Comprehensive evaluation method for heat storage temperature of hydrothermal geothermal system

Abstract

A comprehensive evaluation method for heat reservoir temperature of a hydrothermal geothermal system is based on the temperature and pressure monitoring data of geothermal wells, logging curves and scaling conditions in the wellbore and surrounding areas, geothermal fluid hydrochemical data, hot spring / boiling spring temperature, spring mouth sediment distribution and fluid component characteristics. The method analyzes the geochemical process experienced by geothermal fluids as they rise from deep reservoirs through boreholes or natural fracture systems to the surface. A reasonable combination of geothermometers is selected based on common degassing, scaling and mixing effects and the application prerequisites of various geothermometers. A reasonable and reliable calculation method is selected for each geothermometer in the combination. The heat reservoir temperature is calculated based on the combination of geothermometers. If the data obtained are consistent, it is considered that the result represents the deep heat reservoir temperature, and a reasonable and reliable heat reservoir temperature of the hydrothermal geothermal system is given.

Description

Technical Field

[0001] The invention belongs to the field of geothermal technology and relates to a comprehensive evaluation method for heat storage temperature of a hydrothermal geothermal system. Background Art

[0002] Heat reservoir temperature is one of the key parameters for conducting geothermal resource research, and is also an important basis for geothermal resource classification, mining potential evaluation, and development and utilization. The acquisition methods include borehole temperature measurement and estimation based on fluid geothermometers. However, in actual work, especially in the early stages of exploration, there are many places where there are no boreholes or the boreholes do not reach the actual heat reservoir. In this case, it is impossible to obtain temperature information of deep heat reservoirs through borehole temperature measurement. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a comprehensive evaluation method for the heat reservoir temperature of a hydrothermal geothermal system. According to the hydrochemical data, the geochemical process is analyzed, and a reasonable combination of geothermometers and calculation formulas are selected. On the basis of establishing a comprehensive evaluation process for the heat reservoir temperature, multiple methods are used in combination to determine the deep heat reservoir temperature of the geothermal system, accurately evaluate the heat reservoir temperature of the hydrothermal geothermal system, and provide a reliable basis for the exploration, development and utilization of geothermal resources.

[0004] In order to solve the above technical problems, the technical solution adopted by the present invention is: a comprehensive evaluation method for heat storage temperature of a hydrothermal geothermal system, which comprises the following steps:

[0005] Step 1, process analysis affecting fluid composition, analyzes the geochemical processes that geothermal fluids undergo as they rise from deep reservoirs through boreholes or natural fracture systems to the surface;

[0006] Step 2: Determine the combination of geothermometers, and determine the applicable combination of geothermometers for geothermal fluids with different effects;

[0007] Step 2-1, for geothermal fluids that have undergone degassing, use a SiO2 adiabatic boiling calibrated geothermometer, a quartz / chalcedony geothermometer based on the SiO2 content in the thermal reservoir fluid components, and a mineral geothermometer of a mineral combination that has undergone degassing correction;

[0008] Step 2-2, for geothermal fluids that have undergone mixing, use the SiO2 / Cl-enthalpy mixing model, the Na-K-Mg triangle diagram, and a mineral combination geothermometer corrected for dilution;

[0009] Step 2-3, for geothermal fluids that have undergone scaling and are accompanied by degassing, a quartz / chalcedony geothermometer based on the SiO2 content of the thermal reservoir fluid and a mineral combination geothermometer corrected for degassing are used;

[0010] Step 2-4, for geothermal fluids that experience degassing, scaling and mixing, or two of these effects, a mineral geothermometer using a Na-K-Mg triangle diagram, a SiO2 / Cl-enthalpy mixing model, and a mineral combination corrected for degassing / mixing effects;

[0011] Step 3, heat reservoir temperature calculation, using different methods to calculate the heat reservoir temperature according to the mineral geothermometer of the mineral combination in step 2;

[0012] Step 4, result evaluation, comprehensively evaluates the heat storage temperature of the geothermal system based on the calculation results of the above different methods.

[0013] In step 1, the analysis is based on the temperature and pressure monitoring data of geothermal wells, logging curves, scaling conditions in the wellbore and surrounding areas, geothermal fluid hydrochemistry data, hot spring / boiling spring temperature, spring mouth sediment distribution and fluid components. Degassing in the wellbore of medium and high temperature geothermal systems will cause a large amount of water vapor and CO2 gas to escape, causing the carbonate mineral saturation index in the remaining geothermal fluid to change, and the content of various ion components to increase. The degree of influence is related to the amount of degassing. The degassing process of boiling springs is similar. After degassing occurs, carbonate rock minerals, SiO2 or other metal sulfides or iron hydroxides in geothermal fluids are prone to supersaturation, and then produce corresponding scaling. The mixing process with shallow groundwater is the dilution process, because the solute content of shallow groundwater is generally much lower than that of geothermal fluids, and it is mostly Ca-type water.

[0014] In step 1, geothermal fluid analysis data including TDS, Na + , K + , Ca 2+ Mg 2+ , Cl - 、SO4 2- 、HCO3 - / CO3 2- , SiO2, Al, B, Br, Li.

[0015] SiO2 adiabatic boiling correction thermometer,

[0016] T=-53.5+0.11236·S-0.5559×10 -4 ·S 2 +0.1772×10 -7 ·S 3 +88.39logS; Quartz thermometer, T = -55.3 + 0.3659·S -5.3954×10 -4 ·S 2 +5.5132×10 -7 ·S 3 +74.36logS; Chalcedony geothermometer, Where T is the heat reservoir temperature, unit is °C; S is the concentration of SiO2 in the geothermal fluid, unit is mg / L.

[0017] Na-K geothermometer in Na-K-Mg triangle diagram, K-Mg geothermometer, Where T is the heat storage temperature in °C; Na / K and K 2 The unit of concentration of Na, K and Mg in / Mg is mg / L.

[0018] Cl-enthalpy mixed model, in which the enthalpy value of a single sample is selected. For cold water and spring water with lower temperature, the temperature is measured. The relationship between temperature and enthalpy corresponds to the saturated water vapor table to obtain the enthalpy value of liquid water at that temperature.

[0019] The mineral assemblage geothermometer uses the geochemical applet GEOT or SOLVEQ to estimate the temperature of the heat reservoir.

[0020] The beneficial effects of the present invention are:

[0021] The geochemical processes that geothermal fluids undergo when rising from deep heat reservoirs to the surface are analyzed, and a combination of geothermometers corresponding to different geochemical processes is established. For each thermometer in the combination, the heat reservoir temperature is calculated using the corresponding calculation method. Based on the heat reservoir temperatures calculated by various geothermometers and a comprehensive evaluation using a geochemical applet, the representative deep heat reservoir temperature is determined. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The present invention will be further described below in conjunction with the accompanying drawings and embodiments:

[0023] Figure 1 It is a flow chart for comprehensive evaluation of heat reservoir temperature in hydrothermal geothermal system.

[0024] Figure 2 It is the Cl-Li and Cl-TDS correlation diagram of geothermal water;

[0025] Figure 3 It is the Na-K-Mg triangle diagram of geothermal water.

[0026] Figure 4 It is the geothermal water Cl- enthalpy mixing diagram.

[0027] Figure 5 It is a geothermal thermometer diagram of geothermal water mineral combination. DETAILED DESCRIPTION

[0028] like Figure 1 to Figure 5 A method for comprehensively evaluating the thermal storage temperature of a hydrothermal geothermal system comprises the following steps:

[0029] Step 1, process analysis affecting fluid composition, analyzes the geochemical processes that geothermal fluids undergo as they rise from deep reservoirs through boreholes or natural fracture systems to the surface; the purpose of this step is to identify the geochemical processes that geothermal fluids undergo at the surface.

[0030] Preferably, the geochemical processes occurring when geothermal fluids rise from deep underground through a borehole or fracture system to the surface mainly include degassing, scaling and mixing.

[0031] Preferably, degassing: It is usually possible to judge whether degassing has occurred based on the relevant characteristics of geothermal fluids collected from the surface. For geothermal wells, it is possible to judge whether degassing has occurred based on the wellhead sample conditions, such as fluid temperature and gas conditions, and the wellbore temperature and pressure curve. For naturally exposed hot springs, it can be judged based on the fluid temperature at the spring mouth. Generally, when the temperature is lower than the local boiling point, it can be considered that no degassing has occurred or the degassing effect can be ignored. For geothermal fluids with temperatures exceeding the local boiling point, it is assumed that a certain degree of degassing has occurred, especially when the CO2 content in the gas is high, and the degassing effect has a greater impact on the chemical composition of the geothermal fluid.

[0032] Preferably, scaling effect: observe the sediment in the wellbore, wellhead or spring to determine whether scaling occurs; or monitor the wellhead temperature, pressure and flow data. If the pressure increases and the flow decreases, it is considered that scaling occurs in the wellbore. Alternatively, use the logging curve or multi-claw test to determine whether scaling occurs in the wellbore.

[0033] Preferably, mixing: Generally, it can be analyzed with the help of fluid hydrochemistry and isotope data, such as using the correlation between the conservative element Cl content of geothermal fluid and Li and TDS and the Na-K-Mg triangle diagram to determine whether mixing has occurred during its ascent to the surface. If the Cl content shows a good linear correlation with the Li and TDS content, and the geothermal fluid sample points on the Na-K-Mg triangle diagram show a straight line distribution passing through the Mg end member, it is considered that mixing has occurred.

[0034] Step 2, geothermometer combination, determine the applicable geothermometer combination for geothermal fluids with different effects; the purpose of this step is to reasonably select a geothermometer combination. Since there are multiple empirical formulas for the same geothermometer, such as 13 SiO2 geothermometers, 6 quartz geothermometers, and 3 chalcedony geothermometers, it is necessary to select the most reasonable and reliable calculation method based on the establishment conditions and data of each method.

[0035] Step 2-1, for geothermal fluids that have undergone degassing, use a SiO2 adiabatic boiling calibrated geothermometer, a quartz / chalcedony geothermometer based on the SiO2 content of the thermal reservoir fluid, and a mineral geothermometer of a mineral combination that has undergone degassing correction;

[0036] Step 2-2, for geothermal fluids that have undergone mixing, use the SiO2 / Cl-enthalpy mixing model, the Na-K-Mg triangle diagram, and a mineral combination geothermometer corrected for dilution;

[0037] Step 2-3, for geothermal fluids that have undergone scaling and are accompanied by degassing, a quartz / chalcedony geothermometer based on the SiO2 content of the thermal reservoir fluid and a mineral combination geothermometer corrected for degassing are used;

[0038] Step 2-4, for geothermal fluids that experience degassing, scaling and mixing, or two of these effects, use a Na-K-Mg triangle diagram, a SiO2 / Cl-enthalpy mixing model, and a mineral combination geothermometer corrected for degassing / mixing effects;

[0039] Step 3, heat storage temperature calculation, according to the geothermometer in step 2, the heat storage temperature is calculated by different methods;

[0040] Step 4, result evaluation, comprehensively evaluate the heat reservoir temperature of the geothermal system based on the calculation results of the above different methods. Based on the determination of the geochemical process that the geothermal fluid goes through when it rises from the deep heat reservoir to the surface, a reasonable combination of geothermometers is used to determine the representative deep heat reservoir temperature.

[0041] In the preferred scheme, in step 1, the analysis is based on the temperature and pressure monitoring data of the geothermal well, the logging curve and the scaling conditions of the wellbore and the surrounding area, as well as the water chemistry data of the geothermal fluid, the temperature of the hot spring / boiling spring, the distribution of the spring mouth sediments and the fluid composition.

[0042] In a preferred embodiment, in step 1, the geothermal fluid analysis data includes TDS, Na + , K + , Ca 2+ Mg 2+ , Cl - 、SO4 2- 、HCO3 - / CO3 2- , SiO2, Al, B, Br, Li.

[0043] In the preferred embodiment, the SiO2 adiabatic boiling correction thermometer,

[0044] T=-53.5+0.11236·S-0.5559×10 -4 ·S 2 +0.1772×10 -7 ·S 3 +88.39logS; Quartz thermometer, T = -55.3 + 0.3659·S -5.3954×10 -4 ·S2 +5.5132×10 -7 ·S 3 +74.36logS; Chalcedony geothermometer, Where T is the heat reservoir temperature, unit is °C; S is the concentration of SiO2 in the geothermal fluid, unit is mg / L.

[0045] Preferably, the temperature of the geothermal water exceeds or approaches the local boiling point of 89°C, so the geothermal hot spring fluid may have been degassed. A SiO2 adiabatic boiling thermometer, a quartz / chalcedony thermometer based on the SiO2 content of the heat storage fluid, and a mineral combination thermometer corrected for degassing are used.

[0046] In the preferred embodiment, the Na-K geothermometer in the Na-K-Mg triangle diagram, K-Mg geothermometer, Where T is the heat storage temperature in °C; Na / K and K 2 The unit of concentration of Na, K and Mg in / Mg is mg / L.

[0047] Preferably, the analysis is performed with the aid of fluid water chemistry data, for the conservative element Cl-Li relationship diagram, Cl-TDS correlation diagram and Na-K-Mg triangle diagram proposed by Giggenbach, see the attached Figure 2 and Figure 3 , all show a good linear relationship, indicating that deep fluids can mix with shallow water to varying degrees during the process of rising to the shallow part. If mixing occurs, geothermal water exposed to the surface is formed.

[0048] Preferably, the composition of the springs near different geothermal water outlets is different. Only a small amount of springs are found near the spring mouth. The main minerals of the springs are calcite, gypsum, and quartz precipitation, of which calcite accounts for 94.0%. As the pressure decreases during the ascent, carbon dioxide escapes from the solution, and the result of carbonation produces carbonate precipitation.

[0049] Preferably, geothermal fluids mainly undergo mixing and degassing during their ascent. Based on the effect of geothermal water on chemical composition changes during its ascent to the surface, it is more accurate to evaluate the thermal reservoir temperature by combining the Na-K-Mg triangle diagram, the silicon / Cl-enthalpy mixing model, and a mineral combination geothermometer corrected for degassing / mixing effects.

[0050] Preferably, according to the selected Giggenbach's cation geothermal thermometer Na-K-Mg triangle diagram (see Figure 3 ), it can be seen that the water samples are distributed along the mixing line, indicating a tendency to mix with cold water. The reservoir temperature obtained from the Na-K-Mg triangle diagram is about 200-210 °C.

[0051] In the preferred scheme, the Cl-enthalpy mixed model is used, in which the enthalpy value of a single sample is selected. For cold water and spring water with a lower temperature, the temperature is measured. The relationship between temperature and enthalpy corresponds to the saturated water vapor table, and the enthalpy value of liquid water at this temperature is obtained.

[0052] Preferably, the Cl-enthalpy diagram is very effective for evaluating the specific cooling process that the geothermal fluid undergoes during the ascent. Cl is a conservative element that indicates the mixing process of the geothermal fluid. Due to processes such as adiabatic degassing during the ascent, the enthalpy of hot water under mixing is less than the enthalpy of hot water in the deep reservoir. Therefore, the reservoir temperature and Cl concentration of deep geothermal fluids can be evaluated by the Cl-enthalpy mixing model (see Figure 2). Figure 4 ). The enthalpy of geothermal water samples is obtained from the saturated steam table of pure water at the sampling temperature.

[0053] Preferably, the adiabatic degassing line of the deep heat reservoir is composed of a line connecting two points, one of which is a point with an enthalpy corresponding to the enthalpy of saturated steam at 100°C (2676kJ / kg) and a chloride ion concentration of 0mg / L. The other point is the sample point of the straight line with the most negative slope passing through the geothermal water sample. Next, a mixing line is drawn, one end of which is the end member of the shallow cold water, represented by the enthalpy value and the average chloride ion concentration of the river water sample point, and the other end forms a mixing trend line through the geothermal water point where mixing occurs. The mixing line intersects with the adiabatic degassing line with the largest negative slope at one point, which represents the state of the geothermal fluid deep in the heat reservoir. The enthalpy of the deep geothermal fluid is 898kJ / kg. The reservoir temperature obtained by checking the saturated steam table is about 210°C, which is consistent with the heat reservoir temperature obtained by the cation geothermometer.

[0054] In the preferred solution, the mineral combination geothermometer uses the geochemical applet GEOT or SOLVEQ to estimate the heat reservoir temperature. The purpose of this step is to select a reasonable geothermometer combination and a reliable geothermometer calculation formula based on the geochemical process experienced by the geothermal fluid collected from the surface, and determine the representative heat reservoir temperature.

[0055] Preferably, the thermal reservoir temperature obtained by the above method is the temperature of the original geothermal fluid, that is, the temperature of the fluid whose original chemical composition characteristics have not been changed.

[0056] Preferably, the mineral combination geothermal thermometer simulated by geochemical thermodynamics is a thermometer that simulates the deep reservoir temperature of geothermal fluid based on the multi-component chemical equilibrium of the geothermal system. This example uses the SOLVEQ-XPT program to calculate the saturation index of each mineral at different temperatures. The mineral combination geothermometer calculates the mineral saturation index at different temperatures based on the chemical composition of the geothermal water through the SOLVEQ-XPT program, so as to obtain the equilibrium temperature of water and this group of minerals (such as Figure 5), the step size of temperature growth is set to 20℃, the selection of equilibrium minerals depends on the reservoir lithology and hydrogeochemical characteristics of the study area, in order to eliminate the influence of CO2 degassing, equal amounts of HCO3 and H are added to geothermal water to generate additional CO2, when 0.1 mol / L CO2 gas is added to the geothermal fluid, the saturation index curves of each mineral converge to one point, the temperature range of this point is 180~210℃, which is consistent with the heat reservoir temperature obtained by the Cl-enthalpy thermometer and the cation thermometer. In summary, the deep heat reservoir temperature of this geothermal field is 180~210℃, which belongs to a high-temperature geothermal system.

[0057] Embodiment 1, estimation of geothermal field heat storage temperature;

[0058] If the temperature of geothermal water collected from the surface exceeds or approaches the local boiling point of 89°C, it is considered to have degassed;

[0059] Field observations revealed a small amount of sediment at the mouths of hot springs or boiling springs. Analysis showed that its chemical composition was carbonate, which suggests that a small amount of scaling also occurred during the ascent of the geothermal fluid.

[0060] In addition, the geothermal water Cl-Li, Cl-TDS and Na-K-Mg triangle diagrams show that Figure 2 and Figure 3 , obvious mixing occurs during the rise of geothermal fluids to the surface.

[0061] The Na-K-Mg triangle diagram, the Si / Cl-enthalpy mixing model and the mineral combination geothermometer with degassing / mixing correction were used to calculate the reservoir temperature according to the formula: Na-K geothermometer in the Na-K-Mg triangle diagram, K-Mg geothermometer, Where T is the heat storage temperature in °C; Na / K and K 2 The concentration units of Na, K and Mg in / Mg are mg / L. Figure 3 to Figure 5 shown.

[0062] The above-mentioned embodiments are only preferred technical solutions of the present invention and should not be regarded as limitations of the present invention. The embodiments and features in the embodiments of the present application can be arbitrarily combined with each other without conflict. The protection scope of the present invention shall be the technical solutions recorded in the claims, including the equivalent replacement solutions of the technical features in the technical solutions recorded in the claims. That is, equivalent replacement improvements within this scope are also within the protection scope of the present invention.

Claims

1. A comprehensive evaluation method for heat storage temperature of a hydrothermal geothermal system, characterized in that: It includes the following steps: Step 1, process analysis affecting fluid composition, analyzes the geochemical processes that geothermal fluids undergo as they rise from deep reservoirs through boreholes or natural fracture systems to the surface; Step 2, geothermal thermometer combination determination, for geothermal fluids with different geochemical reactions, determine the applicable geothermal thermometer combination; Step 2-1, for geothermal fluids that have undergone degassing, use a SiO2 adiabatic boiling calibrated geothermometer, a quartz / chalcedony geothermometer based on the SiO2 content of the thermal reservoir fluid, and a mineral combination geothermometer calibrated for degassing; Step 2-2, for geothermal fluids that have undergone mixing, use the SiO2 / Cl-enthalpy mixing model, the Na-K-Mg triangle diagram, and a mineral combination geothermometer corrected for dilution; Step 2-3, for geothermal fluids that have undergone scaling and are accompanied by degassing, a quartz / chalcedony geothermometer based on the SiO2 content of the thermal reservoir fluid and a mineral combination geothermometer corrected for degassing are used; Step 2-4, for geothermal fluids that experience degassing, scaling and mixing, or two of these effects, use a Na-K-Mg triangle diagram, a SiO2 / Cl-enthalpy mixing model, and a mineral combination geothermometer corrected for degassing / mixing effects; Step 3, heat storage temperature calculation, according to the combination of geothermal thermometers in step 2, different methods are used to calculate the heat storage temperature respectively; Step 4, result evaluation, comprehensively evaluates the heat storage temperature of the geothermal system based on the calculation results of the above different methods.

2. The method for comprehensive evaluation of heat storage temperature of a hydrothermal geothermal system according to claim 1 is characterized in that: In step 1, the analysis is based on the temperature and pressure monitoring data of the geothermal well, the logging curve, the scaling conditions in the wellbore and surrounding areas, the hydrochemical data of the geothermal fluid, the temperature of the hot spring / boiling spring, the distribution of spring mouth sediments and the fluid composition.

3. The method for comprehensive evaluation of heat storage temperature of a hydrothermal geothermal system according to claim 1 is characterized in that: In step 1, geothermal fluid analysis data includes TDS, Na + , K + , Ca 2+ Mg 2+ , Cl - 、SO4 2- 、HCO3 - / CO3 2- , SiO2, Al, B, Br, Li.

4. The method for comprehensive evaluation of heat storage temperature of a hydrothermal geothermal system according to claim 1 is characterized by: SiO2 adiabatic boiling correction thermometer, T=-53.5+0.11236·S-0.5559×10 -4 ·S 2 +0.1772×10 -7 ·S 3 +88.39logS; Quartz thermometer, T = -55.3 + 0.3659·S -5.3954×10 -4 ·S 2 +5.5132×10 -7 ·S 3 +74.36logS; Chalcedony geothermometer, Where T is the heat reservoir temperature, unit is °C; S is the concentration of SiO2 in the geothermal fluid, unit is mg / L.

5. The method for comprehensive evaluation of heat storage temperature of a hydrothermal geothermal system according to claim 1, characterized in that: Na -Na-K geothermometer in K-Mg triangle diagram, K-Mg geothermometer, Where T is the heat storage temperature in °C; Na / K and K 2 The unit of concentration of Na, K and Mg in / Mg is mg / L.

6. The method for comprehensive evaluation of heat storage temperature of a hydrothermal geothermal system according to claim 1 is characterized by: Cl-enthalpy mixed model, in which the enthalpy value of a single sample is selected. For cold water and spring water with lower temperature, the temperature is measured. The relationship between temperature and enthalpy corresponds to the saturated water vapor table to obtain the enthalpy value of liquid water at that temperature.

7. The method for comprehensive evaluation of heat storage temperature of a hydrothermal geothermal system according to claim 1 is characterized by: The mineral assemblage geothermometer uses the geochemical applet GEOT or SOLVEQ to estimate the temperature of the heat reservoir.

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