Experimental Study on Mechanical Properties of Crushed Coal Seams Enhanced by Freezing

In crushed coal seams, artificial fractures cannot effectively extend during hydraulic fracturing. In this paper, a method of temporarily enhancing the mechanical properties of crushed coal seams by freezing is proposed, which can make the hydraulic fracture extend significantly. The effects of freezing rate on mechanical properties of coal were considered. The saturated and dry coal were frozen at different freezing rates, and the MTS816 rock mechanics test system was used to conduct the uniaxial compression test and Brazilian test on the coal specimens. The results show that the compressive strength, tensile strength and elastic modulus of coal are significantly increased after freezing, and the increase range decreases with the increase of freezing rate. When the ice frozen coal fail, the crack tends to be single. The research in this paper provides a basis for using freezing method to promote the formation of artificial fractures in hydraulic fracturing.