Application Of CSAMT To Geothermal Exploration In Songjianghe Area

As a new type of green energy, geothermal resources have caused more andmore attentions. Because of abundant geothermal resources, ChangBaiShanareas has a good development potential. Tianchi volcano group and Longgangvolcanic group in Changbai Mountain areas are well-known for modernvolcanic activity and contain amount of geothermal resources, deep magmachamber of Changbai Mountain provides heat energy for the geothermal fieldin this area.Controlled audio-frequency Magnetotelluric method (CSAMT) is anelectromagnetic sounding method which is use of the electrical properties ofrocks and minerals difference resistance, and observes response toelectromagnetic fields which are generated by an artificial source in the earth.Itis widely used in geothermal exploration in recent years and develops veryquickly. First of all, the paper described the research background and researchstatus of the controlled source audio-frequency Magnetotelluric method andall-time apparent resistivity;then collected the geological and geophysical datain this area.This paper presents a convenient method for convert the Cagniardresistivity to the all-time apparent resistivity. Computation of the apparentresistivity of the two or three layer sections and the result calculated by theCSAMT can reflect that in far-field area the results are equal to Cagniardresistivity,but in near-field area and transient area, the results have greatlyimproved the strong distortion of Cagniard resistivity.This method will increasethe depth of CSAMT exploration and reflect the changes of the verticalsubsurface electric vividly.Finally,the paper takes the CSAMT exploration applications inSongJiangHe areas as example, the study area based on geological andgeophysical data,gravity and magnetic and hydrological data as thebasis,combined with work-around data,analyzed and discussed the electricallyabnormal characteristic of CSAMT region apparent resistivity electricallyinversion section,and in which the initial division of strata,faults tendencyand determine favorable wells. The following conclusions of the CSAMTmethod in geothermal exploration.1、In far-field area the results are equal to Cagniard resistivity,but innear-field area and transient area, the results have greatly improved the strongdistortion of Cagniard resistivity. 2、The inversion using all-time apparent resistivity can reflect the verticalvariation of medium resistivity.And increasing the depth of the probe.3、 The forward method is simple and fast operation.In practica,thismethod has great value.4、 Through the work in the study area, the following results wereobtained:a. The study area can be divided into four tectonic layers from the surfaceto2000meters underground.b. The study area has two sets of fracture, respectively NEE andNS-trending.c. It identified two favorable wells depend on the configuration of therelationship between the fracture and the aquifer.