A cement slurry and its use in cementing natural gas hydrate-bearing formations

Abstract

The application provides a cement slurry for well cementation and application of the cement slurry in well cementation of a natural gas hydrate-containing formation, raw materials of the cement slurry include, by mass fraction, oil well cement 100 parts, low-temperature early strength material 10-50 parts, solid-solid phase change endothermic agent 5-30 parts and lightening agent 30-50 parts. The low-temperature low-hydration heat well cementing slurry system of the application has the characteristics of low-temperature early strength, low hydration heat, low density, low fluid loss and anti-channeling, and the thickening time and the development of compressive strength also meet the requirements of field well cementation construction. The low-temperature low-hydration heat well cementing slurry system is especially suitable for deep water well cementation operation of a natural gas hydrate-containing formation.

Description

Technical Field

[0001] This invention relates to a low-temperature cementing technology, and more particularly to a cementing slurry and its application in cementing formations containing natural gas hydrates. Background Technology

[0002] With the continuous exploitation of conventional oil and gas resources, these resources can no longer meet the ever-increasing energy demand, and the difficulty of increasing and stabilizing production is growing. To address the shortage of oil and gas resources and ensure energy security, future oil and gas exploration and development are gradually shifting towards unconventional resources. Natural gas hydrates are a new type of unconventional potential energy source, mainly distributed in seabed sediments and onshore permafrost. Natural gas hydrates are considered one of the most promising new clean energy sources to replace coal, oil, and natural gas.

[0003] Cementing technology for natural gas hydrates is a crucial step in the exploitation of natural gas hydrates. Natural gas hydrate wells are characterized by large water depths, shallow drilling depths, and difficulties in controlling wellbore temperature. Natural gas hydrate reservoirs are generally deep. During cementing, the heat released during cement hydration raises the ambient temperature around the wellbore, altering the temperature environment of the surrounding hydrates and causing their decomposition. The decomposition of hydrates leads to a dramatic expansion, generating a large amount of gas that intrudes into the cement slurry. This results in several problems: firstly, it causes micro-annular voids between the already well-bonded cement sheath and the wellbore, degrading cementing quality; secondly, the continuous upward ejection of gas has serious consequences. Furthermore, the decomposition of hydrates destabilizes the formation in the area. If a collapse occurs, it can destroy the entire formation, creating a vicious cycle that leads to the complete decomposition of surrounding hydrates, ultimately resulting in cementing failure and a series of other problems.

[0004] Given the abundant natural gas hydrate resources, accelerating the development of marine natural gas hydrates is of great significance for ensuring energy supply and security. The cementing process is a crucial link and safety guarantee in the development of marine natural gas hydrates. During cementing, it is necessary to reduce the heat of hydration of the cement slurry, control and eliminate the impact of natural gas hydrate decomposition on cementing quality, and simultaneously possess properties such as low heat of hydration, low-temperature early strength, and prevention of gas channeling. Therefore, it is essential to construct a low-temperature, early-strength, low-heat-of-hydration cement slurry system suitable for natural gas hydrate wells.

[0005] CN105462571A discloses a low-temperature cement slurry system and its composition. The cement slurry system has the characteristics of low-temperature early strength, low density, and low water loss. The thickening time and compressive strength development also meet the field requirements. However, this invention only considers the deep water environment and does not involve the problem of hydrate decomposition that needs to be faced when cementing hydrate-bearing formations, nor does it involve the relevant research on low hydration heat of cement.

[0006] CN101328050A discloses a low-heat hydration cement slurry system for cementing natural gas hydrate formations. This system uses G-grade oil well cement as a base material and incorporates materials that reduce overall hydration heat release, improving the overall performance of the cement under low heat release conditions. The heat release of cement hydration is controlled by adding high-specific-surface-area slag and fly ash, thereby preventing the decomposition of deep-water hydrates. However, this invention uses large amounts of low-hydration-activity cementitious materials such as fly ash and blast furnace slag, resulting in low early compressive strength of the cement paste.

[0007] CN106634899A discloses a liquid colloidal-filled low-temperature cementing slurry system. This system uses a ternary four-component particle size distribution system formed by hollow glass microspheres, silicate cement, ultrafine silicate cement, and microsilica. Under low-temperature conditions, it exhibits low density, high strength, and low permeability. A certain amount of liquid colloid is added to further fill the cement slurry system. Silica sol is a novel anti-gas channeling material that can rapidly improve the anti-gas channeling performance of the cement slurry system. However, this invention mainly considers the slurry's slurry properties and does not address the regulation of the exothermic reaction of cement hydration. Summary of the Invention

[0008] To address the challenges of natural gas hydrate decomposition and gas channeling during cementing, and to prevent the decomposition of natural gas hydrate during cementing, ensuring the safety and quality of cementing in natural gas hydrate formations, this invention aims to provide a low-temperature, low-heat cementing slurry suitable for cementing formations containing natural gas hydrate.

[0009] To achieve the above objectives, the present invention provides a cementing slurry, the raw materials of which, by mass parts, include: 100 parts of oil well cement, 10-50 parts of low-temperature early strength material, 5-30 parts of solid-solid phase change endothermic agent, and 30-50 parts of weight-reducing agent.

[0010] The solid-solid phase change endothermic agent includes nano-silica and surface adsorption materials, wherein the surface adsorption materials include expanded graphite and paraffin wax; the paraffin wax is the core material and the expanded graphite is the encapsulating material.

[0011] The cement slurry of this invention features low heat of hydration and early strength at low temperatures, and its properties such as water loss and thickening time meet the requirements of low-temperature cementing operations. In this invention, the addition of a solid-solid phase change endothermic agent effectively regulates the heat release during cement slurry hydration, effectively reducing the adiabatic temperature rise of the cement slurry. The water loss reducing agent has the advantages of not thickening and minimal side effects from slowing settling at low temperatures, making it suitable for low-temperature cementing of natural gas hydrates.

[0012] Preferably, the raw materials of the above-mentioned cementing slurry also include: 1.2-2.8 parts of fluid loss reducing agent, 0.3-2.2 parts of dispersant, 0.1-0.4 parts of defoamer, and 87-160 parts of preparation water.

[0013] This invention first experimentally tests the thickening time and static gel strength development of oil well cement and ultrafine oil well cement at different particle sizes and mass ratios. Based on the experimental results, the particle size and mass ratio of each component are adjusted to optimize the thickening time and static gel strength performance of the system, thus obtaining the basic composition of cement and various admixtures in a low-temperature, low-heat-of-hydration cement slurry system. Secondly, the influence of solid-solid phase change endothermic agents on the hydration heat release characteristics of cement slurry is tested and analyzed. Solid-solid phase change endothermic agents with significant hydration heat control effects and their dosages are selected. Simultaneously, this solid-solid phase change endothermic agent... The heat-generating agent has little impact on the rheological properties of cement slurry and no side effects on the development of the compressive strength of cement stone. Then, the early-strength agent with the best effect on improving compressive strength and its dosage are selected, while the early-strength agent should have little impact on the fluidity of the cement slurry. Finally, by screening dispersants, fluid loss reducers and other admixtures with little side effects on cement hydration under low-temperature conditions, and testing and analyzing the rheological properties, fluid loss and settling stability of cement slurry, the types of dispersants, fluid loss reducers and other admixtures and their optimal dosages are selected, thus forming a low-temperature, low-hydration-heat cement slurry system.

[0014] This invention optimizes the selection of highly active silicate materials (low-temperature early-strength materials), phase change endothermic agents, and weight-reducing agents, and further optimizes the addition amounts of admixtures (fluid loss reducers, dispersants, early-strength agents, and defoamers), ultimately forming a low-temperature, low-heat-of-hydration cement slurry system. This cement slurry system features low-temperature early strength and low heat of hydration, and its thickening time, strength development, and fluid loss properties meet the requirements of field cementing.

[0015] In the above-mentioned cement slurry, preferably, the low-temperature early-strength material includes early-strength cement and hydrated calcium silicate nanocrystal nucleus early-strength agent in a mass ratio of 1:0.08-0.38.

[0016] In the above-mentioned cementing slurry, preferably, the hydrated calcium silicate nanocrystal nucleus early strength agent is prepared by a hydrothermal method from calcium nitrate and sodium silicate.

[0017] The specific preparation process of the hydrated calcium silicate nanocrystal nucleus early strength agent of the present invention is as follows: 200 parts by mass of calcium nitrate and sodium silicate (mass ratio 1:0.82-1.05) are dissolved in 500 parts by mass of deionized water and stirred thoroughly in a reaction vessel; the pH of the solution is adjusted to 12-14 with sodium hydroxide, and the solution is placed in a preheated water bath at 80-120°C under nitrogen atmosphere for hydrothermal synthesis reaction for 5-10 hours. Simultaneously, the mixed solution is dispersed using an ultrasonic instrument. After the reaction is complete, hydrated calcium silicate is obtained; the hydrated calcium silicate is repeatedly rinsed with deionized water and anhydrous ethanol, and then the filtered hydrated calcium silicate is placed in a vacuum drying oven for drying for 1-2 days, finally obtaining the hydrated calcium silicate nanocrystal nucleus early strength agent. During the stirring process of calcium nitrate and sodium silicate in the reaction vessel, the fluid rotates under the action of the stirring blades, generating strong eddies. The motion state is turbulent, and the eddies continuously break and merge during the motion. During the hydrothermal synthesis process, the initially generated calcium silicate hydrate product exhibits good fluid adaptability and can be rolled into spherical particles under shear torque. Using this method, the resulting calcium silicate hydrate nanocrystal nucleus early-strength agent has a finer particle size, reaching the nanoscale, and does not agglomerate, which is beneficial for improving the early-strength effect and overall performance of the nucleus.

[0018] In the above-mentioned cementing slurry, preferably, the early-strength cement is obtained by crushing oil well grade G cement and / or oil well grade A cement.

[0019] In the aforementioned cementing slurry, preferably, the early-strength cement has an average particle size of 7.5-13.5 μm and a specific surface area of ​​550-1000 m². 2 / kg.

[0020] The cementing slurry system of the present invention forms a dense packing system between material particles such as silicate cement and oil well ultrafine cement, and the resulting cement stone has the characteristics of low density, high strength and low permeability.

[0021] In the above-mentioned cement slurry, preferably, the mass ratio of expanded graphite to paraffin is 1:10-30.

[0022] In the above-mentioned cementing slurry, preferably, the mass ratio of the nano-silica to the surface adsorption material is 1:5-15.

[0023] The solid-solid phase change endothermic agent of the present invention is prepared by using paraffin or modified paraffin phase change material as core material and expanded graphite as encapsulation material. The preparation method of this solid-solid phase change endothermic agent includes the following steps: (1) Take an appropriate amount of expandable graphite and calcine it in a muffle furnace at 600-1000℃ for 1-5 hours to allow it to fully expand and obtain expanded graphite; (2) Take an appropriate amount of paraffin or modified paraffin phase change material and heat it to a molten state at 40-60℃ to obtain molten paraffin core material; (3) Mix the expanded graphite and molten paraffin core material at a mass ratio of 1:10-1:30 to obtain the adsorbent material; (4) Prepare nano-silica using the sol-gel method, and encapsulate the adsorbent mixture material by the self-assembly of nano-silica deposition, and mix and hydrolyze an appropriate amount of tetraethyl orthosilicate or propyl orthosilicate with an appropriate amount of deionized water and anhydrous ethanol; (5) Mix the hydrolysis product with the adsorbent material at a mass ratio of 1:5-1:15 and stir for 2-4 hours to obtain the solid-solid phase change endothermic agent. This preparation method ensures that no liquid will precipitate after the paraffin undergoes an endothermic phase change, thus reducing the adverse effects of the phase change material on cement hydration and strength.

[0024] In the above-mentioned cementing slurry, preferably, the phase change temperature of the solid-solid phase change endothermic agent is 10-30℃, the latent heat of phase change is 150-300J / g, and the average particle size is 30-150μm.

[0025] In the above-mentioned cementing slurry, preferably, the oil well cement is selected from oil well grade G cement and / or oil well grade A cement (API oil well cement grade).

[0026] In the aforementioned cementing slurry, preferably, the weight-reducing agent is selected from soda lime borosilicate glass microspheres. The true density of the weight-reducing agent added in this invention is 0.32-0.40 g / cm³. 3 With a particle size of 10-50μm and a compressive strength ≥40MPa, it features light weight, high compressive strength, and good chemical stability.

[0027] In the above-mentioned cementing slurry, preferably, the fluid loss reducing agent is selected from non-ionic polyvinyl alcohol crosslinked fluid loss reducing agents. This fluid loss reducing agent has the advantages of not thickening and having minimal low-temperature retarding side effects, making the cementing slurry of the present invention suitable for cementing in hydrate-prone low-temperature environments.

[0028] In the aforementioned cementing slurry, preferably, the dispersant is selected from sulfonated formaldehyde-acetone condensate dispersant. This dispersant has minimal adverse effects on cement setting at low temperatures.

[0029] In the aforementioned cement slurry, preferably, the defoamer is selected from polyether-organosilicon compound defoamers. The defoamer added in this invention can effectively eliminate the large amount of foam generated during the preparation of cement slurry by nonionic polyvinyl alcohol crosslinking fluid loss reducing agent, ensuring that the density of the cement slurry prepared on-site is consistent with the design density, and ensuring the normal progress of cementing slurry preparation and construction.

[0030] Preferably, in the above-mentioned cement slurry, the water used for preparation is selected from clean water, seawater, or formation mineralization water.

[0031] The present invention also provides an application of the above-mentioned cementing slurry in cementing formations containing natural gas hydrates.

[0032] In the above applications, preferably, the ambient temperature is 2-22℃, more preferably 15℃.

[0033] Compared to cement-based cement slurry (water-cement ratio 0.44), the total 24-hour hydration heat release of the cement slurry system of this invention can be reduced by 40%, effectively controlling the hydration heat release of the cement slurry. It is particularly suitable for cementing operations in marine natural gas hydrate formations, and is of great significance for natural gas hydrate development. It provides important technical support for the future development of marine natural gas hydrate cementing technology, related industry standards, and hydrate development. The low-temperature cement slurry system of this invention uses readily available and low-cost raw materials, has good compatibility with conventional cementing admixtures, and is convenient for on-site construction.

[0034] The cementing slurry of the present invention has the following beneficial effects:

[0035] The low-temperature, low-heat-of-hydration cement slurry system provided by this invention possesses characteristics such as low-temperature early strength, low heat of hydration, low density, low fluid loss, and anti-channeling properties. Furthermore, its thickening time and compressive strength development also meet the requirements of on-site cementing operations. This low-temperature, low-heat-of-hydration cement slurry system is particularly suitable for deepwater cementing operations in formations containing natural gas hydrates. Attached Figure Description

[0036] Figure 1 The hydration exothermic and adiabatic temperature rise curves of the cement slurry in Example 1 and Comparative Example 1 are shown.

[0037] Figure 2 The compressive strength of the cement stone formed by the cement slurry of Example 1 and Comparative Example 1. Detailed Implementation

[0038] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail below, but it should not be construed as limiting the scope of implementation of the present invention.

[0039] The hydrated calcium silicate nanocrystal nucleus early strength agent used in this embodiment of the invention is prepared by the following method: 200 parts by mass of calcium nitrate and sodium silicate in a mass ratio of 1:0.87 are dissolved in 500 parts by mass of deionized water and stirred thoroughly in a reaction vessel; the pH of the solution is adjusted to 13 with sodium hydroxide and placed in a preheated water bath at 90°C for hydrothermal synthesis reaction for 8 hours under nitrogen atmosphere, while the mixed solution is dispersed using an ultrasonic instrument. After the reaction is completed, hydrated calcium silicate is obtained; the hydrated calcium silicate is repeatedly rinsed with deionized water and anhydrous ethanol, and then the filtered hydrated calcium silicate is placed in a vacuum drying oven for drying for 1 day, finally obtaining the hydrated calcium silicate nanocrystal nucleus early strength agent.

[0040] The solid-solid phase change endothermic agent used in the embodiments of the present invention is prepared by the following method: (1) Take an appropriate amount of expandable graphite and calcine it in a muffle furnace at 800℃ for 4 hours to make it fully expand and obtain expanded graphite; (2) Take an appropriate amount of paraffin or modified paraffin phase change material and heat it to a molten state at 50℃ to obtain molten paraffin core material; (3) Mix the expanded graphite and molten paraffin core material at a mass ratio of 1:18 to obtain the adsorbent material; (4) Prepare nano-silica using the sol-gel method, and encapsulate the adsorbent mixture material by the self-assembly of nano-silica deposition, and mix and hydrolyze an appropriate amount of tetraethyl orthosilicate or propyl orthosilicate with an appropriate amount of deionized water and anhydrous ethanol; (5) Mix the hydrolysis product with the adsorbent material at a mass ratio of 1:10 and stir for 3 hours to obtain the solid-solid phase change endothermic agent.

[0041] All other raw materials used in the examples are commercially available products.

[0042] The experimental methods used in the examples are as follows: cement slurry was prepared according to the standard deep water cementing test standard API 10B-3-2004, and the compressive strength, hydration heat release and other properties of the cement slurry were measured.

[0043] The present invention will now be described in conjunction with specific embodiments.

[0044] Example 1

[0045] This embodiment provides a low-temperature, low-hydration-heat cementing slurry, which is composed of the following: 100 parts of G-grade cement for oil wells, 35 parts of ultrafine cement (early-strength cement (average particle size 10μm)), 1.5 parts of crystal nucleation early-strength agent (hydrated calcium silicate nanocrystal nucleation early-strength agent), 15 parts of solid-solid phase change endothermic agent, 30 parts of weight-reducing agent (soda lime borosilicate glass microspheres), 2.2 parts of water loss reducing agent (nonionic polyvinyl alcohol crosslinking water loss reducing agent), 1 part of dispersant (sulfonated formaldehyde-acetone condensate dispersant), and 0.3 parts of defoamer (polyether-organosilicon compound defoamer), totaling 110 parts.

[0046] Example 2

[0047] This embodiment provides a low-temperature, low-hydration-heat cementing slurry, the composition of which is as follows: 100 parts of oil well grade G cement, 30 parts of early-strength cement (average particle size 10μm), 2.0 parts of hydrated calcium silicate nanocrystal nucleus early-strength agent, 15 parts of solid-solid phase change endothermic agent, 30 parts of soda lime borosilicate glass microspheres, 2.2 parts of nonionic polyvinyl alcohol crosslinking water loss reducing agent, 1 part of sulfonated formaldehyde-acetone condensate dispersant, 0.3 parts of polyether-organosilicon compound defoamer, and 110 parts of water.

[0048] Example 3

[0049] This embodiment provides a low-temperature, low-hydration-heat cementing slurry, the composition of which is as follows: 100 parts of oil well grade G cement, 40 parts of early-strength cement (average particle size 10μm), 2.0 parts of hydrated calcium silicate nanocrystal nucleus early-strength agent, 15 parts of solid-solid phase change endothermic agent, 30 parts of soda lime borosilicate glass microspheres, 2.2 parts of nonionic polyvinyl alcohol crosslinking water loss reducing agent, 1.2 parts of sulfonated formaldehyde-acetone condensate dispersant, 0.3 parts of polyether-organosilicon compound defoamer, and 118 parts of water.

[0050] Example 4

[0051] This embodiment provides a low-temperature, low-hydration-heat cementing slurry, the composition of which is as follows: 100 parts of oil well grade G cement, 40 parts of early-strength cement (average particle size 10μm), 2.0 parts of hydrated calcium silicate nanocrystal nucleus early-strength agent, 10 parts of solid-solid phase change endothermic agent, 28 parts of soda lime borosilicate glass microspheres, 2.3 parts of nonionic polyvinyl alcohol crosslinking water loss reducing agent, 1 part of sulfonated formaldehyde-acetone condensate dispersant, 0.3 parts of polyether-organosilicon compound defoamer, and 118 parts of water.

[0052] Example 5

[0053] This embodiment provides a low-temperature, low-hydration-heat cementing slurry, which is composed of the following: 100 parts of oil well grade G cement, 40 parts of early-strength cement (average particle size 10μm), 2.0 parts of hydrated calcium silicate nanocrystal nucleus early-strength agent, 20 parts of solid-solid phase change endothermic agent, 25 parts of soda lime borosilicate glass microspheres, 2.3 parts of nonionic polyvinyl alcohol crosslinking water loss reducing agent, 1.5 parts of sulfonated formaldehyde-acetone condensate dispersant, 0.3 parts of polyether-organosilicon compound defoamer, and 120 parts of water.

[0054] Comparative Example 1

[0055] This comparative example provides a cement slurry base for cementing, which is composed of the following: 100 parts of G-grade cement for oil wells, 0.3 parts of polyether-organosilicon compound defoamer, and 44 parts of water.

[0056] Comparative Example 2

[0057] This comparative example provides a low-density cement slurry, the composition of which is as follows: 100 parts of G-grade cement for oil wells, 30 parts of soda lime borosilicate glass microspheres, 2.3 parts of nonionic polyvinyl alcohol crosslinking fluid loss reducing agent, 1.2 parts of sulfonated formaldehyde-acetone condensate dispersant, 0.3 parts of polyether-organosilicon compound defoamer, and 98 parts of water.

[0058] Comparative Example 3

[0059] This comparative example provides a low-density, low-hydration-heat cementing slurry, the composition of which is as follows: 100 parts of G-grade cement for oil wells, 20 parts of solid-solid phase change endothermic agent, 30 parts of soda lime borosilicate glass microspheres, 2.3 parts of nonionic polyvinyl alcohol crosslinking water loss reducing agent, 1.5 parts of sulfonated formaldehyde-acetone condensate dispersant, 0.3 parts of polyether-organosilicon compound defoamer, and 90 parts of water.

[0060] Comparative Example 4

[0061] This comparative example provides a low-density, low-heat-of-hydration, early-strength cement slurry, the composition of which is as follows: 100 parts of oil well grade G cement, 40 parts of early-strength cement (average particle size 10μm), 20 parts of solid-solid phase change endothermic agent, 30 parts of soda lime borosilicate glass microspheres, 2.3 parts of nonionic polyvinyl alcohol crosslinking water loss reducing agent, 1.5 parts of sulfonated formaldehyde-acetone condensate dispersant, 0.3 parts of polyether-organosilicon compound defoamer, and 120 parts of water.

[0062] Comparative Example 5

[0063] This comparative example provides a low-density, low-hydration-heat-of-conversion, early-strength cement slurry, the composition of which is as follows: 100 parts of oil well G-grade cement, 2.0 parts of hydrated calcium silicate nanocrystal nucleus early-strength agent, 20 parts of solid-solid phase change endothermic agent, 30 parts of soda lime borosilicate glass microspheres, 2.3 parts of nonionic polyvinyl alcohol crosslinking water loss reducing agent, 1.5 parts of sulfonated formaldehyde-acetone condensate dispersant, 0.3 parts of polyether-organosilicon compound defoamer, and 120 parts of water.

[0064] Experimental Example 1

[0065] This experimental example tests the hydration heat regulation performance of the cement slurry system in Example 1.

[0066] Using the cement slurry system in Example 1 as the test object, and the cement slurry base slurry in Comparative Example 1 as the comparison, the hydration heat release of the two cement slurries was tested using an I-Cal Flex isothermal calorimeter according to the standard method in GB / T12959-2008, "Determination of Heat of Hydration of Cement". The test results are as follows: Figure 1 As shown in the figure, the maximum adiabatic temperature rise of the cement slurry system in Example 1 is significantly lower than that of the cement slurry base slurry in Comparative Example 1.

[0067] Experiment Example 2

[0068] This experimental example tests the hydration heat performance of the cement slurry systems in the above embodiments and comparative examples.

[0069] Using the cement slurry systems from the above embodiments and comparative examples as test objects, the raw materials were pretreated according to the national standard GB / T33294-2016, "Test Method for Deep Water Cementing," to ensure uniform mixing. After pretreatment, the cement components were accurately weighed according to the design formula, referring to section 5.3.4 of the national standard GB / T 19139-2012, "Test Method for Oil Well Cement." Dry and wet materials were mixed uniformly separately, and then a cement slurry was prepared using an intelligent constant-speed mixer. The density, API water loss, rheological properties, and other properties of the cement slurry were then tested according to the methods described in Chapter 6 of the national standard GB / T 19139-2012, "Test Method for Oil Well Cement." The experimental results are shown in Table 1.

[0070] Table 1. Test results of cement slurry properties (15℃)

[0071]

[0072] The results show that the cement slurry of the present invention has a small hydration exothermic adiabatic temperature rise, high low-temperature early strength, and is lightweight, has low water loss, suitable thickening time, and good rheological properties.

[0073] Experimental Example 3

[0074] This experimental example tests the heat of hydration and compressive strength of the cement slurry systems of the above embodiments and comparative examples.

[0075] Using the cement slurry systems from the above embodiments and comparative examples as test objects, the raw materials were pretreated according to the national standard GB / T33294-2016 "Test Method for Deep Water Cementing" to ensure uniform mixing. After pretreatment, the cement components were accurately weighed according to the design formula, referring to section 5.3.4 of the national standard GB / T 19139-2012 "Test Method for Oil Well Cement". The dry and wet materials were mixed evenly separately, and then a smart constant-speed mixer was used to prepare the cement slurry. The adiabatic temperature rise of the cement slurry was tested according to the method described in GB / T2022-1980 "Test Method for Heat of Hydration of Cement (Direct Method)". The compressive strength of the solidified cement stone was tested according to the method described in Chapter 6 of the national standard GB / T 19139-2012 "Test Method for Oil Well Cement". The experimental results are shown in Table 2.

[0076] The compressive strengths of the low-temperature, low-heat cementing slurry of Example 1 and the cement slurry base of Comparative Example 1 after curing for 24 hours and 48 hours are as follows: Figure 2 As shown, the curing temperature is 15℃.

[0077] Table 2. Test results of hydration heat release, adiabatic temperature rise, and strength properties of cement slurry.

[0078]

[0079] The above results indicate that the cementing slurry of this application has low heat of hydration and good compressive strength.

Claims

1. A cementing slurry, comprising, by weight parts: 100 parts oil well cement, 10-50 parts low-temperature early strength material, 5-30 parts solid-solid phase change endothermic agent, and 30-50 parts weight-reducing agent; The solid-solid phase change endothermic agent includes nano-silica and surface adsorption materials, wherein the surface adsorption materials include expanded graphite and paraffin wax; the paraffin wax is the core material, the expanded graphite is the encapsulating material, and the mass ratio of the expanded graphite to the paraffin wax is 1:10-30. The preparation method of the solid-solid phase change endothermic agent specifically includes the following steps: (1) Take an appropriate amount of expandable graphite and place it in a muffle furnace at 600-1000℃ for calcination for 1-5 hours to allow it to fully expand and obtain expanded graphite; (2) Take an appropriate amount of paraffin wax and heat it to a molten state at 40-60℃ to obtain molten paraffin wax core material; (3) Mix the expanded graphite and molten paraffin wax core material at a mass ratio of 1:10-1:30 to obtain the adsorbent material; (4) Prepare nano-silica using the sol-gel method, and encapsulate the adsorbent mixture material through the deposition and self-assembly of nano-silica; take an appropriate amount of tetraethyl orthosilicate or propyl orthosilicate and mix it with an appropriate amount of deionized water and anhydrous ethanol for hydrolysis; (5) Mix the hydrolysis product with the adsorbent material at a mass ratio of 1:5-1:15 and stir for 2-4 hours to obtain the solid-solid phase change endothermic agent; The low-temperature early strength material includes early strength cement and hydrated calcium silicate nanocrystal nucleus early strength agent in a mass ratio of 1:0.08-0.38; The early-strength cement is obtained by crushing oil well grade G cement and / or oil well grade A cement; the average particle size of the early-strength cement is 7.5-13.5µm, and the specific surface area is 550-1000m². 2 / kg.

2. The cement slurry according to claim 1, wherein, Its raw materials also include: 1.2-2.8 parts of water loss reducing agent, 0.3-2.2 parts of dispersant, 0.1-0.4 parts of defoamer, and 87-160 parts of preparation water.

3. The cement slurry according to claim 1, wherein, The hydrated calcium silicate nanocrystal nucleus early strength agent is prepared from calcium nitrate and sodium silicate by a hydrothermal method.

4. The cement slurry according to claim 1, wherein, The mass ratio of the nano-silica to the surface adsorption material is 1:5-15.

5. The cement slurry according to claim 1, wherein, The solid-solid phase change endothermic agent has a phase change temperature of 10-30℃, a latent heat of phase change of 150-300J / g, and an average particle size of 30-150µm.

6. The cementing slurry according to claim 1, wherein, The oil well cement is selected from oil well grade G cement and / or oil well grade A cement.

7. The cement slurry according to claim 1, wherein, The weight-reducing agent is selected from soda lime borosilicate glass microspheres.

8. The cement slurry according to claim 2, wherein, The water loss reducing agent is selected from nonionic polyvinyl alcohol crosslinking water loss reducing agents.

9. The cement slurry according to claim 2, wherein, The dispersant is selected from sulfonated formaldehyde-acetone condensate dispersants.

10. The cementing slurry according to claim 2, wherein, The defoamer is selected from polyether-organosilicon compound defoamers.

11. The application of the cementing slurry according to any one of claims 1-10 in cementing formations containing natural gas hydrates.

12. The application according to claim 11, wherein, The application environment temperature is 2-22℃.

Images