A method for predicting the helium leakage depth in a salt cavern helium storage reservoir

Abstract

The present invention discloses a method for predicting the leakage depth of helium in a salt cavern helium storage reservoir. First, obtain the porosity, tortuosity, and pore size distribution data of the rock sample, and then combine with the comprehensive permeability prediction method of salt rock proposed by the present invention, which considers the Knudsen effect, viscous flow, and surface diffusion effect, to calculate the comprehensive permeability of helium under the temperature and pressure conditions where the salt cavern is located; finally, according to the wellhead pressure and helium injection and production data, combined with the gas seepage equation, the leakage depth of helium during the storage period can be predicted, providing a theoretical reference for the design and construction of the helium storage reservoir and the safe and efficient storage of helium.

Description

Technical Field

[0001] The present invention relates to the technical field of strategic energy material reserves, and particularly relates to a method for predicting the helium leakage depth for a salt cavern helium storage. Background Art

[0002] As a strategic scarce material, helium is widely used as a pressure agent and booster in the aerospace industry, a coolant in the nuclear industry, and a shielding gas for welding.

[0003] Salt rock formations are excellent geological bodies for deep underground energy storage. They have the characteristics of low permeability (less than 10 -20 m 2 ) and small porosity (less than 1%). They are widely used for natural gas storage in major energy-consuming countries such as the United States, Europe, and China, and are also an important development direction for large-scale helium storage in China. Compared with the underground storage of conventional natural gas, the helium molecule diameter is 0.26 nm, which is about 30% smaller than the methane molecule diameter of 0.38 nm. Under the same operating pressure, the permeation and diffusion effect of helium is stronger, which also puts higher requirements on the tightness of salt cavern gas storage.

[0004] In the tightness evaluation of salt cavern gas storage, great attention is paid to the helium leakage depth, which is mainly manifested in the following aspects: (1) The leakage depth is the core factor for designing and judging whether there is cross-flow between salt cavern helium storage groups, and directly determines the safety pillar distance from the flow perspective; (2) Compared with natural gas, helium has a higher cost, and the leakage depth is also an important factor for evaluating the helium loss, which is an economic issue that must be considered in engineering applications; (3) Compared with salt domes in Europe and the United States, Chinese salt rocks have unfavorable geological factors such as thin salt layers, many interlayers, and developed microfractures. The leakage depth is a key factor that should be considered first when selecting salt cavern sites. Therefore, accurately predicting the helium leakage depth during the long-term strategic reserve process is of great significance for ensuring the safe and efficient storage of helium. Summary of the Invention

[0005] By providing a method for predicting the helium leakage depth for a salt cavern helium storage, the present invention can accurately predict the helium leakage depth during the long-term strategic reserve process.

[0006] The present invention provides a method for predicting the helium leakage depth for a salt cavern helium storage, including:

[0007] Obtaining the porosity, tortuosity, and pore size distribution data of the rock sample;

[0008] Calculating the permeability component k corresponding to viscous flow through the formula ; where λ v is the maximum pore diameter of the salt rock, λ max , and λ minis the minimum pore diameter of the salt rock, λ is the pore diameter of the salt rock, τ is the tortuosity of the salt rock, N is the number of pores with a pore diameter of λ, and A is the seepage area of helium;

[0009] The permeability component k corresponding to the Knudsen effect is calculated through the formula ; where μ is the viscosity of helium, Z is the compressibility factor of helium, p is the gas pressure, R is the gas constant, T is the temperature of helium, M is the molar mass of helium, and K k is the Knudsen coefficient of helium; n

[0010] The permeability component k corresponding to the surface diffusion effect is calculated through the formula ; where δ is the molar diameter of helium, θ is the dimensionless coefficient of the relationship between pore pressure and Langmuir pressure, D s is the surface diffusion coefficient, C s is the maximum gas capacity of the salt rock, p amax is the Langmuir pressure of helium; L

[0011] The comprehensive permeability k of helium is calculated through the formula k = k v + k k + k s ;

[0012] By numerically solving the formula , the leakage law of helium in the surrounding rock of the salt cavern helium storage can be simulated, and the pressure field distribution data within the entire surrounding rock can be obtained; where φ is the porosity of the salt rock, ρ is the density of helium, t is the simulation time, and x is the distance from the surrounding rock to the cavity wall;

[0013] According to the helium leakage simulation, the pressure field distribution in the salt cavern helium storage and the surrounding rock can be obtained, and then the seepage velocity of helium from the cavity wall into the surrounding rock can be obtained;

[0014] The helium leakage depth R is calculated through the formula ; where h is the height of the salt cavern, and R 0 is the radius of the salt cavern at dh.

[0015] Specifically, the C amax is calculated through the formula ; where V L is the Langmuir volume of helium, ρ STG is the density of helium under standard conditions, ρ grain is the density of the rock sample, and ε k is the ratio of the adsorbed substance volume to the total rock volume.

[0016] Specifically, the acquisition of the porosity, tortuosity, and pore size distribution data of the rock sample includes:

[0017] Core samples of the salt rock in the salt cavern are taken to obtain cored rock samples;

[0018] Mercury intrusion tests are carried out on the cored rock samples to obtain the porosity, tortuosity and pore size distribution data of the rock samples.

[0019] Specifically, the pressure field distribution in the salt cavern helium storage and its surrounding rock can be obtained according to the helium leakage simulation, and further the seepage velocity of helium from the cavity wall into the surrounding rock can be obtained, including:

[0020] Through the formula The seepage velocity v of helium from the cavity wall into the surrounding rock is calculated.

[0021] One or more technical solutions provided in the present invention have at least the following technical effects or advantages:

[0022] First, obtain the porosity, tortuosity and pore size distribution data of the rock sample, and then combine with the comprehensive permeability prediction method of salt rock considering the Knudsen effect, viscous flow and surface diffusion effect proposed in the present invention to calculate the comprehensive permeability of helium under the temperature and pressure conditions where the salt cavern is located; finally, according to the wellhead pressure and helium injection and production data, combined with the gas seepage equation, the leakage depth of helium during the storage period can be predicted, providing a theoretical reference for the design and construction of the helium storage and the safe and efficient storage of helium. Description of the Drawings

[0023] Figure 1 It is a flow chart of the helium leakage depth prediction method for a salt cavern helium storage provided by an embodiment of the present invention;

[0024] Figure 2 It is a structural schematic diagram of a prediction system built based on the helium leakage depth prediction method for a salt cavern helium storage provided by an embodiment of the present invention;

[0025] Among them, 1. Helium flowmeter, 2. Wellhead pressure gauge, 3. Injection and production string, 4. Salt cavern helium storage, 5. Cored salt rock, 6. Rock pore size distribution test device, 7. Signal transmission optical cable, 8. Signal receiving end, 9. Terminal helium leakage depth quantitative prediction system. Detailed Embodiments

[0026] By providing a helium leakage depth prediction method for a salt cavern helium storage, the embodiment of the present invention can accurately predict the leakage depth of helium during the long-term strategic storage process.

[0027] The technical solution in the embodiment of the present invention to achieve the above technical effects has the following general idea:

[0028] In view of the major demand for predicting the helium leakage depth in the engineering design of salt cavern helium storage, the embodiment of the present invention provides a method for quantitatively predicting the helium leakage depth in a salt cavern helium storage: by performing precise mercury intrusion tests on in-situ drilled core samples, data on the porosity, tortuosity, and pore size distribution of the core samples can be obtained; combined with the comprehensive permeability prediction method of salt rock proposed in the embodiment of the present invention, which considers the Knudsen effect, viscous flow, and surface diffusion effects, the comprehensive permeability of helium under the temperature and pressure conditions of the salt cavern can be calculated; finally, based on the wellhead pressure and helium injection / production data monitored on the ground, combined with the gas seepage equation, the leakage depth of helium during the storage period can be predicted, providing a theoretical reference for the design and construction of the helium storage and the safe and efficient storage of helium.

[0029] To better understand the above technical solution, the following will describe the above technical solution in detail in combination with the accompanying drawings of the specification and specific implementation manners.

[0030] See Figure 1 , the method for predicting the helium leakage depth for a salt cavern helium storage provided by the embodiment of the present invention includes:

[0031] Step S110: Obtain data on the porosity, tortuosity, and pore size distribution of the core sample;

[0032] Specifically describing this step, obtaining data on the porosity, tortuosity, and pore size distribution of the core sample includes:

[0033] Core the salt rock in the salt cavern cavity to obtain a cored sample;

[0034] Perform a mercury intrusion test on the cored sample to obtain data on the porosity, tortuosity, and pore size distribution of the core sample.

[0035] More specifically, during the construction stage of the salt cavern helium storage, core the salt rock at the buried depth position of the salt cavern cavity through a coring tool. Perform a mercury intrusion test on the cored sample in a ground laboratory to obtain data on the porosity, tortuosity, and pore size distribution of the core sample.

[0036] Step S120: Calculate the permeability component k corresponding to viscous flow through the formula ; where λ v ; λ max is the maximum pore size of the salt rock, λ min is the minimum pore size of the salt rock, λ is the pore size of the salt rock, τ is the tortuosity of the salt rock, N is the number of pores with a pore size of λ, and A is the seepage area of helium;

[0037] Step S130: Calculate the permeability component k corresponding to the Knudsen effect through the formula ; k; where μ is the viscosity of helium, Z is the compressibility factor of helium, p is the gas pressure, R is the gas constant, T is the temperature of helium, M is the molar mass of helium, and K n is the Knudsen coefficient of helium;

[0038] Step S140: Calculate the permeability component k corresponding to the surface diffusion effect through the formula ; where δ is the molar diameter of helium, θ is the dimensionless coefficient of the relationship between pore pressure and Langmuir pressure, D s is the surface diffusion coefficient, C s is the maximum gas capacity of salt rock, p amax is the Langmuir pressure of helium; L ;

[0039] Specifically, C amax is calculated through the formula ; where V L is the Langmuir volume of helium, ρ STG is the density of helium under standard conditions, ρ grain is the density of the rock sample, ε k is the ratio of the adsorbed volume to the total rock volume.

[0040] It should be noted here that obtaining k v , k k and k s does not distinguish the order. The following specifically explains the calculation formulas of k v , k k and k s :

[0041] Based on the viscous flow theory, the present invention embodiment considers the Knudsen effect and surface diffusion effect of helium in the pores of heterogeneous salt rock, and invents a comprehensive permeability prediction method for helium under different temperature and pressure conditions. The specific implementation steps are as follows:

[0042] ① Calculate the seepage flux of helium in salt rock

[0043] The Knudsen effect and surface diffusion effect of helium seepage in porous media can be regarded as an additional permeability on the basis of viscous flow. The seepage fluxes of the three effects can be respectively expressed as:

[0044] Viscous flow:

[0045]

[0046] In the formula, Q v is the seepage flux of helium viscous flow, m 3 / s; λ is the pore diameter of salt rock, m; τ is the tortuosity of salt rock; μ is the viscosity of helium, Pa·s; p is the gas pressure, Pa.

[0047] Knudsen effect:

[0048]

[0049] In the formula, Q k is the Knudsen seepage flux of helium, m 3 / s; Z is the compressibility factor of helium; R is the gas constant, with a value of 8.314 J / (mol·K); T is the temperature of helium, K; M is the molar mass of helium, kg / mol; K n is the Knudsen coefficient of helium.

[0050] Surface diffusion effect:

[0051]

[0052] In the formula, Q s is the surface diffusion seepage flux of helium, m 3 / s; δ is the molar diameter of helium, m; θ is the dimensionless coefficient of the relationship between pore pressure and Langmuir pressure; D s is the surface diffusion coefficient; C amax is the maximum gas capacity of salt rock, mol / m 3 , which can be calculated by the following formula (4); p L is the Langmuir pressure of helium, Pa.

[0053]

[0054] In the formula, V L is the Langmuir volume of helium, m 3 / kg; ρ STG is the density of helium under standard conditions, kg / m 3 ; ρ grain is the density of the salt rock sample, kg / m 3 ; ε k is the ratio of the adsorbed volume to the total rock volume.

[0055] ② Calculate the permeability components under the three effects:

[0056] The quantitative relationship between permeability and seepage flux can be established through Darcy's law as follows:

[0057]

[0058] In the formula, A is the seepage area of helium, m 2 .

[0059] Substituting the above equations (1), (2), and (3) into Equation (5), the permeability components corresponding to viscous flow, Knudsen effect, and surface diffusion effect can be obtained as follows:

[0060] Viscous flow:

[0061]

[0062] where λ max , λ min are the maximum pore diameter and minimum pore diameter of the salt rock, respectively, in m; N is the number of pores with pore diameter λ.

[0063] Knudsen effect:

[0064]

[0065] Surface diffusion effect:

[0066]

[0067] Step S150: Calculate the comprehensive permeability k of helium through the formula k = k v + k k + k s ;

[0068] Step S160: By numerically solving the formula , the leakage law of helium in the surrounding rock of the salt cavern helium storage can be simulated to obtain the pressure field distribution data within the entire surrounding rock; where φ is the porosity of the salt rock, ρ is the density of helium, t is the simulation time, and x is the distance from the surrounding rock to the cavity wall;

[0069] The following is a specific description of the formula :

[0070] Since the pressure in the salt cavern helium storage is higher than the formation pressure, helium will leak into the formation along the cavity wall under the pressure difference. The leakage characteristics of helium can be characterized by the seepage equation as follows:

[0071]

[0072] where ρ is the density of helium, in kg / m 3 ; φ is the porosity of the salt rock; t is the simulation time, in s.

[0073] Considering the change in the density of helium under different temperature and pressure conditions, the first term on the left side of the above equation (9) can be transformed as:

[0074]

[0075] Combining equations (9) and (10), the seepage equation of helium in the salt rock can be further transformed as:

[0076]

[0077] Step S170: According to the helium leakage simulation, the pressure field distribution in the salt cavern helium storage and its surrounding rock can be obtained, and then the seepage velocity of helium from the cavity wall into the surrounding rock can be obtained.

[0078] Specifically explaining this step, according to the helium leakage simulation, the pressure field distribution in the salt cavern helium storage and its surrounding rock can be obtained, and then the seepage velocity of helium from the cavity wall into the surrounding rock can be obtained, including:

[0079] Through the formula The seepage velocity v of helium from the cavity wall into the surrounding rock is calculated.

[0080] Step S180: Through the formula The helium leakage depth R is calculated; where h is the height of the salt cavern, in m; R 0 is the radius of the salt cavern at dh, in m.

[0081] Refer to Figure 2 , based on the helium leakage depth prediction method for salt cavern helium storage provided by the embodiments of the present invention, the built helium leakage depth prediction system includes: a helium flowmeter 1, a wellhead pressure gauge 2, a signal transmission optical cable 7, a signal receiving end 8, and a terminal helium leakage depth quantitative prediction system 9; the helium flowmeter 1 and the wellhead pressure gauge 2 are installed on the wellhead surface manifold, and the collected pressure and flow signals are transmitted to the signal receiving end 8 through the signal transmission optical cable 7; the signal receiving end 8 is installed in the central control room of the well site for signal decoding and remote transmission to the terminal helium leakage depth quantitative prediction system 9.

[0082] During the helium storage process, the injection-production string 3 is the connection channel between the surface manifold and the underground salt cavern helium storage 4; the cored salt rock 5 at the beginning of the construction of the helium storage is taken and experimentally analyzed in the rock pore size distribution test device 6 on the ground. Based on the porosity, tortuosity, and pore size distribution data of the cored salt rock 5, considering the Knudsen effect and surface diffusion effect of helium on the basis of the macromolecular gas viscous flow theory, the fine prediction of the comprehensive permeability of helium is realized; after receiving the salt rock permeability data and production operation data, the terminal helium leakage depth quantitative prediction system 9 numerically simulates the penetration and diffusion law of helium in the salt cavern helium storage, and then predicts the helium leakage depth.

[0083] In the embodiments of the present invention, by using limited in-situ coring data, the accurate prediction of the leakage depth of helium in the salt rock formation can be achieved, thereby providing theoretical support for the loss assessment, site selection, and design of the safety pillar distance of the salt cavern helium storage, replacing the traditional manual experience method. Under the support of a complete theoretical model, this method is also in line with the characteristics of on-site rock samples, with simple calculation, being scientific and reasonable.

[0084] Although the preferred embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications to these embodiments once they know the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications falling within the scope of the present invention.

[0085] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these modifications and variations.

Claims

1. A method for predicting the helium leakage depth in a salt cavern helium storage reservoir, characterized in that, it includes: obtaining the porosity, tortuosity, and pore size distribution data of the rock sample; Through the formula the permeability component k corresponding to viscous flow is calculated v ; where λ max is the maximum pore size of the salt rock, λ min is the minimum pore size of the salt rock, λ is the pore size of the salt rock, τ is the tortuosity of the salt rock, N is the number of pores with pore size λ, and A is the seepage area of helium gas; Through the formula the permeability component k corresponding to the Knudsen effect is calculated k ; where μ is the viscosity of helium, Z is the compressibility factor of helium, p is the gas pressure, R is the gas constant, T is the temperature of helium, M is the molar mass of helium, and K n is the Knudsen coefficient of helium; Through the formula the permeability component k corresponding to the surface diffusion effect is calculated s ; where δ is the molar diameter of helium, θ is the dimensionless coefficient of the relationship between pore pressure and Langmuir pressure, D s is the surface diffusion coefficient, C amax is the maximum gas capacity of salt rock, p L is the Langmuir pressure of helium; The comprehensive permeability k of helium is calculated through the formula k = k v + k k + k s ; By numerically solving the formula the leakage law of helium in the surrounding rock of the salt cavern helium storage can be simulated, and the pressure field distribution data within the entire surrounding rock can be obtained; where φ is the porosity of the salt rock, ρ is the density of helium, t is the simulation time, and x is the distance from the surrounding rock to the cavity wall surface; According to the helium leakage simulation, the pressure field distribution in the salt cavern helium storage reservoir and the surrounding rock can be obtained, and then the seepage velocity of helium from the cavity wall into the surrounding rock can be obtained; Through the formula the helium leakage depth R is calculated; where h is the height of the salt cavern, and R 0 is the radius of the salt cavern at dh.

2. The method for predicting the helium leakage depth in a salt cavern helium storage reservoir according to claim 1, characterized in that, The said C amax is calculated through the formula ; Among them, V L is the Langmuir volume of helium, ρ STG is the density of helium under standard conditions, ρ grain is the density of the rock sample, ε k is the ratio of the volume of the adsorbate to the total volume of the rock.

3. The method for predicting the helium leakage depth in a salt cavern helium storage reservoir according to claim 1, characterized in that, the obtaining of the porosity, tortuosity, and pore size distribution data of the rock sample includes: taking cores of the salt rock in the salt cavern cavity to obtain core rock samples; performing mercury intrusion tests on the core rock samples to obtain the porosity, tortuosity, and pore size distribution data of the rock samples.

4. The method for predicting the helium leakage depth in a salt cavern helium storage reservoir according to any one of claims 1-3, characterized in that, the obtaining of the pressure field distribution in the salt cavern helium storage reservoir and the surrounding rock according to the helium leakage simulation, and then the seepage velocity of helium from the cavity wall into the surrounding rock includes: Through the formula the seepage velocity v of the helium gas along the cavity wall into the surrounding rock is calculated.

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