Application Of Comprehensive Geophysical Method In Geothermal Resources Exploration In Minle County,Gansu Province

Geothermal energy is also known as geothermal energy,geothermal field or geothermal resources.Geothermal is widely used in power generation,heating,tourism,drinking,breeding,medical treatment and other fields.It is an excellent natural green energy with the advantages of clean,large energy and renewable.China's geothermal application is still in its infancy,and most of them are hot spring bathing,heating,and tropical aquaculture.Taking the development and utilization of hot springs in Minle County as an example,they are currently only used for hot spring bathing,but there is a lack of systematic research and evaluation on geothermal resources in Minle County.In the exploration of geothermal resources in this area,a variety of effective geophysical exploration methods have been carried out,such as controlled source audio frequency sounding method.Although this method can determine the bedrock fault zone to a certain extent,the effect of only using a single geophysical method to delimit the geothermal exploitation well location is not particularly ideal,and the risk is large.In order to reduce the uncertainty of mining well location in the process of developing geothermal resources in Minle County,it is decided to adopt the comprehensive geophysical method to determine the underground abnormal body and explore geothermal resources.After determining the scope of this geothermal exploration,combined with the previous measured physical property data,it is concluded that the electrical properties of the strata in the research area are obviously different,which has the geophysical premise for electrical exploration.In electrical exploration,CSAMT and MT are the best methods for geothermal exploration.Therefore,these two methods are selected in this electrical exploration.At the same time,because the Liuba normal fault crosses the deep strata of the research area,it is easy to cause the phenomenon of abnormal radon value on the surface,and the above two electrical exploration methods have weak response to the deep information of the fault,which forms the basis of the work of the activated carbon method for measuring radon.Based on the above analysis,it is decided to adopt a comprehensive geophysical prospecting method based on the controllable source audio frequency magnetotelluric sounding method(CSAMT),supplemented by the magnetotelluric sounding method(MT)and activated carbon method for measuring radon.There are 4 controllable source audio magnetotelluric sounding lines,1 magnetotelluric sounding line,and 9 activated carbon method for measuring radon survey lines.Combined with the measured data,the corresponding CSAMT and MT models are designed,and the lower limit of radon anomaly threshold is determined,which provides a theoretical basis for data processing and interpretation,so as to obtain rich crosssection information and effectively determine the accurate location of fault structure,so as to better determine the location of deep geothermal boreholes.At the same time,according to the interpretation of CSAMT and MT data,the upper layer of Quaternary and Neogene is the ideal cover condition for thermal reservoir in this area,and the target layer of thermal reservoir is the lower Neogene layer.Therefore,the drilling in this area is mainly to use geothermal water from the lower Neogene.According to CSAMT and active carbon radon measurement,it is inferred that there are two hidden faults F1 and F2 with developed fissures in the research area.It is found that the structural position of F2 fault obtained by radon measurement method is right than that determined by CSAMT,and the F2 fault is corrected.The results of the three methods are verified and supplemented to each other,which can effectively overcome the one-sided of the single method,and are closer to the actual geological situation.Through the comprehensive exploration of geothermal resources in Minle County by three geophysical methods,the favorable drilling location ZK1 of geothermal water is determined.The accuracy of the comprehensive geophysical prospecting method is verified by the subsequent practical drilling.In addition,the comprehensive exploration of three geophysical methods provides a way of thinking for the exploration of geothermal resources in similar fault basins,which can accurately let us know the situation of geothermal resources and suggest to be popularized.