Conductivity calculation method of supercritical geothermal fluid system KCl-H2O

Abstract

The application discloses a supercritical geothermal fluid system KCl H 2 O Conductivity calculation method, relates to the field of new energy technology, including obtaining basic parameter system temperature, ionic strength, dielectric constant, density of water, constructing conductivity total expression according to parameters to carry out conductivity calculation.The application introduces Shedlovsky Correction model combines step-by-step dilution method, extrapolates experimental data to infinite dilution condition, and then obtains KCl Quantitative relationship of limit molar conductivity with temperature and pressure, introduces Watson Viscosity model and crystallographic ion radius parameter, corrects high-temperature and high-pressure diffusion coefficient calculation formula, so that K + With Cl ‑ The prediction error of diffusion coefficient is reduced to within ±5%, the activity coefficient and the diffusion coefficient are measured synchronously, the coupling law of the activity coefficient and the diffusion coefficient under high temperature and high pressure is revealed, and key parameter support is provided for the deep fluid evolution model of the earth.​

Description

TECHNICAL FIELD

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

[0002] Geothermal energy as a non-carbon-based clean energy has important strategic significance in energy structure adjustment. Supercritical geothermal fluid (temperature > 374℃, pressure > 22.1 MPa) becomes the core target of deep geothermal resource exploration and development due to its high heat enthalpy value (3200 kJ / kg), low viscosity and strong permeability. The physical and chemical properties of electrolytes in fluid under high temperature and high pressure environment are an important research direction in the field of earth science, especially in deep geological process, mineralization and hydrothermal system evolution. The activity coefficient and ion diffusion coefficient of electrolyte solution are not only the core parameters for understanding fluid-rock interaction, element migration mechanism and ore-forming fluid evolution, but also the basic data support for building deep earth material cycle model. However, the measurement of activity coefficient and ion diffusion coefficient of KCl solution under high temperature and high pressure still has limitations, which seriously limits the conductivity calculation.

[0003] Traditional high-pressure devices (such as diamond anvil cell, multi-anvil press) are prone to fluid leakage or electrode contamination under pressure > 500 MPa, and temperature fluctuation (±5℃ or more) leads to poor repeatability of experimental data. For example, Sugenli et al. (2000) measured the conductivity of KCl solution at 100~500℃, 0.1~12 GPa by optimizing the combination of polytetrafluoroethylene sample tube and pyrophyllite pressure transmission medium, and the pressure fluctuation was controlled within ±2%. KCl

[0004] And high-frequency alternating current conductivity method is easily affected by dielectric loss and electrode polarization under high pressure, leading to distortion of conductivity signal. Sugenli team used ZLR-5 type bridge and 12~100 kHz wide frequency alternating current signal, combined with complex impedance plane analysis method, effectively eliminated the interference of electrode polarization.

[0005] Debye-Hückel The limitation of equation, the existing activity coefficient calculation depends on Debye-Hückel theory, but its applicable ionic strength range (<0.1 mol / kg) is invalid in supercritical fluid (such as high temperature and high pressure KCl solution). Sugenli et al. (2000) found through experiments that the deviation between the predicted value and the measured value of the traditional model at 500℃, 50 MPa was more than 20%, and it was necessary to introduce Shedlovsky ​Correct 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:

[0008] S1. Obtaining basic parameters, including system temperature, ionic strength, dielectric constant, and water density;

[0009] S2. Construct conductivity basic expression, salinity correction term expression, and comprehensive correction factor expression based on basic parameters;

[0010] The comprehensive correction factor includes the limiting molar conductivity ∧0 and the average activity coefficient , diffusion effect term and porous medium correction term;

[0011] 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;

[0012] 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;

[0013] 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.

[0014] Preferably, the basic expression of conductivity in S2 is:

[0015] ;

[0016] 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.

[0017] Preferably, the salinity correction term in S2 is expressed as:

[0018] ;

[0019] in, for KCl The quality score, is the salinity correction term, C 3=0.8075.

[0020] Preferably, the expression of the comprehensive correction factor in S2 is:

[0021] ;

[0022] 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 KClReference state self-diffusion coefficient of water in solution (eliminating the disturbance of ions to water structure, as reference of ideal solvent), is the ratio of halite precipitated volume to pore space, is the ratio of original pore volume of rock to total volume.

[0023] The expression of limiting molar conductivity is preferably:

[0024] ;

[0025] wherein, I is the ionic strength based on volume molar concentration, ∧ m is the molar conductivity of KCl measured by experiment, A and B are constants calculated from the dielectric constant, viscosity and temperature of water.

[0026] The modified expression of activity coefficient is preferably:

[0027] ;

[0028] wherein, and are Debye - Hückel coefficients, is the mole fraction of the conversion factor of mass molar concentration, is the ionic strength based on mass molar concentration;

[0029] ;

[0030] ;

[0031] wherein, , are the charges of K + , Cl - respectively, and d represent the expansion term parameter and the ion size parameter of the equation respectively, is the sum of mass molar concentration of all solutes in solution, R is the gas constant and T is the temperature.

[0032] Preferably, K + and Cl - the expression of tracer diffusion coefficient is:

[0033] ;

[0034] wherein, 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;

[0035] Expressed as:

[0036] ;

[0037] Where: η represents the Poisson viscosity of the solution, e is the electron charge, Ionic Stoke cm radius, is pi;

[0038] Thin KCl in solution K + and Cl - The limiting molar conductivity can be expressed as:

[0039] ;

[0040] ;

[0041] 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;

[0042] K + and Cl - The limiting migration number is:

[0043] ;

[0044] ;

[0045] The expression of is:

[0046] ;

[0047] In the formula, is the crystal radius of the ion, for cation = 0.94, for anion = 0.00, is the transference number of anion under infinite dilution condition, is the transference number of cation under infinite dilution condition, is K + Stokes radius of is Cl - Stokes radius, the Stokes radius is the effective radius of the ion when moving in the solution, including the crystallographic radius of the ion itself and the thickness of the surrounding solvation layer, is the fractal characteristic radius of halite KCl （s） precipitation particles.

[0048] The expression of the porous medium correction term is:

[0049] ;

[0050] In the formula, is the ratio of halite precipitation volume to pore space, is the ratio of original pore volume of the rock to the total volume.

[0051] The total expression of the conductivity is preferably:

[0052] ;

[0053] In the formula, is the total conductivity.

[0054] Compared with the conventional technology, the one or more technical solutions provided in the application at least have the following technical effects:

[0055] 1. Multi-parameter coupled calculation model, introducing Shedlovsky correction model, combining stepwise dilution method, extrapolating experimental data to infinite dilution condition, obtaining the quantitative relationship between limit molar conductivity of KCl and temperature, pressure (R²>0.99), introducing Watson viscosity model and crystallographic ion radius parameter, correcting high temperature and high pressure diffusion coefficient calculation formula, making K + and Cl - the prediction error of diffusion coefficient reduced to within ±5%;

[0056] 2. Systematic data set construction: by synchronously measuring activity coefficient and diffusion coefficient, the coupling law of both under high temperature and high pressure is revealed (such as activity coefficient exponentially increases with the increase of pressure, and diffusion coefficient is linearly positively correlated with temperature), which provides key parameter support for deep earth fluid evolution model.

[0057] The technical method of the present application is further described in detail below through the drawings and examples. BRIEF DESCRIPTION OF DRAWINGS

[0058] Figure 1 is the relationship diagram of molar conductivity of 0.01 mol / L KCl solution with density under isothermal condition of the conductivity calculation method of a supercritical fluid system of the present application;

[0059] Figure 2 is the relationship diagram of tracer diffusion coefficient with pressure under isothermal condition of the conductivity calculation method of a supercritical fluid system of the present application; K + and Cl - is the relationship diagram of tracer diffusion coefficient with pressure under isothermal condition of the conductivity calculation method of a supercritical fluid system of the present application; Figure 2 K + is the relationship diagram of tracer diffusion coefficient with pressure under isothermal condition of the conductivity calculation method of a supercritical fluid system of the present application; Figure 2 Cl - is the relationship diagram of tracer diffusion coefficient with pressure under isothermal condition of the conductivity calculation method of a supercritical fluid system of the present application;

[0060] Figure 3 is the relationship diagram of average molar activity coefficient with pressure in 0.01 mol / L KCl solution of the conductivity calculation method of a supercritical fluid system of the present application; KCl

[0061] Figure 4 is the relationship diagram of average molar activity coefficient with pressure in 0.01 mol / L KCl solution of the conductivity calculation method of a supercritical fluid system of the present application; ​​​​​​A flow chart of the conductivity calculation method of the supercritical geothermal fluid system. DETAILED DESCRIPTION

[0062] The technical method of the present application is further illustrated by the accompanying drawings and examples. It should be noted that the relative arrangement, numerical expressions and values of the components and steps set forth in these examples do not limit the scope of the present application unless specifically stated otherwise.

[0063] The following description of at least one exemplary embodiment is merely exemplary in nature and is in no way intended to limit the application or its application or uses.

[0064] Techniques, systems, and apparatus known to those of ordinary skill in the relevant art can not be discussed in detail herein. However, where appropriate, techniques, systems, and apparatus should be considered as being part of the specification.

[0065] In all the examples shown and discussed herein, any specific values should be interpreted as merely exemplary, and not as a limitation. Thus, other examples of the exemplary embodiments can have different values.

[0066] Unless otherwise defined, technical and scientific terms used herein should have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0067] The present application provides a supercritical geothermal fluid system KCl - H 2 O The conductivity calculation method of the supercritical geothermal fluid system includes the following steps:

[0068] S1, obtaining basic parameters, including system temperature, ionic strength, dielectric constant, and density of water;

[0069] The required temperature conditions are provided by a high-temperature furnace, and a thermocouple is 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 covering 500 to 800°C. Based on thermodynamic models and heat transfer equations, the temperature distribution at various points in the system can be obtained by solving the heat transfer equation using computational fluid dynamics (CFD) software or self-programmed programs in numerical simulations of multi-physical process coupling, according to the thermodynamic properties and heat transfer mechanisms of the system. If some temperature data points are known, the temperature field can be constructed by interpolation or fitting methods to estimate the temperature values at other locations.

[0070] Mass spectrometry technology combines fluid samples in high-temperature and high-pressure environments with mass spectrometers to achieve accurate measurement of ionic strength. This technology is suitable for trace ion detection (such as nuclear waste disposal library fluid monitoring) and in-situ analysis of mineral-fluid interface reactions, but needs to overcome the stability of samples under high temperature and high pressure (such asKCl Hydrolysis, container material compatibility and complex matrix interference are the challenges, while high-precision temperature and pressure control system and online dilution / quenching device are relied on to ensure data reliability.

[0071] Dielectric spectroscopy is a technique for in-situ measurement of dielectric constant under extreme conditions by high-temperature and high-pressure dielectric cell. Its core device includes pressure-resistant sapphire or diamond window, platinum electrode and hastelloy sealing container, which can stably contain KCl - H 2 O Solution. In the experiment, the network analyzer applies an alternating electric field of 1 MHz~1 GHz to detect the complex dielectric response of the sample, and combines Cole-Cole figure fitting to analyze the static dielectric constant (ε0) ) and relaxation time (τ) ), revealing the coupling mechanism of ion orientation polarization and temperature and pressure.

[0072] Because the supercritical state temperature is high, the equation of state of water (such as IAPWS formulation) or thermodynamic model (such as Helgeson-Kirkham-Flowers equation of state) is usually used to calculate the density of water according to temperature, pressure and other parameters. Or directly refer to the existing data of the relationship between the density of water and temperature, pressure, and estimate the water density value under specific conditions by interpolation or empirical formula.

[0073] S2, based on the basic parameters to construct the conductivity basic expression, salinity correction term expression, comprehensive correction factor expression;

[0074] The comprehensive correction factor includes the limiting molar conductivity ∧0 and the average activity coefficient , diffusion effect term and porous medium correction term;

[0075] Through experimental data fitting, the conductivity basic expression in S2 is:

[0076] ;

[0077] Where, 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.

[0078] This formula reflects the decrease of σ caused by the increase of ion activity under high temperature due to the association effect, and the hindering effect of density on ion migration.

[0079] Mass fraction It is positively correlated with conductivity, but ion association is enhanced at high salinity.

[0080] 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:

[0081] ;

[0082] in, for KCl The quality score, is the salinity correction term, C 3=0.8075.

[0083] Preferably, the expression of the comprehensive correction factor in S2 is:

[0084] ;

[0085] 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.

[0086] 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);

[0087] The limiting molar conductivity (A0) is calculated using the Debye-Hückel-Onsager equation, which extrapolates the molar conductivity of a solution to the case of infinite dilution. The expression for the limiting molar conductivity is:

[0088] ;

[0089] where, I is the ionic strength based on the volume molar concentration, which quantifies the effect of the electrostatic interactions between ions on the experimental molar conductivity of the KCl solution, m is the molar conductivity of the KCl solution measured experimentally, KCl and A are constants calculated from the dielectric constant, viscosity, and temperature of water. B

[0090] The parameters A , B can be obtained from the following equations:

[0091] ;

[0092] ;

[0093] where, is the relative dielectric constant of the solution, which describes the key parameter of the solution's ability to respond to the polarization of the electric field, the larger the value, the stronger the "shielding effect" of the solution on the Coulomb force between ions (i.e., the weaker the interaction between ions).

[0094] The modified expression for the average molar activity coefficient of the electrolyte in the solution (g) is:

[0095] ;

[0096] where, and are the Debye - Hückel coefficients, is the mole fraction of the conversion factor for mass molar concentration, is the ionic strength based on the mass molar concentration, which quantifies the effect of the electrostatic interactions between ions on the average activity coefficient (reflecting the combined effect of ion concentration and charge) in the KCl solution;

[0097] ;

[0098] ;

[0099] where, , are the​​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.

[0100] 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;

[0101] 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:

[0102] ;

[0103] 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);

[0104] Expressed as:

[0105] ;

[0106] 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;

[0107] 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.

[0108] Thin KCl in solution K + and Cl - The limiting molar conductivity can be expressed as:

[0109] ;

[0110] ;

[0111] 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;

[0112] K + and Cl - The limiting migration number is:

[0113] ;

[0114] ;

[0115] The expression is:

[0116] ;

[0117] wherein, is the ionic crystal radius, for cations = 0.94, for anions = 0.00, is the transport number of anions under infinite dilution condition, is the transport number of cations under infinite dilution condition, is K + Stokes radius of is Cl - Stokes radius of is the fractal characteristic radius of rock salt precipitate particles.

[0118] is obtained from the above formula and , and then K + , Cl - the tracer diffusion coefficient and .

[0119] The expression of the porous medium correction term is preferably:

[0120] ;

[0121] wherein, is the ratio of the volume of rock salt precipitate to the pore space, is the ratio of the original pore volume of the rock to the total volume.

[0122] S3, the salinity correction term expression is adopted, and the comprehensive correction factor expression is adopted to correct the conductivity basic expression to obtain the conductivity total expression.

[0123] The conductivity total expression is: ; wherein, is the total conductivity.

[0124] Embodiment

[0125] The experiment was completed on a tight-packed six-surface top device on YJ-3000t press, which can obtain 10GPa static pressure. The pressure measurement and calibration method adopts the method described by Xie Hongsen. The sample assembly diagram for electric conductivity measurement is similar to that used by Xu Yousheng et al. The sample tube is polytetrafluoroethylene with an inner diameter of 4.5mm and a length of 0.5mm. The wires are led out from the two electrodes and connected to the ZLR-5 type inductance capacitance resistance measuring instrument. The pressure transmission medium is pyrophyllite, and the heater is a stainless steel sheet. The temperature is measured by a NiCr-NiAl thermocouple. 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 and 100kHz was measured at each temperature and pressure point. Finally, the molar conductivity of the solution was obtained by using the complex impedance plane analysis method KCl .

[0126] The tight-packed six-surface top device realizes a stable high-pressure environment of 0.1-12 GPa and 100-500℃ (pressure fluctuation <±2%), solving the leakage problem of traditional devices under supercritical pressure. The anti-interference electric conductivity measurement system: through the ZLR-5 type bridge and 12-100 kHz wide frequency alternating current signal, combined with the complex impedance plane analysis method, the electrode polarization and dielectric loss interference are eliminated, and the electric conductivity measurement error is <±3%.

[0127] Figure 1 The predicted relationship between the molar conductivity of 0.01mol / L KCl solution and the fluid density under supercritical conditions of constant temperature (100-500℃) and pressure range 0.1-12 GPa. The data points are obtained by the anti-interference electric conductivity measurement system (ZLR-5 type bridge, 12-100 kHz wide frequency signal) combined with the complex impedance plane analysis method, and the pressure fluctuation is controlled within ±2%.

[0128] Figure 1 The dual effects of ion migration in supercritical fluid are revealed: the ion activity is enhanced at high temperature, and the ion migration resistance is increased due to high density. The role of this dual effect in the technical scheme is:

[0129] 1. High temperature promotion effect: the increase of temperature enhances the ion kinetic energy, breaks the hydration shell, and improves the ion mobility (positive contribution to electric conductivity).

[0130] 2. High density inhibition effect: the increase of pressure leads to the increase of fluid density, the increase of solvent viscous resistance, and the obstruction of ion migration path (negative contribution to electric conductivity).

[0131] This competitive relationship is manifested as the nonlinear change of molar conductivity with density as shown by the peak value of the curve. The temperature effect dominates on the left side of the peak, and the density resistance dominates on the right side. Figure 1 ​

[0132] 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.

[0133] 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.

[0134] 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.

[0135] 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%).

[0136] 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.

[0137] 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.

[0138] It can be understood that the coupling mechanism: high-pressure compressed water molecular layer, both reduce the ionic hydration radius (γ ± growth) and increase the viscous resistance (D drop), both through the Nernst-Einstein equation physically related.

[0139] Diffusion coefficient correction: introduce Watson viscosity model and crystallographic radius, correct Stokes-Einstein equation, make D prediction error ≤±5%;

[0140] Activity coefficient correction: extend Debye-Hückel equation, increase pressure sensitive term .

[0141] Technical effect: synchronous correlation γ ± and D, break through the limitation of traditional single parameter model in supercritical high salinity (>6wt% KCl ) (such as >400℃, Debye-Hückel deviation >20%).

[0142] In summary, compared with the traditional technology, the multi-parameter coupling calculation model mentioned in one or more technical solutions of the present application introduces Shedlovsky correction model, combines with stepwise dilution method, extrapolates experimental data to infinite dilution condition, obtains KCl The quantitative relationship between the limit molar conductivity and temperature, pressure (R 2 >0.99), introduces Watson viscosity model and crystallographic ion radius parameter, corrects high temperature and high pressure diffusion coefficient calculation formula, makes K + and Cl - The prediction error of diffusion coefficient is reduced to within ±5%, by synchronous measurement of activity coefficient and diffusion coefficient, the coupling law of activity coefficient and diffusion coefficient under high temperature and high pressure is revealed (such as activity coefficient increases exponentially with the increase of pressure, and diffusion coefficient is positively correlated with temperature), which provides key parameter support for deep fluid evolution model.

[0143] Finally, it should be noted that: the above examples are only used to illustrate the technical method of the present application, but not to limit it, although the present application has been described in detail with reference to the preferred embodiment, those skilled in the art should understand that: it can still modify or equivalent replace the technical method of the present application, and these modifications or equivalent replacements also cannot make the modified technical method deviate from the spirit and scope of the technical method of the present application.

Claims

1. Supercritical geothermal fluid system 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 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 and the average activity coefficient , diffusion effect term and porous medium correction term; Introduction The modified model was combined with the stepwise dilution method to extrapolate the experimental data to infinite dilution conditions and obtain The quantitative relationship between the limiting molar conductivity and temperature and pressure is used to obtain the limiting molar conductivity. ; Introduction Watson The viscosity model and crystallographic ionic radius parameters are used to correct the high temperature and high pressure diffusion coefficient calculation. and The tracer diffusion coefficient and Then construct the diffusion effect term; S3. Using the salinity correction term expression and the comprehensive correction factor expression to correct the conductivity basic expression, the total conductivity expression is obtained; and The expression of the tracer diffusion coefficient is: ； in, and Represent the solution tracer diffusion coefficient and limiting molar conductivity of ions, For ionic elements, is the gas constant, Refers to temperature, represent The absolute value of the ion's charge, F is the Faraday constant; Expressed as: ； Where: represents the Poisson viscosity of the solution, is the electron charge, Ionic cm radius, is pi; Thin in solution and The limiting molar conductivity is expressed as: ； ； Where: and They are and The limiting molar conductivity, and They are and The limiting migration number of the ion, , for The limiting molar conductivity, It is the chloride ion in solid rock salt; It is the potassium ion in solid rock salt; and 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 The Stokes radius, for The Stokes radius, is the fractal characteristic radius of rock salt precipitation particles.

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

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

4. The supercritical geothermal fluid system according to claim 3 The conductivity calculation method is characterized in that The expression of the comprehensive correction factor in S2 is: ； in, is the comprehensive correction factor, is the limiting molar conductivity, is the average activity coefficient, which reflects the interaction strength between ions. Its value needs to be combined with the temperature T and the solution density. , correct the effective concentration of ion interaction, substitute the ion 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 and 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 The conductivity calculation method is characterized in that The expression for limiting molar conductivity is: ； in, is the ionic strength based on volume molarity, It is obtained from experimental measurements 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 The conductivity calculation method is characterized in that The corrected expression of the activity coefficient is: ； in, and yes coefficient, is the molar concentration conversion factor, is the ionic strength based on mass molarity; ； ； in, 、 They are 、 The charge, and 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. is the gas constant, Refers to temperature.

7. The supercritical geothermal fluid system according to claim 6 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.

8. The supercritical geothermal fluid system according to claim 6 The conductivity calculation method is characterized in that The overall expression for conductivity is: ； in, is the total conductivity.

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