Initiation and extension offractures and mechanism of permeability enhancement by hydraulic fracturing in underground coal mines

摘要

Hydraulic fracturing is an effective method to increase the permeability of coal seams and has been gradually used in underground coal mines.The initiation and extension of fractures and mechanism of permeability enhancement during the hydraulic fracturing in underground coal mines are unclear.We established a model to calculate the initiation parameters and investigated the influences of in-situ stress and occurrence of coal seams on the hydraulic fracturing initiation pressure.The propagation of fractures when expanding to coal-rock interface and natural fractures was explored.We preferred the viscoelastic surfactant fracturing fluids for fracturing fluid in underground coal mines and revealed the mechanism of gas adsorption and seepage improvement in low permeability coal seams.The laboratory experiment and field test showed that viscoelastic surfactant fracturing fluids could enhance the permeability effectively.This study will provide theoretical basis for the drilling holes arrangement, the fractures controlling and construction parameters optimization.