Application Of Geochemical Techniques In The Exploration Of Rongcheng Geothermal Field

The Rongcheng geothermal field is located in Rongcheng County,Xiong'an New District,Hebei.It is a large karst heat storage like the Niutuo Town geothermal field.Its development and utilization are of great significance to support local geothermal heating and alleviate smog.This study attempted to ascertain the geochemical characteristics of the soil and geothermal water and the distribution characteristics of the heat-controlling structure by carrying out soil geochemistry,radioactive geochemistry,water chemistry,and rock geochemical measurements.On this basis,the formation model of Rongcheng geothermal field was established to evaluate the prospects for the development and utilization of geothermal resources in Rongcheng geothermal field.At the same time,provide scientific data support for exploring the applicability of geochemical technology in the exploration of geothermal resources in areas without hot springs(ie,the geothermal system of the fault depression in the Northern Plains).Soil geochemical characteristics,Hg,As and Sb elements are relatively enriched in the study area,and Cs elements are relatively poor;the skewness of Hg elements is as high as 8.07,indicating that there should be large differences in underground temperature;and soil The distribution of medium element content can better reflect the distribution of hidden structures,especially the three elements Hg,As and Be,which are enriched in the region and are obviously prominent and can be used as an indicator element for further exploration of geothermal fields.Rock geochemical characteristics.The dolomite and limestone of the thermal reservoir have high thermal conductivity(average values of 5.300 W / m K and 5.789 W / m K,respectively),specific heat capacity(saturated at 160 ° C,and specific heat capacity at saturation is 1.316 J /(kg · ?)),which proves that it has good thermal conductivity and the ability to absorb and release thermal energy,plus it can develop rich karst water storage space,and has very high-quality thermal storage capacity and conditions.However,its average value of exothermic heat generation rate is low(only about 0.25?W / m3),which is far lower than the world average radioactive heat generation rate(2.5?W / m3),so the possibility of radioactive heat sources at the geothermal heat source location in the study area is ruled out.Hydrogeochemical characteristics.The underground hot water in the study area is mostly neutral or weakly acidic brackish water.The types of water chemistry mainly include Cl · HCO3-Na type and Cl-Na type water.The water temperature is 34-72 ° C.Most geothermal waters exceed the TDS standard,and the F and Ba contents have reached the hot mineral water naming standard,which has good medical value.Comprehensive evaluation of the thermal storage of Rongcheng geothermal field,the calculated thermal storage temperature range of Cl · HCO3-Na geothermal water is40-110 ?,while the thermal storage temperature range of Cl-Na geothermal water is50-80 ?.After calculation,the circulation depth of geothermal water is mostly between 1-2km.After a comprehensive analysis,it is believed that the temperature of the underground hot water in the Rongcheng geothermal field is mainly affected by two factors,the bedrock burial depth and the thermal control geological structure.Under the same underground burial depth,the shallower the bedrock,the higher the underground hot water temperature.Under the influence of the same heat control structure,the deeper the buried underground hot water,the higher the temperature.It is preliminarily inferred that the main heat source of the genetic model of the Rongcheng geothermal field is heat conduction from deep heat flow,and its replenishment comes from atmospheric precipitation.The salt rock stratum,after long-distance migration and deep cycle heating,is enriched in the Rongcheng bulge,which is conducive to heat accumulation,and is finally used by geothermal wells.