Mechanism of hydraulic fracturing for controlling strong mining-induced earthquakes induced by coal mining

Abstract

The complex geological conditions of coal mine, especially the geological characteristics of coal-bearing strata, determine that mining is one of the most hazardous occupations worldwide. Strong mining-induced earthquakes (E ≥ 105 J) frequently occur in coal mines, where the high-strength thick and hard roofs are developed above coal seams. It seriously threatens the safety of underground miners and ground residents, as well as the productivity and effectiveness of mining activities. The fracture characteristics of the overlying strata and the distribution of mining-induced earthquake characteristics before and after field experiment of hydraulic fracturing is analyzed and revealed using the methods of field monitoring and numerical analysis, and reveals the effect of hydraulic fracturing technology in preventing and controlling strong mining-induced earthquakes, for the frequent occurrence of mining-induced earthquakes in Dongtan coal mine. Combined with the results of microseismic monitoring after hydraulic fracturing, as mining advances, the frequency of small-energy microseismic events is dominant, and the percentage of strong mining-induced earthquakes was reduced by 51.3 %. Numerical calculations show that the existence of hydraulic fractures provided the necessary paths for the expansion of the fracture network in the overlying strata. This results in rock masses near the hydraulic fracture slipping along the fracture under the action of mining stresses. The implementation of hydraulic fracturing can effectively weaken and fracture the integrity of thick and hard rock strata to reduce or eliminate the occurrence of hazardous mining-induced earthquakes with large energy.