Characteristic Scales For Permeable Property Of Fractured Rock Masses In Typical Flow Configurations And Engineering Applications

There are a lot of fractures in the fractured rock masses,which is the case of discontinuity,inhomogeneity and anisotropy in the fractured rock mass.The properties of rock mass are changed with the increase of fractured rock size,in other word,there are different scales in the fractured rock masses,which are the critical scales of the changes in the properties of the fractured rock masses,like connectivity threshold,representation element volume(REV)and so on,which are the critical scales of fractured rock masses from connectedness to disconnectedness,the properties of the rock masses from discreteness to equivalent continuity.The permeability characteristic scales of the fractured rock masses were investigated under the condition of unidirectional flow configuration and radial flow configuration based on the Huangdao underground oil storage project,including permeability representative element volume of fractured fracture masses and connectivity threshold.The detailed results are as follows:(1)Based on a method which to estimate REV size for the permeability under the condition of unidirectional flow configuration and radial flow configuration,the REV size for permeability and equivalent permeability coefficient of the rock mass the reservoir area of Huangdao oil depot was carried out.The REV size is 37.5 m for radial flow configuration,which is 1.3 times of the trace length.The equivalent permeability coefficient is 2.70×10-5 m/d for radial flow configuration,and the predicited seepage volume is close to the measured water seepage according to this permeability coefficient.The REV size is 115 m for unidirectional flow configuration,which is 4.1 times of the trace length.The equivalent permeability coefficient is 4.24×10-5 m/d for unidirectional flow configuration(2)The numerical simulation of different geometric parameters of fracture(including trace length,spacing,gap length)was carried out,and the influence of geometric parameters on the REV size and permeability coefficient of fractured rock masses was obtained.The REV size was increased with the increase of the trace length(or spacing),and was not obvious with the gap length.the equivalent permeability coefficient was increased with the increase of the trace length,and decreased with the increase of the spacing(or gap length).(3)The numerical simulation of fractured rock mass under different stress was carried out,the influence of stress on the REV size and the equivalent permeability coefficient was obtained.With the increase of lateral pressure coefficient,the REV size was first decreased and the increased,and the permeability coefficient was first increased and the decreased.(4)The numerical simulation of the correlation between the trace length and aperture is carried out,and the REV size of correlation was larger than uncorelation and the range of the equivalent permeability coefficient in different direactions was wider.And it is found that the REV size was increased and the range of equivalent permeability coefficient in different directions was wider with the increase of b.(5)Based on the analysis method of percolation theory,the simulation of the connectivity of fractured rock masses under different groundwater flow configuration was conducted;the connectivity threshold(percolation threshold)under different conditions was obtained.Furthermore,the sensitivity analysis of the connectivity threshold was carried out,and the influence of the fracture geometric parameters on the connected threshold was obtained.Based on the field data,the numerical simulation of connectivity of water curtain holes with different distances was conducted,the change curve of the connection probability with the distance and the minimum spaced distance between the water curtain holes was obtained,which provides the basis for the design of the water curtain hole.