Method for calculating conductivity of supercritical geothermal fluid system KCl-H2O

Abstract

The invention discloses a method for calculating the conductivity of a supercritical geothermal fluid system KCl-H2O, which relates to the technical field of new energy, and comprises the following steps: acquiring basic parameters of system temperature, ionic strength, dielectric constant and water density, and constructing a total conductivity expression according to the parameters to calculate the conductivity. According to the method, a Shedlovsky correction model is introduced to be combined with a step-by-step dilution method, experimental data are extrapolated to infinite dilution conditions, then the quantitative relation between the limit molar conductivity of KCl and temperature and pressure is obtained, a Watson viscosity model and crystallographic ion radius parameters are introduced, a high-temperature and high-pressure diffusion coefficient calculation formula is corrected, the prediction error of the diffusion coefficients of K + and Cl-is reduced to be within + / -5%, and the prediction accuracy of the KCl-diffusion coefficient is improved. The coupling rule of the activity coefficient and the diffusion coefficient at high temperature and high pressure is disclosed by synchronously measuring the activity coefficient and the diffusion coefficient, and key parameter support is provided for an earth deep fluid evolution model.

Description

Technical Field

[0001] The present invention relates to the field of new energy technology, in particular to a supercritical geothermal fluid system KCl - H 2 O The conductivity calculation method. Background Art

[0002] Geothermal energy, as a non-carbon, clean energy source, holds strategic importance in energy restructuring. Supercritical geothermal fluids (temperature >374°C, pressure >22.1 MPa) are a core target for deep geothermal resource exploration and development due to their high enthalpy (3200 kJ / kg), low viscosity, and strong permeability. The physicochemical properties of electrolytes in fluids under high-temperature and high-pressure environments are an important research topic in Earth science, playing a key role in deep geological processes, mineralization, and the evolution of hydrothermal systems. The activity coefficient and ion diffusion coefficient of electrolyte solutions are not only core parameters for understanding fluid-rock interactions, element migration mechanisms, and the evolution of ore-forming fluids, but also provide fundamental data support for constructing models of deep Earth material circulation. However, the measurement of the activity coefficient and ion diffusion coefficient of KCl solutions under high-temperature and high-pressure conditions remains limited, severely restricting the calculation of electrical conductivity.

[0003] Conventional high-pressure devices (such as diamond anvil cells and multi-faceted top presses) are prone to fluid leakage or electrode contamination at pressures >500 MPa, and temperature fluctuations (above ±5°C) lead to poor repeatability of experimental data. For example, Su Genli et al. (2000) measured the KCl When measuring solution conductivity, the pressure fluctuation was controlled within ±2% by optimizing the combination of polytetrafluoroethylene sample tube and pyrophyllite pressure transmission medium.

[0004] Furthermore, high-frequency AC conductivity methods are susceptible to dielectric loss and electrode polarization at high voltages, leading to conductivity signal distortion. Su Genli's team employed a ZLR-5 bridge and a 12-100 kHz broadband AC signal, combined with complex impedance plane analysis, to effectively eliminate electrode polarization interference.

[0005] Debye-Hückel The limitation of the equation is that the existing activity coefficient calculation depends on Debye-Hückel Theory, but its applicable ionic strength range (<0.1 mol / kg) in supercritical fluids (such as high temperature and high pressure KCl Su Genli et al. (2000) found through experiments that the deviation between the predicted value and the measured value of the traditional model at 500℃ and 50 MPa exceeded 20%, and it was necessary to introduce ShedlovskyCorrect the model to improve accuracy. Diffusion coefficient extrapolation error. Existing studies mostly extrapolate high-temperature and high-pressure diffusion coefficients using low-pressure test data, but the ion size effect and nonlinear viscosity changes are not fully quantified. Su Genli's team combined Watson Viscosity model and crystallographic ionic radius parameters, K + and Cl - The prediction error of the diffusion coefficient is controlled within ±5%.

[0006] Existing research on high-temperature and high-pressure electrolytes often focuses on a single parameter (such as activity coefficient or diffusion coefficient), and lacks quantitative analysis of the coupling relationship between the two, resulting in insufficient reliability of fluid-rock interaction models (such as hydrothermal alteration and mineralizing fluid migration). Summary of the Invention

[0007] To solve the above problems, this application proposes a supercritical geothermal fluid system KCl - H 2 O The conductivity calculation method comprises the following steps: S1. Obtaining basic parameters, including system temperature, ionic strength, dielectric constant, and water density; S2. Construct conductivity basic expression, salinity correction term expression, and comprehensive correction factor expression based on basic parameters; The comprehensive correction factor includes the limiting molar conductivity ∧0 and the average activity coefficient , diffusion effect term and porous medium correction term; Introduction Shedlovsky The modified model was combined with the stepwise dilution method to extrapolate the experimental data to infinite dilution conditions and obtain KCl The quantitative relationship between the limiting molar conductivity and temperature and pressure gives the limiting molar conductivity ∧0; Introduction Watson The viscosity model and crystallographic ionic radius parameters are used to correct the high temperature and high pressure diffusion coefficient calculation. K + and Cl - The tracer diffusion coefficient and Then construct the diffusion effect term; S3. Use the salinity correction term expression and the comprehensive correction factor expression to correct the basic conductivity expression to obtain the total conductivity expression.

[0008] Preferably, the basic expression of conductivity in S2 is: ; Among them, the constant term C 0=-1.706,C 1=-93.78, C2=3.0781, is the density of water, T is the temperature, The basic conductivity.

[0009] Preferably, the salinity correction term in S2 is expressed as: ; in, for KCl The quality score, is the salinity correction term, C 3=0.8075.

[0010] Preferably, the expression of the comprehensive correction factor in S2 is: ; in, is the comprehensive correction factor, ∧0 is the limiting molar conductivity, is the average activity coefficient, which reflects the strength of ion interaction (deviation between activity and concentration). The value needs to be combined with temperature (T) and solution density (ρ) to correct the "effective concentration" of ion interaction. Substitute the ionic strength into the modified Debye-Hückel correction equation, and then use the Pitzer equation to make high concentration corrections to obtain the average activity coefficient. and represent K + and Cl - The tracer diffusion coefficient, is the density of water, T is the temperature, This is the inhibition term of rock salt precipitation on conductivity, i.e., the porous medium correction term. It is used to correct the problem caused by rock salt precipitation blocking pores, which leads to a reduction in ion migration channels and a decrease in conductivity. Since the pore structure of porous media is fractal (pore size and shape are self-similar), the blocking effect of rock salt precipitation needs to be described using fractal theory. The conductivity model based on fractal porous media (fractal extension of Archie's formula) and the volume effect of rock salt precipitation are derived. Infinite dilution KCl The reference state self-diffusion coefficient of water in solution (eliminating the interference of ions on the water structure, as a reference for an ideal solvent), is the ratio of rock salt precipitation volume to pore space, is the ratio of the original pore volume of the rock to the total volume.

[0011] Preferably, the expression of limiting molar conductivity is: ; in, I is the ionic strength based on volume molarity, ∧ m It is obtained from experimental measurements KCl The molar conductivity, A and B It is a constant calculated from the dielectric constant, viscosity and temperature of water.

[0012] Preferably, the modified expression of the activity coefficient is: ; in, and yes Debye - Hückel coefficient, is the molar concentration conversion factor, is the ionic strength based on mass molarity; ; ; in, 、 K + 、Cl - The charge, and d represent the expansion term parameter and ion size parameter of the equation respectively, It refers to the sum of the mass molar concentrations of all solutes in the solution, R is the gas constant, and T refers to the temperature.

[0013] Preferably, K + and Cl - The expression of the tracer diffusion coefficient is: ; in, and Represent the solution i tracer diffusion coefficient and limiting molar conductivity of ions, i For ionic elements, R is the gas constant, T Refers to temperature, represent i The absolute value of the ion's charge, F is the Faraday constant; Expressed as: ; Where: η represents the Poisson viscosity of the solution, e is the electron charge, Ionic Stoke cm radius, is pi; Thin KCl in solution K + and Cl - The limiting molar conductivity can be expressed as: ; ; Where: and They are K + and Cl - The limiting molar conductivity, and They are K + and Cl - The limiting migration number of the ion, , for KCl The limiting molar conductivity, It is the chloride ion in solid rock salt; It is the potassium ion in solid rock salt; K + and Cl - The limiting migration number is: ; ; The expression is: ; Where, is the crystal radius of the ion, for cations =0.94, for anions =0.00, is the migration number of anions under infinite dilution conditions, is the migration number of the cation under infinite dilution conditions, for K + The Stokes radius, for Cl - The Stokes radius is the effective radius of an ion when it moves in a solution, which includes the crystallographic radius of the ion itself and the thickness of the surrounding solvation layer. For rock salt ( KCl （s）) Fractal characteristic radius of the precipitation particles.

[0014] Preferably, the porous media correction term The expression is: ; in, is the ratio of rock salt precipitation volume to pore space, is the ratio of the original pore volume of the rock to the total volume.

[0015] Preferably, the overall expression of conductivity is: ; in, is the total conductivity.

[0016] Compared with conventional technologies, one or more technical solutions provided by this application have at least the following technical effects: 1. Multi-parameter coupling calculation model, introducing the Shedlovsky correction model, combined with the stepwise dilution method, extrapolating the experimental data to infinite dilution conditions, obtaining the quantitative relationship between the limiting molar conductivity of KCl and temperature and pressure (R²>0.99), introducing the Watson viscosity model and crystallographic ion radius parameters, and correcting the high temperature and high pressure diffusion coefficient calculation formula. K + and Cl - The prediction error of the diffusion coefficient is reduced to within ±5%; 2. Systematic dataset construction: By synchronously measuring the activity coefficient and diffusion coefficient, the coupling law between the two at high temperature and high pressure is revealed (for example, the activity coefficient increases exponentially with increasing pressure, while the diffusion coefficient is linearly positively correlated with temperature), providing key parameter support for the deep Earth fluid evolution model.

[0017] The technical method of the present invention is further described in detail below through the accompanying drawings and examples. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A supercritical fluid system of the present invention The relationship between the molar conductivity of 0.01mol / LKCl solution and density under isothermal conditions; Figure 2 The supercritical fluid system of the present invention The conductivity calculation method under isothermal conditions K + and Cl - The relationship between the tracer diffusion coefficient and pressure, Figure 2(a) is a method for calculating the conductivity of a supercritical fluid system under isothermal conditions. K + The relationship between the tracer diffusion coefficient and pressure, Figure 2 (b) is a method for calculating the conductivity of a supercritical fluid system under isothermal conditions. Cl - Plot of the tracer diffusion coefficient as a function of pressure; Figure 3 It is a supercritical fluid system The conductivity calculation method of 0.01mol / LKCl solution KCl The relationship between the average molar activity coefficient and pressure; Figure 4 It is a supercritical fluid system Flowchart of the conductivity calculation method. DETAILED DESCRIPTION

[0019] The technical method of the present invention is further described below through the accompanying drawings and embodiments. It should be noted that unless otherwise specifically stated, the relative arrangement of components and steps, numerical expressions and values ​​described in these embodiments do not limit the scope of this application.

[0020] The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the present disclosure, its application, or uses.

[0021] Technologies, systems, and devices known to those of ordinary skill in the relevant art may not be discussed in detail, but where appropriate, they should be considered part of the specification.

[0022] In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not limiting. Therefore, other examples of the exemplary embodiments may have different values.

[0023] Unless otherwise defined, technical or scientific terms used in the present invention shall have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs.

[0024] The present invention provides a supercritical geothermal fluid system KCl - H 2 O The conductivity calculation method comprises the following steps: S1. Obtaining basic parameters, including system temperature, ionic strength, dielectric constant, and water density; A high-temperature furnace provides the required temperature conditions, and thermocouples are inserted into the reaction system to directly measure the temperature. Commonly used thermocouple types include platinum-rhodium-platinum (PtRh-Pt) thermocouples, which can remain stable at high temperatures and have a measurement range of 500 to 800°C. Alternatively, based on thermodynamic models and heat transfer equations, computational fluid dynamics (CFD) software or custom programs can be used to solve the heat transfer equations based on the thermodynamic properties and heat transfer mechanisms of the system in numerical simulations of multi-physics processes to obtain the temperature distribution at each point in the system. If some temperature data points are known, the temperature field can be constructed through interpolation or fitting methods to estimate the temperature values ​​at other locations.

[0025] Mass spectrometry technology combines fluid samples in high temperature and high pressure environments with a mass spectrometer to achieve accurate measurement of ion intensity. This technology is suitable for trace ion detection (such as fluid monitoring in nuclear waste disposal repositories) and in-situ analysis of mineral-fluid interface reactions, but it needs to overcome the sample stability under high temperature and high pressure (such as KCl hydrolysis), container material compatibility, and complex matrix interference, while relying on a high-precision temperature and pressure control system and an online dilution / quenching device to ensure data reliability.

[0026] Dielectric spectroscopy technology uses a high-temperature and high-pressure dielectric cell to achieve in-situ measurement of dielectric constants under extreme conditions. Its core device includes a pressure-resistant sapphire or diamond window, a platinum electrode, and a Hastelloy sealed container, which can stably accommodate dielectric constants at 100~500℃ and 100~1200MPa. KCl - H 2 O In the experiment, a network analyzer applied an AC electric field of 1 MHz to 1 GHz to detect the complex dielectric response of the sample, and the static dielectric constant ( ) and relaxation time ( ), revealing the coupling mechanism between ion orientation polarization and temperature and pressure.

[0027] Due to the high temperature of the supercritical state, water's density is typically calculated based on parameters such as temperature and pressure using equations of state (such as the IAPWS formulation) or thermodynamic models (such as the Helgeson-Kirkham-Flowers equations of state). Alternatively, existing data on the relationship between water density, temperature, and pressure can be directly referenced to estimate water density under specific conditions through interpolation or empirical formulas.

[0028] S2. Construct conductivity basic expression, salinity correction term expression, and comprehensive correction factor expression based on basic parameters; The comprehensive correction factor includes the limiting molar conductivity ∧0 and the average activity coefficient , diffusion effect term and porous medium correction term; By fitting the experimental data, the basic expression of conductivity in S2 is: ; Among them, the constant term C 0=-1.706, C 1=-93.78, C2=3.0781, is the density of water, T is the temperature, is the conductivity.

[0029] This formula reflects the decrease in σ due to association after the ion activity is enhanced at high temperature, as well as the hindering effect of density on ion migration.

[0030] Quality score It is positively correlated with conductivity, but ion association is enhanced at high salinity.

[0031] The salinity correction term is obtained by fitting the experimental data through the Hückel equation. The expression of the salinity correction term in S2 is: ; in, for KCl The quality score, is the salinity correction term, C 3=0.8075.

[0032] Preferably, the expression of the comprehensive correction factor in S2 is: ; in, is the comprehensive correction factor, ∧0 is the limiting molar conductivity, is the average activity coefficient, which reflects the strength of ion interaction. The value needs to be combined with the temperature T and the solution density ρ to correct the effective concentration of ion interaction. The ion strength is substituted into the modified Debye-Hückel correction equation, and then the high concentration correction is performed using the Pitzer equation to obtain the average activity coefficient. and represent K + and Cl - The tracer diffusion coefficient, is the density of water, T is the temperature, The inhibition term of rock salt precipitation on conductivity is the porous medium correction term, which is used to correct the problem caused by rock salt precipitation blocking pores, resulting in a reduction in ion migration channels and a decrease in conductivity. Since the pore structure of porous media is fractal, the blocking effect of rock salt precipitation needs to be described by fractal theory. The conductivity model based on fractal porous media and the volume effect of rock salt precipitation are derived. is the reference state self-diffusion coefficient of water in infinitely dilute KCl solution, is the ratio of rock salt precipitation volume to pore space, is the ratio of the original pore volume of the rock to the total volume.

[0033] Introduction Shedlovsky The modified model was combined with the stepwise dilution method to extrapolate the experimental data to infinite dilution conditions and obtain KCl The quantitative relationship between the limiting molar conductivity and temperature and pressure gives the limiting molar conductivity (∧0); The limiting molar conductivity (∧0) is calculated using the Debye-Hückel-Onsager equation. The molar conductivity of the solution is extrapolated to the infinite dilution case to obtain the limiting molar conductivity. The expression of the limiting molar conductivity is: ; in, I It is the ionic strength based on the volume molar concentration and is used to quantify the effect of electrostatic interactions between ions in KCl solution on the experimental molar conductivity. m It is obtained from experimental measurements KCl The molar conductivity, A and B It is a constant calculated from the dielectric constant, viscosity and temperature of water.

[0034] parameter A 、 B It can be calculated according to the following formula: ; ; in, is the relative dielectric constant of the solution, a key parameter that describes the solution's ability to respond to electric field polarization. The larger it is, the stronger the "screening effect" of the solution on the Coulomb force between ions (that is, the weaker the interaction between ions).

[0035] The average molar activity coefficient of electrolytes in solution ( ) is: ; in, and yes Debye - Hückel coefficient, is the molar concentration conversion factor, The ionic strength is based on mass molar concentration and is used to quantify the effect of electrostatic interaction between ions in KCl solution on the average activity coefficient (reflecting the combined effect of ion concentration and charge); ; ; in, 、 They are K + 、 Cl - The charge, and d represent the expansion term parameter and ion size parameter of the equation respectively, m Refers to the sum of the mass molar concentrations of all solutes in a solution. R is the gas constant, T Refers to temperature.

[0036] Introduction Watson The viscosity model and crystallographic ionic radius parameters are used to correct the high temperature and high pressure diffusion coefficient calculation. K + and Cl - The tracer diffusion coefficient and Then construct the diffusion effect term; The relationship between the limiting molar conductivity of an ion and its tracer diffusion coefficient is expressed by the Nernst-Einstein equation, K + and Cl - The expression of the tracer diffusion coefficient is: ; in, and Represent the solution i tracer diffusion coefficient and limiting molar conductivity of ions, i For ionic elements, R is the gas constant (8.31 J·mol -1 ·K -1 ), T Refers to temperature (K), represent i The absolute value of the ion's charge, F is the Faraday constant (96485 C / mol); Expressed as: ; Where: η represents the Poisson viscosity of the solution, e is the electron charge (1.602×10 -19 C), Ionic Stoke cm radius, is pi; Introducing Watson viscosity model and crystallographic ionic radius parameters, correcting K + / Cl — The tracer diffusion coefficient has a prediction error of ≤±5% and is synchronously correlated with the Debye-Hückel activity coefficient. and diffusion coefficient, revealing that under high pressure Exponential growth, The law of linear positive correlation with temperature is as follows Figure 2 As shown in the figure, a new rock salt precipitation inhibition term is added to quantify the attenuation effect of solid phase blockage on conductivity, which solves the distortion problem of traditional models in precipitation scenarios.

[0037] Thin KCl in solution K + and Cl - The limiting molar conductivity can be expressed as: ; ; Where: and They are K + and Cl - The limiting molar conductivity, and They are K + and Cl - The limiting migration number of the ion, , for KCl The limiting molar conductivity, It is the chloride ion in solid rock salt; It is the potassium ion in solid rock salt; K + and Cl - The limiting migration number is: ; ; The expression is: ; Where, is the crystal radius of the ion, for cations =0.94, for anions =0.00, is the migration number of anions under infinite dilution conditions, is the migration number of the cation under infinite dilution conditions, for K + The Stokes radius, for Cl - The Stokes radius, is the fractal characteristic radius of rock salt precipitation particles.

[0038] From the above formula we can get and , and then calculate K + 、 Cl - The tracer diffusion coefficient and .

[0039] Preferably, the porous media correction term The expression is: ; in, is the ratio of rock salt precipitation volume to pore space, is the ratio of the original pore volume of the rock to the total volume.

[0040] S3. Use the salinity correction term expression and the comprehensive correction factor expression to correct the basic conductivity expression to obtain the total conductivity expression.

[0041] The overall expression for conductivity is: ;in, is the total conductivity.

[0042] Example

[0043] The experiment was carried out on a tight-fitting six-sided top device on a YJ-3000t press. The device can obtain a static pressure of 10GPa. The pressure measurement and calibration method adopts the method described by Xie Hongsen. The sample assembly diagram for conductivity measurement is similar to that used by Xu Yousheng et al. The sample tube is made of polytetrafluoroethylene with an inner diameter of 4.5mm and a length of 0.5mm. Wires are led out from the electrodes at both ends and connected to the ZLR-5 inductance, capacitance and resistance measuring instrument. The pressure transmission medium is talc, the heater is a stainless steel sheet, and NiCr~NiAl thermocouples are used for temperature measurement. The welding point of the thermocouple is about 2mm away from the sample, and the measurement error is about ±5℃. During the experiment, the impedance at 50 frequencies between 12Hz~100kHz was measured for each temperature and pressure point, and finally the complex impedance plane analysis method was used to obtain the impedance. KCl The conductivity of the solution.

[0044] The compact six-sided top device achieves a stable high-pressure environment (pressure fluctuation <±2%) in the range of 0.1-12 GPa and 100-500°C, solving the leakage problem of traditional devices at supercritical pressure. The anti-interference conductivity measurement system uses a ZLR-5 bridge and a 12-100 kHz broadband AC signal, combined with the complex impedance plane analysis method, to eliminate interference from electrode polarization and dielectric loss, achieving a conductivity measurement error of <±3%.

[0045] Figure 1 It is predicted that under supercritical conditions of constant temperature (100–500°C) and pressure range of 0.1–12 GPa, 0.01 mol / L KCl The relationship between the molar conductivity of a solution and the fluid density. Data points were obtained using an interference-resistant conductivity measurement system (ZLR-5 bridge, 12-100 kHz broadband signal) combined with complex impedance plane analysis. Pressure fluctuations were controlled within ±2%.

[0046] Figure 1 The dual effects of ion migration in supercritical fluids are revealed: enhanced ion mobility at high temperatures and increased ion migration resistance due to high density. The role of this dual effect in the technical solution is as follows: 1. High temperature promotion effect: The increase in temperature enhances the kinetic energy of ions, breaks the hydration shell, and improves ion mobility (positive contribution to conductivity).

[0047] 2. High-density inhibition effect: Increased pressure leads to increased fluid density, enhanced solvent viscous resistance, and obstructed ion migration path (negative contribution of conductivity).

[0048] This competitive relationship is manifested as a nonlinear change in molar conductivity with increasing density, such as Figure 1 As shown in the peak of the curve, the left side of the peak is dominated by the temperature effect, and the right side is dominated by the density resistance.

[0049] coefficient Quantify the effect of high temperature on migration, coefficient Quantify the drag effect of high density on migration, This expression, as the core term of the overall conductivity formula, enables the model's prediction error to be less than ±3% in the supercritical state (>374°C, >22.1MPa), solving the failure problem of traditional empirical models under extreme conditions.

[0050] Figure 2 Predicted K + and C The variation of the tracer diffusion coefficient with pressure (0.1-12 GPa) under isothermal conditions. The data were calculated using the Watson viscosity model and crystallographic ionic radius parameters, with a prediction error of ±5%. The curve shows that the diffusion coefficient is negatively correlated with pressure, and high pressure inhibits ion migration.

[0051] like Figure 2 As shown, K + / Cl - The diffusion coefficient (D) decreases linearly with increasing pressure (at 12 GPa, the D value drops to 10% of that at normal pressure) because high pressure increases fluid viscosity and ion migration resistance.

[0052] Figure 3 The predicted value is 0.01 mol / L KCl The average molar activity coefficient of the solution (γ ± ) with pressure P The Debye-Hückel limiting formula combined with the ion size parameter (â=0.4 nm) was used to calculate the activity coefficient, which showed an exponential increase with increasing pressure (γ ± an increase of over 200%).

[0053] like Figure 3 As shown, the average activity coefficient (γ ± ) increases exponentially with pressure (>5 GPa γ ± The increase is >200%), because the compression of the hydration layer weakens the electrostatic shielding between ions, and the solution deviates from the ideal state.

[0054] Figure 2 and Figure 3 Joint verification of the synergistic mechanism of diffusion coefficient and activity coefficient in the multi-parameter coupling model: ion hydration layer compression under high pressure leads to γ ± The ion migration resistance increases, causing the D value to decrease.

[0055] It is understandable that the coupling mechanism is that high pressure compresses the water molecule layer, which reduces the ion hydration radius (γ ± The increase in pressure (D) in turn increases the viscous resistance (D decreases), and the two are physically related through the Nernst-Einstein equation.

[0056] Diffusion coefficient correction: Watson viscosity model and crystallographic radius were introduced to modify the Stokes-Einstein equation so that the D prediction error is ≤±5%; Activity coefficient correction: Extend the Debye-Hückel equation and add a pressure-sensitive term .

[0057] Technology Role: Synchronous Correlation γ ± With D, it breaks through the traditional single parameter model in supercritical high salinity (>6wt% KCl ) under certain conditions (e.g. Debye-Hückel deviation >20% at >400°C).

[0058] In summary, compared with traditional technologies, the multi-parameter coupling calculation model mentioned in one or more technical solutions provided by this application introduces the Shedlovsky correction model and combines it with the stepwise dilution method to extrapolate the experimental data to infinite dilution conditions to obtain KCl The quantitative relationship between the limiting molar conductivity and temperature and pressure (R 2 >0.99), introduced Watson viscosity model and crystallographic ion radius parameters, modified the high temperature and high pressure diffusion coefficient calculation formula, K + and Cl - The prediction error of the diffusion coefficient is reduced to within ±5%. By synchronously measuring the activity coefficient and the diffusion coefficient, the coupling law between the two under high temperature and high pressure is revealed (for example, the activity coefficient increases exponentially with increasing pressure, while the diffusion coefficient is linearly positively correlated with temperature), providing key parameter support for the deep earth fluid evolution model.

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical method of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical method of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical method to deviate from the spirit and scope of the technical method of the present invention.

Claims

1. Supercritical geothermal fluid system KCl - H 2 O The conductivity calculation method is characterized in that The following steps are involved: S1. Obtaining basic parameters, including system temperature, ionic strength, dielectric constant, and water density; S2. Construct the conductivity basic expression, salinity correction term expression, and comprehensive correction factor expression based on basic parameters; The comprehensive correction factor includes the limiting molar conductivity ∧0 and the average activity coefficient , diffusion effect term and porous medium correction term; Introduction Shedlovsky The modified model was combined with the stepwise dilution method to extrapolate the experimental data to infinite dilution conditions and obtain KCl The quantitative relationship between the limiting molar conductivity and temperature and pressure gives the limiting molar conductivity ∧0; Introduction Watson The viscosity model and crystallographic ionic radius parameters are used to correct the high temperature and high pressure diffusion coefficient calculation. K + and Cl - The tracer diffusion coefficient and Then construct the diffusion effect term; S3. Use the salinity correction term expression and the comprehensive correction factor expression to correct the basic conductivity expression to obtain the total conductivity expression.

2. The supercritical geothermal fluid system according to claim 1 KCl - H 2 O The conductivity calculation method is characterized in that The basic expression of conductivity in S2 is: ； Among them, the constant term C 0=-1.706, C 1=-93.78, C2=3.0781, is the density of water, T is the temperature, The basic conductivity.

3. The supercritical geothermal fluid system according to claim 2 KCl - H 2 O The conductivity calculation method is characterized in that The expression of the salinity correction term in S2 is: ； in, for KCl The quality score, is the salinity correction term, C 3=0.8075.

4. The supercritical geothermal fluid system according to claim 3 KCl - H 2 O The conductivity calculation method is characterized in that The expression of the comprehensive correction factor in S2 is: ； in, is the comprehensive correction factor, ∧0 is the limiting molar conductivity, is the average activity coefficient, which reflects the strength of ion interaction. The value needs to be combined with the temperature T and the solution density ρ to correct the effective concentration of ion interaction. The ion strength is substituted into the modified Debye-Hückel correction equation, and then the high concentration correction is performed using the Pitzer equation to obtain the average activity coefficient. and represent K + and Cl - The tracer diffusion coefficient, is the density of water, T is the temperature, The inhibition term of rock salt precipitation on conductivity is the porous medium correction term, which is used to correct the problem caused by rock salt precipitation blocking pores, resulting in a reduction in ion migration channels and a decrease in conductivity. Since the pore structure of porous media is fractal, the blocking effect of rock salt precipitation needs to be described by fractal theory. The conductivity model based on fractal porous media and the volume effect of rock salt precipitation are derived. is the reference state self-diffusion coefficient of water in infinitely dilute KCl solution, is the ratio of rock salt precipitation volume to pore space, is the ratio of the original pore volume of the rock to the total volume.

5. The supercritical geothermal fluid system according to claim 4 KCl - H 2 O The conductivity calculation method is characterized in that The expression for limiting molar conductivity is: ； in, I is the ionic strength based on volume molarity, ∧ m It is obtained from experimental measurements KCl The molar conductivity, A and B It is a constant calculated from the dielectric constant, viscosity and temperature of water.

6. The supercritical geothermal fluid system according to claim 5 KCl - H 2 O The conductivity calculation method is characterized in that The corrected expression of the activity coefficient is: ； in, and yes Debye - Hückel coefficient, is the molar concentration conversion factor, is the ionic strength based on mass molarity; ； ； in, 、 They are K + 、 Cl - The charge, and d represent the expansion term parameter and ion size parameter of the equation respectively, Refers to the sum of the mass molar concentrations of all solutes in a solution. R is the gas constant, T Refers to temperature.

7. The supercritical geothermal fluid system according to claim 6 KCl - H 2 O The conductivity calculation method is characterized in that K + and Cl - The expression of the tracer diffusion coefficient is: ； in, and Represent the solution i tracer diffusion coefficient and limiting molar conductivity of ions, i For ionic elements, R is the gas constant, T Refers to temperature, represent i The absolute value of the ion's charge, F is the Faraday constant; Expressed as: ； Where: η represents the Poisson viscosity of the solution, e is the electron charge, Ionic Stoke cm radius, is pi; Thin KCl in solution K + and Cl - The limiting molar conductivity is expressed as: ； ； Where: and They are K + and Cl - The limiting molar conductivity, and They are K + and Cl - The limiting migration number of the ion, , for KCl The limiting molar conductivity, It is the chloride ion in solid rock salt; It is the potassium ion in solid rock salt; K + and Cl - The limiting migration number is: ； ； The expression is: ； Where, is the crystal radius of the ion, for cations =0.94, for anions =0.00, is the migration number of anions under infinite dilution conditions, is the migration number of the cation under infinite dilution conditions, for K + The Stokes radius, for Cl - The Stokes radius, is the fractal characteristic radius of rock salt precipitation particles.

8. The supercritical geothermal fluid system according to claim 6 KCl - H 2 O The conductivity calculation method is characterized in that Porous media correction The expression is: ； in, is the ratio of rock salt precipitation volume to pore space, is the ratio of the original pore volume of the rock to the total volume.

9. The supercritical geothermal fluid system according to claim 6 KCl - H 2 O The conductivity calculation method is characterized in that The overall expression for conductivity is: ； in, is the total conductivity.

Images