Cement paste system with high interface bonding strength and preparation method thereof

Abstract

The invention discloses a cement paste system with high interface bonding strength and a preparation method thereof. The cement paste system with high interface bonding strength comprises the following components in parts by weight: 100 parts of oil well cement, 1-5 parts of an interface reinforcing agent, 0.2-0.5 part of a fluid loss agent, 0.2-0.5 part of a drag reducer, 0.1-0.2 part of a retarder and 44 parts of clear water. The cement paste system further comprises 0.1-0.2 part of a defoaming agent. Through interaction and hydration reaction time difference between different types of cementing materials, the cementing strength and compactness of the system are improved, the purpose of efficiently improving the cementing strength is achieved, a high-strength cement slurry system meeting well cementation construction requirements is screened out, and compared with a pure cement system with the same density, the cementing strength is improved by 30%-50%.

Description

Technical Field

[0001] The present invention belongs to the technical field of cementing, and particularly relates to a cement slurry system with high interfacial bonding strength and a preparation method thereof. Background Art

[0002] Cementing is a non-repetitive project. The simplified method includes two processes: running the casing and injecting cement slurry. These two processes involve flushing the wellbore and injecting the spacer fluid. The casing is run into the wellbore with a clean wall and hole, then the spacer fluid is injected to play an isolating role. Finally, the cement slurry is injected into the annular space between the casing and the wellbore. After the cement slurry solidifies to form a cement sheath, it plays an interlayer sealing role. With the expansion of oil and gas exploration and development, more and more adjustments are made to the cementing technology, and higher requirements are put forward for the cementing quality.

[0003] The cementing interface includes the first interface between the cement sheath and the casing and the second interface between the cement sheath and the wellbore wall. The quality of the interfacial bonding directly affects the safety and service life of oil production. Once the quality of the cementing interface is poor, it will affect the interlayer sealing effect of the cement sheath. Seriously, it will cause the sealing failure of the cement sheath, and the sealing failure will result in the cross-flow of oil and gas, leading to pressure at the wellhead. If workover operations are carried out on the oil well, not only is the repair period long, the repair cost high, but the success rate is also low. To address the above problems and ensure the cementing quality and the safe progress of subsequent operations, it is necessary to improve the bonding strength of the first and second interfaces of the cement sheath. With the continuous increase in drilling depth, the influence of complex formations is increasing, and the performance and technical requirements for the cement sheath of cementing are also continuously improving. The bonding strength of the first and second interfaces of the existing cementing cement slurry system cannot meet the requirements of cementing construction, and it is urgent to further improve the bonding strength of the first and second interfaces of the existing cementing cement slurry system.

[0004] Therefore, a cement slurry system with high interfacial bonding strength and a preparation method thereof are invented to meet the requirements of the bonding strength of the first and second interfaces of the cement sheath for subsequent construction. Summary of the Invention

[0005] In order to solve the above technical problems existing in the prior art, the purpose of the present invention is to provide a cement slurry system with high interfacial bonding strength and a preparation method thereof. The present invention utilizes the interaction between different types of cementitious materials and the time difference of hydration reactions to improve the bonding strength and compactness of the system.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows: The present invention first discloses a cement slurry system with high interfacial bonding strength, which comprises the following components in parts by weight: 100 parts of oil well cement 1 - 5 parts of interfacial enhancer 0.2 - 0.5 parts of fluid loss reducer Drag reducer: 0.2 - 0.5 parts Defoamer: 0.1 - 0.2 parts Retarder: 0.1 - 0.2 parts Fresh water: 44 parts

[0007] As a further improvement to the technical solution of the present invention, the high interface bonding strength cement slurry system further includes 0.1 - 0.2 parts by weight of defoamer.

[0008] As a further preferred solution of the present invention, the interface enhancer is a mixture composed of one or more of modified calcium silicate hydrate powder, potassium hexatitanate whiskers, metakaolin, silica, flake graphite, and latex powder.

[0009] A further preferred solution is that the fineness of the modified calcium silicate hydrate powder is 1000 - 2000 mesh, the fineness of the potassium hexatitanate whiskers is 1000 - 2000 mesh, the fineness of the metakaolin is 1000 - 2000 mesh, the fineness of the silica is 1000 - 2000 mesh, the fineness of the flake graphite is 1000 - 2000 mesh, and the fineness of the latex powder is 1000 - 2000 mesh.

[0010] In a preferred technical solution of the present invention, the interface enhancer is composed of 1000 - mesh modified calcium silicate hydrate powder, 1000 - mesh potassium hexatitanate whiskers, and 2000 - mesh silica powder compounded in a mass ratio of (2 - 6):(1 - 3):(0.2 - 1).

[0011] In another preferred technical solution of the present invention, the interface enhancer is composed of 1500 - mesh modified calcium silicate hydrate powder, 1500 - mesh potassium hexatitanate whiskers, and 1000 - mesh metakaolin compounded in a mass ratio of (1 - 4):(1 - 3):(1 - 3).

[0012] In another preferred technical solution of the present invention, the interface enhancer is composed of 1000 - mesh modified calcium silicate hydrate powder, 2000 - mesh potassium hexatitanate whiskers, 1250 - mesh metakaolin, 500 - mesh flake graphite, and 1500 - mesh latex powder compounded in a mass ratio of (1 - 4):(1 - 3):(0.5 - 2):(1 - 2):(1 - 2).

[0013] As a further preferred solution of the present invention, the preparation method of the modified calcium silicate hydrate includes the following steps: a. Weigh calcium silicate hydrate powder with a fineness of 300 - 500 mesh and a silane coupling agent, add them to 200 mL of a modified solvent, perform ultrasonic dispersion treatment for 30 min, and then adjust the pH to 4 - 5 with anhydrous oxalic acid; wherein the mass ratio of the calcium silicate hydrate powder to the silane coupling agent is (2 - 3):(0.5 - 1); b. Continuously add a certain amount of calcium silicate hydrate powder. After ultrasonic dispersion for 2 - 3 h, transfer the reaction solution to a 500 mL flask, keep the liquid temperature at 60 - 70 °C, and carry out condensation reflux at a speed of 500 - 800 r / min for 3 h to obtain a milky white gel liquid; The mass of the calcium silicate hydrate powder in this step is 10% - 20% of the mass of the calcium silicate hydrate powder in step a; c. First, wash and purify the milky white gel liquid obtained in step b with absolute ethanol to remove the unreacted silane coupling agent, then carry out suction filtration, and dry it in an incubator at 60 °C for 24 h. Put the dried powder, ball mill grinding balls, and water into a ball mill tank according to the mass ratio of (1 - 2):(1 - 2):(0.5 - 1) and carry out wet grinding for 2 - 3 h. During the wet grinding process, control the rotation speed at 600 - 800 r / min. After grinding, take it out and pass through a 1000 - 2000 - mesh sieve to obtain the modified calcium silicate hydrate powder.

[0014] Preferably, the modified solvent is a mixed solution formed by mixing absolute ethanol and deionized water according to a volume ratio of (2 - 5):1.

[0015] As a further preferred scheme of the present invention, the preparation method of the potassium hexatitanate whiskers is as follows: Using analytical - grade TiO₂ and K₂CO₃ as raw materials, compound the two according to a molar ratio of (4 - 6):1, and dry at a temperature of 60 °C for 24 h. After drying, grind and mix them dry with a pulverizer. Put the mixed raw materials into a ceramic crucible, heat in a muffle furnace at 800 - 1000 °C for 1 - 4 h, take it out after cooling to room temperature with the furnace, and pass through a 1000 - 2000 - mesh sieve to obtain the potassium hexatitanate whiskers.

[0016] Preferably, the retarder is an organic acid - type retarder or an acrylamide - type retarder.

[0017] Furthermore, the organic acid - type retarder is one or several of citric acid, sodium citrate, tartaric acid, potassium tartrate, acrylic acid, sodium acrylate, organic acid - type DRH for well - cementing oil - well cement, and organic acid - type JXH for well - cementing oil - well cement; the acrylamide - type retarder can preferably be acrylamide - type DRH for well - cementing oil - well cement.

[0018] The present invention further protects a preparation method of a cement slurry system with high interfacial bonding strength, including the following steps: S1. Take 100 parts by weight of oil - well cement and 1 - 5 parts by weight of an interfacial enhancer, mix the two evenly to obtain a dry powder mixture; S2. Weigh 44 parts by weight of water. Mix 0.2 - 0.5 parts by weight of fluid loss reducer, 0.2 - 0.5 parts by weight of friction reducer, 0.1 - 0.2 parts by weight of defoamer, and 0.1 - 0.2 parts by weight of retarder into the water, then pour the mixture into a stirrer. The stirrer rotates at a low speed of 4000 ± 200 revolutions per minute. S3. Add the dry powder mixture obtained in step S1 to the stirrer in step S2 within 15 seconds. Adjust the rotation speed of the stirrer and continue to stir at a high speed of 12000 ± 500 revolutions per minute for 35 seconds to obtain the cement slurry system with high interfacial bonding strength.

[0019] Compared with the prior art, the present invention has the following beneficial effects: 1. By means of the interaction between different materials and different hydration times, the present invention improves the hydration depth, forms a denser cementitious body in the interfacial transition zone, and further improves the strength of the system. Compared with the pure cement system with the same density, the bonding strength is increased by 30 - 50%.

[0020] 2. Through a large number of experiments, the present invention explores suitable material ratios to achieve the following: without changing the original water / cement ratio and without adjusting the density, the new system not only has a high increase in bonding strength but also retains good cementing construction performance. Through various detection experiments, it is verified that under the conditions of correct material ratios and water / cement ratios, the interaction between the components in the interfacial enhancer can improve the interfacial bonding strength, solving the problems in the original system technology, such as increasing the bonding strength by reducing the water / cement ratio, adding various ultra-fine materials for grading, using various activators, etc.; solving the disadvantages of the original technology, such as a significant increase in the system density, a significant increase in the slurry consistency, a significant shortening of the thickening time, and a substantial increase in cost. The present invention simply relies on the interaction between materials to increase the bonding strength of the system.

[0021] 3. The materials selected in the present invention are all relatively conventional cementing materials. Without changing the ratio of dry ash to fresh water, without changing the density of the system, and without increasing the system cost, a significant improvement in the cementitious compactness and bonding strength of the system is obtained by relying on the appropriate ratio of conventional materials, providing a reliable and low-cost cement slurry system for well types that require high-strength cement sheath completion (such as: fully fracturing wells, plugging perforation wells, etc.).

[0022] 4. The present invention uses modified calcium silicate hydrate powder. Compared with ordinary calcium silicate hydrate powder, the silane coupling agent used in the modification reduces the number of hydroxyl groups on the surface of calcium silicate hydrate particles and introduces a hydrophobic organic part, changing it from a substance with extremely strong hydrophilicity to a substance with slightly poor hydrophilicity, improving the dispersibility. After grinding, the particle size of calcium silicate hydrate is smaller, which can fill the pores in the cement matrix, improve the compactness of the matrix, and thus improve the interfacial bonding strength of the cement stone.

[0023] 5. The present invention uses self-made potassium hexatitanate whiskers, which reduces the cost and can introduce new materials with stable chemical properties, excellent mechanical and physical properties, especially high tensile strength, into the cement slurry system.

[0024] The above description is only an overview of the technical solution of the present invention. In order to understand the technical means of the present invention more clearly and be able to implement it according to the content of the description, the following will describe in detail with reference to the preferred embodiments of the present invention and the accompanying drawings. Description of the Drawings

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other design solutions and drawings can also be obtained based on these drawings.

[0026] Figure 1 It is a schematic diagram of the cementing strength test device; Figure 2 It is a microscopic morphology diagram of the interface of the control group system; Figure 3 It is a microscopic morphology diagram of the interface of the experimental group 1 system; Figure 4 It is a microscopic morphology diagram of the interface of the experimental group 2 system; Figure 5 It is a microscopic morphology diagram of the interface of the experimental group 3 system; Figure 6 It is a schematic diagram of the backscattering test sample; Figure 7 It is a nanoindentation test diagram under a transmission electron microscope; Figure 8 It is a bar chart of the indentation modulus strength of the control group interface; Figure 9 It is a distribution diagram of the indentation modulus strength of the control group interface; Figure 10 It is a bar chart of the indentation modulus strength of the experimental group 1 interface; Figure 11 It is a distribution diagram of the indentation modulus strength of the experimental group 1 interface; Figure 12 It is a bar chart of the indentation modulus strength of the experimental group 2 interface; Figure 13 It is a distribution diagram of the indentation modulus strength of the experimental group 2 interface; Figure 14 It is a bar chart of the indentation modulus strength of the experimental group 3 interface; Figure 15 It is a distribution diagram of the indentation modulus strength of the experimental group 3 interface; Figure 16 It is an analysis diagram of the hydration products at the nano-indentation point; Figure 17 It is the micro-morphology diagram of the interface of System 2 in the control group; Figure 18 It is the micro-morphology diagram of the interface of System 2 in Experimental Group 1; Figure 19 It is the micro-morphology diagram of the interface of System 2 in Experimental Group 2; Figure 20 It is the micro-morphology diagram of the interface of System 2 in Experimental Group 3.

[0027] Explanation of the reference numerals in the drawings: 1. Strong magnetic upper cover; 2. Strong magnetic lower cover; 3. Cementing cylinder; 4. Sealing ring; 5. Simulated casing or core.

[0028] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below in conjunction with the drawings and specific embodiments. Specific embodiments

[0029] The content of the present invention can be further understood by combining the following detailed description of the preferred implementation methods of the present invention and the included embodiments. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as the ordinary understanding of those of ordinary skill in the technical field to which the present invention belongs. If the definition of a specific term disclosed in the prior art is inconsistent with any definition provided in the present invention, the definition provided in the present invention shall prevail.

[0030] It should be noted that the implementation conditions adopted in the embodiments can be further adjusted according to the specific experimental environment, and the implementation conditions not specified are usually the conditions in conventional experiments. The preparation methods mentioned in the present invention are all conventional methods unless otherwise specified; all chemical reagents and chemical supplies mentioned in the present invention are well-known and commonly used chemical reagents and chemical supplies in the prior art unless otherwise specified.

[0031] In order to achieve the purpose of efficiently improving the cementing strength and screen out a high-strength cement slurry system that meets the requirements of cementing construction, the main research content of the present invention is as follows: I. Introduction of the materials used 1. Cement Select high-sulfur-resistant type (HSR) Grade G oil well cement that meets the GB10238-2015 oil well cement standard. In this experiment, Sichuan Jiahua Grade G high-sulfur-resistant oil well cement was used.

[0032] 2. Interface enhancer The interface enhancer is a mixture composed of one or more of modified hydrated calcium silicate powder (with a fineness of 1000 mesh to 2000 mesh), potassium hexatitanate whiskers (1000 to 2000 mesh), metakaolin (1000 mesh to 2000 mesh), silica (1000 mesh to 2000 mesh), flake graphite (1000 mesh to 2000 mesh), and latex powder (1000 mesh to 2000 mesh), with a fineness between 1000 and 2000 mesh.

[0033] 3. Fluid loss reducer Select products that comply with the SY / T5504.2-2013 Evaluation Method for Oil Well Cement Additives - Part 2: "Fluid Loss Reducer" standard. For this experiment, select the publicly available "Fluid Loss Reducer G33S for Oil Well Cement" (Enterprise Standard Q / WHGS 049-2016) from Weihui Chemical Industry Co., Ltd. that complies with the above petroleum industry standard.

[0034] 4. Friction reducer Select products that comply with the SYT5504.3-2018 Evaluation Method for Oil Well Cement Additives - Part 3: "Friction Reducer" standard. For this experiment, select the publicly available "Friction Reducer USZ for Oil Well Cement" from Weihui Chemical Industry Co., Ltd. that complies with the above petroleum industry standard.

[0035] 5. Retarder Organic acid retarders or acrylamide retarders.

[0036] For this experiment, preferably select the organic acid type DRH retarder for well cementing in oil wells and the organic acid type JXH retarder for well cementing in oil wells produced by China National Petroleum Corporation Engineering Technology Research Institute Co., Ltd.

[0037] 6. Defoamer Ester defoamers. For this experiment, select the publicly available "Defoamer DF-T for Oil Well Cement" from Weihui Chemical Industry Co., Ltd.

[0038] II. Solutions and Effects for Improving Bond Strength (1) Through the interaction between different types of cementitious materials and the time difference of hydration reactions, improve the bond strength and compactness of the system, achieve the purpose of efficiently improving the bond strength, and screen out a high-strength cement slurry system that meets the requirements of well cementing construction.

[0039] (2) Test sample design The designed solutions and detection standards are as follows: Control group: 100 parts of G-class oil well cement + 0.2 parts of fluid loss reducer G33S for oil well cement + 0.2 parts of friction reducer USZ for oil well cement + 0.2 parts of retarder + 44 parts of fresh water Experimental Group 1: 100 parts of G-class oil well cement + 2 parts of interfacial enhancer (compounded by modified hydrated calcium silicate powder with a mesh size of 1000, potassium hexatitanate whiskers with a mesh size of 1000, and silica powder with a mesh size of 2000 at a mass ratio of 4:1:0.5) + 0.2 parts of fluid loss reducer G33S for oil well cement + 0.5 parts of friction reducer USZ for oil well cement + 0.2 parts of retarder + 44 parts of fresh water.

[0040] Experimental Group 2: 100 parts of G-class oil well cement + 3 parts of interfacial enhancer (compounded by modified hydrated calcium silicate powder with a mesh size of 1500, potassium hexatitanate whiskers with a mesh size of 1500, and metakaolin with a mesh size of 1000 at a mass ratio of 1:1:1) + 0.5 parts of fluid loss reducer G33S for oil well cement + 0.2 parts of friction reducer USZ for oil well cement + 0.2 parts of retarder + 44 parts of fresh water.

[0041] Experimental Group 3: 100 parts of G-class oil well cement + 5 parts of interfacial enhancer (compounded by modified hydrated calcium silicate powder with a mesh size of 1000, potassium hexatitanate whiskers with a mesh size of 2000, metakaolin with a mesh size of 1250, flake graphite with a mesh size of 1500, and latex powder with a mesh size of 1500 at a mass ratio of 1:1:0.5:1:1) + 0.2 parts of fluid loss reducer G33S for oil well cement + 0.2 parts of friction reducer USZ for oil well cement + 0.2 parts of retarder + 44 parts of fresh water.

[0042] (3) Preparation method of modified hydrated calcium silicate: Take the mixed solution of absolute ethanol and deionized water with a volume ratio of 2:1 - 5:1 as the modification solvent. Weigh 2 parts of hydrated calcium silicate powder with a mesh size of 300 - 500 and a silane coupling agent, add them into 200 mL of the modification solvent. After ultrasonic dispersion for 30 min, adjust the pH to about 4.5 with anhydrous oxalic acid; the mass ratio of hydrated calcium silicate powder to silane coupling agent is (2 - 3):(0.5 - 1); then add 0.2 parts of hydrated calcium silicate powder, after ultrasonic dispersion for 2 - 3 h, transfer the above reaction solution to a 500 mL flask, and at 65 °C, condense and reflux at a speed of 500 - 800 r / min for 3 h to obtain a milky white gel liquid. Wash and purify it with absolute ethanol to remove the unreacted coupling agent, then filter it by suction, and dry it in an incubator at 60 °C for 24 h. Put the dried powder, grinding balls for the ball mill, and water into the ball mill tank at a mass ratio of 1:1:0.5 for wet grinding for 2 - 3 h, with a rotation speed of 600 - 800 r / min. After grinding, take it out and screen it through a 1000 - 2000 mesh sieve to obtain the modified hydrated calcium silicate powder.

[0043] (4) Preparation method of potassium hexatitanate whiskers: Using analytical pure TiO2 and K2CO3 as raw materials, the two are proportioned according to a molar ratio of 4:1 to 6:1, dried and then ground and dry-mixed with a XA-1 type high-speed universal grinder. The mixed raw materials are placed in a ceramic crucible and heated in a muffle furnace at 800-1000 °C for 1-4 h. After cooling to room temperature with the furnace, it is taken out and sieved through a 1000-2000 mesh sieve to obtain potassium hexatitanate whiskers.

[0044] (5)Testing standards and experimental procedures: The experimental process for testing the properties of cement slurry is carried out according to the following standards: Standardization Administration of the People's Republic of China, Test Methods for Oil Well Cement, GB / T 19139-2012; Weigh the ash sample and water according to the above cement slurry formula. According to the GB / T19139-2012 standard, use a constant speed stirrer to prepare the cement slurry. After preparation, measure the density of the cement slurry; pour the mixed cement slurry into the slurry cup of the atmospheric thickening instrument, and prefabricate it for 30 min at atmospheric pressure at 50 °C and 70 °C respectively using the thickening instrument, and then pour it into a cylindrical compressive strength test mold with a size of Φ25mm×25mm and a cementing strength test device. The diagram of the cementing strength test device is as Figure 1 shown. The cementing strength test device includes a cementing cylinder 3. There is a cavity in the cementing cylinder 3 for accommodating the simulated casing or core 5. A strong magnetic upper cover 1 and a strong magnetic lower cover 2 are respectively fixedly installed at the upper and lower ends of the cementing cylinder 3, and the cementing cylinder 3 and the strong magnetic upper cover 1 are sealed through a sealing ring 4. After injecting 40 mm high cement slurry into the annulus zone of the cementing strength test device and covering the strong magnetic upper cover, it is respectively placed in an OWC-118F dual-temperature strength curing box for curing. After the curing time of 1 d, 2 d, and 7 d, demold and measure the various properties of the hardened cement stone.

[0045] The calculation of the interfacial cementing strength is carried out using the following formula: ,

[0046] In the formula, S is the numerical value of the cementing strength, with the unit of MPa; P is the loading pressure numerical value when the casing or core detaches, with the unit of N; mg is the gravity of the test rod, with the unit of N; D is the diameter of the core or casing, with the unit of mm; h is the height of the cement sheath, with the unit of mm.

[0047] (I)Comprehensive performance test, compressive strength and cementing strength test The water slurry fluidity, density, free fluid, water loss and thickening time of the comparative example and experimental groups 1, 2 and 3 were measured respectively in accordance with the national standard GB / T 19139-2012. The measurement results are shown in Table 1. It can be seen from the comprehensive performance of the water slurry system in the table that, compared with the comparative example, the high interface bonding strength water slurry system has better stability, the density difference between top and bottom ≤ 0.04 g / cm 3 , the thickening time is adjustable, the water loss ≤ 50 mL, and the comprehensive performance of the water slurry system meets the requirements of well cementing construction.

[0048] Table 1 Evaluation of the construction performance of the water slurry system

[0049] The test results of the compressive strength are shown in Table 2: Table 2 Compressive strength of the cement stone at different ages (MPa)

[0050] The results in Table 2 show that the compressive strength of the experimental group with the interface enhancer meets the engineering requirements.

[0051] The test results of the bonding strength are shown in detail in Tables 3 and 4: Table 3 The first interface bonding strength of the cement stone at different ages (MPa)

[0052] Table 4 The second interface bonding strength of the cement stone at different ages (MPa)

[0053] The results in Tables 3 and 4 show that, compared with the control group, the bonding strength of the experimental group with the interface enhancer is increased by 30-50%, achieving the expected effect.

[0054] (2) SEM detection of the cement sample ① Test method Mix the water slurry according to the standard of GB / T19139-2012. Take out the cement sample cured at 50 °C and normal pressure for 48 h, soak it in absolute ethanol for 3 d to terminate the hydration, then put it in an oven at 60 °C for 3 d to dry the moisture, take it out and knock it into small pieces for scanning electron microscope (SEM) test. The sample volume should be less than 5 mm × 5 mm × 5 mm. After gold spraying treatment, the test is carried out. The test results are as Figure 2 , Figure 3 , Figure 4 , Figure 5 shown. In this experiment, the ZEISS EVO / MA15 scanning electron microscope of Carl Zeiss Company in Germany was selected.

[0055] ② Test results It can be seen that Figure 2 there are a large number of calcium silicate hydrate (C-S-H) structures inside the control group system. The calcium silicate hydrate structure is a gel-like substance with poor mechanical properties, unable to form a tight packing, having a low interaction force with the interface, and a low interfacial bonding strength.

[0056] It can be seen that Figure 3 under the low-magnification scanning electron microscope, the interface of the experimental group 1 system shows a tight particle packing effect. From the high-magnification scanning electron microscope, it can be seen that there are many flaky CH crystal structures and many unhydrated particles on the interface. They are tightly packed together with a high packing density, having strength and increasing the frictional resistance with the interface, playing a role in improving the interfacial bonding strength. The experimental group system has more CH structures in the hydration products, so its interfacial bonding strength is high. Therefore, the magnitude of the interfacial bonding strength is consistent with the content of CH crystal structures in the system.

[0057] It can be seen that Figure 4 under the low-magnification scanning electron microscope of the experimental group 2 system, the interface is uneven, with a connected smooth structure and a fragmented gravel accumulation structure. From the high-magnification scanning electron microscope, it can be seen that the smooth structure is a combined calcium silicate hydrate gel system, and the gravel accumulation structure is composed of some ettringite, CH, and unhydrated cement particles. The interface has good bonding, large frictional resistance, and large mechanical interlocking force.

[0058] It can be seen from the following Figure 5 that under the low-magnification scanning electron microscope of the experimental group 3 system, the interface is uneven, and there are many rod-shaped AFt structures and flaky CH structures on the surface. From the high-magnification scanning electron microscope, it can be seen that there is an interface enhancer on the surface of the system, and the interface enhancer and AFt structures fill the pores on the surface of the solidified body, improving the roughness of the interface. The enrichment of AFt phase on the surface of the experimental group 3 system improves the interfacial bonding strength.

[0059] (3) Microscopic testing of the interfacial transition zone (ITZ) (1) According to the specific requirements of the "General Rules for Instrumented Nanoindentation Test Methods": the thickness of the specimen shall not be less than 10 times the indentation depth or 6 times the indentation radius, taking the larger value. The thickness of the test specimens in this experiment is about 5 mm - 8 mm. When the indentation depth h is at least 20 times the surface roughness Rn, the uncertainty of the indentation depth due to the surface roughness will reach a very low error range. Keep the test surface flat and without any inclination. The indenter should be aligned with the surface of the specimen test surface, ensuring that the surface of the specimen test surface is clean and there are no lubricating fluids or other impurities.

[0060] Cut the experimental materials of the second cementing interface. The small sandstone and limestone cemented samples used are about 2mm×2mm×2mm in size. Place them in a cylindrical mold with a diameter of Φ5mm×10mm for curing. After curing, demold them, conduct hydration termination treatment, and then cut and grind off the excess parts. Put the cut samples into a drying oven at 60°C for drying. After drying, put the samples into a vacuum embedding machine for embedding (pressure embedding can also be used). After embedding, grind the samples with sandpapers of 300, 500, 1000, 1500, 2000, and 3000 meshes. After each mesh size is polished, use an ultrasonic cleaner to clean them 2 - 3 times with anhydrous ethanol as the cleaning medium. During the grinding process, use a liquid with a ratio of glycerol to anhydrous ethanol of 1:1 as the lubricant to prevent surface hydration and avoid affecting the grinding quality and the microscopic structure of the specimen surface. For subsequent polishing, use a polishing cloth and polish with diamond suspensions of 3µm, 1µm, and 0.5µm. When there are few scratches on the sample surface under the electron microscope, the sample preparation is completed and can be used for nanoindentation and backscattered scanning electron microscopy tests. The prepared samples are as Figure 6 shown.

[0061] (2)Select the samples of the second cementing interface after 2 days of curing. After preparing the test samples, use a German Bruker Hysitron TI980 nanoindentation instrument to conduct nanoindentation tests. Its dynamic touch module (DCM) head is equipped with a diamond Berkovich indenter with a tip radius less than 20nm and is tested in the continuous stiffness measurement mode. The load and displacement resolutions are 50nN and 0.04nm respectively. The test set a 25 (5×5) dot matrix, and the spacing of the measurement points was set to 40µm to eliminate the mutual influence between different points. The standard nanoindentation test process mainly includes the following three steps: ① Load at a constant strain rate (0.05s -1 ) to a preset depth of 2000nm; ② Hold the load for 10s at the maximum load to eliminate the creep effect; ③ First unload to 0.

[0062] (3)For the samples of the second cementing interface after 2 days of curing, use a German ZEISS Sigma 300 backscattered scanning electron microscope for testing. Utilize the gray value of the backscattered image and conduct quantitative analysis through the gray value of the pixel points. With the help of Image-Pro Plus6.0 software, conduct quantitative analysis on the hydration products of the interface transition layer.

[0063] ① ITZ Microhardness Test Analysis Figure 7 is the nanoindentation test diagram under the transmission electron microscope, which includes the tested dot matrix and the morphology of the interface transition zone.

[0064] Generally speaking, the elastic modulus of the hydration products is between 10 and 40 GPa, and the hardness is between 0.4 and 2 GPa. Those greater than this range can be considered as unhydrated particles, and those less than this range can be considered as void defects; among the hydration products, CH (40 ± 4.3 GPa) has the highest elastic modulus and hardness values; the elastic modulus of HD C-S-H (26 ± 3.4 GPa) is slightly higher than that of LD C-S-H (18.2 ± 4.2 GPa), and these two hydration products are relatively close. Therefore, based on the results of a large number of nanoindentation tests in a certain micro-region of the hardened cement paste, if there is no large amount of experimental data, the modulus distribution maps near each indentation hole can be tested to calculate the content of the relevant hydration products. In this experiment, the latter method is proposed to calculate the content of its hydration products.

[0065] From Figure 8 , Figure 9 , Figure 10 , Figure 11 , Figure 12 , Figure 13 , Figure 14 , Figure 15 It can be seen from the elastic modulus strength distribution map that the elastic modulus and hardness values gradually increase with the increase of the distance from the interfacial zone. From the modulus distribution map, the number of points of the effective modulus in the systems of experimental group 1 and experimental group 3 is more than that in the control group and experimental group 2. In terms of numerical distribution, the number of indentation modulus points of CH in the systems of experimental group 1 and experimental group 3 is more than that in the other two systems. However, the number of indentation modulus points of HD C-S-H and LDC-S-H inside the other two systems is more than that in the systems of experimental group 1 and experimental group 3. In terms of the interfacial bonding strength, the bonding strength of the control group is less than that of experimental group 1, experimental group 2, and experimental group 3, but the bonding strength of the control group is still in a relatively high strength range.

[0066] Apply statistical analysis to the data obtained from the experiment to analyze the content of the relevant hydration products. The specific content change diagram is as follows Figure 16As shown, the specific contents are shown in Table 5: It can be known from the table that the content of CH in the control group system is 18%, the content of LD C-S-H is 33%, the content of HD C-S-H is 10.8%, and the total content of hydration products reaches 61.8%; the indentation points in the experimental group system are mainly hydration products, among which the content of CH is 48%, the content of LD C-S-H is 9.7%, the content of HD C-S-H is 19%, and the total content of hydration products reaches 76.7%;. The amount of hydration products in the system determines the compressive strength of the system and the bonding strength of the interface. The system with more hydration products has higher strength. Among the hydration products, the close packing of CH crystals and cement particles greatly improves the friction force at the interface and the mechanical interlocking force at the interface. The two hydration products, HD C-S-H and LD C-S-H, control the toughness of the cement matrix, ensure the long-term development of the bonding strength at the interface, and play an important protective role in the safety of oil well construction.

[0067] Table 5 Content Table of Hydration Products

[0068] ② ITZ Microscopic Morphology Test and Analysis Select the backscattered scanning electron microscopy results with better test effects, and the morphology is as follows Figure 17 、 Figure 18 、 Figure 19 and Figure 20 shown.

[0069] From the microscopic morphology of the interface transition layer of the control group system Figure 17 it can be seen that the pore structure in the system is thick and large, the surface of the system is broken and unevenly arranged, the content of C-S-H is small, and the unhydrated particles and the CH structure formed by hydration are alternately stacked, resulting in a fragile and weakly bonded interface.

[0070] As Figure 18 shown, from the microscopic morphology of the interface transition layer of Experimental Group 1, it can be seen that there are more pore structures in the system, and the calcium silicate hydrate gel is mainly distributed at the interface transition layer, tightly connected with other hydration products, resulting in a compact interface transition layer, and the macroscopic manifestation is high interface bonding strength.

[0071] As Figure 19 shown, from the microscopic morphology of the interface transition layer of Experimental Group 2, it can be seen that there are a large number of C-S-H flocculent structures at the interface bonding, there are more CH and AFm phases in the system, the system is relatively compact, and the pore structure is less.

[0072] As Figure 20As shown in the figure, the microscopic morphology of the interfacial transition layer of Experimental Group 3 shows that the C-S-H structure in the system has been hydrated to the extent of HD C-S-H, reaching a fused state with other hydration products in the system. The degree of hydration is relatively high, the pore structure in the system is relatively thick, the gap at the interfacial cementation is small, and the interfacial cementation strength is high.

[0073] Using the gray value of the backscattered image and quantitative analysis through the gray value of pixel points, the analysis results are shown in Table 6.

[0074] Table 6 Specific content of hydration products under backscattering

[0075] (6) Experimental results and discussion: ① There are a large number of calcium silicate hydrate C-S-H structures inside the control group system. The calcium silicate structure is a gel-like substance with poor mechanical properties, and it cannot form a tight packing. The interaction force with the interface is low, and the interfacial cementation strength is low.

[0076] ② In Experimental Group 1 and Experimental Group 2 systems, the interface is uneven under low-magnification scanning electron microscopy, with connected smooth structures and fragmented gravel accumulation structures. From high-magnification scanning electron microscopy, it can be seen that the smooth structure is a combined calcium silicate hydrate gel system, and the gravel accumulation structure is composed of some ettringite, CH, and unhydrated cement particles. The interfacial cementation is good, the frictional resistance is large, and the mechanical interlocking force is large. The CH structure of the hydration products in the experimental group system is relatively large, so the interfacial cementation strength can be improved.

[0077] ③ In the control group system, there is a phenomenon of enrichment of cement particles and hydration products at the interface in the initial stage of hydration. This phenomenon leads to a decrease in the packing density of the cement matrix, and the density inside the cement slurry system cannot be kept consistent. When injecting the annular cement sheath, the interface will attract the migration of moisture inside the slurry to the interface to form a water film. Less C-S-H structure is generated in the initial stage, and a small amount of flaky CH crystals are generated. The disordered arrangement of flaky CH crystals and unhydrated cement particles leads to an increase in the porosity at the interface, thus forming a networked broken microstructure layer enriched with CH crystals and cement particles at the interface, and the early hydration strength changes slowly. The experimental group system with an interface enhancer has stronger penetration ability for the interfacial water film layer, resulting in Ca 2+ 、Fe 3+ 、silicate ions and Al 3+Migrate towards the interface, react with the water film at the interface to generate hydrated products and deposit them. Subsequently, they will nucleate and grow in the crystal structures of calcium silicate hydrate, CH, and ettringite, and the interface strength develops rapidly. At the interface junction, the reactive admixture consumes CH, and the hydrated products recrystallize during the hydration process to form Aft. Due to the increase in the hydrated products with a three-dimensional structure, the interface becomes rough and the interface friction increases, ensuring the stability of the later strength.

[0078] ④ Under the backscattered scanning electron microscope image, the interfaces between the casing and the cement, and between the cement and the core can be clearly seen, and the interfaces are tightly cemented with a small gap width. The interface transition layers of the systems in Experimental Group 1 and Experimental Group 3 are more tightly cemented compared to the control group. A large number of hydrated product structures can be seen in the backscattered images of the systems in Experimental Group 1 and Experimental Group 3. Calcium silicate hydrate (C-S-H) and CH are abundantly present and closely arranged at the interface, and the interface cementation degree is good. It is proved that the interface enhancer plays a role in improving the cementing strength of the well cementing interface.

[0079] In summary, through the interaction between different types of cementitious materials and the time difference of the hydration reaction, the present invention improves the cementing strength and compactness of the system, achieves the purpose of efficiently improving the cementing strength, and screens out a high-interface-cementing-strength cement slurry system that meets the requirements of well cementing construction. This system includes the following components in parts by weight: 100 parts of oil well cement 1 - 5 parts of interface enhancer 0.2 - 0.5 part of fluid loss reducer 0.2 - 0.5 part of friction reducer 0.1 - 0.2 part of retarder 44 parts of fresh water.

[0080] As an improvement, the high-interface-cementing-strength cement slurry system further includes 0.1 - 0.2 parts by weight of defoamer. As a further preferred embodiment, the interface enhancer is a mixture composed of one or more of modified calcium silicate hydrate powder, potassium hexatitanate whiskers, metakaolin, silica, flake graphite, and latex powder.

[0081] As a further preferred embodiment, the fineness of the modified calcium silicate hydrate powder is 1000 - 2000 mesh, the fineness of the potassium hexatitanate whiskers is 1000 - 2000 mesh, the fineness of the metakaolin is 1000 - 2000 mesh, the fineness of the silica is 1000 - 2000 mesh, the fineness of the flake graphite is 1000 - 2000 mesh, and the fineness of the latex powder is 1000 - 2000 mesh.

[0082] In a preferred embodiment, the interface enhancer is prepared by compounding hydrated calcium silicate powder with 1000 mesh, potassium hexatitanate whiskers with 1000 mesh, and silica powder with 2000 mesh in a mass ratio of (2 - 6):(1 - 3):(0.2 - 1).

[0083] In another preferred embodiment, the interface enhancer is prepared by compounding hydrated calcium silicate powder with 1500 mesh, potassium hexatitanate whiskers with 1500 mesh, and metakaolin with 1000 mesh in a mass ratio of (1 - 4):(1 - 3):(1 - 3).

[0084] In another preferred embodiment, the interface enhancer is prepared by compounding hydrated calcium silicate powder with 1000 mesh, potassium hexatitanate whiskers with 2000 mesh, metakaolin with 1250 mesh, flake graphite with 500 mesh, and latex powder with 1500 mesh in a mass ratio of (1 - 4):(1 - 3):(0.5 - 2):(1 - 2):(1 - 2).

[0085] As a further preferred embodiment, the preparation method of the modified hydrated calcium silicate: The preparation method of the modified hydrated calcium silicate includes the following steps: a. Weigh hydrated calcium silicate powder with a fineness of 300 - 500 mesh and a silane coupling agent, add them to 200 mL of a modified solvent, after ultrasonic dispersion treatment for 30 min, adjust the pH to 4 - 5 with anhydrous oxalic acid; wherein the mass ratio of the hydrated calcium silicate powder to the silane coupling agent is (2 - 3):(0.5 - 1); b. Continue to add a certain amount of hydrated calcium silicate powder, after ultrasonic dispersion for 2 - 3 h, transfer the reaction solution to a 500 mL flask, keep the liquid temperature at 60 - 70 °C, and carry out condensation reflux at a speed of 500 - 800 r / min for 3 h to obtain a milky white gel liquid; The mass of the hydrated calcium silicate powder in this step is 10% - 20% of the mass of the hydrated calcium silicate powder in step a; c. First, wash and purify the milky white gel liquid obtained in step b with anhydrous ethanol to remove the unreacted silane coupling agent, then carry out suction filtration, and dry it in an incubator at 60 °C for 24 h. Put the dried powder, ball mill grinding balls, and water into a ball mill tank in a mass ratio of (1 - 2):(1 - 2):(0.5 - 1) for wet grinding for 2 - 3 h. During the wet grinding process, control the rotation speed at 600 - 800 r / min. After grinding, take it out and screen it through a 1000 - 2000 mesh sieve to obtain the modified hydrated calcium silicate powder.

[0086] In a further preferred embodiment, the modified solvent is a mixed liquid formed by mixing anhydrous ethanol and deionized water in a volume ratio of (2 - 5):1.

[0087] As a further preferred embodiment, the preparation method of the potassium hexatitanate whiskers is as follows: Using analytical pure TiO2 and K2CO3 as raw materials, the two are compounded in a molar ratio of (4 - 6):1, dried at 60°C for 24 hours, and after drying, ground and dry-mixed with a pulverizer. The mixed raw materials are placed in a ceramic crucible and heated in a muffle furnace at 800 - 1000°C for 1 - 4 hours. After cooling to room temperature in the furnace, it is taken out and sieved through a 1000 - 2000 mesh sieve to obtain potassium hexatitanate whiskers.

[0088] The present invention further provides a preparation method of a cement slurry system with high interfacial bonding strength, which is characterized by including the following steps: S1. Take 100 parts by weight of oil well cement and 1 - 5 parts by weight of an interfacial enhancer, and mix the two evenly to obtain a dry powder mixture; S2. Weigh 44 parts by weight of water, mix 0.2 - 0.5 parts by weight of a fluid loss reducer, 0.2 - 0.5 parts by weight of a drag reducer, 0.1 - 0.2 parts by weight of an antifoaming agent, and 0.1 - 0.2 parts by weight of a retarder into the water, then pour it into a stirrer, and the stirrer rotates at a low speed of 4000 ± 200 revolutions per minute; S3. Add the dry powder mixture obtained in step S1 to the stirrer in step S2 within 15 seconds, adjust the rotation speed of the stirrer, and continue to stir at a high speed of 12000 ± 500 revolutions per minute for 35 seconds to obtain the cement slurry system with high interfacial bonding strength.

[0089] It is worth mentioning that the performance of the above cement slurry system with high interfacial bonding strength can reach the following indicators: (1) System density: 1.75 - 2.00 g / cm 3 ; (2) Applicable temperature: 30 - 90°C; (3) Requirements for the interfacial bonding strength of the cement stone: Compared with a pure cement system with the same density, the interfacial bonding strength is increased by 30% - 50%.

[0090] The following further describes the present invention in combination with preferred embodiments: Example 1 This example relates to a cement slurry system with high interfacial bonding strength, and its formula is as follows: 100 parts of high sulfate-resistant G-class oil well cement, 3 parts of an interfacial enhancer (a modified hydrated calcium silicate powder with 1000 mesh, potassium hexatitanate whiskers with 1000 mesh, and metakaolin with 1250 mesh are compounded in a mass ratio of 3:1:1), 0.2 parts of a drag reducer USZ for oil well cement, 0.2 parts of a fluid loss reducer G33S for oil well cement, 0.1 part of an antifoaming agent, 0.1 part of a retarder, and 44 parts of fresh water.

[0091] The preparation process of the modified hydrated calcium silicate powder is as follows: Take a mixed solution of absolute ethanol and deionized water with a volume ratio of 5:1 as the modification solvent. Weigh 30% of the silane coupling agent based on the mass of ordinary hydrated calcium silicate powder (300 mesh), add it to 200 mL of the modification solvent, after ultrasonic dispersion for 30 min, adjust the pH to about 4.5 with anhydrous oxalic acid, then add a certain amount of hydrated calcium silicate powder, after ultrasonic dispersion for 2 h, transfer the above reaction solution to a 500 mL flask, and reflux it at 65 °C at a speed of 500 r / min for 3 h to obtain a milky gel liquid, wash and purify it with absolute ethanol to remove the unreacted coupling agent, then filter it by suction, and dry it in an incubator at 60 °C for 24 h. Put the dried powder, grinding balls, and water into a ball mill tank according to the ratio (the mass ratio of powder, balls, and water is 1:1:0.5), wet grind for 2 h at a speed of 600 r / min, take it out and screen it through a 1000-mesh sieve after grinding to obtain the modified hydrated calcium silicate powder.

[0092] The preparation process of potassium hexatitanate whiskers is as follows: Using analytical pure TiO2 and K2CO3 as raw materials, proportion them according to the molar ratio of 4:1, dry them and then grind and mix them dry with a XA-1 type high-speed universal grinder. Put the mixed raw materials into a ceramic crucible, heat them in a muffle furnace at 800 °C for 4 h, take them out after cooling to room temperature with the furnace and screen them through a 1000-mesh sieve to obtain potassium hexatitanate whiskers.

[0093] The preparation process of the cement slurry system is as follows: Take 100 parts of oil well cement and 3 parts of interface enhancer, and mix the dry powders evenly; weigh 44 parts of water, mix 0.2 part of drag reducer USZ for oil well cement, 0.2 part of fluid loss reducer G33S for oil well cement, 0.1 part of defoamer, and 0.1 part of retarder into the water, pour it into a stirrer, the stirrer rotates at a low speed (4000 ± 200 revolutions per minute), and add the weighed dry powder mixture within 15 s, then continue to stir at a high speed (12000 ± 500 revolutions per minute) for 35 s to obtain a cement slurry system with high interface bonding strength.

[0094] Example 2 This example relates to a cement slurry system with high interface bonding strength, and its formula is: 100 parts of high sulfate-resistant G-grade oil well cement, 2 parts of interface enhancer (compounded by mixing 1500-mesh modified hydrated calcium silicate powder, 1000-mesh potassium hexatitanate whiskers, and 2000-mesh silica powder in a mass ratio of 1:1:0.5), 0.5 part of drag reducer USZ for oil well cement, 0.2 part of fluid loss reducer G33S for oil well cement, 0.2 part of defoamer, 0.1 part of retarder, 44 parts of fresh water.

[0095] The preparation process of the modified hydrated calcium silicate powder is as follows: Take a mixed solution of absolute ethanol and deionized water with a volume ratio of 2:1 as the modification solvent. Weigh 40% of the silane coupling agent based on the mass of ordinary hydrated calcium silicate powder (500 mesh), add it to 200 mL of the modification solvent, after ultrasonic dispersion for 30 min, adjust the pH to about 4.5 with anhydrous oxalic acid, then add a certain amount of hydrated calcium silicate powder, after ultrasonic dispersion for 3 h, transfer the above reaction solution to a 500 mL flask, and carry out reflux condensation at 65 °C at a speed of 800 r / min for 3 h to obtain a milky gel liquid, wash and purify it with absolute ethanol to remove the unreacted coupling agent, then filter it by suction, and dry it in an incubator at 60 °C for 24 h. Put the dried powder, grinding balls, and water into a ball mill tank according to the ratio (the mass ratio of powder, balls, and water is 1:1:0.5), wet mill for 2.5 h, the rotation speed is 600 - 800 r / min, after grinding, take it out and sieve it through a 1500-mesh sieve to obtain the modified hydrated calcium silicate powder.

[0096] The preparation process of potassium hexatitanate whiskers is as follows: Using analytical pure TiO2 and K2CO3 as raw materials, proportion the two according to a molar ratio of 5:1, after drying, grind and mix them dry with a XA-1 type high-speed universal grinder, put the mixed raw materials into a ceramic crucible, heat in a muffle furnace at 1000 °C for 4 h, take it out after cooling to room temperature with the furnace and sieve it through a 1000-mesh sieve to obtain potassium hexatitanate whiskers.

[0097] The preparation process of the cement slurry system is as follows: Take 100 parts of oil well cement and 2 parts of interface enhancer, and mix the dry powder evenly; weigh 44 parts of water, mix 0.5 part of drag reducer USZ for oil well cement, 0.2 part of fluid loss reducer G33S for oil well cement, 0.2 part of defoamer, and 0.1 part of retarder into the water and pour it into a stirrer. The stirrer rotates at a low speed (4000 ± 200 revolutions per minute), and add the weighed dry powder mixture within 15 seconds, and continue to stir at a high speed (12000 ± 500 revolutions per minute) for 35 seconds to obtain a cement slurry system with high interface bonding strength.

[0098] Example 3 This example relates to a cement slurry system with high interface bonding strength, and its formula is: 100 parts of high sulfate-resistant G-class oil well cement, 5 parts of interface enhancer (compounded by 1000-mesh modified hydrated calcium silicate powder, 1500-mesh potassium hexatitanate whiskers, 1000-mesh flake graphite, and 1500-mesh latex powder in a mass ratio of 1:1:0.5:1), 0.2 part of drag reducer USZ for oil well cement, 0.5 part of fluid loss reducer G33S for oil well cement, 0.1 part of defoamer, 0.1 part of retarder, and 44 parts of fresh water.

[0099] The preparation process of modified calcium silicate hydrate powder is as follows: Take a mixed solution of absolute ethanol and deionized water with a volume ratio of 3:1 as the modification solvent. Weigh 40% of the silane coupling agent based on the mass of ordinary calcium silicate hydrate powder (500 mesh), add it to 200 mL of the modification solvent, after ultrasonic dispersion for 30 min, adjust the pH to about 4.5 with anhydrous oxalic acid, then add a certain amount of calcium silicate hydrate powder, after ultrasonic dispersion for 3 h, transfer the above reaction solution to a 500 mL flask, and carry out reflux condensation at 65 °C at a speed of 800 r / min for 3 h to obtain a milky gel liquid, wash and purify it with absolute ethanol to remove the unreacted coupling agent, then filter it by suction, and dry it in an incubator at 60 °C for 24 h. Put the dried powder, grinding balls, and water into a ball mill tank according to the ratio (the mass ratio of powder, balls, and water is 1:1:0.5), wet grind for 3 h at a speed of 800 r / min, take it out and sieve it through a 1000-mesh sieve after grinding to obtain the modified calcium silicate hydrate powder.

[0100] The preparation process of potassium hexatitanate whiskers is as follows: Using analytical pure TiO2 and K2CO3 as raw materials, proportion them according to a molar ratio of 5:1, dry them and then grind and mix them dry with an XA-1 type high-speed universal grinder. Put the mixed raw materials into a ceramic crucible, heat them in a muffle furnace at 800 °C for 1 h, take them out after cooling to room temperature with the furnace, and sieve them through a 1500-mesh sieve to obtain potassium hexatitanate whiskers.

[0101] The preparation process of the cement slurry is as follows: Take 100 parts of oil well cement and 5 parts of the interface enhancer, and mix the dry powders evenly; weigh 44 parts of water, mix 0.2 part of the drag reducer USZ for oil well cement, 0.5 part of the fluid loss reducer G33S for oil well cement, 0.1 part of the defoamer, and 0.1 part of the retarder into the water, pour it into a stirrer, the stirrer rotates at a low speed (4000 ± 200 revolutions per minute), and add the weighed dry powder mixture within 15 s, and continue to stir at a high speed (12000 ± 500 revolutions per minute) for 35 s to obtain a cement slurry system with high interface bonding strength.

[0102] Example 4 This example relates to a cement slurry system with high interface bonding strength, and its formula is as follows: 100 parts of high sulfate-resistant G-class oil well cement, 5 parts of the interface enhancer (a compound of 1000-mesh modified calcium silicate hydrate powder, 2000-mesh potassium hexatitanate whiskers, 1250-mesh metakaolin, 1000-mesh flake graphite, and 1500-mesh latex powder in a mass ratio of 1:1:1:1:1), 0.5 part of the drag reducer USZ for oil well cement, 0.5 part of the fluid loss reducer G33S for oil well cement, 0.1 part of the defoamer, 0.1 part of the retarder, and 44 parts of clear water.

[0103] The preparation process of modified calcium silicate hydrate powder is as follows: Take a mixed solution of absolute ethanol and deionized water with a volume ratio of 3:1 as the modification solvent. Weigh 40% of the silane coupling agent based on the mass of ordinary hydrated calcium silicate powder (500 mesh), add it to 200 mL of the modification solvent, after ultrasonic dispersion for 30 min, adjust the pH to about 4.5 with anhydrous oxalic acid, then add a certain amount of hydrated calcium silicate powder, after ultrasonic dispersion for 3 h, transfer the above reaction solution to a 500 mL flask, and carry out reflux condensation at 65 °C at a speed of 800 r / min for 3 h to obtain a milky gel liquid, wash and purify it with absolute ethanol to remove the unreacted coupling agent, then filter it by suction, and dry it in an incubator at 60 °C for 24 h. Put the dried powder, grinding balls, and water into a ball mill tank according to the ratio (the mass ratio of powder, balls, and water is 1:1:0.5), wet mill for 3 h at a speed of 800 r / min, take it out and sieve it through a 1000-mesh sieve after grinding to obtain modified hydrated calcium silicate powder.

[0104] The preparation process of potassium hexatitanate whiskers is as follows: Using analytical pure TiO2 and K2CO3 as raw materials, proportion them according to the molar ratio of 6:1, dry them and grind and mix them dry with a XA-1 type high-speed universal grinder, put the mixed raw materials into a ceramic crucible, heat them in a muffle furnace at 900 °C for 4 h, take them out after cooling to room temperature with the furnace and sieve them through a 2000-mesh sieve to obtain potassium hexatitanate whiskers.

[0105] The preparation process of the cement slurry system is as follows: Take 100 parts of oil well cement and 5 parts of interface enhancer, and mix the dry powder evenly; weigh 44 parts of water, mix 0.5 part of drag reducer USZ for oil well cement, 0.5 part of fluid loss reducer G33S for oil well cement, 0.1 part of defoamer, and 0.1 part of retarder into the water and pour it into a stirrer. The stirrer rotates at a low speed (4000 ± 200 r / min), and add the weighed dry powder mixture within 15 s, and continue to stir at a high speed (12000 ± 500 r / min) for 35 s to obtain a cement slurry system with high interface bonding strength.

[0106] Control example Formula: 100 parts of high sulfate-resistant G-class oil well cement, 0.2 part of drag reducer USZ, 0.5 part of fluid loss reducer G33S, 0.1 part of defoamer, 44 parts of fresh water.

[0107] The preparation process of the cement slurry system is as follows: Take 100 parts of oil well cement and 44 parts of water, mix 0.2 part of drag reducer USZ, 0.5 part of fluid loss reducer, and 0.1 part of defoamer into 44 parts of water and pour it into a stirrer. The stirrer rotates at a low speed (4000 ± 200 r / min), and continue to stir at a high speed (12000 ± 500 r / min) for 35 s to obtain a cement slurry system with high interface bonding strength.

[0108] I. Mechanical Property Tests After curing each cement slurry system at 50°C and 70°C under normal pressure for 1 day, 2 days, and 7 days, the compressive strength of the hardened cement stone was measured. The test results are shown in Table 7.

[0109] Table 7 Compressive Strength of Cement Stone at Different Ages (MPa)

[0110] After curing each cement slurry system at 50°C and 70°C under normal pressure for 1 day, 2 days, and 7 days, the bond strength of the hardened cement stone was measured. The test results are shown in Table 8 and Table 9.

[0111] Table 8 Bond Strength of the First Interface of Cement Stone at Different Ages (MPa)

[0112] Table 9 Bond Strength of the Second Interface of Cement Stone at Different Ages (MPa)

[0113] From the test results in Tables 7, 8, and 9, it can be seen that compared with the control group, the compressive strength and bond strength of the experimental group with the addition of the interface enhancer increased by 30 - 50%, achieving the expected effect.

[0114] II. Comprehensive Property Tests The cement slurry fluidity, density, free liquid, water loss, and thickening time of the comparative example and Examples 1, 2, 3, and 4 were measured respectively in accordance with the national standard GB / T 19139 - 2012. The measurement results are shown in Table 10.

[0115] Table 10 Evaluation of the Construction Performance of Cement Slurry System

[0116] From the comprehensive properties of the cement slurry system in Table 10, it can be seen that compared with the comparative example, the high - interface - bond - strength cement slurry system has better stability, the density difference between top and bottom ≤ 0.04 g / cm 3 , the thickening time is adjustable, the water loss ≤ 50 mL, and the comprehensive properties of the cement slurry system meet the requirements of cementing construction.

[0117] The above are only the preferred embodiments of the present invention, which are illustrative for the present invention rather than limiting the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A cement slurry system with high interfacial bonding strength, characterized in that, It comprises the following components by weight parts: 100 parts of oil well cement 1 - 5 parts of interface enhancer 0.2 - 0.5 parts of fluid loss reducer 0.2 - 0.5 parts of drag reducer 0.1 - 0.2 parts of retarder 44 parts of fresh water.

2. The high-interfacial-bonding-strength cement slurry system according to claim 1, wherein: The high - interface - bonding - strength cement slurry system further comprises 0.1 - 0.2 parts by weight of defoamer.

3. The high-interfacial-bonding-strength cement slurry system according to claim 1, characterized in that: The interface enhancer is a mixture composed of one or more of modified hydrated calcium silicate powder, potassium hexatitanate whiskers, metakaolin, silica, flake graphite, and latex powder.

4. The high-interfacial-bonding-strength cement slurry system according to claim 3, wherein: The fineness of the modified hydrated calcium silicate powder is 1000 - 2000 mesh, the fineness of the potassium hexatitanate whiskers is 1000 - 2000 mesh, the fineness of the metakaolin is 1000 - 2000 mesh, the fineness of the silica is 1000 - 2000 mesh, the fineness of the flake graphite is 1000 - 2000 mesh, and the fineness of the latex powder is 1000 - 2000 mesh.

5. The high-interfacial-bonding-strength cement slurry system according to claim 1, wherein: The interface enhancer is compounded from 1000 - mesh modified hydrated calcium silicate powder, 1000 - mesh potassium hexatitanate whiskers, and 2000 - mesh silica powder according to the mass ratio of (2 - 6):(1 - 3):(0.2 - 1).

6. The high-interfacial-bonding-strength cement slurry system according to claim 1, characterized in that: The interface enhancer is compounded from 1000 - mesh modified hydrated calcium silicate powder, 2000 - mesh potassium hexatitanate whiskers, 1250 - mesh metakaolin, 500 - mesh flake graphite, and 1500 - mesh latex powder according to the mass ratio of (1 - 4):(1 - 3):(0.5 - 2):(1 - 2):(1 - 2).

7. The high-interfacial-bonding-strength cement slurry system according to any one of claims 2-6, characterized in that The preparation method of the modified hydrated calcium silicate comprises the following steps: a. Weigh hydrated calcium silicate powder with a fineness of 300 - 500 mesh and a silane coupling agent, add them into 200 mL of modified solvent, after ultrasonic dispersion treatment for 30 min, adjust the pH to 4 - 5 with anhydrous oxalic acid; wherein the mass ratio of the hydrated calcium silicate powder to the silane coupling agent is (2 - 3):(0.5 - 1); b. Continuously add a certain amount of hydrated calcium silicate powder, after ultrasonic dispersion for 2 - 3 h, transfer the reaction solution to a 500 - mL flask, keep the liquid temperature at 60 - 70 °C, and carry out condensation reflux at a speed of 500 - 800 r / min for 3 h to obtain a milky white gel liquid; the mass of the hydrated calcium silicate powder in this step is 10% - 20% of the mass of the hydrated calcium silicate powder in step a; c. First, wash and purify the milky white gel liquid obtained in step b with anhydrous ethanol to remove the unreacted silane coupling agent, then carry out suction filtration, and dry it in an incubator at 60 °C for 24 h. Put the dried powder, ball mill grinding balls, and water into a ball mill tank according to the mass ratio of (1 - 2):(1 - 2):(0.5 - 1) for wet grinding for 2 - 3 h. During the wet grinding process, control the rotation speed at 600 - 800 r / min. After grinding, take it out and sieve it through a 1000 - 2000 - mesh sieve to obtain the modified hydrated calcium silicate powder.

8. The high-interfacial-bonding-strength cement slurry system according to any one of claims 7, characterized in that, The modified solvent is a mixed liquid composed of anhydrous ethanol and deionized water according to the volume ratio of (2 - 5):

1.

9. The high-interfacial-bonding-strength cement slurry system according to any one of claims 2-6, characterized in that The preparation method of the potassium hexatitanate whiskers is as follows: Using analytical pure TiO2 and K2CO3 as raw materials, the two are compounded in a molar ratio of (4-6):1, dried at 60°C for 24 hours, ground and dry-mixed with a pulverizer after drying, the mixed raw materials are put into a ceramic crucible, heated in a muffle furnace at 800-1000°C for 1-4 hours, taken out after cooling to room temperature with the furnace, and sieved through a 1000-2000 mesh sieve to obtain potassium hexatitanate whiskers.

10. A preparation method of a cement slurry system with high interfacial bonding strength, characterized in that, It includes the following steps: S1. Take 100 parts by weight of oil well cement and 1-5 parts by weight of an interfacial enhancer, and mix the two evenly to obtain a dry powder mixture; S2. Weigh 44 parts by weight of water, mix 0.2-0.5 parts by weight of a fluid loss reducer, 0.2-0.5 parts by weight of a drag reducer, 0.1-0.2 parts by weight of an antifoaming agent, and 0.1-0.2 parts by weight of a retarder into the water, then pour it into a stirrer, and the stirrer rotates at a low speed of 4000±200 revolutions per minute; S3. Add the dry powder mixture obtained in step S1 to the stirrer in step S2 within 15 seconds, adjust the rotation speed of the stirrer, and continue to stir at a high speed of 12000±500 revolutions per minute for 35 seconds to obtain the high interfacial bonding strength cement slurry system.

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