Mechanisms And Technical Features Of Hydraulic Disturbance Method For Improvement Of Coal And Rock Seams Permeability

To meet the requirements of coal mining safety and environment protection,it is necessary to employ an advanced technique for the improvement of gas drainage of the high gas content and low permeability coal seam.Therefore,a technique called“hydraulic disturbance” has been studied and used for improving the efficiency of coal seam gas drainage.In this thesis,three key aspects related to the hydraulic disturbance technique,including,the technical features,the mechanisms of improving coal and rock seams permeability,and the variation characteristics of coal and rock seam permeability,have been studied on the basis of:1)The theoretical work,in which,the gas geology,elastic-plastic mechanics,fracture strength and percolation mechanics,as well as the pore and fracture data collected,have been use.2)The experimental work,such as,a)rock and coal bodies loading and penetration tests,b)simulation tests for coal body structure,c)hydraulic fracturing tests for soft coal during the mining extraction and d)hard coal hydraulic fracture with various confining pressures.3)The numerical modeling,which various commercial programs have been used,such as MShale,COMSOL,and Multiphysics,etc.Based on these studies,the conclusions can be drawn as follows:1)Coal structure,Modulus of elastic,Poisson ratio,brittleness index,layered medium,coal thickness,intrinsic fracture and permeability are very important for fracture network.The fractural network may be easily developed,when better integrity and higher brittleness indix of coal body are encountered.2)The geometrical shape of hydraulic fracture may be described as the wide flat holes.It is noted that the cracking direction of fracture is not always controlled by the stress in soft coal seam.On the other hand,the geometrical shape of fracture is flat,and the cracking direction is subjected to the stress conditions.3)The estimation method has been developed for evaluating the radial tensile,shear fractures,peripheral tension fracture and turning fracture.4)The geometrical shape is spheroid associating with hydraulic flushing in soft coal seam.It is noted that the coal permeability improve gradually with the increase of extraction time.Coal permeability decreases initially,then increases rapidly and finally becomes stable.Also,the coal seam permeability increases with an increasing of quantity of coal extracted.5)Finally,optimization and evaluation methods have been proposed on the basis of AHP.Also,the technique has been used in two collieries,including Zhongmacun and Yu Yang collieries,to evaluate the features of the hydraulicdisturbance and relevant theories proposed.