Treatment methods for controlling production string leakage in wellbore

Abstract

The present application provides a processing method for controlling leakage of a production string in a wellbore, the method comprising: obtaining various operating parameters of the wellbore; obtaining the installation depth of a downhole choke; calculating the annular allowable pressure of the casing annulus according to various operating parameters; segmenting and numbering the production string to obtain a multi-segment production string with numbers; constructing a pressure iteration model according to the segmented pressure and segmented temperature of each segment of the production string obtained; determining a target number of the sub-production string where the downhole choke is located according to the installation depth; determining the annular allowable pressure as the initial pressure of the first segment of the production string; determining the pressure at the target number according to the initial pressure and the pressure iteration model; determining the throttling hole area of ​​the downhole throttling device according to the obtained bottom maximum pressure of the wellbore before throttling, the temperature in the production string and the pressure at the target number; and determining the throttling hole diameter of the downhole throttling device according to the throttling hole area, thereby solving the problem of leakage of the production string.

Description

Technical Field

[0001] The present application relates to the technical field of natural gas drilling and completion, and in particular to a method for controlling leakage of a production tubing in a wellbore. Background Art

[0002] Natural gas has become a viable alternative to high-carbon fossil fuels like coal. Natural gas extraction typically requires establishing a channel from underground to the surface through a wellbore. The production string within the wellbore serves as the direct conduit for natural gas extraction. The production string, comprised of steel tubing and related components, is susceptible to seal failure and perforation cracking under the combined effects of stress, load, and fluid pressure.

[0003] In related technologies, when a production string experiences sealing failure and perforation cracking, it is first necessary to determine the failure or cracking location of the production string, and then to seal the location using chemical plugging agents or mechanical plugging to complete the repair of the production string.

[0004] However, in related technologies, dirt or solid deposits usually exist on the inner wall of the production string. The failure or cracked positions are sealed by chemical plugging agents or mechanical plugging, but an effective seal cannot be formed with the inner wall of the production string, making it impossible to solve the problem of production string leakage. Summary of the Invention

[0005] The present application provides a treatment method for controlling leakage of a production tubing in a wellbore to address the problem of dirt or solid deposits usually present on the inner wall of the production tubing. Blocking failed or cracked locations with chemical plugging agents or mechanical plugging cannot form an effective seal with the inner wall of the production tubing, making it impossible to solve the problem of leakage of the production tubing.

[0006] In a first aspect, the present application provides a method for controlling leakage of a production tubing string in a wellbore, comprising:

[0007] Obtaining operating parameters of a wellbore, wherein the wellbore includes at least a casing annulus, a production tubing string, a packer, and a downhole choke, wherein the casing annulus is the circular space surrounding the production tubing string, and the packer is installed on the production tubing string; the operating parameters include at least the internal pressure resistance of the production casing at the packer, the external collapse resistance of the production tubing string at the packer, the wellhead pressure of the wellbore after production, the minimum internal pressure resistance of the production casing, the minimum internal pressure resistance of the technical casing outside the casing annulus, the minimum external collapse resistance of the production tubing string, and the casing head strength of the production casing;

[0008] Obtaining a predetermined installation depth of the downhole choke, and installing the downhole choke on the production tubing according to the installation depth;

[0009] Calculating the permissible annular pressure of the casing annulus according to the production casing internal pressure resistance strength, the production string external collapse resistance strength, the wellhead pressure, the minimum internal pressure resistance strength of the production casing, the minimum internal pressure resistance strength of the technical casing, the minimum external collapse resistance strength of the production string, and the casing head strength;

[0010] The production string is segmented and numbered according to a preset length to obtain a multi-segment production string with numbers;

[0011] Obtain the segmented pressure and segmented temperature of each section of the production string;

[0012] Constructing a pressure iteration model corresponding to each sub-production string according to the segmented pressure and the segmented temperature;

[0013] Determining the target number of the sub-production string where the downhole choke is located according to the installation depth;

[0014] Determine the annular space allowable pressure as the initial pressure of the first section production string;

[0015] Determine the pressure at the target number according to the initial pressure and the pressure iteration model;

[0016] Obtaining the maximum bottom pressure and the temperature inside the production tubing string before throttling of the wellbore;

[0017] Determine the throttle hole area of ​​the downhole choke when the production string is in a critical leakage state or a non-critical leakage state according to the maximum bottom pressure, the temperature in the production string, and the pressure at the target number;

[0018] The throttle aperture of the downhole throttle is determined according to the throttle aperture area to ensure that the production string is in a critical leakage state or a non-critical leakage state, thereby preventing leakage of the production string.

[0019] In a possible design, the downhole choke needs to be installed below the packer, and the production string is spliced ​​from multiple oil pipes; the operating parameters also include the weight of the production string, the weight per unit length of the production string, the design depth of the packer, the surface temperature, the initial length of a single oil pipe, the geothermal gradient, and the initial temperature of the single oil pipe; accordingly, the process of determining the installation depth of the downhole choke includes: calculating the first initial length of the production string subjected to tension based on the weight of the production string and the weight per unit length of the production string; determining the second initial length of the production string subjected to compression based on the design depth of the packer and the initial length of the production string subjected to tension; and determining the second initial length of the production string subjected to compression based on the design depth of the production string. The stretched length of the production string is calculated based on the weight per unit length of the string, the first initial length and the cross-sectional area of ​​the production string; the compressed length of the production string is calculated based on the weight per unit length of the production string, the second initial length and the cross-sectional area of ​​the production string; the thermal expansion and elongation of any oil pipe is calculated based on the surface temperature, the initial length of the single oil pipe, the geothermal gradient and the initial temperature of the single oil pipe; the total thermal expansion and elongation of the production string is determined based on the thermal expansion and elongation corresponding to each oil pipe; the actual depth of the packer is determined based on the designed depth of the packer, the stretched length, the compressed length and the total thermal expansion and elongation; and the installation depth of the downhole choke is determined based on the actual depth of the packer.

[0020] In one possible design, the calculation formula for calculating the first initial length of the production string subjected to tension based on the weight of the production string and the weight per unit length of the production string includes:

[0021]

[0022] Where H L F is the first initial length of the production string subjected to tension, m; X is the weight of the production string, N; M T is the mass per unit length of the production string, kg / m; g is the acceleration due to gravity, m / s 2 ;

[0023] Accordingly, the calculation formula for determining the second initial length of the production string subjected to compression based on the design depth of the packer and the initial length of the production string subjected to tension includes:

[0024]

[0025] Where H Y H is the second initial length of the production string subjected to compression, m; FS is the design depth of the packer, m; HL is the first initial length of the production string subjected to tension, m;

[0026] Accordingly, the calculation formula for calculating the stretched length of the production string based on the weight per unit length of the production string, the first initial length, and the cross-sectional area of ​​the production string includes:

[0027]

[0028] Where, △H L is the tensile length of the production string, m; E is the elastic modulus of the production string, Pa; A is the cross-sectional area of ​​the production string; H L is the first initial length of the production string subjected to tension, m;

[0029] Accordingly, the calculation formula for calculating the compressed length of the production string based on the weight per unit length of the production string, the second initial length, and the cross-sectional area of ​​the production string includes:

[0030]

[0031] Where, △H Y is the compressed length of the production string, m; E is the elastic modulus of the production string, Pa; A is the cross-sectional area of ​​the production string; H Y is the second initial length of the production string subjected to compression, m;

[0032] Accordingly, the calculation formula for calculating the thermal expansion and elongation of any oil pipe based on the ground surface temperature, the initial length of the single oil pipe, the geothermal gradient, and the initial temperature of the single oil pipe includes:

[0033]

[0034] Where, △H T i is the thermal expansion of the i-th oil pipe, m; T0 is the surface temperature, °C; g e is the geothermal gradient, ℃ / m; i is the number of the oil pipe in the wellbore, which is numbered 1, 2, ..., N from the wellhead to the bottom of the well; H T is the initial length of the single oil pipe, m; T T is the initial temperature of the single oil pipe, °C; α is the thermal expansion coefficient of the oil pipe, °C -1 ;

[0035] Accordingly, the calculation formula for determining the total thermal expansion and elongation of the production string based on the thermal expansion and elongation corresponding to each oil pipe includes:

[0036]

[0037] Where, △H TZ is the total thermal expansion and elongation of the production string above the packer, m; △H T i is the thermal expansion elongation of the i-th oil pipe;

[0038] Accordingly, the calculation formula for determining the actual depth of the packer based on the design depth of the packer, the stretched length, the compressed length, and the total thermal expansion and elongation includes:

[0039]

[0040] Where H F is the actual depth of the packer, m; H FS is the design depth of the packer, m; △H L is the stretched length of the production string, m; ΔH Y is the compressed length of the production string, m; ΔH TZ is the total thermal expansion and elongation of the production string above the packer, m;

[0041] Accordingly, the calculation formula for determining the installation depth of the downhole choke according to the actual depth of the packer includes:

[0042]

[0043] Where H J H is the installation depth of the downhole choke, m; F is the actual depth of the packer, m; H W H is the installation depth allowance. W >0,m.

[0044] In a possible design, the annular allowable pressure of the casing annulus is calculated based on the production casing's internal pressure resistance, the production tubing's external squeeze resistance, the wellhead pressure, the minimum internal pressure resistance of the production casing, the minimum internal pressure resistance of the technical casing, the minimum external squeeze resistance of the production tubing, and the casing head strength, including: calculating the maximum annular allowable pressure determined by the production casing's internal pressure resistance at the packer based on the production casing's internal pressure resistance; calculating the maximum annular allowable pressure determined by the production casing's external squeeze resistance at the packer based on the production tubing's external squeeze resistance and the wellhead pressure; calculating the annular allowable pressure of the casing annulus based on the minimum internal pressure resistance of the production casing, the minimum internal pressure resistance of the technical casing, the minimum external squeeze resistance of the production tubing, the casing head strength, the maximum annular allowable pressure determined by the production casing's internal pressure resistance at the packer, and the maximum annular allowable pressure determined by the production casing's external squeeze resistance at the packer.

[0045] In a possible design, the calculation formula for calculating the maximum allowable annular pressure determined by the production casing internal pressure resistance strength at the packer according to the production casing internal pressure resistance strength includes:

[0046]

[0047] Where, p5 is the maximum allowable annular pressure determined by the internal pressure resistance strength of the production casing at the packer; p7 is the internal pressure resistance strength of the production casing, MPa; ρ cs is the cement slurry density, g / cm 3 ρ co is the annular liquid density, g / cm 3 ; g is the acceleration due to gravity, m 2 / s;h p is the depth of the packer, m;

[0048] Accordingly, the calculation formula for the maximum allowable annular pressure determined by the production casing anti-collapse strength at the packer according to the production string anti-collapse strength and the wellhead pressure includes:

[0049]

[0050] Where, p6 is the maximum permissible annular pressure determined by the anti-collapse strength of the production casing at the packer; p8 is the anti-collapse strength of the production string, MPa; p9 is the wellhead pressure, MPa; ρ cs is the cement slurry density, g / cm 3 ρ co is the annular liquid density, g / cm 3 ; g is the acceleration due to gravity, m 2 / s;hp is the depth of the packer, m;

[0051] Accordingly, the calculation formula for calculating the allowable annular pressure of the casing annulus based on the minimum internal pressure resistance of the production casing, the minimum internal pressure resistance of the technical casing, the minimum external collapse resistance of the production string, the casing head strength, the maximum allowable annular pressure determined by the internal pressure resistance of the production casing at the packer, and the maximum allowable annular pressure determined by the external collapse resistance of the production casing at the packer includes:

[0052]

[0053] Where, △p aA is the allowable annulus pressure of the casing annulus, MPa; p1 is the minimum internal pressure resistance of the production casing, MPa; p2 is the minimum internal pressure resistance of the technical casing, MPa; p3 is the minimum external collapse strength of the production string, MPa; p4 is the casing head strength, MPa; p5 is the maximum allowable annulus pressure determined by the internal pressure resistance of the production casing at the packer, MPa; p6 is the maximum allowable annulus pressure determined by the external collapse strength of the production casing at the packer, MPa.

[0054] In one possible design, the pressure iteration model corresponding to each section of the production tubing is constructed according to the segmented pressure and the segmented temperature, including: calculating the gas density of each section of the production tubing according to the segmented pressure and the segmented temperature; calculating the gravity pressure drop of each section of the production tubing according to the gas density; calculating the gas flow rate of each section of the production tubing according to the gas density; calculating the friction coefficient of each section of the production tubing according to the gas density and the gas flow rate; calculating the friction pressure drop of each section of the production tubing according to the gas density, the gas flow rate and the friction coefficient; and constructing the pressure iteration model corresponding to each section of the production tubing according to the segmented pressure, the gravity pressure drop and the friction pressure drop.

[0055] In a possible design, the calculation formula for calculating the gas density of each sub-production string according to the segment pressure and the segment temperature includes:

[0056]

[0057] Where, is the gas density of the kth sub-production string, kg / m 3 ;p k is the segment pressure of the kth segment, Pa; T s is the standard temperature, ℃; p s is the standard pressure, Pa; T kis the segment temperature of the kth segment, °C; ρ s is the standard density of the gas, kg / m 3 ;

[0058] Accordingly, the calculation formula for calculating the gravity pressure drop of each section of the production string according to the gas density includes:

[0059]

[0060] Where, is the gravity pressure drop of the sub-production string in section k, MPa; H FD is the preset length, m; is the gas density of the k-th section production string, kg / m 3 ; g is the acceleration due to gravity, m 2 / s;H FD is the preset length, m;

[0061] Accordingly, the calculation formula for calculating the gas flow rate of each section of the production string according to the gas density includes:

[0062]

[0063] Where, Q is the gas flow rate of the k-th section production string, m / s; min is the minimum output rate, m 3 / d;d tn is the inner diameter of the production string, m; is the gas density of the kth sub-production string, kg / m 3 ρ s is the standard density of the gas, kg / m 3 ;

[0064] Accordingly, the calculation formula for calculating the friction coefficient of each section of the production string according to the gas density and the gas flow rate includes:

[0065]

[0066] Where, is the friction coefficient of the k-th sub-production string, dimensionless; Ra is the roughness of the corresponding sub-production string, m; d tn is the inner diameter of the production string, m; is the gas viscosity, Pa•s;

[0067] Accordingly, the calculation formula for calculating the friction pressure drop of each section of the production string according to the gas density, the gas flow rate and the friction coefficient includes:

[0068]

[0069] Where, is the friction pressure drop of the k-th section production string, MPa; is the friction coefficient of the k-th section production string, dimensionless; is the gas density of the k-th section production string, kg / m 3 ; is the gas flow rate of the k-th section production string, m / s; d tn is the inner diameter of the production string, m; H FD is the preset length, m;

[0070] Accordingly, the calculation formula for constructing the pressure iteration model corresponding to each sub-production string according to the segmented pressure, gravity pressure drop, and friction pressure drop includes:

[0071]

[0072] Where, is the pressure of the production string corresponding to the k+1th section, MPa; p k is the segment pressure of the kth segment, Pa; is the friction pressure drop of the k-th section production string, MPa; is the gravity pressure drop of the sub-production string in section k, MPa.

[0073] In one possible design, the determining of the throttling hole area of ​​the downhole throttle when the production string is in a critical leakage state or a non-critical leakage state based on the maximum bottom pressure, the temperature in the production string, and the pressure at the target number includes: determining a gas compression factor based on the maximum bottom pressure and the temperature in the production string; judging whether the throttling process type is a critical leakage state or a non-critical leakage state based on the pressure at the target number and the maximum bottom pressure; if the throttling process type is judged to be a critical leakage state, then determining the throttling hole area of ​​the downhole throttle based on the gas compression factor, the maximum bottom pressure of the wellbore before throttling, and the temperature in the production string; if the throttling process type is judged to be a non-critical leakage state, then determining the throttling hole area of ​​the downhole throttle based on the gas compression factor, the pressure at the target number, the maximum bottom pressure of the wellbore before throttling, and the temperature in the production string.

[0074] In a possible design, the calculation formula for determining the gas compressibility factor based on the maximum bottom pressure and the temperature in the production string includes:

[0075]

[0076] Where Zg is the gas compressibility factor, dimensionless; A1, A2, A3, A4, A5, A6, A7, A8, A9, A 10 — constants, dimensionless, 1.1153, -0.079, 0.01588, 0.00886, -2.1619, 1.1575, -0.05368, 0.014655, -1.80997, 0.9548; p max is the maximum pressure at the bottom, MPa; γ g is the relative density of gas, dimensionless; p r is the quasi-comparison pressure, dimensionless, and serves as an intermediate quantity for solving the gas compressibility factor; T r is the temperature to be compared, dimensionless, and serves as an intermediate quantity for solving the gas compressibility factor; T fL is the temperature inside the production column, °C;

[0077] Accordingly, the calculation formula for determining whether the throttling process type is a critical leakage state or a non-critical leakage state based on the pressure at the target number and the maximum pressure at the bottom includes:

[0078]

[0079] Where k g is the adiabatic index of the leaked gas, which is 1.66 and dimensionless; p max is the maximum pressure at the bottom; p J the pressure at the target number;

[0080] Accordingly, if the throttling process type is determined to be a critical leakage state, the calculation formula for the throttling hole area of ​​the downhole throttling device based on the gas compressibility factor, the maximum bottom pressure of the wellbore before throttling, and the temperature in the production string includes:

[0081]

[0082] Where A L is the orifice area, m 2 ;Q min is the minimum output rate, m 3 / d;ρ s is the standard density of the gas, kg / m 3 ; C o is the flow coefficient, the throttling hole is a circular hole, the value is 1.0, and it is dimensionless; p max is the maximum pressure at the bottom, MPa; M g is the molar mass of the gas, kg / mol; k g is the adiabatic index of the leaking gas, which is 1.66 and dimensionless; Zg is the gas compressibility factor, which is dimensionless; R is the gas constant, which is 8.3414; T fLis the temperature inside the production column, °C;

[0083] Accordingly, if the throttling process type is determined to be a non-critical leakage state, the calculation formula for the throttling hole area of ​​the downhole throttling device based on the gas compressibility factor, the pressure at the target number, the maximum bottom pressure of the wellbore before throttling, and the temperature in the production string includes:

[0084]

[0085] Where A L is the orifice area, m 2 ;Q min is the minimum output rate, m 3 / d;ρ s is the standard density of the gas, kg / m 3 ; C o is the flow coefficient, the throttling hole is a circular hole, the value is 1.0, and it is dimensionless; p max is the maximum pressure at the bottom, MPa; M g is the molar mass of the gas, kg / mol; k g is the adiabatic index of the leaking gas, which is 1.66 and dimensionless; Zg is the gas compressibility factor, which is dimensionless; R is the gas constant, which is 8.3414; T fL is the temperature inside the production column, °C; p J The pressure at the target number.

[0086] In one possible design, the calculation formula for determining the target number of the sub-production string where the downhole choke is located according to the installation depth includes:

[0087]

[0088] Where, M is the target number of the production string where the downhole choke is located, a dimensionless integer; H J H is the installation depth; FD The preset length.

[0089] The present application provides a method for controlling leakage of production tubing in a wellbore, which obtains the operating parameters of the wellbore; obtains a predetermined installation depth of a downhole choke; calculates the permissible annular pressure of the casing annulus according to the internal pressure resistance of the production casing, the external squeeze resistance of the production tubing, the wellhead pressure, the minimum internal pressure resistance of the production casing, the minimum internal pressure resistance of the technical casing, the minimum external squeeze resistance of the production tubing and the casing head strength; divides the production tubing into sections and numbers them according to a preset length to obtain a multi-section production tubing with numbers; constructs a pressure iteration model corresponding to each section of the production tubing according to the obtained section pressure and section temperature of each section of the production tubing; determines the wellbore according to the installation depth The target number of the sub-production string where the choke is located is determined; the annular allowable pressure is determined as the initial pressure of the first section of the sub-production string; the pressure at the target number is determined based on the initial pressure and the pressure iteration model; the throttling hole area of ​​the downhole choke when the production string is in a critical leakage state or a non-critical leakage state is determined based on the obtained bottom maximum pressure of the wellbore before throttling, the temperature in the production string and the pressure at the target number; the throttling hole diameter of the downhole choke is determined based on the throttling hole area to ensure that the production string is in a critical leakage state or a non-critical leakage state, prevent the production string from leaking, and solve the problem of production string leakage from the root by reducing the annular pressure to within the safety threshold. BRIEF DESCRIPTION OF THE DRAWINGS

[0090] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, a brief introduction will be given below to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0091] Figure 1 A schematic diagram of the structure of a wellbore provided in an embodiment of the present application;

[0092] Figure 2 Schematic diagram of the process of the method for controlling the leakage of the production string in the wellbore provided in the embodiment of the present application Figure 1 ;

[0093] Figure 3 Schematic diagram of the process of the method for controlling the leakage of the production string in the wellbore provided in the embodiment of the present application Figure 2 . DETAILED DESCRIPTION

[0094] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0095] Natural gas has become a viable alternative to high-carbon fossil fuels such as coal. Meanwhile, the scale of underground hydrogen storage, underground compressed air energy storage, and underground carbon dioxide storage is also growing rapidly. In these scenarios, a wellbore is typically used to establish a channel from underground to the surface, with the production string in the wellbore serving as a direct channel for gas injection and extraction. The production string is made up of steel oil pipes and related components, but is susceptible to seal failure and perforation cracking under the combined effects of stress, load, and fluid pressure. In related art, when seal failure and perforation cracking occur in a production string, the failure or crack location must first be identified. Then, chemical plugging agents or mechanical plugging are used to seal the location to complete the repair. However, in related art, the inner wall of the production string often contains dirt or solid deposits. Using chemical plugging agents or mechanical plugging to seal the failure or crack location fails to form an effective seal with the inner wall of the production string, making it impossible to resolve the problem of production string leakage.

[0096] In order to solve the above technical problems, the embodiments of the present application propose the following technical concepts: the inventors take into account the various operating parameters of the wellbore, the installation depth of the downhole choke and the production tubing of each section, determine the allowable annulus pressure based on the various operating parameters, and use the allowable annulus pressure as the initial pressure of the first section of the production tubing, determine the target number of the sub-production tubing based on the installation depth of the downhole choke, determine the pressure at the target number based on the initial pressure, use the measured maximum bottom pressure, the temperature in the production tubing and the pressure at the target number to determine the throttling hole area of ​​the downhole throttling when the production tubing is in a critical leakage state or a non-critical leakage state, and determine the throttling hole diameter of the downhole throttling, so as to solve the problem of production tubing leakage from the root.

[0097] Figure 1 A schematic diagram of the structure of the wellbore provided in an embodiment of the present application.

[0098] like Figure 1 As shown, the structure of the wellbore specifically includes: a wellhead 101, an oil casing annulus 102, annular fluid 103, casing annulus 104, production casing 105, production tubing string 106, technical casing 107, packer 108 and downhole choke 109;

[0099] The oil casing annulus 102 is an annular space formed by the wellhead 101 , the production casing 105 , the production tubing string 106 and the packer 108 .

[0100] The annular space liquid 103 is stored in the oil casing annulus 102 and is used to protect the production casing 105 and the production tubing string 106 .

[0101] The casing annulus 104 is an annular space formed by the wellhead 101 , the production casing 105 and the technical casing 107 .

[0102] The production string 106 is formed by splicing multiple oil pipes and is used to transmit gas.

[0103] The packer 108 is used to fix the production tubing 106 .

[0104] The downhole choke 109 adjusts the gas flow rate through the principles of pressure balance and fluid mechanics.

[0105] Figure 2 Schematic diagram of the process of the method for controlling the leakage of the production string in the wellbore provided in the embodiment of the present application Figure 1 , the execution subject of this embodiment can be a computer device, and this embodiment is not particularly limited here. Figure 2 As shown, the method includes:

[0106] S201: Acquire the operating parameters of the wellbore, wherein the wellbore at least includes a casing annulus, a production tubing, a packer and a downhole choke, wherein the casing annulus is the circular space around the production tubing, and the packer is installed on the production tubing; the operating parameters at least include the internal pressure resistance of the production casing at the packer, the external collapse resistance of the production tubing at the packer, the wellhead pressure after wellbore production, the minimum internal pressure resistance of the production casing, the minimum internal pressure resistance of the technical casing outside the casing annulus, the minimum external collapse resistance of the production tubing, and the casing head strength of the production casing.

[0107] S202: Obtain a predetermined installation depth of a downhole choke, and install the downhole choke on a production string according to the installation depth.

[0108] Specifically, step S202 is as follows: according to the installation depth, the downhole choke is lowered into the production string by using a coiled tubing or a cable for installation.

[0109] S203: Calculate the permissible annular pressure of the casing annulus based on the production casing internal pressure resistance strength, production string external collapse resistance strength, wellhead pressure, minimum production casing internal pressure resistance strength, minimum technical casing internal pressure resistance strength, minimum production string external collapse resistance strength and casing head strength.

[0110] Specifically, step S203 includes:

[0111] S2031: Calculate the maximum allowable annular pressure based on the production casing's internal pressure resistance at the packer.

[0112] In this embodiment, the maximum allowable annular pressure determined by the production casing internal pressure resistance strength at the packer is calculated based on the production casing internal pressure resistance strength, and the calculation formula includes:

[0113]

[0114] Where, p5 is the maximum allowable annular pressure determined by the internal pressure resistance strength of the production casing at the packer; p7 is the internal pressure resistance strength of the production casing, MPa; ρ cs is the cement slurry density, g / cm 3 ρ co is the annular liquid density, g / cm 3 ; g is the acceleration due to gravity, m 2 / s;h p is the depth of the packer, m.

[0115] S2032: Calculate the maximum allowable annular pressure based on the production string's anti-collapse strength and wellhead pressure, which is determined by the production casing's anti-collapse strength at the packer.

[0116] In this embodiment, the maximum allowable annular pressure determined by the production casing collapse resistance at the packer is calculated based on the production string collapse resistance and the wellhead pressure. The calculation formula includes:

[0117]

[0118] Where, p6 is the maximum allowable annular pressure determined by the anti-collapse strength of the production casing at the packer; p8 is the anti-collapse strength of the production string, MPa; p9 is the wellhead pressure, MPa; ρ cs is the cement slurry density, g / cm 3 ρ co is the annular liquid density, g / cm 3 ; g is the acceleration due to gravity, m 2 / s;h p is the depth of the packer, m.

[0119] S2033: Calculate the allowable annulus pressure of the casing annulus based on the minimum internal pressure resistance of the production casing, the minimum internal pressure resistance of the technical casing, the minimum external collapse resistance of the production string, the casing head strength, the maximum allowable annulus pressure determined by the internal pressure resistance of the production casing at the packer, and the maximum allowable annulus pressure determined by the external collapse resistance of the production casing at the packer.

[0120] In this embodiment, the calculation formula for calculating the allowable annular pressure of the casing annulus is based on the minimum internal pressure resistance of the production casing, the minimum internal pressure resistance of the technical casing, the minimum external collapse resistance of the production string, the casing head strength, the maximum allowable annular pressure determined by the internal pressure resistance of the production casing at the packer, and the maximum allowable annular pressure determined by the external collapse resistance of the production casing at the packer. The formula includes:

[0121]

[0122] Where, △p aA is the allowable annulus pressure of the casing annulus, MPa; p1 is the minimum internal pressure resistance of the production casing, MPa; p2 is the minimum internal pressure resistance of the technical casing, MPa; p3 is the minimum external collapse strength of the production string, MPa; p4 is the casing head strength, MPa; p5 is the maximum allowable annulus pressure determined by the internal pressure resistance of the production casing at the packer, MPa; p6 is the maximum allowable annulus pressure determined by the external collapse strength of the production casing at the packer, MPa.

[0123] S204: The production string is segmented and numbered according to a preset length to obtain a multi-segment production string with numbers.

[0124] In this embodiment, the preset length is ≤ 1 / 1000 of the total length of the production string.

[0125] In this embodiment, the multi-stage sub-production strings are sub-production strings of equal length.

[0126] S205: Obtain the segmented pressure and segmented temperature of each segment of the production string.

[0127] S206: Construct a pressure iteration model corresponding to each section of the production string according to the section pressure and section temperature.

[0128] Specifically, step S206 includes:

[0129] S2061: Calculate the gas density of each section of the production string based on the section pressure and section temperature.

[0130] In this embodiment, the calculation formula for calculating the gas density of each sub-production string according to the segment pressure and segment temperature includes:

[0131]

[0132] Where, is the gas density of the kth sub-production string, kg / m 3 ;p k is the segment pressure of the kth segment, Pa; T s is the standard temperature, ℃; p s is the standard pressure, Pa; Tk is the segment temperature of the kth segment, °C; ρ s is the standard density of the gas, kg / m 3 .

[0133] S2062: Calculate the gravity pressure drop of each section of the production string based on the gas density.

[0134] In this embodiment, the calculation formula for calculating the gravity pressure drop of each section of the production string according to the gas density includes:

[0135]

[0136] Where, is the gravity pressure drop of the sub-production string in section k, MPa; H FD is the preset length, m; is the gas density of the k-th section production string, kg / m 3 ; g is the acceleration due to gravity, m 2 / s;H FD is the preset length, m.

[0137] S2063: Calculate the gas flow rate of each section of the production string based on the gas density.

[0138] In this embodiment, the calculation formula for calculating the gas flow rate of each section of the production string according to the gas density includes:

[0139]

[0140] Where, Q is the gas flow rate of the k-th section production string, m / s; min is the minimum output rate, m 3 / d;d tn is the inner diameter of the production string, m; is the gas density of the kth sub-production string, kg / m 3 ρ s is the standard density of the gas, kg / m 3 .

[0141] S2064: Calculate the friction coefficient of each section of the production string based on the gas density and gas flow rate.

[0142] In this embodiment, the friction coefficient of each section of the production string is calculated based on the gas density and gas flow rate, and the calculation formula includes:

[0143]

[0144] Where, is the friction coefficient of the k-th sub-production string, dimensionless; Ra is the roughness of the corresponding sub-production string, m; d tn is the inner diameter of the production string, m; is the gas viscosity, Pa•s.

[0145] S2065: Calculate the friction pressure drop of each section of the production string based on the gas density, gas flow rate and friction coefficient.

[0146] In this embodiment, the friction pressure drop of each section of the production string is calculated based on the gas density, gas flow rate and friction coefficient, and the calculation formula includes:

[0147]

[0148] Where, is the friction pressure drop of the k-th section production string, MPa; is the friction coefficient of the k-th section production string, dimensionless; is the gas density of the k-th section production string, kg / m 3 ; is the gas flow rate of the k-th section production string, m / s; d tn is the inner diameter of the production string, m; H FD is the preset length, m.

[0149] S2066: Construct a pressure iteration model corresponding to each section of the production string based on the segmented pressure, gravity pressure drop, and friction pressure drop.

[0150] In this embodiment, a pressure iteration model corresponding to each sub-section of the production string is constructed based on the segmented pressure, gravity pressure drop, and friction pressure drop. The calculation formula includes:

[0151]

[0152] Where, is the pressure of the production string corresponding to the k+1th section, MPa; p k is the segment pressure of the kth segment, Pa; is the friction pressure drop of the k-th section production string, MPa; is the gravity pressure drop of the sub-production string in section k, MPa.

[0153] S207: Determine the target number of the sub-production string where the downhole choke is located according to the installation depth.

[0154] In this embodiment, the calculation formula for determining the target number of the sub-production string where the downhole choke is located according to the installation depth includes:

[0155]

[0156] Where M is the target number of the production string where the downhole choke is located, a dimensionless integer; H J H is the installation depth; FD The preset length.

[0157] S208: The annular allowable pressure is determined as the initial pressure of the first section production string.

[0158] S209: Determine the pressure at the target number according to the initial pressure and the pressure iteration model.

[0159] S210: Acquire the maximum bottom pressure and the temperature inside the production string before wellbore throttling.

[0160] Specifically, step S210 is as follows: obtaining the maximum pressure at the bottom of the production string and the temperature inside the production string under the minimum production rate condition before wellbore throttling using a thermometer and a pressure gauge or a distributed optical fiber.

[0161] S211: Determine the throttle hole area of ​​the downhole choke when the production string is in a critical leakage state or a non-critical leakage state according to the maximum bottom pressure, the temperature in the production string, and the pressure at the target number.

[0162] Specifically, step S211 includes:

[0163] S2111: Determine the gas compressibility factor based on the maximum bottom pressure and the temperature inside the production tubing string.

[0164] In this embodiment, the calculation formula for determining the gas compressibility factor based on the maximum bottom pressure and the temperature in the production string includes:

[0165]

[0166] Where Zg is the gas compressibility factor, dimensionless; A1, A2, A3, A4, A5, A6, A7, A8, A9, A 10 — constants, dimensionless, 1.1153, -0.079, 0.01588, 0.00886, -2.1619, 1.1575, -0.05368, 0.014655, -1.80997, 0.9548; p max is the maximum pressure at the bottom, MPa; γ g is the relative density of gas, dimensionless; p r is the quasi-comparison pressure, dimensionless, and serves as an intermediate quantity for solving the gas compressibility factor; T r is the temperature to be compared, dimensionless, and serves as an intermediate quantity for solving the gas compressibility factor; T fL is the temperature inside the production column, ℃.

[0167] S2112: Determine whether the throttling process type is a critical leakage state or a non-critical leakage state based on the pressure at the target number and the maximum pressure at the bottom.

[0168] In this embodiment, the calculation formula for determining whether the throttling process type is a critical leakage state or a non-critical leakage state based on the pressure at the target number and the maximum pressure at the bottom includes:

[0169]

[0170] Where k g is the adiabatic index of the leaked gas, which is 1.66 and dimensionless; p max is the maximum pressure at the bottom; p J Pressure at target number.

[0171] S2113: If the throttling process type is determined to be a critical leakage state, the throttling hole area of ​​the downhole throttling device is determined based on the gas compressibility factor, the maximum bottom pressure of the wellbore before throttling, and the temperature in the production string.

[0172] In this embodiment, if the throttling process type is determined to be a critical leakage state, the calculation formula for the throttling hole area of ​​the downhole throttling device based on the gas compressibility factor, the maximum bottom pressure of the wellbore before throttling, and the temperature in the production string includes:

[0173]

[0174] Where A L is the orifice area, m 2 ;Q min is the minimum output rate, m 3 / d;ρ s is the standard density of the gas, kg / m 3 ; C o is the flow coefficient, the throttling hole is a circular hole, the value is 1.0, and it is dimensionless; p max is the maximum pressure at the bottom, MPa; M g is the molar mass of the gas, kg / mol; k g is the adiabatic index of the leaking gas, which is 1.66 and dimensionless; Zg is the gas compressibility factor, which is dimensionless; R is the gas constant, which is 8.3414; T fL is the temperature inside the production column, ℃.

[0175] S2114: If the throttling process type is determined to be a non-critical leakage state, the throttling hole area of ​​the downhole throttling device is determined based on the gas compressibility factor, the pressure at the target number, the maximum bottom pressure of the wellbore before throttling, and the temperature in the production string.

[0176] In this embodiment, if the throttling process type is determined to be a non-critical leakage state, the calculation formula for the throttling hole area of ​​the downhole throttling device is as follows based on the gas compressibility factor, the pressure at the target number, the maximum bottom pressure of the wellbore before throttling, and the temperature in the production string, including:

[0177]

[0178] Where A L is the orifice area, m 2 ;Q min is the minimum output rate, m 3 / d;ρ s is the standard density of the gas, kg / m 3 ; C o is the flow coefficient, the throttling hole is a circular hole, the value is 1.0, and it is dimensionless; p max is the maximum pressure at the bottom, MPa; M g is the molar mass of the gas, kg / mol; k g is the adiabatic index of the leaking gas, which is 1.66 and dimensionless; Zg is the gas compressibility factor, which is dimensionless; R is the gas constant, which is 8.3414; T fL is the temperature inside the production column, °C; p J Pressure at target number.

[0179] S212: Determine the throttle aperture of the downhole throttle according to the throttle aperture area to ensure that the production string is in a critical leakage state or a non-critical leakage state to prevent leakage of the production string.

[0180] In addition, instructions can be sent through optical fiber, cable or wireless transmission to dynamically adjust the throttling aperture of the downhole choke.

[0181] In this embodiment, the throttle aperture of the downhole throttle is determined according to the throttle aperture area, and the calculation formula is:

[0182]

[0183] Where D J is the throttle aperture of the throttle, m; A L is the orifice area, m 2 .

[0184] In summary, the present embodiment provides a method for controlling leakage of production tubing in a wellbore, which obtains the operating parameters of the wellbore; obtains a predetermined installation depth of the downhole throttle; calculates the permissible annular pressure of the casing annulus according to the internal pressure resistance of the production casing, the external squeeze resistance of the production tubing, the wellhead pressure, the minimum internal pressure resistance of the production casing, the minimum internal pressure resistance of the technical casing, the minimum external squeeze resistance of the production tubing and the casing head strength; segments the production tubing according to the preset length to obtain a numbered multi-section production tubing; constructs a pressure iteration model corresponding to each section of the production tubing according to the obtained section pressure and section temperature of each section; determines the location of the downhole throttle according to the installation depth The target number of the sub-production string is determined; the annular space allowable pressure is determined as the initial pressure of the first section of the sub-production string; the pressure at the target number is determined based on the initial pressure and the pressure iteration model; the throttling hole area of ​​the downhole throttle when the production string is in a critical leakage state or a non-critical leakage state is determined based on the obtained bottom maximum pressure before wellbore throttling, the temperature in the production string and the pressure at the target number; the throttling hole diameter of the downhole throttle is determined based on the throttling hole area to ensure that the production string is in a critical leakage state or a non-critical leakage state, prevent the production string from leaking, and solve the problem of production string leakage from the root by reducing the annular space pressure to within the safety threshold. Furthermore, the method is applicable to various complex leakage conditions.

[0185] Figure 3 Schematic diagram of the process of the method for controlling the leakage of the production string in the wellbore provided in the embodiment of the present application Figure 2 In the embodiment of the present application, Figure 2 Based on the embodiment provided, the specific implementation method for determining the installation depth of the downhole choke in step S202 is described in detail. Figure 3 As shown, the method includes:

[0186] S301: Calculating a first initial length of the production string subjected to tension according to the weight of the production string and the weight per unit length of the production string.

[0187] In this embodiment, the calculation formula for calculating the first initial length of the production string subjected to tension based on the weight of the production string and the weight per unit length of the production string includes:

[0188]

[0189] Where H L F is the first initial length of the production string under tension, m; X is the weight of the production string, N; M T is the mass per unit length of the production string, kg / m; g is the acceleration due to gravity, m / s 2 .

[0190] S302: Determine a second initial length of the production string subjected to compression according to the design depth of the packer and the initial length of the production string subjected to tension.

[0191] In this embodiment, the calculation formula for determining the second initial length of the production string subjected to compression is determined based on the design depth of the packer and the initial length of the production string subjected to tension, including:

[0192]

[0193] Where H Y H is the second initial length of the production string under compression, m; FS is the design depth of the packer, m; H L The first initial length of the production string under tension, m.

[0194] S303: Calculating the stretched length of the production string according to the weight per unit length of the production string, the first initial length, and the cross-sectional area of ​​the production string.

[0195] In this embodiment, the calculation formula for calculating the stretched length of the production string based on the weight per unit length of the production string, the first initial length, and the cross-sectional area of ​​the production string includes:

[0196]

[0197] Where, △H L is the tensile length of the production string, m; E is the elastic modulus of the production string, Pa; A is the cross-sectional area of ​​the production string; H L The first initial length of the production string under tension, m.

[0198] S304: Calculate the compressed length of the production string according to the weight per unit length of the production string, the second initial length, and the cross-sectional area of ​​the production string.

[0199] In this embodiment, the calculation formula for calculating the compressed length of the production string based on the weight per unit length of the production string, the second initial length, and the cross-sectional area of ​​the production string includes:

[0200]

[0201] Where, △H Y is the compressed length of the production string, m; E is the elastic modulus of the production string, Pa; A is the cross-sectional area of ​​the production string; H Y The second initial length of the production string under compression, m.

[0202] S305: Calculate the thermal expansion and elongation of any oil pipe according to the ground surface temperature, the initial length of the single oil pipe, the ground temperature gradient, and the initial temperature of the single oil pipe.

[0203] In this embodiment, the thermal expansion and elongation of any oil pipe is calculated based on the ground surface temperature, the initial length of a single oil pipe, the ground temperature gradient, and the initial temperature of the single oil pipe. The calculation formula includes:

[0204]

[0205] Where, △H T i is the thermal expansion of the i-th oil pipe, m; T0 is the surface temperature, °C; g e is the geothermal gradient, ℃ / m; i is the number of the oil pipe in the wellbore, which is numbered 1, 2, ..., N from the wellhead to the bottom of the well; H T is the initial length of a single oil pipe, m; T T is the initial temperature of a single oil pipe, °C; α is the thermal expansion coefficient of the oil pipe, °C -1 .

[0206] S306: Determine the total thermal expansion and elongation of the production string according to the thermal expansion and elongation corresponding to each oil pipe.

[0207] In this embodiment, the calculation formula for determining the total thermal expansion and elongation of the production string according to the thermal expansion and elongation corresponding to each oil pipe includes:

[0208]

[0209] Where, △H TZ is the total thermal expansion and elongation of the production string above the packer, m; △H T i is the thermal expansion elongation of the i-th oil pipe.

[0210] S307: Determine the actual depth of the packer according to the design depth, stretched length, compressed length and total thermal expansion and elongation of the packer.

[0211] In this embodiment, the actual depth of the packer is determined based on the design depth, tensile length, compression length, and total thermal expansion of the packer. The calculation formula includes:

[0212]

[0213] Where H F is the actual depth of the packer, m; H FS is the design depth of the packer, m; △H L is the stretched length of the production string, m; △H Y is the compressed length of the production string, m; △H TZis the total thermal expansion and elongation of the production string above the packer, m.

[0214] S308: Determine the installation depth of the downhole choke according to the actual depth of the packer.

[0215] In this embodiment, the calculation formula for determining the installation depth of the downhole choke according to the actual depth of the packer includes:

[0216]

[0217] Where H J H is the installation depth of the downhole choke, m; F is the actual depth of the packer, m; H W H is the installation depth allowance. W >0,m.

[0218] In summary, the present embodiment provides a method for controlling leakage of a production string in a wellbore, which calculates the first initial length of the production string subjected to tension according to the weight of the production string and the weight per unit length of the production string; determines the second initial length of the production string subjected to compression according to the design depth of the packer and the initial length of the production string subjected to tension; calculates the tensile length of the production string according to the weight per unit length of the production string, the first initial length, and the cross-sectional area of ​​the production string; calculates the compressive length of the production string according to the weight per unit length of the production string, the second initial length, and the cross-sectional area of ​​the production string. The thermal expansion and elongation of any oil pipe are calculated based on the surface temperature, the initial length of a single oil pipe, the geothermal gradient and the initial temperature of a single oil pipe; the total thermal expansion and elongation of the production string is determined based on the thermal expansion and elongation of each oil pipe; the actual depth of the packer is determined based on the design depth, stretched length, compressed length and total thermal expansion and elongation of the packer; the installation depth of the downhole choke is determined based on the actual depth of the packer, laying the foundation for the subsequent determination of the throttling hole area of ​​the downhole choke when the production string is in a critical leakage state or a non-critical leakage state, thereby solving the problem of production string leakage from the root.

[0219] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for controlling leakage of a production string in a wellbore, characterized in that: include: Obtaining operating parameters of a wellbore, wherein the wellbore includes at least a casing annulus, a production tubing string, a packer, and a downhole choke, wherein the casing annulus is the circular space surrounding the production tubing string, and the packer is installed on the production tubing string; the operating parameters include at least the internal pressure resistance of the production casing at the packer, the external collapse resistance of the production tubing string at the packer, the wellhead pressure of the wellbore after production, the minimum internal pressure resistance of the production casing, the minimum internal pressure resistance of the technical casing outside the casing annulus, the minimum external collapse resistance of the production tubing string, and the casing head strength of the production casing; Obtaining a predetermined installation depth of the downhole choke, and installing the downhole choke on the production tubing according to the installation depth; Calculating the permissible annular pressure of the casing annulus according to the production casing internal pressure resistance strength, the production string external collapse resistance strength, the wellhead pressure, the minimum internal pressure resistance strength of the production casing, the minimum internal pressure resistance strength of the technical casing, the minimum external collapse resistance strength of the production string, and the casing head strength; The production string is segmented and numbered according to a preset length to obtain a multi-segment production string with numbers; Obtain the segmented pressure and segmented temperature of each section of the production string; Constructing a pressure iteration model corresponding to each sub-production string according to the segmented pressure and the segmented temperature; Determining the target number of the sub-production string where the downhole choke is located according to the installation depth; Determine the annular space allowable pressure as the initial pressure of the first section production string; Determine the pressure at the target number according to the initial pressure and the pressure iteration model; Obtaining the maximum bottom pressure and the temperature inside the production tubing string before throttling of the wellbore; Determine the throttle hole area of ​​the downhole choke when the production string is in a critical leakage state or a non-critical leakage state according to the maximum bottom pressure, the temperature in the production string, and the pressure at the target number; The throttle aperture of the downhole throttle is determined according to the throttle aperture area to ensure that the production string is in a critical leakage state or a non-critical leakage state, thereby preventing leakage of the production string.

2. The method according to claim 1, characterized in that The downhole choke needs to be installed below the packer, and the production string is spliced ​​from multiple oil pipes. The operating parameters also include the weight of the production string, the weight per unit length of the production string, the design depth of the packer, the surface temperature, the initial length of a single oil pipe, the geothermal gradient, and the initial temperature of the single oil pipe. Accordingly, the process of determining the installation depth of the downhole choke includes: Calculating a first initial length of the production string subjected to tension according to the weight of the production string and the weight per unit length of the production string; Determining a second initial length of the production string subjected to compression according to the design depth of the packer and the initial length of the production string subjected to tension; Calculating the stretched length of the production string according to the weight per unit length of the production string, the first initial length, and the cross-sectional area of ​​the production string; Calculating the compressed length of the production tubing string according to the weight per unit length of the production tubing string, the second initial length, and the cross-sectional area of ​​the production tubing string; Calculating the thermal expansion and elongation of any oil pipe according to the ground surface temperature, the initial length of the single oil pipe, the geothermal gradient, and the initial temperature of the single oil pipe; Determining the total thermal expansion and elongation of the production string according to the thermal expansion and elongation corresponding to each oil pipe; Determining the actual depth of the packer according to the designed depth of the packer, the stretched length, the compressed length and the total thermal expansion and elongation; The installation depth of the downhole choke is determined according to the actual depth of the packer.

3. The method according to claim 2, characterized in that The calculation formula for calculating the first initial length of the production string subjected to tension based on the weight of the production string and the weight per unit length of the production string includes: Where H L F is the first initial length of the production string subjected to tension, m; X is the weight of the production string, N; M T is the mass per unit length of the production string, kg / m; g is the acceleration due to gravity, m / s 2 ; Accordingly, the calculation formula for determining the second initial length of the production string subjected to compression based on the design depth of the packer and the initial length of the production string subjected to tension includes: Where H Y H is the second initial length of the production string subjected to compression, m; FS is the design depth of the packer, m; H L is the first initial length of the production string subjected to tension, m; Accordingly, the calculation formula for calculating the stretched length of the production string based on the weight per unit length of the production string, the first initial length, and the cross-sectional area of ​​the production string includes: Where, △H L is the tensile length of the production string, m; E is the elastic modulus of the production string, Pa; A is the cross-sectional area of ​​the production string; H L is the first initial length of the production string subjected to tension, m; Accordingly, the calculation formula for calculating the compressed length of the production string based on the weight per unit length of the production string, the second initial length, and the cross-sectional area of ​​the production string includes: Where, △H Y is the compressed length of the production string, m; E is the elastic modulus of the production string, Pa; A is the cross-sectional area of ​​the production string; H Y is the second initial length of the production string subjected to compression, m; Accordingly, the calculation formula for calculating the thermal expansion and elongation of any oil pipe based on the ground surface temperature, the initial length of the single oil pipe, the geothermal gradient, and the initial temperature of the single oil pipe includes: Where, △H T i is the thermal expansion of the i-th oil pipe, m; T0 is the surface temperature, °C; g e is the geothermal gradient, ℃ / m; i is the number of the oil pipe in the wellbore, which is numbered 1, 2, ..., N from the wellhead to the bottom of the well; H T is the initial length of the single oil pipe, m; T T is the initial temperature of the single oil pipe, °C; α is the thermal expansion coefficient of the oil pipe, °C -1 ; Accordingly, the calculation formula for determining the total thermal expansion and elongation of the production string based on the thermal expansion and elongation corresponding to each oil pipe includes: Where, △H TZ is the total thermal expansion and elongation of the production string above the packer, m; △H T i is the thermal expansion elongation of the i-th oil pipe; Accordingly, the calculation formula for determining the actual depth of the packer based on the design depth of the packer, the stretched length, the compressed length, and the total thermal expansion and elongation includes: Where H F is the actual depth of the packer, m; H FS is the design depth of the packer, m; △H L is the stretched length of the production string, m; ΔH Y is the compressed length of the production string, m; ΔH TZ is the total thermal expansion and elongation of the production string above the packer, m; Accordingly, the calculation formula for determining the installation depth of the downhole choke according to the actual depth of the packer includes: Where H J H is the installation depth of the downhole choke, m; F is the actual depth of the packer, m; H W H is the installation depth allowance. W >0,m.

4. The method according to claim 1, wherein The calculation of the permissible annular pressure of the casing annulus according to the production casing internal pressure resistance strength, the production string external collapse resistance strength, the wellhead pressure, the minimum internal pressure resistance strength of the production casing, the minimum internal pressure resistance strength of the technical casing, the minimum external collapse resistance strength of the production string, and the casing head strength includes: Calculating the maximum permissible annular pressure determined by the production casing internal pressure resistance strength at the packer according to the production casing internal pressure resistance strength; Calculate the maximum permissible annular pressure determined by the anti-collapse strength of the production casing at the packer according to the anti-collapse strength of the production string and the wellhead pressure; The annular allowable pressure of the casing annulus is calculated based on the minimum internal pressure resistance of the production casing, the minimum internal pressure resistance of the technical casing, the minimum external collapse resistance of the production tubing, the casing head strength, the maximum annular allowable pressure determined by the internal pressure resistance of the production casing at the packer, and the maximum annular allowable pressure determined by the external collapse resistance of the production casing at the packer.

5. The method according to claim 4, characterized in that The calculation formula for the maximum allowable annular pressure determined by the production casing internal pressure resistance strength at the packer according to the production casing internal pressure resistance strength includes: Where, p5 is the maximum allowable annular pressure determined by the internal pressure resistance strength of the production casing at the packer; p7 is the internal pressure resistance strength of the production casing, MPa; ρ cs is the cement slurry density, g / cm 3 ρ co is the annular liquid density, g / cm 3 ; g is the acceleration due to gravity, m 2 / s;h p is the depth of the packer, m; Accordingly, the calculation formula for the maximum allowable annulus pressure determined by the production casing collapse strength at the packer according to the production string collapse strength and the wellhead pressure includes: Where, p6 is the maximum permissible annular pressure determined by the anti-collapse strength of the production casing at the packer; p8 is the anti-collapse strength of the production string, MPa; p9 is the wellhead pressure, MPa; ρ cs is the cement slurry density, g / cm 3 ρ co is the annular liquid density, g / cm 3 ; g is the acceleration due to gravity, m 2 / s;h p is the depth of the packer, m; Accordingly, the calculation formula for calculating the allowable annular pressure of the casing annulus based on the minimum internal pressure resistance of the production casing, the minimum internal pressure resistance of the technical casing, the minimum external collapse resistance of the production string, the casing head strength, the maximum allowable annular pressure determined by the internal pressure resistance of the production casing at the packer, and the maximum allowable annular pressure determined by the external collapse resistance of the production casing at the packer includes: Where, △p aA is the allowable annulus pressure of the casing annulus, MPa; p1 is the minimum internal pressure resistance of the production casing, MPa; p2 is the minimum internal pressure resistance of the technical casing, MPa; p3 is the minimum external collapse strength of the production string, MPa; p4 is the casing head strength, MPa; p5 is the maximum allowable annulus pressure determined by the internal pressure resistance of the production casing at the packer, MPa; p6 is the maximum allowable annulus pressure determined by the external collapse strength of the production casing at the packer, MPa.

6. The method according to claim 1, characterized in that The step of constructing a pressure iteration model corresponding to each sub-production string according to the segmented pressure and the segmented temperature includes: Calculating the gas density of each production string according to the segment pressure and the segment temperature; Calculating the gravity pressure drop of each section of the production string according to the gas density; Calculating the gas flow rate of each section of the production string according to the gas density; Calculating the friction coefficient of each section of the production string according to the gas density and the gas flow rate; Calculating the friction pressure drop of each section of the production string according to the gas density, the gas flow rate and the friction coefficient; A pressure iteration model corresponding to each section of the production string is constructed according to the section pressure, gravity pressure drop and friction pressure drop.

7. The method according to claim 6, characterized in that The calculation formula for calculating the gas density of each sub-production string according to the segment pressure and the segment temperature includes: Where, is the gas density of the kth sub-production string, kg / m 3 ;p k is the segment pressure of the kth segment, Pa; T s is the standard temperature, ℃; p s is the standard pressure, Pa; T k is the segment temperature of the kth segment, °C; ρ s is the standard density of the gas, kg / m 3 ; Accordingly, the calculation formula for calculating the gravity pressure drop of each section of the production string according to the gas density includes: Where, is the gravity pressure drop of the sub-production string in section k, MPa; H FD is the preset length, m; is the gas density of the k-th section production string, kg / m 3 ; g is the acceleration due to gravity, m 2 / s;H FD is the preset length, m; Accordingly, the calculation formula for calculating the gas flow rate of each section of the production string according to the gas density includes: Where, Q is the gas flow rate of the k-th section production string, m / s; min is the minimum output rate, m 3 / d;d tn is the inner diameter of the production string, m; is the gas density of the kth sub-production string, kg / m 3 ρ s is the standard density of the gas, kg / m 3 ; Accordingly, the calculation formula for calculating the friction coefficient of each section of the production string based on the gas density and the gas flow rate includes: Where, is the friction coefficient of the k-th sub-production string, dimensionless; Ra is the roughness of the corresponding sub-production string, m; d tn is the inner diameter of the production string, m; is the gas viscosity, Pa•s; Accordingly, the calculation formula for calculating the friction pressure drop of each section of the production string based on the gas density, the gas flow rate and the friction coefficient includes: Where, is the friction pressure drop of the k-th section production string, MPa; is the friction coefficient of the k-th section production string, dimensionless; is the gas density of the k-th section production string, kg / m 3 ; is the gas flow rate of the k-th section production string, m / s; d tn is the inner diameter of the production string, m; H FD is the preset length, m; Accordingly, the calculation formula for constructing the pressure iteration model corresponding to each sub-production string according to the segmented pressure, gravity pressure drop, and friction pressure drop includes: Where, is the pressure of the production string corresponding to the k+1th section, MPa; p k is the segment pressure of the kth segment, Pa; is the friction pressure drop of the k-th section production string, MPa; is the gravity pressure drop of the sub-production string in section k, MPa.

8. The method according to claim 1, characterized in that The determining, based on the maximum bottom pressure, the temperature in the production string, and the pressure at the target number, of the throttle hole area of ​​the downhole choke when the production string is in a critical leakage state or a non-critical leakage state includes: determining a gas compressibility factor according to the maximum bottom pressure and the temperature in the production tubing string; Determining whether the throttling process type is a critical leakage state or a non-critical leakage state according to the pressure at the target number and the maximum pressure at the bottom; If the throttling process type is determined to be a critical leakage state, the throttling hole area of ​​the downhole throttling device is determined based on the gas compressibility factor, the maximum bottom pressure of the wellbore before throttling, and the temperature in the production string; If the throttling process type is determined to be a non-critical leakage state, the throttling hole area of ​​the downhole throttling device is determined based on the gas compressibility factor, the pressure at the target number, the maximum bottom pressure of the wellbore before throttling, and the temperature in the production string.

9. The method according to claim 8, characterized in that The calculation formula for determining the gas compressibility factor based on the maximum bottom pressure and the temperature in the production tubing string includes: Where Zg is the gas compressibility factor, dimensionless; A1, A2, A3, A4, A5, A6, A7, A8, A9, A 10 — constants, dimensionless, 1.1153, -0.079, 0.01588, 0.00886, -2.1619, 1.1575, -0.05368, 0.014655, -1.80997, 0.9548; p max is the maximum pressure at the bottom, MPa; γ g is the relative density of gas, dimensionless; p r is the quasi-comparison pressure, dimensionless, and serves as an intermediate quantity for solving the gas compressibility factor; T r is the temperature to be compared, dimensionless, and serves as an intermediate quantity for solving the gas compressibility factor; T fL is the temperature inside the production column, °C; Accordingly, the calculation formula for determining whether the throttling process type is a critical leakage state or a non-critical leakage state based on the pressure at the target number and the maximum pressure at the bottom includes: Where k g is the adiabatic index of the leaked gas, which is 1.66 and dimensionless; p max is the maximum pressure at the bottom; p J the pressure at the target number; Accordingly, if the throttling process type is determined to be a critical leakage state, the calculation formula for the throttling hole area of ​​the downhole throttling device based on the gas compressibility factor, the maximum bottom pressure of the wellbore before throttling, and the temperature in the production string includes: Where A L is the orifice area, m 2 ;Q min is the minimum output rate, m 3 / d;ρ s is the standard density of the gas, kg / m 3 ; C o is the flow coefficient, the throttling hole is a circular hole, the value is 1.0, and it is dimensionless; p max is the maximum pressure at the bottom, MPa; M g is the molar mass of the gas, kg / mol; k g is the adiabatic index of the leaking gas, which is 1.66 and dimensionless; Zg is the gas compressibility factor, which is dimensionless; R is the gas constant, which is 8.3414; T fL is the temperature inside the production column, °C; Accordingly, if the throttling process type is determined to be a non-critical leakage state, the calculation formula for the throttling hole area of ​​the downhole throttling device based on the gas compressibility factor, the pressure at the target number, the maximum bottom pressure of the wellbore before throttling, and the temperature in the production string includes: Where A L is the orifice area, m 2 ;Q min is the minimum output rate, m 3 / d;ρ s is the standard density of the gas, kg / m 3 ; C o is the flow coefficient, the throttling hole is a circular hole, the value is 1.0, and it is dimensionless; p max is the maximum pressure at the bottom, MPa; M g is the molar mass of the gas, kg / mol; k g is the adiabatic index of the leaking gas, which is 1.66 and dimensionless; Zg is the gas compressibility factor, which is dimensionless; R is the gas constant, which is 8.3414; T fL is the temperature inside the production column, °C; p J The pressure at the target number.

10. The method according to any one of claims 1 to 9, characterized in that The calculation formula for determining the target number of the sub-production string where the downhole choke is located according to the installation depth includes: Where, M is the target number of the production string where the downhole choke is located, a dimensionless integer; H J H is the installation depth; FD The preset length.

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