A crystal precipitation type self-healing agent for cementing and its preparation method and application

Abstract

The present invention belongs to the technical field of oil and gas cementing, and specifically relates to a crystalline precipitation type self-healing agent for cementing, and its preparation method and application. The crystalline precipitation type self-healing agent for cementing, its raw material composition is: 1-7 parts of sodium silicate, 1-4 parts of ball-forming material, 4-6 parts of resin, 0.2-0.5 parts of saturated sodium silicate solution, and 0.5-1.5 parts of dispersant. The self-healing agent is prepared by encapsulating and coating sodium silicate, providing a potential calcium source during the coating process. When the cement stone is damaged by stress, the coated sodium silicate is released and reacts with the calcium source, quickly forming calcium silicate enrichment in the microcracks of the cement stone, accelerating the self-healing process. The self-healing agent described in the present invention has a fast self-healing speed, a long action time, a simple preparation process, and has little effect on the performance of the cement slurry.

Description

Technical Field

[0001] The invention belongs to the technical field of oil and gas cementing, and particularly relates to a crystal precipitation type self-healing agent for cementing, a preparation method and application thereof. Background Art

[0002] Cementing stone is a hard and brittle material. Due to various stresses and strains during underground service, microcracks are difficult to avoid. These microcracks can lead to cement seal failure. The most direct solution is to squeeze out cement or resin to seal the well, but these operations are risky and costly.

[0003] Self-healing microcracks in cement paste is an effective solution to cementing failure. Currently, there are three main self-healing mechanisms: expansion and pore clogging by formation water or hydrocarbons; pore clogging by crystallization and precipitation; and release of curing materials from microcapsules. Fiber microcapsules are not suitable for the high shear conditions of cementing pumping. While expansion and pore clogging by formation water or hydrocarbons offers a rapid response, the material suffers from poor downhole durability. Crystallization and precipitation offer a durable response, but the reaction is slow, requiring dozens of days to heal, and are difficult to repair large cracks.

[0004] Sodium silicate reacts with calcium ions in cement slurry to form a calcium silicate gel precipitate. This reaction is rapid, and the resulting calcium silicate has adhesive properties. Using sodium silicate in cement slurry as a crystallized, precipitated, self-healing agent could effectively address seal failures caused by microcracks in cement paste. However, adding sodium silicate directly to cement slurry causes it to solidify rapidly, seriously impacting pumping safety. Summary of the Invention

[0005] To address the challenges of the prior art, the present invention provides a crystalline precipitated self-healing agent for cementing and its preparation method, which are applied to oil and gas well cementing. This self-healing agent is prepared by encapsulating and coating sodium silicate, which provides a potential calcium source during the coating process. When the cement paste is damaged by stress, the coated sodium silicate is released and reacts with the calcium source, rapidly enriching calcium silicate in the microcracks of the cement paste. Compared to conventional crystalline precipitated self-healing agents, this agent accelerates the self-healing process and lasts longer.

[0006] The crystal precipitation type self-healing agent for well cementing disclosed by the present invention comprises the following raw materials: 1-7 parts of sodium silicate, 1-4 parts of spherical material, 4-6 parts of resin, 0.2-0.5 parts of saturated sodium silicate solution, and 0.5-1.5 parts of dispersant.

[0007] The pelletizing material is a mixture of metakaolin and slag, the ratio of metakaolin to slag is 1:1-2:1, and the particle size is 300-2000 mesh.

[0008] The resin is a mixture of phenolic resin and epoxy resin, with the mass ratio of phenolic resin to epoxy resin being 3:1-5:1.

[0009] The dispersant is calcium hydroxide powder or calcium sulfate powder with a particle size of 800-2000 meshes.

[0010] The preparation method of the crystallized precipitation type self-healing agent for cementing comprises the following specific steps:

[0011] (1) Sodium silicate and pelletized materials are poured into a disc granulator, and a saturated sodium silicate solution is sprayed on the disc granulator while the disc is rotating to granulate, thereby obtaining particles I. Spraying the sodium silicate solution can adhere the pelletized materials to the surface of the sodium silicate particles. At the same time, the saturated sodium silicate solution can prevent the sodium silicate particles from dissolving.

[0012] (2) Calcinate particles I to obtain particles II. After calcination, particles I will have a certain strength, which is convenient for subsequent coating with resin. Otherwise, particles II will break when subjected to external forces. The calcination temperature is 600℃-900℃.

[0013] (3) Prepare a mixed system of phenolic resin and epoxy resin, mix particles II and the resin mixed system evenly, add a dispersant, disperse the resin-coated particles II, and obtain particles III; the mass ratio of particles II to the resin mixed system is 10:3~2:1.

[0014] (4) Particle III is heated and cured to form a crystalline precipitation type self-healing agent. The resin curing time at room temperature is as long as 24 hours, and the cross-linking degree of the resin cured at room temperature is not high, which leads to poor packaging effect. After heating and curing, the resin curing time can be shortened to 1 hour, and the cross-linking degree of the resin cured by heating is high. The curing temperature is 85-95℃.

[0015] The present invention uses metakaolin and slag, which have the following effects: (1) ensuring that sodium silicate is well dispersed; (2) protecting the sodium silicate particles, achieving the slow release of sodium silicate to a certain extent, and ensuring that the self-healing agent has a certain strength.

[0016] The present invention adopts phenolic resin and epoxy resin compounding, and the phenolic resin consumption is mainly utilized, and mainly utilizes phenolic resin to have brittleness after solidification. When cement stone is damaged by stress, the phenolic resin coating layer can be destroyed, releasing sodium silicate. The effect of mixing epoxy resin is to increase the viscosity of phenolic resin, which can better adhere to the surface of microsphere particles. The resin forms a continuous protective film on the surface of microsphere, and acts together with the coating layer formed by metakaolin and slag, further enhancing the protection of sodium silicate, ensuring that before microcracks are generated in the slurry mixing and cement stone curing process, sodium silicate will not be discharged. At the same time, it is ensured that after the cement stone generates microcracks, a channel is provided for the timely release of sodium silicate.

[0017] In the present invention, calcium hydroxide and calcium sulfate provide calcium sources for the sodium silicate reaction, accelerate the formation of calcium silicate, and improve the healing speed.

[0018] During the self-healing process of cementing, different amounts and speeds of sodium silicate release are required at different stages. At the initial stage of the crack, a certain amount of sodium silicate needs to be released quickly as soon as the crack appears to initially fill the crack, and then it needs to be released slowly to continue the healing reaction and enhance the healing effect. In the self-healing agent described in the present invention, at the initial stage of crack generation, the stress generated by the crack is transferred to the resin coating layer, causing the resin coating to produce microcracks, providing a channel for the release of sodium silicate; after the microcracks in the cement stone are generated, the high humidity environment at the cracks will rapidly promote the dissolution and diffusion of sodium silicate. In the initial stage, the concentration gradient of sodium silicate is large, that is, the concentration of sodium silicate inside the self-healing agent is much higher than the concentration in the microcracks. This large concentration difference will prompt sodium silicate to diffuse rapidly into the microcracks. Subsequently, when cement reacts with sodium silicate, a gelling substance is formed, which coats the surface of the microspheres. This reduces the contact between the microspheres and the external environment, gradually reducing the subsequent release rate of the sodium silicate, achieving a sustained and slow release. Furthermore, as the sodium silicate is continuously released, the concentration of sodium silicate inside the microspheres gradually decreases, and the concentration difference with the microcracks gradually decreases, reducing the diffusion rate. As a result, the release rate of the sodium silicate gradually slows, exhibiting a state of sustained and slow release. Therefore, compared with the healing time of conventional crystallization precipitation-type self-healing agents of dozens of days, the self-healing agent of the present invention has a self-healing effect in a shorter time and for a longer time.

[0019] The crystallized precipitation self-healing agent for cementing described in the present invention can be used in cementing of oil and gas wells. After the self-healing agent described in the present invention is added to cement slurry, the compressive strength of the cement stone remains basically unchanged during the thickening time at 90°C and after curing at 90°C for 24 hours.

[0020] Compared with the prior art, the present invention has the following beneficial effects: the self-healing agent of the present invention has a fast self-healing speed, a long action time, a simple preparation process and has little effect on the performance of cement slurry. DETAILED DESCRIPTION

[0021] Cement slurry preparation was carried out in accordance with GB / T 19139-2012, Test Methods for Oil Well Cement. Grade G oil well cement was used, with a water-cement ratio of 0.44, a self-healing agent dosage of 5% (by weight of cement), and a fluid loss additive (model G33S) dosage of 1.5% (by weight of cement). To investigate the self-healing effect, the permeability recovery of the cement paste was evaluated. The paste was water-bath cured at 80°C for three days, then subjected to alternating failure and tested for permeability. The paste was then water-bath cured for a further period at 80°C and tested again for permeability. If the cement paste self-heals, the permeability has recovered. Permeability testing was performed using a pressure-based porosity testing system.

[0022] Comparative Example 1

[0023] Fly ash, as an active material, hydrates more slowly than cement. When microcracks appear in the cement paste, secondary hydration occurs, healing them. Therefore, fly ash was selected for comparison in crystallization precipitation self-healing. Grade G oil well cement has a water-to-solid ratio of 0.44, a fly ash content of 30% (by weight of cement), and a fluid loss additive (model G33S) of 1.5% (by weight of cement).

[0024] Comparative Example 2

[0025] A crystal precipitation type self-healing agent for cementing, whose raw materials are composed of: 7 parts of sodium silicate, 3 parts of ball-forming material, and 0.3 parts of saturated sodium silicate solution.

[0026] The pelletizing material is a mixture of metakaolin and slag, the ratio of metakaolin to slag is 2:1, and the particle size is 2000 meshes.

[0027] The specific preparation steps are:

[0028] (1) Pour the mixture of sodium silicate, metakaolin and slag into a disc granulator, start the machine, and use the disc granulation method to spray saturated sodium silicate solution while rotating the granulator to form microsphere particles containing sodium silicate, which are recorded as particles I.

[0029] (2) Particle I was calcined at 900°C. The calcined particles were designated as Particle II, forming a crystalline precipitation-type self-healing agent S1. The corresponding cement slurry was designated C1, and the setting time of the cement slurry was significantly shortened. The thickening time of the cement slurry at 90°C was shortened to 42 minutes.

[0030] Comparative Example 3

[0031] A crystal precipitation type self-healing agent for well cementing, whose raw material composition is: 7 parts of sodium silicate, 3 parts of ball-forming material, 4 parts of resin, 0.3 parts of saturated sodium silicate solution, and 0.5 parts of dispersant, wherein the dispersant is silica sand powder.

[0032] The pelletizing material is a mixture of metakaolin and slag; the ratio of metakaolin to slag is 2:1, and the particle size is 2000 meshes.

[0033] The resin is a mixture of phenolic resin and epoxy resin, with the mass ratio of phenolic resin to epoxy resin being 3:1.

[0034] The specific preparation steps are:

[0035] (1) Pour the mixture of sodium silicate, metakaolin and slag into a disc granulator, start the machine, and use the disc granulation method to spray saturated sodium silicate solution while rotating the granulator to form microsphere particles containing sodium silicate, which are recorded as particles I.

[0036] (2) Particle I was calcined at a temperature of 900°C. The calcined particles were designated as particles II.

[0037] (3) Prepare a mixture of phenolic resin and epoxy resin, and mix particles II and the resin mixture evenly. Use silica sand powder with a particle size of 2000 mesh as a dispersant to disperse the resin-coated particles II to form particles III.

[0038] (4) Particle III is heated to 95°C and cured to form a crystalline precipitation type self-healing agent S2, and its corresponding cement slurry is C2.

[0039] Comparative Example 4

[0040] A crystal precipitation type self-healing agent for well cementing, whose raw material composition is: 7 parts of sodium silicate, 3 parts of ball-forming material, 4 parts of resin, 0.3 parts of saturated sodium silicate solution, and 0.5 parts of dispersant, wherein the dispersant is silica sand powder.

[0041] The pelletizing material is slag, and its particle size is 2000 meshes.

[0042] The resin is a mixture of phenolic resin and epoxy resin, with the mass ratio of phenolic resin to epoxy resin being 3:1.

[0043] The specific preparation steps are:

[0044] (1) Pour the mixture of sodium silicate, metakaolin and slag into a disc granulator, start the machine, and use the disc granulation method to spray saturated sodium silicate solution while rotating the granulator to form microsphere particles containing sodium silicate, which are recorded as particles I.

[0045] (2) Particle I was calcined at a temperature of 900°C. The calcined particles were designated as particles II.

[0046] (3) Prepare a mixture of phenolic resin and epoxy resin, and mix particles II and the resin mixture evenly. Use silica sand powder with a particle size of 2000 mesh as a dispersant to disperse the resin-coated particles II to form particles III.

[0047] (4) Particle III is heated to 95°C and cured to form a crystalline precipitation type self-healing agent S3, and its corresponding cement slurry is C3.

[0048] Comparative Example 5

[0049] A crystal precipitation type self-healing agent for well cementing, whose raw material composition is: 7 parts of sodium silicate, 3 parts of ball-forming material, 4 parts of resin, 0.3 parts of saturated sodium silicate solution, and 0.5 parts of dispersant, wherein the dispersant is silica sand powder.

[0050] The ball-forming material is metakaolin with a particle size of 2000 meshes.

[0051] The resin is a mixture of phenolic resin and epoxy resin, with the mass ratio of phenolic resin to epoxy resin being 3:1.

[0052] The specific preparation steps are:

[0053] (1) Pour the mixture of sodium silicate, metakaolin and slag into a disc granulator, start the machine, and use the disc granulation method to spray saturated sodium silicate solution while rotating the granulator to form microsphere particles containing sodium silicate, which are recorded as particles I.

[0054] (2) Particle I was calcined at a temperature of 900°C. The calcined particles were designated as particles II.

[0055] (3) Prepare a mixture of phenolic resin and epoxy resin, and mix particles II and the resin mixture evenly. Use silica sand powder with a particle size of 2000 mesh as a dispersant to disperse the resin-coated particles II to form particles III.

[0056] (4) Particle III is heated to 95°C and cured to form a crystalline precipitation type self-healing agent S4, and its corresponding cement slurry is C4.

[0057] Comparative Example 6

[0058] A crystal precipitation type self-healing agent for well cementing, whose raw material composition is: 7 parts of sodium silicate, 3 parts of ball-forming material, 4 parts of resin, 0.3 parts of saturated sodium silicate solution, and 0.5 parts of dispersant, wherein the dispersant is silica sand powder.

[0059] The pelletizing material is a mixture of metakaolin and slag; the ratio of metakaolin to slag is 2:1, and the particle size is 2000 meshes.

[0060] The resin is epoxy resin.

[0061] The specific preparation steps are:

[0062] (1) Pour the mixture of sodium silicate, metakaolin and slag into a disc granulator, start the machine, and use the disc granulation method to spray saturated sodium silicate solution while rotating the granulator to form microsphere particles containing sodium silicate, which are recorded as particles I.

[0063] (2) Particle I was calcined at a temperature of 900°C. The calcined particles were designated as particles II.

[0064] (3) Prepare a mixture of phenolic resin and epoxy resin, and mix particles II and the resin mixture evenly. Use silica sand powder with a particle size of 2000 mesh as a dispersant to disperse the resin-coated particles II to form particles III.

[0065] (4) Particle III is heated to 95°C and cured to form a crystalline precipitation type self-healing agent S5, and its corresponding cement slurry is C5.

[0066] Example 1

[0067] A crystal precipitation type self-healing agent for cementing, whose raw materials are composed of: 1 part of sodium silicate, 3 parts of spherical material, 4 parts of resin, 0.3 parts of saturated sodium silicate solution, and 0.5 parts of dispersant.

[0068] The pelletizing material is a mixture of metakaolin and slag; the ratio of metakaolin to slag is 2:1, and the particle size is 300 meshes.

[0069] The resin is a mixture of phenolic resin and epoxy resin, with the mass ratio of phenolic resin to epoxy resin being 3:1.

[0070] The specific preparation steps are:

[0071] (1) Pour the mixture of sodium silicate, metakaolin and slag into a disc granulator, start the machine, and use the disc granulation method to spray saturated sodium silicate solution while rotating the granulator to form microsphere particles containing sodium silicate, which are recorded as particles I.

[0072] (2) Particle I was calcined at a temperature of 600°C. The calcined particles were designated as particles II.

[0073] (3) Prepare a mixture of phenolic resin and epoxy resin, and mix particles II and the resin mixture evenly. Then, use calcium hydroxide powder with a particle size of 800 mesh as a dispersant to disperse the resin-coated particles II to form particles III.

[0074] (4) Particle III is heated to 85°C and cured to form a crystalline precipitation type self-healing agent S6, and its corresponding cement slurry is C6.

[0075] Example 2

[0076] A crystal precipitation type self-healing agent for cementing, whose raw materials are composed of: 1 part of sodium silicate, 1 part of ball-forming material, 5 parts of resin, 0.3 part of saturated sodium silicate solution, and 0.5 part of dispersant.

[0077] The pelletizing material is a mixture of metakaolin and slag, the ratio of metakaolin to slag is 2:1, and the particle size is 1000 mesh.

[0078] The resin is a mixture of phenolic resin and epoxy resin, with the mass ratio of phenolic resin to epoxy resin being 4:1.

[0079] The specific preparation steps are:

[0080] (1) Pour the mixture of sodium silicate, metakaolin and slag into a disc granulator, start the machine, and use the disc granulation method to spray saturated sodium silicate solution while rotating the granulator to form microsphere particles containing sodium silicate, which are recorded as particles I.

[0081] (2) Particle I was calcined at a temperature of 700°C. The calcined particles were designated as particles II.

[0082] (3) Prepare a mixture of phenolic resin and epoxy resin, and mix particles II and the resin mixture evenly. Then, use calcium hydroxide powder with a particle size of 1500 mesh as a dispersant to disperse the resin-coated particles II to form particles III.

[0083] (4) Particle III is heated to 90°C and cured to form a crystalline precipitation type self-healing agent S7, and its corresponding cement slurry is C7.

[0084] Example 3

[0085] A crystal precipitation type self-healing agent for cementing, whose raw materials are composed of: 2 parts of sodium silicate, 1 part of spherical material, 6 parts of resin, 0.3 parts of saturated sodium silicate solution, and 0.5 parts of dispersant.

[0086] The pelletizing material is a mixture of metakaolin and slag; the ratio of metakaolin to slag is 2:1, and the particle size is 1500 meshes.

[0087] The resin is a mixture of phenolic resin and epoxy resin, with the mass ratio of phenolic resin to epoxy resin being 5:1.

[0088] The specific preparation steps are:

[0089] (1) Pour the mixture of sodium silicate, metakaolin and slag into a disc granulator, start the machine, and use the disc granulation method to spray saturated sodium silicate solution while rotating the granulator to form microsphere particles containing sodium silicate, which are recorded as particles I.

[0090] (2) Particle I was calcined at 800°C. The calcined particles were designated as particles II.

[0091] (3) Prepare a mixture of phenolic resin and epoxy resin, and mix particles II and the resin mixture evenly. Then, use ultrafine calcium sulfate powder with a particle size of 1250 mesh as a dispersant to disperse the resin-coated particles II to form particles III.

[0092] (4) Particle III is heated to 95°C and cured to form a crystalline precipitation type self-healing agent S8, and its corresponding cement slurry is C8.

[0093] Example 4

[0094] A crystal precipitation type self-healing agent for cementing, whose raw materials are composed of: 7 parts of sodium silicate, 4 parts of spherical material, 5 parts of resin, 0.2 parts of saturated sodium silicate solution, and 1.5 parts of dispersant.

[0095] The pelletizing material is a mixture of metakaolin and slag; the ratio of metakaolin to slag is 1:1, and the particle size is 2000 mesh.

[0096] The resin is a mixture of phenolic resin and epoxy resin, with the mass ratio of phenolic resin to epoxy resin being 5:1.

[0097] The specific preparation steps are:

[0098] (1) Pour the mixture of sodium silicate, metakaolin and slag into a disc granulator, start the machine, and use the disc granulation method to spray saturated sodium silicate solution while rotating the granulator to form microsphere particles containing sodium silicate, which are recorded as particles I.

[0099] (2) Particle I was calcined at a temperature of 900°C. The calcined particles were designated as particles II.

[0100] (3) Prepare a mixture of phenolic resin and epoxy resin, and mix particles II and the resin mixture evenly. Then, use ultrafine calcium sulfate powder with a particle size of 1000 mesh as a dispersant to disperse the resin-coated particles II to form particles III.

[0101] (4) Particle III is heated to 90°C and cured to form a crystalline precipitation type self-healing agent S9, and its corresponding cement slurry is C9.

[0102] Table 1 Cement stone permeability recovery test

[0103] .

[0104] The self-healing agent of the present invention can achieve self-healing of micro-cracks in cement stone within 14 days, and the self-healing effect is enhanced after 28 days, and the self-healing effect is still exerted. It has the advantages of fast action speed, long action time, simple preparation process, and basically no effect on the performance of cement slurry.

Claims

1. A crystal precipitation type self-healing agent for cementing, characterized in that: The raw material composition is: 1-7 parts of sodium silicate, 1-4 parts of pelletizing material, 4-6 parts of resin, 0.2-0.5 parts of saturated sodium silicate solution, and 0.5-1.5 parts of dispersant; The specific preparation steps are: (1) Pour sodium silicate and spherical materials into a disc granulator, and spray saturated sodium silicate solution while rotating the granulator to obtain granules I; (2) calcining particle I to obtain particle II; (3) preparing a mixed system of phenolic resin and epoxy resin, mixing particles II and the resin mixed system evenly, adding a dispersant, and dispersing the resin-coated particles II to obtain particles III; (4) Particle III is heated and cured to form a crystalline precipitation type self-healing agent.

2. A crystal precipitation type self-healing agent for cementing according to claim 1, characterized in that: The pelletizing material is a mixture of metakaolin and slag; the mass ratio is 1:1-2:1; and the particle size is 300-2000 meshes.

3. A crystal precipitation type self-healing agent for cementing according to claim 1, characterized in that: The resin is a mixture of phenolic resin and epoxy resin, with the mass ratio of phenolic resin to epoxy resin being 3:1-5:

1.

4. A crystal precipitation type self-healing agent for cementing according to claim 1, characterized in that: The dispersant is calcium hydroxide powder or calcium sulfate powder.

5. A crystal precipitation type self-healing agent for cementing according to claim 1, characterized in that: The calcination temperature in step (2) is 600°C-900°C.

6. A crystal precipitation type self-healing agent for cementing according to claim 1, characterized in that: The curing temperature in step (4) is 85-95°C.

7. Use of the crystalline precipitation self-healing agent for cementing according to any one of claims 1 to 6 in cementing oil and gas wells.