Study On The Reservoir Temperature And Scaling Of Borehole Geothermal Water Of Carbonate Rocks In Chongqing

Geothermal water has become an important object of new energy research.Chongqing,as a typical representative of geothermal water,is rich in geothermal water resources.However,there has been a certain degree of scaling,which has become a constraint on the development,utilization and operate normally,securely of geothermal water.Reservoir temperature is the critical factor that affects the chemical composition,content and source of geothermal water,and then affects the scaling of geothermal water.Therefore,it is very important for the sustainable development and utilization of geothermal water to study the geochemical characteristics of geothermal water,reservoir temperature and scaling.This paper based on the analysis of the physical and chemical characteristics of 36 borehole geothermal water in downtown of Chongqing,through the comparative analysis of geothermometer methods,such as silica,chalcedony,cation geothermometer,determine the applicable geothermometer and calculate the reservoir temperature and circulation depth.Calculating and judging the scaling tendency of borehole geothermal water by the Ron Greer index,Reznor index,gypsum and the amorphous SiO2 saturation indices,and judging the the main scaling products by the mineral saturation index.At the same time,analyzing the actual scaling of geothermal water with Tongjing geothermal water as the typical case in Chongqing,and based on the influence of geothermal water on metal pipeline and boiler,to investigate the antiscaling suggestions,which have contributed to provide scientific basis for the development and utilization of geothermal water in the whole area of Chongqing.The results show that the hydrochemical characteristics of Chongqing borehole geothermal water are consistent,water chemistry type is Ca·Mg-SO₄ or Ca-SO₄;the temperature is 32.5⁵7?,belong to low temperature geothermal water;pH value is 7.3⁸.4,showing weak alkaline;the dissolution of gypsum in the surrounding rock is the dominant process of controlling chemistry of the geothermal water,which caused high concentration of Ca²⁺,Mg²⁺,and low concentration of HCO3-.The reservoir temperature varies widely by using silica,chalcedony and cationic geothermometer,the selection of steam loss of quartz and modified SiO2 geothermometer are applicable with analysis,and the average reservoir temperature is 64.9⁹3.4?,the circulation depth is 1579²520m.Theoretically,most of the geothermal water have slight or serious scaling.The main precipitated scaling matters are calcium carbonate,calcium sulfate,not calcium silicate by using index of Langelier,Ryznar,Relative saturation index of gypsum and amorphous SiO2.Calcite,dolomite are responsible for the scaling by saturation indices.But in fact,most of the borehole geothermal water in Chongqing have slight calcium carbonate scale,which are consistent with the results by using RI2 lithology of the study area..The chemical type of geothermal water is Ca·Mg-SO₄ or Ca-SO₄,and the contents of TDS,Ca²⁺,Mg²⁺,SO42-and trace elements are higher than that of non geothermal water,which affected by temperature and cycle path.Figure Schoeller shows that the shallow water has mixed with deep geothermal water,the mixing ratio of cold water in borehole geothermal water is lower than that of natural hot springs because of the influence of surrounding cement.Geothermal water and non-geothermal water are derived from meteoric water,and the recharge altitute of geothermal water is 1200¹800m,1000¹400m m by judging with deuterium and oxygen isotope individually.It is found that there is a slight or moderate scaling tendency of geothermal water in Tongjing by using the index,which inconsistent with the actual situation.The outlet of geothermal water is lacking obvious fouling phenomenon,white sediments appeared in the hot and cold springs on the pool wall,which the main components are Ca,O,C,is carbonate mineral;the black product flowed from the outlet of geothermal water are mainly iron compounds,corrosion products by the analysis of EDS and XRD.The total scale of the boiler is 2440.5²985.5 mg/l and the corrosion coefficient is 2.3⁴.6 mg/l,which belongs to the geothermal water with a lot of fouling and strong corrosiveness.The scaling for pipeline and boiler of geothermal water are affected by the hydrodynamic conditions and the chemical composition of the water,and the corrosion is mainly affected by the ions of F-,Cland SO₄^2-,sulfate reducing bacteria and iron bacteria,H2 S.Putting forward that we should monitore the water hydrodynamic conditions and scaling corrosion components in different time and places regularly,and take mechanical measures for antiscaling according to the actual situation.