Studies Of Hydraulic Characterization Of Low-Permeable Fractured Medium And Its Application

With the need of studies of geological disposal of high-level radioactive waste (HLW),more and more attention has been paid on the hydrogeology of rocks of low permeability.A better understanding of the hydrologic behavior of these rocks, especially fractured rocks becomes critical.On the basis of environmental hydrogeological features in the Beishan preselected area,Gansu province—the most potential area for the China's HLW repository and underground research laboratory,this dissertation attempts to conduct the research of techniques and approaches of characterizing the spatial structure and hydraulic features of fractured rocks in low-permeability deep environments.The considerations of the progress and status of studies on the geological disposal of China's HLW have been taken into.The numerical modeling combined with isotope analysis technology and geophysical survey and hydraulic tests in situ have been used.The purpose of this dissertation is to provide technology in support of Site Characterization and Performance Assessment Studies of China's HLW Repository. The main research work and its achievement are as follows.The description of spatial structure of fractured medium is import content of research of hydraulic characterization of rocks of low permeability.The traditional approach of fractures recording for rock core has been modified and improved.A new one,called baseline-three points for fractures recording is presented and its application to fractures investigation in situ is carried out.Meanwhile,high resolution acoustic borehole televiewer(BHTV) logging technique has been comprehensively applied to the research of spatial structure of fractured medium in deep environment.Simple introduction of the acoustic imaging method is presented,and its application and integrated studies on the research of the spatial structure of fractures in deep environment are described.It has been shown from the results that new generation BHTV is characterized by high accuracy and resolution,high logging velocity and advanced interpretation and analysis of data. BHTV is one of the most direct and effective methods to detect fracture in boreholes.Base on the environmental hydrogeological condition in the Beishan preselected area,custom-built hydraulic test system with double packer has been used to estimate the hydraulic parameters of fractured medium of low permeability.The technique of hydraulic test with double packer has been established and its major contents consist of advanced equipments,test design in detail,test preparation, implementation in situ and comprehensive interpretation of data.By using the isolation of double packer,water-sampling campaign has been conducted and real groundwater sample has been taken from different depth in deep environment. Tritium and CFC have not been detected in the groundwater collected from deep environment.It has been shown from the results of isotope and water chemical analysis that the age of groundwater sample is more than 50 years and the groundwater is not one of componets of comtemporary hydrologic cycle.It is first time to collect real groundwater without content of tritium in the Beishan preselected area.It provides valuable data for the research of features of groundwater system and site characterization in the deep environment.By comparison of all existed hydraulic-test approaches,a new one is put forward to estimate the hydraulic parameters of fractured medium of low permeability in the deep environment.It is called slug test with double packer,which is component of shut-in slug test and pulse test with double packer.A 3-D numerical model of groundwater flow,SSLUG model is presented.The consideration of the temperature effect has been taken into the SSLUG model,borehole storage effect and instantaneous change of water level as well.The computer code,SSLUG code for the model is also presented.The theory of traditional slug test is improved and the range of use of pulse test is extended by this research.By using this approach, hydraulic tests have been done in the Beishan preselected area and the maxium depth of tests is reached 489m.It has been shown that slug test with double packer is an advanced and reliable approach suitable for the esitimation of hydraulic parameters of fractured medium of low permeability in the deep environment in practice. By use of SSLUG code,sensitivity analysis of parameters has been finished and the research of the relationship among temperature effect,borehole storage effect, the use of shut-in valve,the radius of tubing,hydraulic conductivity and duration of tests is conducted.On the basis of the results of applied research,the recommendation of optimization of application of slug test with double packer to esitimate of hydraulic parameters of fractured medium of low permeability in the deep environment is presented in practice.