Study on technology of acid fracturing pressure relief and coal burst reduction in surface wells with extremely thick conglomerate roof

Thick and hard roof over the coal mining working face failed to fall and break in time, forming a suspended structure, which is difficult to break, easy to accumulate elastic energy, and easy to impact when broken. It is very easy to concentrate stress and induce impact risks, which seriously endangers the safe production of the working face. Taking the MZ21010 working face of Changcun Coal Mine as the engineering background, theoretical analysis, experimental testing, numerical simulation, engineering testing and other means are used to carry out research on surface well acid fracturing pressure relief and disaster reduction technology. The results show that: The roof conglomerate and conglomerate gravel are mainly composed of limestone, quartzite and quartz sandstone, with calcareous cementation; After acidification with 15% dilute hydrochloric acid for 30 minutes, the compressive and tensile strengths decreased by 56%−64% and 46%−64% respectively, which has the basis for surface well acid fracturing pressure relief; Combined with the top plate drilling data and theoretical calculations, the thick conglomerate layer at 0−487.45 m and the sandy conglomerate layer at 578.95−624.9 m are determined to be the high and low key layers respectively. The combination of acidizing fluid + large fluid volume (12 m³/min) fracturing in the low key layer can effectively extend the acid penetration Flow distance, fracture length 380 m, fracture width 65−80 m, fracture height 19 m; The high-level key layer adopts the fracturing process of acidizing fluid + large fluid volume (10 m³/min) + large sand ratio (16%) + gradient sand oscillation, the fracture length 275 m, fracture width 40−47 m, fracture height 24 m; Frequency resonance monitoring shows that there are obvious vertical and horizontal fracture zones in the fracturing layer, the wave impedance of the acid fracturing point is reduced, the average pressure of the hydraulic support of the working face is reduced by 21.99%, indicating that the pressure relief effect of the top plate of the working face is obvious.