Study On The Origin And Exploitation Of Geothermal Resources In The Wuji Research Area

This thesis takes Wuji County and its northern area as the research area,studies the characteristics of heat storage and geothermal field according to geothermal geological data,analyzes the origin of geothermal resources combined with hydrogeochemical methods,and calculates and evaluates the geothermal resources in the research area.Using FEFLOW software as a tool,the coupling model of hydrodynamic field and temperature field was established to simulate and analyze the variation of geothermal dynamic field and temperature field under different mining conditions.The main conclusions are as follows:1)The main thermal reservoirs in this area are Neogene Guantao Formation thermal reservoir and bedrock thermal reservoir.The cumulative thickness of the pore type heat reservoir of Guantao Formation is 170～260m,and the water temperature in the middle of the heat reservoir is 46～60℃.The hydrochemical type is Cl·HCO₃-Na type or Cl-Na type.The thermal reservoir thickness of Cambrian Ordovician bedrock is generally 80～140m,the temperature in the middle of the thermal reservoir is96～130℃,and the hydrochemical type is HCO₃·Cl-Na type or Cl-Na type.The thickness of the basement thermal reservoir in the Jixian System of Changcheng is70～120m,and the roof temperature of the thermal reservoir is generally 106～140℃.It is Cl·HCO₃-Na or HCO₃·Cl-Na type water.2)The northwestern Cenozoic area of the study area has an obvious geothermal anomaly,and the geothermal gradient is greater than 4.0℃/100m,while that in other areas is generally 3～4℃/100m.The southeast corner is the smallest,less than3.0℃/100m,and the basement geothermal gradient is uniformly 2.1℃/100m.At a depth of 500m and 1000m,the Cenozoic geothermal gradient at the center of the bulge and the temperature at the same depth are both higher than the periphery of the bulge,forming obvious thermal anomalies.The ground temperature anomaly at 2000m and3000m shifted to the southeast.3)The study area belongs to the medium and low temperature geothermal field mainly based on heat conduction.Regional terrestrial heat flow is the constant"heat source"of thermal reservoir.The Quaternary and Neogene Minghuazhen formations in the area constitute the Guantao Formation thermal reservoir cap layer,and the overlying strata of Upper Paleozoic,Mesozoic and Cenozoic constitute the double cap layer of bedrock thermal reservoir.According to the isotopic data analysis ofδ¹⁸O andδD,it is found that the source of geothermal water recharge is atmospheric precipitation.According to the analysis of tritium and ¹⁴C,the age of geothermal water is about24,000 years,which belongs to"ancient water".The geothermal temperature scale method shows that the circulating depth of bedrock hot water is greater than the depth of well formation.4)Calculate the amount of geothermal resources and geothermal fluid storage in the study area,and select three methods to determine the recoverable geothermal fluid resources.At 3000m,the shallow geothermal resource is 460.91×10¹⁶J;The geothermal fluid storage capacity was 3666.57×10⁶m³,and the total heat resource was 78.74×10¹⁶J.The amount of recoverable geothermal fluid resources is 106.28×10⁶m³.5)Based on geothermal geological data,historical water level and temperature data,a geothermal numerical model was established based on the thermal reservoir of Guantao Formation in the Wuji research area as the target layer.In 15 years during the model recognition period,under the condition of single well with the current actual production volume,there is a falling funnel in the pole 12 of concentrated mining well,the water level drops about 7.5m,and the temperature rises about 3℃.Keep the production volume unchanged,add the same amount of recharge well at 400m,recharge temperature is 15℃,the water level of pole 12 well drops about 3m,the temperature basically remains unchanged;Under the mining conditions of pole 12,WJR1,WJR2,WJR4 and WJR8,the water level of mining Wells all showed a downward trend,among which,the water level of WJR1 dropped by about 9m at most,and the temperature of each mining well increased.Under the condition of the same amount of recharge,the temperature of heat storage fluid at the centralized mining well drops greatly,and the maximum temperature drops about 7℃,but it can still maintain at 50℃.