A method for predicting the gas-liquid interface depth in a sediment-type salt cavern gas storage facility

Abstract

This application discloses a method for predicting the gas-liquid interface depth in a sediment-type salt cavern gas storage facility, comprising the following steps: S1 obtaining the brine discharge flow rate variation curve over time through on-site monitoring; S2 determining the mining morphology of the salt cavern cavity and obtaining the variation curve of the effective cross-sectional area of ​​the brine in the cavity with depth; S3 calculating the gas-liquid interface depth when the gas-liquid interface is in the injection well and has not entered the salt cavity, when the gas-liquid interface is in the upper clean brine space of the salt cavity and has not entered the sediment, and when the gas-liquid interface is in the sediment accumulation space; S4 determining whether the gas-liquid interface depth calculated in S3 meets the corresponding applicable range, and obtaining the gas-liquid interface depth value; this application can not only detect the gas-liquid interface depth in the upper clean brine space of the salt cavity, but also detect the gas-liquid interface depth in the sediment accumulation space, realizing the detection of the gas-liquid interface depth in the entire cavity of the sediment-type salt cavern gas storage facility.

Description

Technical Field

[0001] This application relates to the field of oil and gas engineering technology, and in particular to a method for predicting the gas-liquid interface depth in a sediment-type salt cavern gas storage facility. Background Technology

[0002] Salt rock underground gas storage facilities are ideal for underground energy reserves due to their advantages such as high safety, high injection and production efficiency, large working gas volume, and low gas content in the subgrade. However, salt rock strata in my country are characterized by 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 interlayers collapse, 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, which seriously reduces 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 sediment for gas storage. High-pressure gas is used to discharge the brine in the sediment voids to store natural gas, which can solve the problem of large-scale gas storage in low-grade, multi-layered salt mines. Gas injection and brine discharge technology is the key step to successfully realize gas storage in sediment voids.

[0003] The most crucial aspect of operating a salt cavern gas storage facility is ensuring gas safety and preventing leaks. One key aspect of this is controlling the depth of the gas-liquid interface. During gas injection and brine discharge, if the gas-liquid interface depth is too low, the brine at the bottom of the salt cavity cannot guarantee the airtightness of the gas inside, leading to gas leaks. Conversely, if the gas-liquid interface depth is too high, the usable gas storage space in the sediment voids of the salt cavity cannot be fully utilized, preventing the salt cavity from reaching its maximum gas storage capacity. Therefore, accurately predicting the gas-liquid interface depth of a salt cavern gas storage facility is of paramount importance.

[0004] Traditional fiber optic gas-liquid interface instruments can only detect the gas-liquid interface depth in the upper brine space of the salt cavern, and cannot detect the gas-liquid interface in the sediment accumulation space. Therefore, there is an urgent need for a method that can detect the gas-liquid interface depth in sediment-type salt cavern gas storage tanks from all angles. Summary of the Invention

[0005] To address the aforementioned problems, this application provides a method for predicting the gas-liquid interface depth in a sediment-type salt cavern gas storage facility. This method can detect not only the gas-liquid interface depth in the upper brine space of the salt cavity but also the gas-liquid interface depth in the sediment accumulation space, achieving full-space gas-liquid interface depth detection within the sediment-type salt cavern gas storage facility. The technical solution is as follows:

[0006] This application provides a method for predicting the gas-liquid interface depth in a sediment-type salt cavern gas storage facility, including the following steps:

[0007] S1 obtains the curve of brine discharge flow rate changing over 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 brine in the cavity as a function of depth;

[0009] S3 calculates the gas-liquid interface depth when the gas-liquid interface is in the gas injection well but has not entered the brine cavity, when the gas-liquid interface is in the upper brine space of the brine cavity but has not entered 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 meets the corresponding applicable range, and obtains the gas-liquid interface depth value.

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

[0012]

[0013] In equation (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 tubing, m 2 t represents the brine removal time, in hours.

[0014] For example, in the gas-liquid interface depth prediction method for a sediment-type salt cavern gas storage provided in one embodiment, in step S3, when the gas-liquid interface is in the upper brine space of the salt cavity and has not entered the sediment, the gas-liquid interface depth h is calculated according to the following formula:

[0015]

[0016] In equation (2), A2 is the cross-sectional area of ​​the net brine space above the salt cavity, in m³. 2 H top Let m be the cavity top depth.

[0017] For example, in the gas-liquid interface depth prediction method for a sediment-type salt cavern gas storage facility provided in one embodiment, in step 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 equation (3), A3 is the effective cross-sectional area of ​​the brine in the lower sediment space of the salt chamber, in m³. 2 H s The depth of the sediment surface is in meters (m).

[0020] For example, in the gas-liquid interface depth prediction method for sediment-type salt cavern gas storage provided in one embodiment, in equation (3), the depth is obtained by sonar cavity measurement method. The value.

[0021] For example, in the gas-liquid interface depth prediction method for sediment-type salt cavern gas storage provided in one embodiment, the method in step S4 for determining whether the gas-liquid interface depth calculated in step S3 meets the corresponding applicable range is as follows:

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

[0023] When the gas-liquid interface is in the upper brine space of the brine chamber and has not entered the sediment, the gas-liquid interface depth calculated according to equation (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 equation (3) should satisfy: H s ≤h≤H it , where H it This refers to the depth of the cavity floor.

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

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

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

[0028] In equation (4), A 11 The cross-sectional area of ​​the cavity in the lower sediment accumulation space is m. 2 n is the porosity of the sediment, and the porosity n of the sediment varies with the sediment accumulation depth according to the following calculation formula.

[0029]

[0030] In equation (5), γ s Density of insoluble particles, in g / cm³ 3 γ0 is the bulk density of the top layer of sediment, in g / cm³. 3 ;γ m The bulk density of the sediment at the bottom is expressed in g / cm³. 3 α is related to the sediment density and cavity diameter.

[0031] The beneficial effects of the gas-liquid interface depth prediction method for sediment-type salt cavern gas storage provided in some embodiments of this application are as follows: This application utilizes the mass conservation principle of the discharged brine during the gas injection and brine discharge process of sediment-type salt cavern gas storage. By using the brine discharge flow rate variation curve measured on-site, different formulas are used 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 upper clean brine space of the salt cavity and has not entered the sediment, and when the gas-liquid interface is in the sediment accumulation space. The gas-liquid interface depth can be accurately obtained. It can detect not only the gas-liquid interface depth in the upper clean brine space of the salt cavity, but also the gas-liquid interface depth in the sediment accumulation space, realizing the detection of the gas-liquid interface depth in the entire cavity of the sediment-type salt cavern gas storage. The formula parameters are few and the calculation is simple. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of this specification or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

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

[0034] Figure 2 The flowchart is shown below for the gas-liquid interface depth prediction method of sediment-type salt cavern gas storage in this application.

[0035] Figure 3 A graph showing the change in brine discharge flow rate over time in a certain salt cavity;

[0036] Figure 4 This is a graph showing the change in the effective flow area of ​​a brine cavity with depth.

[0037] Figure 5 This is a schematic diagram of the low-level brine discharge structure of the gas-liquid interface during gas injection wells.

[0038] Figure 6 This is a schematic diagram of the low-level brine discharge structure when the gas-liquid interface is in the upper brine space of the salt chamber.

[0039] Figure 7 This is a schematic diagram of the low-level brine discharge structure at the bottom of the brine chamber when the gas-liquid interface is in the sediment accumulation space. Detailed Implementation

[0040] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0041] Unless otherwise defined, the technical or scientific terms used in this disclosure shall have the ordinary meaning understood by one of ordinary skill in the art to which this disclosure pertains. The terms “first,” “second,” and similar terms used in this disclosure do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as “comprising” or “including” mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. Terms such as “connected” or “linked” are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as “upper,” “lower,” “left,” and “right” are used only to indicate relative positional relationships, and these relative positional relationships may change accordingly when the absolute position of the described objects changes.

[0042] Low-level brine discharge gas storage expansion structure of sedimentation type salt cavern gas storage, such as Figure 1 As shown, the sediment-type salt cavern gas storage facility 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 top and a sediment accumulation space 3 at the bottom. Due to the accumulation of a large amount of insoluble sediment at the bottom of the salt cavity, during the gas injection and brine discharge process, gas is injected into the existing injection well 1, and a new brine discharge well 4 is constructed next to the injection well 1, connected to the bottom of the sediment accumulation space 3 at the bottom of the salt cavity, to discharge the brine. Assuming that the brine is incompressible, based on the mass conservation of the discharged brine, the following relationship is obtained:

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

[0044]

[0045] (2) When the gas-liquid interface is in the upper brine space 2 of the salt chamber and no sediment has entered:

[0046]

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

[0048]

[0049] Where q1 is the brine discharge flow rate, m 3 / h;H topA1 is the depth at the top of the cavity, in meters; A2 is the effective cross-sectional area of ​​the brine in the injection well tubing, in meters. 2 H s H represents the depth of the sediment surface, in meters (m). it A1 is the depth of the cavity bottom, in meters; A2 is the cross-sectional area of ​​the net brine space above the salt cavity, in meters. 2 A3 is the effective cross-sectional area of ​​the brine in the lower sedimentation space of the salt chamber, in meters. 2 t represents the brine removal time, in hours.

[0050] Based on the principle of mass conservation of brine discharged during the gas injection and brine discharge process, this application provides a method for predicting the gas-liquid interface depth in a sediment-type salt cavern gas storage facility, such as... Figure 2 As shown, it includes the following steps:

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

[0052] Specifically, a flow meter was installed at the wellhead of brine discharge well No. 4 for on-site measurement, and the curve of brine discharge flow rate changing over time was obtained. A typical curve is shown below. 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 brine in the cavity as a function of depth;

[0054] Specifically, sonar detection methods were used to obtain the curves showing the variation of the effective cross-sectional area A1 of brine in the injection well 1 tubing and the cross-sectional area A2 of the net brine space 2 above the brine cavity with depth. Typical curves are shown below. Figure 4 As shown.

[0055] S3 calculates the gas-liquid interface depth when the gas-liquid interface is in the gas injection well 1 and has not entered the brine cavity, when the gas-liquid interface is in the upper brine space 2 of the brine cavity and has not entered the sediment, and when the gas-liquid interface is in the sediment accumulation space 3.

[0056] Specifically:

[0057] like Figure 5 As shown, when the gas-liquid interface is in injection well 1 but 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, when the gas-liquid interface is in the upper brine space 2 of the salt chamber and has not entered the sediment, 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 located in the salt cavity sediment accumulation space 3, the gas-liquid interface depth h is calculated according to the following formula:

[0062]

[0063] In equation (3), the cavity measurement method is used to obtain... The value.

[0064] The effective cross-sectional area A3 of the brine in the lower sedimentation space of the salt chamber is calculated as follows:

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

[0066] In equation (4), A 11 The cross-sectional area of ​​the cavity in the lower sediment accumulation space is m. 2 n is the porosity of the sediment. Considering the lamination of the sediment layer, the porosity of the sediment gradually decreases with the increase of sediment accumulation depth. The change of sediment porosity n with sediment accumulation depth satisfies the following calculation formula.

[0067]

[0068] In equation (5), γ s Density of insoluble particles, in g / cm³ 3 γ0 is the bulk density of the top layer of sediment, in g / cm³. 3 ;γ m The bulk density of the sediment at the bottom is expressed in g / cm³. 3 α is related to the sediment density and cavity diameter.

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

[0070] Specifically, the method for determining whether the gas-liquid interface depth calculated in S3 meets the corresponding applicable range is as follows:

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

[0072] When the gas-liquid interface is in the upper brine space of the brine chamber and has not entered the sediment, the gas-liquid interface depth calculated according to equation (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 equation (3) should satisfy: H s ≤h≤H it .

[0074] The gas-liquid interface depth prediction method for sediment-type salt cavern gas storage in this application calculates the gas-liquid interface depth when the gas-liquid interface is in the injection well but not in the salt cavity, in the upper clean brine space of the salt cavity but not in the sediment, and in the sediment accumulation space, based on the brine discharge flow rate variation curve measured in the field. This method can accurately obtain the gas-liquid interface depth. In the method for obtaining the change of effective cross-sectional area of ​​the brine in the cavity with depth, the upper clean brine space is obtained by precise measurement data using sonar, and the lower sediment accumulation space is obtained by estimation using historical sonar data overlay and sediment porosity. The formula has fewer parameters and is easy to calculate. It can detect not only the gas-liquid interface depth in the upper clean brine space of the salt cavity, but also the gas-liquid interface depth in the sediment accumulation space, realizing the detection of the gas-liquid interface depth in the entire cavity of the sediment-type salt cavern gas storage.

[0075] Although the embodiments of this application have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for this application. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, this application is not limited to the specific details and the illustrations shown and described herein.

Claims

1. A method for predicting the gas-liquid interface depth in a sedimented salt cavern gas storage, characterized in that, The method comprises the following steps: S1: obtaining a curve of the brine discharge flow rate changing with time through field monitoring; S2: determining the mining shape of the salt cavern cavity and obtaining a curve of the effective cross-sectional area of the cavity brine changing with depth; S3: respectively calculating the gas-liquid interface depth when the gas-liquid interface is in the gas injection well without entering the salt cavity, when the gas-liquid interface is in the upper space of the salt cavity without entering the sediment, and when the gas-liquid interface is in the sediment accumulation space; When the gas-liquid interface is in the gas injection well without entering the salt cavity, the gas-liquid interface depth h is calculated according to the following formula: Formula (1); In formula (1), is the discharge flow rate, m 3 / h; is the effective cross-sectional area of the brine in the gas injection well string, m 2 ; is the discharge time, h; When the gas-liquid interface is in the upper space of the salt cavity without entering the sediment, the gas-liquid interface depth h is calculated according to the following formula: Formula (2); In formula (2), A is the cross-sectional area of the upper salt cavity, m 2 ; A is the cross-sectional area of the upper salt cavity, m When the gas-liquid interface is in the sediment accumulation space, the gas-liquid interface depth h is calculated according to the following formula: Equation (3); In formula (3), Aeff is the effective cross-sectional area of the brine in the lower salt cavern sludge space, m2 2 ; h is the sludge surface depth, m; S4: judging whether the gas-liquid interface depth calculated in S3 satisfies the corresponding applicable interval to obtain the gas-liquid interface depth value.

2. The method of claim 1, wherein, In the formula (3), the value of is obtained by the sonar cavity method. .

3. The method of claim 2, wherein the method further comprises: The method for judging whether the gas-liquid interface depth calculated in S3 satisfies the corresponding applicable interval in S4 is: When the gas-liquid interface is in the injection well without entering the salt cavity, the gas-liquid interface depth calculated according to formula (1) should satisfy: ; When the gas-liquid interface is in the pure brine space above the salt cavity and has not entered the sediment, the depth of the gas-liquid interface calculated according to formula (2) should satisfy: ; When the gas-liquid interface is in the sediment accumulation space, the depth of the gas-liquid interface calculated according to formula (3) should satisfy: wherein, is the depth of the cavity bottom.

4. The method of claim 3, wherein the method further comprises: In the S2, the effective cross-sectional area of the brine in the gas injection well string is obtained by using the sonar detection method and the cross-sectional area of the net brine space in the upper part of the salt cavity curve of change with depth.

5. The method of claim 4, wherein the method further comprises: Effective cross-sectional area of brine in the lower sediment space of the salt cavern The calculation method is: Formula (4); In formula (4), A is the cross-sectional area of the cavity, m 2 ; n is the sediment void fraction, and the sediment void fraction n satisfies the following calculation formula with the change of the sediment accumulation depth Formula (5); In formula (5), is the density of the insoluble particulate solids, g / cm 3 ; is the bulk density of the uppermost portion of the settled residue, g / cm 3 ; is the bulk density of the lowermost portion of the settled residue, g / cm 3 ; is related to the bulk density of the settled residue and the diameter of the cavity.

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