Device and method for measuring shear bonding strength of cement sheath interface

Abstract

The invention discloses a device and a method for determining the shear bonding strength of a cement sheath interface, and belongs to the field of petroleum and natural gas well cementation. The device comprises a kettle body, a simulation sleeve, a simulation surrounding rock, a lower bottom plate, an upper cover plate, a first interface measurement cushion cylinder, a second interface measurement cushion cylinder, a first interface measurement pressing block, a second interface measurement pressing block, a hydraulic pump, a heating insulation sleeve and a temperature control system. The method comprises the steps that cement paste is poured into a simulated annulus, and the cement paste is maintained for preset time; respectively placing a first interface measurement cushion cylinder and a second interface measurement cushion cylinder on a pressure testing machine, turning over the kettle body by 180 degrees and then placing the kettle body on the cushion cylinders, respectively placing a first interface measurement pressing block and a second interface measurement pressing block at the top end of the simulation sleeve or the cement sheath, and starting the pressure testing machine to slowly apply pressure to obtain peak pressure for pushing the simulation sleeve from the cement sheath or pushing the cement sheath from the simulation surrounding rock; and calculating the shear bonding strength of the cement sheath interface. The method accords with the actual working condition, and the cementing performance and the cementing quality of the first and second interfaces of the well cementation can be accurately evaluated.

Description

Technical Field

[0001] The invention belongs to the field of oil and natural gas cementing, and in particular relates to a device and method for measuring the shear bonding strength of a cement sheath interface. Background Art

[0002] For oil and gas well cementing and completion projects, the bonding surface between the casing and the cement sheath is usually called the cementing interface I, and the bonding surface between the cement sheath and the formation is called the cementing interface II.

[0003] Accurately evaluating the bonding performance of the first and second interfaces of cementing and optimizing the cementing slurry formula with the best sealing effect, thereby improving oil and gas recovery, has great economic value and practical significance.

[0004] At present, there are three main methods to characterize the bonding performance of cement sheath, namely measuring and calculating the shear bonding strength of cement sheath, the hydraulic bonding strength of cement sheath and the radial bonding strength of cement sheath.

[0005] Shear bond strength refers to the ratio of the force required to make the casing or cement ring in the wellbore move longitudinally to the surface area of ​​the outer wall of the casing or the outer wall of the cement ring, that is, shear bond strength = shear force / contact area, which plays a supporting role in the casing suspension.

[0006] Hydraulic bond strength refers to the ability of the cement sheath and casing or formation interface to prevent fluid from passing through, reflecting the ability of the cement sheath to isolate oil, gas and water layers.

[0007] The radial bond strength refers to the ratio of the force required to radially separate the casing from the cement ring or the cement ring from the formation after the cement ring is bonded to the casing or formation to the corresponding bonding area, that is, radial bond strength = force required for radial pull-off / bonding area, which reflects the degree of firmness of the cement ring's radial bonding with the casing and formation.

[0008] Years of practice have shown that among the three types of bond strength, the interface shear bond strength between cement sheath and formation and casing is relatively simple to measure and the measurement results are more reliable, so it is used more frequently.

[0009] In terms of the determination of the shear bond strength of an interface, it is usually carried out by curing the cementing cylinder (or simulated casing) containing cement slurry. After curing, the cement stone formed by the solidification of the cement slurry is pushed out (or pressed out) using equipment such as a pressure tester, and the maximum force at the moment of pushing (or pressing out) is recorded. Then, combined with the bonding area of ​​the inner wall of the cementing cylinder (or simulated casing), the shear bond strength of an interface is calculated. The "cementing interface bond strength test device" (CN205280557U) has a relatively simple structure and is easy to operate; the "cementing cement bond strength test device and method" (CN105092465A) can simulate the effect of the casing surface roughness on the shear bond strength of an interface. However, the positional relationship between the cement slurry and the casing of both is opposite to the actual situation, and it is impossible to explore the effect of the pressure change in the casing and the thickness of the cement ring on the shear bond strength of an interface. "An experimental device and method for testing the bonding strength between cement ring and casing" (CN106593414A) simulates the geological environment of the formation and cementing working conditions, and tests the effects of cement ring curing time and different casing roughness on the shear bonding strength of an interface by changing the cement ring curing time and casing roughness. However, the device involves multiple components, has high maintenance costs, and is relatively complicated to operate.

[0010] In terms of the determination of the shear bond strength of the two interfaces, the "Test method for shear strength of cement sheath and formation interface in non-uniform geostress cementing" (CN114047082A) prepares a cylindrical specimen of a "cement-core" assembly, places it on a true triaxial rock press, applies different levels of geostress to a preset value at a certain rate, and then slowly applies an axial load. The peak load value is recorded, and the shear bond strength of the two interfaces is calculated using the ratio of the peak load value to the bonding area. This method can explore the shear strength of the two interfaces of cementing under different cement sheath thicknesses and non-uniform geostress. However, the position of the cement and the core during the measurement does not match the actual situation of cementing, and it is also impossible to explore the effect of changes in casing internal pressure on the shear bond strength of the two interfaces. "A device and method for testing the shear bond strength of the interface between cement sheath and brittle formation in oil and gas wells" (CN111456715A) determines the internal friction angle and the angle between the failure surface and the maximum principal stress surface through triaxial mechanical compression experiments on brittle rocks, prepares specific cylindrical cores and casts cement slurry for curing to form composite specimens, applies uniaxial compression loads after fixation to record the peak pressure, and calculates the shear bond strength of the second interface in combination with the geometric parameters of the elliptical interface. However, it focuses on the determination of the shear bond strength of the second interface of brittle rocks (such as shale), which can reduce the risk of damaging the core and cement sheath when measuring the shear bond strength by the "extrusion method", but cannot simulate the actual internal and external relationship between the formation and cement sheath in the actual cementing operation, nor can it explore the influence of the pressure inside the casing and the wall thickness of the cement sheath on the shear bond strength of the second interface.

[0011] Only by measuring the shear bond strength of the first and second interfaces at the same time can the sealing and cementing quality of the cement sheath be more comprehensively evaluated. "A cement cement bond strength testing device" (CN105422080A) forms an annular space between the trapezoidal casing and the core, injects a cement sample for curing, and then tests the pressure of the cement sheath when it is peeled off from the casing and the core on a pressure testing machine to obtain the shear bond strength of the first and second interfaces. The operation is simple, and the internal oblique parallel cement ring structure is easy to mold. However, due to the oblique parallel cement ring structure, the device needs to indirectly calculate the shear force, which has a large calculation error, and the position of the casing and cement ring does not match the actual operation. It is impossible to explore the impact of the change in casing internal pressure on the first interface bond strength, nor the impact of different cement ring wall thicknesses on the shear bond strength of the first and second interfaces of cementing. Summary of the invention

[0012] The purpose of the present invention is to provide a cement sheath interface shear bonding strength measuring device, which has novel structural design and is easy to operate. It can test the shear bonding strength between cement sheath and casing, and cement sheath and surrounding rock at room temperature and pressure, which is more in line with the actual working conditions on site, and can more accurately evaluate the bonding performance of the first and second interfaces of cementing and the cementing quality. At the same time, the influence of pressure changes in the casing, different surface roughness of the casing and cement sheath thickness on the shear bonding strength can be considered.

[0013] Another object of the present invention is to provide a method for measuring the shear bond strength of the cement sheath interface using the above-mentioned device. The method has a reliable principle, a controllable process, and accurate results. It can simultaneously take into account the maintenance of the first and second interfaces and the measurement of the shear bond strength, and can achieve multiple groups of measurements under conditions of different casing internal pressures, different casing surface roughnesses, different cement sheaths and surrounding rocks and their thicknesses, thereby shortening the experimental process and time and effectively reducing the experimental cost.

[0014] In order to achieve the above technical objectives, the present invention adopts the following technical solutions.

[0015] A cement ring interface shear bonding strength measuring device comprises a kettle body, a simulated casing, a simulated surrounding rock, a lower bottom plate supporting the simulated casing and the simulated surrounding rock, an upper cover plate pressing the simulated casing and the simulated surrounding rock, fastening bolts, sealing gaskets, simulated casing pressure / pressure relief pipelines and valves, simulated annulus pressure / pressure relief pipelines and valves, confining pressure chamber pressure / pressure relief pipelines and valves, a first interface measuring cushion cylinder, a second interface measuring cushion cylinder, a first interface measuring pressure block and a second interface measuring pressure block.

[0016] The kettle body is a hollow thick-walled steel cylinder with openings at both ends and internal threads provided on the upper and lower end faces. It is connected to the lower base plate and the upper cover plate by bolts to form an inner cavity for placing simulated casing and simulated surrounding rock. The outer wall of the kettle body is provided with a heating and insulation sleeve connected to the temperature control system.

[0017] The lower base plate is composed of a small-diameter inner circular steel plate with an upper boss, a corresponding hollow large-diameter outer circular steel plate with a lower groove, and fastening bolts. The two are connected by fastening bolts to form a circular plate with a diameter close to the outer diameter of the kettle body, and then connected to the kettle body by fastening bolts to form an inner cavity for accommodating simulated casing and simulated surrounding rock. At the same time, an annular sealing gasket is provided at the fitting surface of the two to achieve sealing between the two.

[0018] The simulation casing is a closed steel cylinder with the same height as the inner cavity of the kettle body, located in the center of the kettle body, and has a liquid inlet pressure / liquid discharge pressure relief port on the upper end surface, which is connected to the hydraulic pump through a pipeline. The pressure of the simulation casing is adjusted by pressure relief.

[0019] The simulated surrounding rock is an annular permeable rock ring with the same height as the inner cavity of the kettle body, which is used to simulate the underground strata and is located outside the simulated casing; a simulated annulus is formed between the simulated surrounding rock and the simulated casing, which is used to hold cement slurry and cement stone formed after solidification; a confining pressure chamber is formed between the simulated surrounding rock and the inner wall of the kettle body, which is used to provide confining pressure by liquid injection to prevent the simulated surrounding rock from breaking due to excessive pressure difference on both sides.

[0020] The upper cover plate is similar in structure to the lower base plate, except that a hole is provided at its center for the liquid inlet pressure / liquid discharge pressure relief port on the upper end face of the simulated casing to extend out; after being connected to the kettle body by bolts, the simulated casing and simulated surrounding rock are pressed to prevent the simulated casing and simulated surrounding rock from moving.

[0021] The upper cover plate is provided with a liquid inlet pressure injection / liquid discharge pressure relief port at the corresponding position between the confining pressure chamber and the simulated annulus, which is connected to the hydraulic pump through a pipeline to pressurize and relieve the pressure of the confining pressure chamber and the simulated annulus, and adjust the pressure of the confining pressure chamber and the simulated annulus.

[0022] The inner circular steel plates of the upper cover plate and the lower bottom plate have a diameter slightly larger than the inner diameter of the surrounding rock, so that after the cement slurry solidifies and the inner circular steel plates of the upper cover plate and the lower bottom plate are removed, the upper and lower end faces of the cement ring are fully exposed, so that pressure is applied on the end faces to push it out of the surrounding rock.

[0023] The sealing gaskets include simulated casing sealing gaskets and simulated surrounding rock sealing gaskets, which are placed on the upper and lower end faces of the simulated casing and the simulated surrounding rock respectively. After the upper cover plate and the lower base plate are compressed, the upper and lower end faces of the simulated casing and the simulated surrounding rock are sealed to prevent the pressure between the simulated annulus and the confining pressure chamber from passing through.

[0024] The pressure / pressure relief pipelines and valves of the simulated casing, simulated annulus, and confining pressure chamber can be connected to the pressure relief system to pressurize and relieve the simulated casing, simulated annulus, and confining pressure chamber, adjust the pressure therein, and measure the interface shear bond strength under corresponding conditions to study the influence of relevant factors on the interface shear bond strength.

[0025] The first interface measurement pad tube or the second interface measurement pad tube is a thick-walled steel tube with an opening at the upper end and two symmetrical notches on the upper end surface. When measuring the shear bonding strength of the first interface or the second interface, it is placed on the pressure testing machine to support the cement ring in the inverted kettle body or the upper end surface of the simulated surrounding rock, and the connecting pipeline of the pressure / pressure relief port of the simulated casing is led out through the notch. Among them, the inner diameter of the first interface measurement pad tube should be slightly larger than the outer diameter of the simulated casing and smaller than the outer diameter of the cement ring, and the inner diameter of the second interface measurement pad tube should be slightly larger than the outer diameter of the cement ring and smaller than the outer diameter of the inner circular steel plate of the upper cover plate.

[0026] The one-interface measurement block or the two-interface measurement block is placed on the lower end face of the simulated casing or cement ring in the inverted kettle body when measuring the bonding strength of the one-interface or the two-interface, and the simulated casing or cement ring is pushed out by transmitting the downward pressure of the pressure testing machine, and the pressure required to push the simulated casing out of the cement ring or the cement ring out of the simulated surrounding rock is obtained. Among them, the one-interface measurement block is a thick-walled hollow steel cylinder, and its outer diameter is slightly smaller than the outer diameter of the simulated casing, and the two-interface measurement block is a round steel block with an open upper end and a cylindrical groove in the center, and the inner diameter of the groove is slightly larger than the outer diameter of the simulated casing, and the outer diameter of the steel block is slightly smaller than the inner diameter of the simulated surrounding rock.

[0027] The method for measuring the shear bond strength of the cement sheath interface using the above device comprises the following steps in sequence:

[0028] 1) Place a simulated casing filled with clean water and simulated surrounding rock saturated with clean water on the sealing gasket of the lower bottom plate;

[0029] 2) Pour the prepared cement slurry into the simulated annulus, with the top surface 1-2mm away from the upper end surface of the simulated casing;

[0030] 3) Pour simulated formation water into the confining pressure chamber, with the top surface 1-2 mm away from the upper end surface of the simulated surrounding rock;

[0031] 4) Connect the upper cover plate to the kettle body through fastening bolts, start the hydraulic pump, and apply the set initial pressure through the connecting pipelines of the simulated casing, simulated annulus, and the liquid inlet pressure relief port / liquid discharge pressure relief port of the confining pressure chamber;

[0032] 5) Start the temperature control system, heat and insulate the kettle body, adjust the pressure of the simulated casing, simulated annulus, and confining pressure chamber, ensure that the cement slurry solidifies at the set temperature and pressure, and after curing the cement slurry for a predetermined time, turn off the temperature control system, and release the pressure in the simulated annulus and confining pressure chamber to zero after the temperature drops to room temperature or the set temperature;

[0033] 6) Place an interface measurement cushion cylinder on the pressure testing machine, remove the inner circular steel plates of the lower bottom plate and the upper cover plate, turn the kettle body 180° and place it on the cushion cylinder, and lead the connecting pipeline of the liquid inlet pressure test / liquid discharge pressure relief port of the simulated casing through the notch of the cushion cylinder;

[0034] 7) Place an interface measurement block at the top of the simulated casing, adjust the pressure in the simulated casing by a hydraulic pump as needed, start the pressure tester and slowly apply pressure to obtain the peak pressure that pushes the simulated casing out of the cement sheath;

[0035] 8) Remove the kettle body and the first interface measurement cushion cylinder from the pressure testing machine; place the second interface measurement cushion cylinder on the pressure testing machine, place the kettle body turned 180° on the cushion cylinder, place the second interface measurement block on the top of the cement sheath, adjust the pressure in the simulated casing as needed, start the pressure testing machine and slowly apply pressure to obtain the peak pressure that pushes the cement sheath out of the simulated surrounding rock;

[0036] 9) Calculate the shear bond strength between the cement sheath and simulated casing, and between the cement sheath and simulated surrounding rock.

[0037] Furthermore, the simulated surrounding rocks with different wall thicknesses were replaced and the above steps were repeated to obtain the first and second interface shear bonding strengths under different cement sheath wall thicknesses.

[0038] Furthermore, the simulated casing with different surface roughness is replaced, and the above steps are repeated to obtain the first and second interface shear bonding strengths of the simulated casing under different surface roughness conditions.

[0039] Furthermore, by comparing the shear bond strength of the first and second interfaces under different cement sheath wall thicknesses or simulated casing surface roughness conditions, the variation law of the shear bond strength of the first and second interfaces is analyzed.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] 1) It can simulate the first and second interfaces of cementing at the same time and measure the shear bonding strength of the first and second interfaces of cementing at one time;

[0042] 2) By designing the internal and external dimension relationship of the confining pressure chamber, surrounding rock, cement sheath and simulated casing, the real internal and external relationship of the formation, cement sheath and casing in the actual cementing operation is simulated, so that the measurement results are more consistent with the actual situation downhole;

[0043] 3) By setting up a confining pressure chamber and providing confining pressure to support the surrounding rock, it is possible to avoid the situation where the surrounding rock and cement stone are broken due to lack of support when the pressure in the casing increases significantly, thereby affecting the measurement of the shear bond strength of the first and second interfaces of cementing;

[0044] 4) By adjusting the inner and outer diameters of the surrounding rock and the wall thickness of the cement sheath, the influence of different cement sheath wall thicknesses on the shear bonding strength of the first and second cementing interfaces was studied, avoiding the shortcoming that a single-size device can only test the cementing interface bonding strength of a cement sheath of one thickness, thus expanding the practicality of the device;

[0045] 5) The pressure inside the simulated casing is adjusted by the hydraulic pump system to explore the effect of the pressure change inside the casing on the shear bonding strength of the first and second interfaces of cementing;

[0046] 6) Experiments were conducted using casings with different surface roughness to explore the effect of casing surface roughness on the shear bond strength of the cementing interface. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 This is a schematic diagram of the kettle structure of the cement shear ring interface shear bond strength testing device.

[0048] Figure 2 (a) and (b) are schematic diagrams of the structure of the first and second interface measurement pad cylinders of the measuring device, respectively.

[0049] Figure 3 (a) and (b) are schematic diagrams of the first and second interface measurement blocks of the measuring device, respectively.

[0050] In the figure: 1-kettle body, 2-lower bottom plate, 201-outer circular steel plate, 202-inner circular steel plate, 203, 301, 302, 401, 402, 503-sealing gaskets, 3-simulated casing, 4-simulated surrounding rock, 5-upper cover plate, 501-outer circular steel plate, 502-inner circular steel plate, 6-valve, 7-fastening bolts, 8-simulated casing pressure / pressure relief connecting pipeline, 9-simulated annulus pressure / pressure relief connecting pipeline, 10-confining pressure chamber pressure / pressure relief connecting pipeline, 11-first interface measurement pad cylinder, 12-second interface measurement pad cylinder, 13-first interface measurement pressure block, 14-second interface measurement pressure block. DETAILED DESCRIPTION

[0051] The present invention is further described below with reference to the accompanying drawings and examples, so that those skilled in the art can understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific embodiments, and for those skilled in the art, as long as various changes are within the spirit and scope of the present invention defined and determined by the attached claims, they are all protected.

[0052] See also Figure 1 , Figure 2 , Figure 3 .

[0053] A cement sheath interface shear bonding strength measuring device comprises a kettle body 1, a simulated casing 3, a simulated surrounding rock 4, a lower base plate 2, an upper cover plate 5, a first interface measurement cushion cylinder 11, a second interface measurement cushion cylinder 12, a first interface measurement pressure block 13, a second interface measurement pressure block 14, a hydraulic pump, a heating and insulation sleeve and a temperature control system.

[0054] The kettle body 1 is a hollow thick-walled steel cylinder with openings at both ends, connected to the lower bottom plate 2 and the upper cover plate 5 by fastening bolts 7, forming an inner cavity for placing a simulated casing 3 and a simulated surrounding rock 4, and a heating and heat-insulating sleeve is provided on the outer wall of the kettle body to connect the temperature control system; the lower bottom plate 2 includes a small-diameter inner circular steel plate 202 with an upper boss and a correspondingly fitted hollow large-diameter outer circular steel plate 201 with a lower groove, which are connected by fastening bolts to form a circular plate with a diameter close to the outer diameter of the kettle body, and a sealing gasket 203 is provided on the fitting surface of the two; The simulated casing 3 is located at the center of the lower bottom plate, the simulated surrounding rock 4 is located outside the simulated casing, a simulated annulus is formed between the simulated casing and the simulated surrounding rock, and a confining pressure chamber is formed between the simulated surrounding rock and the inner wall of the kettle body. The upper end surfaces of the simulated casing, the simulated annulus and the confining pressure chamber are all provided with liquid inlet pressure relief / liquid discharge pressure relief ports, which are respectively connected to the hydraulic pump through connecting pipelines 8, 9, 10, and a valve 6 is arranged on the connecting pipeline; the upper cover plate 5 has the same structure as the lower bottom plate, and includes a small diameter inner circular steel plate 50 with an upper boss 2 and a correspondingly fitted hollow outer circular steel plate 501 with a lower groove are connected by fastening bolts to form a circular plate with a diameter close to the outer diameter of the kettle body. A sealing gasket 503 is provided on the fitting surface of the two, and corresponding holes are provided at the positions corresponding to the liquid inlet pressure / liquid discharge pressure relief ports of the upper cover plate, the simulated casing, the simulated annulus and the confining pressure chamber; the first interface measurement pad cylinder 11 or the second interface measurement pad cylinder 12 is a thick-walled steel cylinder with an upper opening and two symmetrical notches on the upper end surface, which is used to measure the shear of the first interface or the second interface. When measuring the bonding strength, they are placed on a pressure testing machine to support the cement ring or simulated surrounding rock in the inverted kettle body, and the connecting pipeline of the pressure / pressure relief port of the simulated casing is led out through the notch; the first interface measurement block 13 or the second interface measurement block 14 are respectively placed on the top of the simulated casing or cement ring in the inverted kettle body, and the simulated casing or cement ring is pushed out by transmitting the downward pressure of the pressure testing machine, and the pressure required to push the simulated casing out of the cement ring or the cement ring out of the simulated surrounding rock is obtained.

[0055] Furthermore, sealing gaskets 301 and 302 are provided at the contact positions between the upper cover plate, the lower bottom plate and the simulated casing, and sealing gaskets 401 and 402 are provided at the contact positions between the upper cover plate, the lower bottom plate and the simulated surrounding rock, thereby achieving sealing of the upper and lower end faces of the simulated casing and the simulated surrounding rock, and preventing pressure from passing through between the simulated annulus and the confining pressure chamber.

[0056] Furthermore, the diameter of the inner circular steel plates of the upper cover plate and the lower bottom plate is slightly larger than the inner diameter of the simulated surrounding rock, so that after the cement slurry solidifies and the inner circular steel plates of the upper cover plate and the lower bottom plate are removed, the end face of the cement ring can be fully exposed, and pressure can be applied on its end face to push it out of the simulated surrounding rock.

[0057] Furthermore, the inner diameter of the first interface measurement gasket tube should be slightly larger than the outer diameter of the simulated casing and smaller than the outer diameter of the cement ring; the inner diameter of the second interface measurement gasket tube should be slightly larger than the outer diameter of the cement ring and smaller than the outer diameter of the inner circular steel plate of the upper cover plate.

[0058] Furthermore, the first interface measurement block is a thick-walled hollow steel cylinder, whose outer diameter is slightly smaller than the outer diameter of the simulated casing, and the second interface measurement block is a circular steel block with an open upper end and a cylindrical groove in the center, whose inner diameter is slightly larger than the outer diameter of the simulated casing, and the outer diameter of the steel block is slightly smaller than the inner diameter of the simulated surrounding rock.

[0059] The above device is used to measure the shear bond strength of the cement sheath interface. The specific process is as follows:

[0060] 1) Place the sealing gasket, inner steel plate and outer steel plate on the inverted lower bottom plate, fasten them with fastening bolts to form a complete lower bottom plate, assemble the complete upper cover plate in the same way, then evenly apply a thin layer of sealing grease on the upper end surface of the lower bottom plate and the lower end surface of the upper cover plate, and connect the lower bottom plate to the kettle body with bolts;

[0061] 2) Place the lower end sealing gaskets of the simulated casing and the simulated surrounding rock at the predetermined positions on the lower base plate;

[0062] 3) Place a simulated casing filled with clean water and simulated surrounding rock saturated with clean water on the corresponding sealing gasket;

[0063] 4) Pour the prepared cement slurry into the simulated annulus, with the top surface 1-2mm away from the upper end surface of the simulated casing;

[0064] 5) Pour simulated formation water into the confining pressure chamber, with the top surface 1-2 mm away from the upper end surface of the simulated surrounding rock;

[0065] 6) Place sealing gaskets on the simulated surrounding rock and simulated casing, and connect the upper cover plate to the kettle body by fastening bolts;

[0066] 7) Connect the pipelines of the simulated casing, simulated annulus, and confining pressure chamber to the liquid inlet / liquid discharge pressure relief ports, and apply the set initial pressure to them through a hydraulic pump;

[0067] 8) Start the temperature control system to heat and insulate the kettle, and timely observe and adjust the pressure of the simulated casing, simulated annulus, and confining pressure chamber to ensure that the cement slurry solidifies at the set temperature and pressure;

[0068] 9) After the cement slurry is cured for a predetermined time, the temperature control system is turned off, and after the temperature drops to room temperature or the set temperature, the pressure in the simulated annulus and confining pressure chamber is released to zero;

[0069] 10) Place an interface measurement cushion cylinder on the pressure testing machine with the notch of the cushion cylinder facing up, remove the inner circular steel plates of the lower bottom plate and the upper cover plate, turn the kettle body 180° and place it on the cushion cylinder, and lead the connecting pipeline of the liquid inlet pressure test / liquid discharge pressure relief port of the simulated casing through the notch on the cushion cylinder;

[0070] 11) Place an interface measurement block at the center of the top of the simulated casing, adjust the pressure in the simulated casing by a hydraulic pump as needed, then start the pressure tester to slowly apply pressure, test and obtain the peak pressure that pushes the simulated casing out of the cement sheath;

[0071] 12) Remove the kettle body and the first interface measurement cushion cylinder from the pressure testing machine; place the second interface measurement cushion cylinder on the pressure testing machine, and place the kettle body upside down on it; place the second interface measurement block at the center of the top of the cement sheath, adjust the pressure in the simulated casing as needed, and then start the pressure testing machine to slowly apply pressure, test and obtain the peak pressure that pushes the cement sheath out of the simulated surrounding rock;

[0072] 13) Calculate the shear bond strength between the cement sheath and the simulated casing, and between the cement sheath and the simulated surrounding rock, that is, the shear bond strength of the first and second interfaces:

[0073] Interface shear bond strength A1=πd1h;

[0074] Two-interface shear bond strength A2=πd2h

[0075] Where P1 is the interfacial shear bond strength, kPa;

[0076] P2 is the shear bond strength of the two interfaces, kPa;

[0077] F1 is the peak pressure at the moment when the simulated casing is separated from the cement sheath, kN;

[0078] F2 is the peak pressure at the moment when the cement sheath separates from the simulated surrounding rock, kN;

[0079] A1 is the contact area between the simulated casing and cement sheath, m 2 ;

[0080] A2 simulates the contact area between surrounding rock and cement sheath, m 2 ;

[0081] d1 is the inner diameter of cement sheath, m;

[0082] d2 is the inner diameter of the simulated surrounding rock, m;

[0083] h is the height of the cement ring, m.

[0084] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not limitations of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made on the basis of the above description. All obvious changes or modifications derived from the technical solution of the present invention are still within the scope of protection of the present invention.

Claims

1. A cement sheath interface shear bond strength measuring device, comprising a kettle (1), a simulated casing (3), a simulated surrounding rock (4), a lower base plate (2), an upper cover plate (5), a first interface measurement cushion cylinder (11), a second interface measurement cushion cylinder (12), a first interface measurement pressure block (13), a second interface measurement pressure block (14), a hydraulic pump, a heating and insulation sleeve and a temperature control system, characterized in that: The kettle body (1) is a hollow thick-walled steel cylinder with openings at both ends, and is connected to the lower bottom plate (2) and the upper cover plate (5) by fastening bolts, forming an inner cavity for placing a simulated casing (3) and simulated surrounding rock (4). The outer wall of the kettle body is provided with a heating and heat-insulating sleeve connected to the temperature control system; the lower bottom plate (2) comprises a small-diameter inner circular steel plate (202) with an upper boss and a correspondingly fitted hollow large-diameter outer circular steel plate (201) with a lower groove, which are connected by fastening bolts to form a circular plate with a diameter close to the outer diameter of the kettle body, and a sealing gasket is provided on the fitting surface of the two; the simulated casing (3) is located at the center of the lower bottom plate, and the simulated surrounding rock (4) is located outside the simulated casing, a simulated annulus is formed between the simulated casing and the simulated surrounding rock, and a confining pressure chamber is formed between the simulated surrounding rock and the inner wall of the kettle body, and the upper end surfaces of the simulated casing, the simulated annulus and the confining pressure chamber are all provided with liquid inlet pressure relief / liquid discharge pressure relief ports, which are respectively connected to the hydraulic pump through connecting pipelines. , a valve is arranged on the connecting pipeline; the structure of the upper cover plate (5) is the same as that of the lower bottom plate, and corresponding holes are arranged at positions corresponding to the upper cover plate and the liquid inlet pressure relief / liquid discharge pressure relief ports of the simulated casing, the simulated annulus and the confining pressure chamber; the first interface measurement cushion cylinder (11) or the second interface measurement cushion cylinder (12) is a thick-walled steel cylinder with an upper opening and two symmetrical notches arranged on the upper end surface. When measuring the shear bonding strength of the first interface or the second interface, it is placed on the pressure testing machine to support the cement ring or simulated surrounding rock in the inverted kettle body, and the connecting pipeline of the liquid inlet pressure relief / liquid discharge pressure relief port of the simulated casing is led out through the notch; the first interface measurement pressure block (13) or the second interface measurement pressure block (14) is placed on the top of the simulated casing or the cement ring, and the simulated casing or the cement ring is pushed out by transmitting the downward pressure of the pressure testing machine, and the pressure required to push the simulated casing out of the cement ring or the cement ring out of the simulated surrounding rock is obtained.

2. A cement sheath interface shear bond strength measuring device as claimed in claim 1, characterized in that: Sealing gaskets are provided at the contact positions between the upper cover plate, the lower bottom plate, the simulated casing and the simulated surrounding rock to seal the upper and lower end faces of the simulated casing and the simulated surrounding rock and prevent pressure from flowing between the simulated annulus and the confining pressure chamber.

3. A cement sheath interface shear bond strength measuring device as claimed in claim 1, characterized in that: The inner circular steel plates of the upper cover plate and the lower bottom plate have a diameter slightly larger than the inner diameter of the simulated surrounding rock, so that after the cement slurry solidifies and the inner circular steel plates of the upper cover plate and the lower bottom plate are removed, the end face of the cement ring can be fully exposed and pressurized on its end face to push it out of the simulated surrounding rock.

4. A cement sheath interface shear bond strength measuring device as claimed in claim 1, characterized in that: The inner diameter of the first interface measurement pad tube should be slightly larger than the outer diameter of the simulated casing and smaller than the outer diameter of the cement ring; the inner diameter of the second interface measurement pad tube should be slightly larger than the outer diameter of the cement ring and smaller than the outer diameter of the inner circular steel plate of the upper cover plate.

5. A cement sheath interface shear bond strength measuring device as claimed in claim 1, characterized in that: The first interface measurement block is a thick-walled hollow steel cylinder, whose outer diameter is slightly smaller than the outer diameter of the simulated casing. The second interface measurement block is a round steel block with an open upper end and a cylindrical groove in the center. The inner diameter of the groove is slightly larger than the outer diameter of the simulated casing, and the outer diameter of the steel block is slightly smaller than the inner diameter of the simulated surrounding rock.

6. A method for measuring the shear bond strength of cement sheath interface using the device described in claim 1, 2, 3, 4 or 5, comprising the following steps in sequence: 1) Place a simulated casing filled with clean water and simulated surrounding rock saturated with clean water on the sealing gasket of the lower bottom plate; 2) Pour the prepared cement slurry into the simulated annulus, with the top surface 1-2mm away from the upper end surface of the simulated casing; 3) Pour simulated formation water into the confining pressure chamber, with the top surface 1-2 mm away from the upper end surface of the simulated surrounding rock; 4) Connect the upper cover plate to the kettle body through fastening bolts, start the hydraulic pump, and apply the set initial pressure through the connecting pipelines of the simulated casing, simulated annulus, and the liquid inlet pressure / liquid discharge pressure relief port of the confining pressure chamber; 5) Start the temperature control system, heat and insulate the kettle body, adjust the pressure of the simulated casing, simulated annulus, and confining pressure chamber to ensure that the cement slurry solidifies at the set temperature and pressure, and after curing the cement slurry for a predetermined time, turn off the temperature control system, and release the pressure in the simulated annulus and confining pressure chamber to zero after the temperature drops to room temperature or the set temperature; 6) Place an interface measurement cushion cylinder on the pressure testing machine, remove the inner circular steel plates of the lower bottom plate and the upper cover plate, turn the kettle body 180° and place it on the cushion cylinder, and lead the connecting pipeline of the liquid inlet pressure test / liquid discharge pressure relief port of the simulated casing through the notch of the cushion cylinder; 7) Place an interface measurement block at the top of the simulated casing, adjust the pressure in the simulated casing through the hydraulic pump as needed, start the pressure tester and slowly apply pressure to obtain the peak pressure that pushes the simulated casing out of the cement sheath; 8) Remove the kettle body and the first interface measurement cushion cylinder from the pressure testing machine; place the second interface measurement cushion cylinder on the pressure testing machine, place the kettle body turned 180° on the cushion cylinder, place the second interface measurement block on the top of the cement sheath, adjust the pressure in the simulated casing as needed, start the pressure testing machine and slowly apply pressure to obtain the peak pressure that pushes the cement sheath out of the simulated surrounding rock; 9) Calculate the shear bond strength between the cement sheath and simulated casing, and between the cement sheath and simulated surrounding rock.

7. The method according to claim 6, characterized in that By replacing the simulated surrounding rock with different wall thicknesses, the shear bond strength of the first and second interfaces under different cement sheath wall thickness conditions were obtained.

8. The method according to claim 6, characterized in that By replacing simulated casings with different surface roughness, the shear bonding strength of the first and second interfaces of the simulated casings under different surface roughness conditions were obtained.

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