Method for determining in-situ composition of geothermal water

Abstract

The invention provides a method for determining in-situ composition of geothermal water, and belongs to the technical field of geothermal energy development. Geothermal water, geothermal gas and spring bloom or scale samples are collected, chemical composition analysis of the geothermal water, component analysis of the geothermal gas (including absolute content of CO2 and H2S) and mineral composition analysis of the spring bloom or scale are carried out, and then according to the geochemical process of mother geothermal fluid rising from a deep reservoir to the earth surface, the geothermal gas is analyzed. And determining whether cold water mixing, gas escape and mineral precipitation occur in the geothermal water, finally correcting the influence of the generated geochemical action on the chemical components of the geothermal water, and calculating the chemical components of the in-situ geothermal fluid. According to the invention, the problem that the scaling property, corrosivity and thermal storage temperature evaluation of the thermal storage fluid are inaccurate due to the fact that the chemical composition of the mother geothermal fluid cannot be represented due to the geochemical effect of changing the composition of the existing surface thermal spring water or borehole geothermal well water in the upflow process can be solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of geothermal energy development, and particularly relates to a method for determining in-situ composition of geothermal water. BACKGROUND

[0002] In the process of geothermal energy development, geothermal geochemical exploration is the most economical exploration method, which can obtain information about the temperature of geothermal reservoir, the characteristics (scaling and corrosive) of geothermal fluid and the potential of associated resources (such as associated helium and hydrogen, Li, Rb, Cs and other rare metals). The in-situ composition of geothermal fluid (parent geothermal fluid) is the basis for analyzing these information, which refers to the geothermal fluid that reaches partial equilibrium or full equilibrium under the temperature and pressure conditions of deep reservoir. Since the parent geothermal fluid is usually formed in deep reservoir, and is easily affected by cold water mixing, gas escape and mineral precipitation during the ascending process, the geothermal water collected at the surface often cannot represent the composition of the deep geothermal fluid, and needs to be determined by special sampling and analysis techniques. For geothermal water with low water vapor content, mainly non-condensable gas and easy to mix with cold water, the gas content given by the traditional gas collection method and analysis technique is relative content, and it is difficult to determine the absolute content. Based on the surface geothermal water data, the evaluation of the temperature of geothermal reservoir, the scaling and corrosive of geothermal water and the associated resources will give unscientific and unreliable results, and some even mislead the subsequent exploration and development and utilization. Therefore, it is urgent to develop an in-situ composition determination method for geothermal water, especially for geothermal water with small amount of water vapor. SUMMARY

[0003] Therefore, the present application aims to provide a method for determining the in-situ composition of geothermal water. The method provided by the present application can correct the influence of cold water mixing, gas escape and mineral precipitation on the chemical composition of geothermal water, and improve the reliability of the in-situ composition results of geothermal water.

[0004] In order to achieve the above-mentioned application purposes, the present application provides the following technical solutions: The present application provides a method for determining the in-situ composition of geothermal water, wherein the geothermal water includes hot spring water or geothermal well water, and the method for determining the in-situ composition of geothermal water comprises the following steps: (1) collecting geothermal water, geothermal gas, and when there is sinter or scale at the collection site, collecting sinter or scale; (2) determining the chemical composition of geothermal water, the mineral composition of sinter or scale and the composition of geothermal gas, wherein the composition of geothermal gas includes the absolute content of CO2 and H2S; (3) judging the geochemical process experienced by the parent geothermal fluid in ascending from the deep reservoir to the surface according to the outcropping conditions of geothermal water, wherein the geochemical process includes one or more of cold water mixing, gas escape and mineral precipitation; and correcting the in-situ composition of geothermal water in the order of gas escape, mineral precipitation and cold water mixing. The correction method of the gas escape includes: inputting the chemical composition of the geothermal gas and the geothermal water into a geochemical program to obtain the fluid composition of the corrected escape gas; The correction method of the mineral precipitation includes: inputting the fluid composition of the corrected escape gas into a geochemical program, setting the sufficient precipitation mineral composition and making the saturation index 0 to correct the precipitation, and obtaining the fluid composition of the corrected mineral precipitation; The correction method of the cold water mixing includes: determining the cold water mixing ratio X, taking the fluid composition of the corrected mineral precipitation as a sample, and obtaining the in-situ composition of the geothermal water according to Formula 1: Formula 1; In Formula 1, is the concentration of a component in the in-situ geothermal fluid, mg / L; is the concentration of a component in the sample, mg / L; X is the cold water mixing ratio.

[0005] Preferably, in the step (2), the chemical composition of the geothermal water includes the total dissolved solid content, Na + , K + , Ca 2+ , Mg 2 + , F - , Cl - , SO4 2- , HCO3 - / CO3 2- , SiO2, Al, Fe, B and Br - , and the determination of the chemical composition of the geothermal water further includes testing the pH value of the geothermal water and the temperature when the pH value is tested; The mineral composition of the sinter or scale includes the mineral analysis of the whole rock.

[0006] Preferably, the geochemical process experienced by the parent geothermal fluid rising from the deep reservoir to the surface according to the outcropping condition of the geothermal water includes: Observing whether there are bubbles or gas at the spring orifice or the geothermal well mouth, and if there are, it indicates that gas escape has occurred; Observing whether there are sinter or scale at the spring orifice or the geothermal well mouth, and if there are, it indicates that mineral precipitation has occurred; When there is only one spring or geothermal well in the collection area, the state of the geothermal water is determined according to the Na-K-Mg triangular diagram, and if the single geothermal point is in the non-equilibrium zone, partial equilibrium or mixed zone in the Na-K-Mg triangular diagram, it indicates that cold water mixing has occurred; when there are multiple springs or geothermal wells in the collection area, the state of the geothermal water is determined according to the Cl - or δ 2 HH2O If multiple geothermal water samples show Cl-SiO2 linear relationship or linear relationship on Na-K-Mg triangular diagram, it is considered that cold water mixing has occurred.

[0007] Preferably, the method for determining the mixing ratio of cold water is method one, method two or method three, the method one comprising the following steps: Assuming that there are multiple geothermal water samples in the collection area and no boiling has occurred, assuming that the SiO2 concentration and enthalpy of the in-situ geothermal fluid remain unchanged, and knowing the enthalpy and SiO2 concentration of the cold water end member and the geothermal water, the mixing ratio of cold water under different hot water end member conditions is calculated using formula 2 and formula 3 and ; plot the mixing ratio and the corresponding hot water end member temperature, and the intersection of the two curves is the mixing ratio of cold water; Formula 2; Formula 3; In formula 2 and formula 3, is the enthalpy of the cold water end member, kJ / kg; is the enthalpy of the hot water end member, kJ / kg; is the enthalpy of the geothermal water, kJ / kg; is the SiO2 concentration of the cold water end member, mg / L; is the SiO2 concentration of the hot water end member, mg / L; is the SiO2 concentration of the geothermal water, mg / L; The method two comprises the following steps: Draw the quartz solubility curve with enthalpy as the horizontal coordinate and SiO2 content as the vertical coordinate; Plot a straight line through the cold water end member and the geothermal water sample on the graph and intersect with the quartz solubility curve, and calculate the mixing ratio of cold water according to the SiO2 concentration values corresponding to the cold water end member, the hot water end member and the geothermal sample point; The method three comprises the following steps: The geothermal water and geothermal gas data are inputted into geochemistry program GEOT or SOLVEQ, possible mineral combination is selected according to reservoir lithology, enrichment coefficient and steam loss mass fraction are adjusted, saturation index of different mineral combination under different temperature conditions is calculated, temperature-saturation index curve is drawn with temperature as horizontal coordinate and saturation index as vertical coordinate, when saturation index curves of multiple minerals converge to one point with temperature change, the cold water mixing ratio corresponding to the enrichment coefficient is considered as the actual cold water mixing ratio.

[0008] Preferably, the geochemistry program comprises one or more of WATCH, GEOT and SOLVEQ.

[0009] Preferably, the geothermal gas collection method comprises the following steps: A three-way bottle with known mass and volume is prepared, 50 mL of 40% NaOH lye is filled in the three-way bottle, and the three-way bottle is vacuumized for standby; The geothermal gas is collected into the vacuumized three-way bottle by using a gas sampling device, and a mixed solution absorbing CO2, H2S and water vapor is obtained; The gas sampling device is a funnel and silica gel tube, or a water-gas separator.

[0010] Preferably, the testing method of CO2 and H2S content in the geothermal gas comprises: titrating the mixed solution absorbing CO2, H2S and water vapor by using standard hydrochloric acid and standard mercury acetate respectively, and determining absolute content of CO2 and H2S in combination with mass change of the mixed solution before and after sampling.

[0011] Preferably, the Na + , K + , Ca 2+ , Mg 2+ , F - , Cl - , SO4 2- and Br - are determined by using ion chromatograph; The HCO3 - / CO3 2- is determined by using reverse titration method; The SiO2, Al, Fe and B are determined by using ICP-AES or ICP-OES; The mineral composition of the whole rock is determined by using X-ray diffractometer.

[0012] The present application provides a method for determining the in-situ composition of geothermal water. The method comprises the following steps: collecting geothermal water, geothermal gas and scale or spring sinter samples, and performing chemical composition analysis of geothermal water, geothermal gas composition analysis (mainly the absolute content of CO2 and H2S) and mineral composition analysis of scale or spring sinter. Then, according to the geochemical processes experienced by the parent geothermal fluid when rising from the deep reservoir to the surface, it is determined whether the geothermal water has undergone cold water mixing, gas escape and mineral precipitation. Finally, the influence of the geochemical processes on the chemical composition of geothermal water is corrected, and the in-situ chemical composition of geothermal fluid is calculated. The present application can solve the problem that the existing surface hot spring water or geothermal well water cannot represent the chemical composition of the parent geothermal fluid due to the geochemical processes that change its composition during the rising process, thereby leading to inaccurate evaluation of the scaling and corrosive properties of the geothermal reservoir fluid and the temperature of the geothermal reservoir. The present application corrects the gas escape, especially the escape of CO2 and H2S which have a great influence on the chemical composition, from the perspective of determining the absolute content of geothermal gas, thereby solving the problem of ignoring the influence of gas escape on the composition.

[0013] Further, the present application uses a vacuumed three-way bottle containing alkaline solution to collect geothermal gas. The alkaline solution stored therein absorbs water vapor, CO2 and H2S. The absolute content of CO2 and H2S is determined by using the mass difference before and after collecting the gas sample and the titration method, thereby correcting the influence of the escape of CO2 and H2S on the parent geothermal fluid. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 Flow chart for determining the in-situ composition of geothermal water; Figure 2 Structure diagram of a three-way bottle and schematic diagram of a geothermal gas collection method; Figure 3 Schematic diagram of quantitative composition analysis of CO2 and H2S in geothermal gas; Figure 4 Schematic diagram for determining cold water mixing and calculation diagram for mixed ratio; Figure 5 Schematic diagram for correcting the in-situ composition of geothermal water; Figure 6 Determination of the cold water mixing ratio of a certain hot spring in Fengshun area, Guangdong; DETAILED DESCRIPTION

[0015] The present application provides a method for determining the in-situ composition of geothermal water, which includes surface hot spring water or geothermal well water. The method comprises the following steps: (1) collecting geothermal water, geothermal gas, and when there is scale or spring sinter, collecting scale or spring sinter; (2) determining the chemical composition of the geothermal water, the mineral composition of the sinter or scale, and the geothermal gas composition, which includes the absolute content of CO2 and H2S; (3) judging the geochemical processes that the parent geothermal fluid has experienced in ascending from the deep reservoir to the surface according to the outcropping conditions of the geothermal water, the geochemical processes including one or several of cold water mixing, gas escape, and mineral precipitation; and correcting the in-situ composition of the geothermal water in turn according to the gas escape, the mineral precipitation, and the cold water mixing; the correction method of the gas escape includes: inputting the geothermal gas composition and the chemical composition of the geothermal water into a geochemical program to obtain the fluid composition of the corrected escaped gas; the correction method of the mineral precipitation includes: inputting the fluid composition of the corrected escaped gas into the geochemical program, correcting the precipitation by setting a sufficient amount of precipitated mineral composition and making the saturation index 0 to obtain the fluid composition of the corrected mineral precipitation; the correction method of the cold water mixing includes: determining the cold water mixing ratio X, taking the fluid composition of the corrected mineral precipitation as a sample, and obtaining the in-situ composition of the geothermal water according to Formula 1: Formula 1; in Formula 1, is the concentration of a certain component in the in-situ geothermal fluid, mg / L; is the concentration of a certain component in the sample, mg / L; X is the cold water mixing ratio.

[0016] In the present application, the flow chart of the method for determining the in-situ composition of the geothermal water is as shown in Figure 1 .

[0017] In the present application, the geothermal water, the geothermal gas, and when the collection site contains sinter or scale, the sinter or scale are collected first.

[0018] The geothermal water sample is collected according to the requirements in the Specification for Collection and Preservation of Geothermal Fluid Samples. The present application does not have special requirements for the collection method of the geothermal water scale, and the collection method known to those skilled in the art can be used. In the present application, the collection method of the geothermal gas preferably includes the following steps: Prepare a tee bottle with a known mass and volume, the tee bottle contains 50 mL of 40% mass concentration NaOH lye, and is vacuumed for standby; Use a gas sampling device to collect the geothermal gas into the tee bottle containing the lye to obtain the lye absorbing CO2, H2S, and water vapor.

[0019] In the present application, the material of the three-way bottle is preferably glass. In the present application, the three-way bottle is preferably provided with two inlets, one control valve and three sealing gaskets to ensure that the three-way bottle has good sealing performance and can completely isolate air.

[0020] In the present application, the volume of the three-way bottle is preferably 300-500 mL, more preferably 350 mL. In the present application, the gas sampler is a funnel and a silica gel tube, or a water vapor separator. In the present application, the air in the funnel, the pipeline and the container needs to be completely discharged before sampling, and the content test of CO2 and H2S needs to be completed within 1 week after collecting the geothermal gas.

[0021] Specifically, when the geothermal gas is hot spring gas, the present application uses a funnel and a silica gel tube to collect the gas into a container containing alkaline solution. First, the funnel connected with the silica gel tube is filled with water and inverted in water. The exhaust time is estimated according to the volume of the silica gel tube. After the air is completely discharged, the funnel is connected with one inlet of a three-way bottle which has been vacuumized, and the other inlet is connected with a silica gel tube which is sealed with a water stop clamp. At the same time, the three-way bottle is inverted. Slowly open the control valve to let the gas enter the three-way bottle. The water vapor, CO2 and H2S will be absorbed into the alkaline solution, and other non-condensable gases will gather in the upper space of the three-way bottle. When the bubbles stop entering the three-way bottle or the alkaline solution enters the silica gel tube through the pipeline, close the control valve and seal the silica gel tubes of the two inlets with water stop clamps.

[0022] When the geothermal gas is geothermal well gas, the present application uses a water vapor separator to collect the gas into a container containing alkaline solution. The sampling method refers to the "Standard for Collection and Preservation of Geothermal Fluid Samples".

[0023] In the present application, the structural diagram of the three-way bottle and the schematic diagram of the geothermal gas sampling method are shown in Figure 2 Figure 2 , wherein (a) is the structural diagram of the three-way bottle, and (b) is the schematic diagram of the geothermal gas sampling method.

[0024] The present application determines the chemical composition of geothermal water, the mineral composition of spring sinter or scale and the composition of geothermal gas. In the present application, the chemical composition of geothermal water includes total dissolved solids content (TDS), Na + , K + , Ca 2+ , Mg 2+ , F - , Cl - , SO4 2- , HCO3 - / CO3 2- , SiO2, Al, Fe, B and Br - , and preferably includes δ 2 H H2O and δ​18 O H2O , the above concentration data are preferably expressed in mg / L, mmol / L or mmol / kg. In the present application, the Na + , K + , Ca 2+ , Mg 2+ , F - , Cl - , SO4 2- and Br - are preferably determined by ion chromatography, the HCO3 - / CO3 2- are preferably determined by reverse titration, and the SiO2, Al, Fe and B are preferably determined by ICP-AES or ICP-OES. In the present application, the chemical composition of the geothermal water is determined by also testing the pH value of the geothermal water and the temperature at which the pH value is tested, and the pH value, the temperature at which the pH value is tested and the TDS are preferably determined by a portable multi-parameter analyzer.

[0025] In the present application, the mineral composition of the sinter or scale includes the mineral quantitative analysis of the whole rock, which is preferably determined by an X-ray diffractometer.

[0026] In the present application, the geothermal gas components mainly refer to CO2 and H2S, and the content is expressed in mg / kg or mmol / kg. In the present application, the testing method of the CO2 and H2S content of the geothermal gas includes titrating the mixed solution absorbing CO2, H2S and water vapor by using standard hydrochloric acid and standard mercury acetate respectively, and determining the absolute content of CO2 and H2S by combining the mass change of the lye before and after sampling. As a specific embodiment of the present application, the testing method of the CO2 and H2S content of the geothermal gas includes the following steps: Before sampling, the mass and volume of the three-way bottle are determined and marked as and respectively; a NaOH solution with a mass concentration of 40% is prepared, the content of HCO3 - and CO3 2- in the solution is determined, expressed in the form of CO2, and marked as ; 50 mL of the prepared 40% NaOH solution (hereinafter referred to as lye) is loaded into the three-way bottle, the three-way bottle is vacuumed, and then weighed again, marked as .

[0027] The geothermal gas is collected by the above method to obtain the lye absorbing the geothermal gas, marked as mixed solution. It is assumed that the concentrations of CO2 and H2S in the mixed solution are and .

[0028] First, determine the molar amount of H2S in the geothermal gas (which is also the molar amount of H2S in the mixed solution). Weigh the three-way bottle after sampling and record the mass as follows: Take 5 mL of 5 mol / L NaOH solution and 5 mL of acetone into a 100 mL Erlenmeyer flask; add 2 mL of dithizone indicator; then take 1~50 mL of the mixed solution into a 100 mL Erlenmeyer flask. If the sample volume is less than 10 mL, dilute with deionized water to 10 mL. Using a 2 mL microtitrator and a certain concentration of mercuric acetate ( Titrate with 0.001 mol / L of mercuric acetate, and record the volume of mercuric acetate consumed when the solution changes from yellow to pink. The molar amount of H2S can be calculated using equation a: Formula a; In formula a, The concentration of mercuric acetate is expressed in mol / L. The volume of mercuric acetate consumed is in mL.

[0029] Next, determine the molar amount of CO2 in the geothermal gas. Take 2 mL of the mixed solution from the three-way bottle and transfer it to a 150 mL beaker. Add 100 mL of deionized water (without carbonic acid). Adjust the pH of the solution to 8.30. Add 1 mol / L standard hydrochloric acid to the solution. When the pH value is 9.0~9.5, add 0.1 mol / L standard hydrochloric acid until the pH value is 8.30. Titrate with 0.1 mol / L standard hydrochloric acid until the pH value of the solution is 3.80, and record the amount of hydrochloric acid consumed. Then the molar amount of CO2 in it As shown in equation b: Formula b; In formula b, The molar amount of CO2, in mmol; The concentration of hydrochloric acid is 0.1 mol / L; The volume of hydrochloric acid consumed is in mL. denoted as the molar amount of H2S in the mixed solution, in mmol.

[0030] molar amount of CO2 in geothermal gas As shown in equation c: Formula c; In equation c, , where is the molar amount of CO2 in geothermal gas, in mmol; is the molar amount of CO2 in the mixed solution, mmol; is the molar amount of CO2 in the mixed solution, mmol; is the concentration of hydrochloric acid, 0.1 mol / L; is the volume of hydrochloric acid consumed, mL; is the molar amount of H2S in the mixed solution, mmol; is the concentration of CO2 in the alkali solution, mol / L.

[0031] The mass of the condensed water is shown as formula d: Formula d; In formula d, is the mass of the condensed water, mg; is the mass of the three-way bottle after sampling, mg; is the mass of the three-way bottle containing the alkali solution, mg; is the mass of CO2 in the geothermal gas, mg; is the mass of H2S in the geothermal gas, mg; is the molar amount of CO2 in the geothermal gas, mmol; is the molar amount of H2S in the geothermal gas, mmol.

[0032] The content of CO2 and H2S in the geothermal gas can be represented as and respectively: and .

[0033] In the present application, the flow chart of the quantitative composition analysis of the geothermal gas CO2 and H2S is shown as Figure 3 .

[0034] In the present application, the process experienced by the mother geothermal fluid rising to the surface is usually first mixed with cold water, and then gas escape and / or mineral precipitation occur. According to the conditions of geothermal water outcrop, the geochemical processes experienced by the mother geothermal fluid rising from the deep reservoir to the surface include: Observe whether there are bubbles or gas at the spring or wellhead of the hot spring, if there are, it indicates that gas escape has occurred; Observe whether there are sinter or scale in the spring or wellbore of the hot spring, if there are, it indicates that mineral precipitation has occurred; When there is only one hot spring or geothermal well in the sampling area, the type of geothermal water is determined according to the Na-K-Mg triangle diagram. If the single geothermal hot spot is in a non-equilibrium, partially equilibrium, or mixed zone in the Na-K-Mg triangle diagram, it indicates that cold water has been mixed in. (Refer to...) Figure 4 (b) in the middle.

[0035] When there are multiple hot springs or geothermal wells in the collection area, utilize Cl - or δ 2 H H2O The relationship between Cl / B / SiO2 is used to determine whether geothermal water has mixed. When multiple geothermal water samples show a linear relationship between Cl and SiO2 (reference...), the mixing of geothermal water is determined. Figure 4 If there is a linear relationship in (a) or the Na-K-Mg triangular diagram, it indicates that cold water has been mixed in (see reference). Figure 4 (b) in the text. Specifically, it uses Cl... - Content or δ 2 H H2O The x-axis represents the area of ​​Br ions, B elements, or SiO2 content, and the y-axis represents the area of ​​Br ions, B elements, or SiO2 content. Geothermal water samples and shallow groundwater or river water samples from the collection area are plotted as cold water end-members on the graph, or on a Na-K-Mg triangular graph. If there is a linear relationship, it indicates that cold water contamination has occurred.

[0036] Based on experience, when the local hot water is hot spring water, cold water will usually mix in; when the local hot water is geothermal well water, cold water usually will not mix in.

[0037] In this invention, the method for determining the cold water mixing ratio is Method 1, Method 2, or Method 3, wherein Method 1 includes the following steps: Assuming there are multiple geothermal water samples in the collection area and no boiling occurs, and assuming the SiO2 concentration and enthalpy of the in-situ geothermal fluid remain constant, and given the enthalpy and SiO2 concentration of the cold water end-member and the geothermal water, the cold water mixing ratio under different hot water end-member conditions can be calculated using Equations 2 and 3. and Plot the mixing ratio against the corresponding hot water end-point temperature; the intersection of the two curves represents the cold water mixing ratio. Formula 2; Formula 3; In Equations 2 and 3, Enthalpy of the cold water end element, kJ / kg; Enthalpy of the hot water end element, kJ / kg; The enthalpy of geothermal water is expressed in kJ / kg. SiO2 concentration of cold water end member, mg / L; SiO2 concentration of hot water end member, mg / L; SiO2 concentration of geothermal water, mg / L.

[0038] In the present application, the relationship between enthalpy and SiO2 concentration under different temperature conditions is shown in Table 1.

[0039] Table 1 Relationship between enthalpy and SiO2 concentration under different temperature conditions

[0040] The method two estimates the cold water mixing ratio according to the SiO2-enthalpy mixing model, comprising the following steps: Taking the enthalpy as the horizontal coordinate and the SiO2 content as the vertical coordinate, a quartz solubility curve is drawn; The cold water end member and the geothermal water sample are plotted on the graph, a straight line is drawn through the cold water end member and the geothermal water sample and intersects with the quartz solubility curve, and the cold water mixing ratio is calculated according to the SiO2 concentration values corresponding to the cold water end member, the hot water end member and the geothermal sample points; The method three calculates the cold water mixing ratio according to the multi-mineral equilibrium method, comprising the following steps: The geothermal water and geothermal gas data are input into the geochemical program GEOT or SOLVEQ, the possible mineral combination is selected according to the reservoir lithology, the enrichment coefficient and the steam loss mass fraction are adjusted, the saturation index of different mineral combinations under different temperature conditions is calculated, the temperature-saturation index curve is drawn with the temperature as the horizontal coordinate and the saturation index as the vertical coordinate, and when the saturation index curves of multiple minerals converge to a point, it is considered that the cold water mixing ratio corresponding to the enrichment coefficient is the actual cold water mixing ratio.

[0041] Figure 4 It is a cold water mixing determination schematic diagram and a mixing ratio calculation diagram. Figure 4 In the present application, (a) is the relationship between Cl ion and SiO2 of river water (cold water end member), hot spring water and geothermal well water, (b) is a cold water mixing determination diagram based on Na-K-Mg triangular diagram, (c) is a schematic diagram of method one, and (d) is a schematic diagram of method two.

[0042] The present application corrects the in-situ composition of geothermal water in sequence according to gas escape, mineral precipitation and cold water mixing. In the present application, the correction method of gas escape includes: inputting geothermal gas composition and chemical composition of geothermal water into a geochemical program to obtain fluid composition of corrected escape gas. In the present application, when the geochemical process does not have the process of gas escape, the step of correction of gas escape is omitted, and the chemical composition of geothermal water is directly used as the fluid composition of corrected escape gas for subsequent correction.

[0043] The correction method of mineral precipitation includes: inputting the fluid composition of corrected escape gas into a geochemical program, setting sufficient precipitated mineral composition and making the saturation index 0 to correct the precipitation, and obtaining the fluid composition of corrected mineral precipitation. In the present application, the saturation index is the saturation index under the temperature condition of the reservoir. In the present application, the composition of the precipitated mineral is the mineral composition of spring sinter or scale. In the present application, when the geochemical process does not have the process of mineral precipitation, the step of correction of mineral precipitation is omitted, and the fluid composition of corrected escape gas is directly used as the fluid composition of corrected mineral precipitation for subsequent correction.

[0044] The correction method of cold water mixing includes: determining the cold water mixing ratio X, taking the fluid composition of corrected mineral precipitation as a sample, and obtaining the in-situ composition of geothermal water according to formula 1: Formula 1; In formula 1, is the concentration of a certain component in the in-situ geothermal fluid, mg / L; is the concentration of a certain component in the sample, mg / L; X is the cold water mixing ratio.

[0045] In the present application, the value of X is between 0 and 1, and when the geochemical process does not have the process of cold water mixing, the value of X is 0.

[0046] In the present application, the geochemical program includes one or more of WATCH, GEOT and SOLVEQ.

[0047] Specifically, in the present application, when geothermal water only has cold water mixing and does not have gas escape and mineral precipitation, the in-situ composition of geothermal water is obtained according to formula 1 by taking geothermal water as a sample: Formula 1; In formula 1, is the concentration of a certain component in the in-situ geothermal fluid, mg / L; is the concentration of a certain component in the sample, mg / L; X is the cold water mixing ratio.

[0048] When the cold water mixing and gas escape occur in the geothermal water without mineral precipitation, the quantitative composition of the geothermal gas and the chemical composition of the geothermal water are input into the geochemical program to obtain the composition of the mixed fluid A, and the composition of the fluid A is taken as a sample to obtain the in-situ composition of the geothermal water according to Formula 1.

[0049] When the cold water mixing, gas escape and mineral precipitation occur in the geothermal water, the quantitative composition of the geothermal gas and the chemical composition of the geothermal water are input into the geochemical program to obtain the composition of the mixed fluid A, which is input into the geochemical program to correct the precipitation by setting the sufficient amount of precipitated minerals and the saturation index of the precipitated minerals to 0, to obtain the composition of the fluid B, and the composition of the fluid B is taken as a sample to obtain the in-situ composition of the geothermal water according to Formula 1. In the present application, the geochemical program includes one or more of WATCH, GEOT and SOLVEQ.

[0050] When the cold water mixing and gas escape do not occur in the geothermal water, only the mineral precipitation occurs, the chemical composition of the geothermal water is input into the geochemical program, and the sufficient amount of precipitated mineral composition is set to have a saturation index of 0 under the reservoir temperature condition, and the obtained chemical composition is the in-situ composition of the geothermal fluid.

[0051] When the cold water mixing and mineral precipitation do not occur in the geothermal water, only the gas escape occurs, the chemical composition of the geothermal water and the quantitative composition of the escaped gas are simultaneously input into the geochemical program WATCH or SOLVEQ, and the program is run to obtain the in-situ composition of the geothermal fluid.

[0052] When the cold water mixing does not occur in the geothermal water, only the gas escape and mineral precipitation occur, firstly, the chemical composition of the geothermal water and the quantitative composition of the escaped gas are simultaneously input into the geochemical program WATCH or SOLVEQ, and the program is run to obtain the in-situ composition I of the geothermal fluid; then, the in-situ composition I of the geothermal fluid is input into the geochemical program, and the sufficient amount of precipitated mineral composition is set to have a saturation index of 0 under the reservoir temperature condition, and the obtained chemical composition is the in-situ composition of the geothermal fluid.

[0053] As a specific embodiment of the present application, the in-situ composition correction schematic diagram of the geothermal water is shown in Figure 5 .

[0054] The determination method of the in-situ composition of the geothermal water provided by the present application is described in detail below in combination with examples, but they cannot be understood as limitations to the protection scope of the present application.

[0055] Example 1 Determination of the in-situ composition of a geothermal fluid in a hot spring in Fengshun region, Guangdong (cold water mixing effect): A hot spring emerges in Fengshun County, Guangdong Province. The chemical composition of a sample collected from the surface is shown in Test1 of Table 2. At the time of sampling, the temperature of the hot spring was measured to be 58.3℃, the pH value was 8.23, no bubbles were observed, and there was no scale buildup around the springhead. Preliminary assessment suggests that the hot spring water did not experience gas escape or mineral precipitation.

[0056] Multiple hot springs emerge simultaneously in this area. Based on the Cl-Br and Cl-SiO2 relationship diagrams of multiple hot spring sites and their geological conditions, it is determined that they have undergone cold water mixing. The cold water mixing ratio can be calculated using methods one and three. Figure 6 This diagram illustrates the determination of the mixing ratio of cold water into a geothermal fluid at a hot spring in Fengshun, Guangdong. Figure 6 In the figure, (a) Cl-Br diagram of Fengshun Hot Spring Area; (b) Cl-SiO2 diagram of Fengshun Hot Spring Area; (c) Calculation diagram of the proportion of cold water mixed in hot spring using method one; (d) Calculation diagram of the proportion of cold water mixed in hot spring using method three.

[0057] Following Method 1, a graph was plotted between the mixing ratio and the corresponding hot water end-point temperature. The intersection of the two curves represents the cold water mixing ratio, which was determined to be 0.72, or 72%. Figure 6 (c)); Method 3, the multi-mineral balance method, calculates an enrichment coefficient of 1.4, then the proportion of cold water mixed in is 71.4% ( Figure 6 (d) in the middle.

[0058] Assuming that the content of various ions mixed into the cold water is low and negligible, the in-situ composition of the hot spring water is the chemical composition corresponding to Test1' in Table 2.

[0059] Table 2. In-situ composition results of a hot spring in Fengshun area, Guangdong Province

[0060] Example 2 Determination of the in-situ composition of geothermal fluids in a borehole at Yangbajing (gas escape and mineral precipitation): Yangbajing geothermal field is rich in geothermal resources, with many drilled wells, and hot springs or boiling springs distributed around the area. There are more data of geothermal water and gas samples in the area. In this example, the composition of geothermal water in situ was calculated based on the data of geothermal water and gas samples in the article published by Zhao Ping et al. in 1998. According to the description, there are water and gas phases when sampling at the wellhead, indicating that geothermal water has gas escaping due to decompression. It is not clear whether calcium carbonate scale appears in this well, but relevant data show that there is a problem of calcium scale in the process of geothermal well exploitation in Yangbajing area, so it is assumed that the problem of calcium carbonate precipitation also occurs in geothermal water. Since geothermal water is directly pumped out from the reservoir, it is not affected by the mixing of cold water in the shallow layer. Therefore, it is necessary to correct the gas escape and mineral precipitation to obtain the composition of deep geothermal water in situ. First, the composition of geothermal water YBJ1 and geothermal gas is input into the geochemical program WATCH to add the escaped gas to the geothermal water, and the geothermal fluid YBJ1' is obtained; then it is input into PHREEQC to add calcium carbonate to achieve equilibrium state, and the geothermal fluid YBJ1'' is obtained, which is considered to represent the composition of geothermal fluid in situ.

[0061] Table 3 Composition of geothermal water and geothermal gas in a geothermal well in Yangbajing

[0062] The above only describes the preferred embodiments of the present application, and it should be noted that those skilled in the art can make some improvements and refinements without departing from the principles of the present application, and these improvements and refinements should also be considered within the protection scope of the present application.

Claims

1. A method for determining the in-situ composition of geothermal water, characterized in that, The geothermal water includes hot spring water or geothermal well water, and the method for determining the in-situ composition of the geothermal water includes the following steps: (1) Collecting geothermal water and geothermal gas; when there is travertine or scale at the collection site, it also includes collecting travertine or scale. (2) Determine the chemical composition of the geothermal water, the mineral composition of the travertine or scale, and the geothermal gas composition, wherein the geothermal gas composition includes the absolute content of CO2 and H2S; (3) Based on the geothermal water outburst conditions, determine the geochemical processes that the parent geothermal fluid undergoes as it rises from the deep reservoir to the surface. The geochemical processes include one or more of the following: cold water mixing, gas escape, and mineral precipitation. Correct the in-situ composition of the geothermal water in the order of gas escape, mineral precipitation, and cold water mixing. The method for correcting gas escape includes: inputting the geothermal gas composition and the chemical composition of the geothermal water into a geochemical program to obtain the fluid composition of the escaped gas; The method for correcting mineral precipitation includes: inputting the fluid composition of the escaped gas into a geochemical program, correcting the precipitation by adding sufficient precipitated mineral components and setting their saturation index to 0, and obtaining the fluid composition of the corrected mineral precipitation. The correction method for cold water contamination includes: determining the cold water contamination ratio X, using the fluid composition of the corrected mineral precipitation as a sample, and obtaining the in-situ composition of the geothermal water according to Equation 1: Formula 1; In Equation 1, The concentration of a certain component in the in-situ geothermal fluid is expressed in mg / L. The concentration of a certain component in the sample is expressed in mg / L. X represents the proportion of cold water mixed in.

2. The method according to claim 1, characterized in that, In step (2), the chemical composition of the geothermal water includes the total dissolved solids content, Na... + K + Ca 2+ Mg 2+ F - Cl - SO4 2- HCO3 - / CO3 2- SiO2, Al, Fe, B and Br - Determining the chemical composition of geothermal water also includes testing the pH value of the geothermal water and the temperature at which the pH value is tested; The mineral composition of the travertine or scale includes whole-rock mineral analysis.

3. The method according to claim 1, characterized in that, The geochemical processes involved in determining the ascent of parent geothermal fluids from deep reservoirs to the surface, based on geothermal outburst conditions, include: Observe whether there are bubbles or gas at the hot spring or geothermal well opening. If so, it indicates that gas has escaped. Observe whether there is travertine or scale at the hot spring outlet or geothermal well. If so, it indicates that mineral precipitation has occurred. When there is only one hot spring or geothermal well in the collection area, the state of the geothermal water is determined according to the Na-K-Mg triangle diagram. If the single geothermal hot spot is in the non-equilibrium, partially equilibrium, or mixed zone in the Na-K-Mg triangle diagram, it indicates that cold water has been mixed in. When there are multiple hot springs or geothermal wells in the collection area, the Cl... - or δ 2 H H2O The relationship between Br / B / SiO2 can be used to determine whether geothermal water has been mixed. If multiple geothermal water samples show a linear relationship between Cl-SiO2 or a linear relationship on the Na-K-Mg triangular diagram, it indicates that cold water has been mixed in.

4. The method according to claim 1, characterized in that, The method for determining the cold water mixing ratio is Method 1, Method 2, or Method 3, wherein Method 1 includes the following steps: Assuming there are multiple geothermal water samples in the collection area and no boiling occurs, and assuming the SiO2 concentration and enthalpy of the in-situ geothermal fluid remain constant, and given the enthalpy and SiO2 concentration of the cold water end-member and the geothermal water, the cold water mixing ratio under different hot water end-member conditions can be calculated using Equations 2 and 3. and Plot the mixing ratio against the corresponding hot water end-point temperature; the intersection of the two curves represents the cold water mixing ratio. Formula 2; Formula 3; In Equations 2 and 3, Enthalpy of the cold water end element, kJ / kg; Enthalpy of the hot water end element, kJ / kg; The enthalpy of geothermal water is expressed in kJ / kg. The SiO2 concentration in the cold water end element is mg / L. The concentration of SiO2 in the hot water end element is mg / L; The SiO2 concentration in the geothermal water is expressed in mg / L. The second method includes the following steps: Plot the quartz solubility curve with enthalpy on the x-axis and SiO2 content on the y-axis. Plot the cold water end-unit and geothermal water sample onto the graph, draw a straight line that passes through the cold water end-unit and geothermal water sample and intersects the quartz solubility curve, and calculate the cold water mixing ratio based on the SiO2 concentration values ​​corresponding to the cold water end-unit, hot water end-unit and geothermal sample points. Method 3 includes the following steps: Geothermal water and gas data are input into the geochemical program GEOT or SOLVEQ. Based on the reservoir lithology, possible mineral combinations are selected, enrichment coefficients and steam loss mass fractions are adjusted, and saturation indices of different mineral combinations are calculated under different temperature conditions. Temperature-saturation index curves are plotted with temperature as the x-axis and saturation index as the y-axis. When the curves of multiple mineral saturation indices with temperature change converge to a point, the cold water mixing ratio corresponding to that enrichment coefficient is considered to be the actual cold water mixing ratio.

5. The method according to claim 1, characterized in that, The geochemical procedures include one or more of WATCH, GEOT, and SOLVEQ.

6. The method according to claim 1, characterized in that, The method for collecting geothermal gas includes the following steps: Prepare a three-way bottle with known mass and volume. Fill the three-way bottle with 50 mL of NaOH alkaline solution with a mass concentration of 40% and evacuate it for later use. Geothermal gas was collected into a vacuum-sealed three-way bottle using a gas sampling device, resulting in a mixed solution that absorbed CO2, H2S, and water vapor. The gas sampling device is a funnel and a silicone tube, or a water-gas separator.

7. The method according to claim 6, characterized in that, The method for testing the CO2 and H2S content in the geothermal gas includes: titrating a mixed solution containing CO2, H2S and water vapor with standard hydrochloric acid and standard mercuric acetate, respectively, and determining the absolute content of CO2 and H2S by combining the changes in the mass of the mixed solution before and after sampling.

8. The method according to claim 2, characterized in that, The Na + K + Ca 2+ Mg 2+ F - Cl - SO4 2- and Br - The determination was performed using ion chromatography. The HCO3 - / CO3 2- Determined by back titration; The SiO2, Al, Fe and B were determined by ICP-AES or ICP-OES. The mineral composition of the whole rock was determined using X-ray diffraction.

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