, the more fractures developed, the better connectivity between pore and fracture, and the better permeability, the effective of H₂S solution to expansion and permeability is more obvious after acidification.