Study On Water-rock Interaction In The Fault Zone And Its Hydrological Significance

Water-rock interaction(WRI)has significant influence on the evolution of geological environment in terms of several key project such as High Level Radioactive Waste Disposal,CO2 Capture&Storage,Utilization of Hot Dry Rock,which is also an important part of THMC multi-field coupling,of which chemical water-rock interaction is a hot spot and difficult problem to be studied.This research takes Nuclear Disposal project as background,in which water-rock interaction and related products i.e.fissure fillings in the special geological structural units of the fault zone are studied.Based on the chemical kinetic theory,the water-rock reaction simulation experiment is designed and carried out,and the influence of the main factors is analyzed.The study shows that the reaction rate is positively related to temperature,pH value and flow velocity are not simple linear relationship with the reaction rate.Through microscopic observation and XRD mineral identification,the geochemical characteristics of the related products of the chemical water-rock reaction and the microscopic morphology of the filled fissures are studied.Filled fissures can be divided into 5 types according to the filling form,and can be generalized feature model as pore-fracture double medium and its corresponding seepage characteristics in micro scale is also analyzed.The changing rules of chemical weathering of the fault core rock with chemical index—change rate and microscopic comprehensive weathering index Ip is studied with XRF technique,on what basis,a relative simple and visual chemical index parameter—element leaching rate Cm is proposed to represent the degree of chemical weathering of different depth samples which is found to be linear with the depth of the sample.By in situ pressure water test,the coefficient of permeability of single fracture filled(10-10?10-8m/s)and non-filled(10-8?10-5m/s)can be got,by contrasting the two types of fracture,the influence of fracture fillings on the seepage characterstics can be easily seen.Besides,the permeability coefficient of each structural unit of the fault from the core to the surrounding rock is generally exponentially decreasing,and the permeability coefficient is mostly lies between 5.3×10-9?2.2×10-6m/s.On the basis of relevant research result above,the relationship between the permeability of the structural units of the fault zone and secondary-mineral ratio of the responding structural unit can be established.Moreover,by 3D topography scanning,the difference of JRC(Joint Roughness Coefficient)(0.27-14.29)of non-water-rock-reacted and water-rock-reacted fracture surfaces of the same borehole core from a specific structural unit can be gained,which can be connected with permeability of corresponding structural unit.Through the above research,the chemical action mechanism,the influence factors and the macro effect of the water rock in the fracture are discussed,which is also can be seen as exploration of relevant current geochemical information and application of it in the study of hydrological characteristics of fault zone.Besides,this study can provide a reference for the prediction of the geological environment evolution of the fault zone.