A device and method for testing the gas sealability of a tubular thread under alternating conditions

Abstract

This invention provides an apparatus and method for testing the gas-tightness of tubing threads under alternating operating conditions. The apparatus for testing the gas-tightness of tubing threads under alternating operating conditions includes: a hydraulic testing machine for applying axial alternating loads to the tubing; a pressure gauge for detecting whether the threaded joints of the tubing leak; a strain gauge for measuring the radial displacement of the inner wall of the tubing; an outer tube gas collection sleeve; the tubing; an internal pressure gauge; a booster pump; a gas source valve; a gas source; and an automatic control system. The tubing has threaded joints and is mounted on top of the hydraulic testing machine. The outer tube gas collection sleeve is fitted onto the threaded joints. The pressure gauge is connected to the outer tube gas collection sleeve, which is mounted at the bottom of the tubing. The gas source is connected to the gas source valve via a pipeline, and the gas source valve is connected to the booster pump via a pipeline. The booster pump is connected to the top of the tubing via a pipeline. The internal pressure gauge is connected to the pipeline between the booster pump and the tubing. The automatic control system is connected to the hydraulic testing machine, the strain gauge, and the booster pump.

Description

Technical Field

[0001] This invention relates to the field of wellbore integrity technology for gas storage wells, and in particular to an apparatus and method for testing the gas-tightness of tubing threads under alternating operating conditions. Background Technology

[0002] The long-term alternating injection and production processes in gas storage wells cause significant fluctuations in wellbore temperature and pressure, subjecting the tubing string to low-cycle alternating stress. In particular, the injection and production tubing strings endure alternating axial tension and internal pressure during injection and production, making the threads a weak point in the tubing seal, prone to fatigue damage and sealing failure. To ensure the safe operation of gas storage facilities, the thread sealing performance of the wellbore tubing string under alternating loads must be tested and evaluated during well engineering design or operational condition transitions.

[0003] Therefore, it is necessary to establish an evaluation method and device to meet the gas-tightness requirements of tubing threads under alternating operating conditions, and to guide the selection and evaluation of tubing strings in gas storage wells. Currently, the sealing capacity of gas storage well tubing strings is mostly tested through static sealing via pressure testing, without considering the influence of axial alternation. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide an apparatus and method for testing the gas-tightness of pipe thread under alternating working conditions, in order to address the shortcomings of the prior art.

[0005] The technical solution of this invention to solve the above-mentioned technical problems is as follows: A device for testing the gas-tightness of a tubing thread under alternating working conditions, comprising: a hydraulic testing machine for applying axial alternating loads to the tubing, a pressure gauge for detecting whether the threaded joint of the tubing leaks, a strain gauge for measuring the radial displacement of the inner wall of the tubing, an outer tube gas collecting sleeve, the tubing, an internal pressure gauge, a booster pump, a gas source valve, a gas source, and an automatic control system. The tubing is provided with a threaded joint, the tubing is installed on the top of the hydraulic testing machine, the outer tube gas collecting sleeve is fitted onto the threaded joint, the pressure gauge is connected to the outer tube gas collecting sleeve, the outer tube gas collecting sleeve is installed at the bottom of the tubing, the gas source is connected to the gas source valve through a pipeline, the gas source valve is connected to the booster pump through a pipeline, the booster pump is connected to the top of the tubing through a pipeline, the internal pressure gauge is connected to the pipeline between the booster pump and the tubing, and the automatic control system is connected to the hydraulic testing machine, the strain gauge, and the booster pump respectively.

[0006] The beneficial effects of adopting the technical solution of this invention are as follows: An axial alternating load is applied to the tubing string using a hydraulic testing machine, while simultaneously applying high and low internal pressures through a gas pressurization system. An automatic control system enables the automatic measurement, acquisition, and recording of internal pressure and axial alternating load. This evaluates the sealing capacity of the tubing thread after a certain number of axial alternation cycles and assesses the critical number of cycles for thread leakage under a certain internal pressure, thereby quantitatively testing the thread sealing capacity and sealing life. The test results can directly guide the operational adaptability assessment of gas storage wells, providing a basis for the development of gas storage pressurization operation and production differential pressure operation plans. It also guides the engineering assessment of underground gas storage wells. Alternating loads and continuously varying tubing internal pressure can be applied, fully simulating the alternating operation conditions of underground gas storage injection and production. This allows for the detection of the gas-tightness of the tubing thread under different alternating load conditions, closely integrating with actual field engineering, and providing recommended upper limits for alternating loads under safe working conditions of the tubing thread in actual engineering, guiding the safe operation of gas storage facilities.

[0007] Furthermore, an internal pressure relief bypass valve is provided on the pipeline between the booster pump and the internal pressure gauge.

[0008] The beneficial effects of adopting the above-mentioned further technical solution are: the setting of the internal pressure relief bypass valve is used for pressure relief, which facilitates the pressure relief of the internal pressure of the tubing, prevents the internal pressure of the tubing from overload, prevents the booster pump from overload, and improves the stability and reliability of the device.

[0009] Furthermore, the tubing is an injection-production tubing, and the tubing is connected to the hydraulic testing machine via a rubber ring.

[0010] The beneficial effects of adopting the above-mentioned further technical solutions are: the tubing is an injection / production tubing, serving as the test sample, thus improving the accuracy of the test; the rubber ring improves the sealing between the tubing and the hydraulic testing machine, preventing gas leakage from affecting the accuracy of the experiment.

[0011] Furthermore, the present invention also provides a method for testing the gas-tightness capability of a tubing thread under alternating operating conditions. Based on the apparatus described in any one of the above claims for testing the gas-tightness capability of a tubing thread under alternating operating conditions, the method for testing the gas-tightness capability of a tubing thread under alternating operating conditions includes:

[0012] S1. Apply axial tensile load to the tubing using a hydraulic testing machine, and inject gas into the tubing using a booster pump until the internal pressure of the tubing reaches the first test internal pressure, and maintain it for the first preset time.

[0013] S2. Remove the test internal pressure and axial tensile load to zero, apply axial compression load to the tubing using a hydraulic testing machine, and fill the tubing with gas using a booster pump until the internal pressure of the tubing reaches the second test internal pressure, and maintain it for the second preset time.

[0014] S3. Release the test internal pressure to zero, apply the rated compressive load to the tubing using a hydraulic testing machine, and maintain it for the third preset time;

[0015] S4. Adjust the rated compression load of the tubing to the axial compression load using a hydraulic testing machine, and inject gas into the tubing using a booster pump until the internal pressure of the tubing reaches the third test internal pressure, and maintain it for the fourth preset time.

[0016] S5. Remove the axial compressive load to zero and maintain for the fifth preset time;

[0017] S6. Apply an axial tensile load to the tubular column using a hydraulic testing machine and maintain it for the sixth preset time.

[0018] S7. Release the test internal pressure to zero, and repeat steps S1 to S7 until the preset number of times to determine the sealing capacity of the tubing under alternating load.

[0019] The beneficial effects of adopting the technical solution of this invention are as follows: An axial alternating load is applied to the tubing string using a hydraulic testing machine, while simultaneously applying high and low internal pressures through a gas pressurization system. An automatic control system enables the automatic measurement, acquisition, and recording of internal pressure and axial alternating load. This evaluates the sealing capacity of the tubing thread after a certain number of axial alternation cycles and assesses the critical number of cycles for thread leakage under a certain internal pressure, thereby quantitatively testing the thread sealing capacity and sealing life. The test results can directly guide the operational adaptability assessment of gas storage wells, providing a basis for the development of gas storage pressurization operation and production differential pressure operation plans. It also guides the engineering assessment of underground gas storage wells. Alternating loads and continuously varying tubing internal pressure can be applied, fully simulating the alternating operation conditions of underground gas storage injection and production. This allows for the detection of the gas-tightness of the tubing thread under different alternating load conditions, closely integrating with actual field engineering, and providing recommended upper limits for alternating loads under safe working conditions of the tubing thread in actual engineering, guiding the safe operation of gas storage facilities.

[0020] Furthermore, it also includes: if a leak occurs in the tubing during the test in steps S1 to S7, the test is terminated.

[0021] The beneficial effects of adopting the above-mentioned further technical solutions are: the test is terminated when leakage occurs in the tubing string. It evaluates the sealing capacity of the threads after a certain number of axial alternation cycles, assesses the critical number of cycles for thread leakage under a certain internal pressure, and thus quantitatively tests the thread sealing capacity and sealing life. The test results can directly guide the operational adaptability assessment of gas storage wells, providing a basis for the development of gas storage pressurization operation and production pressure differential expansion operation plans. It also guides the engineering assessment of underground gas storage wells.

[0022] Furthermore, the value of the axial tensile load is the product of the first safety factor and the maximum tensile load of the tubing, and the value of the axial compressive load is the product of the second safety factor and the maximum compressive load of the tubing.

[0023] The beneficial effects of adopting the above-mentioned further technical solutions are: based on the injection and production operation conditions of natural gas wells and gas storage facilities, the maximum working load that the tubing string can withstand is calculated, and considering the differences between oilfield operation conditions and indoor simulation tests, the working load is multiplied by the corresponding safety factor as the test load.

[0024] Furthermore, the first safety factor has a value range of 1.0 to 1.5, the second safety factor has a value range of 1.2 to 1.5, and the third safety factor has a value range of 1.1 to 1.5.

[0025] The beneficial effects of adopting the above-mentioned further technical solutions are: the setting of the safety factor fully considers the differences between oilfield operating conditions and indoor simulation tests, and the working load multiplied by the corresponding safety factor is used as the test load, thereby improving accuracy.

[0026] Furthermore, the axial tensile load is less than or equal to the rated tensile load, and the axial compressive load is less than or equal to the rated compressive load.

[0027] The beneficial effects of adopting the above-mentioned further technical solutions are: the applied test load should be less than or equal to the rated load of the tubing string. This prevents overload testing of the tubing string and accurately determines the gas-tightness of the tubing string threads under alternating operating conditions.

[0028] Furthermore, the numerical range of the first preset time, the second preset time, the third preset time, the fourth preset time, the fifth preset time, and the sixth preset time is 5 to 15 minutes, and the preset number of times is 30.

[0029] The beneficial effects of adopting the above-mentioned further technical solutions are as follows: given that the underground gas storage well has a design life of at least 30 years, and gas is injected and produced once a year, the pressure and temperature inside the injection and production tubing change alternately (tensile and compressive loads repeat), so the tubing must withstand at least 30 cycles of load alternation.

[0030] Furthermore, the step of determining the sealing capacity of the tubing string under alternating loads includes: recording tensile and compressive loads, internal pressure change curves, and test phenomena; and analyzing the sealing capacity of the tubing string under alternating loads based on the tensile and compressive loads, internal pressure change curves, and test phenomena.

[0031] The beneficial effects of adopting the above-mentioned further technical solution are: by analyzing tensile and compressive loads, internal pressure variation curves, and experimental phenomena, the sealing capacity of the tubing thread after a certain number of cycles of axial alternating loads can be evaluated, as well as the critical number of cycles for thread leakage under a certain internal pressure, thereby quantitatively testing the thread sealing capacity and sealing life. Based on the tensile and compressive loads, internal pressure variation curves, and experimental phenomena, the gas-tightness of the tubing thread under alternating working conditions is evaluated, and engineering guidance is provided.

[0032] The advantages of additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the device for testing the gas-tightness of tubular threads under alternating operating conditions, provided in an embodiment of the present invention.

[0034] Figure 2 This is a schematic flowchart illustrating a method for testing the gas-tightness of tubular threads under alternating operating conditions, as provided in an embodiment of the present invention.

[0035] Figure 3 This is one of the test curves provided in the embodiments of the present invention for testing the gas-tightness of the test column thread.

[0036] Figure 4 This is the second test curve provided for testing the gas-tightness of the test column thread in an embodiment of the present invention.

[0037] Explanation of reference numerals in the attached diagram: 1. Hydraulic testing machine; 2. Pressure gauge; 3. Strain gauge; 4. Outer tube gas collection sleeve; 5. Tubing column; 6. Internal pressure gauge; 7. Internal pressure relief bypass valve; 8. Booster pump; 9. Air source valve; 10. Internal pressure pipeline; 11. Air source; 12. Automatic control system; 13. Threaded joint. Detailed Implementation

[0038] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0039] like Figure 1 As shown, this embodiment of the invention provides an apparatus for testing the gas-tightness of a tubing thread under alternating operating conditions. The apparatus includes: a hydraulic testing machine 1 for applying axial alternating loads to the tubing; a pressure gauge 2 for detecting whether the threaded joint 13 of the tubing 5 leaks; a strain gauge 3 for measuring the radial displacement of the inner wall of the tubing 5; an outer tube gas collecting sleeve 4; the tubing 5; an internal pressure gauge 6; a booster pump 8; a gas source valve 9; a gas source 11; and an automatic control system 12. The tubing 5 is equipped with a threaded joint 13 and is mounted on top of the hydraulic testing machine 1. The outer tube gas collecting sleeve 4... The air jacket 4 is fitted onto the threaded joint 13. The pressure gauge 2 is connected to the outer tube air collection sleeve 4. The outer tube air collection sleeve 4 is installed at the bottom of the tube column 5. The air source 11 is connected to the air source valve 9 through a pipeline. The air source valve 9 is connected to the booster pump 8 through a pipeline. The booster pump 8 is connected to the top of the tube column 5 through a pipeline. The internal pressure gauge 6 is connected to the pipeline between the booster pump 8 and the tube column 5. The automatic control system 12 is connected to the hydraulic testing machine 1, the strain gauge 3, and the booster pump 8, respectively.

[0040] The beneficial effects of adopting the technical solution of this invention are as follows: An axial alternating load is applied to the tubing string using a hydraulic testing machine, while simultaneously applying high and low internal pressures through a gas pressurization system. An automatic control system (booster pump and gas source) enables the automatic measurement, acquisition, and recording of high and low internal pressures and axial alternating loads. This simulates the actual working conditions of the gas storage tubing string under alternating loads, and evaluates the thread gas-tightness of the tubing string by simulating the bearing capacity of alternating axial loads under different internal pressures. It evaluates the thread sealing capacity of the tubing string after a certain number of cycles of axial alternation, and assesses the critical number of cycles of thread leakage under a certain internal pressure, thereby quantitatively testing the thread sealing capacity and sealing life. The test results can directly guide the operational adaptability assessment of gas storage wells, providing a basis for the development of gas storage well pressurization operation and production pressure differential operation plans. It also guides the engineering assessment of underground gas storage wells. It can apply alternating loads and continuously varying internal pressure of the tubing, fully simulating the alternating operation conditions of underground gas storage tanks during gas injection and extraction. It can detect the gas sealing capacity of the tubing threads under different alternating load conditions, and is closely integrated with actual field engineering. It provides recommended upper pressure limits for alternating loads under safe working conditions of tubing threads in actual engineering projects, guiding the safe operation of gas storage tanks.

[0041] The piping between components can be internal pressure piping 10.

[0042] The device for testing the gas-tightness of tubing threads under alternating operating conditions provides a solution for evaluating the gas-tightness and sealing life of tubing threads under axial alternating operating conditions, thereby guiding the engineering assessment of underground gas storage wells. Samples of injection and production tubing (tubing string) threaded connections (threaded joints) are prepared, and the sealing testing device (the device for testing the gas-tightness of tubing threads under alternating operating conditions) is assembled and installed on a hydraulic testing machine. Through the axial alternating load application system (hydraulic testing machine), alternating internal pressure system (booster pump and gas source), sealing testing system (pressure gauge 2 and outer pipe gas collection sleeve 4), and automatic control system settings, the device achieves the testing of thread gas-tightness under preset axial alternating load and continuous loading and unloading of internal pressure. Based on the upper limit pressure, the critical number of cycles for thread leakage is tested. This addresses the deficiency in existing gas storage tubing sealing performance evaluations that do not consider alternating loads, directly guiding the wellbore adaptability evaluation of gas storage facilities.

[0043] This invention presents a columnar sealing device comprising an axial alternating load application system (hydraulic testing machine), an alternating internal pressure system (booster pump and air source), a sealing detection system (pressure gauge 2 and outer pipe gas collection sleeve 4), and an automatic control system. It can apply alternating loads and continuously varying internal pressure within the pipe column, fully simulating the alternating operation conditions of underground gas storage tanks during injection and extraction. It can detect the gas-tightness of the pipe column threads under different alternating load conditions, closely integrating with actual field engineering practices and increasing its practicality.

[0044] Considering the influence of actual materials, pressure-temperature and other factors, the sealing ability of the tubing thread to gas is directly tested. By measuring tensile and compressive loads, internal pressure change curves and experimental phenomena, the sealing ability of the tubing thread after a certain number of cycles of axial alternating loads can be evaluated. This method and device can also evaluate the critical number of cycles of thread leakage under a certain internal pressure, thereby quantitatively testing the thread sealing ability and sealing life.

[0045] The recommended upper pressure limit for alternating loads under safe operating conditions of pipe thread in actual engineering is given to guide the safe operation of gas storage facilities.

[0046] It can also simulate the gas-tightness of tubing threads under different temperatures and pressures downhole, providing experimental guidance for indoor optimization design of gas-tight threads and for gas-tightness testing and experiments before entering the well.

[0047] like Figure 1 As shown, further, an internal pressure relief bypass valve 7 is provided on the pipeline between the booster pump 8 and the internal pressure gauge 6.

[0048] The beneficial effects of adopting the above-mentioned further technical solution are: the setting of the internal pressure relief bypass valve is used for pressure relief, which facilitates the pressure relief of the internal pressure of the tubing, prevents the internal pressure of the tubing from overload, prevents the booster pump from overload, and improves the stability and reliability of the device.

[0049] like Figure 1 As shown, the tubing 5 is a injection-production tubing, and the tubing 5 is connected to the hydraulic testing machine 1 by a rubber ring.

[0050] The beneficial effects of adopting the above-mentioned further technical solutions are: the tubing is an injection / production tubing, serving as the test sample, thus improving the accuracy of the test; the rubber ring improves the sealing between the tubing and the hydraulic testing machine, preventing gas leakage from affecting the accuracy of the experiment.

[0051] The device for testing the gas-tightness of tubing threads under alternating working conditions can be a combination of tubing-hydraulic testing machine and sealing equipment. By setting up tensile and compressive loads and internal pressure application, adjustment and measurement pipelines, the device can test the strength of the gas-tightness of tubing threads under continuous loading and unloading of axial loads and internal pressure heating conditions, in order to achieve the purpose of simulating and evaluating the sealing performance of tubing threads.

[0052] The hydraulic testing machine 1 has a known structure and is connected to the automatic control system 12. The automatic control system 12 can apply an axial alternating load to the tube column 5, generating alternating changes in pressure and temperature (repeated tensile and compressive loads).

[0053] The tubing string 5 is an injection and production tubing string with a threaded connection. It is located in the center of the hydraulic testing machine 1, passes through the top cover, and is sealed with a rubber ring. The top end is connected to the internal pressure pipeline 10.

[0054] The alternating internal pressure system includes an internal pressure air source (air source 11), an internal pressure pipeline 10, an internal pressure air source valve (air source valve 9), an internal pressure booster pump (booster pump 8), an internal pressure gauge 6, and an internal pressure relief bypass valve 7. The internal pressure air source (air source 11) and the internal pressure booster pump (booster pump 8) can provide stable internal pressure. The internal pressure gauge 6 can monitor the internal pressure in real time. The internal pressure booster pump (booster pump 8) is connected to the automatic control system 12, and pressure control and measurement recording can be performed through the automatic control system 12.

[0055] The sealing detection system includes a pressure gauge 2 and an external gas collection sleeve (external gas collection sleeve 4), wherein the external gas collection sleeve (external gas collection sleeve 4) is connected to the pressure gauge 2 to detect whether the thread is leaking.

[0056] The strain gauge 3 is installed at the bottom of the tubular column 5 and connected to the automatic control system 12. It is a measuring device used to measure the radial displacement of the inner wall of the tubular column 5.

[0057] like Figure 2 As shown, in addition, the present invention also provides a method for testing the gas-tightness of a tubing thread under alternating operating conditions. Based on the apparatus for testing the gas-tightness of a tubing thread under alternating operating conditions described in any one of the above claims, the method for testing the gas-tightness of a tubing thread under alternating operating conditions includes:

[0058] S1. Apply axial tensile load to the tubing using a hydraulic testing machine, and inject gas into the tubing using a booster pump until the internal pressure of the tubing reaches the first test internal pressure, and maintain it for the first preset time.

[0059] S2. Remove the test internal pressure and axial tensile load to zero, apply axial compression load to the tubing using a hydraulic testing machine, and fill the tubing with gas using a booster pump until the internal pressure of the tubing reaches the second test internal pressure, and maintain it for the second preset time.

[0060] S3. Release the test internal pressure to zero, apply the rated compressive load to the tubing using a hydraulic testing machine, and maintain it for the third preset time;

[0061] S4. Adjust the rated compression load of the tubing to the axial compression load using a hydraulic testing machine, and inject gas into the tubing using a booster pump until the internal pressure of the tubing reaches the third test internal pressure, and maintain it for the fourth preset time.

[0062] S5. Remove the axial compressive load to zero and maintain for the fifth preset time;

[0063] S6. Apply an axial tensile load to the tubular column using a hydraulic testing machine and maintain it for the sixth preset time.

[0064] S7. Release the test internal pressure to zero, and repeat steps S1 to S7 until the preset number of times to determine the sealing capacity of the tubing under alternating load.

[0065] The beneficial effects of adopting the technical solution of this invention are as follows: An axial alternating load is applied to the tubing string using a hydraulic testing machine, while simultaneously applying high and low internal pressures through a gas pressurization system. An automatic control system enables the automatic measurement, acquisition, and recording of internal pressure and axial alternating load. This evaluates the sealing capacity of the tubing thread after a certain number of axial alternation cycles and assesses the critical number of cycles for thread leakage under a certain internal pressure, thereby quantitatively testing the thread sealing capacity and sealing life. The test results can directly guide the operational adaptability assessment of gas storage wells, providing a basis for the development of gas storage pressurization operation and production differential pressure operation plans. It also guides the engineering assessment of underground gas storage wells. Alternating loads and continuously varying tubing internal pressure can be applied, fully simulating the alternating operation conditions of underground gas storage injection and production. This allows for the detection of the gas-tightness of the tubing thread under different alternating load conditions, closely integrating with actual field engineering, and providing recommended upper limits for alternating loads under safe working conditions of the tubing thread in actual engineering, guiding the safe operation of gas storage facilities.

[0066] like Figure 3 As shown, Figure 3 The figure shows the test curves obtained by testing the gas-tightness of the tubing thread according to the method described above for testing the gas-tightness of the tubing thread under alternating operating conditions. The test object is the first tubing string. Under the axial load level shown in the figure, no leakage occurred after 10 cycles of tensile-compressive alternation, proving that the thread can seal an internal pressure of 50 MPa. In the figure, the horizontal axis represents time in minutes (min), the first vertical axis (left vertical axis) represents axial force in kN, and the second vertical axis (right vertical axis) represents internal pressure in MPa. The straight line represents the axial load in kN, and the dashed line represents the internal pressure in MPa. After 10 cycles of loading, no leakage occurred in the tubing string.

[0067] like Figure 4 As shown, Figure 4 The figure shows the test curves obtained by testing the gas-tightness of the tubing thread according to the method described above for testing the gas-tightness of the tubing thread under alternating operating conditions. The test object is the second tubing string. Under the axial load level shown in the figure, leakage occurred in the second cycle at an internal pressure of 50 MPa. In the figure, the horizontal axis represents time in minutes (min), the first vertical axis (left vertical axis) represents axial force in kN, and the second vertical axis (right vertical axis) represents internal pressure in MPa. The straight line represents the axial load in kN, and the dashed line represents the internal pressure in MPa. Leakage occurred in the tubing string in the second cycle.

[0068] Furthermore, it also includes: if a leak occurs in the tubing during the test in steps S1 to S7, the test is terminated.

[0069] The beneficial effects of adopting the above-mentioned further technical solutions are: the test is terminated when leakage occurs in the tubing string. It evaluates the sealing capacity of the threads after a certain number of axial alternation cycles, assesses the critical number of cycles for thread leakage under a certain internal pressure, and thus quantitatively tests the thread sealing capacity and sealing life. The test results can directly guide the operational adaptability assessment of gas storage wells, providing a basis for the development of gas storage pressurization operation and production pressure differential expansion operation plans. It also guides the engineering assessment of underground gas storage wells.

[0070] Furthermore, the value of the axial tensile load is the product of the first safety factor and the maximum tensile load of the tubing, and the value of the axial compressive load is the product of the second safety factor and the maximum compressive load of the tubing.

[0071] The beneficial effects of adopting the above-mentioned further technical solutions are: based on the injection and production operation conditions of natural gas wells and gas storage facilities, the maximum working load that the tubing string can withstand is calculated, and considering the differences between oilfield operation conditions and indoor simulation tests, the working load is multiplied by the corresponding safety factor as the test load.

[0072] Furthermore, the first safety factor has a value range of 1.0 to 1.5, the second safety factor has a value range of 1.2 to 1.5, and the third safety factor has a value range of 1.1 to 1.5.

[0073] The beneficial effects of adopting the above-mentioned further technical solutions are: the setting of the safety factor fully considers the differences between oilfield operating conditions and indoor simulation tests, and the working load multiplied by the corresponding safety factor is used as the test load, thereby improving accuracy.

[0074] Furthermore, the axial tensile load is less than or equal to the rated tensile load, and the axial compressive load is less than or equal to the rated compressive load.

[0075] The beneficial effects of adopting the above-mentioned further technical solutions are: the applied test load should be less than or equal to the rated load of the tubing string. This prevents overload testing of the tubing string and accurately determines the gas-tightness of the tubing string threads under alternating operating conditions.

[0076] Furthermore, the numerical range of the first preset time, the second preset time, the third preset time, the fourth preset time, the fifth preset time, and the sixth preset time is 5 to 15 minutes, and the preset number of times is 30.

[0077] The beneficial effects of adopting the above-mentioned further technical solutions are as follows: given that the underground gas storage well has a design life of at least 30 years, and gas is injected and produced once a year, the pressure and temperature inside the injection and production tubing change alternately (tensile and compressive loads repeat), so the tubing must withstand at least 30 cycles of load alternation.

[0078] Furthermore, the step of determining the sealing capacity of the tubing string under alternating loads includes: recording tensile and compressive loads, internal pressure change curves, and test phenomena; and analyzing the sealing capacity of the tubing string under alternating loads based on the tensile and compressive loads, internal pressure change curves, and test phenomena.

[0079] The beneficial effects of adopting the above-mentioned further technical solution are: by analyzing tensile and compressive loads, internal pressure variation curves, and experimental phenomena, the sealing capacity of the tubing thread after a certain number of cycles of axial alternating loads can be evaluated, as well as the critical number of cycles for thread leakage under a certain internal pressure, thereby quantitatively testing the thread sealing capacity and sealing life. Based on the tensile and compressive loads, internal pressure variation curves, and experimental phenomena, the gas-tightness of the tubing thread under alternating working conditions is evaluated, and engineering guidance is provided.

[0080] A method for testing the gas-tightness of tubular threads under alternating operating conditions, comprising the following steps:

[0081] 1. Prepare a sample of the threaded connection joint of the injection and extraction tubing (tubing 5 with threaded joint 13), and assemble the sealing test device (pressure gauge 2 and outer tube gas collection sleeve 4) and install it on the hydraulic testing machine 1.

[0082] 2. Calculation of test load

[0083] a) Based on the injection and production operation conditions of natural gas wells and gas storage facilities, calculate the working load that the tubing string will bear, i.e., the maximum tensile load T. to Maximum compressive load T co Maximum injection-production pressure P io Considering the differences between oilfield operating conditions and indoor simulation tests, the working load multiplied by the corresponding safety factor is used as the test load, i.e., the (axial tensile load) T. t =(1.0~1.5)T to (Axial compressive load) T c = (1.2~1.5)T co (Test internal pressure) P i = (1.1~1.5)P io Loads are applied for the final test.

[0084] b) It should be noted that the applied test load should be less than or equal to the rated load of the tubing, i.e., T t ≤T te T c ≤T ce T te T ce These are the rated tensile load and rated compressive load of the tubing (generally T). te =T ce ), and the tensile load (axial tensile load) T applied in the test t At least 85% Tte .

[0085] 3. Test load loading procedure

[0086] a) Applying a tensile load T to the tubular string t (Axial tensile load), then pressurize the gas in the tubing to P. i (First test internal pressure), hold load for 5-15 minutes (first preset time);

[0087] b) Remove the internal pressure to zero, remove the tensile load to zero, and then apply a compressive load T. c (Axial compression load), and pressurize the gas in the tubing to P. i (Second test internal pressure), hold load for 5-15 minutes (second preset time);

[0088] c) Release the internal pressure to zero and apply a compressive load to T. ce (Rated compressive load), hold load for 5-15 minutes (third preset time);

[0089] d) Reduce the compressive load to T c (Axial compressive load), and apply internal pressure to P i (Third test internal pressure), hold load for 5-15 minutes (fourth preset time);

[0090] e) Remove the compressive load to zero and maintain the load for 5–15 minutes (fifth preset time);

[0091] f) Apply tensile load to T t (Axial tensile load), hold for 5-15 minutes (sixth preset time);

[0092] g) Release the internal pressure to zero, and repeat steps a) to f) for a total of 30 sealing cycles to determine the long-term sealing performance of the tubing under alternating loads.

[0093] h) If a leak occurs during the test, the test shall be terminated.

[0094] 4. Record the test process, including tensile and compressive loads, internal pressure change curves, and test phenomena.

[0095] 5. Evaluate the gas-tightness of the tubular thread under alternating working conditions based on tensile and compressive loads, internal pressure variation curves, and test phenomena, and provide engineering guidance.

[0096] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method of testing the gas tightness of a tubular string thread under alternating conditions of use, characterized in that, Based on a device for testing the gas-tightness of tubing threads under alternating operating conditions, the device includes: a hydraulic testing machine for applying axial alternating loads to the tubing, a pressure gauge for detecting whether the threaded joints of the tubing leak, a strain gauge for measuring the radial displacement of the inner wall of the tubing, an outer tube gas collecting sleeve, the tubing, an internal pressure gauge, a booster pump, a gas source valve, a gas source, and an automatic control system. The tubing is equipped with threaded joints and is mounted on top of the hydraulic testing machine. The outer tube gas collecting sleeve is fitted onto the threaded joints. The pressure gauge is connected to the outer tube gas collecting sleeve, which is mounted at the bottom of the tubing. The gas source is connected to... The gas source valve is connected to the booster pump via a pipeline. The booster pump is connected to the top of the tubing via a pipeline. The internal pressure gauge is connected to the pipeline between the booster pump and the tubing. The automatic control system is connected to the hydraulic testing machine, the strain gauge, and the booster pump. An internal pressure relief bypass valve is provided on the pipeline between the booster pump and the internal pressure gauge. The tubing is an injection / production tubing, and the tubing is connected to the hydraulic testing machine via a rubber ring. The method for testing the threaded gas-tightness of the tubing under alternating operating conditions includes: S1, applying an axial tensile load to the tubing using a hydraulic testing machine, and injecting gas into the tubing using a booster pump until the internal pressure of the tubing is reduced. S1. The pressure reaches the first test internal pressure and is maintained for the first preset time; S2. The test internal pressure and axial tensile load are released to zero. An axial compressive load is applied to the tubing using a hydraulic testing machine. Gas is injected into the tubing using a booster pump until the internal pressure reaches the second test internal pressure and is maintained for the second preset time; S3. The test internal pressure is released to zero. A rated compressive load is applied to the tubing using a hydraulic testing machine and is maintained for the third preset time; S4. The rated compressive load on the tubing is adjusted to an axial compressive load using a hydraulic testing machine. Gas is injected into the tubing using a booster pump until the internal pressure reaches the third test internal pressure and is maintained for the fourth preset time; S5. The axial compressive load is released to zero and is maintained for the fifth preset time; 6. Apply axial tensile load to the tubing using a hydraulic testing machine and maintain it for a preset time (S6); S7. Release the test pressure to zero and repeat steps S1 to S7 until the preset number of times to determine the sealing capacity of the tubing under alternating load; This also includes: if leakage occurs in the tubing during steps S1 to S7, the test is terminated; the value of the axial tensile load is the product of the first safety factor and the maximum tensile load of the tubing, and the value of the axial compressive load is the product of the second safety factor and the maximum compressive load of the tubing; the value range of the first safety factor is 1.0 to 1.5, the value range of the second safety factor is 1.2 to 1.5, and the value range of the third safety factor is 1.1 to 1.5; The axial tensile load is less than or equal to the rated tensile load, and the axial compressive load is less than or equal to the rated compressive load; the numerical ranges of the first, second, third, fourth, fifth, and sixth preset times are all 5–15 min, and the preset number of times is 30; the steps for determining the sealing capacity of the tubing under alternating loads include: recording the tensile and compressive loads, internal pressure change curves, and test phenomena; analyzing the sealing capacity of the tubing under alternating loads based on the tensile and compressive loads, internal pressure change curves, and test phenomena.

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