1、翻 译 部 分英文原文Hydraulic fracturing after water pressure control blasting forincreased fracturingBingxiang Huang,Changyou Liu,Junhui Fu,Hui GuanSchool of Mines,China University of Mining and Technology,South 3rd Ring Road,Xuzhou,Jiangsu 221116,ChinaAbstract:Traditional hydraulic fracturing techniques ge
2、nerally form main hydraulic cracks and airfoil branch fissures,but main hydraulic cracks are relatively few in number.Hydraulic fracturing after water pressure control blasting can transform the structure of coal and rock mass.Experiments prove that it is an effective method for increasing the numbe
3、r and range of hydraulic cracks,as well as for improving the permeability of coal seams.The technical principle is as follows.First,a hole is drilled in the coal seam and is injected with a gel explosive(a mining water-proof explosive).Then,water is injected into the hole to seal it,at low enough pr
4、essure to prevent cracks from forming.Third,water pressure blasting is done by detonating the explosive.The water shock waves and bubble pulsations produced by the explosion cause a high strain rate in the rock wall surrounding the hole.When the stress imposed on the rock wall surrounding the hole e
5、xceeds its dynamic critical fracture strength,the surrounding rock breaks and numerous circumferential and radial fractures propagate outward.Lastly,water injection processes,such as general injection,pulse injection,and/or cyclic injection,are carried out to promote hydraulic fracturing.Depending o
6、n the fissure water pressure,detonation fissures continue to expand and additional hydraulic fractures with a wider range are formed.Under the effect of detonation pressure,joints and fissures in the coal mass open and propagate,leading to reduced adhesive forces on structural surfaces and thereby e
7、nhancing coal cutting.Therefore,this method improves the permeability of the coal seam,effectively weakens the strength of the coal and rock mass,and reduces the surrounding rock stress of the weakened area,effectively solving the problem of having a small number of big cracks.It is a useful technic
8、al approach for improving top coal caving,preventing rock burst,preventing coal and gas outbursts,and raising the gas extraction efficiency in colliery.Key words:Hydraulic fracturing;Water pressure blasting;Crack propagation1 IntroductionLow-permeability coal-seam gas extraction;hard,thick coal-seam
9、 fully mechanized top coal caving;and rock burst control are technical challenges in colliery at present.Hydraulic fracturing is an effective technical approach to resolve these challenges1.The structure of coal and rock mass is altered through hydraulic fracturing,which can increase cracks in coal
10、and rock mass improve permeability,and weaken strength to reduce any rock bursting liability.After decades of development,more study on hydraulic fracturing has been conducted both in China and else-where214.Simulation experiments and field investigations of hydraulic fracturing show that the tradit
11、ional hydraulic fracturingin number.In the case of homogeneous rock,a single hydraulic main crack is generally generated and cracks are mainly concen-trated in a band around the hydraulic main crack,whose extent issmall.However,to improve hard,thick top coal cavability,handle hard roof,prevent rock
12、burst,increase permeability of gassy coal seams,and prevent coal and gas outbursts,full re-formation of the structure of coal and rock mass by hydraulic fracturing is needed.This requires that hydraulic fracturing produce more hydraulic cracks,i.e.,increase the number of hydraulic cracks.Therefore,t
13、here is an urgent need to study hydraulic control fracturing technology to increase the number of hydraulic cracks,which has important theoretical and practical significance in guaranteeing efficient and safe colliery production.Common explosives blasting for gassy coal seams has safety risks,so the
14、y are not suitable.Water pressure blasting,developedin the past century as a kind of controlled blasting method,can effectively control the generation of blasting flying rocks,air shock waves,blasting tremors,and detonation toxic gases1518.Water pressure blasting is a gun-hole blasting technology th
15、at uses water as a coupling medium between the cartridge and the charge hole to techniques mainly form water pressure main cracks and airfoil branch fissures,but water pressure main cracks are relatively fewin number.In the case of homogeneous rock,a single hydraulic main crack is generally generate
16、d and cracks are mainly concern-trated in a band around the hydraulic main crack,whose extent is small.However,to improve hard,thick top coal cavability,handle hard roof,prevent rock burst,increase permeability of gassy coal seams,and prevent coal and gas outbursts,full re-formation of the structure of coal and rock mass by hydraulic fracturing is needed.This requires that hydraulic fracturing produce more hydraulic cracks,i.e.,increase the n
