Method for simulating A annulus under pressure when leakage point of gas storage injection-production string is located on liquid level of annulus protection liquid

Abstract

The invention discloses an A annulus under-pressure simulation method for leakage points of a gas storage injection-production string on the liquid level of annulus protection liquid, which comprises the following steps: setting the depths and equivalent diameters of different leakage points of the injection-production string to obtain the external pressure of the injection-production string and the equivalent area of the leakage points corresponding to the leakage points; acquiring the volume of gas leaked from the ith leakage point at the nth time node of the injection-production pipe column; acquiring the top pressure of the A-ring air column at each time node; judging whether the internal and external pressures of the injection-production string at the ith leakage point are balanced or not, and if so, stopping the leakage at the point; when all leakage points stop leakage, the pressure of the A annulus is stable; and drawing a simulated pressure recovery curve through the top pressure of the A-ring air column at each time node, comparing the simulated pressure recovery curve with an actual pressure recovery curve, and judging whether the set depths and equivalent diameters of different leakage points are reasonable or not. According to the method, possible pipe column leakage points can be judged, the underground operation workload is reduced, and the working efficiency is improved.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas production, and in particular to a method for simulating the pressure of an annulus A in a gas storage reservoir where a leakage point of an injection and production pipe string is located on the liquid surface of annulus protection liquid. Background Art

[0002] The construction and safe operation of gas storage groups are important guarantees for gas peak regulation, national gas use, and even stable and controllable national energy. The wellbore structure of conventional gas storage injection and production wells includes surface casing, technical casing, and oil layer casing from the outside to the inside. The A annulus is between the injection and production string and the oil layer casing, and the B annulus, C annulus, and D annulus are located outward. The injection and production string adopts an airtight string and is equipped with a safety valve, a circulating sleeve, a packer, etc. The upper part of the A annulus is filled with nitrogen, and the lower part is filled with annulus protection fluid.

[0003] During the injection and production operation of the gas storage, if the injection and production pipe string in the well is not tightly sealed due to injection and production vibration, fluid corrosion, etc., or the pipe string body is perforated, and a leakage point appears in the injection and production pipe string, the gas in the pipe string will leak into the A annulus, that is, the casing annulus, through the injection and production pipe string leakage point, which will cause the A annulus to be pressurized. If the injection and production pipe string leakage point is above the annulus protection liquid level, the pressure difference between the inside and outside of the leakage point is large at the beginning of the leakage. If it cannot be treated in time, it will cause great harm to the safe and stable operation of the injection and production well.

[0004] At present, there is a lack of quantitative simulation analysis of the process of A annulus pressure caused by injection and production string leakage (leakage point is above the annulus protection liquid level), so the pressure law is still unclear. Therefore, it is necessary to carry out quantitative simulation analysis based on mathematical models according to the underlying physical logic, and through numerical calculation and comparison, determine the possible leakage points of the string, so as to provide a basis for the treatment of A annulus pressure problem and daily operation and maintenance of gas storage injection and production wells. Summary of the invention

[0005] The purpose of the present invention is to propose a method for simulating the A annulus pressure when the leakage point of the injection and production pipe string of a gas storage reservoir is located on the liquid surface of the annulus protection liquid, which can determine the possible leakage points of the pipe string, save the workload of downhole operations, improve work efficiency, and provide a certain basis for the treatment of the A annulus pressure problem of the injection and production well of the gas storage reservoir.

[0006] To achieve the above purpose, the present application proposes a method for simulating the pressure of annulus A in which the leakage point of the injection and production pipe string of a gas storage reservoir is located on the liquid surface of the annulus protection liquid, comprising:

[0007] Set the depth and equivalent diameter of different leakage points of the injection and production string to obtain the external pressure of the injection and production string and the equivalent area of ​​the leakage point corresponding to the leakage point;

[0008] Get the gas volume V_leak leaked from the i-th (i=1, 2, 3, ..., j) leakage point at the n-th time node of the injection and production stringi n ;

[0009] Obtain the top pressure of the A-ring air column at each time node, and reassign parameters such as the A-ring air column volume, A-ring air column length, A-ring protection fluid volume, A-ring protection fluid density, and injection and production string external pressure at the leakage point;

[0010] Determine whether the pressure inside and outside the injection and production string of the i-th leakage point is balanced. If balanced, the leakage at this point stops. When all leakage points stop leaking, the pressure in the A annulus is stable.

[0011] The simulated pressure recovery curve is drawn by the top pressure of the A-ring air column at each time node. Compared with the actual pressure recovery curve, it is judged whether the depth and equivalent diameter of different leakage points are reasonable.

[0012] Furthermore, using the leaked gas volume V_leak i n , according to the volume-pressure coupling variation mathematical model of gas leakage into the A annulus at a unit time node, the top pressure of the A annulus air column at each time node is obtained.

[0013] Furthermore, the mathematical model of volume-pressure coupling change of gas leakage into annulus A at a unit time node is:

[0014]

[0015] Where: P_leak_tube_g i is the pressure in the injection and production string at the i-th leakage point, in MPa;

[0016] V_leak i n is the volume of gas leaked from the ith leakage point at the nth time node, in m 3 ;

[0017] P_bubble i n is the bubble pressure leaking into the annulus A from the ith leakage point at the nth time node, in MPa;

[0018] P g n is the top pressure of the air column in ring A at the nth time node, in MPa;

[0019] P g n-1 is the top pressure of the air column of ring A at the n-1th time node, in MPa;

[0020] L g n-1is the length of the air column of ring A at the n-1th time node, in meters;

[0021] S is the cross-sectional area of ​​the annulus A, in m 2 ;

[0022] M is the molar mass of the gas, in kg / mol;

[0023] Z is the gas deviation coefficient, dimensionless;

[0024] R is the gas constant, in J / (mol·K);

[0025] T g is the temperature of the air column in ring A, in K;

[0026] C m is the compression coefficient of the casing annulus protection fluid, unit: MPa -1 ;

[0027] V m n-1 The volume of annular space protection fluid at the n-1th time node A, unit: m 3

[0028] V g n-1 is the volume of the air column in ring A at the n-1th time node, in m 3 ;

[0029] g is the acceleration due to gravity, unit is N / Kg;

[0030] L_leak i is the distance from the i-th leakage point to the wellhead, in m;

[0031] DV 1 n is the total compressed volume of the gas column and protective fluid in the annulus A at the nth time node compared to the n-1th time node, in m 3 ;

[0032] DV 2 n is the compressed volume of annular space protection fluid A at time node n compared to time node n-1, in m 3 ;

[0033] DV 3 n is the compressed volume of the upper gas column in annulus A at the nth time node compared to the n-1th time node, in m 3 .

[0034] Furthermore, the small hole model is used to obtain the gas volume V_leak of the i-th (i=1, 2, 3, ..., j) leakage point at the n-th time node of the injection and production string. i n .

[0035] Furthermore, the small hole model is:

[0036] when

[0037]

[0038] when

[0039]

[0040] Where: m_leak i n is the gas mass leaked from the ith leakage point at the nth time node, in kg;

[0041] V_leak i n is the volume of gas leaked from the ith leakage point at the nth time node, in m 3 ;

[0042] P_leak_casing_l i n-1 The external pressure of the injection and production string at the i-th leakage point at the n-1th time node, in MPa;

[0043] k is the gas adiabatic index, dimensionless; it can be 1.28;

[0044] C is the flow coefficient, dimensionless (the value of the small circular hole is 1).

[0045] d_leak i is the equivalent diameter of the leakage point of the i-th leakage point, in m;

[0046] T_leak_tube_g i is the gas temperature in the injection and production string at the i-th leakage point, in K.

[0047] Furthermore, the volume of the A annulus protection liquid and the volume of the A annulus air column are respectively:

[0048]

[0049] Where: V m n —Volume of annular space protection fluid at time node A at nth time, m 3

[0050] V g n —The volume of the air column in ring A at the nth time node, m 3 .

[0051] Furthermore, before the method is implemented, the outer diameter of the oil pipe; the inner diameter of the oil layer casing; the depth of the packer; the initial A-ring air column top pressure, height, and temperature; the initial A-ring space protection fluid density and compression coefficient; the wellhead pressure and temperature of the injection and production string; the gas adiabatic index, molar mass, etc. are obtained first.

[0052] Furthermore, the leakage points of the injection and production string are located above the liquid level of the annulus protection fluid, and the number of leakage points is ≥1.

[0053] Compared with the prior art, the above technical scheme adopted by the present invention has the advantages that the simulation method of the present invention has good calculation stability and high field applicability. Through this method, the annulus pressure of the A annulus pressurized due to the leakage of the injection and production string (different leakage points located on the liquid surface of the annulus protection liquid) can be obtained, and the simulation of the A annulus pressurized process can be realized. By comparing with the actual A annulus pressure recovery curve, it can be judged whether the depth and equivalent diameter of the set different leakage points are reasonable, which provides a certain basis for the treatment of the A annulus pressurized problem of the injection and production wells of the gas storage reservoir. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 This is a schematic diagram of the wellbore structure of the gas storage injection and production well;

[0055] Figure 2 A flow chart of a method for simulating the pressure of an annulus in a gas storage facility where the leakage point of the injection and production pipe string is located on the surface of the annulus protection liquid;

[0056] Explanation of the serial numbers in the figure: 1. Surface casing; 2. Technical casing; 3. Oil layer casing; 4. Injection and production string; 5. Packer.

[0057] Specific implementation methods

[0058] In order to make the purpose, technical solutions and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application, that is, the embodiments described are only part of the embodiments of the present application, not all of the embodiments.

[0059] This embodiment provides a method for simulating the pressure of the A annulus when the leakage point of the injection and production string of a gas storage is located on the liquid surface of the annulus protection liquid. Before the implementation of the method, the outer diameter of the oil pipe; the inner diameter of the oil layer casing; the depth of the packer; the initial pressure, height and temperature of the top of the A annulus air column; the initial density and compression coefficient of the A annulus protection liquid; the wellhead pressure and temperature of the injection and production string; the gas adiabatic index and molar mass, etc. are obtained first; specifically including:

[0060] Step 1. Set the depth and equivalent diameter of different leakage points of the injection and production string above the annular protection liquid level to obtain the external pressure of the injection and production string and the equivalent area of ​​the leakage point at the corresponding leakage point.

[0061] Step 2. Use formula (2) to obtain the gas volume V_leak leaked from the i-th (i=1, 2, 3, ..., j) leakage point at the n-th time node i n ;

[0062] Step 3. Use formula (1) to obtain the top pressure of the A-ring air column at each time node. The nonlinear equation solving methods such as the dichotomy method and Newton's method can be used. After the calculation of the current time node is completed, the parameters such as the A-ring air column volume, the A-ring air column length, the A-ring protective fluid volume, the A-ring protective fluid density, and the external pressure of the injection and production string at the leakage point are reassigned to provide data for the calculation of the next time node.

[0063] Step 4. Determine whether the pressure inside and outside the injection and production string of the i-th (i=1, 2, 3, ..., j) leakage point is equal. If they are equal, the leakage of this point stops, and the calculation of the remaining leakage points continues at the next time node; when all leakage points stop leaking, the calculation ends, and the pressure at the top of the A-ring air column is stable.

[0064] Step 5. Draw a simulated pressure recovery curve based on the top pressure of the A-ring air column at each time node to simulate the pressure of the A-ring. By comparing the simulated pressure recovery curve of the A-ring with the actual pressure recovery curve, it can be determined whether the depth and equivalent diameter of the assumed different leakage points are reasonable.

[0065] In this application, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements that are inherent to such process, method, article, or apparatus.

[0066] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for simulating the pressure of annulus A in a gas storage reservoir where the leakage point of the injection and production pipe string is located on the liquid surface of the annulus protection liquid, characterized in that: include: Set the depth and equivalent diameter of different leakage points of the injection and production string to obtain the external pressure of the injection and production string and the equivalent area of ​​the leakage point corresponding to the leakage point; Get the gas volume V_leak leaked from the i-th (i=1, 2, 3, ..., j) leakage point at the n-th time node of the injection and production string i n ; Obtain the top pressure of the A-ring air column at each time node, and reassign the A-ring air column volume, A-ring air column length, A-ring protection fluid volume, A-ring protection fluid density, and injection and production string external pressure parameters at the leakage point; Determine whether the pressure inside and outside the injection and production string of the i-th leakage point is balanced. If balanced, the leakage at this point stops; When all leakage points stop leaking, the pressure in annulus A is stable; The simulated pressure recovery curve is drawn by the top pressure of the A-ring air column at each time node. Compared with the actual pressure recovery curve, it is judged whether the depth and equivalent diameter of different leakage points are reasonable.

2. According to claim 1, a method for simulating annular pressure in which the leakage point of the injection and production pipe string of a gas storage reservoir is located above the liquid level of the annular protection liquid, characterized in that: Using the leaked gas volume V_leak i n , according to the volume-pressure coupling variation mathematical model of gas leakage into the A annulus at a unit time node, the top pressure of the A annulus air column at each time node is obtained.

3. According to claim 2, a method for simulating annular pressure in a gas storage reservoir where the leakage point of the injection and production pipe string is located above the liquid level of the annular protection liquid, characterized in that: The mathematical model of volume-pressure coupling change of gas leakage into annulus A at unit time node is: Where: P_leak_tube_g i is the pressure in the injection and production string at the i-th leakage point, in MPa; V_leak i n is the volume of gas leaked from the ith leakage point at the nth time node, in m 3 ; P_bubble i n is the bubble pressure leaking into the annulus A from the ith leakage point at the nth time node, in MPa; P g n is the top pressure of the air column in ring A at the nth time node, in MPa; P g n-1 is the top pressure of the air column of ring A at the n-1th time node, in MPa; L g n-1 is the length of the air column of ring A at the n-1th time node, in meters; S is the cross-sectional area of ​​the annulus A, in m 2 ; M is the molar mass of the gas, in kg / mol; Z is the gas deviation coefficient, dimensionless; R is the gas constant, in J / (mol·K); T g is the temperature of the air column in ring A, in K; C m is the compression coefficient of the casing annulus protection fluid, unit: MPa -1 ; V m n-1 The volume of annular space protection fluid at the n-1th time node A, unit: m 3 V g n-1 is the volume of the air column in ring A at the n-1th time node, in m 3 ; g is the acceleration due to gravity, unit is N / Kg; L_leak i is the distance from the i-th leakage point to the wellhead, in m; DV1 n is the total compressed volume of the gas column and protective fluid in the annulus A at the nth time node compared to the n-1th time node, in m 3 ; DV2 n is the compressed volume of annular space protection fluid A at time node n compared to time node n-1, in m 3 ; DV3 n is the compressed volume of the upper gas column in annulus A at the nth time node compared to the n-1th time node, in m 3 .

4. The method for simulating annular pressure in a gas storage reservoir with a leakage point of the injection and production pipe string located above the liquid level of the annular protection liquid according to claim 1, characterized in that: Use the pinhole model to obtain the gas volume V_leak of the i-th (i=1, 2, 3, ..., j) leakage point at the n-th time node of the injection and production string i n .

5. According to claim 4, a method for simulating annular pressure in a gas storage reservoir where the leakage point of the injection and production pipe string is located above the liquid level of the annular protection liquid, characterized in that: The pinhole model is: Where: m_leak i n is the gas mass leaked from the ith leakage point at the nth time node, in kg; V_leak i n is the volume of gas leaked from the ith leakage point at the nth time node, in m 3 ; P_leak_casing_l i n-1 The external pressure of the injection and production string at the i-th leakage point at the n-1th time node, in MPa; k is the gas adiabatic index, dimensionless; it can be 1.28; C is the flow coefficient, dimensionless (the value of the small circular hole is 1). d_leak i is the equivalent diameter of the leakage point of the i-th leakage point, in m; T_leak_tube_g i is the gas temperature in the injection and production string at the i-th leakage point, in K.

6. The method for simulating annular pressure in a gas storage reservoir with a leakage point of the injection and production pipe string located above the liquid level of the annular protection liquid according to claim 1, characterized in that: The volume of the A annulus protection liquid and the volume of the A annulus air column are respectively: Where: V m n —Volume of annular space protection fluid at time node A, m 3 V g n —The volume of the air column in ring A at the nth time node, m 3 .

7. The method for simulating annular pressure in a gas storage reservoir with a leakage point of the injection and production pipe string located above the liquid level of the annular protection liquid according to claim 1, characterized in that: Before the method is implemented, the outer diameter of the oil pipe; the inner diameter of the oil layer casing; the depth of the packer; the initial A-ring air column top pressure, height, and temperature; the initial A-ring space protection fluid density and compression coefficient; the wellhead pressure and temperature of the injection and production string; and the gas adiabatic index and molar mass are obtained.

8. The method for simulating annular pressure in a gas storage facility with a leakage point of the injection and production pipe string located above the liquid level of the annular protection liquid according to claim 1, characterized in that: The leakage point of the injection and production string is located above the liquid level of the annulus protection fluid, and the number of leakage points is ≥1.

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