UHPC self-sealing shell based on olivine fiber and preparation method and application thereof

Abstract

The invention discloses a UHPC self-sealing shell based on olivine fibers and a preparation method and application thereof, and belongs to the technical field of material science and geological engineering. The preparation method comprises the following steps: firstly, mixing olivine (Mg2SiO4) powder with a polyvinyl alcohol (PVA) solution, preparing fibers with the diameter of 10-50 microns through wet spinning, and doping UHPC (1-3% by volume); in a supercritical CO2 environment, olivine fibers are expected to be hydrolyzed into Mg (OH) 2 and carbonated into MgCO3, pores are filled, and the permeability is reduced. The preparation method comprises the steps of fiber spinning, UHPC preparation and jet molding (the distance is 10-50 cm, and the pressure is 0.2-0.5 MPa). The CO2 sealing performance of the UHPC is improved through self-sealing, the global carbon dioxide reserve is potentially improved, and the UHPC has excellent mechanical property and durability and is suitable for deep ground engineering.

Description

Technical Field

[0001] The present invention relates to the field of materials science and geological engineering technology, and in particular to an olivine fiber-based UHPC self-sealing shell, a preparation method thereof, and applications thereof. Background Art

[0002] As the world urgently seeks ways to reduce carbon emissions to combat climate change, geological CO2 storage has become a highly sought-after technology. The principle is to inject captured CO2 into deep geological reservoirs, less than a kilometer below the surface, achieving long-term, stable storage and fundamentally reducing the amount of CO2 in the atmosphere. Geological CO2 storage requires a low-permeability caprock (permeability <0.01 mD) to prevent CO2 from leaking back to the surface, ensuring its safety and durability. However, the scarcity of such caprocks in natural reservoirs has limited reserve expansion and hindered the large-scale deployment of geological CO2 storage technology.

[0003] Ultra-high performance concrete (UHPC) has low internal porosity and has a strong barrier to fluid penetration. Its high durability allows it to maintain stable performance for a long time in complex geological environments such as high temperature and high pressure. Therefore, it is regarded as a suitable artificial barrier for geological CO2 storage. However, traditional UHPC formulas do not perform well in supercritical CO2 environments. Supercritical CO2 has both gas and liquid properties, and has extremely strong diffusion and penetration capabilities. After long-term contact, it will penetrate into the pores of UHPC. On the one hand, it reacts chemically with internal components, such as reacting with cement hydration products, to change the microstructure; on the other hand, continuous penetration will slowly expand the pores, and even connect the pores, resulting in a sharp decline in sealing performance, which cannot meet the sealing requirements for long-term storage of geological CO2.

[0004] Olivine (Mg2SiO4), a common mineral, can react with CO2 to form carbonates, a property that makes it possible to use it to enhance the self-sealing ability of UHPC. Adding olivine fiberization to UHPC is expected to give UHPC self-sealing capabilities: when UHPC develops tiny cracks or pores due to stress, temperature changes, etc. in a supercritical CO2 environment, the olivine fibers react with the infiltrated CO2, and the resulting carbonates can promptly fill the defects, preventing further CO2 penetration and improving long-term sealing performance. However, current research on olivine is mostly focused on block applications or simple chemical reactions. The difficulties of preparing olivine fiberization and uniformly integrating it into the UHPC system urgently need to be overcome. Summary of the Invention

[0005] The purpose of the present invention is to provide a UHPC self-sealing shell based on olivine fiber, a preparation method and application thereof, wherein olivine is made into fibers and applied to UHPC, and MgCO3 is generated through the hydrolysis and carbonation reaction of olivine to fill the pores of UHPC, reduce the permeability, and thereby improve the sealing ability of UHPC for CO2.

[0006] To achieve the above objectives, the present invention provides an olivine fiber-based UHPC self-sealing shell, comprising a UHPC matrix and olivine-PVA fibers, wherein the olivine-PVA fibers are incorporated into the UHPC matrix at a volume ratio of 1-3%.

[0007] Preferably, the UHPC matrix has a water-binder ratio of 0.15-0.20, contains 20-25% silica fume, and has an initial porosity of 1.5-2.5%.

[0008] Preferably, the olivine-PVA fiber has a fiber diameter of 10-50 μm and a fiber length of 5-15 mm.

[0009] The present invention also provides a method for preparing the above-mentioned UHPC self-sealing shell based on olivine fiber, comprising the following steps:

[0010] (1) Olivine powder was mixed with PVA solution, ultrasonically dispersed for 20-40 min, and then wet-spinned to prepare olivine-PVA fibers;

[0011] (2) adding olivine-PVA fibers into the UHPC matrix and stirring uniformly to obtain a mixture;

[0012] (3) The mixture is sprayed onto the substrate to form a shell and then cured at 20°C for 28 days.

[0013] Preferably, in step (1), the particle size of the olivine powder is less than 50 nm, the concentration of the PVA solution is 10 wt %; and the mass ratio of the olivine powder to the PVA solution is 1:1.5-1:2.5.

[0014] Preferably, in step (1), during wet spinning, the nozzle diameter is 50-150 μm and the spinning temperature is 40-60°C.

[0015] Preferably, in step (2), the fiber after wet spinning is dried and has a surface roughness of 1-5 μm.

[0016] Preferably, in step (3), the spraying is carried out under an environment of pressure ≥7.38 MPa and temperature ≥31.1° C., the spraying distance is 10-50 cm, and the spraying pressure is 0.2-0.5 MPa.

[0017] Preferably, in step (3), the thickness of the shell formed is 2-5 mm.

[0018] The present invention also provides an application of the above-mentioned olivine fiber-based UHPC self-sealing shell. The olivine fiber-based UHPC self-sealing shell is used for geological CO2 storage, which increases the reservoir capacity through self-sealing and is used in deep abandoned mines or high-permeability geological environments.

[0019] The method combines olivine powder with a polyvinyl alcohol (PVA) solution, wet-spinning it into fibers with a diameter of 10-50 μm. This fiber is then incorporated into UHPC (1-3% by volume). In a supercritical CO2 environment, when tiny cracks or pores appear in the UHPC, the olivine hydrolyzes into Mg(OH)2, which then carbonates to MgCO3, filling the pores. This improves the UHPC's sealing properties and reduces its permeability.

[0020] Therefore, the present invention provides a UHPC self-sealing shell based on olivine fiber and its preparation method and application, which have the following beneficial effects:

[0021] (1) The present invention innovatively introduces olivine fibers into the ultra-high performance concrete (UHPC) system, achieving dynamic self-sealing of UHPC in a supercritical CO2 environment. When tiny cracks or pores appear in the UHPC structure under the influence of factors such as complex geological stress or temperature changes, supercritical CO2 will quickly invade. At this time, the olivine fibers react chemically with CO2 to generate carbonate minerals. These carbonate products will gradually deposit and grow inside the cracks or pores, building a "self-healing" barrier at the cracks, dynamically filling the defects, continuously restoring and maintaining the sealing performance of UHPC, and realizing a dynamic self-repair process that is difficult to achieve with traditional UHPC.

[0022] (2) The present invention significantly reduces the permeability of UHPC by introducing olivine fiber, thereby greatly enhancing the CO2 barrier capacity of UHPC, thereby greatly improving the effectiveness and safety of geological CO2 storage, and providing a strong guarantee for expanding the CO2 storage capacity and extending the storage period.

[0023] (3) The olivine fiber preparation and addition process involved in the present invention is simple and controllable, making the technology adaptable to the complex and harsh construction environment of deep underground.

[0024] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of the preparation process of olivine-PVA fiber according to an embodiment of the present invention; wherein 1 is olivine powder; 2 is PVA solution; 3 is a mixing tank; 4 is ultrasonic dispersion; 5 is a spinning nozzle; 6 is olivine-PVA fiber;

[0026] Figure 2 Schematic diagram of the self-sealing mechanism of the olivine-PVA-UHPC self-sealing shell prepared in an embodiment of the present invention; wherein 1 is the initial pore; 2 is the olivine-PVA fiber; 3 is the CO2 molecule; 4 is the MgCO3 precipitate; and 5 is the sealed pore. DETAILED DESCRIPTION

[0027] The technical solution of the present invention is further described below by means of the accompanying drawings and examples. It should be understood that these examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention. Any other changes, modifications, substitutions, combinations, and simplifications made without violating the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the protection scope of the present invention. In addition, it should be understood that after reading the contents of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the claims attached to this application and belong to the scope of protection of the present invention.

[0028] References to "embodiments" herein mean that the specific features, structures, or characteristics described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the word "embodiment" in various places in the specification does not necessarily refer to the same embodiment, nor does it particularly limit its independence or relevance to other embodiments. In principle, in this application, as long as there are no technical contradictions or conflicts, the various technical features mentioned in the embodiments can be combined in any manner to form a corresponding implementable technical solution.

[0029] Unless otherwise defined, the technical terms used herein have the same meanings as those generally understood by those skilled in the art to which this application belongs; the use of relevant terms herein is only for describing specific embodiments and is not intended to limit this application.

[0030] Unless otherwise specified in the present invention, the reagents, instruments, and equipment used are those commonly used by those skilled in the art.

[0031] Example 1

[0032] This embodiment provides a method for preparing a UHPC self-sealing shell based on olivine fiber, comprising the following steps:

[0033] (1) Preparation of olivine-PVA fibers, such as Figure 1 As shown, olivine powder 1 and PVA solution 2 are mixed in a mixing tank 3, ultrasonically dispersed 4, and then wet-spun through a spinning nozzle 5, and dried to form olivine-PVA fibers 6.

[0034] Specifically, 10 g of olivine powder with a particle size of less than 50 nm was mixed with 20 g of a PVA solution with a concentration of 10 wt%. After ultrasonic dispersion for 30 minutes, olivine-PVA fibers were prepared by wet spinning and then dried. The nozzle diameter was 100 μm, the spinning temperature was 50°C, the obtained fiber had a diameter of 20 μm and a length of 10 mm, and the surface roughness (Ra) value of the dried fiber was 0.65 microns.

[0035] (2) A UHPC matrix with a water-binder ratio of 0.18 and containing 22% silica fume was selected, and the initial low porosity was 1.5-2.5%. Then, olivine-PVA fiber was added to the UHPC matrix at a volume ratio of 2% and stirred for 8 minutes to obtain a mixture.

[0036] (3) Under the conditions of deep supercritical CO2 (7.38 MPa, 31.1 °C), the mixture was sprayed onto a prefabricated ordinary concrete slab to form a shell with a thickness of 3 mm. The shell was then cured at 20 °C for 28 days to obtain an olivine-PVA-UHPC self-sealing shell. The spraying distance was 30 cm and the spraying pressure was 0.3 MPa.

[0037] Schematic diagram of the self-sealing mechanism of olivine-PVA-UHPC self-sealing shell Figure 2 As shown in Figure 1, the olivine-PVA fibers 2 in the initial pores 1 react with CO2 molecules 3 to generate MgCO3 precipitates 4, which eventually fill and form sealed pores 5.

[0038] Performance Verification:

[0039] A high-temperature and high-pressure relative permeability tester was used to conduct CO2 permeation tests on mudstone, conventional jet UHPC, and the olivine-PVA-UHPC self-sealing shell prepared in the above embodiment, and the results were analyzed.

[0040] Carbonation corrosion was conducted using a CCB-70A concrete carbonation test chamber. The carbonation environment was set to a relative humidity of (55±5)%, a temperature of (20±5)°C, and a carbon dioxide concentration of (20±2)% for a total of 7 days. All specimens were dried in an electric forced-air drying oven at 60°C for 48 hours. All specimens were 25 mm in length and 25 mm in diameter. The permeability test results are shown in Table 1 below.

[0041] Table 1 Permeability test data

[0042]

[0043] From the data in Table 1, it can be seen that the permeability of olivine-PVA-UHPC decreased by 76% after carbonization, indicating that the hydrolysis and carbonation reaction of olivine produced MgCO3, which filled the micropores of UHPC and significantly enhanced the CO2 storage effect.

[0044] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A UHPC self-sealing shell based on olivine fiber, characterized by: The invention comprises a UHPC matrix and olivine-PVA fibers, wherein the olivine-PVA fibers are mixed into the UHPC matrix at a volume ratio of 1-3%.

2. The olivine fiber-based UHPC self-sealing shell according to claim 1, characterized in that: The UHPC matrix has a water-to-binder ratio of 0.15-0.20, contains 20-25% silica fume, and has an initial porosity of 1.5-2.5%.

3. The olivine fiber-based UHPC self-sealing shell according to claim 1, characterized in that: The fiber diameter of the olivine-PVA fiber is 10-50 μm, and the fiber length is 5-15 mm.

4. The method for preparing a UHPC self-sealing shell based on olivine fiber according to any one of claims 1 to 3, characterized in that: The following steps are involved: (1) Olivine powder was mixed with PVA solution, ultrasonically dispersed for 20-40 min, and then wet-spinned to prepare olivine-PVA fibers; (2) adding olivine-PVA fibers into the UHPC matrix and stirring uniformly to obtain a mixture; (3) The mixture is sprayed onto the substrate to form a shell and then cured at 20°C for 28 days.

5. The method for preparing a UHPC self-sealing shell based on olivine fiber according to claim 4, characterized in that: In step (1), the particle size of the olivine powder is less than 50 nm, the concentration of the PVA solution is 10 wt %; and the mass ratio of the olivine powder to the PVA solution is 1:1.5-1:2.

5.

6. The method for preparing a UHPC self-sealing shell based on olivine fiber according to claim 4, characterized in that: In step (1), during wet spinning, the nozzle diameter is 50-150 μm and the spinning temperature is 40-60° C.

7. The method for preparing a UHPC self-sealing shell based on olivine fiber according to claim 4, characterized in that: In step (1), the wet-spun fiber is dried and has a surface roughness of 1-5 μm.

8. The method for preparing a UHPC self-sealing shell based on olivine fiber according to claim 4, characterized in that: In step (3), the spraying is carried out under an environment of pressure ≥7.38 MPa and temperature ≥31.1° C., the spraying distance is 10-50 cm, and the spraying pressure is 0.2-0.5 MPa.

9. The method for preparing a UHPC self-sealing shell based on olivine fiber according to claim 4, characterized in that: In step (3), the thickness of the shell is formed to be 2-5 mm.

10. The use of an olivine fiber-based UHPC self-sealing shell according to any one of claims 1 to 3, characterized in that: The olivine fiber-based UHPC self-sealing shell is used for geological CO2 storage, improves reservoir capacity through self-sealing, and is used in deep abandoned mines or high-permeability geological environments.

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