System and method for testing cementing strength of two interfaces of well cementation cement sheath

Abstract

The invention relates to a well cementation cement sheath two-interface bonding strength testing system and method, the well cementation cement sheath two-interface bonding strength testing system comprises a kettle body device, the bottom of the kettle body device is connected with a drain valve through a drain pipeline, and the kettle body device is provided with a first input pipeline and a second input pipeline; the liquid storage tank comprises a flushing liquid storage tank and a drilling liquid storage tank, the first input pipeline is connected with the output end of the liquid storage tank, and the input end of the liquid storage tank and the second input pipeline are connected with an external water source and an air source through the pneumatic liquid pressure increasing valve; and the temperature control system is arranged on the kettle body device, and the temperature control system comprises a thermocouple and a temperature sensor. The system and the method for testing the cementing strength of the two interfaces of the well cementation cement sheath can provide a more real simulation effect and improve more accurate test data.

Description

Technical Field

[0001] The present invention belongs to the field of oil and gas well exploration and development, and particularly relates to a high-temperature and high-pressure test device and method for the bonding strength of the second interface of a cement sheath in well cementing. Background Art

[0002] The cementing interface is an important component unit for the sealing integrity of the cement sheath. Generally, the bonding interface between the cement sheath and the casing is called the first cementing interface, and the bonding interface between the cement sheath and the formation wellbore is called the second cementing interface. Affected by various factors such as drilling fluid performance, flushing efficiency, cement slurry performance, and formation fluid, the bonding quality of the second cementing interface becomes the key to effective interlayer isolation, and the bonding strength of the second interface is an important index to characterize the bonding quality of the second interface.

[0003] The existing bonding strength evaluation devices do not simultaneously consider the following factors affecting the bonding strength: the real formation temperature and pressure environment; the dynamic filtration of the drilling fluid on the wellbore to form a mud cake; the rotation speed of the rotating cylinder during the formation and flushing of the mud cake; the shrinkage of the mud cake caused by the change of the bonding test temperature, specifically: the influence of the experimental temperature and humidity changes on the physical state such as the strength, permeability, and compressibility of the mud cake and the chemical state such as decomposability due to the discontinuity of the mud cake formation process and the mud cake flushing process, thus unable to truly simulate the downhole working fluid circulation, cement solidification, and bonding process, unable to obtain accurate test data, difficult to guide the optimization of the flushing fluid and cement slurry systems, and difficult to provide guiding opinions for improving the bonding quality. Summary of the Invention

[0004] In order to solve all or part of the above problems, the purpose of the present invention is to provide a test system and method for the bonding strength of the second interface of a well-cemented cement sheath to provide a more realistic simulation effect and obtain more accurate test data.

[0005] According to the first aspect of the present invention, there is provided a test system for the bonding strength of the second interface of a well-cemented cement sheath, including: a kettle body device, the bottom of the kettle body device is connected with a drain valve through a drain pipeline, and a first input pipeline and a second input pipeline are arranged on the kettle body device; a liquid storage tank, the liquid storage tank includes a flushing liquid storage tank and a drilling fluid storage tank, the first input pipeline is connected to the output end of the liquid storage tank, and the input end of the liquid storage tank and the second input pipeline are connected to an external water source and a gas source through a pneumatic liquid booster valve; and a temperature control system, which is arranged on the kettle body device, and the temperature control system includes a thermocouple and a temperature sensor.

[0006] In some embodiments, the kettle body device includes: a kettle body, a cavity is formed inside the kettle body, a top cavity opening is formed in the upper part of the kettle body, and a bottom cavity opening is formed in the lower part of the kettle body; a functional kettle cover, the functional kettle cover is sealingly connected to the top cavity opening; a core base, the core base is sealingly connected to the bottom cavity opening, and an axially penetrating base through hole is formed in the middle of the core base; a core, which is arranged along the axis of the base through hole, the bottom end of the core is sealingly connected inside the base through hole, and a core cap is arranged at the top end of the core; a threaded lower plug, which is arranged at the bottom of the core base and is threadedly connected to the base through hole, a threaded drain hole is formed along the axis inside the threaded lower plug, and the top end of the threaded lower plug abuts against the core.

[0007] In some embodiments, a kettle body thread portion is formed on the inner peripheral wall of the top cavity opening, the functional kettle cover is threadedly connected to the kettle body thread portion, and a kettle cover sealing ring is arranged on the stepped surface of the functional kettle cover that cooperates with the kettle body.

[0008] In some embodiments, a core sealing ring is arranged between the core and the core base, and a core base sealing ring is arranged between the core base and the bottom cavity opening.

[0009] In some embodiments, the functional kettle cover is configured as a magnetic stirring kettle cover. The magnetic stirring kettle cover includes: a magnetic stirring system, which is arranged inside the magnetic stirring kettle cover; a stirring rod, which is arranged along the axis of the magnetic stirring kettle cover. At the same time, one end of the stirring rod is connected to the driving end of the magnetic stirring system, and the other end of the stirring rod is rotatably connected to the core cap; and a rotating cylinder, the bottom of the cylinder of which is connected to the stirring rod, the cylinder opening of which is arranged downward, and the core is arranged at intervals inside the rotating cylinder.

[0010] In some embodiments, an annular vertical wall is formed at the top surface edge of the core base. The kettle body device further includes an annular sleeve and a bolt plug. The annular sleeve is fittingly sleeved inside the annular vertical wall, and the bolt plug is sealingly connected to the threaded drain hole.

[0011] In some embodiments, the functional kettle cover is configured as a cementation strength test kettle cover. The cementation strength test kettle cover includes: a hydraulic control system, which is arranged inside the cementation strength test kettle cover; a test oil cylinder, which is arranged inside the cementation strength test kettle cover and is connected to the hydraulic control system; and a force application rod, one end of the force application rod is connected to the driving end of the test oil cylinder, and the other end of the force application rod faces the core. Among them, the test oil cylinder can drive the force application rod to move closer to and away from the core under the control of the hydraulic control system.

[0012] According to a second aspect of the present invention, there is provided a method for testing the bonding strength of the second interface of a cement sheath in well cementing, which is applied to the above-mentioned testing system for the bonding strength of the second interface of a cement sheath in well cementing, and includes a method for simulating the annular return velocity of downhole working fluid circulation. Among them, the formula for converting the annular return velocity of drilling fluid into the rotational speed of the rotating cylinder in the method for simulating the annular return velocity of downhole working fluid circulation is:

[0013]

[0014] Wherein, R1 is the core radius, in mm; R2 is the inner radius of the rotating cylinder, in mm; N h is the rotational speed of the device, in r / min; D is the wellbore diameter, in m; d is the outer diameter of the casing, in m; τ y is the fluid shear stress, in Pa; n is the fluid flow behavior index; K is the fluid consistency coefficient, in Pa·s n ; V is the annular return velocity, in m / s.

[0015] In some embodiments, the method for simulating the annular return velocity of downhole working fluid circulation includes the formula for converting the annular return velocity of the flushing fluid into the rotational speed of the rotating cylinder:

[0016]

[0017] Wherein, R1 is the core radius, in mm; R2 is the inner radius of the rotating cylinder, in mm; N h is the rotational speed of the device, in r / min; D is the wellbore diameter, in m; d is the outer diameter of the casing, in m; V is the annular return velocity, in m / s.

[0018] In some embodiments, the bonding strength test in the method for testing the bonding strength of the second interface of a cement sheath in well cementing is an in-situ temperature-bearing test.

[0019] As can be seen from the above technical solutions, according to the testing system and method for the bonding strength of the second interface of a cement sheath in well cementing of the present invention, the construction displacement on site can be corresponded to the rotational speed of the rotating cylinder of the device according to the downhole temperature and pressure conditions, so as to accurately simulate the formation of mud cake and the flushing process due to drilling fluid filtration, perform curing according to the downhole temperature and pressure environment, and measure the shear bonding strength of the second interface in this environment. Compared with the prior art, it can more accurately reflect the formation and flushing process of the mud cake on the wellbore wall, and more accurately reflect the bonding strength value of the second interface. The device is simple to operate, the bonding data is more reasonable and accurate, and the use function of the device is more comprehensive. It can not only be used for measuring the bonding strength of the second interface, but also for evaluating the performance of drilling fluid systems and the flushing efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a schematic diagram of the system connection of the testing system for the bonding strength of the second interface of a cement sheath in well cementing according to an embodiment of the present invention;

[0021] Figure 2Schematic structural diagram of the first embodiment of the kettle body device according to the embodiment of the present invention;

[0022] Figure 3 is Figure 2 Schematic structural diagram of the magnetic stirring kettle cover shown in the figure;

[0023] Figure 4 Schematic structural diagram of the second embodiment of the kettle body device according to the embodiment of the present invention;

[0024] Figure 5 Schematic process diagram of the cementing test stage according to the embodiment of the present invention;

[0025] Figure 6 is Figure 4 Schematic structural diagram of the cementing strength test kettle cover shown in the figure. Detailed implementation manners

[0026] In order to better understand the purpose, structure and function of the present invention, the following further describes in detail a system and method for testing the bonding strength of the second interface of a cement sheath for well cementing in conjunction with the accompanying drawings.

[0027] Figure 1 Shows a system connection diagram of a well cementing cement sheath second interface bonding strength test system 100 according to an embodiment of the present invention. In conjunction with Figure 1 Shown in the figure, the well cementing cement sheath second interface bonding strength test system 100 includes: a kettle body device 200, the bottom of the kettle body device 200 is connected with a drain valve through a drain pipeline, and a first input pipeline 201 and a second input pipeline 202 are arranged on the kettle body device 200; a liquid storage tank 300, the liquid storage tank 300 includes a flushing liquid storage tank and a drilling fluid storage tank, the first input pipeline 201 is connected to the output end of the liquid storage tank 300, and the input end of the liquid storage tank 300 and the second input pipeline 202 are connected to an external water source and a gas source through a pneumatic liquid booster valve; and a temperature control system 400, which is arranged on the kettle body device 200, and the temperature control system 400 includes a thermocouple and a temperature sensor.

[0028] Please refer to Figure 2, in some embodiments, the kettle body device 200 may include: a kettle body 1, a cavity is formed inside the kettle body 1, a top cavity opening is formed in the upper part of the kettle body 1, and a bottom cavity opening is formed in the lower part of the kettle body 1; a functional kettle cover, the functional kettle cover is sealingly connected to the top cavity opening; a core base 2, the core base 2 is sealingly connected to the bottom cavity opening, and a through hole is formed axially in the middle of the core base 2; a core 3, which is arranged along the axis of the through hole of the base, the bottom end of the core 3 is sealingly connected inside the through hole of the base, and a core cap 4 is arranged at the top end of the core 3; a threaded lower plug 5, which is arranged at the bottom of the core base 2 and is threadedly connected to the through hole of the base, a threaded drain hole 51 is formed along the axis inside the threaded lower plug 5, and the top end of the threaded lower plug 5 abuts against the core 3.

[0029] Please continue to refer to Figure 2 , in some embodiments, a kettle body threaded portion may be formed on the inner peripheral wall of the top cavity opening, the functional kettle cover is threadedly connected to the kettle body threaded portion, and a kettle cover sealing ring 6 is arranged on the stepped surface of the functional kettle cover that cooperates with the stepped surface of the kettle body 1.

[0030] Please continue to refer to Figure 2 , in some embodiments, a core sealing ring 7 may be arranged between the core 3 and the core base 2, and a core base sealing ring 21 is arranged between the core base 2 and the bottom cavity opening.

[0031] Figure 2 The structure of the first embodiment of the kettle body device 200 according to the embodiment of the present invention is shown, wherein the functional kettle cover is a magnetic stirring kettle cover 81. Please refer to Figure 2 and Figure 3 , the functional kettle cover can be configured as a magnetic stirring kettle cover 81, and the magnetic stirring kettle cover 81 includes: a magnetic stirring system 811, the magnetic stirring system 811 is arranged inside the magnetic stirring kettle cover 81; a stirring rod 812, which is arranged along the axis of the magnetic stirring kettle cover 81, at the same time, one end of the stirring rod 812 is connected to the driving end of the magnetic stirring system 811, and the other end of the stirring rod 812 is rotatably connected to the core cap 4; and a rotating cylinder 813, the bottom of the cylinder of which is connected to the stirring rod 812, the cylinder opening of which is arranged downward, and the core 3 is arranged at intervals inside the rotating cylinder 813.

[0032] Figure 4 The structure of the second embodiment of the kettle body device 200 according to the embodiment of the present invention is shown, wherein the functional kettle cover is a cementation strength test kettle cover 82. Please refer to Figure 4 and Figure 6 , a circular vertical wall 814 may be formed at the edge of the top surface of the core base 2, the kettle body device 200 further includes a circular sleeve 815 and a bolt plug 816, the circular sleeve 815 is fitted and sleeved inside the circular vertical wall 814, and the bolt plug 816 is sealingly connected to the threaded drain hole 51.

[0033] Please continue to refer toFigure 4 and Figure 6 In some embodiments, a preset distance may be provided between the bottom of the core 3 and the top of the screw lower plug 5.

[0034] Please continue to refer to Figure 4 and Figure 6 In some embodiments, the functional kettle lid can be configured as a cement bond strength test kettle lid 82. The cement bond strength test kettle lid 82 may include: a hydraulic control system 821 disposed inside the cement bond strength test kettle lid 82; a test oil cylinder 822 disposed inside the cement bond strength test kettle lid 82 and connected to the hydraulic control system 821; and a force application rod 823, one end of the force application rod 823 is connected to the driving end of the test oil cylinder 822, and the other end of the force application rod 823 faces the core 3. Wherein, the test oil cylinder 822 can drive the force application rod 823 to move closer to and away from the core 3 under the control of the hydraulic control system 821.

[0035] Combined with Figures 1 to 5 As shown, according to the cement sheath second interface cement bond strength test method of the embodiment of the present invention, which is applied to the above cement sheath second interface cement bond strength test system 100, it includes a method for simulating the annulus return velocity of the downhole working fluid circulation. Among them, the formula for converting the drilling fluid annulus return velocity into the rotational speed of the rotating cylinder 813 in the method for simulating the annulus return velocity of the downhole working fluid circulation is:

[0036]

[0037] Wherein, R1 is the radius of the core 3, in mm; R2 is the inner radius of the rotating cylinder 813, in mm; N h is the device rotational speed, in r / min; D is the wellbore diameter, in m; d is the outer diameter of the casing, in m; τ y is the fluid shear stress, in Pa; n is the fluid flow behavior index; K is the fluid consistency coefficient, in Pa·s n ; V is the annulus return velocity, in m / s.

[0038] In some embodiments, the method for simulating the annulus return velocity of the downhole working fluid circulation includes a formula for converting the annulus return velocity of the flushing fluid into the rotational speed of the rotating cylinder 813:

[0039]

[0040] Wherein, R1 is the radius of the core 3, in mm; R2 is the inner radius of the rotating cylinder 813, in mm; N h is the device rotational speed, in r / min; D is the wellbore diameter, in m; d is the outer diameter of the casing, in m; V is the annulus return velocity, in m / s.

[0041] In some embodiments, the cement bond strength test in the cement sheath second interface cement bond strength test method is an in-situ temperature-bearing test.

[0042] As described above, when the cement sheath second interface bonding strength test system 100 according to the embodiments of the present invention is specifically used, it includes a mud cake formation stage, a mud cake flushing stage, a cement slurry curing stage, and a bonding test stage (please refer to Figure 5 ). The specific working principle is as follows:

[0043] (1) Mud cake formation stage: Combine Figure 1 and Figure 2 As shown, after fixing the core 3 on the core base 2, the whole is placed in the kettle body 1. Use the magnetic stirring kettle cover 81 to connect the magnetic stirring kettle cover 81 with the kettle body 1. Open the external air source, pressure regulating valve, working fluid valve (installed in the pipeline of the external water source), drilling fluid valve (installed in the pipeline of the drilling fluid storage tank), turn on the booster pump switch, pump pressure into the drilling fluid storage tank through the air source, and pump the drilling fluid into the kettle body 1. After the drilling fluid is pumped in, close the drilling fluid valve. Then pump pressure into the kettle body 1 through the external air source again, monitor the pressure in the kettle body 1 through the pressure sensor and pressure gauge. When the pressure in the kettle body 1 reaches the experimental value, close the working fluid valve, pressure regulating valve, and turn off the booster pump. Turn on the thermocouple, monitor the temperature in the kettle body 1 through the temperature sensor, and make the temperature reach the experimental value. After the temperature and pressure in the kettle body 1 reach the experimental values, start the magnetic stirring system 811 to start the mud cake formation experiment, and the mud cake formation time is t1. After the mud cake formation is completed, open the high-pressure release switch and the drain valve switch, drain the drilling fluid out of the kettle body 1 through the drain valve, and then close all the valves of the device.

[0044] (2) Mud cake flushing stage: Combine Figure 1 and Figure 2 As shown, open the external air source, pressure regulating valve, working fluid valve (installed in the pipeline of the external water source), flushing fluid valve (installed in the pipeline of the flushing fluid storage tank), turn on the booster pump switch, pump pressure into the flushing fluid storage tank through the air source, and pump the flushing fluid into the kettle body 1. After the flushing fluid is pumped in, close the flushing fluid valve. Then pump pressure into the kettle body 1 through the external air source again, observe the pressure sensor and pressure gauge. When the pressure in the kettle body 1 reaches the experimental value, close the working fluid valve, pressure regulating valve, and turn off the booster pump. Turn on the thermocouple, observe the temperature sensor, and make the temperature reach the experimental value. After the temperature and pressure in the kettle body 1 reach the experimental values, start the magnetic stirring system 811 to start the mud cake flushing experiment, and the mud cake flushing time is t2. After the mud cake flushing is completed, open the high-pressure release switch and the drain valve switch, drain the flushing fluid out of the kettle body 1 through the drain valve, and close all the valves of the device after draining.

[0045] (3) Cement slurry curing stage: Combine Figure 1 and Figure 4As shown, remove the magnetic stirring kettle cover 81, place the copper mold (ring sleeve 815) on the core base 2, pour the prepared cement slurry into the annulus between the copper mold (ring sleeve 815) and the core 3, and then cover the cementation strength test kettle cover 82. Open the water inlet valve and the working fluid valve, turn on the pneumatic liquid booster pump, pump the water source into the kettle body 1, observe the pressure values of the pressure sensor and the pressure gauge. After the pressure in the kettle body 1 reaches the cement slurry curing pressure, turn off the pneumatic liquid booster pump, the water inlet valve and the working fluid valve; at the same time, turn on the thermocouple, observe the temperature sensor. After the temperature in the kettle body 1 reaches the specified temperature, start the cement slurry curing for a time t3.

[0046] (4) Cementation test stage: Combine Figure 1 、 Figure 4 and Figure 5 As shown, after the cement slurry curing is completed, open the high-pressure release, drain the curing water in the kettle body 1, and then close the high-pressure release valve. Turn on the small hydraulic control system 821 on the cementation strength test kettle cover 82. The test oil cylinder 822 will push the piston to press down the force application rod 823. The force application rod 823 drives the core 3 to move downward, causing a shear displacement with the cement ring, and record the pressure value measured by the hydraulic control system 821.

[0047] In the cementation test stage, keep the downhole temperature and pressure in the kettle body 1 (temperature-bearing test). Rotate the external thread lower plug 5 outward to separate the lower end face of the core 3 by a certain distance. The cementation measuring oil cylinder of the cementation strength test kettle cover 82 is supplied with oil by the small hydraulic control system 821 to push the force application rod 823 to move downward, contact the upper end face of the core 3 and drive the core 3 to move downward to cause a shear action between the core 3 and the cement ring. The computer connected to the small hydraulic control system 821 records the change in the force application load of the force application rod 823, obtains the maximum pressure at the moment when the cementation interface between the core 3 and the cement ring is damaged, and finally obtains the shear cementation strength of the interface. This test method is the in-situ temperature-bearing test.

[0048] It should be noted that Figure 1 shows each control valve required above. Among them, the pressure relief pump control (two-way three-way valve), the pressure relief pump, and the drain valve are used for automatic pressure relief when the pressure in the kettle body 1 is overpressure.

[0049] According to the above settings, the cement sheath second interface bonding strength test system 100 and method of the embodiments of the present invention can correspond the construction displacement on site with the rotation speed of the rotating cylinder 813 of the device according to the temperature and pressure conditions downhole. At the same time, according to the annular return velocity of the working fluid on site and the wellbore structure, it can more accurately simulate the formation of mud cake on the wellbore wall during the drilling fluid circulation, the flushing of the mud cake by the preflush fluid circulation, and the in-situ measurement of the second interface bonding strength after the curing of the cement slurry, so that the measurement data of the second interface bonding strength is more reliable and accurate. Compared with the prior art, the cement sheath second interface bonding strength test system 100 and method of the embodiments of the present invention can more accurately reflect the formation and flushing process of the mud cake on the wellbore wall, and more accurately reflect the value of the second interface bonding strength. In addition, the cement sheath second interface bonding strength test system 100 of the embodiments of the present invention is simple to operate, the bonding data is more reasonable and accurate, and the device has more comprehensive functions. It can not only be used for measuring the second interface bonding strength, but also for evaluating the performance of the drilling fluid system and the flushing efficiency.

[0050] It should be noted that unless otherwise specified, the technical terms or scientific terms used in this application should have the ordinary meanings understood by those skilled in the art to which the present invention belongs.

[0051] In the description of this application, it should be understood that the orientation or positional relationships indicated by the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. are based on the orientation or positional relationships shown in the drawings. They are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation to the present invention.

[0052] In addition, the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. In the description of the present invention, the meaning of "a plurality" is two or more unless otherwise specifically defined.

[0053] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the various embodiments of the present invention, and they should all be covered within the scope of the claims and the specification of the present invention. In particular, as long as there is no structural conflict, the technical features mentioned in each embodiment can be combined in any way. The present invention is not limited to the specific embodiments disclosed in the text, but includes all technical solutions falling within the scope of the claims.

Claims

1. A testing system for the bonding strength of the second interface of a cement sheath in well cementing, characterized in that, Comprising: A kettle body device, the bottom of the kettle body device is connected with a drain valve through a drain pipeline, and a first input pipeline and a second input pipeline are arranged on the kettle body device; A liquid storage tank, the liquid storage tank includes a flushing liquid storage tank and a drilling fluid storage tank, the first input pipeline is connected to the output end of the liquid storage tank, and the input end of the liquid storage tank and the second input pipeline are connected to an external water source and a gas source through a pneumatic liquid booster valve; and, A temperature control system, which is arranged on the kettle body device, and the temperature control system includes a thermocouple and a temperature sensor.

2. The testing system for the bonding strength of the second interface of a cement sheath in well cementing according to claim 1, characterized in that, The kettle body device includes: A kettle body, a cavity is formed inside the kettle body, a top cavity opening is formed in the upper part of the kettle body, and a bottom cavity opening is formed in the lower part of the kettle body; A functional kettle cover, the functional kettle cover is sealingly connected to the top cavity opening; A core base, the core base is sealingly connected to the bottom cavity opening, and an axially penetrating base through hole is formed in the middle of the core base; A core, which is arranged along the axis of the base through hole, the bottom end of the core is sealingly connected inside the base through hole, and a core cap is arranged at the top end of the core; A threaded lower plug, which is arranged at the bottom of the core base and is threadedly connected to the base through hole, a threaded drain hole is formed along the axis inside the threaded lower plug, and the top end of the threaded lower plug abuts against the core.

3. The testing system for the bonding strength of the second interface of a cement sheath in well cementing according to claim 2, characterized in that, The inner peripheral wall of the top cavity opening forms a kettle body thread part, the functional kettle cover is threadedly connected to the kettle body thread part, and a kettle cover sealing ring is arranged on the stepped surface of the functional kettle cover that cooperates with the kettle body.

4. The testing system for the bonding strength of the second interface of a cement sheath in well cementing according to claim 2, characterized in that, A core sealing ring is arranged between the core and the core base, and a core base sealing ring is arranged between the core base and the bottom cavity opening.

5. The testing system for the bonding strength of the second interface of a cement sheath in well cementing according to any one of claims 2 to 4, characterized in that, The functional kettle cover is configured as a magnetic stirring kettle cover, and the magnetic stirring kettle cover includes: A magnetic stirring system, the magnetic stirring system is arranged inside the magnetic stirring kettle cover; A stirring rod, which is arranged along the axis of the magnetic stirring kettle cover. At the same time, one end of the stirring rod is connected to the driving end of the magnetic stirring system, and the other end of the stirring rod is rotatably connected to the core cap; and, A rotating cylinder, the bottom of the cylinder is connected to the stirring rod, the cylinder mouth is arranged downward, and the core is arranged at intervals inside the rotating cylinder.

6. The testing system for the bonding strength of the second interface of a cement sheath in well cementing according to any one of claims 2 to 4, characterized in that, A ring-shaped vertical wall is formed at the top surface edge of the core base. The kettle body device further includes a ring-shaped sleeve and a bolt plug. The ring-shaped sleeve is fitted and sleeved inside the ring-shaped vertical wall, and the bolt plug is sealingly connected to the threaded drain hole.

7. The testing system for the bonding strength of the second interface of a cement sheath in well cementing according to claim 6, characterized in that, The functional kettle cover is configured as a cementation strength test kettle cover, and the cementation strength test kettle cover includes: A hydraulic control system, the hydraulic control system is arranged inside the cementation strength test kettle cover; A test oil cylinder, the test oil cylinder is arranged inside the cementation strength test kettle cover and is connected to the hydraulic control system; and, A force application rod, one end of the force application rod is connected to the driving end of the test oil cylinder, and the other end of the force application rod faces the core. Among them, the test oil cylinder can drive the force application rod to move closer to and away from the core under the control of the hydraulic control system.

8. A testing method for the bonding strength of the second interface of a cement sheath in well cementing, applied to the testing system for the bonding strength of the second interface of a cement sheath in well cementing according to any one of claims 1 to 7, characterized in that, A method for simulating the annular return velocity of downhole working fluid is provided. Among them, the formula for converting the annular return velocity of drilling fluid into the rotational speed of the rotating cylinder in the method for simulating the annular return velocity of downhole working fluid is as follows: Among them, R1 is the core radius, in mm; R2 is the inner radius of the rotating cylinder, in mm; N h is the rotational speed of the device, in r / min; D is the wellbore diameter, in m; d is the outer diameter of the casing, in m; τ y is the fluid shear stress, in Pa; n is the fluid flow behavior index; K is the fluid consistency coefficient, in Pa·s n ; V is the annular return velocity, in m / s.

9. The testing method for the bonding strength of the second interface of a cement sheath in well cementing according to claim 8, characterized in that, The method for simulating the annular return velocity of downhole working fluid includes a formula for converting the annular return velocity of the flushing fluid into the rotational speed of the rotating cylinder: Among them, R1 is the core radius, in mm; R2 is the inner radius of the rotating cylinder, in mm; N h is the rotational speed of the device, in r / min; D is the wellbore diameter, in m; d is the outer diameter of the casing, in m; V is the annular return velocity, in m / s.

10. The method for testing the bonding strength of the second interface of the cement sheath in well cementing according to claim 8, characterized in that, The cement bond strength test in the method for testing the cement bond strength at the second interface of the cement sheath is an in-situ temperature-bearing test.

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