Research On The Occurrence Characteristics And Formation Mechanism Of Underground Hot Water In Pu'er Basin

Pu'er basin is located in Ning'er County,Yunnan province.The basin area is about 30km2.The tectonic movement is intense since the Cenozoic,and it is rising into a relative tectonic uplift area after the late Quaternary period.There are signs of magmatic activity in the basin,faults develop,earthquakes occur frequently,hydrothermal activities are obvious,and hot springs are concentrated.Geothermal water is mainly controlled by the deep and deep faults of the south and north,and the near east and west is the main space of hot water,and the two groups of faults are in the hot spring.Geothermal water in carbonate formations is also abundant,but the water temperature is lower than that in the fault zone.The heat source of the geothermal field in Puer basin is the deep molten magma below 5km underground.Fracture in the region is crisscross,the near north-south compression fracture(F1,F2,F3)is the main heat conduction fracture,and the near east-west fault is water diversion,and the intersection of the two faults is often a strong area of geothermal display.The lower Longtan sandstone and maokou limestone strata have been destroyed by many tectonic movements and fractures,which provide favorable conditions for the migration and storage of hot water,forming deep band thermal storage and small range and banded thermal storage.The Upper Mesozoic sandstones are cemented densely,poorly permeable,and relatively low fissure rates,forming a good cap rock with Quaternary strata.The chemical type of geothermal water is relatively simple,mainly HCO3-Ca water,the temperature and flow of spring water varied with the dry season of the rainy season,and the water chemistry was stable.Most water chemical composition of hot water mostly increases with the temperature,the hot water is immature water.Using the geochemical temperature scale and Si O2 mixed model,the temperature of the hot reservoir was calculated,and the average water circulation depth was calculated to be 4578m;In the process of rising water,more than 80% of the cold water is mixed in,the chemical composition changes,and the temperature of the hot water decreases.The main source of the geothermal water supply is atmospheric precipitation,and the groundwater is recharged at the high altitude surrounding the ground,and then the hot springs with low temperature are formed along the surface of the fracture.Based on the geological structure,geophysical data and geothermal borehole data,the concept model of geothermal field was established,and the occurrence characteristics of underground hot water were analyzed.According to the analysis data of hot water chemical components and hydrogen and oxygen isotopes,the thermal storage temperature,the depth of hot water circulation,the proportion of cold water mixing and the source of recharge are studied in the geothermal field,the formation mechanism of geothermal water in pu 'er basin is summarized,and theoretical support is provided for further development of underground hot water in pu 'er basin.