Using Several Methods To Estimate The Temperatures Of Deep Geothermal Reservoirs

The temperature of deep geothermal reservoirs is an important parameter for evaluating geothermal resources potential.Common methods to estimate geothermal reservoir temperatures are described in detail in this paper,including silica geothermometers,multiple mineral equilibrium diagrams,Na-K-Mg trigonometric method and mixed proportion methods.The water samples were collected in many provinces.By analyzing the geothermal reservoir temperatures of a large number of hot springs and the applicable conditions,the advantages and disadvantages of different methods are summarized.There are four kinds of calculation methods,among which the SiO₂geothermometers and cations geothermometers are commonly used.The results obtained by different types of geothermometers are empirical approximate formulas.Aqueous solution environment has great influence on the results,and the calculation results must be selected.The formula calculation methods should be combined with other methods to improve the accuracy of the results.At first,SiO₂ geothermometers can be used to determine the dominant types of SiO₂ minerals in the solution.When cations geothermometers is used,it is needed to judge the mineral-fluid chemical equilibrium state and hydration type.In general,the results estimated with the Na-K geothermometers are higher than those with the Na-K-Ca geothermometers and K-Mg geothermometers.The mineral equilibrium diagram method shows the mineral information in the saturated state in the water sample environment by calculating the SI value under different temperature conditions.PHREEQC and WATCH97 software can be used to draw patterns in this method.The two softwares have differences in mineral selection,and PHREEQC software can be used simply.The calculation results of the mineral equilibrium diagram method are different in measuring the temperatures of geothermal reservoir of hot springs and boiling springs.The Na-K-Mg triangle diagram method can show the equilibrium state of a large number of water samples in a single diagram,distinguish the mixed water and equilibrium water,and obtain a series of maturity indexes MI through the simultaneous geothermometers.For completely balanced water samples,the results obtained by different types of geothermometers are similar.For partially balanced water samples and immature water samples,the results should be treated dialectically,not negated completely.The mixed proportion method includes the silicon-enthalpy equation method and silicon-enthalpy graphic method.When the geothermal reservoir temperature is obtained,the portion of cold water mixed by hot water in the process of rising hot water can be obtained.There is a situation that some water samples cannot obtain the geothermal reservoir results by the mixing proportion method,because the average temperature of such water samples is low and the proportion of cold water is large.The mineral controlling the silicon content in the water is chalcedon,while the silicon mineral used in the calculation by mixing proportion method is quartz.The results obtained by the silicon-enthalpy equation method and the graphical method are roughly the same.Different methods are combined to verify each other to further improve the accuracy of the calculation results of geothermal reservoir temperatures and provide favorable conditions for subsequent development and utilization of geothermal resources.