Method and apparatus for obtaining a computational model for evaluating the resistance of a casing to external pressure

Abstract

The present application relates to the technical field of casing, especially relates to a method and device for obtaining a calculation model for evaluating the anti-external extrusion capacity of casing, which comprises the following steps: performing an anti-external extrusion test on the casing after temperature-internal pressure alternating load treatment, and obtaining the instability extrusion collapse external extrusion load values of the casing under different temperatures, internal pressures and alternating cycle numbers; and obtaining the calculation model according to each instability extrusion collapse external extrusion load value and the corresponding temperature, internal pressure and alternating cycle number. The present application proposes a new calculation method, which can quickly give the anti-external extrusion strength calculation value of the casing according to the temperature and internal pressure values under the field working conditions, not only significantly shortens the time required by the traditional test, but also greatly reduces the test cost, and brings higher economic benefits and comprehensive benefits for industrial application.

Description

Technical Field

[0001] This invention relates to the field of casing technology, and in particular to a method and apparatus for obtaining a calculation model for evaluating the external extrusion resistance of casing. Background Technology

[0002] Oil and gas wells operate under varying conditions and at different times, leading to complex external pressure conditions on the casing string. Crushing is a significant cause of casing failure or damage during production and development; crush resistance measures the casing's ability to withstand external pressure without instability or deformation.

[0003] Under complex pressure conditions during the exploitation of shale gas wells and oil and gas wells, the casing is subjected to alternating loads of internal pressure and temperature cycles (i.e., alternating temperature and pressure loads). This may cause micro-deformation of the casing or reduce its strength, thereby affecting the integrity and safety of the wellbore. However, the evaluation of the crush resistance after internal pressure and temperature cycles has not yet been addressed. Summary of the Invention

[0004] The purpose of this invention is to provide a method and apparatus for obtaining a calculation model for evaluating the external extrusion resistance of casing. This method can calculate the external extrusion resistance of casing under different fracturing conditions, providing technical support for casing strength design.

[0005] To achieve the above objectives, the present invention provides a method for obtaining a calculation model for evaluating the external extrusion resistance of casing, comprising:

[0006] An external extrusion test was conducted on the casing after temperature-internal pressure alternating load treatment to obtain the instability and bursting external extrusion load values ​​of the casing under different temperatures, internal pressures and alternating cycle numbers.

[0007] The calculation model is obtained based on the external extrusion load values ​​of each instability and collapse, and the corresponding temperature, internal pressure, and number of alternating cycles.

[0008] The present invention also provides an apparatus for obtaining a calculation model for evaluating the external extrusion resistance of casing, comprising:

[0009] The test unit is used to conduct external extrusion tests on the casing after temperature-internal pressure alternating load treatment, and to obtain the instability and bursting external extrusion load values ​​of the casing under different temperatures, internal pressures and alternating cycle numbers.

[0010] The unit is used to obtain the calculation model based on the external extrusion load values ​​of each instability and collapse, as well as the corresponding temperature, internal pressure, and number of alternating cycles.

[0011] The technical effects and advantages of this invention are as follows:

[0012] (1) Traditional static load strength analysis of casing ignores the influence of dynamic factors such as temperature fluctuation and internal pressure circulation on casing performance. The core of this invention is to introduce experimental simulation of these complex working conditions, so that the analysis results are closer to the actual working conditions.

[0013] (2) A comprehensive dimensional simulation test procedure for temperature and internal pressure cyclic loading conditions was developed, abandoning the traditional method of small-sized material specimens. The high degree of simulation of the test conditions makes the data and conclusions more relevant to practical applications, providing strong data support for sleeve design and optimization.

[0014] (3) This invention proposes a new calculation method that can quickly give the calculated value of the casing's resistance to external extrusion based on the temperature and internal pressure values ​​under field working conditions. This not only significantly shortens the time required for traditional tests, but also greatly reduces the test cost, bringing higher economic and comprehensive benefits to industrial applications.

[0015] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of a temperature-internal pressure alternating load processing unit.

[0018] Figure 2 This is a schematic diagram of the casing's resistance to external extrusion test;

[0019] Figure 3 This is the load-time curve for Example 1. Detailed Implementation

[0020] 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.

[0021] It should be noted that the structures, proportions, sizes, etc., illustrated in the accompanying drawings are merely for illustrative purposes to aid those skilled in the art and to facilitate understanding and reading. They are not intended to limit the scope of the invention and therefore have no substantial technical significance. Any modifications to the structure, changes in proportions, or adjustments to size, without affecting the effectiveness and purpose of the invention, should still fall within the scope of the technical content disclosed herein. Furthermore, the terms "upper," "lower," "left," "right," "middle," and "one" used in this specification are merely for clarity and not intended to limit the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention.

[0022] To address the shortcomings of existing technologies, this invention discloses a method for obtaining a computational model for evaluating the external extrusion resistance of casing, comprising the following steps:

[0023] S1. Statistical analysis of extreme temperature values ​​(T) for casing service under complex fracturing conditions in the field. max and the extreme value of pressure load P max This is the service boundary condition for casing under fracturing conditions.

[0024] Among them, the extreme temperature T max 200℃; extreme pressure load P max The pressure is 200 MPa.

[0025] The total length of the sleeve is greater than 8D, where D is the outer diameter of the sleeve.

[0026] S2. A temperature-internal pressure alternating load processing unit is constructed using a full-size testing machine. This unit includes sealing plugs 1 and 2, a heating component (preferably a heating pad 4), and a testing machine 5. Figure 1 As shown.

[0027] Among them, the two ends of the sleeve 3 are welded with plugs 1 and 2. The plug 2 is provided with a pressure hole. The pressure hole of the plug 2 sleeve is connected to the testing machine 5. The outer wall of the sleeve is provided with a heating pad 4. The heating pad 4 tightly covers the outer wall of the sleeve and heats it evenly.

[0028] S3. Start the heating pad covering the outer wall of the sleeve, and set the maximum temperature of the heating pad to 0-T. max The temperature is a certain temperature (i.e., the target temperature), and the holding time is the interval t during the multi-stage fracturing operation on site.

[0029] S4. Fill the casing with fracturing fluid or water until the entire internal space of the casing is filled. Use a testing machine to pressurize the fracturing fluid or water from 0 MPa to 0-P. maxA certain pressure (i.e., target pressure) is specified in the formula, and the pressure holding time under the target pressure is t, where t is the pressure holding time under the fracturing conditions of oil and gas well construction.

[0030] During this process, while filling with fracturing fluid or water, the heating pad switch is turned off, and the casing begins to cool down naturally.

[0031] S5. Depressurize the fracturing fluid or water inside the casing from the target pressure value to 0. At the same time, start the heating pad to heat the casing. The heating duration is equal to the interval t during the multi-stage fracturing operation in the field.

[0032] S6. Pressurize the casing again with fracturing fluid or water, and repeat steps S4 to S5. The number of repetitions is the same as the number of multi-stage fracturing cycles n in the field.

[0033] The range of the nth iteration is 0-100.

[0034] S7. After completing the alternating load treatment of sleeve temperature and internal pressure, remove the heating pad on the outer wall and allow the sleeve to cool naturally to room temperature.

[0035] S8. Physical simulation test of the casing's resistance to external extrusion.

[0036] Specifically, after temperature-internal pressure alternating load treatment, a physical simulation test is conducted by applying a uniform external extrusion hydraulic load to the casing. The load-time curve during the uniform external extrusion test is recorded, such as... Figure 2 As shown. The instability and collapse external extrusion load value of the casing string is determined based on the load-time curve.

[0037] S9. Obtain the calculation model for evaluating the casing's resistance to external extrusion. The specific process is as follows:

[0038] 1. A series of full-scale experimental data were obtained using steps S1-S8, including the external extrusion load value of instability and crushing, temperature, internal pressure, and number of cycles.

[0039] 2. Convert the internal pressure value into the ratio of the internal pressure value to the maximum internal pressure resistance of the casing body, and ensure that the data format meets the modeling requirements.

[0040] 3. Input the collected data into processors such as Excel and 1stOpt, and select the multinomial regression model type according to the characteristics of the data.

[0041] 4. Processors such as Excel and 1stOpt will generate fitting formulas and R-squared values. The larger the R-squared value, the better the fitting effect. By comparing the R-values ​​of different models, the optimal fitting formula can be selected to obtain the calculation model.

[0042] The calculation model is: σ 挤=-0.02P′ 2 +2.03P′-0.0002n 2 -0.14n-0.002T+95.92

[0043] In the formula, σ 挤 P' represents the external extrusion load value that causes instability and collapse; P' is the percentage of the target internal pressure to the extreme value of the casing pressure load; n is the number of cycles; and T is the target temperature.

[0044] To better understand this solution, the following embodiments are also provided.

[0045] Example 1

[0046] The instability bursting external extrusion load value used to evaluate the casing's resistance to external extrusion is calculated according to the above method, specifically including:

[0047] S1, Extreme temperature value T of casing during operation under complex fracturing conditions in the field max For 100℃, the extreme value of the pressure load P max It is 100 MPa.

[0048] S2. A temperature-internal pressure alternating load processing unit is built using a full-size testing machine. This unit includes sealing plugs 1 and 2, heating pad 4, and testing machine 5.

[0049] Among them, the two ends of the sleeve 3 are welded with plugs 1 and 2. The plug 2 is provided with a pressure hole. The pressure hole of the plug 2 sleeve is connected to the testing machine 5. The outer wall of the sleeve is provided with a heating pad 4. The heating pad 4 tightly covers the outer wall of the sleeve and heats it evenly.

[0050] Among them, the sleeve 3 is made of Q125 steel, with an outer diameter of 139.7mm, a wall thickness of 10.54mm, and a length of 1250mm.

[0051] S3. Activate the heating pad covering the outer wall of the sleeve, and set the highest temperature of the heating pad to the extreme temperature T calculated in step one. max Set the temperature to 100℃ and keep it warm for 80 minutes.

[0052] S4. Fill the casing with fracturing fluid or water until the casing is full. Use a testing machine to pressurize the fracturing fluid or water from 0 MPa to the maximum pressure load of 100 MPa and maintain the pressure for 4 hours. The 4 hours is the long pressure holding time under the fracturing conditions in the field construction of oil and gas wells.

[0053] During this process, while filling with fracturing fluid or water, the heating pad switch is turned off, and the casing begins to cool down naturally.

[0054] S5. Depressurize the fracturing fluid or water inside the casing from 100MPa to 0. At the same time, start the heating pad to heat the casing. The heating duration is equal to the interval time t = 80min during the multi-stage fracturing operation in the field.

[0055] S6. Pressurize the fracturing fluid or water filling the casing again, and repeat steps S4 to S5 to complete the specified 20 cycles of the experiment.

[0056] S7. After completing the circulation process of internal temperature and pressure of the bushing, remove the heating pad on the outer wall and allow the bushing to cool naturally to room temperature.

[0057] S8, the extreme temperature T max For 100℃, the extreme value of the pressure load P max Substituting 100 MPa and 20 cycles into the calculation model, the instability and crushing external extrusion load value under this working condition is obtained as 143.99 MPa.

[0058] To verify the accuracy of the calculation model, an external extrusion test was conducted on the casing after temperature-internal pressure alternating load treatment. Based on its load-time curve, the instability and collapse external extrusion load value was obtained as 149.5 MPa. Figure 3 As shown, the error between the two values ​​of unstable crushing external extrusion load is 3.7%, indicating that the results of the calculation model protected by this invention are reliable.

[0059] Example 2

[0060] The only difference from Example 1 is the extreme temperature T. max For 100℃, the extreme value of the pressure load P max The pressure is 144 MPa and the number of cycles is 50.

[0061] Temperature extreme value T max For 100℃, the extreme value of the pressure load P max Substituting 144 MPa and 50 cycles into the calculation model, the instability and crushing external extrusion load value under this working condition is obtained as 122.82 MPa.

[0062] Example 3

[0063] The only difference from Example 1 is the extreme temperature T. max For 100℃, the extreme value of the pressure load P max The pressure is 100 MPa and the number of cycles is 50.

[0064] Temperature extreme value T max For 100℃, the extreme value of the pressure load P maxSubstituting 100 MPa and 50 cycles into the calculation model, the instability and crushing external extrusion load value under this working condition is obtained as 139.57 MPa.

[0065] The present invention also provides an apparatus for obtaining a calculation model for evaluating the external extrusion resistance of casing, comprising:

[0066] The test unit is used to conduct external extrusion tests on the casing after temperature-internal pressure alternating load treatment, and to obtain the instability and bursting external extrusion load values ​​of the casing under different temperatures, internal pressures and alternating cycle numbers.

[0067] The unit is used to obtain the calculation model based on the external extrusion load values ​​of each instability and collapse, as well as the corresponding temperature, internal pressure, and number of alternating cycles.

[0068] Since the protection provided by this device is similar to that provided by the method described above, it will not be described in detail here. Please refer to the discussion section of the method described above for more information.

[0069] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for obtaining a computational model for evaluating the resistance of casing to external extrusion, characterized in that, include: An external extrusion test was conducted on the casing after temperature-internal pressure alternating load treatment to obtain the instability and bursting external extrusion load values ​​of the casing under different temperatures, internal pressures and alternating cycle numbers. The calculation model is obtained based on the external extrusion load values ​​of each instability and collapse, and the corresponding temperature, internal pressure, and number of alternating cycles.

2. The method according to claim 1, characterized in that, Obtaining a bushing after temperature-internal pressure alternating load treatment includes: Determine the extreme temperature T during casing service max and the extreme value of pressure load P max ; Start the external heating of the sleeve, heat it to the target temperature, and then maintain the temperature. Fill the casing that is beginning to cool with liquid, pressurize the liquid to the target pressure, and then maintain the pressure. After the liquid is depressurized to 0, the casing is subjected to multiple temperature-internal pressure alternating load treatments to obtain the casing after temperature-internal pressure alternating load treatment.

3. The method according to claim 2, characterized in that, Temperature extreme value T max 200℃; extreme pressure load P max The pressure is 200 MPa; the target temperature range is 0-T. max The target pressure range is 0-P. max The number of iterations ranges from 0 to 100.

4. The method according to claim 2, characterized in that, The casing subjected to temperature-internal pressure alternating load treatment was subjected to an external extrusion test to obtain the instability and collapse external extrusion load values ​​of the casing under different temperatures, internal pressures, and alternating cycle numbers, including: A uniform external hydraulic load was applied to the casing after temperature-internal pressure alternating load treatment, and the load-time curves of the casing under different target temperatures, target internal pressures and alternating cycle numbers were obtained. Based on the load-time curves of the casing under different target temperatures, target internal pressures, and alternating cycles, the maximum load value on the load-time curve is taken as the outward extrusion load value for instability and collapse.

5. The method according to claim 4, characterized in that, Obtain the computational model, including: Each target internal pressure is converted into the ratio of the target internal pressure to the extreme value of the casing pressure load; Different target temperatures, target internal pressures, and alternating cycle numbers, along with the corresponding instability and bursting external extrusion load values, are input into the processor. The processor is then fitted using a multinomial regression model to obtain the computational model.

6. The method according to claim 5, characterized in that, The formula for the calculation model is as follows: s 挤 =-0.02P′ 2 +2.03P′-0.0002n 2 -0.14n-0.002T+95.92 In the formula, σ 挤 P' represents the external extrusion load value that causes instability and collapse; P' is the percentage of the target internal pressure to the extreme value of the casing pressure load; n is the number of cycles; and T is the target temperature.

7. The method according to claim 2, characterized in that, The time for heat preservation and pressure holding are the interval time and pressure holding time during multi-stage fracturing operations in the field under the fracturing conditions of oil and gas well construction, respectively.

8. An apparatus for obtaining a computational model for evaluating the resistance of casing to external extrusion, characterized in that, include: The test unit is used to conduct external extrusion tests on the casing after temperature-internal pressure alternating load treatment, and to obtain the instability and bursting external extrusion load values ​​of the casing under different temperatures, internal pressures and alternating cycle numbers. The unit is used to obtain the calculation model based on the external extrusion load values ​​of each instability and collapse, as well as the corresponding temperature, internal pressure, and number of alternating cycles.

9. The apparatus according to claim 8, characterized in that, The test unit includes a temperature-internal pressure alternating load treatment unit, which is used to perform temperature-internal pressure alternating load treatment on the bushing.

10. The apparatus according to claim 9, characterized in that, The temperature-internal pressure alternating load processing unit includes: a heating component covering the outer wall of the casing, sealing plugs at both ends of the casing, and a full-size testing machine connected to the sealing plugs.

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