Hard roof control technology under residual coal pillar through hydraulic fracturing with long directional borehole

DAI Guisheng

doi:10.11799/ce202507013

Abstract：In order to effectively control the strong mine pressure caused by residual coal pillars during shallow contiguous coal seams mining in the Shendong mining area,and ensure the safe extraction of the No.22105 working face in Shangwan Coal Mine,the regulating effect of directional hydraulic fracturing technology on roof stress was studied.Through theoretical analysis,it was determined to implement directional long borehole segmented hydraulic fracturing in a thick and hard siltstone layer 20 meters away from the coal seam roof.The BYW65/400 emulsion pump set was used to perform the"double-seal single-card"segmented fracturing process,and a UDEC discrete element model of"residual coal pillar-hard roof"was constructed for hydraulic fracturing simulation.Research has shown that:① When the working face advances beneath the residual coal pillar,the sudden fracture of the coal boundary leading to the cutting of the bearing system is the dominant cause of strong mine pressure disasters;② The impact range of the advanced support pressure caused by the working face mining before fracturing is significantly larger than that after the roof weakening by fracturing,which confirms that the stress concentration under the residual coal pillars and the hard roof seriously restrict the mining;③ The weakened surface formed by hydraulic fracturing promotes the orderly collapse of the key layer of the roof,which significantly increases the filling rate of the goaf,and forms a collaborative support system with the residual coal pillars.On site application showed that,the hydraulic fracturing effectively transferred and dissipated the high stress concentration in the coal wall of the No.22105 mining face,and ensured the safe mining.The research results confirm that hydraulic fracturing can effectively block the high stress transmission path,which can provide an engineering demonstration for safe mining of shallow contiguous coal seams.