Research on aquosity and watertightness for Fengfeng formation in Yangquan coal mining area

By the systematic observation of core from the 17 drills for hydrological supplementary exploration, and combined with analyses of polarizing microscope, scanning electron microscopic, pressured-mercury test, stress-strain experiment, we studied the characteristics of aquosity and watertightness for Fengfeng formation in this paper. The Fengfeng formation are composed of carbonate, evaporites and secondary breccia, which can be divided into 17 rock microfacies. The lithology of Fengfeng formation can be divided into two segments, the lithology of lower segment is mostly dolomite and anhydrite rocks, which was formed in dolomitic flat and gypsum-halite lake of supratidal; and the upper segment is micrite-grain limestone, which was formed in open platform. Fengfeng formation experienced a complex transformation of diagenesis, the main types of hole are corrosion pore, microporous between crystalline, structure cracks and corrosion cracks. Pressured-mercury tests show that the pore structure is mainly microporous, and lower segment is more developed than the upper segment. The results of the stress-strain experiment show that Fengfeng formation has low permeability, which is belonged to weak-impermeable scope of the permeability. The permeability of the upper segment is 5∼10 times to the lower segment. The aquosity and watertightness for Fengfeng formation are controlled by the types and development of corrosion pore, holes and cracks in the area where the structure did not vary develop. In the simple structure block, Fengfeng group can be seen as a relatively impermeable layer, which is favorable for mining of No.15 coal with belt pressure.