Micro Pore Analysis And Permeability Response Of Aquifer Rock Under Different Confining Pressures

In view of the rich water content of Ordovician confined aquifer in the coal mine floor,the water inrush from the floor threatens the safety production of the mine.It is found that the change of pore fissure and permeability after deformation of main types of aquifer rock directly affects the stability of aquifer.Therefore,it is of great significance to study the law of permeability change and the characteristics and response of pore and fracture evolution in the process of rock stress-strain in the main rock types of Ordovician aquifer under different confining pressures for mine water inrush prevention and control.In this paper,the common aquifer rock Ordovician limestone,Ordovician Dolomite,Ordovician marl and Oolitic Limestone are taken as experimental samples.By the method of ultra-high precision micro CT and digital core analysis scanning,the permeability change rule and micro response of pore and fracture evolution in the process of stress-strain of aquifer rock under different confining pressures are studied.The main experimental conclusions are as follows:(1)Through the uniaxial mechanical experiment,the peak strength of Ordovician marl is 12 MPa;the peak strength of Ordovician Dolomite is 95 MPa;the peak strength of Ordovician limestone is 98 MPa;the peak strength of Oolitic Limestone is 26 MPa.Through the triaxial mechanical experiment,the ultimate strength of Oolitic Limestone is 55 MPa under 2 MPa confining pressure,74 MPa under 4 MPa confining pressure and 89 MPa under 6 MPa confining pressure.When the confining pressure of Ordovician marlstone is 2 MPa,the peak strength of the rock is 25 MPa;when the confining pressure is 4 MPa,the ultimate strength of the test piece is 40 MPa;when the confining pressure is 6 MPa,the ultimate strength of the test piece is 51 MPa.The ultimate strength of Ordovician Dolomite and Ordovician limestone is higher than 120 MPa.The elastic limit of Ordovician marl under confining pressure of 2 MPa,4 MPa and 6 MPa is 1.6,2 and 3.6 times of uniaxial compression,and the strength limit is 2.08,3.33 and 4.25 times of uniaxial compression;the elastic limit of oolite under confining pressure of 2 MPa,4 MPa and 6 MPa is 1.6,3 and 4 times of uniaxial compression,and the strength limit is increased to 2.16,2.84 and 3.42 times of uniaxial compression.(2)Through the mechanical seepage experiment,the change rule of seepage velocity in the process of stress-strain of rock is that it decreases with the increase of stress in the stage of pore compaction;after entering the elastic stage,the seepage velocity begins to increase slowly with the increase of stress;after entering the plastic deformation stage,the seepage velocity begins to increase sharply until it reaches the peak value.The permeability of rock decreases with the increase of confining pressure.In the initial stage of Ordovician marl,the permeability of 2 MPa is 6.94 nd,that of 4 MPa is 1.23 nd is 0.177 times of 2 MPa,and that of 6 MPa is 0.001 times of 2 MPa;in the corresponding elastic stage,the permeability of 2 MPa is 21.9nd,that of 4 MPa is 0.25 times of 2 MPa,and that of 6 MPa is 0.05 times of 2 MPa;in the plastic stage,the permeability of 2 MPa is 54 nd,and that of 4 MPa The permeability of MPA decreased to 0.37 times of 2 MPa at 20 nd and 0.188 times of 2 MPa at 6 MPa confining pressure.(3)Through the micro CT experiment and 3D digital core reconstruction,it is found that the average porosity changes significantly in the process of stress loading.The average porosity of yc0301,yc0302 and yc303 are 0.23%,1.037% and 1.2614% respectively in the original condition of Oolitic Limestone;the average porosity of yc0301,yc0302 and yc303 in the elastic stage are 0.07%,0.79% and 0.37% respectively;the average porosity of yc0301,yc0302 and yc303 in the plastic stage are 1.19%,3.71% and 3.59% respectively.(4)Through the analysis of permeability and porosity data,it is found that under the same confining pressure condition,from the beginning of axial compression loading to the stage of compaction,both permeability and average porosity decrease with the increase of stress;after entering the elastic section,micro fracture and porosity are produced.Permeability and porosity increase with the increase of stress.The macro permeability of rock responds to the change of internal micro porosity,and the change trend of micro porosity and macro permeability is consistent with that of stress loading...