被动式超低频电磁法在深部地热资源勘察中的应用——以JR-119井及JR-168井为例

分析了深部地热资源勘察中的地球物理电磁法应用现状,阐明了被动式超低频电磁法在深部地热资源勘察中的可用性和优势;重点论述了被动式超低频电磁法在深部地热资源勘察中的探测机理.利用北京大学研制的BD-6型被动式超低频电磁探测仪在京热119井和168井附近布点探测,在探测过程中利用硬件滤波和水平旋转探头方向的方法消除了工频50Hz的部分谐波干扰,同时探测曲线的重复性也非常好,得到了相应井位的超低频电磁探测数据.在对深部热水储层和盖层岩性界面进行地质解释后,得到热储层赋存深度的绝对误差为23-50 m,盖层岩性界面的相对误差小于6.3%.探测结果表明借助被动式超低频电磁探测仪,可以较准确地获得深部岩溶裂隙地热水的分布信息.

Applications of the passive Super Low Frequency (SLF) electromagnetic technique to exploration of geothermal energy sources

The actually application of magnetotelluric method to exploration of geothermal energy sources is analyzed. The basic theory of the passive SLF electromagnetic techniqueis preseated, especially the mechanism of exploring geothermal energy sources by this kind of technique. The type BD-6 passive SLF electromagnetic explorer, which is developed by the Peking University, was used in the experiments of exploring two geothermal wells in Beijing, JR.119 and JR. 168. The reduplicative performance, attenuation compensating gain of signals and interpretable of BD-6 explorer were improved. In the experiment, industrial frequency (50Hz) noise and its harmonious waves were filtered by use of hardware filter and adjusting the horizontal orientation of sensor. The SLF electromagnetic curves of wells were obtained and their reduplicative characteristics were excellent. The lower apparent resistivity of geothermal area is the result of water and the difference of resistivity between the geothermal area and wall rocks can be detected by using passive SLF electromagnetic explorer, and then the interface between the geothermal area and cap rock and the depth of the area of lower resistivity are derived. The geothermal reservoir and cap rock were interpreted. The absolute error of the depth of geothermal reservoir is between 23 m and 50 m, and the relative error of interface of cap rock is less than 6.3%. The experiment results showed that the distribution of geothermal reservoirs can be found by using the passive SLF electromagnetic explorer.