基于双通道雷达的跨孔电阻率CT方法与应用

Dual channel radar resistivity tomography and its application

电阻率是岩石重要的物性参数.它是判断地层岩性、矿物组成、含水状态及地质构造背景的重要依据.为精确地获得孔间地质剖面内岩石电阻率的分布,开发了雷达电阻率CT方法.采用双通道跨孔雷达,同时记录发射信号和接收信号.通过两个信号的时差准确地测量电磁波在岩土中传播的时间,使用两个信号的幅值比,确定电磁波传播中幅值的衰减.利用电磁波的走时反演电磁波速的分布.在波速CT的基础上,构建由单元速度组成的脱耦矩阵,用以将衰减方程中的电阻率变量线性化.最后,基于Radon的由投影重建图像的原理,求解以电阻率为变量的衰减方程,获得电阻率CT图像.这种方法获得的电阻率分布,比直流电阻率CT方法的结果具有更高的分辨率和可靠性,而且避免了在孔内布设电极的困难.应用实例中通过对CT图像中的高阻与高波速异常的分析,成功地在花岗岩体中识别出了石英脉和云母富集带.雷达电阻率CT是一种新的物探方法,在水文地质、工程地质与金属矿产勘查中有广泛的应用前景.

Resistivity is an important physical property of rock.It is a basis to identify stratum,lithology,minerals,water content and tectonic setting for geological environment.In order to obtain the resistivity distribution in geological section accurately,a new resistivity tomography method is developed by using dual channel radar.The dual channel radar can record both of the transmit and received signals at the same time.The trave time of electromagnetic wave along the path in geological section are determined by the time difference between the transmit and received signals.The attenuation of electromagnetic wave in the path is measured reliably by amplitude ratio between the transmit and received signal.Using travel time of all paths,the velocity distribution is inverted following Radon principle.After conducting velocity tomography,the resistivity variable in the attenuation equation can be linearized by using the decoupling matrix which is constitutive with the element velocity values.Using all of amplitude ratio,the resistivity distribution of the section is finally obtained by solving the linearized attenuation equation.Compared to direct current resistivity tomography method,this technique offers better resolution,more reliable,and avoiding the difficulty to lay electrodes in the holes.In an application,quartz veins and mica enrichment zones are identified in granite with high resistivity and high velocity anomalies.Radar resistivity tomography is a new technology,which has bright future in hydrogeology,engineering and minerals exploration projects.