煤层超高压定点水力压裂防冲试验研究

Field tests on fixed-point hydraulic fracture with extra-high pressure in coal seam for rock burst prevention

针对国内外没有成熟的区域主动防冲技术的现状,介绍了一种采用超高压定点压裂煤层形成区域性低应力区,从而为快速掘进和回采创造条件的新技术。现场试验在采深1000 m的山东省华丰煤矿进行,采用微地震监测煤岩体破裂、应力动态实时监测系统监测煤岩体应力变化和压力传感器监测管路压力,实现试验全过程监测。试验得到的主要结论如下:1压裂的压力达到24 MPa并持续11 s之后,煤体产生初次破裂,持续13 min后压裂半径达到8 m;2压裂过程中压裂点附近煤体应力动态为:管路加压后距离压裂点9.5 m的煤层内应力值明显升高—煤体产生破裂并产生微震—管路压力骤降—测点应力趋于稳定;3压裂过程中将煤体切割成了近似6.2 m×8.0 m×6.2 m的长方体,同时随着大量水的注入有效降低了煤体的冲击倾向性;4试验证明定点压裂能够实现"转移应力、弱化煤体和降低蓄能"的防冲机理。

Considering the current domestic and overseas situations of lacking mature active regional technology for rock burst prevention, a kind of new technology is introduced using fixed-point hydraulic fracturing with ultra-high pressure to form regional low stress areas in coal body for facilitating rapid excavation and mining. The field tests are carried out at the mining depth of about 1000 m in Shandong Huafeng Coal Mine. In order to monitor the whole process of the tests, microseismic monitoring system, stress dynamic real-time monitoring system and pressure sensors are used to monitor coal and rock fracture,stress variation in coal and rock and line pressure, respectively. The main conclusions are as follows:(1) After the fracture pressure reaches 24 MPa and remaines for about 11 seconds, the first fracture occurs in the coal, and then the fracture radius reaches 8 m when the pressure stays at the same level for around 13 minutes;(2) The stress performance of time sequence in the whole fracture process is that: the stress of the observation point 9.5 m away from the fracture point increases significantly after the water is pressurized→fracture occurs in the coal→line pressure plunges→stress at the observation point tends to be stable;(3) The fracture process approximately cuts the coal into cuboids of 6.2 m×8.0 m×6.2 m, and reduces coal burst tendency effectively with the injection of a great deal of water;(4) The tests show that the fixed-point hydraulic fracture can achieve rock burst prevention by means of 'stress transfer, coal weakening and energy storage decrease'.