Well cementation cement bonding strength experiment mold, experiment device and method

Abstract

The invention relates to a well cementation cement bonding strength experiment mold, experiment device and method, and belongs to the technical field of cement bonding strength experiment devices.The well cementation cement bonding strength experiment mold comprises a salt rock mold with a containing hole in the middle and a hollow or solid pipe body, and a filling area is formed between the outer wall of the pipe body and the salt rock mold; the pipe body is arranged in a solid or hollow mode, the hollow sleeve allows independent and parallel evaluation of the first cementing surface and the second cementing surface, and the design of the solid steel core rod which does not interfere with each other provides a testing environment closer to an underground real stress state. According to the method, the interface strength of the complex multi-layer structure can be decoupled, two data with extremely high relevance can be obtained by using one sample, the efficiency is high, the discreteness is small, the test method particularly embodies the advantages, the decoupling test on the interface strength of the complex multi-layer structure is realized through ingenious loading head replacement and load application sequence, the method is scientific, the data is accurate, the experiment efficiency is high, and the method is suitable for large-scale popularization and application. And a standardized means is provided for optimization and performance evaluation of the salt cavern CAES well cementing cement.

Description

Technical Field

[0001] This invention belongs to the technical field of cement bonding strength testing devices, and specifically relates to a cement bonding strength testing mold, testing device and method for well cement. Background Technology

[0002] The integrity of compressed air storage wells in salt caverns depends on the effective sealing of the cement sheath. Its core mechanical properties are the bonding strength between cement and casing (first bonding surface) and between cement and salt rock formation (second bonding surface). Existing conventional methods for testing the bonding strength of oil and gas wells have significant shortcomings: First, the test mold material usually does not match the actual downhole materials, failing to accurately reflect the specific interfacial behavior between N80 casing steel, salt rock, and cement; second, existing methods primarily focus on the cement-casing bonding surface, lacking a systematic evaluation standard for the cement-salt rock formation bonding surface; existing multi-unit split tests are not only inefficient but also introduce systematic errors due to differences in material curing conditions; furthermore, the mold size design does not fully consider the similarity to downhole conditions and the matching of salt rock coring dimensions, resulting in poor engineering extrapolation of experimental results.

[0003] Therefore, there is an urgent need for a dedicated experimental device and method that can accurately simulate the actual working conditions of salt cavern CAES wells and simultaneously or sequentially measure the strength of two key cemented surfaces. This has both pressing engineering requirements and significant technical value. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a mold, apparatus, and method for testing the cement bonding strength of well cement, thereby achieving accurate measurement of the bonding strength of each cemented surface.

[0005] To achieve the above objectives, the present invention provides the following solution: A cement bonding strength test mold includes a salt rock mold with a placement hole in the middle and a hollow or solid tube for placement in the placement hole, wherein the outer wall of the tube and the salt rock mold form a filling area for filling cement slurry.

[0006] Preferably, the tube body is a hollow N80 steel sleeve, and the inside of the sleeve is used to fill the cement slurry.

[0007] Preferably, the sleeve has an inner diameter of 50 mm, an outer diameter of 100 mm, and a height of 100 mm.

[0008] Preferably, the tube body is a solid N80 steel core rod.

[0009] A cement bonding strength testing device includes a material testing machine, which is used to load the cement bonding strength testing mold.

[0010] Preferably, the material testing machine includes a loading device and a pressure platform for placing the cement bonding strength testing device. The pressure platform has an opening for the cement slurry to fall out of the steel core rod or sleeve and for the cement slurry to fall between the pipe and the salt rock mold.

[0011] A method for testing the cement bond strength of well cementing includes the following steps: Cement grout is poured into the filling area and then cured. The area of ​​cement slurry or steel core rod is loaded and then detached from the cement bond strength test mold. During loading, an axial compressive load is applied at a constant rate until the cement sample undergoes shear failure along the cementing interface and is completely ejected from the cementing cement bond strength test mold. The peak load collected by the testing machine's measurement and control system is the ultimate shear load Pb of the bonded surface.

[0012] Preferably, the bonding strength is calculated using the following formula. Using formula F b =P b The calculation is performed using / (π×d×h).

[0013] F b — Bonding strength; P b —Ultimate shear load; d—diameter of the bonded surface; h—Effective bond height of cement sample.

[0014] Preferably, the contact surface between the sleeve and the cement slurry inside the sleeve is defined as the first bonding surface, the contact surface between the outer wall of the sleeve or the outer wall of the steel core rod and the cement slurry in the filling area is defined as the second bonding surface, and the contact surface between the inner wall of the salt rock mold and the cement slurry in the filling area is defined as the third bonding surface.

[0015] The present invention achieves the following technical effects compared to the prior art: This invention utilizes either a solid or hollow tube. The hollow sleeve allows for independent and parallel evaluation of the first and second cemented surfaces, while the solid steel core provides a testing environment closer to the actual downhole stress state. It also enables the acquisition of two highly correlated data points from a single sample, resulting in high efficiency and low dispersion. This advantage is particularly evident in the testing method, which achieves decoupled testing of the interface strength of complex multi-layered structures through ingenious loading head replacement and load application sequence. The method is scientific, the data is accurate, and the experimental efficiency is high, providing a standardized means for the selection and performance evaluation of cementing materials for salt cavern CAES wells. Attached Figure Description

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

[0017] Figure 1 This is a schematic diagram of the mold structure simulating the first bonding surface of the present invention; Figure 2 This is a schematic diagram of the mold structure for simulating the second bonding surface of the present invention; Figure 3 This is a schematic diagram of the mold structure for the present invention, in which the tube body is a steel core rod; Among them, 1. Cement grout inside the casing; 2. Sleeve; 3. Cement grout inside the salt rock mold; 4. Salt rock mold; 5. Steel core rod; 6. Cement grout in the filling area. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] This invention provides a mold, apparatus and method for testing the bonding strength of cement in well cementing, so as to achieve the purpose of accurately measuring the bonding strength of each cemented surface.

[0020] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0021] refer to Figures 1 to 3A test mold for cement bonding strength includes a salt rock mold with a placement hole in the middle and a hollow or solid tube for placement in the placement hole. The outer wall of the tube and the salt rock mold form a filling area for filling cement slurry. By setting the tube to be solid or hollow, the hollow sleeve allows for independent and parallel evaluation of the first and second bonding surfaces, while the solid steel core design provides a test environment that is closer to the actual downhole stress state. It can obtain two highly correlated data from a single sample, which is efficient and has low dispersion. The test method particularly reflects this advantage. Through clever loading head replacement and load application sequence, it achieves decoupled testing of the interface strength of complex multi-layer structures. The method is scientific, the data is accurate, and the experimental efficiency is high, providing a standardized means for the selection and performance evaluation of cementing cement for salt cavern CAES wells.

[0022] refer to Figure 1 The tube body is a hollow N80 steel sleeve, and the inside of the sleeve is filled with cement slurry. Because N80 steel and in-situ salt rock are used as the matrix materials of the mold, the cementation interface is highly consistent with the actual situation downhole in terms of materials science. This solves the problem of experimental result distortion caused by material mismatch in the existing technology, and greatly improves the simulation authenticity of the experiment and the engineering guidance value of the data.

[0023] Furthermore, the sleeve has an inner diameter of 50 mm, an outer diameter of 100 mm, and a height of 100 mm.

[0024] Furthermore, the tube body is made of solid N80 steel core rod.

[0025] A cement bonding strength testing device includes a material testing machine, which is used to load the cement bonding strength testing mold.

[0026] Furthermore, the material testing machine includes a loading device and a pressure platform for placing the cement bonding strength testing device. The pressure platform has openings for the cement slurry to fall out of the steel core rod or sleeve and for the cement slurry to fall between the pipe body and the salt rock mold.

[0027] Furthermore, the contact surface between the casing and the cement grout inside the casing is defined as the first bonding surface, the contact surface between the outer wall of the casing or the outer wall of the steel core rod and the cement grout in the filling area is defined as the second bonding surface, and the contact surface between the inner wall of the salt rock mold and the cement grout in the filling area is defined as the third bonding surface.

[0028] To achieve the above objectives, the present invention employs the following two independent technical solutions: Option 1: Test plan when the tube is hollow The first bonding surface testing device consists of a sleeve made of N80 steel as its core component. Its key dimensions are: inner diameter Φ50mm, outer diameter Φ100mm, and height 100mm. This inner wall surface is used to simulate the inner wall of the sleeve, forming the first bonding surface with the injected cement.

[0029] The second cemented surface testing device: its core component is a salt rock mold, fabricated from salt rock cores of the target strata. Two preferred specifications are further provided to accommodate different core sources: Specification A: Based on a standard salt rock core of Φ100 mm × 100 mm, drill a central through hole of Φ50 mm along its axial direction.

[0030] Specification B: Based on a small-sized salt rock core of Φ50mm×100mm, drill a Φ25mm central through hole along its axial direction.

[0031] The inner wall of the central hole of the salt rock mold is used to simulate the well wall, forming a second bonding surface with the injected cement.

[0032] Test process: Sample preparation and simulated curing: The standardized cement slurry was injected into the first and second cemented surface test molds respectively. The sealed molds were placed in a high-temperature and high-pressure curing autoclave, and the curing regime was set according to the actual working conditions of the target reservoir well, and curing was carried out for the specified time.

[0033] Ultimate shear load test: a. After curing, install the mold on the universal testing machine.

[0034] b. Select an upper pressure head that matches the diameter of the cement sample in the mold (e.g., Φ≈50 mm). The lower pressure platform is a hollow structure with a through-hole diameter slightly larger than the cement sample diameter to ensure that the cement column can be smoothly pushed out while the mold is supported.

[0035] c. Apply an axial compressive load at a constant rate until the cement specimen undergoes shear failure along the cementation interface and is completely ejected from the mold.

[0036] d. Record the peak load collected by the testing machine's measurement and control system, which is the ultimate shear load Pb of the bonded surface.

[0037] Bond strength calculation: using formula F b =P b The calculation is performed using / (π×d×h).

[0038] F b — Bond strength, unit: megapascals (MPa); P b —Ultimate shear load, unit: Newton (N); d—diameter of the bonding surface (for the first bonding surface, it is the inner diameter of the steel mold; for the second bonding surface, it is the diameter of the center hole of the salt rock mold), unit: millimeters (mm); h—Effective bond height of cement sample, unit: millimeters (mm).

[0039] Option 2: Mold sequence testing scheme when the tube body is solid This scheme uses an integrated combination mold, which can sequentially test two cemented surfaces on a single sample, more realistically reproducing the ternary composite structure of "casing-cement sheath-formation" in the well.

[0040] The combined mold structure consists of a salt rock outer cylinder and an N80 steel core rod.

[0041] The dimensions of the salt rock outer cylinder are: outer diameter Φ100 mm, height 100 mm, and central through hole diameter Φ60 mm.

[0042] The N80 steel core rod has the following dimensions: diameter Φ20 mm and height 100 mm.

[0043] Integrated molding mold: The steel core rod is coaxially placed inside the central hole of the salt rock outer cylinder, naturally forming an annular cylindrical cavity between them. This cavity is used to pour cement grout, which, after curing, simultaneously forms a bond with the outer wall of the steel core rod (first bonding surface) and the inner wall of the salt rock outer cylinder (second bonding surface).

[0044] Test process: Sample preparation and simulated curing: Cement slurry was injected into the annular cavity of the integrated mold. Subsequently, the same simulated formation conditions as in Scheme 1 were applied for curing.

[0045] Second bonded surface strength test: a. Place the cured assembly mold on the testing machine.

[0046] b. The diameter of the upper pressure head is matched with the outer diameter of the cement ring (i.e., the inner diameter of the salt rock outer cylinder Φ60 mm), and the diameter of the hollow part of the lower pressure platform corresponds to it.

[0047] c. Apply an axial load to push the N80 steel core rod and cement ring assembly out of the salt rock outer cylinder as a whole. Record the ultimate shear load Pb2 during this process.

[0048] d. Calculate the strength of the second bonded surface: F b =P b2 / (π×d2×h), where d2=60 mm.

[0049] e. After completing the previous step, replace the upper pressure head so that its diameter matches the diameter of the N80 steel core rod (Φ20 mm), and adjust the lower pressure platform accordingly.

[0050] f. Position the "steel core-cement ring" assembly in place, apply an axial load, and push the N80 steel core rod out of the cement ring. Record the ultimate shear load P during this process. b1 .

[0051] g. Calculate the strength of the first bonded surface: F b1 = Pb1 / (π×d1×h), where d1=20 mm.

[0052] Any adaptive changes made according to actual needs are within the scope of protection of this invention.

[0053] It should be noted that, for those skilled in the art, it is obvious that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A mold for testing the cement bond strength of well cementing, characterized in that, It includes a salt rock mold with a placement hole in the middle and a hollow or solid tube for placement in the placement hole, wherein the outer wall of the tube and the salt rock mold form a filling area for filling cement slurry.

2. The cement bonding strength test mold according to claim 1, characterized in that, The tube body is a hollow N80 steel sleeve, and the inside of the sleeve is used to fill the cement slurry.

3. The cement bonding strength test mold according to claim 2, characterized in that, The sleeve has an inner diameter of 50 mm, an outer diameter of 100 mm, and a height of 100 mm.

4. The cement bond strength test mold according to claim 1, characterized in that, The tube body is a solid N80 steel core rod.

5. A testing device for cement bond strength in well cementing, characterized in that, The cementing strength test mold according to any one of claims 1 to 4 includes a material testing machine, which is used to load the cementing strength test mold.

6. The cement bond strength testing apparatus according to claim 5, characterized in that, The material testing machine includes a loading device and a pressure platform for placing the cement bonding strength testing device. The pressure platform has openings for the cement slurry to fall out of the steel core rod or sleeve and for the cement slurry to fall between the pipe and the salt rock mold.

7. A method for testing the cement bond strength of well cement, characterized in that, The cement bond strength testing apparatus according to claims 5 to 6 includes the following steps: Cement grout is poured into the filling area and then cured. The area of ​​cement slurry or steel core rod is loaded and then detached from the cement bond strength test mold. During loading, an axial compressive load is applied at a constant rate until the cement sample undergoes shear failure along the cementing interface and is completely ejected from the cementing cement bond strength test mold. The peak load collected by the testing machine's measurement and control system is the ultimate shear load Pb of the bonded surface.

8. The method for testing the cement bond strength of well cement according to claim 7, characterized in that, The bonding strength is calculated using the following formula. Using formula F b =P b The calculation is performed using / (π×d×h). F b — Bonding strength; P b —Ultimate shear load; d—diameter of the bonded surface; h—Effective bond height of cement sample.

9. The method for testing the cement bond strength of well cement according to claim 7, characterized in that, The contact surface between the sleeve and the cement slurry inside the sleeve is defined as the first bonding surface, the contact surface between the outer wall of the sleeve or the outer wall of the steel core rod and the cement slurry in the filling area is defined as the second bonding surface, and the contact surface between the inner wall of the salt rock mold and the cement slurry in the filling area is defined as the third bonding surface.

Images