High-temperature and high-pressure natural gas solubility determination and isotope fractionation simulation experiment device and method

Abstract

The invention discloses a high-temperature and high-pressure natural gas solubility determination and isotope fractionation simulation experiment device and method. The device comprises a gas supply module, a liquid supply module, an integrated reaction kettle, a vacuum module, an independent double-path gas collection module, a test analysis module and a computer control system. The method comprises the following steps: injecting a solution and natural gas into a reaction kettle until dissolution equilibrium, and introducing a state equation to directly calculate theoretical dissolved gas volume and solubility; independently collecting residual free gas in an equilibrium state and overall desolventized gas, determining isotopes, and calculating a thermodynamic equilibrium fractionation coefficient in the dissolution process; natural gas is induced to be continuously desolventized, instantaneous desolventized gas is collected in sections, isotopes are measured, and solvokinetic fractionation parameters are calculated in combination with a Rayleigh model. The whole process is completed in situ in the same kettle body, fluid transfer errors are thoroughly eliminated, and a reliable evaluation means is provided for deep natural gas reservoir forming simulation.

Description

Technical Field

[0001] This invention relates to the field of oil and gas exploration and development technology, specifically to an experimental apparatus and method for measuring the solubility of high-temperature and high-pressure natural gas and simulating isotope fractionation. Background Technology

[0002] As global oil and gas exploration continues to expand into deeper and ultra-deep strata, the geological conditions encountered, including high temperature, high pressure, and even ultra-high pressure, are becoming increasingly common. The phase evolution and solubility assessment of natural gas in deep underground fluids (especially formation water) are crucial for reservoir formation evolution, quantitative resource estimation, and dynamic prediction of gas field development. Deep natural gas, in extremely closed systems, maintains long-term contact with formation water and reaches thermodynamic equilibrium. Accurately evaluating the solubility and isotopic fractionation characteristics of natural gas under these steady-state conditions is a core means of tracing deep gas sources, reconstructing natural gas migration paths, and assessing the potential for dissolved gas release.

[0003] However, current equipment and techniques for physical simulation experiments of natural gas dissolution and isotope fractionation under extreme temperature and pressure conditions have significant limitations, specifically in the following four core aspects:

[0004] 1. The separation function of the apparatus has inherent defects, easily leading to secondary fractionation: Traditional purely closed experimental systems (such as conventional PVT cylinders or high-pressure reactors) severely lack in-situ gas-liquid separation capabilities after reaching dissolution equilibrium. During sampling tests, it is usually necessary to transfer the fluid across chambers to external sampling bottles or reduce pressure through valves and pipelines. This process is highly susceptible to abrupt changes in the gas-liquid phase due to the dead volume of the pipeline and the instantaneous pressure drop, causing the dissolved gas to prematurely desolve and escape. This uncontrollable pressure drop during the physical separation process can trigger strong secondary kinetic fractionation (i.e., preferential escape of light isotopes), thus completely masking the true thermodynamic equilibrium state originally achieved within the reactor.

[0005] 2. Difficulty in accurately determining solubility under extreme temperatures and pressures: Currently used methods for solubility determination, such as the single PVT method or conventional dissolution experiments, struggle to accurately obtain the true gas-liquid two-phase volume distribution after dissolution equilibrium has been reached under extreme high-temperature and high-pressure conditions. Because high-temperature and high-pressure sealed containers typically have observation blind spots, and traditional volume measurement methods relying on depressurization and degassing cannot guarantee the complete recovery of dissolved gas, material balance calculations are difficult, leading to significant errors in the measured deep natural gas solubility data.

[0006] 3. Distortion in the Extraction of Thermodynamic Steady-State Isotope Fractionation Characteristics: The accurate calculation of the isotope thermodynamic equilibrium fractionation coefficient in the natural gas dissolution process highly depends on the non-destructive extraction of both the "residual free phase" and the "overall dissolved phase" within the same closed equilibrium system. Due to the interference from the aforementioned equipment transfer errors and sampling pressure drops, existing methods cannot achieve in-situ full extraction without disrupting the original thermodynamic equilibrium. This results in the measured isotope values ​​being a mixture of thermodynamic equilibrium effects and sampling process kinetic effects, severely impacting the accuracy of determining the true thermodynamic fractionation patterns under deep geological conditions.

[0007] 4. Lack of kinetic fractionation simulation methods for dynamic desolvation processes: Tectonic uplift during geological history or depressurization and drainage during gas field development is essentially a dynamic, open process of continuous desolvation of natural gas from formation water. Existing static evaluation methods and single-point sampling devices cannot realistically simulate this continuous depressurization dynamic geological process, nor can they meet the high-precision segmented sampling requirements of the Rayleigh fractionation model. Therefore, current technologies cannot accurately simulate the isotopic kinetic fractionation characteristics (such as instantaneous isotopic evolution curves, isotopic diffusion coefficient ratio D) throughout the entire dynamic desolvation cycle. * Continuous tracking and quantitative characterization of / D).

[0008] In summary, there is a need to develop a novel experimental apparatus and method for measuring the solubility of high-temperature and high-pressure natural gas and simulating isotope fractionation, in order to overcome fluid transfer errors and achieve a perfect combination of thermodynamic equilibrium evaluation of closed systems and kinetic desolvation tracking of open systems. Summary of the Invention

[0009] To address the problems in the background technology, this application provides an experimental apparatus and method for determining the solubility of high-temperature and high-pressure natural gas and simulating isotope fractionation. This technical solution overcomes the limitations of a single solubility test, providing a comprehensive experimental platform and method. The invention completes the entire process in situ within the same reactor, completely eliminating fluid transfer errors and providing a reliable evaluation method for simulating deep natural gas reservoir formation.

[0010] The technical solution adopted in this application is:

[0011] (i) A high-temperature and high-pressure natural gas solubility determination and isotope fractionation simulation experimental device, comprising: a gas supply module, a liquid supply module, a core reaction module, a vacuum module, a gas collection module, a testing and analysis module, and a computer control system;

[0012] The gas supply module includes a high-pressure gas cylinder. The outlet end of the high-pressure gas cylinder is connected to the upper part of the integrated reactor in the core reaction module through a pipeline. A gas booster pump, a high-pressure regulating valve, a high-precision pressure sensor, and an inlet valve V1 are installed sequentially on the pipeline between the high-pressure gas cylinder and the integrated reactor.

[0013] The liquid supply module includes a salt solution storage tank. The outlet of the salt solution storage tank is connected to the lower part of the integrated reactor in the core reaction module through a pipeline. A constant pressure and constant flow pump and an inlet valve V2 are installed sequentially on the pipeline between the salt solution storage tank and the integrated reactor.

[0014] The core reaction module includes an integrated reactor; the integrated reactor is externally fitted with a programmed heating jacket, and internally equipped with a magnetic stir bar and a high-precision temperature sensor, with the temperature control and stirring actions controlled by the computer control system. The top and bottom of the integrated reactor are respectively connected to ultra-high pressure inlet / outlet fluid pipelines and micro-sampling valves.

[0015] The vacuum module includes a vacuum pump, the inlet of which is connected to the top of the integrated reactor in the core reaction module via a pipeline, and valves V3 are installed sequentially on the pipeline between the vacuum pump and the integrated reactor.

[0016] The gas collection module includes free gas collection and desoluble gas collection:

[0017] The free gas collection includes a first set of drainage and gas collection devices, which are connected to the top of the integrated reactor via a pipeline. A valve V4 is installed on the pipeline between the first set of drainage and gas collection devices and the integrated reactor.

[0018] The desolvation gas collection includes a second set of drainage and gas collection devices. The second set of drainage and gas collection devices is connected to the upper part of the integrated reactor through a pipeline. A valve V5 is installed on the pipeline between the second set of drainage and gas collection devices and the integrated reactor.

[0019] The test and analysis module is an isotope mass spectrometer, which is connected to the first set of drainage and gas collection devices and the second set of drainage and gas collection devices; the waste liquid discharge module includes a waste liquid discharge container, which is connected to the bottom outlet of the integrated reactor through a pipeline, and a valve V6 is installed on the pipeline between the waste liquid discharge container and the integrated reactor.

[0020] The computer control system is electrically connected to the pressure sensor P1, the gas booster pump, the constant pressure and constant flow pump, the isotope mass spectrometer, and the inlet valves V1, V2, V3, V4, V5, and V6.

[0021] (II) A method for determining the solubility of high-temperature and high-pressure natural gas using an experimental apparatus, comprising the following steps:

[0022] Step 1: System vacuuming and airtightness check:

[0023] Connect all modules and pipelines of the above experimental setup tightly; turn on the vacuum pump and open valve V3 to evacuate the entire system's gas phase space; close valve V3 and maintain pressure for 10 minutes, monitoring pressure fluctuations with a high-precision pressure sensor to verify that the system is tight and leak-free;

[0024] Step 2: Quantitative injection and spatial calibration:

[0025] The constant pressure and constant flow pump and the inlet valve V2 are turned on to inject the mineralized salt solution from the salt solution storage tank into the integrated reactor; the computer control system automatically calculates the initial free space volume V of the gas phase inside the reactor based on the total volume of the reactor. free = V total - V w ;

[0026] Step 3: Simulation Environment Construction and Gas Injection:

[0027] Turn on the gas booster pump and high-pressure regulating valve to inject the prepared natural gas sample from the high-pressure gas cylinder into the integrated reactor through the inlet valve V1 to the preset initial high pressure P0; simultaneously start the programmed heating mantle to heat to the target temperature T0, and start the magnetic stirrer at 300 rpm to accelerate the mass transfer equilibrium between the gas and liquid phases; wherein: the natural gas sample is prepared by volume percentage as follows: methane: 86.8%, ethane: 1.66%, carbon dioxide: 5.07%, nitrogen: 6.47%;

[0028] Step 4: Determining Dissolution Equilibrium and Recording Data:

[0029] The computer control system collects pressure curves in real time. As natural gas continuously dissolves in the aqueous phase, the pressure inside the integrated reactor gradually decreases. When the pressure change rate per unit time is <0.01MPa / h and the temperature fluctuation displayed by the high-precision temperature sensor is less than the preset threshold for one consecutive hour, the computer control system determines that a thermodynamic equilibrium state has been reached and automatically records the equilibrium pressure P at this time. eq .

[0030] (III) The calculation method after determining the solubility of high-temperature and high-pressure natural gas includes the following steps:

[0031] Because the experiment takes place in a high-temperature and high-pressure environment, the ideal gas law is no longer applicable. Therefore, a compressibility factor Z is introduced to correct for deviations from the real gas law; its basic form is:

[0032] (1);

[0033] Where P is the system pressure, MPa; V is the volume occupied by the gas, mL; n is the number of moles of gas, mol; Z is the gas compressibility factor under the corresponding temperature and pressure conditions; R is the molar gas constant, 8.314 J / (mol·K); and T is the system temperature, K.

[0034] In the initial stage, the gas phase space V of the integrated reactor is injected. free The total number of moles of natural gas is n0:

[0035] (2);

[0036] After the system reaches dissolution equilibrium, the residue in the gas phase free space V free The number of gas moles in the container is n eq :

[0037] (3);

[0038] According to the principle of mass balance, the number of moles of gas dissolved in the liquid phase is equal to the difference between the initial total number of moles and the number of moles of free gas remaining after equilibrium.

[0039] (4);

[0040] Substituting into the above formula, we get:

[0041] (5);

[0042] For easier comparison, the number of moles dissolved needs to be converted to volume under standard conditions:

[0043] (6);

[0044] Where P0 is the initial injection pressure, P eq For the dissolution equilibrium pressure, V free Let Z0 and Z be the initial free space volume of the gas phase. eq These represent the gas compressibility factors under corresponding temperature and pressure conditions; R is the molar gas constant; T0 is the initial temperature; T eq To reach the equilibrium temperature; V m This refers to the molar volume of the gas under standard conditions.

[0045] Solubility S is defined as the volume of gas that can be dissolved in a unit volume of solvent; that is, the volume of dissolved gas V under standard conditions. dissolved The volume V of the solution injected into the reactor w The ratio:

[0046] (7);

[0047] Among them, V w The volume of the injected solution is given. Substituting the theoretical dissolved gas volume into the formula, the solubility of natural gas in formation water under different temperature and pressure conditions is calculated.

[0048] (iv) A method for determining isotopic thermodynamic fractionation parameters of natural gas dissolution under high temperature and high pressure using the above-mentioned experimental apparatus, comprising the following steps:

[0049] Steps 1-3 are the same as the method for determining the solubility of natural gas;

[0050] Step 4: Determining Dissolution Equilibrium and Collecting Free Gas:

[0051] When the pressure change rate per unit time is ≤0.01MPa / h, the dissolution equilibrium state is determined to be reached; open valve V4, use the first set of drainage and gas collection device to collect the undissolved residual free gas in the upper part, and use isotope mass spectrometry to perform methane carbon isotope analysis.

[0052] Step 5: Induced desolvation and complete collection of dissolved gas:

[0053] Close valve V4, set the heating jacket to raise the temperature at a certain rate to completely desolvate the natural gas from the solution, open valve V5, and use the second set of drainage and gas collection device to collect the completely desolvated gas, and use an isotope mass spectrometer for isotope analysis.

[0054] (V) The calculation method for isotope thermodynamic fractionation parameters of natural gas dissolution under high temperature and high pressure includes the following steps:

[0055] Isotopic composition is usually expressed as the abundance ratio R of heavy isotopes to light isotopes. For carbon isotopes:

[0056] (8);

[0057] Thermodynamic equilibrium fractionation coefficient α eq Defined as: the ratio of isotopic ratios of substances in two phases at equilibrium. In the "gas-liquid" equilibrium system simulated by this device, the fractionation coefficient α is defined as: eq The ratio of dissolved phase to free phase:

[0058] (9);

[0059] In the formula, R dissolved R represents the abundance ratio of heavy isotopes to light isotopes in the dissolved phase under equilibrium conditions. free The abundance ratio of heavy isotopes to light isotopes in the downstream gas phase under equilibrium conditions;

[0060] Because the absolute change in the isotope ratio R is extremely small, laboratories typically measure the part-thousandth deviation δ relative to the standard material. 13 C:

[0061] (10);

[0062] In the formula, Rstd The isotopic abundance ratio of international standard reference materials;

[0063] Transform the formula and solve for R:

[0064] (11);

[0065] Substituting the R expressions for the dissolved phase and the free phase into equation (9):

[0066] (12);

[0067] Simplifying, we get:

[0068] (13);

[0069] Where: α eq δ is the isotopic thermodynamic equilibrium fractionation coefficient; 13 C free The carbon isotope value (‰) of residual free methane gas in equilibrium state; δ 13 C dissolved The carbon isotope value (‰) of dissolved methane in equilibrium state corresponds to this value.

[0070] (vi) A method for determining isotope kinetic fractionation parameters of natural gas desolvation process under high temperature and high pressure using the above-mentioned experimental apparatus, comprising the following steps:

[0071] Steps 1-3 are the same as the method for determining the solubility of natural gas;

[0072] Step 4: Initial equilibrium state isotope reference acquisition:

[0073] Valve V4 is opened, and the undissolved residual free gas in the upper part is collected using the first set of drainage and gas collection devices for isotope analysis to determine the initial isotopic characteristics of the system. Simultaneously, the methane carbon isotope value δ of the initially dissolved natural gas is determined based on the thermodynamic evaluation results. 13 C0;

[0074] Step 5: Inducing continuous desolvation and segmented instantaneous sampling:

[0075] Based on the dissolution equilibrium, valve V4 is closed; the system continuously and slowly depressurizes through precise control of the integrated reactor to simulate the formation uplift or depressurization process during drainage; during this dynamic desolvation process, valve V5 is opened, and the second drainage gas collection device is used to collect the instantaneous desolvation gas in segments and independently according to preset pressure nodes, and the instantaneous isotopic composition δ at each stage is measured. 13 C exsolved .

[0076] (vii) Calculation method for isotope kinetic fractionation parameters of natural gas desolvation process under high temperature and high pressure, including the following steps:

[0077] Before depressurization and solvent removal, based on the principle of material balance, the carbon isotope value δ of the total amount of desoluble gas methane measured in the thermodynamic equilibrium evaluation experiment was used. 13 C dissolved The isotopic reference value δ of the initial dissolved gas in the liquid phase is calibrated. 13 C0, i.e., setting δ 13 C0 = δ 13 C dissolved ;

[0078] In the physical process of continuous production of desoluble gas from liquid-phase dissolved gas, the isotope ratio R of the remaining dissolved gas in the liquid phase is... res The classic expression for the variation of the residual fraction f, the Rayleigh fractional distillation equation, is:

[0079] (14);

[0080] Where R0 is the isotope ratio of the dissolved gas at f=1 in the initial state; R res The isotope ratio of the residual dissolved gas in the liquid phase at the current pressure node; f is the fraction of residual dissolved gas, 0 <f≤ 1;

[0081] Based on the kinetic fractionation coefficient α k The definition is the ratio R of gases instantaneously released at any instantaneous desolvation moment. ex R, the ratio of the current liquid phase residual gas res The relationship between them is:

[0082] (15);

[0083] Substitute (15) into (14) to eliminate R. res After sorting, we can obtain:

[0084] (16);

[0085] After logarithmic transformation, we get:

[0086] (17);

[0087] Due to the α-propagation in natural gas isotope research k Extremely close to 1, ln(α) k ) ≈α k – 1; The simplified expression of the above formula is:

[0088] (18);

[0089] Using the standard conversion relationship between the isotope ratio R and the experimentally measured δ isotope ratio:

[0090] (19);

[0091] Substituting this relationship into equation (18), we get:

[0092] (20);

[0093] Solve for the fractionation coefficient α k :

[0094] (twenty one);

[0095] In the Rayleigh model, α k Defined as the ratio of the dissolved gas from the instantaneous products to the dissolved gas from the remaining reactants;

[0096] (twenty two);

[0097] In the kinetic desolvation process, the isotope ratio R of the gaseous products that escape instantaneously 产物 It depends on the ratio of the flux of the heavy and light isotope molecules across the gas-liquid interface:

[0098] (twenty three);

[0099] Among them, J * heavy isotope molecules 13 The diffusion flux of CH4, where J is a light isotope molecule. 12 The diffusion flux of CH4;

[0100] According to Fick's first law, the diffusion flux J of a certain component is related to the diffusion coefficient D and the concentration gradient. Proportional:

[0101] (twenty four);

[0102] Substituting into equation (23), we get:

[0103] (25);

[0104] In the formula, R 产物 The ratio of heavy to light isotope abundance of transient products; D * For heavy isotope molecules ( 13 The diffusion coefficient of CH4); D is the light isotope molecule ( 12 The diffusion coefficient of CH4); C * The concentration gradient of heavy isotope molecules in the diffusion boundary layer; C represents the concentration gradient of light isotope molecules in the diffusion boundary layer.

[0105] In a liquid-phase (reactant) system, because isotope molecules have extremely similar properties, within the diffusion boundary layer, the ratio of the concentration gradients of heavy and light isotopes is approximately equal to their concentration ratio in the bulk liquid phase.

[0106] (26);

[0107] In the formula, R 产物 The ratio of the heavy to light isotope abundance of the remaining reactants; C * The concentration gradient of heavy isotope molecules in the diffusion boundary layer; C represents the concentration gradient of light isotope molecules in the diffusion boundary layer; C * denoted as α, where α is the concentration of heavy isotope molecules in the liquid phase; C is the concentration of light isotope molecules in the liquid phase.

[0108] Substituting equation (26) into equation (25), we get:

[0109] (27);

[0110] The instantaneous isotope values ​​δ measured during the continuous desolvation process were analyzed. 13 C dissolved The remaining dissolved gas fraction f was calculated using Rayleigh equation (21) to obtain D under different temperature and pressure conditions. * / D(α) k )value.

[0111] Compared with the prior art, the beneficial effects of this application are as follows:

[0112] 1. Solving the problems of "secondary kinetic fractionation" and "dead volume error" caused by fluid transfer across chambers under extreme temperature and pressure conditions: Existing equipment requires cross-chamber transfer during sampling and testing, which easily disrupts the original phase equilibrium. This invention aims to construct an integrated reaction vessel and an independent dual-path gas collection module through modular design and in-situ integrated separation function, enabling the entire dissolution and desolvation process to be completed in-situ within the same sealed vessel, and achieving independent and non-destructive collection of free gas and desolvated gas, completely eliminating interference caused by transfer errors.

[0113] 2. Addressing the challenges of calculating the true mass equilibrium and determining solubility in closed, high-temperature, and high-pressure systems: Existing single-phase dissolution experiments struggle to accurately obtain the true volume distribution of the gas and liquid phases under extreme conditions. This invention aims to achieve high-precision determination of deep natural gas solubility by injecting a known volume of fluid into a reactor until thermodynamic dissolution equilibrium is reached, introducing a gas compressibility factor to correct the true gas equation of state, and directly calculating the theoretical dissolved gas volume under standard conditions based on equilibrium parameters.

[0114] 3. Solving the problem of extracting true isotopic thermodynamic fractionation characteristics after steady-state equilibrium: Due to the interference of sampling pressure drop in traditional equipment, the isotopic data measured by existing methods are often a mixture of thermodynamic and kinetic effects. This invention aims to independently collect residual free gas in thermodynamic equilibrium and completely desorbed gas in a completely closed system at the same temperature and pressure. By accurately comparing the isotopic composition of the two phases, the true isotopic thermodynamic equilibrium fractionation coefficient of the natural gas dissolution process can be restored and calculated.

[0115] 4. Addressing the challenge of quantitatively tracking isotope kinetic fractionation effects during dynamic drainage or formation uplift: Existing static physical simulation methods cannot accurately reflect the dynamic open process of continuous natural gas desolvation from formation water. This invention aims to achieve quantitative tracking and characterization of the dynamic fractionation effects throughout the entire desolvation cycle by precisely controlling pressure reduction to induce continuous and slow desolvation of natural gas based on a dissolution equilibrium state. The isotope composition of the instantaneously desolvated gas is collected and measured in segments according to pressure nodes. Combined with the Rayleigh fractionation model, isotope kinetic diffusion parameters are calculated, enabling quantitative tracking and characterization of the dynamic fractionation effects throughout the desolvation cycle. Attached Figure Description

[0116] Figure 1 This is a schematic diagram of the experimental apparatus for the dissolution and desolvation of high-temperature and high-pressure natural gas.

[0117] In the diagram: 1 – Integrated reactor; 2 – Heating jacket; 3 – Magnetic stir bar; 4 – Temperature sensor; 5 – Pressure sensor P1; 6 – Inlet valve V1; 7 – High-pressure gas cylinder; 8 – Gas booster pump; 9 – High-pressure regulating valve; 10 – Salt solution storage tank; 11 – Constant pressure and constant flow pump; 12 – Liquid inlet valve V2; 13 – Vacuum pump; 14 – Valve V3; 15 – Valve V4; 16 – First drainage and gas collection device; 17 – Valve V5; 18 – Second drainage and gas collection device; 19 – Valve V6; 20 – Waste liquid discharge container; 21 – Isotope mass spectrometer; 22 – Computer control system.

[0118] Figure 2 It is a graph showing the variation of natural gas solubility in formation water under different temperatures and pressures;

[0119] Figure 3 This is a comparison chart of carbon isotope results of residual free gas and dedissolved methane under different temperatures and pressures;

[0120] Figure 4 This is a graph showing the evolution of the kinetics of continuous desolvation and fractionation of natural gas under conditions of 60℃ and 60MPa. Detailed Implementation

[0121] To clarify the technical advantages of the present invention, the design scheme of the present invention will be described in further detail and clearly below with reference to the accompanying drawings and embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0122] Example 1

[0123] A high-temperature and high-pressure natural gas solubility determination and isotope fractionation simulation experimental device includes: a gas supply module, a liquid supply module, a core reaction module, a vacuum module, a gas collection module, a testing and analysis module, and a computer control system;

[0124] The gas supply module includes a high-pressure gas cylinder 7. The outlet of the high-pressure gas cylinder 7 is connected to the upper part of the integrated reactor 1 in the core reaction module via a pipeline. A gas booster pump 8, a high-pressure regulating valve 9, a high-precision pressure sensor 5, and an inlet valve V16 are sequentially installed on the pipeline between the high-pressure gas cylinder 7 and the integrated reactor 1. The natural gas sample in the high-pressure gas cylinder 7 is pressurized by the gas booster pump 8, and after being stabilized by the high-pressure regulating valve 9, it enters the integrated reactor 1 through the inlet valve V16. The high-precision pressure sensor 5 is used to monitor the gas pressure injected into the reactor in real time.

[0125] The liquid supply module includes a salt solution storage tank 10. The outlet of the salt solution storage tank 10 is connected to the lower part of the integrated reactor 1 in the core reaction module via a pipeline. A constant pressure and constant flow pump 11 and an inlet valve V212 are installed sequentially on the pipeline between the salt solution storage tank 10 and the integrated reactor 1. The experimentally prepared salt solution is injected into the integrated reactor 1 from the salt solution storage tank 10 through the inlet valve V212 under the drive of the constant pressure and constant flow pump 11.

[0126] The core reaction module includes an integrated reactor 1. The integrated reactor 1 is externally fitted with a programmed heating jacket 21. Inside the integrated reactor 1 are a magnetic stirrer 3 and a high-precision temperature sensor 4. The computer control system controls the temperature control and stirring. The top and bottom of the integrated reactor 1 are connected to ultra-high pressure inlet / outlet fluid pipelines and micro-sampling valves, respectively. This integrated reactor 1 is a high-pressure sealed container; after liquid injection, its interior is divided into a lower liquid phase space (solution and dissolved gas) and an upper free gas space. The computer control system controls the temperature control and stirring.

[0127] The vacuum module includes a vacuum pump 13. The inlet of the vacuum pump 13 is connected to the top of the integrated reactor 1 in the core reaction module via a pipeline. A valve V314 is installed in sequence on the pipeline between the vacuum pump 13 and the integrated reactor 1. This valve is used to evacuate the residual air in the system pipeline and the integrated reactor 1 before the experiment begins, ensuring that the experiment is carried out in a pure system.

[0128] The gas collection module includes free gas collection and desoluble gas collection:

[0129] The free gas collection includes a first set of drainage and gas collection device 16, which is connected to the top of the integrated reactor 1 via a pipeline. A valve V415 is installed on the pipeline between the first set of drainage and gas collection device 16 and the integrated reactor 1; it is used to collect the residual free gas sample in the upper part during the dissolution equilibrium stage.

[0130] The desolvation gas collection includes a second set of drainage gas collection device 18, which is connected to the upper part of the integrated reactor 1 via a pipeline. A valve V517 is installed on the pipeline between the second set of drainage gas collection device 18 and the integrated reactor 1 to collect the desolvation gas that escapes from the solution during the heating stage.

[0131] It should be noted that valves V415 and V517 open at different times. After dissolution equilibrium is reached, valve V415 is opened first to collect the current residual free gas. After valve V415 is closed, a heating operation is performed to induce desolvation, at which point valve V517 is opened to collect the newly generated desolvated gas. The two valves open at different stages and are connected to different gas collection devices, thereby achieving independent collection of gases in different phases.

[0132] The test and analysis module is an isotope mass spectrometer 21, which is connected to the first set of drainage gas collection device 16 and the second set of drainage gas collection device 18; it is used to perform methane carbon isotope analysis on the collected gas samples.

[0133] The waste liquid discharge module includes a waste liquid discharge container 20, which is connected to the bottom outlet of the integrated reactor 1 via a pipeline. A valve V619 is installed on the pipeline between the waste liquid discharge container 20 and the integrated reactor 1; it is used to discharge waste liquid and clean the reactor body after the experiment.

[0134] The computer control system 22 is electrically connected to pressure sensor P15, gas booster pump 8, constant pressure and constant flow pump 11, isotope mass spectrometer 22, and inlet valves V16, V212, V314, V415, V517, and V619. It is used to collect pressure and temperature data in real time and control the automated operation of the entire process.

[0135] Example 2

[0136] The method for determining the solubility of high-temperature and high-pressure natural gas using the above-described experimental setup includes the following steps:

[0137] Step 1: System vacuuming and airtightness check:

[0138] Connect all modules and pipelines of the experimental apparatus in Example 1 tightly; turn on vacuum pump 13 and open valve V314 to evacuate the entire system's gas phase space to 0.05 MPa. Close valve V314 and maintain the pressure for 10 minutes, monitoring pressure fluctuations through high-precision pressure sensor 5 to verify that the system is tight and leak-free.

[0139] Step 2: Quantitative injection and spatial calibration:

[0140] Turn on the constant pressure and constant flow pump 11 and the inlet valve V212 to pump the known volume V w = 200 mL of mineralized salt solution is injected from salt solution storage tank 10 into integrated reactor 1. Computer control system 22 calculates the total volume V of reactor based on the total volume V. total = 500 mL The initial free space volume V of the gas phase inside the vessel is automatically calculated. free = V total - V w = 300 mL.

[0141] Step 3: Simulation Environment Construction and Gas Injection:

[0142] Turn on the gas booster pump 8 and high-pressure regulating valve 9 to inject the prepared natural gas sample from the high-pressure gas cylinder 7 into the integrated reaction vessel 1 through the inlet valve V16 to the preset initial high pressure P0 (test range: 20, 40, 60, 80, 100 MPa). Simultaneously, start the programmed heating mantle 2 to heat to the target temperature T0 (test range: 20, 40, 60, 80, 100℃), and start the magnetic stirrer 3 at 300 rpm to accelerate the mass transfer equilibrium between the gas and liquid phases. The natural gas sample is prepared by volume percentage as follows: methane: 86.8%, ethane: 1.66%, carbon dioxide: 5.07%, and nitrogen: 6.47%.

[0143] Step 4: Determining Dissolution Equilibrium and Recording Data:

[0144] The computer control system 22 acquires the pressure curve in real time. As natural gas continuously dissolves in the aqueous phase, the pressure inside the integrated reactor 1 gradually decreases. When the pressure change rate per unit time is <0.01 MPa / h and the reading tends to stabilize, the computer control system 22 determines that a thermodynamic equilibrium state has been reached and automatically records the equilibrium pressure P at this time. eq The results are shown in Table 1.

[0145] Table 1 Natural gas dissolution equilibrium pressure P under different temperature and pressure conditions eq (MPa)

[0146]

[0147] Example 3

[0148] The method for calculating the solubility of high-temperature and high-pressure natural gas in Example 2 includes the following steps:

[0149] Because the experiment takes place in a high-temperature and high-pressure environment, the ideal gas law is no longer applicable. Therefore, a compressibility factor Z is introduced to correct for deviations from the real gas law; its basic form is:

[0150] (1);

[0151] Where P is the system pressure, MPa; V is the volume occupied by the gas, mL; n is the number of moles of gas, mol; Z is the gas compressibility factor under the corresponding temperature and pressure conditions; R is the molar gas constant, 8.314 J / (mol·K); and T is the system temperature, K.

[0152] In the initial stage, the gas phase space V of the integrated reactor is injected. free The total number of moles of natural gas is n0:

[0153] (2);

[0154] After the system reaches dissolution equilibrium, the residue in the gas phase free space V free The number of gas moles in the container is n eq :

[0155] (3);

[0156] According to the principle of mass balance, the number of moles of gas dissolved in the liquid phase is equal to the difference between the initial total number of moles and the number of moles of free gas remaining after equilibrium.

[0157] (4);

[0158] Substituting into the above formula, we get:

[0159] (5);

[0160] For easier comparison, the number of moles dissolved needs to be converted to volume under standard conditions:

[0161] (6);

[0162] Where P0 is the initial injection pressure, P eq For the dissolution equilibrium pressure, V free Let Z0 and Z be the initial free space volume of the gas phase. eq These represent the gas compressibility factors under corresponding temperature and pressure conditions; R is the molar gas constant; T0 is the initial temperature; T eq To reach the equilibrium temperature; V m This refers to the molar volume of the gas under standard conditions.

[0163] Dissolved gas volume V dissolved The calculation results are shown in Table 2 below:

[0164] Table 2. Dissolved gas volume (mL) at different temperatures and initial pressures.

[0165]

[0166] Solubility S is defined as the volume of gas that can be dissolved in a unit volume of solvent; that is, the volume of dissolved gas V under standard conditions. dissolved The volume V of the solution injected into the reactor w The ratio:

[0167] (7);

[0168] Among them, V w This refers to the volume of the injected solution.

[0169] Substituting the theoretical dissolved gas volume from Table 2 into the formula, the solubility of natural gas in formation water under different temperature and pressure conditions was calculated. The specific data are shown in Table 3.

[0170] Table 3. Natural gas solubility S (mL / g) at different temperatures and initial pressures

[0171]

[0172] Plot the natural gas solubility data in Table 3 as a variation curve (see details). Figure 2 (Combining the data in Table 3 with...) Figure 2 The curve trend shows that: solubility has a significant positive correlation with pressure. The figure shows that at the same temperature, the solubility of natural gas in formation water increases significantly with increasing pressure, and the rate of increase gradually slows down as the pressure increases; solubility has a negative correlation with temperature. At the same pressure, the solubility gradually decreases with increasing temperature.

[0173] Example 4

[0174] The determination of isotope thermodynamic fractionation parameters during the natural gas dissolution process under high temperature and high pressure using the experimental apparatus of Example 1 includes the following steps:

[0175] Step 1: System vacuuming and airtightness check

[0176] Connect all modules and pipelines of the above-mentioned device tightly. Turn on vacuum pump 13 and open valve V314 to evacuate the entire system's gas phase space to 0.05 MPa. Close valve V314 and maintain the pressure for 10 minutes. Monitor pressure fluctuations using high-precision pressure sensor 5 to verify that the system is tight and leak-free.

[0177] Step 2: Quantitative injection and spatial calibration:

[0178] The constant pressure and constant flow pump 11 is turned on, and the known volume V is pumped through the inlet valve V212. w = 200 mL of mineralized salt solution is injected into the integrated reaction vessel 1. The computer control system 22 calculates the total volume V of the reaction vessel based on the total volume V. total = 500 mL The initial free space volume V of the gas phase inside the vessel is automatically calculated. free = V total - V w = 300 mL.

[0179] Step 3: Simulation Environment Construction and Gas Injection:

[0180] Turn on the gas booster pump 8 and high-pressure regulating valve 9, and inject the prepared natural gas sample into the reactor through the inlet valve V16 to the preset initial high pressure P0 (test range: 20, 40, 60, 80, 100 MPa). Simultaneously start the programmed heating mantle 2 to heat to the target temperature T0 (test range: 20, 40, 60, 80, 100℃), and start the magnetic stirrer 3 at 300 rpm to accelerate the mass transfer equilibrium between the gas and liquid phases. The natural gas sample is prepared by volume percentage as follows: methane: 86.8%, ethane: 1.66%, carbon dioxide: 5.07%, and nitrogen: 6.47%.

[0181] Step 4: Determining Dissolution Equilibrium and Collecting Free Gas

[0182] When the pressure change rate per unit time is ≤0.01MPa / h, the dissolution equilibrium state is determined to be reached. Valve V415 is opened, and the undissolved residual free gas in the upper part is collected using the first set of drainage and gas collection devices 16 for methane carbon isotope analysis. The free gas isotope results under various temperature and pressure conditions are shown in Table 4 below:

[0183] Table 4. Carbon isotopic composition (‰) of residual free gas methane at different temperatures and initial pressures.

[0184]

[0185] Step 5: Induced desolvation and complete collection of dissolved gas:

[0186] Close valve V415. Set heating jacket 2 to linear heating mode, using high-precision temperature sensor 4 for real-time monitoring to ensure the temperature is raised at a certain rate (2 °C / min) to completely desolvate the natural gas from the solution. Open valve V517 and use the second drainage and gas collection device 18 to collect the completely dissolved gas (representing the initial dissolved gas) for isotope analysis. The results are shown in Table 5 below:

[0187] Table 5. Carbon isotope composition (‰) of desolvated methane gas at different temperatures and initial pressures.

[0188]

[0189] Example 5

[0190] The method for calculating isotope thermodynamic fractionation parameters of natural gas dissolution under high temperature and high pressure, as measured in Example 4, includes the following steps:

[0191] Isotopic composition is usually expressed as the abundance ratio R of heavy isotopes to light isotopes. For carbon isotopes:

[0192] (8);

[0193] Thermodynamic equilibrium fractionation coefficient α eq Defined as: the ratio of isotopic ratios of substances in two phases at equilibrium. In the "gas-liquid" equilibrium system simulated by this device, the fractionation coefficient α is defined as: eq The ratio of dissolved phase to free phase:

[0194] (9);

[0195] In the formula, R dissolved R represents the abundance ratio of heavy isotopes to light isotopes in the dissolved phase under equilibrium conditions. free The abundance ratio of heavy isotopes to light isotopes in the downstream gas phase under equilibrium conditions;

[0196] Because the absolute change in the isotope ratio R is extremely small, laboratories typically measure the part-thousandth deviation δ relative to the standard material. 13 C:

[0197] (10);

[0198] In the formula, R std The isotopic abundance ratio of international standard reference materials;

[0199] Transform the formula and solve for R:

[0200] (11);

[0201] Substituting the R expressions for the dissolved phase and the free phase into equation (9):

[0202] (12);

[0203] Simplifying, we get:

[0204] (13);

[0205] Where: αeq δ is the isotopic thermodynamic equilibrium fractionation coefficient; 13 C free The carbon isotope value (‰) of residual free methane gas in equilibrium state; δ 13 C dissolved The carbon isotope value (‰) of dissolved methane in equilibrium state corresponds to this value.

[0206] Substituting the data from Tables 4 and 5 into the formula, we can calculate α under various temperature and pressure conditions. eq The calculation results are as follows (Table 6):

[0207] Table 6. Isotope thermodynamic equilibrium fractionation coefficients (α) at ​​different temperatures and initial pressures. eq )

[0208]

[0209] Plot a comparison curve between the data in Tables 4 and 5 (see details). Figure 3 (Combined with Table 6) Figure 3 The following conclusions can be drawn:

[0210] (1) Under all set temperature and pressure conditions, α eq All are greater than 1. The isotopic values ​​of the desoluble gas (Table 5) are significantly heavier than those of the residual free gas under the corresponding conditions (Table 4), confirming that there is a significant isotopic fractionation effect during the dissolution of methane, and that heavy isotopes tend to accumulate in the dissolved phase; (2) As the equilibrium temperature increases, the equilibrium fractionation coefficient α eq It gradually decreases and approaches 1. This indicates that high temperature weakens the carbon isotope fractionation effect during the dissolution process; (3) at the same temperature, as the injection pressure increases, α eq The slight downward trend indicates that the effect of pressure on steady-state thermodynamic isotope fractionation is much smaller than that of temperature.

[0211] Example 6

[0212] Isotope kinetic fractionation parameters of natural gas desolvation process under high temperature and high pressure were determined using the experimental apparatus of Example 1:

[0213] Step 1: System vacuuming and airtightness check

[0214] Connect the integrated reactor 1, all module pipelines, and testing equipment tightly. Turn on vacuum pump 13 and open valve V314 to evacuate the entire system's gas phase space to 0.05 MPa. Close the valve and maintain the pressure for 10 minutes. Monitor pressure fluctuations using high-precision pressure sensor 5 to verify that the system is leak-free.

[0215] Step 2: Quantitative injection and spatial calibration

[0216] The constant pressure and constant flow pump 11 is turned on, and the known volume V is pumped through the inlet valve V212. w = 200 mL of mineralized salt solution is injected into the integrated reaction vessel 1. The computer control system 22 calculates the total volume V of the reaction vessel based on the total volume V. total = 500 mL The initial free space volume V of the gas phase inside the vessel is automatically calculated. free = V total - V w = 300 mL.

[0217] Step 3: High-pressure isothermal dissolution simulation in a closed system

[0218] Turn on the gas booster pump 8 and the high-pressure regulating valve 9 to inject the natural gas sample into the reactor to the preset initial high pressure P0. Turn on the heating mantle 2 to raise the temperature to the target temperature T0, and start the magnetic stir bar 3 (300 rpm) to accelerate mass transfer. When the pressure change rate per unit time is ≤ 0.01 MPa / h, the dissolution equilibrium state is determined to be reached.

[0219] Step 4: Initial equilibrium state isotope reference acquisition

[0220] Valve V415 is opened, and the first set of drainage and gas collection device 16 is used to collect the undissolved residual free gas in the upper part for isotopic analysis to determine the initial isotopic characteristics of the system. Simultaneously, the methane carbon isotope value δ of the initially dissolved natural gas is determined based on the thermodynamic evaluation results. 13 C0.

[0221] Step 5: Inducing continuous desolvation and segmented instantaneous sampling

[0222] Based on the dissolution equilibrium, valve V415 is closed. The system continuously and slowly reduces the pressure in the integrated reactor 1 through precise control, simulating the formation uplift or drainage depressurization process. During this dynamic desolvation process, valve V517 is opened, and the second drainage gas collection device 18 is used to collect the instantaneous desolvation gas in segments and independently according to preset pressure nodes, and the instantaneous isotopic composition δ at each stage is measured. 13 C exsolved Taking the conditions of 60℃ and 60MPa as an example, the segmented tracking test data are shown in Table 7:

[0223] Table 7 Kinetic tracking test data of continuous desolvation stage at 60℃ and 60MPa

[0224]

[0225] The instantaneous isotopic data of the continuous desolvation stage in Table 7 were plotted with the remaining dissolved gas fraction f to form an evolution curve. Figure 4 ).Depend on Figure 4As can be clearly seen from the data in Table 7, as the desolvation process progresses (pressure decreases, f value decreases), the natural gas removed in the early stage is significantly lighter, while the gas removed in the later stage is heavier, showing a gradual trend of increasing weight.

[0226] Example 7

[0227] The method for calculating isotope kinetic fractionation parameters of natural gas desolvation under high temperature and high pressure, as measured in Example 6, includes the following steps:

[0228] Before depressurization and solvent removal, based on the principle of material balance, the carbon isotope value (δ¹⁸) of the total amount of desoluble gas methane measured in the thermodynamic equilibrium evaluation experiment (Example 4) was used. 13 C dissolved The value is calibrated as the isotopic reference value (δ) of the initial dissolved gas in the liquid phase. 13 C0), that is, setting δ 13 C0 = δ 13 C dissolved .

[0229] In the physical process of continuous production of desoluble gas from liquid-phase dissolved gas, the isotope ratio R of the remaining dissolved gas in the liquid phase is... res The classic expression for the variation of the residual fraction f, the Rayleigh fractional distillation equation, is:

[0230] (14);

[0231] Where R0 is the isotope ratio of the dissolved gas at f=1 in the initial state; R res The isotope ratio of the residual dissolved gas in the liquid phase at the current pressure node; f is the fraction of residual dissolved gas, 0 <f≤ 1;

[0232] Based on the kinetic fractionation coefficient α k The definition is the ratio R of gases instantaneously released at any instantaneous desolvation moment. ex R, the ratio of the current liquid phase residual gas res The relationship between them is:

[0233] (15);

[0234] Substitute (15) into (14) to eliminate R. res After sorting, we can obtain:

[0235] (16);

[0236] After logarithmic transformation, we get:

[0237] (17);

[0238] Due to the α-propagation in natural gas isotope research kExtremely close to 1, ln(α) k ) ≈α k – 1; The simplified expression of the above formula is:

[0239] (18);

[0240] Using the standard conversion relationship between the isotope ratio R and the experimentally measured δ isotope ratio:

[0241] (19);

[0242] Substituting this relationship into equation (18), we get:

[0243] (20);

[0244] Solve for the fractionation coefficient α k :

[0245] (twenty one);

[0246] In the Rayleigh model, α k Defined as the ratio of the dissolved gas from the instantaneous products to the dissolved gas from the remaining reactants;

[0247] (twenty two);

[0248] In the kinetic desolvation process, the isotope ratio R of the gaseous products that escape instantaneously 产物 It depends on the ratio of the flux of the heavy and light isotope molecules across the gas-liquid interface:

[0249] (twenty three);

[0250] Among them, J * heavy isotope molecules 13 The diffusion flux of CH4, where J is a light isotope molecule. 12 The diffusion flux of CH4;

[0251] According to Fick's first law, the diffusion flux J of a certain component is related to the diffusion coefficient D and the concentration gradient. C is directly proportional to:

[0252] (twenty four);

[0253] Substituting into equation (23), we get:

[0254] (25);

[0255] In the formula, R 产物 The ratio of heavy to light isotope abundance of transient products; D *For heavy isotope molecules ( 13 The diffusion coefficient of CH4); D is the light isotope molecule ( 12 The diffusion coefficient of CH4); C * The concentration gradient of heavy isotope molecules in the diffusion boundary layer; C represents the concentration gradient of light isotope molecules in the diffusion boundary layer.

[0256] In a liquid-phase (reactant) system, because isotope molecules have extremely similar properties, within the diffusion boundary layer, the ratio of the concentration gradients of heavy and light isotopes is approximately equal to their concentration ratio in the bulk liquid phase.

[0257] (26);

[0258] In the formula, R 产物 The ratio of the heavy to light isotope abundance of the remaining reactants; C * The concentration gradient of heavy isotope molecules in the diffusion boundary layer; C represents the concentration gradient of light isotope molecules in the diffusion boundary layer; C * denoted as α, where α is the concentration of heavy isotope molecules in the liquid phase; C is the concentration of light isotope molecules in the liquid phase.

[0259] Substituting equation (26) into equation (25), we get:

[0260] (27);

[0261] The instantaneous isotope values ​​δ measured during the continuous desolvation process were analyzed. 13 C dissolved By applying Rayleigh's equation (Equation 21) to the remaining dissolved gas fraction f, the corresponding D under different temperature and pressure conditions can be obtained. * / D(α) k The values ​​are shown in the table below:

[0262] Table 8. Isotope diffusion coefficient ratios (D) at different temperatures and initial pressures. * / D)

[0263] <![CDATA[D * / D]]> <![CDATA[P0=20MPa]]> <![CDATA[P0=40MPa]]> <![CDATA[P0=60MPa]]> <![CDATA[P0=80MPa]]> <![CDATA[P0=100MPa]]> T=20℃ 0.9925 0.9926 0.9927 0.9928 0.9929 T=40℃ 0.9936 0.9937 0.9938 0.9939 0.9940 T=60℃ 0.9945 0.9946 0.9948 0.9949 0.9951 T=80℃ 0.9968 0.9969 0.9970 0.9971 0.9972 T=100℃ 0.9991 0.9992 0.9993 0.9994 0.9995

[0264] This invention achieves the following core technical objectives through an integrated device and computational model:

[0265] 1. Eliminate transfer error: Achieve in-situ non-destructive separation and independent extraction of gas and liquid phases within the same reactor, reducing fluid cross-chamber transfer and dead volume errors in traditional equipment;

[0266] 2. Accurate solubility measurement: Overcoming the limitation that closed equipment cannot take samples in situ, it successfully obtained a high-precision steady-state dissolution equilibrium pressure and complete solubility chart, providing reliable support for the assessment of deep natural gas resources;

[0267] 3. Revealing the thermodynamic fractionation law of isotopes: The thermodynamic equilibrium fractionation coefficient of isotopes during the dissolution process was extracted under fully enclosed conditions, confirming the significant enrichment effect of the desolvated phase;

[0268] 4. Revealing the dynamic fractionation law of desolvation: By combining controlled depressurization staged gas collection with Rayleigh model, the precise quantification of desolvation kinetic diffusion parameters was achieved, filling the gap in the evaluation of dynamic fractionation characteristics during the formation drainage evolution process.

[0269] The application scenarios of this invention mainly cover the following four core technical fields: 1. Construction of an integrated high-temperature and high-pressure experimental device with in-situ separation to eliminate transfer errors; 2. Accurate determination of the solubility of natural gas under high temperature and high pressure in a closed system; 3. Static determination of isotope thermodynamic fractionation characteristics during the natural gas dissolution process; 4. Dynamic simulation of isotope kinetic fractionation characteristics during the natural gas desolvation process.

Claims

1. A high-temperature, high-pressure natural gas solubility determination and isotope fractionation simulation experimental apparatus, comprising: Gas supply module, liquid supply module, core reaction module, vacuum module, gas collection module, testing and analysis module, waste liquid discharge module, and computer control system; The gas supply module includes a high-pressure gas cylinder (7). The outlet end of the high-pressure gas cylinder (7) is connected to the upper part of the integrated reactor (1) in the core reaction module through a pipeline. A gas booster pump (8), a high-pressure regulating valve (9), a high-precision pressure sensor (5), and an inlet valve V1 (6) are installed sequentially on the pipeline between the high-pressure gas cylinder (7) and the integrated reactor (1). The liquid supply module includes a salt solution storage tank (10). The outlet end of the salt solution storage tank (10) is connected to the lower part of the integrated reactor (1) in the core reaction module through a pipeline. A constant pressure constant flow pump (11) and a liquid inlet valve V2 (12) are installed in sequence on the pipeline between the salt solution storage tank (10) and the integrated reactor (1). The core reaction module includes an integrated reactor (1); the integrated reactor (1) is covered with a programmed heating jacket, and the integrated reactor (1) is equipped with a magnetic stir bar (3) and a high-precision temperature sensor (4) inside. The computer control system controls the constant temperature and stirring action. The top and bottom of the integrated reactor (1) are respectively connected to ultra-high pressure inlet and outlet fluid pipelines and micro-sampling valves. The vacuum module includes a vacuum pump (13), the inlet end of which is connected to the top of the integrated reactor (1) in the core reaction module via a pipeline, and valves V3 (14) are installed sequentially on the pipeline between the vacuum pump (13) and the integrated reactor (1). The gas collection module includes free gas collection and desoluble gas collection: The free gas collection includes a first set of drainage and gas collection device (16), which is connected to the top of the integrated reactor (1) through a pipeline. A valve V4 (15) is installed on the pipeline between the first set of drainage and gas collection device (16) and the integrated reactor (1). The desolvation gas collection includes a second set of drainage gas collection device (18), which is connected to the upper part of the integrated reactor (1) through a pipeline. A valve V5 (17) is installed on the pipeline between the second set of drainage gas collection device (18) and the integrated reactor (1). The test and analysis module is an isotope mass spectrometer (21), which is connected to the first set of drainage and gas collection device (16) and the second set of drainage and gas collection device (18); the waste liquid discharge module includes a waste liquid discharge container (20), which is connected to the bottom outlet of the integrated reactor (1) through a pipeline, and a valve V6 (19) is installed on the pipeline between the waste liquid discharge container (20) and the integrated reactor (1); The computer control system (22) is electrically connected to the pressure sensor P1 (5), the gas booster pump (8), the constant pressure and constant flow pump (11), the isotope mass spectrometer (21), and the inlet valve V1 (6), the liquid inlet valve V2 (12), the valve V3 (14), the valve V4 (15), the valve V5 (17), and the valve V6 (19), respectively.

2. A method for determining the solubility of high-temperature and high-pressure natural gas using the experimental apparatus described in claim 1, comprising the following steps: Step (1): System vacuuming and airtightness check: Connect the pipelines of each module of the above experimental device tightly; turn on the vacuum pump (13), open valve V3 (14) to evacuate the gas phase space of the entire system; close valve V3 (14) and maintain the pressure for 10 minutes, and monitor the pressure fluctuation through a high-precision pressure sensor (5) to verify that the system is tight and leak-free; Step 2: Quantitative injection and spatial calibration: The constant pressure and constant flow pump (11) and the inlet valve V2 (12) are turned on to inject the mineralized salt solution from the salt solution storage tank (10) into the integrated reactor (1); the computer control system (22) automatically calculates the initial gas phase free space volume V inside the reactor according to the total volume of the reactor. free = V total - V w ; Step 3: Simulation Environment Construction and Gas Injection: Turn on the gas booster pump (8) and the high-pressure regulating valve (9), and inject the prepared natural gas sample from the high-pressure gas cylinder (7) into the integrated reactor (1) through the inlet valve V1 (6) to the preset initial high pressure P0; simultaneously turn on the programmed heating jacket (2) to heat to the target temperature T0, and start the magnetic stir bar (3) to accelerate the mass transfer balance between the gas and liquid phases at a speed of 300 rpm; wherein: the natural gas sample is prepared by volume percentage as follows: methane: 86.8%, ethane: 1.66%, carbon dioxide: 5.07%, nitrogen: 6.47%; Step 4: Determining Dissolution Equilibrium and Recording Data: The computer control system (22) collects the pressure curve in real time; as natural gas continuously dissolves in the aqueous phase, the pressure inside the integrated reactor (1) will gradually decrease; when the pressure change rate per unit time is <0.01MPa / h and the temperature fluctuation displayed by the high-precision temperature sensor (4) is less than the preset threshold for 1 hour, the computer control system (22) determines that a thermodynamic equilibrium state has been reached and automatically records the equilibrium pressure P at this time. eq .

3. The determination method according to claim 2, characterized in that: Methods for calculating solubility Includes the following steps: Because the experiment takes place in a high-temperature and high-pressure environment, the ideal gas law is no longer applicable. Therefore, a compressibility factor Z is introduced to correct for deviations from the real gas law; its basic form is: （1）； Where P is the system pressure, MPa; V is the volume occupied by the gas, mL; n is the number of moles of gas, mol; Z is the gas compressibility factor under the corresponding temperature and pressure conditions; R is the molar gas constant, 8.314 J / (mol·K); and T is the system temperature, K. In the initial stage, the gas phase space V of the integrated reactor is injected. free The total number of moles of natural gas is n0: （2）； After the system reaches dissolution equilibrium, the residue in the gas phase free space V free The number of gas moles in the container is n eq : （3）； According to the principle of mass balance, the number of moles of gas dissolved in the liquid phase is equal to the difference between the initial total number of moles and the number of moles of free gas remaining after equilibrium. （4）； Substituting into the above formula, we get: （5）； For easier comparison, the number of moles dissolved needs to be converted to volume under standard conditions: （6）； Where P0 is the initial injection pressure, P eq For the dissolution equilibrium pressure, V free Let Z0 and Z be the initial free space volume of the gas phase. eq These represent the gas compressibility factors under corresponding temperature and pressure conditions; R is the molar gas constant; T0 is the initial temperature; T eq To reach the equilibrium temperature; V m This refers to the molar volume of the gas under standard conditions. Solubility S is defined as the volume of gas that can be dissolved in a unit volume of solvent; that is, the volume of dissolved gas V under standard conditions. dissolved The volume V of the solution injected into the reactor w The ratio: （7）； Among them, V w The volume of the injected solution is given. Substituting the theoretical dissolved gas volume into the formula, the solubility of natural gas in formation water under different temperature and pressure conditions is calculated.

4. A method for determining isotope thermodynamic fractionation parameters during the natural gas dissolution process under high temperature and high pressure using the experimental apparatus described in claim 1, comprising the following steps: Steps 1-3 are the same as the method for determining the solubility of natural gas; Step 4: Determining Dissolution Equilibrium and Collecting Free Gas: When the pressure change rate per unit time is ≤0.01MPa / h, it is determined that the dissolution equilibrium state has been reached; open valve V4 (15), use the first set of drainage and gas collection device (16) to collect the undissolved residual free gas in the upper part, and use the isotope mass spectrometer (21) to perform methane carbon isotope analysis. Step 5: Induced desolvation and complete collection of dissolved gas: Close valve V4 (15), set heating jacket (2) to raise the temperature at a certain heating rate so that natural gas is completely desoluble from the solution, open valve V5 (17), use the second set of drainage gas collection device (18) to collect the completely desoluble gas, and use isotope mass spectrometer (21) for isotope analysis.

5. The determination method according to claim 4, characterized in that: The calculation method for isotope thermodynamic fractionation parameters in the natural gas dissolution process includes the following steps: Isotopic composition is usually expressed as the abundance ratio R of heavy isotopes to light isotopes. For carbon isotopes: （8）； Thermodynamic equilibrium fractionation coefficient α eq Defined as: the ratio of isotopic ratios of substances in two phases at equilibrium. In the "gas-liquid" equilibrium system simulated by this device, the fractionation coefficient α is defined as: eq The ratio of dissolved phase to free phase: （9）； In the formula, R dissolved R represents the abundance ratio of heavy isotopes to light isotopes in the dissolved phase under equilibrium conditions. free The abundance ratio of heavy isotopes to light isotopes in the downstream gas phase under equilibrium conditions; Because the absolute change in the isotope ratio R is extremely small, laboratories typically measure the part-thousandth deviation δ relative to the standard material. 13 C: （10）； In the formula, R std The isotopic abundance ratio of international standard reference materials; Transform the formula and solve for R: （11）； Substituting the R expressions for the dissolved phase and the free phase into equation (9): （12）； Simplifying, we get: （13）； Where: α eq δ is the isotopic thermodynamic equilibrium fractionation coefficient; 13 C free The carbon isotope value (‰) of residual free methane gas in equilibrium state; δ 13 C dissolved The carbon isotope value (‰) of dissolved methane in equilibrium state corresponds to this value.

6. A method for determining isotope kinetic fractionation parameters of natural gas desolvation process under high temperature and high pressure using the experimental apparatus described in claim 1, comprising the following steps: Steps 1-3 are the same as the method for determining the solubility of natural gas; Step 4: Initial equilibrium state isotope reference acquisition: Open valve V4 (15) and use the first set of drainage and gas collection device (16) to collect the undissolved residual free gas in the upper part for isotopic analysis to determine the initial isotopic characteristics of the system; at the same time, determine the methane carbon isotope value δ of the initial dissolved natural gas based on the thermodynamic evaluation results. 13 C0; Step 5: Inducing continuous desolvation and segmented instantaneous sampling: Based on the dissolution equilibrium, valve V4 (15) is closed; the system continuously and slowly reduces the pressure through precise control of the integrated reactor (1) to simulate the formation uplift or drainage depressurization process; during this dynamic desolvation process, valve V5 (17) is opened, and the second drainage gas collection device (18) is used to collect the instantaneous desolvation gas in segments and independently according to the preset pressure nodes, and the instantaneous isotopic composition δ of each stage is measured. 13 C exsolved .

7. The method for calculating isotope kinetic fractionation parameters of natural gas desolvation process under high temperature and high pressure according to claim 6, comprising the following steps: Before depressurization and solvent removal, based on the principle of material balance, the carbon isotope value δ of the total amount of desoluble gas methane measured in the thermodynamic equilibrium evaluation experiment was used. 13 C dissolved The isotopic reference value δ of the initial dissolved gas in the liquid phase is calibrated. 13 C0, i.e., setting δ 13 C0=δ 13 C dissolved ; In the physical process of continuous production of desoluble gas from liquid-phase dissolved gas, the isotope ratio R of the remaining dissolved gas in the liquid phase is... res The classic expression for the variation of the residual fraction f, the Rayleigh fractional distillation equation, is: （14）； Where R0 is the isotope ratio of the dissolved gas at f=1 in the initial state; R res The isotope ratio of the residual dissolved gas in the liquid phase at the current pressure node; f is the fraction of residual dissolved gas, 0 <f≤ 1; Based on the kinetic fractionation coefficient α k The definition is the ratio R of gases instantaneously released at any instantaneous desolvation moment. ex R, the ratio of the current liquid phase residual gas res The relationship between them is: （15）； Substitute (15) into (14) to eliminate R. res After sorting, we can obtain: （16）； After logarithmic transformation, we get: （17）； Due to the α-propagation in natural gas isotope research k Extremely close to 1, ln(α) k ) ≈α k – 1; The simplified expression of the above formula is: （18）； Using the standard conversion relationship between the isotope ratio R and the experimentally measured δ isotope ratio: （19）； Substituting this relationship into equation (18), we get: （20）； Solve for the fractionation coefficient α k : （21）； In the Rayleigh model, α k Defined as the ratio of the dissolved gas from the instantaneous products to the dissolved gas from the remaining reactants; （22）； In the kinetic desolvation process, the isotope ratio R of the gaseous products that escape instantaneously 产物 It depends on the ratio of the flux of the heavy and light isotope molecules across the gas-liquid interface: （23）； Among them, J * heavy isotope molecules 13 The diffusion flux of CH4, where J is a light isotope molecule. 12 The diffusion flux of CH4; According to Fick's first law, the diffusion flux J of a certain component is related to the diffusion coefficient D and the concentration gradient. C is directly proportional to: （24）； Substituting into equation (23), we get: （25）； In the formula, R 产物 The ratio of heavy to light isotope abundance of transient products; D * heavy isotope molecules 13 The diffusion coefficient of CH4; D is a light isotope molecule. 12 The diffusion coefficient of CH4; C * The concentration gradient of heavy isotope molecules in the diffusion boundary layer; C represents the concentration gradient of light isotope molecules in the diffusion boundary layer; In a liquid-phase reactant system, due to the extremely similar properties of isotope molecules, the ratio of the concentration gradients of heavy and light isotopes within the diffusion boundary layer is approximately equal to their concentration ratio in the bulk liquid phase. （26）； In the formula, R 产物 The ratio of the heavy to light isotope abundance of the remaining reactants; C * The concentration gradient of heavy isotope molecules in the diffusion boundary layer; C represents the concentration gradient of light isotope molecules in the diffusion boundary layer; C * denoted as , where is the concentration of heavy isotope molecules in the liquid phase; C is the concentration of light isotope molecules in the liquid phase; Substituting equation (26) into equation (25), we get: （27）； The instantaneous isotope values ​​δ measured during the continuous desolvation process were analyzed. 13 C dissolved The remaining dissolved gas fraction f was calculated using Rayleigh equation (21) to obtain D under different temperature and pressure conditions. * / D(α) k )value.

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