Technology system and application of surface fracturing for weakening thick-hard roofs in Ordos mining area

GAO Jiaming; QIN Xufeng; ZHU Yanfei; YANG Guangyu; CHENG Shizhong; CHEN Xuehui; LI Yan

doi:10.11799/ce202510002

Abstract：In view of the problems during implementing surface hydraulic fracturing in coal mine roof weakening,caused by the shallow burial depth,complex formation stress,structural development,undulating coal seam and proximity to goaf,we studied and applied the key technologies of surface hydraulic fracturing for weakening thick and hard roof of coal seam.The results show that:From the perspective of rock strata structure modification,the pre-generated fracture networks disrupt local rock layers,thus reducing their structural bearing capacity;From the standpoint of physical property modification,the radial effect of fracturing injection pressure eliminates local stress concentration zones in the rock layers,promoting a trend towards stress homogenization.We proposed a method for identifying target fracturing layers based on theoretical calculations and open-hole logging measurements,to improve high-precision drilling trajectory control and high horizontal-to-vertical ratio casing running technology through formation delineation and the application of floating coupling tools;employed directional perforation,efficient fracture network temporary plugging,and diversion technologies to control the orientation and scale of near-wellbore fracture networks;and established a dynamic fracture network monitoring method integrated with surface-underground data analysis during mining.In engineering practice,applications of vertical wells for multiple target layers and horizontal wells with shallow burial depth and high horizontal-to-vertical ratio for fracturing and weakening were carried out,successfully achieving technical objectives including dynamic optimization of multiple target layers,unilateral temporary plugging and diversion of fracture networks,precise control of drilling trajectories between coal seams,casing completion with a high horizontal-to-vertical ratio of 2.82,and control over fracture network orientation and scale.Ultimately,a technological system for surface fracturing and weakening of thick-hard roofs in coal mines was established.