Preparation method of CO2 response type semi-interpenetrating network self-repairing gel

Abstract

The invention discloses a preparation method of CO2 response type semi-interpenetrating network self-repairing gel, and belongs to the technical field of oil and gas well cementing cement admixtures. The preparation method comprises the following steps: dissolving sodium alginate in water, mixing with acrylamide and dimethylaminoethyl methacrylate in proportion, adding a cross-linking agent, introducing nitrogen, adding an initiator, reacting at constant temperature, washing, drying and crushing the product, and soaking in a CaCl2 solution. The gel has excellent CO2 responsiveness, salt tolerance and self-repairing performance, the integrity and compressive strength of set cement can be remarkably improved, a cement sheath is compact in structure, the comprehensive performance is enhanced, the gel can adapt to oil and gas well cementing operation of different environments and temperatures, and the well cementing safety and reliability are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of oil and gas well cementing cement admixtures, and particularly relates to a method for preparing a CO2-responsive semi-interpenetrating network self-healing gel. Background Art

[0002] In the oil and gas production sector, cementing technology is crucial for ensuring wellbore structural stability. With the widespread application of CCUS-EOR technology, large amounts of CO2 are injected into the formation, dissolving the resulting weakly acidic carbonic acid, which exacerbates cement corrosion. During the cementing process, internal and external loads, as well as the volumetric shrinkage caused by hydration and solidification of the cement slurry, can easily cause microcracks in the brittle cement material. The acidic environment can further propagate these microcracks, ultimately forming macrocracks that compromise wellbore integrity and trigger annular crossflow, posing a serious threat to production safety.

[0003] Currently, the traditional remediation method for microcracks in cement paste is secondary cement extrusion, but this method is costly, has a high failure rate, and is prone to construction accidents. Existing self-repair technologies for cement paste cracks, such as microcapsules and mineralized microbial self-repair (MICP), also have significant drawbacks. Microcapsules are prone to breakage and premature reaction during the mixing process, making it impossible to effectively repair cracks when they occur. MICP technology is also prohibitively expensive, making it uneconomical for large-scale application.

[0004] Therefore, there is an urgent need to develop an efficient, reliable, and economical technology for repairing microcracks in cement paste. Based on this, the present invention designs a CO2-responsive gel that combines physical plugging and chemical deposition mechanisms to effectively address the above issues and maintain the long-term integrity of the cement sheath. Summary of the Invention

[0005] In view of this, the purpose of the embodiments of the present application is to provide a method for preparing a CO2-responsive semi-interpenetrating network self-healing gel to solve the problem of CO2 aggravating the expansion of microcracks in cement stone and damaging the integrity of the wellbore in the application of CCUS-EOR technology, thereby overcoming the high cost and high failure rate of traditional remedial methods and the shortcomings of existing self-healing technologies.

[0006] The embodiment of the present application is implemented as follows:

[0007] The present application also provides a method for preparing a CO2-responsive semi-interpenetrating network self-healing gel, comprising the following steps:

[0008] S1. Dissolve an appropriate amount of sodium alginate in an aqueous solution, stir in a constant temperature water bath for 2 hours, and then cool to obtain solution A;

[0009] S2. acrylamide, dimethylaminoethyl methacrylate, and sodium alginate solution were mixed in a certain amount ratio to obtain solution B;

[0010] S3. A cross-linker was added to solution B. After nitrogen was passed through the mixed solution for 30 minutes, an initiator was added and the mixture was reacted at a constant temperature for 6 hours. The reaction product was then washed, dried, and crushed. After that, it was immersed in a CaCl2 solution of a certain concentration for a corresponding period of time to obtain a CO2-responsive self-healing gel.

[0011] Furthermore, in step 2, the molar ratio of acrylamide, dimethylaminoethyl methacrylate and sodium alginate is 1.8:2:0.6, and the amount of the three monomers, acrylamide, dimethylaminoethyl methacrylate and sodium alginate, is 30% of the total mass.

[0012] Furthermore, in step S3, the amount of the cross-linking agent N,N'-methylenebisacrylamide used is 0.2% of the total mass.

[0013] Furthermore, the amount of the initiator 2,2-azobisisobutylamidine dihydrochloride used in step S3 is 0.7% of the total mass.

[0014] Furthermore, the molar concentration of the CaCl2 solution in step S3 is 0.05 mol / L.

[0015] Based on the above steps, a CO2-responsive semi-interpenetrating network self-healing gel was obtained. The gel sealed microcracks by physical expansion and chemical deposition (Ca 2+ The dual mechanism of promoting calcium carbonate formation can repair micro-cracks in cement stone caused by CO2 corrosion in CCUS-EOR technology and maintain the integrity of the wellbore.

[0016] This application also provides the application of CO2-responsive semi-interpenetrating network self-healing gel.

[0017] Furthermore, the CO2-responsive semi-IPN self-healing gel is mixed with cement to prepare cement slurry or cement stone. The gel is stable in an alkaline environment. When microcracks are generated in the cement stone and it comes into contact with CO2 and H2O, the gel expands to seal the cracks and releases Ca2+. 2+ It promotes calcium carbonate deposition to fill cracks, and has the dual functions of physical plugging and chemical repair. It can effectively deal with the problem of micro-crack expansion caused by CO2 corrosion in CCUS-EOR technology, enhance the long-term integrity of the cement sheath, and improve the safety and reliability of oil well cementing under complex working conditions.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] 1. The CO2-responsive semi-IPN self-healing gel provided in this application has an ingenious structural design, with acrylamide, dimethylaminoethyl methacrylate, and sodium alginate as monomers, and Ca 2+The coordination effect with the carboxylic acid groups in sodium alginate realizes ionic crosslinking and forms a unique semi-interpenetrating network structure. This structure gives the gel excellent mechanical properties. 2+ The complexation with carboxyl groups enhances the toughness and strength of the gel, enabling it to maintain stable structure and performance under complex working conditions, providing a reliable physical basis for practical applications.

[0020] 2. The CO2-responsive semi-interpenetrating network self-healing gel provided in this application exhibits excellent CO2 responsiveness and pH responsiveness. In the presence of CO2 or when pH is less than 7, the tertiary amine group of the dimethylaminoethyl methacrylate unit in the gel structure is protonated to form a positively charged quaternary ammonium salt, thereby significantly improving the swelling ratio of the gel. This characteristic enables it to respond and expand quickly under specific circumstances, thereby effectively sealing cracks and achieving rapid repair of microcracks in cement stone. At the same time, after being soaked in CO2 in sodium chloride solutions of different concentrations, the gel can still maintain good response performance, indicating that it has a stable response mechanism in a complex chemical environment and can adapt to different application scenarios, providing an efficient technical means for solving the problem of microcracks in cement stone.

[0021] 3. The CO2-responsive semi-IPN self-healing gel provided in this application significantly optimizes the basic properties of cement slurry. Its retarding effect on the cement slurry is relatively weak, preventing significant interference with the normal setting process. It also increases the viscosity of the cement slurry, ensuring that its rheological properties meet the plasticity model and improving its construction performance. Furthermore, the gel's water absorption allows it to absorb some free water during the initial curing phase, effectively reducing water loss and further enhancing the structural density of the cement paste.

[0022] 4. The CO2-responsive semi-IPN self-healing gel provided in this application demonstrates significant effectiveness in self-repairing cement sheath cracks. It exhibits high repair efficiency and can achieve efficient self-repair under diverse environmental conditions, significantly reducing the permeability of cement paste and increasing its compressive strength. The gel is suitable for a wide range of crack widths and demonstrates superior repair performance compared to traditional materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0024] Figure 1 This is the infrared spectrum of the CO2 self-repairing gel prepared in Example 1 of the present invention;

[0025] Figure 2 This is the XPS graph of the CO2 self-repairing gel prepared in Example 1 of the present invention;

[0026] Figure 3 This is a thermogravimetric curve of the CO2 self-repairing gel prepared in Example 1 of the present invention;

[0027] Figure 4 This is a microscopic morphology of the CO2 self-repairing gel prepared in Example 1 of the present invention;

[0028] Figure 5 This is a stress-strain curve of the CO2 self-repairing gel prepared in Example 1 of the present invention;

[0029] Figure 6 This is a diagram showing the swelling performance of the CO2 self-repairing gel prepared in Example 1 of the present invention in aqueous solution;

[0030] Figure 7 This is a graph showing the swelling ratio of the CO2 self-repairing gel prepared in Example 1 of the present invention in different NaCl solutions;

[0031] Figure 8 Graph showing the effect of temperature on the swelling of the CO2 self-healing gel prepared in Example 1 of the present invention;

[0032] Figure 9 This is a diagram showing the swelling ratio of the CO2 self-repairing gel prepared in Example 1 of the present invention in solutions with different pH values;

[0033] Figure 10 This is a swelling curve of the CO2 self-repairing gel prepared in Example 1 of the present invention in a NaCl+CO2 solution;

[0034] Figure 11 This is the thickening curve of the cement stone of the self-repairing gel prepared in Example 2 of the present invention at different addition amounts, where Figure 2 (a) Ca-AGH addition amount is 0wt%, Figure 2 (b) Ca-AGH addition amount is 1wt%, Figure 2 (b) Ca-AGH addition amount is 2 wt%;

[0035] Figure 12 The compressive strength diagram of the cement paste with the self-repairing gel prepared in Example 2 of the present invention at different addition amounts;

[0036] Figure 13 The figure shows the effect of temperature on the self-repairing performance of cement paste made from the self-repairing gel of Example 2 of the present invention, where Figure 13 (a) is the permeability, Figure 13 (b) is the recovery rate;

[0037] Figure 14This is the effect of CO2 pressure on the self-repairing performance of cement paste cracks, where Figure 14 (a) is the permeability, Figure 14 (b) is the recovery rate;

[0038] Figure 15 The SEM-EDS characterization diagram of cement stone cracks before and after self-repair using the self-repair gel prepared in Example 2 of the present invention, wherein Figure 15 (ab) are SEM-EDS characterization images before and after repair with 0wt% Ca-AGH, where Figure 15 (cd) are SEM-EDS characterization images before and after repair with 1wt% Ca-AGH; DETAILED DESCRIPTION

[0039] To make the objectives, technical solutions, and advantages of this application more clearly understood, this application is further described in detail below in conjunction with examples. The illustrative embodiments and descriptions of this application are intended only to explain this application and are not intended to limit this application. Any product identical or similar to the present application that is derived by anyone under the guidance of this application or by combining the features of this application with other prior arts shall fall within the scope of protection of this application.

[0040] Specific experimental steps or conditions not specified in the examples may be performed according to the conventional experimental steps or conditions described in the prior art in the art. Reagents and other instruments used, for which the manufacturer is not specified, are all commercially available conventional reagent products. Furthermore, the accompanying drawings are merely schematic illustrations of the embodiments of the present application and are not necessarily drawn to scale. Identical or similar parts are indicated by the same reference numerals in the figures, and their repeated description will be omitted. Some block diagrams shown in the accompanying drawings are functional entities and do not necessarily correspond to physically or logically independent entities.

[0041] Example 1: Preparation and structural characterization of CO2-responsive self-healing gel

[0042] 5 g of sodium alginate was added to 145 mL of deionized water, and the mixture was stirred in a constant temperature water bath at 60° C. for 2 h. After the sodium alginate was completely dissolved, the mixture was cooled to room temperature to obtain solution A.

[0043] Acrylamide and dimethylaminoethyl methacrylate were added to the above solution A at a molar ratio of 1.8:2, and stirred to mix evenly so that the total mass of the three monomers accounted for 30% of the total mass of solution B, thereby obtaining solution B.

[0044] N,N'-methylenebisacrylamide (0.2 wt%) was added to Solution B as a crosslinker, and nitrogen was introduced for 30 minutes to exclude oxygen. 2,2-Azobisisobutylamidine dihydrochloride (0.7 wt%) was added as an initiator, and the mixture was allowed to react at 60°C for 6 hours. After the reaction, the product was washed three times with deionized water, dried in an oven at 60°C to constant weight, and pulverized to obtain a gel powder.

[0045] The gel powder was immersed in a 0.05 mol / L CaCl2 solution for 24 h to form an ion-crosslinked network and obtain a CO2-responsive self-healing gel (Ca-AGH).

[0046] The CO2-responsive self-healing gel prepared in this example was structurally characterized.

[0047] Infrared characterization

[0048] Take a small amount of dried KBr and press it into a tablet using an infrared tablet press; smear the CO2 responsive self-healing gel prepared in this embodiment on the KBr sheet and dry it; use a WQF-520 infrared spectrometer to perform infrared spectrum scanning and collect the instrument background. The infrared spectrum of the CO2 responsive self-healing gel is as follows: Figure 1 shown.

[0049] Figure 1 This is the infrared spectrum of CO2 responsive self-healing gel. Figure 1 It can be obtained at 3151cm -1 、1660cm -1 The peak at 1176cm is the absorption peak of -NH and -C=O in acrylamide; -1 , 1222cm -1 The peak at 3015cm represents the stretching and bending vibration absorption peak of tertiary amino group -CN. -1 At 3423 cm, it corresponds to the stretching and bending vibration of the tertiary amine CH. -1 There is a broad absorption peak corresponding to the -OH group of sodium alginate near 1616 cm -1 and 1399cm -1 The asymmetric and symmetric stretching vibration absorption peaks of -COO- (C=O and -CO-) were observed at the 400 nm spectral bands. 2+ After the introduction of Ca ions into the AGH hydrogel network, the absorption peak associated with COO- stretching vibration showed a blue shift (increased wave number), indicating that Ca 2+ The above results indicate that AGH was successfully synthesized and Ca 2+ Grafted onto the polymer.

[0050] X-ray photoelectron spectroscopy

[0051] Figure 2 The XPS diagrams of AGH and Ca-AGH are shown in Figure 2. Figure 2 It can be seen that the elemental composition difference between AGH and Ca-AGH gel is as follows: with C1s binding energy of 284.8eV as calibration standard, the XPS spectrum of AGH gel shows that it mainly contains C, N, and O elements, corresponding to the characteristic peaks of C1s, N1s, and O1s with balanced intensity distribution; while in the spectrum of Ca-AGH gel, in addition to the above element peaks, obvious Ca 2p electron binding energy characteristic peaks appear at 346.80eV and 350.20eV, confirming that Ca 2+ Introduced into the gel network by reaction with COO- groups.

[0052] Thermogravimetric curve

[0053] After the Ca-AGH gel was dried at 40°C in vacuum for 48 hours to remove free water, the thermal stability was tested using a thermal analyzer. The thermogravimetric curve of the Ca-AGH gel was obtained as shown in the figure below. Figure 3 shown.

[0054] Figure 3 This is the thermal weight loss curve of Ca-AGH gel. The thermal weight loss process of Ca-AGH is divided into four stages: the first stage is 70-104℃, which is mainly due to the volatilization of residual free water and small molecular substances; the second and third stages at 104-293℃ lose 24.4% of weight, which is caused by the thermal decomposition of sodium alginate carboxyl groups, volatilization of bound water and decomposition of methyl and tertiary amine groups in the molecule; the fourth stage loses 56.8% of weight, which is due to the breakage, decomposition and carbonization of the polymer main chain at high temperature.

[0055] Micromorphology

[0056] Figure 4 The microscopic morphology of Ca-AGH gel after freeze-drying at different magnifications. Figure 4 As can be clearly observed in (a) and (b), the gel surface exhibits a typical porous network structure, with distinct pores and gaps between the meshes. This structure significantly increases the internal surface area of ​​the Ca-AGH gel, providing more adsorption sites for water molecules, making them more easily adsorbed and immobilized, and endowing the gel with exceptionally high water absorption capacity.

[0057] Example 2: Performance Analysis of Ca-AGH

[0058] Effect of Ca-AGH on mechanical properties

[0059] Figure 5 The stress-strain curves of AGH and Ca-AGH are shown in Figure 2. Figure 5It can be seen that between 0% and 10% strain, the stress growth of the two is slow and the difference is small. After the strain exceeds 20%, the stress of Ca-AGH rises sharply, while the stress of AGH increases more slowly. When the compressive strain reaches 50%, the stress of AGH reaches 90kPa, while that of Ca-AGH reaches 877kPa, the latter being 10 times that of the former. Analysis suggests that AGH only contains a chemically cross-linked structure, while Ca-AGH combines physical and chemical cross-linking, introducing an ionic network and metal coordination bonds, enhancing the network dissipation mechanism and improving the compression resistance. This indicates that the composite cross-linked network structure is more stable, which is conducive to gel deformation and movement.

[0060] Effect of Ca-AGH on swelling properties

[0061] The swelling properties of Ca-AGH in pure water, different NaCl concentrations and temperature conditions were evaluated, and its pH responsiveness, CO2 responsiveness, and swelling properties in cement slurry filtrate before and after CO2 flow in NaCl solutions of different concentrations were investigated.

[0062] Figure 6 This is the swelling performance diagram of AGH / Ca-AGH in aqueous solution. The swelling ratio of AGH is about 100 g / g, and the swelling ratio of Ca-AGH is 8.76 g / g, which confirms that the ionic network significantly reduces the swelling of the gel.

[0063] Figure 7 The swelling ratio of Ca-AGH in different NaCl solutions is shown in Figure 2. Figure 7 It can be seen that the swelling ratio of Ca-AGH first decreases significantly with the increase of NaCl concentration, and then tends to fluctuate slightly.

[0064] Figure 8 The effect of temperature on the swelling of Ca-AGH is shown in Figure 2. Figure 8 As temperature increases, the gel's swelling equilibrium ratio first increases and then decreases, reaching a minimum of 8.96 g / g at 25°C. This is because molecular motion within the gel network is relatively slow at low temperatures, and the hydrophilic groups on polymer chains like sodium alginate bind more stably to water molecules, resulting in a relatively low swelling degree. Above 85°C, the swelling equilibrium ratio begins to decrease. This is because the excessively high temperature destroys the gel's crosslinking points, preventing the gel's swelling degree from increasing indefinitely with increasing temperature.

[0065] Figure 9 Figure 3 is the swelling ratio of Ca-AGH in different pH solutions. In the presence of CO2 or when pH is less than 7, the swelling ratio is higher than that of pure water. This is attributed to the protonation of the tertiary amine group of the DMAEMA unit to form a positively charged quaternary ammonium salt, which exhibits CO2 response characteristics.

[0066] Figure 10This is the swelling curve of Ca-AGH in NaCl+CO2 solution. After soaking in CO2 in NaCl solution with different concentrations, the swelling ratio shows an upward trend.

[0067] Example 3: Preparation of cement slurry

[0068] The G-grade high-resistance oil well cement purchased from the market was manufactured by Jiahua Special Cement Co., Ltd.; the G33S fluid loss additive purchased from the market is a commonly used product in oil fields and is manufactured by Weihui Chemical Co., Ltd. The product is a multi-component copolymer; the SXY-2 dispersant purchased from the market is a commonly used product in oil fields and is manufactured by Chengdu Chuanfeng Chemical Co., Ltd.; the GS-8S retarder purchased from the market was manufactured by Weihui Chemical Co., Ltd. The BP-113 defoamer purchased from the market was manufactured by Sichuan Hongsheng Petroleum Engineering Technology Service Co., Ltd.

[0069] The preparation and performance evaluation method of this cement slurry refers to the standard "Test Method for Oil Well Cement". Specifically, the Ca-AGH gel powder prepared in Example 1 was mixed with cementing cement at 0wt%, 1wt%, and 2wt% respectively, and passed through a 100-mesh sieve to remove lumps and impurities. The reagents were weighed according to the formula in Table 1 and added to the slurry cup. The components were mixed at 500r / min for 5s, then adjusted to 4000r / min, and cement was quickly added after starting the stirring and adjusted to 12000r / min. / min high-speed stirring for 35s, then add 3-4 drops of defoaming agent after stopping, and stir at 500r / min for 4-5s; Ca-AGH is made into powder and mixed into cement ash (water-cement ratio 0.44) to avoid water absorption and swelling resulting in uneven slurry. The slurry is then poured into a cylindrical mold (25mm diameter × 50mm height), cured in an 80℃ water bath for 48h, demoulded, and transferred to a 60℃ water bath for further curing for 5d. This is used to study the self-healing properties of microcracks in cement stone under different curing conditions.

[0070] Table 1 Cement slurry formula

[0071]

[0072] Example 4: Performance Analysis of Cement Slurry

[0073] Thickening performance test:

[0074] Pour the cement slurry into the high temperature and high pressure thickener, under the conditions of 60℃ and 20.2MPa, record the time when the consistency rises to 100Bc and the transition stage data. Figure 11 As shown in Table 2, the initial consistency of the cement slurry with 1% and 2% Ca-AGH addition was 24.1Bc and 27.3Bc, respectively. The thickening time was shortened to 132 minutes and 108 minutes, and the transition time was short, which met the construction requirements.

[0075] Table 2 Cement slurry thickening test data under different Ca-AGH additions

[0076] Serial number Initial consistency / Bc Transition time / min Thickening time / min <![CDATA[X0]]> 10.3 41 208 <![CDATA[X1]]> 24.1 48 132 <![CDATA[X2]]> 27.3 52 108

[0077] Rheological properties test:

[0078] After the cement slurry was thickened in a normal pressure viscometer for 20 minutes, a six-speed rotary viscometer was used to measure the readings at different rotation speeds, and the flow pattern index n and consistency coefficient K were calculated. The results are shown in Table 3.

[0079] Table 3 Six-speed values ​​of cement slurry systems with different Ca-AGH contents

[0080]

[0081] Compressive strength test:

[0082] The compressive strength of cement paste with different curing times was tested. The test was carried out using a pressure testing machine, loading at a standard loading rate, recording the maximum pressure at the time of failure of the cement paste, and calculating the compressive strength. The compressive strength of cement paste with different Ca-AGH additions at 1d / 3d / 7d is as follows: Figure 12 The results show that compared to blank cement paste, cement paste with Ca-AGH exhibits lower compressive strength after one day of curing. However, after two days of curing, the compressive strength difference remains similar. After seven days of curing, the negative effect of Ca-AGH on the compressive strength of cement paste disappears. This suggests that Ca-AGH delays strength development in the early stages of cement paste curing, but has no adverse effect on its ultimate strength over time.

[0083] Fluid loss reduction performance test:

[0084] The water loss of the cement slurry was tested in accordance with relevant standards. During the test, parameters such as test time and pressure were controlled to ensure the accuracy of the test results. The results are shown in Table 4. Ca-AGH has a certain water absorption capacity in alkaline cement slurry. During the initial stage of cement curing, it absorbs some of the free water in the cement slurry, reducing the water loss of the cement slurry. When the Ca-AGH addition amount is 1-2wt%, the water loss of the cement slurry meets the requirements of cementing construction, effectively preventing the performance degradation of the cement slurry due to excessive water loss in the well.

[0085] Table 4 Water loss reduction under different content conditions

[0086] sample <![CDATA[X0]]> <![CDATA[X1]]> <![CDATA[X2]]> Water loss / mL 35.0 13.0 8.0

[0087] Flow and density testing:

[0088] The fluidity and density of cement slurries with different addition amounts were tested. The fluidity test was conducted using the truncated cone mold method in accordance with standard operating procedures to ensure the reliability of the test results. The density test was conducted using a densitometer to accurately measure the density of the cement slurry. The results are shown in Table 5. When the Ca-AGH addition amount was 0wt%, 1wt%, and 2wt%, the fluidity of the cement slurry was higher than 20cm, and the density of the cement slurry was 1.891g / cm, respectively. 3 、1.897g / cm 3 and 1.900g / cm 3 , meeting the construction requirements of cementing cement slurry, ensuring the smooth transportation of cement slurry in the pipeline and the filling effect underground.

[0089] Table 5 Fluidity of cement slurry with different Ca-AGH additions

[0090] sample <![CDATA[X0]]> <![CDATA[X1]]> <![CDATA[X2]]> Fluidity / cm 23.2 21.3 20.1 <![CDATA[Density / g / cm 3 > 1.891 1.897 1.9

[0091] Example 5: Evaluation of the self-repairing performance of cement paste microcracks

[0092] Repair effect of different crack widths: Cement stone specimens with different crack widths (0.163mm, 0.095mm, 0.086mm, 0.569mm, 0.431mm) were prepared. During the preparation process, the accuracy of the crack width was strictly controlled, and specific molds and processes were used. A blank group and an experimental group with 2wt% Ca-AGH added were set up for curing. The curing process was carried out under a standard environment, controlling temperature, humidity and other conditions. After 28 days of curing, the permeability of the cement stone was tested using a permeability tester. The results showed that at different microcrack widths, the permeability of the cement stone with the addition of Ca-AGH showed a significant downward trend, indicating that Ca-AGH still exhibits excellent repair ability, can effectively seal microcracks of different widths, reduce the permeability of cement stone, and improve its anti-seepage performance.

[0093] The influence of temperature on the repair effect:

[0094] Under different temperature conditions (25℃, 50℃, 80℃), the micro-crack specimens of cement stone with 2wt% Ca-AGH were cured. The curing environment was precisely controlled by a constant temperature box to ensure temperature stability. After 21 days of curing, the repair rate of micro-cracks in the cement stone was tested. The repair rate was calculated by comparing the permeability of the cement stone before and after curing. The results are as follows Figure 13 As shown, the permeability of cement paste increases with increasing temperature, indicating that rising temperature increases the swelling rate of Ca-AGH and the binding rate of calcium ions and carbonates, thereby more quickly plugging microcracks and enabling self-repair of the cement paste. When the repair temperature is 80°C, the microcrack repair rate reaches 95%, significantly improving the self-repair ability of cement paste in high-temperature environments.

[0095] Effect of CO2 pressure on repair effect:

[0096] Cement paste microcrack specimens with 2 wt% Ca-AGH added were cured under different CO2 pressures (2 MPa, 4 MPa, 6 MPa, 8 MPa). The curing process was carried out in a high-pressure reactor with precise control of CO2 pressure. After 21 days of curing, the repair rate was tested. The results are as follows: Figure 14 As shown, when CO2 pressure is between 8 and 10 MPa, the permeability of cement paste cracks decreases with increasing pressure. Within this range, CO2 pressure has a positive effect on cement paste healing. At 8 MPa, the 21-day repair rate even reached 96.5%, further verifying the efficient repair performance of Ca-AGH for cement paste microcracks under different CO2 pressure environments.

[0097] Micromorphology and composition analysis:

[0098] The micromorphology and composition of the cement paste cracks were analyzed using advanced analytical instruments such as optical microscopy, scanning electron microscopy (SEM), and X-ray diffractometer (XRD). Optical microscopy was used to observe the macroscopic morphology and repair of the cracks, SEM was used to observe the microstructure and surface morphology of the cracks, and XRD was used to analyze the mineral composition of the cracks. The results showed that hydrogel and healing substances were clearly present in the cracks. The amount of hydrogel and self-healing substances filling the cracks increased with increasing hydrogel dosage. When the hydrogel dosage reached 2 wt%, the cracks were almost completely closed. Only a small amount of healing substances was present in the microcracks of the blank cement paste, and the crack width remained essentially unchanged. XRD analysis showed that the healing substances in the blank group were primarily CSH gel, a hydration product produced by unhydrated particles. The healing substances in the experimental group were CSH gel, calcium carbonate, and Ca-AGH, indicating that the addition of gel to the cement paste enhanced the healing effect. Ca-AGH plays a key role in the self-healing process of the cement paste microcracks, promoting crack healing not only through physical blocking but also through chemical reactions.

Claims

1. A method for preparing a CO2-responsive semi-interpenetrating network self-healing gel, characterized in that: The following steps are involved: S1. Dissolve an appropriate amount of sodium alginate in an aqueous solution, stir for 2 h in a constant temperature water bath, and then cool to obtain solution A; S2. acrylamide, dimethylaminoethyl methacrylate, and sodium alginate solution were mixed in a certain amount ratio to obtain solution B; S3. A cross-linker was added to solution B. After nitrogen was passed through the mixed solution for 30 minutes, an initiator was added and the mixture was reacted at a constant temperature for 6 hours. The reaction product was then washed, dried, and crushed. After that, it was immersed in a CaCl2 solution of a certain concentration for a corresponding period of time to obtain a CO2-responsive self-healing gel.

2. The method for preparing the CO2-responsive semi-IPN self-healing gel according to claim 1, characterized in that: In step S2, the molar ratio of acrylamide, dimethylaminoethyl methacrylate and sodium alginate is 1.8:2:0.6, and the amount of the three monomers, acrylamide, dimethylaminoethyl methacrylate and sodium alginate, is 30% of the total mass.

3. The method for preparing the CO2-responsive semi-interpenetrating network self-healing gel according to claim 1, characterized in that: The amount of the cross-linking agent N,N'-methylenebisacrylamide used in step S3 is 0.2% of the total mass.

4. The method for preparing the CO2-responsive semi-IPN self-healing gel according to claim 1, characterized in that: The amount of the initiator 2,2-azobisisobutylamidine dihydrochloride used in step S3 is 0.7% of the total mass.

5. The method for preparing the CO2-responsive semi-IPN self-healing gel according to claim 1, characterized in that: The molar concentration of the CaCl2 solution in step S3 is 0.05 mol / L.

6. An application of the CO2-responsive semi-interpenetrating network self-healing gel according to claim 5.

7. The use of the CO2-responsive semi-IPN self-healing gel according to claim 6, characterized in that: The CO2 responsive semi-interpenetrating network self-healing gel powder is mixed with cementing cement to prepare cement slurry and / or cement stone.

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