An interfacial shear strength test method

Abstract

The application provides an interface shear strength test method, which comprises the following steps: step one, curing device manufacturing, manufacturing a hollow circular table with a preset inclined angle θ with the horizontal plane as a curing device; step two, combination body manufacturing, inverting and fixing the curing device on a first flat plate, pouring the prepared cement slurry into the cavity of the curing device until it overflows, placing a second flat plate on top to compact, curing and forming in a high-temperature and high-pressure environment, and then removing the first flat plate and the second flat plate to obtain a combination body; and step three, pressure test, placing the combination body on a fixing device, coaxially placing a pressure head on the top surface of the curing device, and starting a pressure test device to measure the interface shear strength. According to the test method, the curing device is designed as a hollow circular table with a certain inclined angle with the horizontal plane, and the inclined angle is specified to be within a certain range, so that the integrity of the demoulded sample can be effectively ensured, the reliability of the experimental results is ensured, and the demoulded sample can be further analyzed.

Description

Technical Field

[0001] This invention relates to the field of cementing engineering technology in oil and gas drilling operations, and more specifically, to a method for testing interfacial shear strength. Background Technology

[0002] Cementing is a crucial part of oil and gas drilling and completion. The quality of the bonding between the cement sheath and the casing / formation interface is a key factor affecting the overall cementing quality of oil and gas wells, determining the well's interlayer sealing capability throughout its lifespan. Good bonding quality reduces the formation of micro-annulus at the interface, preventing annular flow of formation fluids along the interface and avoiding safety accidents such as blowouts.

[0003] Among the common interface bonding failure modes in downhole drilling, shear failure is a frequent occurrence. It typically results from relative slippage between the cement sheath and the casing or formation under complex load variations in high-temperature, high-pressure environments. Therefore, interface shear strength is a crucial indicator for evaluating interface bonding performance. Currently, a common method for testing interface shear strength is the "extrusion method," which involves curing a cylindrical simulated core or cement stone in the center of a mold. A vertical load is applied to the simulated core or cement stone, causing it to detach from the cement-core or cement-casing interface. The shear strength is then calculated by dividing the load by the contact area (Lu Chenghui, Wang Jie, Yang Qingjiang, et al. Testing Device for Cement Interface Bond Strength [P]. Beijing: CN205280557U, 2016-06-01.). However, this method has limitations. During the application of the load, the frictional force between the interfaces can introduce significant errors into the measurement results, leading to high data dispersion and poor repeatability. Furthermore, this type of evaluation method is greatly affected by the precision of mold processing. Inconsistent mold inner diameter will further amplify experimental errors and may even cause the specimen to be damaged during the loading process. Summary of the Invention

[0004] In view of this, the present invention proposes a method for testing interfacial shear strength, comprising the following steps:

[0005] Step 1: Fabrication of the curing device. Construct a hollow truncated cone with a preset tilt angle θ to the horizontal plane as the curing device.

[0006] Step 2: Assembly fabrication. Invert the curing device and fix it on the first plate. Pour the prepared cement slurry into the cavity of the curing device until it overflows. Place the second plate on top and compact it. Cure it in a high temperature and high pressure environment. Then remove the first plate and the second plate to obtain the assembly.

[0007] Step 3: Pressure test. Place the assembly upright on the fixing device, place the pressure head coaxially on the top surface of the curing device, and start the pressure test device to measure the interface shear strength.

[0008] Furthermore, the formula for calculating the interfacial shear strength is as follows:

[0009] Where P is the interfacial shear strength, MPa; F is the failure load, kN; θ is the inclination angle of the curing device; h is the height of the curing device, mm; d is the inner diameter of the top surface of the curing device, mm; and D is the inner diameter of the bottom surface of the curing device, mm.

[0010] Furthermore, the shear strength of the first and second interfaces was tested using the operation methods of steps one to three.

[0011] Furthermore, both the first and second flat plates are made of smooth stainless steel.

[0012] Furthermore, when the maintenance device is placed on the first plate, a thin layer of sealant is applied to the contact surface.

[0013] Furthermore, the included tilt angle θ is greater than 40° and less than 90°.

[0014] Furthermore, the curing device used for the interfacial shear strength test is made of stainless steel.

[0015] Furthermore, the curing device used for the two-interface shear strength test is made of rock.

[0016] Furthermore, the included tilt angle θ is preferably 50°, 60°, 70° or 80°.

[0017] The interfacial shear strength testing method provided by this invention improves upon the classic "extrusion method" by creating a certain angle between the simulated interface and the load during the test. This avoids errors in the experimental results caused by factors such as friction between the mold and the sample and the mold processing accuracy during shear failure, reducing data dispersion and improving the reliability of the test results. It also facilitates further analysis of the demolded sample. Furthermore, by switching the material of the curing device, the simulation experiments of the first and second interfaces can be converted, demonstrating good applicability. Attached Figure Description

[0018] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0019] Figure 1 This is a schematic diagram of the steps of the interface shear strength testing method provided in the embodiments of the present invention;

[0020] Figure 2This is a schematic diagram of the interface shear strength testing device provided in an embodiment of the present invention;

[0021] Figure 3 This is the state of the cement stone that was removed after testing in an interface experiment provided in an embodiment of the present invention;

[0022] Figure 4 This refers to the state of the cement stone that was removed after testing in the two-interface experiment provided in this embodiment of the invention.

[0023] 1. Pressure head, 2. Curing device, 3. Fixing device, 4. Pressure testing device. Detailed Implementation

[0024] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the disclosure to those skilled in the art. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0025] See Figure 1 As shown, this is an embodiment of the present invention providing a method for testing interfacial shear strength, comprising the following steps: Step 1, fabrication of a curing device: a hollow frustum with a preset angle θ to the horizontal plane is fabricated as a curing device; Step 2, fabrication of an assembly: the curing device is inverted and fixed on a first plate, and the prepared cement slurry is poured into the cavity of the curing device until it overflows. A second plate is placed on top and compacted, and the assembly is cured in a high temperature and high pressure environment. Then, the first and second plates are removed to obtain the assembly; Step 3, pressure test: the assembly is placed upright on the fixing device, and the pressure head is coaxially placed on the top surface of the curing device. The pressure test device is activated to measure the interfacial shear strength.

[0026] In this embodiment, the formula for calculating the interfacial shear strength is:

[0027] Where P is the interfacial shear strength, MPa; F is the failure load, kN; θ is the inclination angle of the curing device; h is the height of the curing device, mm; d is the inner diameter of the top surface of the curing device, mm; and D is the inner diameter of the bottom surface of the curing device, mm.

[0028] In this embodiment, steps one through three are used to test the shear strength of the first and second interfaces. Both the first and second plates are smooth, flat stainless steel plates. When the curing device is placed on the first plate, a thin layer of sealant is applied to the contact surface. The tilt angle θ is greater than 40° and less than 90°. The curing device used for the first interface shear strength test is made of stainless steel. The curing device used for the second interface shear strength test is made of rock. The tilt angle θ is preferably 50°, 60°, 70°, or 80°.

[0029] A specific embodiment of testing the interfacial shear strength using the above-described interfacial shear strength test method is as follows: Example 1

[0030] (1) A hollow truncated cone made of stainless steel with a preset tilt angle θ of 80° to the horizontal plane is used as a maintenance device.

[0031] (2) Cement slurry preparation: Cement slurry was prepared according to GB / T 19139-2012 standard, and shear strength performance was tested by simulating the cement ring interface; the cement slurry formula is as follows: 100g of Jiahua G-grade oil well cement + 4g of fluid loss reducer BXF-200L(AF) + 0.2g of retarder BXR-200L + 40g of fresh water + 0.5g of defoamer G603;

[0032] (3) Invert the curing device with the busbar at an 80° angle to the horizontal plane and fix it on a flat and smooth stainless steel plate. Apply a thin layer of sealant to the contact surface between the device and the stainless steel plate. Pour the prepared cement slurry into the cavity of the curing device until it overflows. Place another stainless steel plate on top and compact it. Place the assembly under a 20MPa, 80℃ water bath for 3 days until it is cured and formed.

[0033] (4) Remove the assembly from the curing autoclave, remove the stainless steel plate, and place the curing device upright on the fixing device. Place the pressure head coaxially on the top surface of the curing device. Measure the load required for relative slippage between the cement stone and the curing device using a pressure testing device. Refer to... Figure 2 The method of use is shown, and the interfacial shear strength is calculated using the following formula:

[0034]

[0035] Wherein, P is the interfacial shear strength, MPa; F is the failure load, kN; θ is the tilt angle of the curing device; h is the height of the curing device, mm; d is the inner diameter of the top surface of the curing device, mm; D is the inner diameter of the bottom surface of the curing device, mm; In this embodiment, the specific parameters of the curing device are the same as those used in the conventional "extrusion method", except that the tilt angle θ is set, which will not be disclosed in detail here. The final results of the tested interfacial shear strength are shown in Table 1.

[0036] (5) Four sets of curing devices were set up, and each set was tested 5 times. The specific shear strength test results are shown in Table 1.

[0037] Example 2

[0038] A hollow frustum with an included angle θ of 70° was used as the curing device, and the same experiment was carried out according to the method of Example 1. The specific shear strength test results are shown in Table 1.

[0039] Example 3

[0040] A hollow frustum with an included angle θ of 60° was used as the curing device, and the same experiment was carried out according to the method of Example 1. The specific shear strength test results are shown in Table 1.

[0041] Example 4

[0042] A hollow frustum with an included angle θ of 50° was used as the curing device, and the same experiment was carried out according to the method of Example 1. The specific shear strength test results are shown in Table 1.

[0043] Comparative Example 1

[0044] A hollow frustum with an included angle θ of 90° was used as the curing device, and the same experiment was carried out according to the method of Example 1. The specific shear strength test results are shown in Table 1.

[0045] Comparative Example 2

[0046] A hollow frustum with an included angle θ of 40° was used as the curing device, and the same experiment was carried out according to the method of Example 1. The specific shear strength test results are shown in Table 1.

[0047] Table 1. Results of interfacial shear strength test

[0048]

[0049] In the above experimental examples and comparative examples, a stainless steel curing device was used to simulate an interface. Table 1 shows that, compared to Comparative Example 1 (θ = 90°), the angle θ between the generatrix of the curing device designed in Examples 1-4 (θ = 80°-50°) and the horizontal plane gradually decreased. At this time, the angle between the simulated interface and the load gradually increased, while the interfacial shear strength measured with the same cement slurry formula decreased significantly. Simultaneously, the standard deviation of the measurement results also decreased, indicating that the design of reducing the angle θ significantly reduced the influence of interfacial friction on the measurement results. While the measurement results approached the true value, the measurement accuracy and repeatability were significantly improved. This can also be seen from the state of the detached cement stone. Figure 3As shown, in Comparative Example 1, the cement stone that detached due to interfacial friction was difficult to maintain its intact shape, while in Examples 1-4, all the detached cement stones were intact, with damage occurring only at the interface. When the tilt angle θ decreased to a certain extent, such as in Comparative Example 2 (θ = 40°), the detached cement stone underwent solid-body damage. This is because the damage at the interface was discontinuous, becoming a process close to "tearing." Therefore, the tilt angle θ needs to be controlled within a certain range. In this example, the tilt angle θ was controlled within the range of greater than 40° and less than 90° to ensure the experimental results.

[0050] The following is a specific embodiment of testing the interfacial shear strength using the above-described interfacial shear strength test method: Example 1

[0051] (1) A hollow truncated cone made of rock with a preset tilt angle θ of 80° to the horizontal plane is used as a curing device. In this embodiment, rock material is selected to simulate the two interfaces, which can effectively perform the two-interface shear strength test.

[0052] (2) Cement slurry preparation: Cement slurry was prepared according to GB / T 19139-2012 standard, and shear strength performance was tested by simulating the cement sheath interface; the cement slurry formula is as follows: 100g of Jiahua G-grade oil well cement + 4g of fluid loss reducer BXF-200L(AF) + 0.2g of retarder BXR-200L + 40g of fresh water + 0.5g of defoamer G603;

[0053] (3) Invert the curing device with the busbar at an 80° angle to the horizontal plane and fix it on a flat and smooth stainless steel plate. Apply a thin layer of sealant to the contact surface between the device and the stainless steel plate. Pour the prepared cement slurry into the cavity of the curing device until it overflows. Place another stainless steel plate on top and compact it. Place the assembly under a 20MPa, 80℃ water bath for 3 days until it is cured and formed.

[0054] (4) Remove the assembly from the curing autoclave, remove the stainless steel plate, and place the curing device upright on the fixing device. Place the pressure head coaxially on the top surface of the curing device. Measure the load required for relative slippage between the cement stone and the curing device using a pressure testing device. Refer to... Figure 2 The operating method is shown, and the interfacial shear strength is calculated using the following formula:

[0055]

[0056] Where P is the interfacial shear strength, MPa; F is the failure load, kN; θ is the tilt angle of the curing device; h is the height of the curing device, mm; d is the inner diameter of the top surface of the curing device, mm; D is the inner diameter of the bottom surface of the curing device, mm; In this embodiment, the specific parameters of the curing device are the same as those used in the conventional "extrusion method", except that the tilt angle θ is set, which will not be disclosed here. The final results of the tested interfacial shear strength are shown in Table 1.

[0057] (5) Four sets of curing devices were set up, and each set was tested 5 times. The specific shear strength test results are shown in Table 1.

[0058] Example 2

[0059] A hollow frustum with an included angle θ of 70° was used as the curing device, and the same experiment was carried out according to the method of Example 1. The specific shear strength test results are shown in Table 1.

[0060] Example 3

[0061] A hollow frustum with an included angle θ of 60° was used as the curing device, and the same experiment was carried out according to the method of Example 1. The specific shear strength test results are shown in Table 1.

[0062] Example 4

[0063] A hollow frustum with an included angle θ of 50° was used as the curing device, and the same experiment was carried out according to the method of Example 1. The specific shear strength test results are shown in Table 1.

[0064] Comparative Example 1

[0065] A hollow frustum with an included angle θ of 90° was used as the curing device, and the same experiment was carried out according to the method of Example 1. The specific shear strength test results are shown in Table 1.

[0066] Comparative Example 2

[0067] A hollow frustum with an included angle θ of 40° was used as the curing device, and the same experiment was carried out according to the method of Example 1. The specific shear strength test results are shown in Table 1.

[0068] Table 2. Results of the two-interface shear strength test

[0069]

[0070] In the simulation experiment of the two-interface shear strength, the same test method and data parameters as those for the one-interface experiment were used. Table 2 shows that the two-interface experiment yielded similar results to the one-interface experiment. In the two-interface test, as the angle θ between the designed curing device's generatrix and the horizontal plane gradually decreased, the angle between the simulated interface and the load gradually increased. However, the interfacial shear strength measured with the same cement paste formula decreased significantly, and the standard deviation of the measurement results also decreased accordingly. This indicates that the design of reducing the angle θ significantly reduced the influence of interfacial friction on the measurement results. While the measurement results approached the true value, the measurement accuracy and repeatability were significantly improved. This can also be seen from the state of the detached cement paste. Figure 4 As shown, in Comparative Example 1, the cement stone detached from the two interfaces is difficult to maintain its intact shape due to the influence of interfacial friction. However, in Examples 1-4, all the detached cement stones are intact, and the damage only occurs at the interface, which is completely consistent with the results of the single-interface experiment. When the tilt angle θ decreases to a certain extent, such as in Comparative Example 2 (θ = 40°), the detached cement stone will undergo bulk damage. This is because the damage at the interface is discontinuous, becoming a process close to "tearing". Therefore, the tilt angle θ needs to be controlled within a certain range. In this embodiment, the tilt angle θ is preferably controlled within the range of greater than 40° and less than 90° to ensure the experimental effect. It can be seen that the shear strength test results of the two interfaces show a similar trend to those of the single interface. The interface shear strength test method provided in this embodiment is applicable to the shear strength measurement of both single and two interfaces.

[0071] The interfacial shear strength testing method provided in this invention has the following advantages: It improves upon the classic "extrusion method" by creating a certain angle between the simulated interface and the load during the test, avoiding errors caused by factors such as friction between the mold and the sample and the mold's machining accuracy during shear failure. This reduces data dispersion, improves the reliability of test results, and reflects the interface bonding situation. The interfacial shear strength testing and evaluation method is simple to operate and sample preparation. The conversion between the primary and secondary interface simulations can be achieved by replacing the material of the curing device with rock. Furthermore, the curing device is small in size and easily combined with equipment such as curing vessels for simulating high-temperature and high-pressure conditions in underground mines. It also allows for large-scale batch curing, facilitating comparative experiments with control groups.

[0072] It should be noted that in the description of this invention, the terms "upper", "lower", "left", "right", "inner", "outer", etc., which indicate directions or positional relationships, are based on the directions or positional relationships shown in the accompanying drawings. This is only for the convenience of description and is not intended to indicate or imply that the device or element must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation of this invention.

[0073] Furthermore, it should be noted that, in the description of this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0074] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. An interfacial shear strength test method characterized by, The method comprises the following steps: Step 1: making a curing device, a hollow circular table with a preset inclination angle θ with the horizontal plane is made as the curing device; Step 2: making a combination, the curing device is fixed upside down on the first flat plate, the prepared cement slurry is poured into the cavity of the curing device until it overflows, the second flat plate is placed on top to compact, and then the first flat plate and the second flat plate are removed to obtain the combination; Step 3: pressure test, the combination is placed upright on the fixing device, the pressure head is coaxially placed on the top surface of the curing device, and the pressure test device is started to measure the interfacial shear strength. The interface shear strength calculation formula is: ; Wherein, P is the interfacial shear strength, MPa; F is the failure load, kN; θ is the inclination angle of the curing device; h is the height of the curing device, mm; d is the inner diameter of the top surface of the curing device, mm; and D is the inner diameter of the bottom surface of the curing device, mm.

2. The interfacial shear strength test method of claim 1, wherein, The operation method of steps 1 to 3 is used to test the interfacial shear strength and the interfacial shear strength.

3. The interfacial shear strength test method of claim 1, wherein, The first flat plate and the second flat plate are both smooth stainless steel plates.

4. The interfacial shear strength test method of claim 1, wherein, When the curing device is placed on the first flat plate, a layer of thin sealing grease is coated on the contact surface.

5. The interfacial shear strength test method of claim 1, wherein, The inclination angle θ is greater than 40° and less than 90°.

6. The interfacial shear strength test method of claim 2, wherein, The curing device used for the interfacial shear strength test is made of stainless steel.

7. The interfacial shear strength test method of claim 2, wherein, The curing device used for the interfacial shear strength test is made of rock.

8. The interfacial shear strength test method of claim 5, wherein, The inclination angle θ is 50°, 60°, 70° or 80°.

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