A stepwise-cured geopolymer and a preparation method and application thereof

Abstract

The present application relates to a kind of cascade solidification geopolymer and its preparation method and application.The raw materials of the geopolymer include geopolymer material and activator;The geopolymer material is selected from at least two of latent active geopolymer material, low active geopolymer material, medium active geopolymer material and high active geopolymer material.The raw materials of the geopolymer described in the present application contain different active geopolymer materials, and different active geopolymer materials can occur in sequence when activator is encountered Solidification reaction, so that the solidification performance of the geopolymer can be controlled by adjusting the type and proportion of different active geopolymer materials, so that the geopolymer described in the present application can overcome the harm caused by its fast solidification speed while exerting the performance advantage of geopolymer material.

Description

Technical Field

[0001] This invention belongs to the field of geopolymer technology, specifically relating to a graded-curing geopolymer, its preparation method, and its application. Background Technology

[0002] The concept of geopolymers was proposed by Professor Davidovits of France in 1978. It refers to a type of alkaline-active aluminosilicate material, such as metakaolinite, which, under the action of an alkaline activator, transforms from [SiO4]... 4- With [AlO4] 5- Geopolymers are three-dimensional, network-structured silica-alumina cementitious materials composed of structural units. Compared to other commonly used hydraulic materials, geopolymers offer significant advantages. Their preparation process can reduce energy consumption by over 70% and carbon emissions by over 80% compared to traditional cement, with no sulfur or nitrogen oxide emissions. Geopolymers are also known as "green cement." Their three-dimensional network structure endows them with a series of excellent physicochemical properties, including high-temperature stability, mechanical properties, corrosion resistance, and durability. They are a highly promising non-traditional cementitious material with the potential to replace traditional silicate cement. Therefore, geopolymers are attracting increasing attention from researchers.

[0003] However, although geopolymers have superior physicochemical properties compared to silicate cement, their excessively rapid hydration rate is the biggest obstacle to their application. Geopolymers require strong alkali treatment to achieve better performance, but their short setting time (<0.5h at 80℃ with retarders) does not meet operational requirements, severely hindering their widespread use, especially in oilfield cementing projects. The main drawbacks are twofold: 1. Short curing time, especially uncontrollable at high temperatures, affecting construction safety. 2. High slurry consistency, a major reason why they cannot be industrially applied. Therefore, controlling the curing time of geopolymers is a primary research direction in this field.

[0004] Currently, research in this area mainly focuses on selecting high-performance geopolymer retarders to control their curing time. Invention patent CN201910426647.3 discloses a suitable retarder for geopolymer materials, composed of 30-40 wt% potassium dihydrogen phosphate, 30-50 wt% borax, and 20-30 wt% calcium chloride. Invention patent CN201810851330.X uses lignin sulfonate water-reducing agents and phosphate retarders to achieve good workability in concrete. Invention patent CN201810095913.4 discloses a hydrophobic spherical inorganic material that exerts a ball-bearing effect in geopolymer slurries to reduce friction. Invention patent CN201810770099.1 discloses a carbohydrate-based geopolymer retarder, comprising 0%-80% carbohydrate compounds, 0%-80% sugar alcohol compounds, and 10%-90% water. Invention patent CN200810020859.3 discloses a method using divalent alkaline earth metal salts magnesium chloride, calcium chloride, barium chloride, calcium nitrate, and barium nitrate as retarder. The literature "Influence of Different Admixtures on the Setting and Hardening Properties of Geopolymers" proposes using boric acid to retard and control the fluidity of slag powder-based geopolymers. Experiments show that within the dosage range of 0-4%, the setting time of the geopolymer increases significantly with increasing boric acid dosage, while the fluidity loss over time decreases and the compressive strength slightly increases.

[0005] However, the aforementioned patents and literature all control the curing time of geopolymer materials by adding admixtures, which inevitably increases costs and operational complexity. Therefore, there is an urgent need to develop a new method for controlling the curing time of geopolymers and a corresponding geopolymer. Summary of the Invention

[0006] This invention addresses the significant limitations of traditional silicate cement materials in improving their high-temperature stability, mechanical properties, corrosion resistance, and durability in the oil and gas well cementing industry. While geopolymers offer significant advantages in these areas, their curing time is too rapid. Although adding admixtures can optimize the curing time to some extent, it increases cost and operational complexity, and the optimization effect and stability are limited. This invention provides a geopolymer capable of stepwise curing. The geopolymer contains geopolymer materials with different activities. Under the action of an activator, these geopolymer materials with different activities cure at different times, and thus, under the activation of the activator, they can undergo stepwise curing. By adjusting the types and proportions of different active geopolymer materials in the geopolymer, the curing time can be controlled within 7-12 hours, allowing the geopolymer of this invention to overcome the harmful effects of its excessively rapid curing speed while leveraging the performance advantages of geopolymer materials.

[0007] Therefore, in a first aspect, the present invention provides a graded-curing geopolymer, the raw materials of which include geopolymer materials and activators; wherein the geopolymer materials are selected from at least two of latently active geopolymer materials, low-activity geopolymer materials, medium-activity geopolymer materials and high-activity geopolymer materials.

[0008] In some preferred embodiments of the present invention, the mass ratio of the activator to the geopolymer material is 0.3 to 0.8; preferably 0.4 to 0.6.

[0009] In some embodiments of the present invention, under the action of the activator, the time required for the latently active geopolymer material, the low-activity geopolymer material, the medium-activity geopolymer material, and the high-activity geopolymer material to cure and the mechanical properties of the cured products are all different.

[0010] In some preferred embodiments of the present invention, under the action of the activator, the time required for the latently active geopolymer material, the low-activity geopolymer material, the medium-activity geopolymer material, and the high-activity geopolymer material to cure decreases sequentially.

[0011] In some embodiments of the present invention, the latently active geopolymer material, the low-activity geopolymer material, the medium-activity geopolymer material, and the high-activity geopolymer material are respectively prepared by calcining kaolin at different temperatures.

[0012] In some embodiments of the present invention, the calcination temperature of the latently active geopolymer material is not higher than 600°C or the calcination temperature is higher than 950°C.

[0013] The calcination temperature of the low-activity geopolymer material is higher than 600°C and not higher than 650°C or higher than 850°C and not higher than 950°C.

[0014] The calcination temperature of the active geopolymer material is higher than 650°C and not higher than 700°C or higher than 750°C and not higher than 850°C.

[0015] The calcination temperature of the highly active geopolymer material is higher than 700℃ and not higher than 750℃.

[0016] In some embodiments of the present invention, the calcination time is 1.5 to 2.5 hours; preferably 1.8 to 2.2 hours.

[0017] In some embodiments of the present invention, the activator is an aqueous solution containing an alkaline substance, preferably an aqueous solution containing an alkali metal hydroxide and a silicate; more preferably an aqueous solution containing sodium hydroxide and sodium silicate.

[0018] In some preferred embodiments of the present invention, the concentration of sodium hydroxide in the activator is 2-6 mol / L, preferably 3-5 mol / L, and / or the concentration of sodium silicate is 1-6 mol / L, preferably 2-4 mol / L.

[0019] In some embodiments of the present invention, the curing properties of the geopolymer are controlled by adjusting the types and contents of latently active, low-activity, medium-activity, and high-activity geopolymers in the geopolymer material; preferably, the curing properties include curing time and the mechanical properties of the product obtained after curing.

[0020] In other embodiments of the present invention, the curing time of the geopolymer can be controlled within 7 to 12 hours at a curing temperature of 30 to 300°C.

[0021] In some specific embodiments of the present invention, when the geopolymer material contains 40 to 60 parts by weight of medium-active geopolymer material and 90 to 110 parts by weight of highly active geopolymer material, the curing time of the geopolymer at a curing temperature of 30 to 50°C can be controlled within 7 to 12 hours.

[0022] In other specific embodiments of the present invention, when the geopolymer material contains 40-60 parts by weight of low-activity geopolymer material, 90-110 parts by weight of medium-activity geopolymer material and 8-12 parts by weight of high-activity geopolymer material; or when it contains 40-60 parts by weight of latently active geopolymer material and 90-110 parts by weight of medium-activity geopolymer material, the curing time of the geopolymer at a curing temperature of 30-200°C can be controlled within 7-12 hours.

[0023] In some specific embodiments of the present invention, when the geopolymer material contains 40 to 60 parts by weight of low-activity geopolymer material and 70 to 90 parts by weight of medium-activity geopolymer material, the curing time of the geopolymer at a curing temperature above 50°C and not above 300°C can be controlled within 7 to 12 hours.

[0024] In other specific embodiments of the present invention, when the geopolymer contains 90-110 parts by weight of latently active geopolymer and 8-12 parts by weight of moderately active geopolymer, or contains 90-110 parts by weight of low-activity geopolymer and 15-25 parts by weight of moderately active geopolymer, the curing time of the geopolymer at a curing temperature above 200°C and not above 300°C can be controlled within 7-12 hours.

[0025] A second aspect of the present invention provides a method for preparing a graded-curing geopolymer as described in the first aspect of the present invention, comprising the following steps:

[0026] S1, kaolin was calcined at different temperatures to obtain latently active geopolymer materials, low-activity geopolymer materials, medium-activity geopolymer materials and high-activity geopolymer materials respectively;

[0027] S2, at least two of the latently active geopolymer material, low-activity geopolymer material, medium-activity geopolymer material and high-activity geopolymer material are mixed with an activator to cause the geopolymer materials with different activities to undergo stepwise solidification, thereby obtaining the stepwise solidified geopolymer.

[0028] The third aspect of the present invention provides the application of a graded-curing geopolymer as described in the first aspect of the present invention or a graded-curing geopolymer prepared by the method described in the second aspect of the present invention in oilfield cementing.

[0029] The beneficial effects of this invention are as follows: The raw materials of the geopolymer of this invention contain geopolymer materials with different activities, and these geopolymer materials with different activities can undergo curing reactions sequentially when exposed to an activator. Therefore, the curing performance of the geopolymer, such as the curing time, can be controlled and regulated simply by adjusting the types and proportions of the geopolymer materials with different activities. This allows the geopolymer of this invention to overcome the hazards caused by its excessively fast curing speed while leveraging the performance advantages of geopolymer materials. Specifically, the curing time of the geopolymer of this invention can be controlled within 7 to 12 hours, the bond strength after 1 day of curing can reach over 12 MPa, and the cement stone strength after 7 days can reach over 21 MPa. Detailed Implementation

[0030] The present invention will now be described in detail.

[0031] As mentioned earlier, although geopolymers have outstanding advantages in terms of high-temperature stability, mechanical properties, corrosion resistance, and durability, their development and application are restricted due to their excessively fast curing time.

[0032] The inventors of this application discovered through research that calcining kaolin, a raw material for geopolymers, at different temperatures can produce geopolymer materials with different activities—metakaolin. These geopolymer materials with different activities exhibit varying curing times upon contact with an activator, as well as different mechanical properties of the cured products. Therefore, by adjusting the types and contents of different active geopolymer materials in the geopolymer raw material, the curing properties (e.g., curing time) of the geopolymer can be controlled and regulated, achieving curing control and long-term strength development. This allows the advantages of geopolymer materials to be utilized while overcoming the harmful effects of excessively rapid curing.

[0033] Therefore, the step-curing geopolymer involved in the first aspect of the present invention comprises geopolymer materials and activators as raw materials; the geopolymer materials are selected from at least two of the following: latently active geopolymer materials, low-activity geopolymer materials, medium-activity geopolymer materials, and high-activity geopolymer materials.

[0034] In some preferred embodiments of the present invention, the mass ratio of the activator to the geopolymer material is 0.3 to 0.8; preferably 0.4 to 0.6; and more preferably 0.5.

[0035] In some embodiments of the present invention, under the action of the activator, the time required for the latently active geopolymer material, the low-activity geopolymer material, the medium-activity geopolymer material, and the high-activity geopolymer material to cure and the mechanical properties of the cured products are all different.

[0036] In some preferred embodiments of the present invention, under the action of the activator, the time required for the latently active geopolymer material, the low-activity geopolymer material, the medium-activity geopolymer material, and the high-activity geopolymer material to cure decreases sequentially.

[0037] In this invention, "tiered curing" refers to the sequential curing reaction of highly active geopolymer materials, moderately active geopolymer materials, low-active geopolymer materials, and latently active geopolymer materials in geopolymer materials under the action of an activator.

[0038] The geopolymer materials of this invention feature a reasonable interval between different active components and a clear sequence of reactions. The active components complement each other, with lower-activity components ensuring later strength development and higher-activity components providing early strength support. All active components are uniformly distributed within the geopolymer system, enabling uniform curing.

[0039] In some embodiments of the present invention, the latently active geopolymer material, the low-activity geopolymer material, the medium-activity geopolymer material, and the high-activity geopolymer material are respectively prepared by calcining kaolin at different temperatures.

[0040] Kaolin has a layered silicate structure, with layers bonded by van der Waals bonds, where OH- ions are firmly bound. Its crystal building blocks consist of silicon-oxygen tetrahedra and aluminum-oxygen octahedra, stacked in a specific ratio by sharing oxygen atoms. In this crystal structure, silicon and aluminum atoms are confined within the crystal lattice, lacking chemical reactivity, not participating in hydration reactions, and exhibiting no cementing properties. However, when kaolin is heated in air, it undergoes several structural changes. At approximately 600°C, the layered structure of kaolin breaks down due to dehydration, forming a poorly crystallized, cementing transition phase—metakaolin. Metakaolin formed from kaolin calcined at different temperatures exhibits varying degrees of molecular irregularity and displays different thermodynamic metastable states, making it an ideal raw material for achieving stepwise solidification reactions in geopolymers.

[0041] In some embodiments of the present invention, the calcination temperature of the latently active geopolymer material is not higher than 600°C or the calcination temperature is higher than 950°C. In some specific embodiments of the present invention, the calcination temperature of the latently active geopolymer material can be 100°C, 200°C, 300°C, 400°C, 500°C, 600°C, 980°C, or 1100°C, etc.

[0042] In some embodiments of the present invention, the calcination temperature of the low-activity geopolymer material is higher than 600°C and not higher than 650°C, or higher than 850°C and not higher than 950°C. In some specific embodiments of the present invention, the calcination temperature of the low-activity geopolymer material can be 620°C, 650°C, 880°C, 900°C, or 950°C, etc.

[0043] In some embodiments of the present invention, the calcination temperature of the moderately active geopolymer material is higher than 650°C and not higher than 700°C, or higher than 750°C and not higher than 850°C. In some specific embodiments of the present invention, the calcination temperature of the moderately active geopolymer material can be 680°C, 700°C, 780°C, 800°C, or 850°C, etc.

[0044] In some other embodiments of the present invention, the calcination temperature of the highly active geopolymer material is higher than 700°C and not higher than 750°C. In some specific embodiments of the present invention, the calcination temperature of the highly active geopolymer material can be 710°C, 720°C, 730°C, 740°C, or 750°C, etc.

[0045] In some embodiments of the present invention, the calcination time is 1.5 to 2.5 hours; preferably 1.8 to 2.2 hours; and more preferably 2 hours.

[0046] In some embodiments of the present invention, the activator is an aqueous solution containing an alkaline substance, preferably an aqueous solution containing an alkali metal hydroxide and a silicate; more preferably an aqueous solution containing sodium hydroxide and sodium silicate.

[0047] In some preferred embodiments of the present invention, the concentration of sodium hydroxide in the activator is 2-6 mol / L, preferably 3-5 mol / L, and / or the concentration of sodium silicate is 1-6 mol / L, preferably 2-4 mol / L.

[0048] In some specific embodiments of the present invention, the concentration of sodium hydroxide in the activator is 4 mol / L and the concentration of sodium silicate is 3 mol / L.

[0049] In some embodiments of the present invention, the curing properties of the geopolymer are controlled by adjusting the types and contents of latently active, low-activity, medium-activity, and high-activity geopolymers in the geopolymer material; preferably, the curing properties include curing time and the mechanical properties of the product obtained after curing.

[0050] That is, the present invention does not specifically limit the types and contents of latently active geopolymer materials, low-activity geopolymer materials, medium-activity geopolymer materials and high-activity geopolymer materials in the stepwise curing geopolymer raw materials. They can be appropriately adjusted according to the final required curing performance (such as curing time and mechanical properties of the product obtained after curing).

[0051] In some embodiments of the present invention, the curing time of the geopolymer can be controlled within 7 to 12 hours at a curing temperature of 30 to 300°C.

[0052] In some specific embodiments of the present invention, when the geopolymer material contains 40 to 60 parts by weight of medium-active geopolymer material and 90 to 110 parts by weight of highly active geopolymer material, the curing time of the geopolymer at a curing temperature of 30 to 50°C can be controlled within 7 to 12 hours.

[0053] In other specific embodiments of the present invention, when the geopolymer material contains 40-60 parts by weight of low-activity geopolymer material, 90-110 parts by weight of medium-activity geopolymer material and 8-12 parts by weight of high-activity geopolymer material; or when it contains 40-60 parts by weight of latently active geopolymer material and 90-110 parts by weight of medium-activity geopolymer material, the curing time of the geopolymer at a curing temperature of 30-200°C can be controlled within 7-12 hours.

[0054] In some specific embodiments of the present invention, when the geopolymer material contains 40 to 60 parts by weight of low-activity geopolymer material and 70 to 90 parts by weight of medium-activity geopolymer material, the curing time of the geopolymer at a curing temperature above 50°C and not above 300°C can be controlled within 7 to 12 hours.

[0055] In other specific embodiments of the present invention, when the geopolymer contains 90-110 parts by weight of latently active geopolymer and 8-12 parts by weight of moderately active geopolymer, or contains 90-110 parts by weight of low-activity geopolymer and 15-25 parts by weight of moderately active geopolymer, the curing time of the geopolymer at a curing temperature above 200°C and not above 300°C can be controlled within 7-12 hours.

[0056] In this invention, the "curing time" refers to the time required for the local polymer API standard thickening curve to reach 100 Bc under test conditions of normal pressure and corresponding temperature.

[0057] The second aspect of this invention relates to a method for preparing a graded-curing geopolymer as described in the first aspect of this invention, comprising the following steps:

[0058] S1, kaolin was calcined at different temperatures to obtain latently active geopolymer materials, low-activity geopolymer materials, medium-activity geopolymer materials and high-activity geopolymer materials respectively;

[0059] S2, at least two of the latently active geopolymer material, low-activity geopolymer material, medium-activity geopolymer material and high-activity geopolymer material are mixed with an activator to cause the geopolymer materials with different activities to undergo stepwise solidification, thereby obtaining the stepwise solidified geopolymer.

[0060] In some embodiments of the present invention, the calcination temperature of the latently active geopolymer material is not higher than 600°C or the calcination temperature is higher than 950°C. In some specific embodiments of the present invention, the calcination temperature of the latently active geopolymer material can be 100°C, 200°C, 300°C, 400°C, 500°C, 600°C, 980°C, or 1100°C, etc.

[0061] In some embodiments of the present invention, the calcination temperature of the low-activity geopolymer material is higher than 600°C and not higher than 650°C, or higher than 850°C and not higher than 950°C. In some specific embodiments of the present invention, the calcination temperature of the low-activity geopolymer material can be 620°C, 650°C, 880°C, 900°C, or 950°C, etc.

[0062] In some embodiments of the present invention, the calcination temperature of the moderately active geopolymer material is higher than 650°C and not higher than 700°C, or higher than 750°C and not higher than 850°C. In some specific embodiments of the present invention, the calcination temperature of the moderately active geopolymer material can be 680°C, 700°C, 780°C, 800°C, or 850°C, etc.

[0063] In some other embodiments of the present invention, the calcination temperature of the highly active geopolymer material is higher than 700°C and not higher than 750°C. In some specific embodiments of the present invention, the calcination temperature of the highly active geopolymer material can be 710°C, 720°C, 730°C, 740°C, or 750°C, etc.

[0064] In some embodiments of the present invention, the calcination time is 1.5 to 2.5 hours; preferably 1.8 to 2.2 hours; and more preferably 2 hours.

[0065] In some embodiments of the present invention, the activator is an aqueous solution containing an alkaline substance, preferably an aqueous solution containing an alkali metal hydroxide and a silicate; more preferably an aqueous solution containing sodium hydroxide and sodium silicate.

[0066] In some preferred embodiments of the present invention, the concentration of sodium hydroxide in the activator is 2-6 mol / L, preferably 3-5 mol / L, and / or the concentration of sodium silicate is 1-6 mol / L, preferably 2-4 mol / L.

[0067] In some specific embodiments of the present invention, the concentration of sodium hydroxide in the activator is 4 mol / L and the concentration of sodium silicate is 3 mol / L.

[0068] In some embodiments of the present invention, in step S1, the mass ratio of the activator to the geopolymer material is 0.3 to 0.8; preferably 0.4 to 0.6; more preferably 0.5.

[0069] The third aspect of the present invention relates to the application of a graded-curing geopolymer as described in the first aspect of the present invention or a graded-curing geopolymer prepared by the method described in the second aspect of the present invention in oilfield cementing.

[0070] The curing time of the step-curing geopolymer described in this invention can be adjusted within 7 to 12 hours. The bonding strength after 1 day of curing can reach more than 12 MPa, and the strength of 7D cement stone can reach more than 21 MPa. It can be widely used in oilfield cementing.

[0071] Example

[0072] To make the present invention easier to understand, the present invention will be further described in detail below with reference to embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of application of the present invention. Unless otherwise specified, the raw materials or components used in the present invention can be obtained commercially or by conventional methods.

[0073] In the following implementation, the initial and final setting times and compressive strength of the geopolymer were tested on the samples in accordance with the method of GB / T 19139-2012.

[0074] Example 1: Preparation of different reactive geopolymer materials

[0075] Kaolin, the raw material for geopolymers, was calcined and activated at different temperatures using a high-temperature tubular furnace to form geopolymer materials with varying activities. The calcination method involved calcining in air for two hours, followed by cooling. The calcination temperatures ranged from 600℃ to 850℃, with intervals of 50℃. Thermogravimetric analysis and balance weighing were used to evaluate the weight loss after calcination; the results are shown in Table 1.

[0076] Table 1. Experimental results of calcination modification

[0077]

[0078] Note: "Activation strength at 20℃" in Table 1 refers to the strength of the material after it has been activated by the activator and cured for 1 day at 20℃.

[0079] The activity classification of geopolymer materials generated by calcination using the above methods is shown in Table 2 below.

[0080] Table 2. Geopolymer Material Activity Classification Table

[0081]

[0082] Example 2

[0083] Weigh 50 parts of the medium-activity geopolymer material (condition 3) and 100 parts of the high-activity geopolymer material prepared in Example 1 according to the specified ratio, and mix them evenly to obtain the geopolymer material. An activation experiment was conducted using an aqueous solution containing 4 mol / L sodium hydroxide and 3 mol / L sodium silicate as an activator. The mass ratio of the activator to the geopolymer material was 0.5. The initial and final setting times of the obtained geopolymer at different curing temperatures are shown in Table 3. The strength test conditions were 7 days of curing at a set temperature, and the strength development of the geopolymer is shown in Table 4.

[0084] Example 3

[0085] Weigh out 50 parts of the low-activity geopolymer material prepared in Example 1, 100 parts of the medium-activity geopolymer material (condition 3), and 10 parts of the high-activity geopolymer material according to the specified proportions, and mix them evenly to obtain the geopolymer material. An activation experiment was conducted using an aqueous solution containing 4 mol / L sodium hydroxide and 3 mol / L sodium silicate as an activator. The mass ratio of the activator to the geopolymer material was 0.5. The initial and final setting times of the obtained geopolymer at different curing temperatures are shown in Table 3. The strength test conditions were 7 days of curing at a set temperature, and the strength development of the geopolymer is shown in Table 4.

[0086] Example 4

[0087] 100 parts of the latently active geopolymer material prepared in Example 1 and 10 parts of the moderately active geopolymer material (condition 3) were weighed according to the proportion and mixed evenly to obtain the geopolymer material. An activation experiment was conducted using an aqueous solution containing 4 mol / L sodium hydroxide and 3 mol / L sodium silicate as an activator. The mass ratio of the activator to the geopolymer material was 0.5. The initial and final setting times of the obtained geopolymer at different curing temperatures are shown in Table 3. The strength test conditions were 7 days of curing at a set temperature, and the strength development of the geopolymer is shown in Table 4.

[0088] Example 5

[0089] Weigh 50 parts of the latently active geopolymer material prepared in Example 1 and 100 parts of the moderately active geopolymer material (condition 3) according to the specified ratio, and mix them evenly to obtain the geopolymer material. An activation experiment was conducted using an aqueous solution containing 4 mol / L sodium hydroxide and 3 mol / L sodium silicate as an activator. The mass ratio of the activator to the geopolymer material was 0.5. The initial and final setting times of the obtained geopolymer at different curing temperatures are shown in Table 3. The strength test conditions were 7 days of curing at a set temperature, and the strength development of the geopolymer is shown in Table 4.

[0090] Example 6

[0091] Weigh 50 parts of the low-activity geopolymer material prepared in Example 1 and 80 parts of the medium-activity geopolymer material (condition 3) according to the proportion, and mix them evenly to obtain the geopolymer material. An activation experiment was conducted using an aqueous solution containing 4 mol / L sodium hydroxide and 3 mol / L sodium silicate as an activator. The mass ratio of the activator to the geopolymer material was 0.5. The initial and final setting times of the obtained geopolymer at different curing temperatures are shown in Table 3.

[0092] The strength test conditions were set at a temperature and cured for 7 days. The strength development of the geopolymer is shown in Table 4.

[0093] Example 7

[0094] 100 parts of the low-activity geopolymer material prepared in Example 1 and 20 parts of the medium-activity geopolymer material (condition 3) were weighed according to the proportion and mixed evenly to obtain the geopolymer material. An activation experiment was conducted using an aqueous solution containing 4 mol / L sodium hydroxide and 3 mol / L sodium silicate as an activator. The mass ratio of the activator to the geopolymer material was 0.5. The initial and final setting times of the obtained geopolymer at different curing temperatures are shown in Table 3. The strength test conditions were 7 days of curing at a set temperature, and the strength development of the geopolymer is shown in Table 4.

[0095] Comparative Example 1

[0096] 150 portions of the latently active geopolymer material prepared in Example 1 were weighed. An activation experiment was conducted using an aqueous solution containing 4 mol / L sodium hydroxide and 3 mol / L sodium silicate as the activator. The mass ratio of the activator to the geopolymer material was 0.5. The initial and final setting times of the obtained geopolymer at different curing temperatures are shown in Table 3. The strength test was conducted under the set temperature for 7 days, and the strength development of the geopolymer is shown in Table 4.

[0097] Comparative Example 2

[0098] 150 portions of the highly active geopolymer material prepared in Example 1 were weighed. An activation experiment was conducted using an aqueous solution containing 4 mol / L sodium hydroxide and 3 mol / L sodium silicate as an activator. The mass ratio of the activator to the geopolymer material was 0.5. The initial and final setting times of the obtained geopolymer at different curing temperatures are shown in Table 3. The strength test was conducted under the set temperature for 7 days, and the strength development of the geopolymer is shown in Table 4.

[0099] Comparative Example 3

[0100] The raw materials used to prepare the geopolymer were basically the same as in Example 2, except that the mass ratio of the activator to the geopolymer material was 1. The initial and final setting times of the obtained geopolymer at different curing temperatures are shown in Table 3. The strength test was conducted under the set temperature for 7 days, and the strength development of the geopolymer is shown in Table 4.

[0101] Table 3: Initial and final setting times of geopolymers at different curing temperatures

[0102]

[0103] The experimental results show that the geopolymers in Examples 2-7, through the combination of different active components, can achieve a stepwise curing reaction, thereby controlling the curing time. The curing time can be controlled within the range of 30-300℃, approximately 7-12 hours, meeting the requirements of well cementing operations. Examples 2, 3, and 5 are suitable for low-temperature cementing (30℃ ≤ temperature ≤ 50℃); Examples 3, 5, and 6 are suitable for medium-high temperature cementing (50℃ < temperature ≤ 200℃); and Examples 4, 6, and 7 are suitable for high-temperature and ultra-high-temperature cementing (200℃ < temperature ≤ 300℃). The geopolymers in Comparative Examples 1 and 2, containing only one active ingredient, have a limited curing time (too fast or too slow), making the curing time uncontrollable during construction. In Comparative Example 3, the excessive amount of activator resulted in an excessively fast curing time, causing inconvenience during construction.

[0104] Table 4: Geopolymer Strength Development

[0105]

[0106] As shown in Table 4, the geopolymers obtained in Examples 2-7 can all achieve a 1-day cementitious strength of over 12 MPa, with a maximum of 25 MPa, and a 7-day cement stone strength of over 21 MPa, with a maximum of 39 MPa, within the applicable temperature range. Furthermore, the strength not only does not decrease at high temperatures but can even increase within a certain range. This is because the low-activity geopolymer material continues to solidify at high temperatures, further supporting the strength development. This is a performance that conventional silicate cementing materials rarely possess.

[0107] It should be noted that the embodiments described above are only for explaining the present invention and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from the scope and spirit of the present invention. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications with the same function.

Claims

1. A method for preparing a graded-curing geopolymer, comprising the following steps: S1, kaolin was calcined at different temperatures to obtain latently active geopolymer materials, low-activity geopolymer materials, medium-activity geopolymer materials and high-activity geopolymer materials respectively; S2, the geopolymer material is mixed with the activator to allow the geopolymer materials with different activities to undergo stepwise solidification, thereby obtaining the stepwise solidified geopolymer. The geopolymer material is selected from at least two of the following: latently active geopolymer materials, low-activity geopolymer materials, medium-activity geopolymer materials, and highly active geopolymer materials. The mass ratio of the activator to the geopolymer material is 0.3 to 0.8; The calcination temperature of the latently active geopolymer material is not higher than 600℃ or the calcination temperature is higher than 950℃. The calcination temperature of the low-activity geopolymer material is higher than 600°C and not higher than 650°C or higher than 850°C and not higher than 950°C. The calcination temperature of the active geopolymer material is higher than 650°C and not higher than 700°C or higher than 750°C and not higher than 850°C. The calcination temperature of the highly active geopolymer material is higher than 700℃ and not higher than 750℃; The curing properties of the geopolymer can be controlled by adjusting the types and contents of latently active, low-activity, medium-activity, and high-activity geopolymers in the geopolymer material. The curing time of the geopolymer can be controlled within 7 to 12 hours under a curing temperature of 30 to 300°C. The curing time required for the latently active geopolymer, the low-activity geopolymer, the medium-activity geopolymer, and the high-activity geopolymer are all different, as are the mechanical properties of the cured products. The curing performance includes the curing time and the mechanical properties of the product obtained after curing.

2. The preparation method according to claim 1, characterized in that, The mass ratio of the activator to the geopolymer material is 0.4 to 0.

6.

3. The preparation method according to claim 1, characterized in that, Under the action of the activator, the time required for the latently active geopolymer material, the low-activity geopolymer material, the medium-activity geopolymer material, and the high-activity geopolymer material to cure decreases sequentially.

4. The preparation method according to claim 1, characterized in that, The calcination time is 1.5 to 2.5 hours.

5. The preparation method according to claim 4, characterized in that, The calcination time is 1.8 to 2.2 hours.

6. The preparation method according to any one of claims 1-5, characterized in that, The activator is an aqueous solution of alkali metal hydroxide and silicate.

7. The preparation method according to claim 6, characterized in that, The activator is an aqueous solution containing sodium hydroxide and sodium silicate.

8. The preparation method according to claim 7, characterized in that, The activator contains sodium hydroxide at a concentration of 2–6 mol / L and / or sodium silicate at a concentration of 1–6 mol / L.

9. The preparation method according to claim 8, characterized in that, The activator contains sodium hydroxide at a concentration of 3–5 mol / L and / or sodium silicate at a concentration of 2–4 mol / L.

10. The preparation method according to any one of claims 1-5, characterized in that, When the geopolymer contains 40-60 parts by weight of medium-activity geopolymer and 90-110 parts by weight of high-activity geopolymer, the curing time of the geopolymer at a curing temperature of 30-50°C can be controlled within 7-12 hours.

11. The preparation method according to any one of claims 1-5, characterized in that, When the geopolymer material contains 40-60 parts by weight of low-activity geopolymer material, 90-110 parts by weight of medium-activity geopolymer material and 8-12 parts by weight of high-activity geopolymer material; or contains 40-60 parts by weight of latently active geopolymer material and 90-110 parts by weight of medium-activity geopolymer material, the curing time of the geopolymer at a curing temperature of 30-200°C can be controlled within 7-12 hours.

12. The preparation method according to any one of claims 1-5, characterized in that, When the geopolymer contains 40-60 parts by weight of low-activity geopolymer and 70-90 parts by weight of medium-activity geopolymer, the curing time of the geopolymer at a curing temperature above 50°C and not above 300°C can be controlled within 7-12 hours.

13. The preparation method according to any one of claims 1-5, characterized in that, When the geopolymer contains 90-110 parts by weight of latently active geopolymer and 8-12 parts by weight of moderately active geopolymer, or 90-110 parts by weight of low-activity geopolymer and 15-25 parts by weight of moderately active geopolymer, the curing time of the geopolymer at a curing temperature above 200°C and not above 300°C can be controlled within 7-12 hours.

14. A step-cured geopolymer prepared by the method according to any one of claims 1-13.

15. The application of the graded-curing geopolymer of claim 14 in oilfield cementing.

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