The Geothermal Favorable Area Prediction For Fangzheng Fault Depression In Yi-Shu Graben

As a clean and renewable energy with large scale reserves,geothermal resource is one of the most promising new energy to deal with climate change and ensure energy security and sustainability.In recent years,with the increasing demand of geothermal resources,researches on geothermal resource such as geothermal genesis,geothermal exploration,the prediction of prospective areas and geothermal resources assessment,are gaining widely appreciated.For geothermal systems,sufficient heat source and reservoirs with high permeability are two crucial factors.However,the complicated geologic structures not only limit the geothermal exploitation,investment and operation cost,but also influence the utilization efficiency of geothermal resources.Therefore,it is necessary to predict the geothermal favorable area based on geophysical exploration,regional geological and hydrogeological conditions.MT(magnetotelluric)and CSAMT(Controlled Source Audio Magnetotelluric)explorations were performed at the Wuyapao and Chuangye area of the Fangzheng fault depression in Yi-Shu graben to identify the stratigraphic sequence and geologic structures related to geothermal reservoirs.And then the geothermal favorable area were determined according to the geophysical and drilling data,geologic and hydrogeologic information.The main conclusions drawn from the study are as follows:(1)The favorable geothermal reservoirs are sandstone and gravel in the first section of Paleogene Oilgocene Baoquanling.And the depths of top and bottom of the reservoir are 1530 m and 1760 m,respectively,with the reservoir thickness of 230 m.(2)The geothermal reservoir temperature in the study area has been estimated to be 50-58? with an average value of 54? calculated by the temperature gradient of 3.3?/100 m based on the available borehole temperature logging.It belongs to the low-medium conductive geothermal system,and convective type can be found in the growth area of structural fissures.(3)Two favorable prospecting region are determined:(a)The region from the starting point of Line 6 to Well of Fang 6.The optimize well(ZK1)located at X=4500m with the designed depth of 2500 m.(b)The region between inferred fault F1 and F2 lying on Line 0.The optimize well(ZK2)located at X=4000m with the designed depth of 2500 m.This study testifies to the effictiveness of CSAMT and MT in the geothermal exploration.Besides,the results fill the gap pf geothermal exploration of the Fangzheng fault depression in Yi-Shu graben and provide the basis for the assessment of geothermal resource potential,the surveying direction,exploitation and utilization of geothermal resources.