CN-122016554-A - High-temperature high-pressure natural gas solubility determination and isotope fractionation simulation experiment device and method

CN122016554ACN 122016554 ACN122016554 ACN 122016554ACN-122016554-A

Abstract

The invention discloses a high-temperature high-pressure natural gas solubility determination and isotope fractionation simulation experiment device and method. The device comprises an air 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 steps of injecting solution and natural gas into a reaction kettle to dissolve balance, introducing a state equation to directly calculate theoretical dissolved gas quantity and solubility, independently collecting residual free gas in an equilibrium state and integral desolventizing gas, measuring isotopes, calculating thermodynamic equilibrium fractionation coefficients in a dissolving process, inducing continuous desolventizing of the natural gas, collecting instantaneous desolventizing gas in sections, measuring isotopes, and calculating dissolution kinetic fractionation parameters by combining a Rayleigh model. The invention completes the whole process in situ in the same kettle body, thoroughly eliminates the fluid transfer error and provides a reliable evaluation means for deep natural gas reservoir simulation.

Inventors

HE HONGCHENG
LI WENBIAO
WANG JUN
ZHANG PENGFEI
CHEN GUOHUI
ZHOU NENGWU
Wang Zidie

Assignees

东北石油大学三亚海洋油气研究院

Dates

Publication Date: 20260512
Application Date: 20260416

Claims (7)

1. The high-temperature high-pressure natural gas solubility measurement and isotope fractionation simulation experiment device comprises a gas supply module, a liquid supply module, a core reaction module, a vacuum module, a gas collection module, a test analysis module, a waste liquid discharge module and a computer control system; The gas supply module comprises a high-pressure gas cylinder (7), the outlet end of the high-pressure gas cylinder (7) is communicated with the upper part of an integrated reaction kettle (1) in the core reaction module through a pipeline, and a gas booster pump (8), a high-pressure regulating valve (9), a high-precision pressure sensor (5) and a gas inlet valve V1 (6) are sequentially arranged on the pipeline between the high-pressure gas cylinder (7) and the integrated reaction kettle (1); The liquid supply module comprises a salt solution storage tank (10), the outlet end of the salt solution storage tank (10) is communicated with the lower part of an integrated reaction kettle (1) in the core reaction module through a pipeline, and a constant pressure constant flow pump (11) and a liquid inlet valve V2 (12) are sequentially arranged on the pipeline between the salt solution storage tank (10) and the integrated reaction kettle (1); The core reaction module comprises an integrated reaction kettle (1), wherein a temperature programming heating sleeve is sleeved outside the integrated reaction kettle (1), a magnetic stirrer (3) and a high-precision temperature sensor (4) are arranged inside the integrated reaction kettle (1), the computer control system controls the constant temperature and stirring actions, and the top and the bottom of the integrated reaction kettle (1) are respectively connected with an ultrahigh pressure inlet and outlet fluid pipeline and a microsampling valve; The vacuum module comprises a vacuum pump (13), the inlet end of the vacuum pump (13) is communicated with the top of the integrated reaction kettle (1) in the core reaction module through a pipeline, and a valve V3 (14) is sequentially arranged on the pipeline between the vacuum pump (13) and the integrated reaction kettle (1); the gas collection module comprises free gas collection and desolventizing gas collection: The free gas collection comprises a first set of drainage gas collecting device (16), the first set of drainage gas collecting device (16) is communicated with the top of the integrated reaction kettle (1) through a pipeline, and a valve V4 (15) is arranged on the pipeline between the first set of drainage gas collecting device (16) and the integrated reaction kettle (1); The desolventizing gas collection comprises a second set of drainage gas-collecting device (18), the second set of drainage gas-collecting device (18) is communicated with the upper part of the integrated reaction kettle (1) through a pipeline, and a valve V5 (17) is arranged on the pipeline between the second set of drainage gas-collecting device (18) and the integrated reaction kettle (1); The test analysis module is an isotope mass spectrometer (21) and is communicated with a first set of drainage gas collecting device (16) and a second set of drainage gas collecting device (18), the waste liquid discharge module comprises a waste liquid discharge container (20), the waste liquid discharge container (20) is communicated with a bottom liquid outlet of the integrated reaction kettle (1) through a pipeline, and a valve V6 (19) is arranged on a pipeline between the waste liquid discharge container (20) and the integrated reaction kettle (1); The computer control system comprises a computer control system (22) which is respectively and electrically connected with a pressure sensor P1 (5), a gas booster pump (8), a constant pressure and constant flow pump (11), an isotope mass spectrometer (21), an air inlet valve V1 (6), a liquid inlet valve V2 (12), a valve V3 (14), a valve V4 (15), a valve V5 (17) and a valve V6 (19).
2. The method for measuring the solubility of the high-temperature and high-pressure natural gas by using the experimental device of claim 1, comprising the following steps: step (1), system vacuum chamber and air tightness inspection: The experimental device is characterized by comprising the steps of connecting the pipelines of all modules of the experimental device tightly, starting a vacuum pump (13), opening a valve V3 (14) to vacuumize a gas phase space of the whole system, closing the valve V3 (14) to maintain the pressure for 10 minutes, monitoring pressure fluctuation through a high-precision pressure sensor (5), and verifying that the system is tight and has no leakage; and 2, quantitatively injecting liquid and calibrating space: Starting a constant pressure constant flow pump (11) and a liquid inlet valve V2 (12) to inject mineralized salt solution into the integrated reaction kettle (1) from a salt solution storage tank (10), and automatically calculating the initial gas phase free space volume V free = V total - V w in the kettle by a computer control system (22) according to the total volume of the reaction kettle; Step 3, simulating environment construction and gas injection: Starting a gas booster pump (8) and a high-pressure regulating valve (9), injecting a prepared natural gas sample into an integrated reaction kettle (1) from a high-pressure gas bottle (7) to a preset initial high pressure P 0 through an air inlet valve V1 (6), synchronously starting a temperature programming heating sleeve (2) to heat to a target temperature T 0 , and starting a magnetic stirrer (3) to accelerate mass transfer balance between gas and liquid at a rotating speed of 300 rpm, wherein the natural gas sample comprises, by volume, 86.8% of methane, 1.66% of ethane, 5.07% of carbon dioxide and 6.47% of nitrogen; Step 4, dissolution balance judgment and data recording: The computer control system (22) collects a pressure curve in real time, the pressure in the integrated reaction kettle (1) gradually drops due to the fact that natural gas is continuously dissolved in a water phase, and when the pressure change rate in unit time is less than 0.01MPa/h and the temperature fluctuation displayed by the high-precision temperature sensor (4) is continuously smaller than a preset threshold value for 1 hour, the computer control system (22) judges that a thermodynamic equilibrium state is achieved, and the equilibrium pressure P eq at the moment is automatically recorded.
3. The method for measuring a solubility according to claim 2, wherein the method for calculating the solubility comprises the steps of: because the experiment is in a high-temperature and high-pressure environment, an ideal gas state equation is not applicable any more, and the compression factor Z is introduced to correct the deviation of the real gas, and the basic form is as follows: (1); Wherein P is the system pressure, MPa, V is the volume occupied by gas, mL, n is the mole number mol of the gas, Z is the gas compression factor under the corresponding temperature and pressure condition, R is the mole gas constant, 8.314J/(mol.K), T is the temperature of the system, K; At the beginning, the total mole number of the natural gas injected into the gas phase space V free of the integrated reaction kettle is n 0 : (2); When the system reaches a dissolution equilibrium state, the number of moles of gas remaining in the gas phase free space V free 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 balancing: (4); Substituting the above formula can result in: (5); For ease of comparison, the number of moles dissolved needs to be converted to volume under standard conditions: (6); Wherein, P 0 is initial gas injection pressure, P eq is dissolution equilibrium pressure, V free is initial gas phase free space volume, Z 0 、Z eq is gas compression factor under the corresponding temperature and pressure conditions, R is mole gas constant, T 0 is initial temperature, T eq is temperature reaching equilibrium state, V m is gas mole volume under standard condition; The solubility S is defined as the volume of gas which can be dissolved in a unit volume of solvent, namely the ratio of the standard dissolved gas volume V dissolved to the volume of solution V w injected into the reaction kettle: (7); Wherein V w is the volume of the injected solution, and the theoretical dissolved gas is substituted into the formula to calculate and obtain the solubility of the natural gas in the formation water under different temperature and pressure conditions.
4. A method for determining the isotopic thermodynamic fractionation parameters of a natural gas dissolution process at high temperature and high pressure using the experimental apparatus of claim 1, comprising the steps of: step 1-step 3 are the same as the natural gas solubility determination method; Step 4, judging dissolution balance and collecting free gas: when the pressure change rate in unit time is less than or equal to 0.01MPa/h, judging that the dissolution balance state is reached, opening a valve V4 (15), collecting undissolved residual free gas at the upper part by using a first set of water and gas collecting device (16), and performing methane carbon isotope analysis by using an isotope mass spectrometer (21); and 5, induction desolventizing and total-amount collection of dissolved gas: Closing a valve V4 (15), setting a heating sleeve (2) to raise the temperature at a certain heating rate, completely desolventizing natural gas from the solution, opening a valve V5 (17), integrally collecting completely resolved and escaped desolventized gas by using a second set of water and gas collecting device (18), and performing isotope analysis by using an isotope mass spectrometer (21).
5. The method for determining the isotope thermodynamic fractionation parameters of a natural gas dissolving process according to claim 4, wherein the method for calculating the isotope thermodynamic fractionation parameters of the natural gas dissolving process comprises the steps of: the isotopic composition is generally expressed by the abundance ratio R of heavy isotopes to light isotopes, for carbon isotopes: (8); Thermodynamic equilibrium fractionation coefficient α eq is defined as the ratio of the isotope ratio of a substance in two phases at equilibrium, and in the "gas-liquid" equilibrium system simulated by the present apparatus, fractionation coefficient α eq is defined as the ratio of the dissolved phase to the free phase: (9); Wherein R dissolved is the abundance ratio of heavy isotope to light isotope in the dissolved phase in the equilibrium state, R free is the abundance ratio of heavy isotope to light isotope in the free gas phase in the equilibrium state; Since the absolute variation of the isotope ratio R is extremely small, the laboratory typically determines the micrometer deviation value δ 13 C from the standard: (10); Wherein R std is the isotope abundance ratio of an international standard substance; deforming the formula to solve R: (11); Substituting the R expression of the dissolved and free phases into formula (9): (12); The simplification can be obtained: (13); wherein, alpha eq is the isotope thermodynamic equilibrium fractionation coefficient, delta 13 C free is the equilibrium state residual free gas methane carbon isotope value (mill), and delta 13 C dissolved is the equilibrium state corresponding solution gas methane carbon isotope value (mill).
6. The method for determining the isotope dynamics fractionation parameters in the process of desolventizing natural gas at high temperature and high pressure by using the experimental device of claim 1, comprising the following steps: step 1-step 3 are the same as the natural gas solubility determination method; Step 4, initial equilibrium isotope reference acquisition: Opening a valve V4 (15), collecting undissolved residual free gas at the upper part by using a first set of water and gas drainage and collection device (16) for isotope analysis, and determining the initial isotope characteristic of the system; Step 5, inducing continuous desolventizing and sectional instantaneous sampling: On the basis of dissolution balance, a valve V4 (15) is closed, the system continuously and slowly reduces pressure through a precise control integrated reaction kettle (1) to simulate the stratum lifting or drainage pressure reduction process, in the dynamic desolventizing process, a valve V5 (17) is opened, the instantaneous desolventizing gas is collected in sections and independently according to preset pressure nodes by a second drainage gas collecting device (18), and the instantaneous isotope composition delta 13 C exsolved of each stage is measured.
7. The method for calculating the isotope kinetic fractionation parameters in the process of desolventizing natural gas at high temperature and high pressure according to claim 6, comprising the following steps: Before depressurization desolventizing, the isotope value delta 13 C dissolved of the total desolventized gas methane carbon measured in a thermodynamic equilibrium evaluation experiment is calibrated to be an isotope reference value delta 13 C 0 of the initial dissolved gas in a liquid phase based on a substance balance principle, namely delta 13 C 0 = δ 13 C dissolved is set; in the physical process of continuously producing desolventized gas from liquid phase dissolved gas, the classical expression that the isotope ratio R res of the residual dissolved gas in the liquid phase changes along with the residual fraction f is shown in the equation of Rayleigh Li Fenliu: (14); Wherein R 0 is the isotope ratio of f=1 dissolved gas in the initial state, R res is the isotope ratio of residual dissolved gas in the liquid phase at the current pressure node, f is the residual dissolved gas fraction, and f is more than 0 and less than or equal to 1; According to the definition of the kinetic fractionation coefficient alpha k , at any instant desolventizing moment, the relation between the instant desolventizing gas ratio R ex and the current liquid-phase residual gas ratio R res is as follows: (15); Substituting (15) into (14), and eliminating R res to obtain the product: (16); and carrying out logarithmic treatment to obtain: (17); Since α k is extremely close to 1 in natural gas isotope studies, ln (α k ) ≈α k -1; the above formula is expressed in simplified form: (18); Using the standard conversion relationship between the isotope ratio R and the experimentally measured delta isotope ratio: (19); substituting this relationship into expression (18) yields: (20); Solving for fractional coefficient alpha k : (21); in the rayleigh model, α k is defined as the ratio of instantaneous product desolventizing gas to the remaining reactant dissolving gas; (22); During kinetic desolventization, the isotope ratio R Product(s) of the instantaneously evolved gas product depends on the ratio of the fluxes of the two heavy and light isotope molecules across the gas-liquid interface: (23); Wherein J * is the diffusion flux of heavy isotope molecule 13 CH 4 and J is the diffusion flux of light isotope molecule 12 CH 4 ; According to Fick's first law, a certain component diffuses flux J and diffusion coefficient D and concentration gradient C is proportional to: (24); substituting into the formula (23) to obtain: (25); Wherein R Product(s) is the heavy and light isotope abundance ratio of the transient product, D * is the diffusion coefficient of the heavy isotope molecule 13 CH 4 , D is the diffusion coefficient of the light isotope molecule 12 CH 4 ; C * is the concentration gradient of the heavy isotopic molecules in the diffusion boundary layer; C is the concentration gradient of the light isotope molecules in the diffusion boundary layer; in liquid phase reactant systems, due to the extreme proximity of isotopic molecular properties, the concentration gradient ratio of heavy and light isotopes in the diffusion boundary layer is approximately equal to the concentration ratio of them in the liquid phase bulk: (26); wherein R Product(s) is the heavy and light isotope abundance ratio of the remaining reactants; C * is the concentration gradient of the heavy isotopic molecules in the diffusion boundary layer; C is the concentration gradient of the light isotope molecules in the diffusion boundary layer, C * is the concentration of the heavy isotope molecules in the liquid phase, C is the concentration of the light isotope molecules in the liquid phase; Bringing formula (26) into (25) gives: (27); The corresponding D * /D（α k ) values under different temperature and pressure conditions are obtained by carrying out Rayleigh Li Gongshi (21) calculation on the instantaneous isotope value delta 13 C dissolved and the residual solution gas fraction f which are measured in the continuous desolventizing process.

Description

High-temperature high-pressure natural gas solubility determination and isotope fractionation simulation experiment device and method Technical Field The invention relates to the technical field of oil and gas exploration and development, in particular to a device and a method for measuring solubility of high-temperature high-pressure natural gas and simulating isotope fractionation. Background As global oil and gas exploration continues to evolve into deep and ultra-deep fields, the facing high temperature, high pressure, and even ultra-high pressure geological conditions are becoming increasingly prevalent. The phase evolution and solubility evaluation of natural gas in deep underground fluid (especially stratum water) have important roles in gas reservoir evolution, quantitative estimation of resource quantity and dynamic prediction of gas field development. The deep natural gas is in long-term contact with formation water under an extreme closed system and achieves thermodynamic dynamic balance, and the accurate evaluation of the natural gas solubility and isotope fractionation characteristics under the steady-state condition is a core means for tracking a deep gas source, recovering a natural gas migration path and evaluating water-soluble gas release potential. However, currently, for the physical simulation experiments of natural gas dissolution and isotope fractionation under the extreme temperature and pressure conditions, the existing equipment and technical methods have obvious limitations, and the obvious limitations are embodied in the following four core aspects: 1. The separation function of the device has congenital defect, is easy to induce secondary fractionation, and the traditional experimental equipment of a pure closed system (such as a conventional PVT cylinder or a high-pressure reaction kettle) extremely lacks in-situ gas-liquid separation capability after dissolution balance is completed. In performing sampling tests, it is often necessary to transfer fluid across the chamber to an external sampling bottle or to depressurize through a valve line. The process is extremely easy to cause gas-liquid phase mutation due to the dead volume and the instant pressure drop of the pipeline, so that the dissolved gas is dissolved and dissipated in advance. The uncontrolled pressure drop during such physical separation can trigger intense secondary kinetic fractionation (i.e., preferential escape of the light isotopes) to thoroughly mask the true thermodynamic equilibrium state that would otherwise be achieved in the reaction vessel. 2. The solubility of the Wen Yaxia is difficult to accurately measure, namely, the single PVT method or the conventional dissolution experiment method which are commonly used for measuring the solubility at present is difficult to accurately obtain the real volume distribution of gas and liquid phases after the dissolution equilibrium is achieved under the condition of extremely high temperature and high pressure. Because the high-temperature high-pressure sealed container usually has an observation blind area, and the traditional volumetric measurement method which relies on depressurization and degassing can not ensure the full recovery of dissolved gas, the calculation of material balance is difficult, and the measured deep natural gas solubility data often has larger errors. 3. The thermodynamic steady-state isotope fractionation characteristic extraction distortion, namely the accurate calculation of the isotope thermodynamic equilibrium fractionation coefficient in the natural gas dissolution process, is highly dependent on the lossless extraction of the residual free phase and the integral dissolved phase under the same closed equilibrium system. Due to the interference of the transfer error of the equipment and the sampling pressure drop, the existing method cannot realize in-situ full extraction on the premise of not damaging the original thermodynamic equilibrium. This results in a measured isotope value that is actually a mixed superposition of thermodynamic equilibrium effects and sampling process dynamics effects, severely affecting the accuracy of the determination of the true thermodynamic fractionation law under deep geological conditions. 4. The dynamic fractionation simulation means of the dynamic desolventizing process is missing, namely the structural lifting in the geological history period or the depressurization drainage in the gas field development period, and is essentially a dynamic opening process for continuously desolventizing natural gas from stratum water. The existing static evaluation method and single-point sampling device cannot truly simulate the continuous depressurization dynamic geological process, and further cannot meet the high-precision segmented sampling requirement required by the Rayleigh fractionation model. Therefore, the prior art cannot realize continuous tracking and quantitative characterization of isotope dynamics