A method for simulating annular pressure in a gas storage reservoir with an injection and production string leakage point located on the annular protection liquid level

Abstract

The present invention discloses a method for simulating the pressure of the A annulus in a gas storage reservoir where a leakage point of the injection and production string is located above the annular protection liquid level. The method includes setting the depth and equivalent diameter of different leakage points in the injection and production string to obtain the external pressure of the injection and production string and the equivalent area of ​​the leakage point at the corresponding leakage point; obtaining the volume of gas leaked at the i-th leakage point in the injection and production string at the n-th time node; obtaining the top pressure of the A annular air column at each time node; determining whether the internal and external pressures of the injection and production string at the i-th leakage point are balanced; if so, leakage at that point stops; when all leakage points stop, the A annular pressure stabilizes; and using the top pressure of the A annular air column at each time node to draw a simulated pressure recovery curve, which is compared with the actual pressure recovery curve to determine whether the depths and equivalent diameters of the different leakage points set are reasonable. This method can identify possible pipe string leakage points, save downhole operation workload, and improve work efficiency.

Description

Technical Field

[0001] The present 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 surface of an annulus protection liquid. Background Art

[0002] The construction and safe operation of gas storage clusters are crucial for peak-shaving gas supply, ensuring gas consumption for the public, and ultimately ensuring stable and controllable national energy resources. The wellbore structure of a conventional gas storage injection and production well comprises, from the outside in, surface casing, technical casing, and reservoir casing. Annulus A is located between the injection and production tubing and the reservoir casing, followed outward by annulus B, annulus C, and annulus D. The injection and production tubing is a gas-tight string equipped with safety valves, circulating sleeves, and packers. The upper portion of annulus A is filled with nitrogen, while the lower portion is filled with annulus protection fluid.

[0003] During gas storage injection and production operations, if the downhole injection and production tubing develops a leak due to vibration, fluid corrosion, or other factors, resulting in a loose thread seal or perforation of the tubing itself, gas within the tubing can leak through the leak into the A annulus (the oil-casing annulus), causing pressure in the A annulus. If the leak is above the level of the annular protection fluid, the pressure differential between the inside and outside of the leak is significant in the early stages of leakage. If not promptly addressed, this can significantly compromise the safe and stable operation of the injection and production well.

[0004] Currently, there is a lack of quantitative simulation analysis of the process by which injection and production string leakage (the leakage point is located above the annular protection fluid level) leads to annular pressure in the A annulus, and the pressure pattern is still unclear. Therefore, it is necessary to conduct quantitative simulation analysis based on mathematical models based on underlying physical logic. Through numerical calculation and comparison, the possible location of string leakage can be identified, providing a basis for the treatment of annular pressure in the A annulus of gas storage injection and production wells and daily operation and maintenance. Summary of the Invention

[0005] The purpose of the present invention is to propose a method for simulating the pressure in the annulus A of a gas storage injection and production string where the leakage point is located above the liquid level of the annular protection fluid. The method can determine the possible leakage point of the string, save the workload of downhole operations, improve work efficiency, and provide a certain basis for the treatment of the pressure problem in the annulus A of the injection and production well of the gas storage.

[0006] To achieve the above objectives, this application proposes a method for simulating annular pressure in a gas storage reservoir where the leakage point of the injection and production string is located above the annular protection liquid level, comprising:

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

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

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

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

[0012] Furthermore, 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 The volume of gas leaked from the i-th leakage point at the n-th time node, in m 3 ;

[0017] P_bubble i n is the bubble pressure leaking into the annulus A at the i-th leakage point at the n-th 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 in ring A at the n-1th time node, in MPa;

[0020] L g n-1is the length of the air column in 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, unit is 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 annulus protection fluid at time node n-1, in m 3

[0028] V g n-1 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 between the i-th leakage point and the wellhead, in meters;

[0031] 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 ;

[0032] 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 ;

[0033] DV3 n is the compressed volume of the upper gas column in annulus A at time n compared to time n-1, 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 mass of gas leaked from the i-th leakage point at the n-th time node, in kg;

[0041] V_leak i n The volume of gas leaked from the i-th leakage point at the n-th 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, 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 implementing this 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-ring air column; the initial density and compression coefficient of the A-ring protective fluid; the wellhead pressure and temperature of the injection and production string; the gas adiabatic index and molar mass, etc. are obtained.

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

[0053] Compared with the prior art, the above technical solution adopted by the present invention has the following advantages: the simulation method of the present invention has good computational stability and high field applicability. Through this method, the annular space pressure of the A annulus caused by leakage of the injection and production string (different leakage points located on the liquid surface of the annular space protection liquid) can be obtained, and the A annular space pressure process can be simulated. By comparing with the actual A annular space 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 annular space pressure problem in 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 for simulating annular pressure in a gas storage facility where the leakage point of the injection and production string is located above the annular protection liquid level.

[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. Specific implementation methods

[0057] In order to make the purpose, technical solutions and advantages of this application more clearly understood, this application is further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application. That is, the embodiments described are only part of the embodiments of this application, not all of them.

[0058] This embodiment provides a method for simulating the pressure in the A annulus of a gas storage injection and production string where the leakage point is located on the annular protection fluid level. Before implementing the method, the outer diameter of the oil pipe; the inner diameter of the oil layer casing; the packer depth; the initial pressure, height, and temperature of the top of the A annular air column; the initial density and compressibility of the A annular protection fluid; the wellhead pressure and temperature of the injection and production string; the gas adiabatic index and molar mass are obtained. Specifically, the following are obtained:

[0059] 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.

[0060] Step 2. Use formula (2) to obtain the gas volume V_leak of the i-th (i=1, 2, 3, ..., j) leakage point at the n-th time node i n ;

[0061] 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 bisection method and Newton method can be used. After the calculation of the current time node is completed, the parameters such as the A-ring air column volume, A-ring air column length, A-ring space protection fluid volume, A-ring space protection 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.

[0062] Step 4. Determine whether the internal and external pressures of the injection and production string at the i-th (i=1, 2, 3, …, j) leakage point are equal. If so, leakage at that point ceases, and calculations for the remaining leakage points proceed to the next time point. When all leakage points cease, the calculation ends, and the pressure at the top of the A-ring air column stabilizes.

[0063] Step 5. Draw a simulated pressure recovery curve based on the top pressure of the air column in annulus A at each time point to simulate the pressure in annulus A. Comparing the simulated pressure recovery curve with the actual pressure recovery curve for annulus A can determine whether the depths and equivalent diameters of the assumed leakage points are reasonable.

[0064] 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 comprises a list of elements includes not only those elements but also other elements not expressly listed or that are inherent to such process, method, article, or apparatus.

[0065] While 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 these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for simulating annular pressure in a gas storage facility where the leakage point of the injection and production string is located above the liquid level of the annular protection liquid, characterized in that: include: Set the depth and equivalent diameter of different leakage points in the injection and production string to obtain the external pressure of the injection and production string and the equivalent area of ​​the leakage point; Get the gas volume V_leak leaked at the i-th leakage point at the n-th time node of the injection and production string i n , i=1,2,3,…,j; 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 the external pressure of the injection and production string at the leakage point; Determine whether the pressure inside and outside the injection and production string at the i-th leakage point is balanced. If so, the leakage at that point stops. When all leakage points stop leaking, the pressure in annulus A is stable; By plotting the simulated pressure recovery curve based on the top pressure of the A-ring air column at each time point, and comparing it with the actual pressure recovery curve, we can determine whether the depth and equivalent diameter of the set leakage points are reasonable. 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 each time node, the top pressure of the A annulus air column at each time node is obtained; The mathematical model of volume-pressure coupling change of gas leakage into annulus A at a 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 The volume of gas leaked from the i-th leakage point at the n-th time node, in m 3 ; P_bubble i n is the bubble pressure leaking into the annulus A at the i-th leakage point at the n-th 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 in ring A at the n-1th time node, in MPa; L g n-1 is the length of the air column in 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, unit is 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 annulus protection fluid at time node n-1, in m 3 V g n-1 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 between the i-th leakage point and the wellhead, in meters; 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 time n compared to time n-1, in m 3 .

2. The method for simulating annular pressure in a gas storage reservoir with a leakage point of the injection and production string located above the annular protection liquid level 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 .

3. The method for simulating annular pressure in a gas storage reservoir with a leakage point of the injection and production string located above the annular protection liquid level according to claim 2, characterized in that: The pinhole model is: Where: m_leak i n is the mass of gas leaked from the i-th leakage point at the n-th time node, in kg; V_leak i n The volume of gas leaked from the i-th leakage point at the n-th 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; take 1.28; C is the flow coefficient, dimensionless, and the value for 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.

4. The method for simulating annular pressure in a gas storage reservoir with a leakage point of the injection and production string located above the annular protection liquid level 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 .

5. The method for simulating annular pressure in a gas storage reservoir with a leakage point of the injection and production string located above the annular protection liquid level according to claim 1, characterized in that: Before implementing 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-ring air column; the initial density and compressibility of the A-ring protective fluid; the wellhead pressure and temperature of the injection and production string; and the gas adiabatic index and molar mass are obtained.

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

Images