Method for predicting gas-liquid interface depth of sediment type salt cavern gas storage

Abstract

The invention discloses a sediment type salt cavern gas storage gas-liquid interface depth prediction method. The method comprises the following steps that S1, a change curve of brine discharge flow along with time is obtained through on-site monitoring; s2, determining the mining form of the salt cavern cavity, and obtaining a change curve of the effective cross section area of the cavity brine along with the depth; s3, respectively calculating gas-liquid interface depths when the gas-liquid interface is in the gas injection well and does not enter the salt cavity, when the gas-liquid interface is in the pure brine space at the upper part of the salt cavity and does not enter sediment, and when the gas-liquid interface is in the sediment accumulation space; s4, judging whether the gas-liquid interface depth obtained through calculation in S3 meets a corresponding application interval or not, and obtaining a gas-liquid interface depth value; the gas-liquid interface depth of the pure brine space on the upper portion of the salt cavern can be detected, the gas-liquid interface depth of the sediment accumulation space can also be detected, and gas-liquid interface depth detection of the whole space of the inner cavity of the sediment type salt cavern gas storage is achieved.

Description

Technical Field

[0001] The present application relates to the field of petroleum and natural gas engineering technology, and in particular to a method for predicting the depth of a gas-liquid interface in a sediment-type salt cavern gas storage. Background Art

[0002] Salt rock underground gas storage is an ideal place for underground energy storage with its advantages of high safety, high injection and production efficiency, large working gas volume, and less cushion gas. However, my country's salt rock strata have the geological characteristics of high impurities and multiple interlayers. The content of insoluble impurities is mostly between 30% and 50%, and the proportion of interlayers is mostly above 40%. After the collapse of the interlayer, the fragments and insoluble particles accumulate at the bottom of the salt cavity, filling more than 80% of the total volume of the salt cavity, seriously reducing the effective gas storage volume of the salt cavity. With the advancement of salt cavern construction technology, the industry has proposed using the void space of salt mine water to store gas, and using high-pressure gas to discharge the brine in the void space of the sediment to store natural gas. This can solve the problem of large-scale gas storage in low-grade, multi-interlayer salt mines, and gas injection and brine removal technology is a key step in the smooth realization of sediment void gas storage.

[0003] The most important thing in the operation of salt cavern gas storage is to ensure the safety of gas storage and prevent gas leakage. One of the issues is to control the depth of the gas-liquid interface. During the process of gas injection and brine removal, when the depth of the gas-liquid interface is too low, the brine at the bottom of the salt cavity cannot ensure the sealing of the gas inside the salt cavity, causing gas leakage accidents; when the depth of the gas-liquid interface is too high, the available gas storage space in the gaps of the salt cavity sediment cannot be utilized, resulting in the salt cavity being unable to exert its maximum gas storage capacity. Therefore, it is particularly important to accurately predict the depth of the gas-liquid interface of the salt cavern gas storage.

[0004] The traditional fiber optic gas-liquid interface instrument can only detect the gas-liquid interface depth in the clean brine space above the salt cavity, but cannot detect the gas-liquid interface in the sediment accumulation space. Therefore, there is an urgent need for a method that can fully detect the gas-liquid interface depth of sediment-type salt cavern gas storage. Summary of the invention

[0005] In order to solve the above problems, the present application provides a method for predicting the depth of the gas-liquid interface of a sediment-type salt cavern gas storage, which can not only detect the depth of the gas-liquid interface of the clean brine space in the upper part of the salt cavity, but also detect the depth of the gas-liquid interface of the sediment accumulation space, thereby realizing the gas-liquid interface depth detection of the entire space of the inner cavity of the sediment-type salt cavern gas storage. The technical solution is as follows:

[0006] The present application provides a method for predicting the depth of the gas-liquid interface in a sediment-type salt cavern gas storage, comprising the following steps:

[0007] S1 obtains the curve of brine discharge flow rate changing with time through on-site monitoring;

[0008] S2 determines the mining morphology of the salt cavern cavity and obtains the curve of the effective cross-sectional area of ​​the cavity brine changing with depth;

[0009] S3 calculates the depth of the gas-liquid interface when the gas-liquid interface is in the gas injection well and does not enter the salt cavity, when the gas-liquid interface is in the clean brine space above the salt cavity and does not enter the sediment, and when the gas-liquid interface is in the sediment accumulation space;

[0010] S4 determines whether the gas-liquid interface depth calculated in S3 satisfies the corresponding applicable range, and obtains the gas-liquid interface depth value.

[0011] For example, in the method for predicting the gas-liquid interface depth of the sediment-type salt cavern gas storage provided in one embodiment, in S3, when the gas-liquid interface is in the gas injection well and has not entered the salt cavity, the gas-liquid interface depth h is calculated according to the following formula:

[0012]

[0013] In formula (1), q1 is the brine discharge flow rate, m 3 / h; A1 is the effective cross-sectional area of ​​brine in the gas injection well string, m 2 ; t is the brine discharge time, h.

[0014] For example, in the method for predicting the gas-liquid interface depth of the sediment-type salt cavern gas storage provided in one embodiment, in S3, when the gas-liquid interface is in the clean brine space at the upper part of the salt cavity without sediment, the gas-liquid interface depth h is calculated according to the following formula:

[0015]

[0016] In formula (2), A2 is the cross-sectional area of ​​the net brine space above the salt cavity, m 2 ;H top is the cavity top depth, m.

[0017] For example, in the method for predicting the gas-liquid interface depth of the sediment-type salt cavern gas storage provided in one embodiment, in S3, when the gas-liquid interface is in the sediment accumulation space, the gas-liquid interface depth h is calculated according to the following formula:

[0018]

[0019] In formula (3), A3 is the effective cross-sectional area of ​​brine in the sediment space at the bottom of the salt cavity, m 2 ;H s is the depth of sediment surface, m.

[0020] For example, in the method for predicting the gas-liquid interface depth of the sediment-type salt cavern gas storage provided in one embodiment, in the formula (3), the sonar cavity measurement method is used to obtain The numerical value of .

[0021] For example, in the method for predicting the gas-liquid interface depth of the sediment-type salt cavern gas storage provided in one embodiment, the method for judging in S4 whether the gas-liquid interface depth calculated in S3 satisfies the corresponding applicable interval is:

[0022] When the gas-liquid interface is in the gas injection well and has not entered the salt cavity, the gas-liquid interface depth calculated according to formula (1) should satisfy: h <H top ;

[0023] When the gas-liquid interface is in the clean brine space at the top of the salt cavity without sediment, the depth of the gas-liquid interface calculated according to formula (2) should satisfy: H top ≤h≤H s ;

[0024] When the gas-liquid interface is in the sediment accumulation space, the gas-liquid interface depth calculated according to formula (3) should satisfy: H s ≤h≤H it , where H it is the cavity bottom depth.

[0025] For example, in the method for predicting the gas-liquid interface depth of the sediment-type salt cavern gas storage provided in one embodiment, in S2, a sonar detection method is used to obtain the curves of the effective cross-sectional area A1 of the brine in the gas injection well string and the cross-sectional area A2 of the net brine space in the upper part of the salt cavity changing with depth.

[0026] For example, in the method for predicting the gas-liquid interface depth of the sediment-type salt cavern gas storage provided in one embodiment, the calculation method of the effective cross-sectional area A3 of the brine in the sediment space at the bottom of the salt cavity is:

[0027] A3=A 11 n Formula (4);

[0028] In formula (4), A 11 is the cross-sectional area of ​​the lower sediment accumulation space, m 2 ; n is the sediment porosity, and the sediment porosity n changes with the sediment accumulation depth to satisfy the following calculation formula;

[0029]

[0030] In formula (5), γ s is the solid density of insoluble particles, g / cm 3 ; γ0 is the top bulk density of the sediment, g / cm 3 ; γ m is the bulk density of the bottom part of the sediment, g / cm 3 ; α is related to the sediment packing density and cavity diameter.

[0031] A method for predicting the gas-liquid interface depth of a sediment-type salt cavern gas storage provided in some embodiments of the present application has the following beneficial effects: the present application utilizes the principle of conservation of mass of brine discharged during the gas injection and brine discharge process of a sediment-type salt cavern gas storage, and uses different formulas to calculate the gas-liquid interface depth when the gas-liquid interface is in the gas injection well and has not entered the salt cavity, when the gas-liquid interface is in the clean brine space above the salt cavity and has not entered the sediment, and when the gas-liquid interface is in the sediment accumulation space, respectively, through the on-site tested curve of the brine discharge flow rate changing with time. The gas-liquid interface depth can be accurately obtained, and not only the gas-liquid interface depth of the clean brine space above the salt cavity can be detected, but also the gas-liquid interface depth of the sediment accumulation space can be detected, thereby realizing the gas-liquid interface depth detection of the entire space of the cavity of the sediment-type salt cavern gas storage, with fewer formula parameters and simple calculation. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the embodiments of this specification or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0033] Figure 1 This is a schematic diagram of the low-level brine discharge structure of the sediment-type salt cavern gas storage;

[0034] Figure 2 This is a flow chart of the method for predicting the depth of the gas-liquid interface in the sediment-type salt cavern gas storage of the present application;

[0035] Figure 3 It is a curve diagram of the brine discharge flow rate of a salt cavity changing with time;

[0036] Figure 4 It is a curve diagram showing the change of effective flow area of ​​a brine salt cavity with depth;

[0037] Figure 5 It is a schematic diagram of the low-level brine drainage structure when the gas-liquid interface is in the gas injection well;

[0038] Figure 6 It is a schematic diagram of the low-level brine discharge structure when the gas-liquid interface is in the net brine space at the upper part of the salt cavity;

[0039] Figure 7 Schematic diagram of the low-level brine drainage structure when the gas-liquid interface is in the sediment accumulation space at the bottom of the salt cavity. DETAILED DESCRIPTION

[0040] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0041] Unless otherwise defined, the technical terms or scientific terms used in the present disclosure should be understood by people with ordinary skills in the field to which the present disclosure belongs. The "first", "second" and similar words used in the present disclosure do not indicate any order, quantity or importance, but are only used to distinguish different components. "Include" or "comprise" and similar words mean that the elements or objects appearing before the word cover the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0042] The low-level brine removal and gas storage expansion structure of sediment-type salt cavern gas storage is as follows: Figure 1 As shown, the sediment-type salt cavern gas storage includes an injection well 1, the bottom of which leads to a salt cavity. The salt cavity includes a clean brine space 2 at the upper part of the salt cavity and a sediment accumulation space 3 at the bottom of the salt cavity. Since a large amount of insoluble sediment is accumulated at the bottom of the salt cavity, during the process of injecting gas and discharging brine, gas is injected into the original injection well 1, and a new brine discharge well 4 connected to the bottom of the sediment accumulation space 3 at the bottom of the salt cavity is built beside the injection well 1 to discharge brine. Assuming that brine is incompressible, the following relationship is obtained according to the mass conservation of the discharged brine:

[0043] (1) When the gas-liquid interface is in the gas injection well 1 and has not entered the salt cavity:

[0044]

[0045] (2) When the gas-liquid interface is in the clean brine space 2 at the top of the salt cavity and no sediment enters:

[0046]

[0047] (3) When the gas-liquid interface is in the sediment accumulation space 3:

[0048]

[0049] Among them, q1 is the brine discharge flow rate, m 3 / h; H topis the cavity top depth, m; A1 is the effective cross-sectional area of ​​brine in the gas injection well string, m 2 ;H s is the depth of sediment surface, m; H it is the depth of the cavity bottom, m; A2 is the cross-sectional area of ​​the net brine space above the salt cavity, m 2 ; A3 is the effective cross-sectional area of ​​brine in the sediment space at the bottom of the salt cavity, m 2 ; t is the brine discharge time, h.

[0050] According to the mass conservation principle of brine discharged during the above-mentioned gas injection and brine removal process, the present application provides a method for predicting the depth of the gas-liquid interface of a sediment-type salt cavern gas storage, such as Figure 2 As shown, the following steps are included:

[0051] S1 obtains the curve of brine discharge flow rate changing with time through on-site monitoring;

[0052] Specifically, a flow meter was installed at the wellhead of brine discharge well 4 for on-site measurement to obtain a curve of brine discharge flow rate changing with time. The typical curve is as follows: Figure 3 As shown;

[0053] S2 determines the mining morphology of the salt cavern cavity and obtains the curve of the effective cross-sectional area of ​​the cavity brine changing with depth;

[0054] Specifically, the sonar detection method is used to obtain the curves of the effective cross-sectional area A1 of the brine in the gas injection well 1 pipe string and the cross-sectional area A2 of the net brine space 2 in the upper part of the salt cavity with depth. The typical curves are as follows: Figure 4 shown.

[0055] S3 calculates the depth of the gas-liquid interface when the gas-liquid interface is in the gas injection well 1 and does not enter the salt cavity, when the gas-liquid interface is in the clean brine space 2 at the upper part of the salt cavity and does not enter the sediment, and when the gas-liquid interface is in the sediment accumulation space 3;

[0056] Specifically:

[0057] like Figure 5 As shown in FIG. 1 , when the gas-liquid interface is in the gas injection well 1 and has not entered the salt cavity, the gas-liquid interface depth h is calculated according to the following formula:

[0058]

[0059] like Figure 6 As shown in the figure, when the gas-liquid interface is in the clean brine space 2 at the upper part of the salt cavity and no sediment enters, the depth h of the gas-liquid interface is calculated according to the following formula:

[0060]

[0061] like Figure 7 As shown, when the gas-liquid interface is in the salt cavity sediment accumulation space 3, the gas-liquid interface depth h is calculated according to the following formula:

[0062]

[0063] Among them, in formula (3), the sonar cavity measurement method is used to obtain The numerical value of .

[0064] The calculation method of the effective cross-sectional area A3 of brine in the sediment space at the bottom of the salt cavity is:

[0065] A3=A 11 n Formula (4);

[0066] In formula (4), A 11 is the cross-sectional area of ​​the lower sediment accumulation space, m 2 ; n is the porosity of the sediment. When the sediment layer is compacted, the porosity of the sediment gradually decreases as the sediment accumulation depth increases. The porosity n of the sediment changes with the sediment accumulation depth and satisfies the following calculation formula;

[0067]

[0068] In formula (5), γ s is the solid density of insoluble particles, g / cm 3 ; γ0 is the top bulk density of the sediment, g / cm 3 ; γ m is the bulk density of the bottom part of the sediment, g / cm 3 ; α is related to the sediment packing density and cavity diameter.

[0069] S4 determines whether the gas-liquid interface depth calculated in S3 satisfies the corresponding applicable range, and obtains the gas-liquid interface depth value.

[0070] Specifically, the method for judging whether the gas-liquid interface depth calculated by S3 satisfies the corresponding applicable range is:

[0071] When the gas-liquid interface is in the gas injection well and has not entered the salt cavity, the gas-liquid interface depth calculated according to formula (1) should satisfy: h <H top ;

[0072] When the gas-liquid interface is in the clean brine space at the top of the salt cavity without sediment, the depth of the gas-liquid interface calculated according to formula (2) should satisfy: H top ≤h≤H s ;

[0073] When the gas-liquid interface is in the sediment accumulation space, the gas-liquid interface depth calculated according to formula (3) should satisfy: H s ≤h≤H it .

[0074] The gas-liquid interface depth prediction method of the sediment-type salt cavern gas storage of the present application uses the curve of the change of brine discharge flow rate over time in the field test, and uses formulas (1)-(3) to calculate the gas-liquid interface depth when the gas-liquid interface is in the gas injection well and does not enter the salt cavity, when the gas-liquid interface is in the clean brine space above the salt cavity and does not enter the sediment, and when the gas-liquid interface is in the sediment accumulation space, so that the gas-liquid interface depth can be accurately obtained. Among them, in the method for obtaining the change of the effective cross-sectional area of ​​the cavity brine with depth, the upper clean brine space is accurately measured by sonar, and the lower sediment accumulation space is estimated by the historical sonar data overlay map and sediment porosity. The formula has fewer parameters and is simple to calculate. It can not only detect the gas-liquid interface depth of the clean brine space above the salt cavity, but also detect the gas-liquid interface depth of the sediment accumulation space, so as to realize the gas-liquid interface depth detection of the entire cavity space of the sediment-type salt cavern gas storage.

[0075] Although the implementation scheme of the present application has been disclosed as above, it is not limited to the applications listed in the specification and implementation modes, and it can be fully applicable to various fields suitable for the present application. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present application is not limited to the specific details and the illustrations shown and described herein.

Claims

1. A method for predicting the depth of the gas-liquid interface of a sediment-type salt cavern gas storage, characterized in that: The following steps are involved: S1 obtains the curve of brine discharge flow rate changing with time through on-site monitoring; S2 determines the mining morphology of the salt cavern cavity and obtains the curve of the effective cross-sectional area of ​​the cavity brine changing with depth; S3 calculates the depth of the gas-liquid interface when the gas-liquid interface is in the gas injection well and does not enter the salt cavity, when the gas-liquid interface is in the clean brine space above the salt cavity and does not enter the sediment, and when the gas-liquid interface is in the sediment accumulation space; S4 determines whether the gas-liquid interface depth calculated in S3 satisfies the corresponding applicable range, and obtains the gas-liquid interface depth value.

2. The method for predicting the gas-liquid interface depth of a sediment-type salt cavern gas storage according to claim 1 is characterized in that: In S3, when the gas-liquid interface is in the gas injection well and has not entered the salt cavity, the gas-liquid interface depth h is calculated according to the following formula: In formula (1), q1 is the brine discharge flow rate, m 3 / h; A1 is the effective cross-sectional area of ​​brine in the gas injection well string, m 2 ; t is the brine discharge time, h.

3. The method for predicting the gas-liquid interface depth of a sediment-type salt cavern gas storage according to claim 2 is characterized in that: In S3, when the gas-liquid interface is in the clean brine space at the upper part of the salt cavity without sediment entering, the gas-liquid interface depth h is calculated according to the following formula: In formula (2), A2 is the cross-sectional area of ​​the net brine space above the salt cavity, m 2 ;H top is the cavity top depth, m.

4. The method for predicting the gas-liquid interface depth of a sediment-type salt cavern gas storage according to claim 3 is characterized in that: In S3, when the gas-liquid interface is in the sediment accumulation space, the gas-liquid interface depth h is calculated according to the following formula: In formula (3), A3 is the effective cross-sectional area of ​​brine in the sediment space at the bottom of the salt cavity, m 2 ;H s is the depth of sediment surface, m.

5. The method for predicting the gas-liquid interface depth of a sediment-type salt cavern gas storage according to claim 4 is characterized in that: In the formula (3), the sonar cavity measurement method is used to obtain The numerical value of .

6. The method for predicting the gas-liquid interface depth of a sediment-type salt cavern gas storage according to claim 5 is characterized in that: The method for judging whether the gas-liquid interface depth calculated by S3 satisfies the corresponding applicable range in S4 is: When the gas-liquid interface is in the gas injection well and has not entered the salt cavity, the gas-liquid interface depth calculated according to formula (1) should satisfy: h <H top ; When the gas-liquid interface is in the clean brine space at the top of the salt cavity without sediment, the gas-liquid interface depth calculated according to formula (2) should satisfy: Hs top ≤h≤H s ; When the gas-liquid interface is in the sediment accumulation space, the gas-liquid interface depth calculated according to formula (3) should satisfy: H s ≤h≤H it , where H it is the cavity bottom depth.

7. The method for predicting the gas-liquid interface depth of a sediment-type salt cavern gas storage according to claim 6 is characterized in that: In S2, a sonar detection method is used to obtain the curves of the effective cross-sectional area A1 of the brine in the gas injection well pipe string and the cross-sectional area A2 of the net brine space in the upper part of the salt cavity as a function of depth.

8. The method for predicting the gas-liquid interface depth of a sediment-type salt cavern gas storage according to claim 4 is characterized in that: The calculation method of the effective cross-sectional area A3 of brine in the sediment space at the bottom of the salt cavity is: A3=A 11 n Formula (4); In formula (4), A 11 is the cross-sectional area of ​​the lower sediment accumulation space, m 2 ; n is the sediment porosity, and the sediment porosity n changes with the sediment accumulation depth to satisfy the following calculation formula; In formula (5), γ s is the solid density of insoluble particles, g / cm 3 ; γ0 is the top bulk density of the sediment, g / cm 3 ; γ m is the bulk density of the bottom part of the sediment, g / cm 3 ; α is related to the sediment packing density and cavity diameter.

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