Coiled tubing buckling experiment method and experiment device

Abstract

The invention discloses a continuous oil pipe buckling experiment method and device, and the method comprises the steps: driving a simulation oil pipe to move upwards through a pressure loading mechanism, and enabling the simulation oil pipe to be in a free suspension state; the pressure loading mechanism drives the simulation oil pipe to move downwards, the bottom end of the simulation oil pipe makes contact with the pressure sensing mechanism and extrudes the pressure sensing mechanism, the simulation oil pipe is changed into a pressed state from a free suspension state, and the loading pressure of the pressure loading mechanism and the bearing pressure of the pressure sensing mechanism are collected; wherein the compression state comprises a straight compression state and a buckling compression state; recording the maximum loading pressure of the pressure loading mechanism as an actual critical buckling load; and correcting the theoretical critical buckling load calculation formula according to the actual critical buckling load. According to the method, the corrected theoretical critical buckling load calculation formula can be used for providing more accurate theoretical guidance for buckling judgment and running-in analysis of the actual coiled tubing in the horizontal well and the highly-deviated well.

Description

Technical Field

[0001] This invention relates to the field of coiled tubing operation technology in oilfields, and in particular, to a method and apparatus for testing coiled tubing buckling. Background Technology

[0002] Coiled tubing is a continuous tubing string welded together from several flexible tubing segments, reaching lengths of up to thousands of meters. Due to its advantages such as high running-in efficiency, convenient operation, and low operating costs, it is widely used in oilfield downhole operations. However, as oil and gas resource development gradually moves towards deeper ground, deep water, and unconventional areas, the increasing number of horizontal and ultra-deep wells presents significant challenges to coiled tubing running operations. Coiled tubing has low rigidity and a relatively small diameter compared to conventional tubing, resulting in a large gap with the external annulus during the running-in process. On the one hand, the coiled tubing experiences frictional resistance from the wellbore during running-in; on the other hand, during drilling operations such as drilling and flushing, the coiled tubing is subjected to axial compressive loads. When the compressive load exceeds the critical buckling load of the coiled tubing, buckling instability will occur. After buckling, the increased contact area between the coiled tubing and the wellbore leads to a significant increase in frictional resistance. The axial load bearing capacity and the axial load transmission law of the coiled tubing will change significantly. That is, after the load is applied at the wellhead, the magnitude of the working load transmitted to the bottom end of the well will be difficult to predict accurately. In some cases, after buckling and self-locking, the load may not be transmitted to the end, which will affect the running of the coiled tubing and downhole operations.

[0003] Existing technologies theoretically classify coiled tubing buckling into sinusoidal buckling and helical buckling, and derive axial load transfer formulas for some extreme operating conditions through stress analysis. However, the inventors of this invention have found that due to the numerous influencing factors in coiled tubing field operations, it is difficult to determine downhole buckling behavior from changes in surface suspended loads. These theoretical analysis formulas lack sufficient verification with real-world downhole load data, making it difficult to provide accurate guidance for judging downhole buckling and analyzing the downhole performance of coiled tubing. Summary of the Invention

[0004] The purpose of this invention is to provide a method and apparatus for testing the buckling of coiled tubing, in order to solve the technical problem that current theoretical analysis formulas lack sufficient real-world load data for verification, making it difficult to provide accurate guidance for the judgment of downhole buckling and the analysis of the insertion performance of coiled tubing.

[0005] The above-mentioned objectives of the present invention can be achieved by the following technical solutions:

[0006] This invention provides a method for conducting a continuous tubing buckling test, comprising the following steps: preparing a simulated tubing, a simulated casing, a pressure loading mechanism, and a pressure sensing mechanism; wherein, the simulated casing is mounted on a test bench, and the simulated casing has a top opening and a bottom opening; the bottom end of the simulated tubing extends into the simulated casing from the top opening; the pressure loading mechanism is connected to the top of the simulated tubing; the pressure sensing mechanism is installed at the bottom opening of the simulated casing; the pressure loading mechanism drives the simulated tubing upward, placing the simulated tubing in a free-suspension state; the pressure loading mechanism drives the simulated tubing downward, causing the bottom end of the simulated tubing to... The simulated oil pipe comes into contact with and is compressed by the pressure sensing mechanism, changing from a free-suspension state to a compressed state. The loading pressure of the pressure loading mechanism and the pressure bearing capacity of the pressure sensing mechanism are collected. The compressed state includes a straight compressed state and a buckling compressed state. When the pressure bearing capacity of the pressure sensing mechanism decreases, and the loading pressure of the pressure loading mechanism no longer increases with the descent of the simulated oil pipe, it is determined that the simulated oil pipe has changed from a straight compressed state to a buckling compressed state. The maximum loading pressure of the pressure loading mechanism is recorded as the actual critical buckling load. The theoretical critical buckling load calculation formula is then corrected based on the actual critical buckling load.

[0007] In an embodiment of the present invention, the experimental method further includes: recording the tension at the top of the simulated oil pipe in the free suspension state.

[0008] In an embodiment of the present invention, the experimental method further includes the following steps: after the simulated tubing changes to the buckling and compressive state, the simulated tubing continues to move downward through the pressure loading mechanism, and the loading pressure of the pressure loading mechanism and the bearing pressure of the pressure sensing mechanism are collected; based on the tensile force of the simulated tubing and the loading pressure of the pressure loading mechanism and the bearing pressure of the pressure sensing mechanism after the buckling and compressive state, the transmission law of the axial load after the buckling of the simulated tubing is analyzed.

[0009] In an embodiment of the present invention, the analysis of the transmission law of the axial load after buckling of the simulated tubing includes the following steps: calculating the front-to-rear pressure ratio based on the tensile force of the simulated tubing, the loading pressure of the pressure loading mechanism after buckling and compression, and the pressure borne by the pressure sensing mechanism; wherein, the formula for calculating the front-to-rear pressure ratio is: Where k is the front-to-back pressure ratio, F u F is the loading pressure of the pressure loading mechanism. d The pressure that the pressure sensing mechanism can withstand.

[0010] In an embodiment of the present invention, the experimental method further includes the following steps: calculating the frictional resistance of the simulated oil pipe under the straight compression state based on the tensile force, the loading pressure of the pressure loading mechanism under the straight compression state, and the bearing pressure of the pressure sensing mechanism; calculating the frictional resistance of the simulated oil pipe under the buckling compression state based on the tensile force, the loading pressure of the pressure loading mechanism under the buckling compression state, and the bearing pressure of the pressure sensing mechanism; and calculating the additional frictional resistance of the simulated oil pipe after buckling based on the frictional resistance of the simulated oil pipe under the straight compression state and the frictional resistance of the simulated oil pipe under the buckling compression state.

[0011] In an embodiment of the present invention, the experimental method further includes the following steps: changing the influence parameters of the additional frictional resistance; wherein the influence parameters include the elastic modulus of the simulated tubing, the radial clearance between the simulated tubing and the simulated casing, and the diameter of the simulated tubing; conducting buckling experiments on the simulated tubing under different influence parameters to obtain the additional frictional resistance and the loading pressure of the loading mechanism under different buckling experiments; and fitting an empirical calculation formula for the additional frictional resistance of the simulated tubing under the buckling compression state based on the influence parameters, the additional frictional resistance, and the loading pressure of the loading mechanism under different buckling experiments.

[0012] The present invention also provides a continuous tubing buckling test apparatus, comprising: a test stand; a simulated sleeve mounted on the test stand, the simulated sleeve having a top opening and a bottom opening; a simulated tubing, the bottom end of which extends into the simulated sleeve from the top opening; a pressure loading mechanism connected to the top of the simulated tubing, the pressure loading mechanism being configured to drive the simulated tubing to move up and down; a pressure sensing mechanism mounted at the bottom opening of the simulated sleeve; and a data acquisition mechanism electrically connected to the pressure sensing mechanism and the pressure loading mechanism, the data acquisition mechanism being able to acquire the pressure borne by the pressure sensing mechanism and the loading pressure of the pressure loading mechanism.

[0013] In an embodiment of the present invention, the pressure loading mechanism includes a hydraulic injection head, which contains a piston that can move up and down under hydraulic drive. The hydraulic injection head is installed at the top opening of the simulated sleeve, and the piston is connected to the top end of the simulated oil pipe.

[0014] In an embodiment of the present invention, the pressure loading mechanism further includes a hydraulic pump station, which is installed on the experimental bench and connected to the hydraulic injection head.

[0015] In an embodiment of the present invention, the coiled tubing buckling test apparatus further includes a data analysis mechanism, which is electrically connected to the data acquisition mechanism, and is used to analyze and process the bearing pressure and the loading pressure.

[0016] The features and advantages of this invention are:

[0017] The coiled tubing buckling test method and apparatus of the present invention pressurizes a simulated tubing through a pressure loading mechanism, causing the simulated tubing to gradually buckle within a simulated casing. This simulates the buckling behavior of the connected tubing under different axial loads within the casing. The pressure state of the simulated tubing is analyzed based on the pressure received by the pressure sensing mechanism and the loading pressure of the pressure loading mechanism. This allows for accurate determination of the change from a straight pressure state to a buckling pressure state, and the maximum loading pressure of the pressure loading mechanism is recorded as the actual critical buckling load. Furthermore, the theoretical critical buckling load calculation formula is corrected based on the actual critical buckling load. This corrected formula provides more accurate theoretical guidance for judging the buckling and analysis of actual coiled tubing in horizontal and highly deviated wells. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the continuous tubing buckling test apparatus in this invention.

[0020] In the picture:

[0021] 1. Experimental stand; 2. Pressure loading mechanism; 3. Simulated oil pipe; 4. Simulated casing; 5. Casing fixing structure; 6. Pressure sensing mechanism; 7. Computer. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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 are within the scope of protection of the present invention.

[0023] Implementation Method 1

[0024] like Figure 1As shown, the present invention provides a continuous tubing buckling test apparatus, comprising: a test bench 1; a simulated sleeve 4, mounted on the test bench 1, the simulated sleeve 4 having a top opening and a bottom opening; a simulated tubing 3, the bottom end of which extends into the simulated sleeve 4 from the top opening; a pressure loading mechanism 2, connected to the top of the simulated tubing 3, the pressure loading mechanism 2 being configured to drive the simulated tubing 3 to move up and down; a pressure sensing mechanism 6, mounted at the bottom opening of the simulated sleeve 4; and a data acquisition mechanism, electrically connected to the pressure sensing mechanism 6 and the pressure loading mechanism 2 respectively, the data acquisition mechanism being able to acquire the pressure borne by the pressure sensing mechanism 6 and the loading pressure of the pressure loading mechanism 2.

[0025] The simulated casing 4 can be matched to the shape of the working well and has the same diameter and material as the actual casing. The simulated tubing 3 can have the same diameter and material as the actual coiled tubing, thus simulating the buckling behavior of the coiled tubing when it is run into the working well. The working well can be, but is not limited to, diameter, horizontal wells, or highly deviated wells. Furthermore, to reduce the manufacturing and experimental costs of the experimental setup, the length of the simulated casing 4 is shorter than the length of the actual casing, and the length of the simulated tubing 3 is shorter than the length of the actual coiled tubing. However, to ensure that the simulated tubing 3 buckles within the simulated casing 4, the length of the simulated tubing 3 is greater than the length of the simulated casing 4.

[0026] like Figure 1 As shown, the coiled tubing buckling test apparatus of the present invention uses a pressure loading mechanism 2 to press down on a simulated tubing 3, causing the simulated tubing 3 to gradually buckle within a simulated casing 4. This simulates the buckling behavior of the connected tubing under different axial loads within the casing. Based on the pressure received by the pressure sensor 6 and the loading pressure of the pressure loading mechanism 2, the apparatus analyzes the pressure state of the simulated tubing 3, thereby measuring the actual critical buckling load of the simulated tubing 3. The actual critical buckling load is then used to correct the theoretical critical buckling load calculation formula, providing more accurate theoretical guidance for judging the buckling and run-in performance of actual coiled tubing in horizontal and highly deviated wells. Furthermore, based on the pressure received by the pressure sensor 6 and the loading pressure of the pressure loading mechanism 2, the apparatus can also analyze the additional frictional resistance between the simulated tubing 3 and the simulated casing 4 after buckling, as well as the axial load transmission law of the simulated tubing 3 during the buckling process.

[0027] Specifically, the experimental stand 1 is connected to the outer wall of the simulated casing 4 via multiple casing fixing structures 5 to support and fix the simulated casing 4. The multiple casing fixing structures 5 are arranged at intervals along the axial direction of the simulated casing 4. The casing fixing structures 5 are preferably detachably connected to the simulated casing 4 to facilitate the simulation of buckling behavior of the same or different coiled tubing in working wells of different types and / or sizes by replacing simulated casings 4 of different types and / or sizes. The pressure sensing mechanism 6 is also preferably detachably connected to the bottom opening of the simulated casing 4.

[0028] like Figure 1 As shown, in an embodiment of the present invention, by electrically connecting a data analysis mechanism and a data acquisition mechanism, the data analysis mechanism is used to analyze and process the pressure under load and the pressure being applied, thereby achieving automatic data analysis. The data analysis mechanism and the data acquisition mechanism can be integrated into a computer 7.

[0029] like Figure 1 As shown, in an embodiment of the present invention, the pressure loading mechanism 2 includes a hydraulic injection head, which contains a piston capable of moving up and down under hydraulic drive. The hydraulic injection head is installed at the top opening of the simulated sleeve 4, and the piston is connected to the top of the simulated oil pipe 3. Specifically, the pressure loading mechanism 2 also includes a hydraulic pump station, which is installed on the experimental platform 1 and communicates with the hydraulic injection head. The hydraulic pump station can be installed on the top of the experimental platform 1.

[0030] Implementation Method 2

[0031] Combination Figure 1 As shown, the present invention also provides a method for testing the buckling of continuous tubing, comprising the following steps:

[0032] S1. Prepare a simulated tubing 3, a simulated casing 4, a pressure loading mechanism 2, and a pressure sensing mechanism 6; wherein, the simulated casing 4 is mounted on the experimental stand 1, and the simulated casing 4 has a top opening and a bottom opening; the bottom end of the simulated tubing 3 extends into the simulated casing 4 from the top opening; the pressure loading mechanism 2 is connected to the top end of the simulated tubing 3; the pressure sensing mechanism 6 is installed at the bottom opening of the simulated casing 4. Specifically, the continuous tubing buckling test method of the present invention can be implemented using the continuous tubing buckling test apparatus in Embodiment 1.

[0033] S2. The pressure loading mechanism 2 drives the simulated oil pipe 3 to move upward, so that the simulated oil pipe 3 is in a free suspension state.

[0034] Specifically, when the simulated oil pipe 3 moves upward under the action of the pressure loading mechanism 2 until the bottom end of the simulated oil pipe 3, which was originally in contact with the pressure sensing mechanism 6, gradually disengages, until the pressure on the pressure sensing mechanism 6 is exactly zero, it indicates that the simulated oil pipe 3 is in a free suspension state, and at this time, the tension F at the top of the simulated oil pipe 3 can be recorded. g The pulling force F g This is equivalent to the gravity of the simulated oil pipe 3.

[0035] S3. The pressure loading mechanism 2 drives the simulated oil pipe 3 to move downward, so that the bottom end of the simulated oil pipe 3 contacts the pressure sensing mechanism 6 and squeezes the pressure sensing mechanism 6. The simulated oil pipe 3 changes from a free suspension state to a pressure state, and the loading pressure of the pressure loading mechanism 2 and the pressure bearing of the pressure sensing mechanism 6 are collected. The pressure state includes a flat pressure state and a buckling pressure state. When the pressure bearing of the pressure sensing mechanism 6 decreases and the loading pressure of the pressure loading mechanism 2 no longer increases with the descent of the simulated oil pipe 3, it is determined that the simulated oil pipe 3 has changed from a flat pressure state to a buckling pressure state.

[0036] Specifically, under straight pressure, the simulated oil pipe 3 is stable, and the loading pressure of the pressure loading structure gradually increases. The pressure bearing of the pressure sensing mechanism 6 also gradually increases with the increase of the loading pressure. When the simulated oil pipe 3 changes from a straight pressure state to a buckling pressure state, the simulated oil pipe 3 becomes unstable. As a result, the pressure bearing of the pressure sensing mechanism 6 drops sharply, and the loading pressure of the pressure loading mechanism 2 no longer increases with the drop of the simulated oil pipe 3.

[0037] S4. Record the maximum loading pressure of the pressure loading mechanism 2 as the actual critical buckling load.

[0038] Specifically, by simulating the pressure of the oil pipe 3 under pressure, the loading pressure of the pressure loading mechanism 2 is collected at a preset frequency, and then the loading pressure variation curve is plotted based on the loading pressure collected at different times. The maximum loading pressure of the pressure loading mechanism 2 is then analyzed based on the loading pressure variation curve, which is the actual critical buckling load.

[0039] S5. The calculation formula for the theoretical critical buckling load is modified based on the actual critical buckling load.

[0040] Specifically, the formula for calculating the theoretical critical buckling load is as follows:

[0041]

[0042] Among them, F cr Theoretical critical buckling load; E is the elastic modulus; I is the moment of inertia of the coiled tubing section; W e r is the unit weight of the coiled tubing work string in the drilling fluid.c R is the radial clearance between the wellbore and the tubing string; R is the diameter of the coiled tubing; α is the inclination angle at the buckling location. The theoretical critical buckling load calculation formula is modified based on the actual critical buckling load. This can be achieved by setting correction coefficients, etc., thereby modifying the theoretical critical buckling load calculation formula according to the relationship between the experimentally obtained actual critical buckling load and the theoretically calculated critical buckling load.

[0043] The coiled tubing buckling test method of the present invention uses a pressure loading mechanism 2 to press down on a simulated tubing 3, causing the simulated tubing 3 to gradually buckle within a simulated casing 4. This simulates the buckling behavior of the connected tubing under different axial loads within the casing. The pressure state of the simulated tubing 3 is analyzed based on the pressure received by the pressure sensing mechanism 6 and the loading pressure of the pressure loading mechanism 2. This allows for the accurate determination of the change from a straight pressure state to a buckled pressure state of the simulated tubing 3, and the recording of the maximum loading pressure of the pressure loading mechanism 2 as the actual critical buckling load. Furthermore, the theoretical critical buckling load calculation formula is corrected based on the actual critical buckling load. This corrected theoretical critical buckling load calculation formula provides more accurate theoretical guidance for the buckling judgment and insertion analysis of actual coiled tubing in horizontal and highly deviated wells.

[0044] In the embodiments of the present invention, the experimental method further includes the following steps: S7, after the simulated tubing 3 changes to a buckling and compressed state, the simulated tubing 3 continues to move downward through the pressure loading mechanism 2, and the loading pressure of the pressure loading mechanism 2 and the bearing pressure of the pressure sensing mechanism 6 are collected; S8, based on the tensile force of the simulated tubing 3 and the loading pressure of the pressure loading mechanism 2 and the bearing pressure of the pressure sensing mechanism 6 after the buckling and compressed state, the transmission law of the axial load after the buckling of the simulated tubing 3 is analyzed. By analyzing the transmission law of the axial load after the buckling of the simulated tubing 3, theoretical guidance can also be provided for the buckling judgment and insertion analysis of actual continuous tubing in horizontal wells and highly deviated wells.

[0045] Specifically, the analysis of the axial load transmission law after the simulated tubing 3 buckles includes the following steps: Based on the tensile force of the simulated tubing 3 and the loading pressure of the pressure loading mechanism 2 and the pressure borne by the pressure sensing mechanism 6 after buckling and compression, the pressure ratio between the front and rear ends is calculated; wherein, the formula for calculating the pressure ratio between the front and rear ends is: Where k is the front-to-back pressure ratio, F u For the loading pressure of pressure loading mechanism 2, F d The pressure sensor 6 is the pressure it can withstand. The closer the front-to-rear pressure ratio is to "1", the smaller the pressure loss from the top (i.e., the rear end) of the simulated tubing 3 to the bottom (i.e., the front end) of the simulated tubing 3. The higher the front-to-rear pressure ratio, the less effective the loading pressure applied at the top of the simulated tubing 3 can be transmitted to the bottom of the well, and the friction pressure loss increases significantly.

[0046] Therefore, the experimental method of the present invention can also calculate the additional frictional resistance generated after the simulated tubing 3 changes to a buckling and compressed state, including the following steps: S9, calculate the frictional resistance of the simulated tubing 3 in a straight compressed state based on the tensile force, the loading pressure of the pressure loading mechanism 2, and the bearing pressure of the pressure sensing mechanism 6 in a straight compressed state; S10, calculate the frictional resistance of the simulated tubing 3 in a buckling and compressed state based on the tensile force, the loading pressure of the pressure loading mechanism 2, and the bearing pressure of the pressure sensing mechanism 6 in a buckling and compressed state; S11, calculate the additional frictional resistance of the simulated tubing 3 after buckling based on the frictional resistance of the simulated tubing 3 in a straight compressed state and the frictional resistance of the simulated tubing 3 in a buckling and compressed state. By analyzing the additional frictional resistance generated after the simulated tubing 3 buckles, theoretical guidance can also be provided for the buckling judgment and insertion analysis of actual continuous tubing in horizontal wells and highly deviated wells.

[0047] Specifically, the formula for calculating the frictional resistance f1 of the simulated oil pipe 3 under straight pressure (i.e., without buckling) is: f1 = F u +F g -F d The formula for calculating the frictional resistance f2 of the simulated tubing 3 under buckling pressure (i.e., after buckling) is: f2 = F u +F g -F d Therefore, the formula for calculating the additional frictional resistance ΔF generated after the simulated oil pipe 3 buckles is: ΔF=f2-f1.

[0048] To facilitate better analysis of the additional modular force generated after buckling of coiled tubing in practical applications, the embodiments of the present invention obtain an empirical calculation formula for the additional simulated force by fitting, including the following steps: S12, changing the influence parameters of the additional frictional resistance; wherein, the influence parameters include the elastic modulus of the simulated tubing 3, the radial clearance between the simulated tubing 3 and the simulated casing 4, and the diameter of the simulated tubing 3; S13, conducting buckling experiments on the simulated tubing 3 under different influence parameters, thereby obtaining the additional frictional resistance and the loading pressure of the loading mechanism under different buckling experiments, that is, conducting multiple buckling experiments after changing different sizes, different materials and / or different simulated casings 4 (equivalent to repeating steps S1-S3, S7 and S9-S11); S14, based on the influence parameters under different buckling experiments and the additional frictional resistance and the loading pressure of the pressure loading mechanism 2, fitting to obtain an empirical calculation formula for the additional frictional resistance of the simulated tubing 3 under buckling compression.

[0049] Specifically, after the simulated tubing 3 buckles, the additional frictional resistance continues to increase as the pressure loading mechanism 2 continues to apply pressure, indicating a positive correlation between the additional frictional resistance and the loading pressure. The empirical formula for calculating the additional frictional resistance is ΔF = f(R, r c,E,F u ), namely, the elastic modulus E of the simulated tubing 3 and the radial clearance r between the simulated tubing 3 and the simulated casing 4. c Given that parameters such as the diameter R of the simulated oil pipe 3 are constant, the additional frictional resistance ΔF and the loading pressure F of the pressure loading mechanism 2 are also considered. u The functional relationship between them.

[0050] The above descriptions are merely a few embodiments of the present invention. Those skilled in the art can make various modifications or variations to the embodiments of the present invention based on the content disclosed in the application documents without departing from the spirit and scope of the present invention.

Claims

1. A method for testing the buckling of continuous tubing, characterized in that, Includes the following steps: Prepare a simulated tubing, a simulated casing, a pressure loading mechanism, and a pressure sensing mechanism; wherein, the simulated casing is mounted on an experimental platform and has a top opening and a bottom opening; the bottom end of the simulated tubing extends into the simulated casing from the top opening; the pressure loading mechanism is connected to the top of the simulated tubing; and the pressure sensing mechanism is installed at the bottom opening of the simulated casing. The pressure loading mechanism drives the simulated oil pipe to move upward, so that the simulated oil pipe is in a free suspension state; The pressure loading mechanism drives the simulated oil pipe downwards, causing its bottom end to contact the pressure sensing mechanism and compress it. This changes the simulated oil pipe from a freely suspended state to a pressurized state. The loading pressure of the pressure loading mechanism and the pressure resistance of the pressure sensing mechanism are collected. The pressurized state includes a straight pressurized state and a buckling pressurized state. When the pressure resistance of the pressure sensing mechanism decreases, and the loading pressure of the pressure loading mechanism no longer increases with the descent of the simulated oil pipe, it is determined that the simulated oil pipe has changed from a straight pressurized state to a buckling pressurized state. The maximum loading pressure of the pressure loading mechanism is recorded as the actual critical buckling load; The formula for calculating the theoretical critical buckling load is modified based on the actual critical buckling load.

2. The method for testing the buckling of coiled tubing as described in claim 1, characterized in that, The experimental method further includes recording the tension at the top of the simulated oil pipe in the free suspension state.

3. The method for testing the buckling of coiled tubing as described in claim 2, characterized in that, The experimental method also includes the following steps: When the simulated tubing changes to the buckling and pressure-bearing state, the pressure loading mechanism continues to drive the simulated tubing downward, and the loading pressure of the pressure loading mechanism and the pressure bearing pressure of the pressure sensing mechanism are collected. Based on the tensile force of the simulated tubing and the loading pressure of the pressure loading mechanism and the bearing pressure of the pressure sensing mechanism after the buckling and compression state, the transmission law of the axial load after the buckling of the simulated tubing is analyzed.

4. The method for testing the buckling of coiled tubing as described in claim 3, characterized in that, The analysis of the axial load transmission law after the simulated tubing buckling includes the following steps: The pressure ratio between the front and rear ends is calculated based on the tensile force of the simulated tubing, the loading pressure of the pressure loading mechanism after the buckling and compression state, and the pressure bearing pressure of the pressure sensing mechanism. The formula for calculating the front-to-back pressure ratio is as follows: Where k is the front-to-back pressure ratio, F u F is the loading pressure of the pressure loading mechanism. d The pressure that the pressure sensing mechanism can withstand.

5. The method for testing the buckling of coiled tubing as described in claim 2, characterized in that, The experimental method also includes the following steps: Based on the tensile force, the loading pressure of the pressure loading mechanism under the flat compression state, and the bearing pressure of the pressure sensing mechanism, calculate the frictional resistance of the simulated oil pipe under the flat compression state. Based on the tensile force, the loading pressure of the pressure loading mechanism under the buckling and compression state, and the bearing pressure of the pressure sensing mechanism, the frictional resistance of the simulated oil pipe under the buckling and compression state is calculated. The additional frictional resistance of the simulated tubing after buckling is calculated based on the frictional resistance of the simulated tubing under the straight pressure state and the frictional resistance of the simulated tubing under the buckling pressure state.

6. The method for testing the buckling of coiled tubing as described in claim 5, characterized in that, The experimental method also includes the following steps: The influence parameters of the additional frictional resistance are changed; wherein, the influence parameters include the elastic modulus of the simulated tubing, the radial clearance between the simulated tubing and the simulated casing, and the diameter of the simulated tubing; The buckling test of the simulated tubing was conducted under different influencing parameters to obtain the additional frictional resistance and the loading pressure of the loading mechanism under different buckling test conditions. Based on the influence parameters under different buckling experiments, the additional frictional resistance, and the loading pressure of the loading mechanism, an empirical calculation formula for the additional frictional resistance of the simulated tubing under buckling pressure is obtained by fitting.

7. A continuous tubing buckling test apparatus, characterized in that, include: Experimental bench; A simulated sleeve is installed on the experimental platform, and the simulated sleeve has a top opening and a bottom opening. A simulated tubing, the bottom end of which extends into the simulated casing from the top opening of the simulated casing; A pressure loading mechanism is connected to the top end of the simulated oil pipe, and the pressure loading mechanism is configured to drive the simulated oil pipe to move up and down. A pressure sensing mechanism is installed at the bottom opening of the simulated sleeve; The data acquisition mechanism is electrically connected to the pressure sensing mechanism and the pressure loading mechanism, respectively. The data acquisition mechanism can acquire the pressure that the pressure sensing mechanism bears and the loading pressure of the pressure loading mechanism.

8. The coiled tubing buckling test apparatus as described in claim 7, characterized in that, The pressure loading mechanism includes a hydraulic injection head, which contains a piston that can move up and down under hydraulic drive. The hydraulic injection head is installed at the top opening of the simulated sleeve, and the piston is connected to the top of the simulated oil pipe.

9. The coiled tubing buckling test apparatus as described in claim 8, characterized in that, The pressure loading mechanism also includes a hydraulic pump station, which is installed on the experimental platform and connected to the hydraulic injection head.

10. The coiled tubing buckling test apparatus as described in claim 7, characterized in that, The coiled tubing buckling test apparatus also includes a data analysis mechanism, which is electrically connected to the data acquisition mechanism. The data analysis mechanism is used to analyze and process the bearing pressure and the loading pressure.

Images