Research On Hydraulic Fracturing Technology For Extremely Thick Rock

Most of domestic coal mines have now entered into the deep mining stage and mine earthquakes are a major problem affecting the safe and efficient production of coal mines.In mine A,the subsidiary of Yanzhou Coal Mining Company Limited,large energy mine earthquakes above 2.0 magnitude occurred frequently during face mining,and all occurred in the giant sandstone layers within the depth of 200-600 m which were in the upper part of the mining area.Based on the locations and periodicities of the large energy mine seismic events,this paper proposes a hydraulic fracturing method to pre-fracture the extremely thick key layers to destroy the integrity of the layers and cause the layers to collapse in time to reduce the frequency of large energy mine seismic events during the mining process and ensure safe and efficient production at the working face.In this paper,Meyer fracturing simulation software has been used to design the fracture size of the fractured formation and to apply it in the field.The parameters such as elastic modulus,Poisson’s ratio,in-situ stress distribution,formation leakage characteristics and the geological stratification of the formation are obtained through a series of combined logging,ground stress tests in different boreholes and indoor leakage experiments.Meanwhile,based on the characteristic that the fracture is easy to expand upwards,this paper adopts the artificial spacing method to create an artificial spacer of about 1 m thick at the upper tip of the fracture to control the fracture within the extremely thick key layer.After fracturing,the actual fracture size has been monitored by micro seismic monitoring in adjacent wells,and the occurrences of earthquakes in the thick critical layer after hydraulic fracturing has also been monitored during the subsequent mining process.The study results show that the designed fracture size is about 10% different from the actual fracture size monitored by micro seismic monitoring,which indicates that the artificial spacer takes a good control effect,and the fracture simulation design provides an important guide for the field construction.After the hydraulic fracturing,the only mine earthquake event of magnitude 2.0 or above occurred near the location of the wellbore,and no large energy mine earthquake events occurred during the further advancement of the working faces.The hydraulic fracturing method is effective in the management of mine earthquakes and provides theoretical and technical support for the management of mine earthquakes at other working faces in the mining area,as well as a reference for the management of mine seismicity in the rest of Yanzhou Coal Mining Company Limited’s mines.