Deep-hole directional fracturing of thick hard roof for rockburst prevention

Abstract Thick hard roof in coal mines is usually a significant factor that induces dynamic disasters, such as rockburst. This study introduces a new technology called directional hydraulic fracturing characterized by cutting out an initial groove in the borehole and then injecting high pressure liquid to break the rock. The abutment pressure on the groove tip and fracture criterion is worked out based on the fracture mechanics taking fluid seepage into consideration. Computational simulations revealed that the vertical compressive stress changed to tension immediately after high pressure liquid injected into the fracturing hole, the concentration factor up to 5 that can easily rupture the roof and reduce the rockburst hazard at the same time. The seamless steel tubes are used instead of high pressure hose and conveyed into fracturing holes by geological drill to the designed locations, so as to break through the depth limitation and make the whole process automated. In situ applications at two longwall faces of LW6305 and LW5307 show that the depth can easily reach to 20 m and the fracture radius more than 13 m within half an hour, the efficiency and security are greatly improved. We can determine whether the roof is split by observing the pressure changes. The pressure of liquid during fracturing process can be divided into three stages: dramatically ascending, descending and stable, corresponding to crack initiation, propagation and dissemination, respectively. Drilling bits method and microseismic system validate prevention effects of this technique notably so that lead to a foundation for large scale popularization and application in China coal mine.

[1]  B. Lenoach,et al.  The crack tip solution for hydraulic fracturing in a permeable solid , 1995 .

[2]  Md. Mofazzal Hossain,et al.  Numerical simulation of complex fracture growth during tight reservoir stimulation by hydraulic fracturing , 2008 .

[3]  B. Atkinson.  Fracture Mechanics of Rock , 1987 .

[4]  G. Dezhong,et al.  Electromagnetic emissions in rock and coal burst failures , 2001 .

[5]  Ruiting Wu,et al.  Some Fundamental Mechanisms of Hydraulic Fracturing , 2006 .

[6]  Mahmudur Rahman,et al.  Investigating production-induced stress change at fracture tips: Implications for a novel hydraulic fracturing technique , 2006 .

[7]  N.G.W. Cook,et al.  A note on rockbursts considered as a problem of stability , 1965 .

[8]  Yan Shao,et al.  The mechanism of hydrobreakage to control hard roof and its test study , 2000 .

[9]  Takatoshi Ito,et al.  Hydraulic fracture reopening pressure and the estimation of maximum horizontal stress , 1999 .

[10]  Panos Papanastasiou,et al.  A coupled elastoplastic hydraulic fracturing model , 1997 .

[11]  He Manchao,et al.  Microcrack analysis of Sanya grantite fragments from rockburst tests , 2010 .

[12]  Shailendra K. Sharan,et al.  A finite element perturbation method for the prediction of rockburst , 2007 .

[13]  Baoyao Tang,et al.  Rockburst control using destress blasting , 2000 .

[14]  Gary Williams,et al.  Fluid injection for rockburst control in deep mining. , 1992 .

[15]  Jiang Heng.  Application of Rock Directional Hydraulic Fracture , 2010 .

[16]  Sergey V. Klishin.  Destruction of rocks by directional hydraulic fracturing on the basis of models of plasticity with internal variables , 2006 .

[17]  B. T. Brady,et al.  Laboratory investigation of the electrodynamics of rock fracture , 1986, Nature.

[18]  V. Mansurov.  Prediction of rockbursts by analysis of induced seismicity data , 2001 .

[19]  Wancheng Zhu,et al.  Numerical simulation on rockburst of underground opening triggered by dynamic disturbance , 2010 .

[20]  C. Fairhurst,et al.  In-Situ Stress Determination At Great Depth By Means Of Hydraulic Fracturing , 1969 .

[21]  Yoshiaki Fujii,et al.  Prediction of coal face rockbursts and microseismicity in deep longwall coal mining , 1997 .

[22]  A. Kijko,et al.  An introduction to mining seismology , 1994 .

[23]  J. Bear.  Dynamics of Fluids in Porous Media , 1975 .

[24]  Meifeng Cai,et al.  A review of mining-induced seismicity in China , 2007 .

[25]  Jose Luiz Antunes de Oliveira e Sousa,et al.  A quasi-analytical model for three-dimensional analysis of hydraulic fracture propagation in reservoir rocks , 1997 .

[26]  Lin-ming Dou,et al.  Prevention and forecasting of rock burst hazards in coal mines , 2009 .

[27]  S. K. Arora,et al.  Use of mining and seismological parameters as premonitors of rockbursts , 1997 .

[28]  A. Beach,et al.  Numerical models of hydraulic fracturing and the interpretation of syntectonic veins , 1980 .