A method, system, device and storage medium for determining a triaxial safety factor of a tubular string based on air tight integrity

Abstract

The application discloses a kind of based on gas seal integrity pipe string design triaxial safety factor determination method, system, equipment and storage medium, belong to petroleum and natural gas development technical field.First, the failure form and failure mechanism of downhole pipe string are counted and analyzed, and a safety factor evaluation method is established;Based on the safety factor evaluation method, the envelope load spectrum is established based on the measured material and geometric size parameters of the pipe body, and the applicable range and dangerous load point of the envelope load spectrum are determined according to the structure and sealing integrity;Then, the production process cycle of the pipe string is analyzed, and the safety factor is revised and determined.This method can solve the problem that the existing pipe string design triaxial safety factor determination does not consider the whole life cycle and downhole pipe string failure form in actual production process, is not targeted and cannot guarantee the safe and reliable use of downhole, and the cost is high, and can be widely applied to the triaxial design and checking safety determination of casing and tubing string for high temperature and high pressure gas well, unconventional multi-section high internal pressure fracturing gas well.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas development technology, and relates to a method, system, equipment and storage medium for determining the triaxial safety factor of tubing string design based on gas seal integrity. Specifically, it relates to a method for determining the triaxial safety factor of well completion tubing and casing string design based on the sealing integrity of special threaded connections with gas seals. Background Technology

[0002] There is still no reliable standard for determining the triaxial safety factor of casing and tubing strings for well completion and production in oil and gas field exploration and development, including high-temperature and high-pressure gas wells, unconventional shale gas wells, and underground gas storage facilities. The main problems with existing methods for determining the triaxial safety factor in tubing string design are: 1) Engineering experience statistical methods for determining the triaxial safety factor: These methods lack scientific classification of specific influencing factors and quantification of their weights, leading to significant safety hazards in downhole applications. 2) Reliability design methods for determining the triaxial safety factor: These methods only consider the maximum internal pressure the tubing string can withstand based on pipe strength analysis, without considering leakage due to differences in sealing between different threaded connection types within the tubing string, or the safety factor throughout the entire life cycle of the tubing string design, i.e., the safety factor for the entire process of well completion pressure testing, fracturing, and gas production. 3) Current standards and specifications for determining the triaxial safety factor: First, they only consider strength performance, not sealing integrity; second, the experience summary is based on differences in product quality from different manufacturers, which can lead to excessively large safety factors, resulting in increased costs or difficulty in selecting suitable tubing materials. These methods for determining the triaxial safety factor are not specific and cannot reasonably determine the triaxial safety factor for the tubing string design. Therefore, they cannot guarantee the safe and reliable use of the downhole tubing string and also result in high tubing string costs. Summary of the Invention

[0003] In order to overcome the shortcomings of the prior art, the present invention aims to provide a method, system, device and storage medium for determining the triaxial safety factor of tubing design based on the integrity of the gas seal, so as to reasonably determine the triaxial safety factor of tubing design.

[0004] To achieve the above objectives, the present invention employs the following technical solution:

[0005] This invention discloses a method for determining the triaxial safety factor of a tubular design based on gas seal integrity, the specific steps of which are as follows:

[0006] 1) Statistically analyze the failure modes and mechanisms of downhole tubing and establish a safety factor evaluation method;

[0007] 2) Establish the envelope load spectrum based on the safety factor evaluation method, measured material and geometric parameters of the pipe body;

[0008] 3) Determine the applicable range and critical load points of the envelope load spectrum based on the structural and sealing integrity;

[0009] 4) Analyze the critical load points based on the cycle integrity variation law of the whole life production process, revise the applicable range of envelope load, and determine the triaxial safety factor.

[0010] Preferably, in step 1), the safety factor evaluation method is as follows: the load that makes the pipe body reach its ultimate bearing capacity is applied to the connecting thread, and the ratio of the thread performance index to the pipe body performance is checked.

[0011] The performance of the tube body includes tensile efficiency, compression efficiency, external pressure efficiency, and internal pressure efficiency.

[0012] More preferably, when the percentages are all 100%, it means that the thread performance is equal to the pipe performance; when the percentages are less than 100%, it means that the thread performance is lower than the pipe performance.

[0013] Preferably, in step 2), the method for establishing the envelope load spectrum is as follows:

[0014] a) Determine the maximum average outer diameter, minimum average wall thickness, and minimum wall thickness point of the pipe body; measure the yield strength of the pipe body and coupling materials according to the test temperature.

[0015] b) Calculate the stress in the tube under axial load tension / compression, external pressure / internal pressure, and bending using elasticity mechanics formulas;

[0016] c) Under load, establish safety factor evaluation envelopes by combining the percentage of pipe stress and measured material yield strength.

[0017] More preferably, in step b), the elasticity formula is:

[0018]

[0019]

[0020]

[0021] d wall =D avg -2t min (Equation 4)

[0022]

[0023] Among them, D avg t represents the measured maximum average outer diameter of the pipe body. min p is the measured minimum wall thickness of the pipe body; OAPI p is the nominal extrusion strength of the pipe body; oavgThe extrusion strength calculated based on the measured geometric dimensions and material yield strength of the pipe body; p i The internal pressure value is determined based on the envelope load; σ VME For von Mises composite stress; σ r For radial stress of the tube body; σ h σ is the circumferential stress of the tube body. a d represents the axial stress of the tube body. wall p is the actual inner diameter of the pipe body. o The external pressure load is used to evaluate the pipe body; r is the radius.

[0024] Preferably, the specific steps of step 3) are as follows: using finite element analysis to determine the sealing energy of each load point under multiple cycles of different ambient temperatures and load envelopes, and based on the sealing energy variation law of the envelope load points, determining the applicable range of the envelope load spectrum and the dangerous load points;

[0025] Among them, the critical load point is the load point with the minimum sealing energy multiple.

[0026] Preferably, after step 4), the process further includes an applicability verification analysis of the determined triaxial safety factor.

[0027] This invention also discloses a triaxial safety factor determination system for tubular design based on gas seal integrity, comprising:

[0028] The statistical analysis module is used to statistically analyze the failure modes and mechanisms of downhole tubing strings and to establish a safety factor evaluation method.

[0029] The envelope load spectrum establishment module is used to establish the envelope load spectrum, the applicable range of the envelope load spectrum, and the critical load points;

[0030] The triaxial safety factor determination module is used to analyze the critical load points by combining the cycle integrity variation law of the whole life production process, revise the applicable range of envelope load, and obtain the triaxial safety factor.

[0031] The present invention also discloses a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the steps of the above-described method for determining the triaxial safety factor of a tubular design based on gastight integrity.

[0032] The present invention also discloses a computer-readable storage medium storing a computer program, which, when executed by a processor, implements the steps of the above-described method for determining the triaxial safety factor of a tubular design based on gastight integrity.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] This invention provides a method for determining the triaxial safety factor of tubing string design based on gas seal integrity. It takes into account actual downhole conditions, fully considers downhole failure modes and mechanisms, and the scientific and reasonable analysis makes the established safety factor evaluation method more reliable. By establishing an envelope load spectrum through the safety factor evaluation method, measured tubing material, and geometric parameters, this quantitative research method for safety factors makes the obtained envelope load spectrum more scientific and accurate. Based on structural and seal integrity criteria, the applicable range and critical load points of the envelope load spectrum are determined, fully considering the worst-case seal and structural integrity. Specifically, it considers the different integrity variation patterns of different threaded connection forms of the casing and tubing, deriving the integrity variation pattern of the envelope load spectrum, thereby determining the applicable range and critical load points of the envelope load, ensuring that the determined triaxial safety factor has sufficient safety margin. Combining the integrity variation pattern throughout the entire production life cycle, the applicable range of the envelope load is revised, and the triaxial safety factor is then determined. This fully considers the impact of integrity changes on safety throughout the entire production life cycle, thus ensuring the safe use of the completion tubing string during production. This method determines the triaxial safety factor of the tubing string based on its failure modes and the entire life cycle during production. It is direct, reasonable, economical, and effective, ensuring the reliability of the determined triaxial safety factor and guaranteeing the safety of the tubing string throughout its production life. Simultaneously, it reduces tubing string costs, addressing the problem that current experience, standards, or specifications for determining triaxial safety factors are based solely on engineering experience and lack specificity, leading to unreasonable triaxial safety factors and high costs. This method can be widely applied to high-temperature, high-pressure gas wells and unconventional multi-stage high internal pressure fracturing gas wells, and is particularly suitable for determining the safety of triaxial design verification of casing and tubing strings used in deep and ultra-deep well completions.

[0035] Furthermore, the thread performance is tested for consistency with the pipe body according to the ultimate yield load of the pipe body. Tensile efficiency, compression efficiency, external pressure efficiency and internal pressure efficiency are used as performance indicators to form four quadrants of the envelope, thereby determining whether the downhole working condition load is within the envelope and how much margin is available.

[0036] Furthermore, finite element modeling is used to model the specific thread geometry, considering the worst-case sealing and structural integrity limit tolerances. The integrity variation law of the threaded connection under different envelope load spectra is analyzed according to the minimum torque value lower limit specified in the product specifications. Based on the structural and sealing integrity criteria, the applicable envelope load range is analyzed and determined. This can overcome the problem that the existing technical specifications do not consider the different threaded connection types of oil casing pipes, which have different integrity variation laws, and the use of a uniform safety factor cannot guarantee that the proposed pipe string has sufficient safety margin. Attached Figure Description

[0037] Figure 1This is a diagram illustrating the method for establishing the triaxial safety factor in the tubular design of the present invention.

[0038] Figure 2 This is a statistical diagram of downhole annular abnormal pressure failure modes according to an embodiment of the present invention;

[0039] Figure 3 This is a diagram showing localized corrosion caused by a downhole sealing leak in an embodiment of the present invention; wherein, A is a topographical diagram of the sealing surface, a is a localized corrosion pit on the sealing surface, B is a topographical diagram of the internal and external threads being threaded, and b is the position of the sealing surface after the internal and external threads are threaded.

[0040] Figure 4 This is a diagram showing the 70-90% envelope of the completion tubing in an embodiment of the present invention.

[0041] Figure 5 This is a graph showing the reduction in sealing after two cycles of high-temperature (180°C) envelope load on the threaded connection of the well completion tubing according to an embodiment of the present invention.

[0042] Figure 6 This is a graph showing the sealing multiple of the second cycle of high-temperature (180°C) envelope load on the threaded connection of the well completion tubing in an embodiment of the present invention;

[0043] Figure 7 The diagram shows the equivalent plastic strain of the sealing surface of the well completion tubing thread connection in an embodiment of the present invention; where (a) is the upper thread and (b) is the 15e load point;

[0044] Figure 8 The results of the high-temperature 180℃ environmental stress relaxation test and the fitting equation graph of the well completion tubing material in this embodiment of the invention are shown.

[0045] Figure 9 This is a graph showing the variation of the sealing performance of the threaded connection of the well completion tubing at a high temperature of 15°C with the holding time, according to an embodiment of the present invention.

[0046] Figure 10 This is a diagram illustrating the sealing performance verification of the well completion tubing thread under high temperature and high pressure conditions in an embodiment of the present invention. Detailed Implementation

[0047] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0048] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0049] The present invention will now be described in further detail with reference to the accompanying drawings:

[0050] like Figure 1 The present invention provides a method for determining the triaxial safety factor of a tubular design based on the integrity of the gas seal, the steps of which are as follows:

[0051] 1. Statistical analysis of failure modes and mechanisms of downhole tubing strings.

[0052] 1) Statistical analysis of downhole tubing failure modes

[0053] By investigating downhole tubing accidents, downhole logging instruments were used to determine the failure mode of the tubing string. Since the threaded connection is the joint connecting the tubing or casing and is also the weakest point in the tubing string, the threaded connection is a key factor causing leakage or breakage during downhole use. For example, a pressurized annulus accident in the wellbore indicates a possible leakage accident in the downhole tubing string. Logging with a downhole leak detector revealed multiple leaks at the tubing-casing threaded connection, confirming the failure mode as threaded joint leakage.

[0054] 2) Analyze and statistically analyze the failure mechanism of downhole tubing strings.

[0055] By analyzing the failure mechanism, the causes of failure can be identified, thereby establishing a targeted safety factor evaluation method.

[0056] Failure Mechanism Analysis: (1) Analyze the possible causes of failure based on the failure mode; (2) Analyze each possible cause of failure one by one, and use the elimination method to determine the main cause of the final failure. Under the condition that the thread is properly threaded, the performance indicators of the product meet the requirements and there are no quality problems, the main cause of failure is that the temperature and pressure of the well working conditions change with the production and development, which causes the stress on the tubing to change. The triaxial design safety factor is not reasonably determined based on the integrity of the thread seal, that is, there is not enough safety margin, which leads to the failure of the thread seal.

[0057] 2. Establish a safety factor evaluation method

[0058] By analyzing failure modes and underlying failure mechanisms, the causes of failure can be identified, and a targeted safety factor evaluation method can be established.

[0059] Because the thread is the joint connecting the tubing or casing, and is also the weakest link in the tubing string, it is a key factor causing leakage or breakage during downhole use (if the threaded connection were eliminated and only the tubing body was used for production, the influence of the thread could be eliminated, but this is not possible in actual production, so the threaded connection must be used for easy transportation and field use). Therefore, it is expected that the performance of the tubing and casing threaded connection is consistent with that of the tubing body.

[0060] Based on the ultimate bearing capacity of the tubing, a safety factor evaluation is conducted on the casing and tubing threaded connections of the completion string, as well as the tubing itself. The safety factor evaluation method is as follows: a load that would bring the tubing to its ultimate bearing capacity is applied to the connecting threads. By examining the ratio of the thread performance index to the tubing performance, it is determined whether the thread leaks or breaks under the load. If no failure occurs, the threaded connection performance is consistent with and equal to that of the tubing, indicating that an ideal unthreaded tubing is used downhole. Only the tubing bearing capacity needs to be selected to meet the downhole load. If failure occurs, it indicates that the threaded connection performance is lower than that of the tubing. The operating conditions for the use of the tubing safety factor should be determined according to the weak point of the threaded connection performance, or a new threaded joint should be selected to meet the safety factor requirements for the tubing used under downhole operating conditions.

[0061] The performance indicators include tensile efficiency, compression efficiency, external pressure efficiency, and internal pressure efficiency; all efficiencies must be 100% to be equal to the pipe body performance, and the remaining percentages represent threaded connection performance indicators that are lower than pipe body performance.

[0062] 3. Establish an envelope load spectrum, and determine the applicable range and critical load points of the envelope load spectrum based on the structural and sealing integrity.

[0063] a) Determine the maximum average outer diameter, minimum average wall thickness, and minimum wall thickness point of the measured pipe body of the test specimen; measure the material yield strength of the pipe body and couplings according to the test temperature;

[0064] b) Calculate the stress in the pipe body under axial load tension / compression, external pressure / internal pressure, and bending using the elasticity mechanics formulas (Equations 1-5); where the elasticity mechanics formulas are as follows:

[0065]

[0066]

[0067]

[0068] d wall =D avg -2t min (Equation 4)

[0069]

[0070] Where: p OAPI Nominal crush strength of the pipe body, MPa; p oavg The calculated extrusion strength (MPa) is the result of the measured geometric dimensions of the pipe body and the yield strength of the material. i : Internal pressure value determined by envelope load, MPa; Davg: Measured maximum average outer diameter of the pipe, mm; t min : Minimum measured wall thickness of the pipe body, mm; σ VME Von Mises composite stress, MPa; σ r Radial stress of the tube body, MPa; σ h Circumferential stress of the tube body, MPa; σ a : Axial stress of the pipe body, MPa; d wall Actual inner diameter of the pipe body, mm; p o External pressure load on the pipe body, MPa; r is the radius.

[0071] c) Under load, σ is calculated using Equation 1, based on the pipe body. VME , using σ VME The percentages of von Mises composite stress and measured material yield strength are used to establish safety factor evaluation envelopes.

[0072] d) Determine the applicable range and critical load points of the envelope load spectrum based on the structure and sealing integrity. Use finite element analysis to analyze the sealing energy of each load point under multiple cycles of different ambient temperatures and load envelopes. Analyze the sealing energy variation law of each load point of the envelope based on the sealing criterion (see example) to determine the applicable envelope range and critical load points, and determine the applicable range and critical load points of the envelope load spectrum.

[0073] The critical load point is the load point with the minimum sealing energy multiple, and it is also the critical leakage point.

[0074] 4. Analyze the production cycle of the tubing string, revise and determine the safety factor.

[0075] Integrity safety assessments were conducted by selecting internal and external pressures corresponding to characteristic points of different tensile and compressive loads, analyzing the integrity variation patterns of critical load points throughout the entire production process based on their service life, revising the applicable envelope load range, and determining the triaxial safety factor for tubing design.

[0076] The service life considerations include the continuous high-temperature environment throughout the gas production process, which causes material stress relaxation and leads to a decrease in thread sealing performance. The specific revision method is as follows: Based on the triaxial design safety factor initially determined by the envelope load sealing performance analysis, the reduction in sealing energy under high-temperature conditions is used for correction. If the sealing energy multiple at the critical load point is less than 1, it indicates that the safety factor VME initially selected based on the envelope is too high, and the VME value needs to be further reduced to correct the assessment of the reduction in sealing performance under long-term high-temperature conditions, thus meeting the sealing integrity requirements Sc / S. D Until it is greater than 1.

[0077] 5. Conduct downhole operating condition applicability verification analysis on the determined safety factor.

[0078] Finite element analysis is used to examine the structure and sealing integrity of the downhole tubing under operating loads. By comparing and analyzing the load range of the safety design factor envelope determined in the above steps, it is possible to determine whether there is sufficient safety margin and long-term safety for downhole use. This overcomes the problem that existing technical standards and documents cannot scientifically quantify specific influencing factors and safety margins in the safety factor.

[0079] Example 1

[0080] (1) Survey and statistical analysis of failure modes of downhole completion string

[0081] The geological conditions of the high-temperature, high-pressure gas reservoir are complex, with a reservoir depth of 7800m, formation pressure of 150MPa, and formation temperature of 180℃. Different blocks using gas-tight special threaded joint tubing and casing have experienced problems with completion string leakage, abnormally high production and technical casing pressures. Annular pressure statistics are shown in […]. Figure 2 Systematic investigation and statistical analysis of abnormal annular pressure revealed that changes in fluid temperature within the completion tubing caused only a small increase in casing pressure, and this effect was short-lived. Once normal production resumed, the pressure increase caused by these temperature changes disappeared automatically. Leaks at the threaded joints of the completion tubing were the true cause of the increased casing pressure. Tubing string problems accounted for 65% of wells, representing a major issue with well integrity. Annular pressure (A) accounted for 65% of wells, making it the most prevalent type of pressure, primarily related to the sealing performance of the tubing threads. Annular pressure problems are common in high-pressure gas wells, and persistent annular pressure is the most frequent manifestation of well integrity issues during the production phase.

[0082] (2) Downhole failure mechanism analysis

[0083] During acidizing and blowout processes in high-temperature, high-pressure gas well tubing, the stress on the tubing changes due to temperature and pressure, leading to thread seal failure. After leakage occurs, CO2 corrosion under high-temperature, high-pressure conditions exacerbates the leakage. Under alternating tensile and compressive loads (production-injection conditions), joints with low compression efficiency are prone to corrosion and leakage. During well workover, corrosion was observed on the sealing surface of the lower tubing gas seal thread (compression efficiency 80%). Figure 3 The tubular design triaxial safety factor was selected based on 80% of VME stress, which is the same as the compression efficiency of the thread performance index. This lack of sufficient safety margin is a key factor leading to leakage, and the safety factor was not selected reasonably.

[0084] (3) Establish a safety factor evaluation method

[0085] The performance of the threaded connection is reflected in its proportion to the overall performance of the pipe body. For example, 100% efficiency means it equals the performance of the pipe body, while 80% efficiency means it is less than the performance of the pipe body (e.g., the pipe body can withstand 100 tons of tensile force and 100 MPa of internal pressure, while the thread can only withstand 80 tons and 80 MPa of internal pressure). Performance indicators include: tensile efficiency, compressive efficiency, external pressure efficiency, and internal pressure efficiency.

[0086] (4) Coefficient Analysis Method

[0087] Based on the safety factor evaluation method, load spectra with different envelopes are established. According to the usage efficiency of the pipe body and the thread, the ultimate load at which the pipe body yields under internal pressure, external pressure, tensile load and compressive load is applied to the threaded connection to analyze the structural and sealing integrity. For example, if the compression efficiency is 100%, the envelope load spectrum is established according to the ultimate compressive yield load of the pipe body.

[0088] The specific steps are as follows: 1) Determine the maximum average outer diameter, minimum average wall thickness, and minimum wall thickness of the tested pipe body; measure the yield strength of the pipe body and coupling materials according to the test temperature, and the results are shown in Table 1; 2) Calculate the pipe body stress under axial load tension / compression, external pressure / internal pressure, and bending using elasticity formulas (Equations 1 to 5); 3) Under load, establish different envelopes based on the percentage of the measured material yield strength of the pipe body's VME composite stress, as shown in Table 1. Figure 4 Where CEEe represents the envelope of the high-temperature threaded joint, and TLEe represents the evaluation load point of the high-temperature threaded joint; tensile efficiency: the ratio of the combined stress (i.e., VME von Mises stress) generated in the pipe body by the combined load (tension + internal pressure) applied to the threaded joint to the yield strength of the pipe material, if both are consistent, is 100% (combined with the envelope load). Figure 4It can be seen that: tensile efficiency refers to the first quadrant: tension + internal pressure, which, if consistent with CEEe100%, equals the tube body; CEEe90% equals 90% of the tube body. Compression efficiency: the ratio of the combined stress (VME von Mises stress) generated in the tube body under the combined load (compression + internal pressure) applied to the threaded joint to the yield strength of the tube material; if both are consistent, it is 100% (considering the envelope load). Figure 4 It can be seen that: Compression efficiency refers to the second quadrant: tension + internal pressure, which, when consistent with CEEe100%, equals the tube body; CEEe90% equals 90% of the tube body. External pressure efficiency: When a combined load (compression / tension + external pressure) is applied to the threaded joint, the ratio of the combined stress (i.e., VME von Mises stress) generated in the tube body to the yield strength of the tube material is 100% when both are consistent (combined with envelope load). Figure 4 It can be seen that: external pressure efficiency refers to the third and fourth quadrants: compression + external pressure / tension + external pressure. If it is consistent with CEEe100%, it equals the pipe body; if CEEe90%, it is 90% of the pipe body. Applying a combined load (tension / compression + internal pressure) to the threaded joint causes the ratio of the combined stress value generated in the pipe body to the yield strength of the pipe material to be 100% (combined with envelope load). Figure 4 It can be seen that: internal pressure efficiency refers to the first and second quadrants: tension + internal pressure / compression + internal pressure. If it is consistent with CEEe100%, it equals the pipe body; CEEe90% equals 90% of the pipe body; and so on for 80% and 70%. Integrity analysis was performed by selecting the internal and external pressures corresponding to different tensile and compressive load characteristic points. Table 1 shows the calculation parameters, and Table 2 shows the calculated values ​​of VME70% for the envelope load points.

[0089]

[0090]

[0091]

[0092] d wall =D avg -2t min (Equation 4)

[0093]

[0094] Where: D avg : Maximum average outer diameter of the pipe body (measured in mm); tavg: Minimum average wall thickness of the pipe body (measured in mm); t min : Minimum measured wall thickness of the pipe body, mm; P OAPI Nominal crush strength of the pipe body, MPa; P oavg The calculated extrusion strength (MPa) is the result of the measured geometric dimensions of the pipe body and the yield strength of the material. i Internal pressure value determined by envelope load, in MPa.

[0095] Table 1. Parameters used for envelope load establishment

[0096]

[0097] Table 2. High Temperature 180℃ Environment VME 70% Test Load Points (TLEe 70%)

[0098] 10e 823 0 12e 823 27 13e 823 53 14e 732 63 15e 341 74 16e 0 68 17e -294 54 18e -588 31 19e -686 21 20e -823 0 21e -823 0 22e -823 -64 23e -589 -74 24e 0 -64 25e 388 -43 26e 787 -5 27e 822 0

[0099] (5) Analyze the patterns of change

[0100] Determining the applicable load envelope of the thread under different temperature environments is a key factor in ensuring the integrity of the seal, and can effectively determine the safety factor of the triaxial design applicable to the thread.

[0101] The reduction in sealing energy (Sc) and the sealing energy ratio (Sc / S) after two cycles of different VME envelope loads under high temperature (180℃) conditions were analyzed. D The variation pattern and method are shown in Equations 5 and 6. Combined with Table 3, determine the applicable range of threaded connections. The reduction in sealing energy is shown in... Figure 5 The change in sealing energy ratio is shown in the figure. Figure 6 .

[0102] S C =∫l l (σω) n (l)dl (Equation 5)

[0103] S D =ADQ m (kp) (Equation 6)

[0104] In the formula: S C —Sealing energy generated by the gas-tight threaded sealing surface (mm.MPa); σ—Contact pressure calculated by finite element method (MPa); w—Ellipticity correction factor for sealing contact pressure; l—Contact length calculated by finite element method (mm); S D —The effective internal pressure of the seal requires sealing energy (mm.MPa); A—Sealing constant MPa.mm.(ml / min)-m; k—Loading rate influence coefficient; p—Sealing gas pressure (MPa); Q—Leakage rate (ml / min); D—Sealing diameter (mm); n—Sealing surface contact pressure weighting coefficient; m—Influence index of gas properties and temperature on leakage;

[0105] Table 3 shows the coefficient values ​​in equations 5 and 6.

[0106] coefficient 27.6 -0.0333 1.18 1.8614 0.7731

[0107] Depend on Figure 5It can be seen that at load point 12e, the sealing energy reduction is the smallest at 70% VME, which is 69%, and the sealing energy multiple is 8.8; the sealing energy reduction at 80% and 90% VME is 80% and 75% respectively, and the sealing energy multiple is 4.4 for both. This indicates that under the conditions of "high tension + low internal pressure", the thread sealing performance is not improved at the envelope load point of ≥80% VME, while the thread sealing performance is significantly improved at the envelope load point of 70% VME. Figure 6 The display shows that the VME 70% envelope sealing energy multiple (S) increases with decreasing tension and increasing internal pressure at load points from 13e to 15e. C / S D The sealing energy multiple of the minimum sealing energy multiple at load point 13e shows an increasing trend, reaching 5.4; while the sealing energy multiples of 80% and 90% VME envelopes show a decreasing trend, reaching 3.4 at load points 14e and 15e. Under the "tension + external pressure" conditions (25e-26e) of 70% VME envelope, the sealing energy multiple increases significantly with decreasing tension and external pressure, reaching a minimum sealing energy multiple of S at load point 25e. C / S D The value is 5.7, corresponding to a minimum sealing energy multiple of 1.1 at VME90% (load point 25e) and 3.2 times at VME80% (load point 25e). In summary, for high-temperature environments, the minimum sealing energy multiple of the material's yield strength VME70% load envelope is greater than 5, and the sealing energy multiple shows a clear monotonically increasing trend as the load decreases (VME70%). This effectively ensures the integrity of the pipe thread seal, meaning the actual triaxial safety factor needs to be greater than 1.43 (i.e., safety factor 100 / 70).

[0108] (6) Production process cycle integrity analysis

[0109] The well completion string production process involves continuous high temperatures. Finite element analysis of a 180°C environment envelope load over two cycles reveals that the point at 90% of the maximum internal pressure load (15°C) has the minimum sealing energy multiple and is a critical leakage point. The maximum equivalent plastic strain of the sealing surface under the limit tolerance thread conditions of the upper thread and the maximum internal pressure load at 15°C is shown in [the figure]. Figure 7 The average plastic strain was 2.26%. The average plastic strain of the sealing surface is a crucial factor affecting sealing performance; therefore, a stress relaxation test was conducted at a high temperature (180℃) with a strain of 3%. The test results and relaxation fitting equation are shown below. Figure 8 The stress relaxation equation fitted based on the 110SS high-temperature stress relaxation test results was analyzed using finite element method to determine the variation of the sealing performance of the gas-tight thread at a high temperature of 180℃ and a load point of 15e over time. Figure 9The sealing performance analysis is shown in Table 4. The sealing performance decreased by 16% within the first 10 hours, and by 22% after one month. The decrease slowed down over time, and decreased by 22.4% after 6 months. At this point, the gas seal thread sealing energy multiple of 2.62 was greater than 1, and it still had sealing performance.

[0110] Table 4. Analysis of sealing performance at load point 15e over time.

[0111]

[0112] (7) Safety factor revision analysis

[0113] To ensure the long-term safe use of high-temperature and high-pressure gas wells, time-effect-based sealing analysis should be added to provide a basis for determining the triaxial design coefficients of the tubing string based on sealing integrity.

[0114] Analysis of the sealing energy multiple under the second cycle of high-temperature (180℃) envelope load shows that the sealing energy multiple at 15e load point with a VME of 70% is 7.44. The sealing energy reduction under long-term high-temperature conditions is 22.4%, at which point the VME of 70% sealing energy multiple at the 15e load point is 5.77. This indicates that using a VME of 70% envelope load can ensure that the sealing energy multiple remains stable at over 5 times under long-term high-temperature conditions.

[0115] (8) Establish the safety factor for the three-axis design

[0116] Based on the variation law of cyclic sealing energy under different envelope loads and the reduction of sealing performance due to stress relaxation of materials during long-term high-temperature production, it can be seen that using VME 70% envelope load, i.e., triaxial design factor (100 / 70 = 1.43), in high-temperature environments can ensure the structural and sealing integrity of the tubing string.

[0117] (9) Applicability verification analysis for downhole working conditions

[0118] The finite element analysis load points are shown in Table 5. The sealing performance analysis of the upper 16 load points is shown in Table 5. Figure 10 Calculation of sealing energy S at characteristic points under operating load conditions. C The sealing energy S required for effective internal / external pressure sealing. D More than 8 times. On-site tracking of the well completion tubing string showed that after acid fracturing and gas production, the daily natural gas production was 688,000 cubic meters and the oil pressure was 37.3 MPa for one year. The wellhead pressure of the A annulus was 0, indicating that the triaxial design coefficient of the tubing string determined according to the threaded joint of the weak link has good sealing integrity at high temperature (≥1.43).

[0119] Table 5 Load Conditions for Completion Tubing String

[0120]

[0121] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A method for determining the triaxial safety factor in tubular design based on gas seal integrity, characterized in that, The specific steps are as follows: 1) Statistically analyze the failure modes and mechanisms of downhole tubing and establish a safety factor evaluation method; 2) Establish the envelope load spectrum based on the safety factor evaluation method, measured material and geometric parameters of the pipe body; 3) Determine the applicable range of the envelope load spectrum and the critical load points based on the structural and sealing integrity; 4) Analyze the critical load points based on the cyclic integrity variation law of the whole life production process, revise the applicable range of envelope load, and determine the triaxial safety factor; In step 1), the safety factor evaluation method is as follows: A load that causes the pipe body to reach its ultimate bearing capacity is applied to the connecting thread, and the ratio of the thread performance index to the pipe body performance is examined; the pipe body performance includes tensile efficiency, compressive efficiency, external pressure efficiency, and internal pressure efficiency; in step 2), the method for establishing the envelope load spectrum is as follows: a) Determine the maximum average outer diameter, minimum average wall thickness, and minimum wall thickness of the pipe body; measure the yield strength of the pipe body and coupling materials according to the test temperature. b) Calculate the stress in the pipe body under axial tensile / compressive, external / internal pressure, and bending loads using the elasticity mechanics formula; the elasticity mechanics formula is: (Equation 1) (Equation 2) (Equation 3) (Equation 4) (Equation 5) in, D avg This represents the measured maximum average outer diameter of the pipe body. t min This represents the minimum measured wall thickness of the pipe body. This refers to the nominal extrusion strength of the pipe body; p oavg The extrusion resistance strength is calculated based on the measured geometric dimensions of the pipe body and the yield strength of the material. The internal pressure value is determined based on the envelope load; This is the von Mises composite stress; This refers to the radial stress of the tube body; This refers to the circumferential stress of the pipe body; This refers to the axial stress of the pipe body; wall This is the actual inner diameter of the pipe. p o To evaluate the external pressure load on the pipe body; r The radius is ; c) Under load, establish safety factor evaluation envelopes by combining the percentage of pipe stress and measured material yield strength.

2. The method for determining the triaxial safety factor of a tubular design based on gas seal integrity as described in claim 1, characterized in that, When the percentages are all 100%, it means that the thread performance is equal to the pipe performance; when the percentages are less than 100%, it means that the thread performance is lower than the pipe performance.

3. The method for determining the triaxial safety factor of a tubular design based on gas seal integrity as described in claim 1, characterized in that, The specific steps of step 3) are as follows: use finite element analysis to determine the sealing energy of each load point under multiple cycles of different ambient temperatures and load envelopes, and determine the applicable range and dangerous load points of the envelope load spectrum based on the sealing energy variation law of the envelope load points. Among them, the critical load point is the load point with the minimum sealing energy multiple.

4. The method for determining the triaxial safety factor of a tubular design based on gas seal integrity as described in claim 1, characterized in that, Step 4) is followed by a process of applicability verification analysis of the determined triaxial safety factor.

5. The system for determining the triaxial safety factor of a tubular design based on gas seal integrity according to claim 1, characterized in that, include: The statistical analysis module is used to statistically analyze the failure modes and mechanisms of downhole tubing strings and to establish a safety factor evaluation method. The envelope load spectrum establishment module is used to establish the envelope load spectrum, the applicable range of the envelope load spectrum, and the critical load points; The triaxial safety factor determination module is used to analyze the critical load points by combining the cycle integrity variation law of the whole life production process, revise the applicable range of envelope load, and obtain the triaxial safety factor.

6. A computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the computer program, it implements the steps of the method for determining the triaxial safety factor of a tubing design based on the integrity of the gas seal as described in any one of claims 1-4.

7. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by the processor, it implements the steps of the method for determining the triaxial safety factor of a tubing design based on the integrity of the gas seal as described in any one of claims 1-4.

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