Experimental research on the methods to remove water blocking effect based on nuclear magnetic resonance testing

In order to improve the effect of coal seam gas drainage,the nuclear magnetic resonance ( NMR) testing method was used,combined with the requirements of mining reality,to conducted an experimental research on the re- moving methods of water blocking effect (WBE) from two aspects of drainage negative pressure and surfactants. The results show that the NMR works well for doing research on the removing methods of WBE. Drainage pressure,for re- moving WBE,can be divided into three stages,“ stable-decrease-stable”,according to T2 cutoff value. When drainage pressure is smaller than 360． 9 Pa,the external water will block coal pores,so that WBE arises; when negative pres- sure of gas drainage is bigger than 769． 6 Pa,it can eliminate the water blocking of coal pore and remove WBE. Anion- ic and nonionic surfactant liquor can remove WBE in coal,which is benefit to gas drainage,and anionic surfactant liq- uor can do better than nonionic surfactant liquor to remove WBE. In addition,cationic surfactant restrains the process of removing WBE,prevents gas movement in coal and restrains gas drainage. The research offers a theoretical guidance for mine gas drainage.