Design and Evaluation of the Elastic and Anti-Corrosion Cement Slurry for Carbon Dioxide Storage

Abstract

Carbon dioxide capture and storage is the primary way to reduce greenhouse gas emissions on a large scale. Carbon dioxide storage is the critical link of this technology, and the way in which to achieve long-term storage is a problem to be considered. The elastic and anti-corrosion cement slurry is the key for the successful storage of carbon dioxide. In order to develop the cement slurry for carbon dioxide storage, the influence of resin with both elastic and anti-corrosion properties on the performance of a cement slurry was investigated. The dispersant, retarder, and filtrate reducer suitable for the cement slurry were studied, and the performance of the designed cement slurry for carbon dioxide storage was evaluated. The experimental results show that the resin can reduce water loss and improve the elasticity and corrosion resistance of cement paste. The elastic modulus and corrosion depth of the resin cement slurry were significantly lower than those of the non-resin cement slurry. By studying the dispersant and retarder, the performances of the cement slurry for carbon dioxide storage was found to be able to meet the requirements of the cementing operation. The water loss of the designed cement slurry was low, the thickening time was more than three hours, and the rheological property was excellent. The elastic modulus and corrosion depth of the designed cement slurry was very low. The cement paste had a strong resistance to damage and corrosion. The structure after corrosion was denser than the conventional cement slurry, and the characteristic peak of corrosion products was weaker. The designed elastic and anti-corrosion cement slurry was well suitable for the cementing operation of carbon dioxide storage wells.

1. Introduction

Currently, the global climate has changed significantly, leading to frequent extreme weather phenomena, and geological disasters caused by extreme weather have also increased [1]. The impact of greenhouse gases on the global climate has become a consensus, and CO₂, as the most important greenhouse gas, has attracted increasingly more attention. All countries in the world have taken actions to control carbon dioxide and other greenhouse gas emissions to mitigate and repair the change in global climate, such as using clean energy to reduce carbon dioxide emissions and increasing carbon dioxide consumption by capture, utilization, and storage. Carbon dioxide capture and storage (CCS) technology is a feasible technical measure that can reduce carbon dioxide emissions by up to 90%. It is also the only method that can decrease greenhouse gas emissions and global warming on a large scale at present [2,3,4]. CCS is of great significance in carbon emission reduction. If there is not this technology, the overall cost of achieving the goal of halving CO₂ emissions will increase by 70% [5]. CCS technology is a system technology project integrating carbon dioxide capture, transportation, and storage. The basic principle of CCS technology is to inject carbon dioxide captured and separated from emission sources into suitable formations in a supercritical state for permanent storage, thus effectively reducing carbon dioxide emissions. In this technology, carbon dioxide storage is the key link of CCS. The way in which to avoid carbon dioxide escaping into the atmosphere again after storage and achieving long-term safe storage is one of the critical problems to be solved [6,7].

Cementing operation with cement slurry is the most critical technology for carbon dioxide storage. The cement sheath is the wellbore sealing barrier of a carbon dioxide storage well, and its sealing ability plays a vital role in the long-term storage of carbon dioxide. Oil well cement, as the sealing material for a carbon dioxide storage well, belongs to Portland cement, which is alkaline after hydration, being easily corroded in an acidic environment [8,9,10]. The microstructure of the corroded cement paste will be greatly deteriorated, and the mechanical properties will also be affected so that the wellbore cannot be effectively sealed for a long time. At the same time, in the process of carbon dioxide injection, the pressure in the wellbore will cause the change of stress state of the cement paste. If the cement paste has poor compression resistance, it is easily damaged by stress, which will destroy the integrity of the wellbore [11,12]. The literature shows that cement slurry with good elasticity can resist the damage of complex stress [13,14]. Therefore, cement slurry is required to have good elasticity and anti-corrosion.

In order to improve the corrosion resistance of cement paste, C.Q. Ren et al. [15], B.J. Zhang et al. [16], Z.G. Peng et al. [17], and B.H. Xu et al. [18] studied the role of latex and resin polymers in improving the corrosion resistance of cement paste. These polymers can reduce the degree of corrosion and the impact of corrosion on the compressive strength. In order to improve the elasticity of cement paste, the modified materials currently used are mainly fiber, polymer emulsion, and elastic particles. The research of M. Safi et al. [19] and J.J. Song et al. [20,21] show that the elastic particles can improve the elasticity of cement slurry the most, with the polymer emulsion also able to improve the elasticity of cement very well, and the fiber having the worst effect. Elastic particles mainly reduce the elastic modulus performance of cement paste by the filling. Its disadvantage is that it has a relatively negative impact on the permeability and compressive strength of cement paste and can easily cause corrosion deterioration. The film-forming effect of polymer emulsion can reduce the elastic modulus and the permeability of cement paste, which is conducive to improving the anti-corrosion ability. The polymer emulsion is a promising modified material to simultaneously improve the corrosion resistance and elasticity of cement paste for carbon dioxide storage, but its stability is crucial.

Liquid resin is a more stable polymer material than latex. In this paper, a kind of resin polymer was used to improve the elasticity and corrosion resistance of cement paste, and its influence on the performance of cement slurry was studied. The suitable additives (resin polymer, filtrate reducer, dispersant, retarder) were selected to make the designed cement slurry meet the requirements of carbon dioxide storage well. The cement slurry for carbon dioxide storage was designed and evaluated. The research results are of great significance for the long-term and safe storage of carbon dioxide.

2. Experiment

2.1. Experimental Materials

Oil well cement is API Class G cement that can be purchased from the market. Its chemical composition is shown in

Table 1. Chemical composition of oil well cement.

Component	CaO	SiO2	Al2O3	Fe2O3	MgO	Others
Content (%)	63.1	21.6	3.7	4.9	1.4	5.3

. The filtrate reducer and dispersant are used to reduce the water loss and adjust the rheology of the cement slurry. The filtrate reducer and dispersant are polyacrylamide polymer and sulfonated acetone formaldehyde condensate, respectively. The main component of the retarder is the borax additive, which is used to adjust the thickening time of cement slurry. The defoamer can inhibit the foaming during the preparation of cement slurry, and its main component is organic silicon. The resin is used to improve the corrosion resistance and elasticity of the cement paste, and it is an epoxy resin with a solid content of 50%. It was purchased from Jingzhou Jiahua Technology Co., Ltd. (Jingzhou, China) Micro silicon is used to improve the compressive strength of cement paste, and it was also purchased from Jingzhou Jiahua Technology Co., Ltd.

2.2. Preparation of Cement Slurry

According to the composition of cement slurry, cement, dispersant, and micro silicon with specified proportions shall be weighed and uniformly mixed as dry powder. The specified proportion of water, retarder, filtrate reducer, and defoamer was weighed and poured into the mixing cup as the preparation liquid. A constant speed mixer was used to mix the dry powder and liquid at 4000 r/min. The prepared cement slurry sample was obtained after mixing evenly. In

Table 2. Composition of cement slurry. Unit: wt.%.

Sample	Cement	Water	Filtrate Reducer	Retarder	Dispersant	Micro Silicon	Resin	Defoamer
S1	100	44	1	0	0.5	0	0	1
S2	100	42	1	0	0.5	0	4	1
S3	100	40	1	0	0.5	0	8	1
S4	100	38	1	0	0.5	0	12	1
S5	100	39	4	0.6	0.8	2	8	1

, S1–S4 are the compositions of cement slurry evaluated by resin, and S5 is the designed cement slurry for carbon dioxide storage.

2.3. Evaluation of Working Performance

After the preparation of the cement slurry, the rheology, thickening time, and water loss were evaluated by a six-speed rotary viscometer, high-temperature and high-pressure thickener, and water loss meter, respectively. The experimental results were obtained by testing the samples. At the same time, because the measured values of rheology were readings at different speeds, it was necessary to process the test data. The fluidity index n and consistency index K, representing the rheological properties of cement slurry, were calculated by the following formula:

$$\mathrm{n}=2.096\lg (\frac{{\mathsf{\Phi }}_{300}}{{\mathsf{\Phi }}_{100}})$$

(1)

$$\mathrm{K}=\frac{0{.511\mathsf{\Phi }}_{300}}{{511}^{\mathrm{n}}}$$

(2)

where Φ₁₀₀ and Φ₃₀₀ are the reading at shear rate of 100 r/min and 300 r/min, respectively.

2.4. Mechanical Properties

After the cement slurry was prepared, the cement slurry was poured into the test mold for its mechanical property, which is a 50.8 mm × 50.8 mm × 50.8 mm cube. The mold with the sample was put into a high-temperature and high-pressure curing kettle and was kept under the temperature and pressure for the specified time. The universal mechanical testing machine was used to test the compressive strength, elastic modulus, and stress-strain behavior of the sample.

2.5. Corrosion Evaluation of Cement Samples

The prepared cement slurry was poured into a cylindrical sample mold with a diameter of 2.5 cm and a height of 2.5 cm and then placed in a cure kettle and cured for three days. The prepared sample is the original sample for corrosion evaluation. Subsequently, the sample was put into the high-temperature and high-pressure corrosion tester and cured in the 15 MPa wet CO₂ environment for the specified time. After the sample was taken out, the corrosion depth and compressive strength of the cement paste were tested. Among them, the test method of corrosion depth refers to the evaluation method of carbonation depth in the concrete field. When the cement slurry was prepared, the oil well cement reacted with water to generate calcium hydroxide, calcium silicate hydrate, and other hydration products, making the cement stone alkaline. The cement sample will turn purple-red when encountering phenolphthalein. After the cement sample is corroded, the alkalinity disappears, so the color will not change. In this case, the thickness of the area where the color has not been changed (Figure 1) is the corrosion depth of the cement paste. The corrosion depth of four areas in different directions was tested, and then the average value was calculated.

2.6. Analysis of Microstructure

The cement sample was destroyed, and the small flat pieces in the middle were selected. The selected sample was terminated by hydration with ethanol. Then, the sample was dried at 60 °C for 24 h, and following this gold spraying was carried out to improve the conductivity of the sample. Finally, the morphology of the samples was observed by scanning electron microscopy (SU8010, Hitachi, Tokyo, Japan).

The cement sample was destroyed and ground into powder, and then the sample was dried at 60 °C for 24 h. The compositions were analyzed by an X-ray diffractometer (D8 Advance, Bruker, Karlsruhe, Germany). The test angle was 5–90°.

3. Design of Cement Slurry for Carbon Dioxide Storage

3.1. Carbonization Process of Cement Slurry

The hydration products formed by oil well cement were calcium hydroxide (CH), calcium silicate hydrate (CSH), ettringite (AFt), and sulfate, among which CH and CSH were the main hydration products, and the initial pH value of cement slurry was 12~13. When carbon dioxide is dissolved in water, it will form a carbonic acid solution (as in Formula (3)) with a pH value of about 3. With the invasion of the carbonic acid solution, the calcium hydroxide reacts with the carbonic acid to generate calcite (as in Formula (4)), and the hydrated calcium silicate reacts with it to generate aragonite and vaterite (as in Formula (5)). The formed calcium carbonate fills the pores of the cement paste, reducing the porosity. With the corrosion reaction, the pH value of cement paste decreases. The calcium hydroxide in the cement matrix dissolves and releases calcium ions and hydroxide ions. The calcium silica ratio of the hydrated calcium silicate gradually decreases, and finally, the amorphous silica remains. As a result of this process, the compressive strength of cement paste decreases and the permeability increases. When the reaction proceeds to a certain extent, calcium carbonate produced by carbonization will react and decompose under a high concentration of hydrogen ions (as shown in Formula (6)). At the same time, due to the difference in calcium ion concentration between pore fluid and corrosion fluid, calcium ions in the pores migrate from areas with high concentration to areas with low concentration (such as Formulas (7) and (8)), further adversely affecting the performance of cement paste [22,23,24].

$${\mathrm{CO}}_2+{\mathrm{H}}_2\mathrm{O}\rightleftharpoons {\mathrm{H}}_2{\mathrm{CO}}_3\rightleftharpoons {\mathrm{H}}^{+}+{\mathrm{HCO}}_3^{-}\rightleftharpoons 2{\mathrm{H}}^{+}+{\mathrm{CO}}_3^{2-}$$

(3)

$$\mathrm{Ca}{\left(\mathrm{OH}\right)}_2+2{\mathrm{H}}^{+}+{\mathrm{CO}}_3^{2-}\to {\mathrm{CaCO}}_3+2{\mathrm{H}}_2\mathrm{O}$$

(4)

$${\mathrm{C}}_{\mathrm{x}}{\mathrm{SH}}_{\mathrm{y}}+2{\mathrm{xH}}^{+}+{\mathrm{xCO}}_3^{2-}\to {\mathrm{xCaCO}}_3+{\mathrm{SiO}}_{\left(2-\mathrm{z}\right)}{\left(\mathrm{OH}\right)}_{2\mathrm{z}}+\left(\mathrm{y}-\mathrm{z}\right){\mathrm{H}}_2$$

(5)

$${\mathrm{CO}}_2+{\mathrm{H}}_2\mathrm{O}+{\mathrm{CaCO}}_3\to \mathrm{Ca}{\left({\mathrm{HCO}}_3\right)}_2$$

(6)

$$\mathrm{Ca}{\left(\mathrm{OH}\right)}_2\to {\mathrm{Ca}}^{2+}+2{\mathrm{OH}}^{-}$$

(7)

$${\mathrm{C}}_{\mathrm{x}}{\mathrm{S}}_{\mathrm{y}}{\mathrm{H}}_{\mathrm{z}}\rightleftharpoons {\mathrm{xCa}}^{2+}+2{\mathrm{xOH}}^{-}+{\mathrm{yH}}_4{\mathrm{SiO}}_4+\left(\mathrm{z}-\mathrm{x}-2\mathrm{y}\right){\mathrm{H}}_2\mathrm{O}$$

(8)

For the corrosion process, the main reason for the cement paste being corroded is that the CO₂ aqueous solution contacts the cement paste, which leads to the chemical reaction between the hydration products and the acid fluid, affecting the structure and reducing the performance of the cement paste. In order to design the cement slurry for carbon dioxide storage well, in addition to the performance meeting the requirements of cementing construction, it is also necessary to enhance the resistance to acid fluid and reduce or slow down the corrosion reaction of hydration products.

3.2. Research on Resin with Anti-Corrosion and Improved Elasticity

3.2.1. Influence of Resin on Working Performances of Cement Slurry

The rheology, thickening time, and water loss of cement slurry are the critical indicators for its application. The rheology is related to the difficulty of pumping, and it is usually measured by the fluidity index (n) and consistency index (K). The greater the fluidity index, the lower the consistency index, and the better the rheological property of cement slurry. The thickening time is closely related to pumping safety, and the water loss can affect the cementing quality of cement slurry. The influence of resin on the performance of cement slurry is shown in Figure 2.

As shown in Figure 2, the consistency index of cement slurry increases, and the fluidity index decreases with the increase in resin content. The rheology of cement slurry is negatively affected, and excessive resin will adversely affect the rheology of cement slurry. When the content of resin exceeds 8%, the rheology of cement slurry shows more apparent changes. Therefore, when the resin is added to the cement slurry, it is necessary to use appropriate dispersants to improve the rheology of the cement slurry. The results in Figure 2 show that the resin will affect the water loss and thickening time of cement slurry. The water loss decreases with the increase in resin content, which is helpful in improving the cementing quality of cement slurry. However, according to the construction standards, the water loss needs to be further controlled by using a filtrate reducer. The thickening time is shortened with the increase in resin content because the polymer improves the consistency of cement slurry, which will shorten the thickening time. The thickening time can be adjusted with a retarder.

3.2.2. Effect of Resin on Mechanical Properties of Cement Slurry

The elasticity of cement paste affects the ability to resist damage when subjected to compressive stress [25]. The elastic modulus is the main index to characterize the elasticity of cement paste. When the cement paste has a low elastic modulus, the ability to resist the damage caused by complex compressive stress is excellent. The influence of polymer resin on the compressive strength and elastic modulus of cement slurry was studied. It can be seen from Figure 3 that the compressive strength and elastic modulus of cement paste decreased due to the incorporation of resin polymer. The decrease in elastic modulus was more significant than the decrease in compressive strength, and the elasticity of cement paste increased. The reason may be that the addition of a large amount of polymer liquid reduced the hydration degree of the cement paste. At the same time, after the cement paste was hardened, the polymer components combined with the cement hydration products to form a flexible structure, improving the elasticity of the cement paste and reducing the strength of the hydration products.

3.2.3. Influence of Resin on the Corrosion Depth of Cement Slurry

The corrosion resistance of cement paste is a crucial performance to be considered in the cementing operation of a carbon dioxide storage well [26]. Due to the existence of carbon dioxide, the cement paste is easily corroded, having a great impact on the mechanical properties and permeability of the cement paste and reducing the sealing ability of the cement slurry. The influence of the resin on the corrosion performance of cement paste is shown in Figure 4.

The experimental results show that the corrosion depth of cement paste increased rapidly at the early stage of corrosion. At the same corrosion time, with the addition of resin, the corrosion depth of cement paste decreased significantly. When the resin dosages were 4%, 8%, and 12%, the corrosion depths of cement paste after 28 days of corrosion were 26.8%, 66.67%, and 69.2% lower than that of pure cement paste, respectively. The resin enhanced the inertia of the CO₂ corrosion reaction by forming a polymer film inside the cement paste, improving the anti-corrosion performance of cement paste and reducing the corrosion degree of cement paste.

3.3. Additives for Designing the Elastic and Anti-Corrosion Cement Slurry

3.3.1. Filtrate Reducer

The water loss of cement slurry without a filtrate reducer is usually large. In the process of cementing operation, since the cement slurry will have a large liquid column pressure difference after reaching the displacement position, the cement slurry will “percolate” when passing through the high-permeability formation, resulting in poor liquidity [27,28]. The water loss of qualified cement slurry shall meet the requirements of a cementing operation, and the water loss of cement slurry is generally required to be less than 50 mL. In order to study the cement slurry with low water loss, the effect of polymer filtrate reducer on the performance of resin cement slurry was evaluated. The experimental results are shown in Figure 5. With the increase in the amount of filtrate reducer, the water loss of the cement slurry was significantly reduced. When the content was 4%, the water loss was less than 50 mL, being able to effectively control the water loss and meet the requirement. The selected filtrate reducer was a water-soluble polymer rich in hydrophilic groups. Its dissolution in an aqueous solution can improve the viscosity of cement slurry and increase the formation filtration resistance. At the same time, polymer molecular chain bundles were embedded in the filter cake to fill the filter cake pores, making it more compact and less porous, reducing the permeability of the filter cake and realizing the function of reducing water loss.

3.3.2. Dispersant

The dispersant is mainly used to adjust the rheology of cement slurry. Since the resin will affect the rheology of cement slurry, it is essential to select a suitable dispersant. The influence of dispersant on the rheology was studied, and the experimental results are shown in Figure 6. The rheology of cement slurry was improved continuously with the addition of dispersant. The fluidity index increased while the consistency index decreased. The rheology of cement slurry with 1% dispersant content can effectively meet the requirements of cementing operation. The dispersant is a kind of anionic surfactant. After being added to the cement slurry, anionic macromolecules will be adsorbed on the surface of cement particles so that the particle will be charged with the same charge and repel each other, so as to achieve the purpose of dispersion. In addition, the repulsive force with the same electrical property can inhibit the aggregation of particles, making the cement slurry in a relatively stable suspension state.

3.3.3. Retarder

In order to achieve the pumping time required for a cementing operation, the flow time of cement slurry must be increased. The retarder is the key material used to adjust the thickening time. The thickening time of cement slurry with different contents of retarder was tested, as shown in Figure 7. With the increase in retarder content, the thickening time of cement slurry was obviously prolonged, and the thickening time could be adjusted. When the content of the retarder reaches 0.6%, the thickening time will be significantly extended, meeting the performance requirements of most cement slurries. After the retarder is mixed into the cement slurry, it will gather on the surface of the hydration products by adsorption, form an insoluble impermeable layer around the cement particles, inhibit the hydration reaction, and extend the thickening time of the cement slurry. The experimental results show that the retarder can effectively adjust the thickening time of cement slurry, which is helpful in designing the elastic and anti-corrosion cement slurry.

4. Evaluation of the Designed Cement Slurry for Carbon Dioxide Storage

4.1. Working Performances

In the research on the resin (which has both anti-corrosion and elasticity-improving functions), the filtrate reducer, dispersant, and retarder of cement slurry, the composition of elastic and anti-corrosion cement slurry is shown in sample S5 of Table 2. For the designed cement slurry, the working performance of the cement slurry at different temperatures was evaluated. The temperature used was the conventional temperature of the carbon dioxide storage well. The experimental results are shown in

Table 3. Construction performance of cement slurry.

Temperature (°C)	Water Loss (mL)	Thickening Time (min)	Fluidity Index	Consistency Index (Pa·Sn)
50	33	248	0.86	0.28
80	41	212	0.86	0.25

. The fluidity index of the cement slurry was greater than 0.7, the consistency index was less than 0.5, and the rheology was excellent. The water loss was less than 50 mL, and the filtration of the cement slurry was low. The final thickening times of the cement slurry under 50 °C and 80 °C were 248 min and 212 min, respectively, and the thickening time was 3–5 h, meeting the requirements of cement slurry construction.

4.2. Corrosion Depth

The corrosion depth is one of the most direct indicators to evaluate the corrosion of cement paste. In order to investigate the corrosion resistance of the cement slurry, the corrosion depth of the cement slurry at different temperatures and different times was evaluated. Figure 8 shows the state of the cement paste after 30 days of corrosion. The red part indicates that the color of the non-corroded area changed when encountering a phenolphthalein solution. This may have been related to the inconsistent pore structure in different areas of the cement paste.

Table 4. Corrosion depth of cement slurry.

Temperature (°C)	7d Corrosion Depth (mm)	30d Corrosion Depth (mm)
50	0.78	1.81
80	0.86	1.94

shows the experimental results of cement paste corroded for 7 days and 30 days. With the increase in corrosion temperature, the corrosion depth of cement paste increased, and the temperature would increase the corrosion degree of cement paste. After the designed cement slurry was corroded for 7 days, the corrosion depth was less than 0.86 mm under temperatures. After 30 days of corrosion, the corrosion depth of the sample was 1.79 mm at 80 °C, which was significantly reduced compared with that of conventional cement slurry. The designed cement slurry had good corrosion resistance, being able to protect the carbon dioxide storage well against acid fluid corrosion.

4.3. Stress–Strain Behavior

After the cement slurry is solidified in the wellbore, it will support the casing pipe. When the temperature and pressure in the wellbore change, the cement paste will be subjected to complex compression load. In serious cases, the integrity of the cement paste will be damaged. For carbon dioxide storage wells, if the integrity of cement paste is damaged, acid gas channeling may occur. Figure 9 shows the result of the stress–strain behavior of cement paste cured at 80 °C after compression. As the stress of cement paste increased, the strain of cement paste increased. When the stress reached the maximum value, the cement paste was damaged, and the stress decreased. When the maximum stress of cement paste reached 18 MPa, the strain reached 0.53%. The elastic modulus of cement paste can be obtained from the stress–strain curve analysis of cement paste. The curve in Figure 9 shows that the elastic modulus of cement paste was 4.5 GPa, which was low and had excellent anti-damage ability.

4.4. Microstructure

In order to analyze the morphology of cement paste before and after corrosion, samples S1 and S5 were selected for comparison. The experimental results are shown in Figure 10. The results show that only the cement sample had a dense structure before corrosion, and the hydration products were able to be observed. When it was corroded, the structure of the sample was loose, the hydration products were not obvious, and the compactness of the sample was poor. In contrast, the structure of cement slurry for carbon dioxide storage before corrosion was relatively dense, and there was a polymer film. On the one hand, the polymer film was filled inside the cement paste, forming a flexible structure to reduce the elastic modulus of the cement paste. On the other hand, it covered the surface of hydration products, which can prevent the hydration products from being corroded by acidic fluids. Moreover, after being corroded, the structure of the cement slurry for carbon dioxide storage was relatively complete. It shows that it had strong corrosion resistance, contributing to the integrity of the long-term sealing of the cement slurry.

By analyzing the components of the two cement pastes before and after corrosion, we obtained the experimental results, which are shown in Figure 11. The analysis results show that before corrosion, the characteristic peaks of the hydration products of the two cement samples were obvious, and the hydration products of the pure cement paste were calcium hydroxide (2θ = 18°) and calcium silicate hydrate (2θ = 28°~34°). The characteristic peak of hydration products of cement paste for carbon dioxide storage was obviously weaker than that of cement paste without resin. This was because the addition of preservative resin reduced the formation of hydration products, which was the main reason for the decrease in compressive strength of cement paste caused by the resin. After the cement paste was corroded by carbon dioxide, calcium hydroxide was consumed. The characteristic peaks of calcium hydroxide and calcium silicate hydrate were no longer able to be observed on the corroded cement paste samples. As the characteristic peak of calcium hydroxide without resin was strong, the corrosion degree was greater, and the corrosion product calcium carbonate (2θ = 26°, 33°, 52°) was stronger than the resin cement paste. The cement slurry for carbon dioxide storage had a weakened characteristic peak of hydration products. Although it was corroded, the degree of corrosion was low. The analysis results show that the cement slurry for carbon dioxide storage had a strong resistance to carbonation.

5. Conclusions

Cement slurry is the key technology for carbon dioxide storage. Improper cement slurry will be corroded and damaged, causing a leakage of the trapped carbon dioxide. In order to study the cement slurry for carbon dioxide storage wells, an elastic anti-corrosion cement slurry was designed and evaluated. As a material that can improve the corrosion resistance and elasticity of cement paste, resin effectively reduced the corrosion depth and elastic modulus when used in the cement slurry. Compared with the pure cement slurry, the elastic modulus and corrosion depth of the cement slurry containing resin were greatly decreased. The studied filtrate reducer, dispersant, and retarder effectively reduced the water loss of the cement slurry, adjusted the rheology, and extended the thickening time. They had an excellent effect on the designed cement slurry. The elastic and anti-corrosion cement slurry was designed by using oil well cement, resin, a filtrate reducer, a dispersant, and a retarder. It had excellent working performance. The rheology and thickening time of the designed cement slurry at different temperatures met the pumping requirements, and it had low water loss. The elastic and anti-corrosion cement slurry had a corrosion depth of less than 2 mm and an elastic modulus of 4.5 GPa. The strong resistance to corrosion and stress damage helped to ensure the long-term sealing integrity of carbon dioxide storage wells. At the same time, the structure of the designed elastic anti-corrosion cement slurry was denser than that of the conventional cement slurry after corrosion, the characteristic peak of the product generated by the corrosion reaction was low, and the corrosion degree was low. The designed cement slurry was evaluated to have good performance and was able to meet the requirements of a cementing operation of carbon dioxide storage well.