Research on the mechanism and practice of fracture initiation during hydraulic fracturing in hard roofs of coal mine

Abstract

A hydraulic fracture extension model was established, an extension criterion and an extension mode of hydraulic fracture were analyzed, and the theoretical prediction was compared with the practical results, a good agreement was observed. Furthermore, the direction of hydraulic fracture extension was also discussed, the results showed that the hydraulic fracture propagates from the cut to the bedding plane, forming a complex mixture of longitudinal and transverse fractures fracture network. The hydraulic fracture extension direction is influenced by its extension critical pressure and its extension pressure in the rock formation. Practice shows that hydraulic fracturing can effectively weaken the strength and integrity of the roof, so that the roof in the mining area can collapse in layers and stages. The present theoretical analysis can be used for reducing or eliminating the hazard of the hard roof to the working faces.