A Comparative Study Of Sedimentary Geothermal Water And Volcanic Geothermal Water With Hydrogeochemistry Method

This paper takes the Guanzhong Basin central section thermal field?sedimentary type geothermal systems?and Tengchong Rehai geothermal field?volcanic type geothermal system?as representatives.we use the hydro-geochemistry method and environmental isotope method to compare theirs geothermal geological structure,the origination of geothermal and degree of heat storage openness,which can explore the similarities and differences of these two systems.Ultimately,the results can provide a scientific basis for utilization of geothermal resources in our country.The regional geological structure shows,the thermal reservoir of Guanzhong Basin has a great heat source,because of the shallow moho.The thermal reservoir that has many fractures is mainly made up of incompact sandstone and glutenite,which has good conditions to store heat and water.Tengchong located in the east side of the India plate and Eurasian plate collision zone and have many times volcanic eruption.the volcanic eruption and fractures structure create a favorable condition for geothermal activity.The hydro-geochemistry of Guanzhong Basin central section thermal field and Tengchong Rehai geothermal field show that the thermal reservoir environment of the Guanzhong basin is closed,and have a deep water-rock reactions,but the water-rock reactions of Tengchong Rehai geothermal field is in its infancy.we use the Multi-mineral balance method and reveal this two field average thermal storage temperature are 98.46?and 199.8?,the average mixed cold water ratio are 22.55%and 53.37%,buried depth are 2736m and1164m.Tengchong Rehai geothermal field has a shallower heat resource and its hot water recycle rate is faster.The study results of?¹⁸O and?D datas indicated that these two field have significant oxygen exchange and water-rock reactions especially in Guanzhong Basin where have more closed thermal reservoir environment and long residence time.The Tengchong Rehai geothermal field is closed too,and its thermal reservoir surrounding is granite and metamorphic rock,which influenced the enrichment of?¹⁸O.The high thermal storage temperature?199.8??is the main factor of?¹⁸O shift.The small ⁸⁷Sr/⁸⁶Sr ratio indicated that the Guanzhong Basin geothermal water comes from precipitation and river in Paleogene System,and part of thermal reservoir is closed to the earth's mantle.The ⁸⁷Sr/⁸⁶Sr ratio of Tengchong geothermal water is equal to the alumino-silicate background,so we can speculate that the geothermal water comes from precipitation and the fluid of Ptgl.?³⁴S data has a negative correlation with ⁸⁷Sr/⁸⁶S data indicated these two thermal reservoir exit gypse dissolving,and the oxidation of H₂S gas is also a common source of sulfates.According to the origin and isotope hydro-geochemical characteristics of geothermal water,we can draw a conclusion that Tengchong Rehai geothermal field and Guanzhong central section thermal field thermal reservoir environment respectively sedimentary-closed-semiclosed and volcanic-half closed type.