Meikuang Anquan (Jul 2023)
Research on the application of stage fracturing technology of L-shaped horizontal well in extra-thick coal seam
Abstract
In the process of extra-thick coal seam mining, the strength of hard roof above the coal seam is high, the breaking step distance is large, and it is difficult to collapse, especially the mining disturbance range is wide, and the rock strata of large area of hard roof is broken and unstable, which causes the impact force of the stope to appear more intense. The research shows that the hydraulic fracturing technology of downhole large aperture pressure relief, coal seam blasting pressure relief and downhole long drilling is limited to local pressure relief and weakening of small roof , it is not effective to weaken and modify the high large area of hard rock above the coal seam; we propose the staged fracturing technology of L-shaped horizontal wells on the surface based on the theoretical analysis of the fracture direction of the rock layer and the comprehensive characteristics of the rock layer, the range of key fracturing horizons is given. Combined with the integrated micro-seismic monitoring technology up and down the well, the control technology system of horizontal horizontal wells under the stage fracturing is formed, and the ground fracturing engineering practice is carried out. The joint monitoring analysis of underground micro-seismic and ground sound shows that: the total energy of micro-seismic monitoring during fracturing reaches 16.93×104 J and the total energy of ground sound monitoring reaches 1.36×108 J. The fracturing process can induce the macroscopic fracture of underground surrounding rock obviously; the surface fracturing has a wide fracture propagation range. The fracture propagation length of the two fracturing wells reaches 790 m and 851 m respectively, the maximum fracture width reaches 380-390 m, and the fracture elevation reaches 375-450 m and 390-410 m. The fracture propagation can cover the working face and two grooving, and penetrate the target horizon. The mine pressure monitoring in underground stope shows that during the periodic pressure period of working face, the support resistance is reduced by 32%, the coal wall slab rate is reduced by 34%, and there is no floor heave and wall convergence in the advanced support range of working face. The total frequency and energy of micro-seismic monitoring decreased by more than 90%. Therefore, segmented fracturing of horizontal wells can effectively reduce the strong rock pressure in the overlying strata of the stope, and then reduce the rock burst disaster during the working face mining.
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