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Article

Preparation and Application of CO2-Resistant Latex in Shale Reservoir Cementing

by
Chunyuan Jiang
1,2,
Xuecheng Zheng
1,2,*,
Yuanqiang Zhu
1,2,
Lei Tang
3,
Yuhao Liu
4,
Zhijun Zhao
5 and
Hongyu Zhang
6
1
College of Chemistry and Chemical Engineering, Southwest Petroleum University, Chengdu 610500, China
2
Oil & Gas Field Applied Chemistry Key Laboratory of Sichuan Province, Chengdu 610500, China
3
Sichuan Ruidong Technology Co., Ltd., Chengdu 610500, China
4
CNPC Chuanqing Drilling Engineering Company Ltd., Chengdu 610066, China
5
Zhundong Drilling Company, CNPC Xibu Drilling Engineering Company Ltd., Changji 831199, China
6
College of Engineering, Southwest Petroleum University, Nanchong 637001, China
*
Author to whom correspondence should be addressed.
Processes 2024, 12(5), 945; https://doi.org/10.3390/pr12050945
Submission received: 10 April 2024 / Revised: 3 May 2024 / Accepted: 4 May 2024 / Published: 7 May 2024
(This article belongs to the Special Issue Advances in Technology for Enhancing Oil and Gas Recovery in Shale Reservoirs)
Browse Figures
Versions Notes

Abstract

:
With the application of CO2 fracturing, CO2 huff and puff, CO2 flooding, and other stimulation technologies in shale reservoirs, a large amount of CO2 remained in the formation, which also lead to the serious corrosion problem of CO2 in shale reservoirs. In order to solve the harm caused by CO2 corrosion, it is necessary to curb CO2 corrosion from the cementing cement ring to ensure the long-term stable exploitation of shale oil. Therefore, a new latex was created using liquid polybutadiene, styrene, 2-acrylamide-2-methylpropanesulfonic acid, and maleic anhydride to increase the cement ring’s resistance to CO2 corrosion. The latex’s structure and characteristics were then confirmed using infrared, particle size analyzer, thermogravimetric analysis, and transmission electron microscopy. The major size distribution of latex is between 160 and 220 nm, with a solid content of 32.2% and an apparent viscosity of 36.8 mPa·s. And it had good physical properties and stability. Latex can effectively improve the properties of cement slurry and cement composite. When the amount of latex was 8%, the fluidity index of cement slurry was 0.76, the consistency index was 0.5363, the free liquid content was only 0.1%, and the water loss was reduced to 108 mL. At the same time, latex has a certain retarding ability. With 8% latex, the cement slurry has a specific retarding ability, is 0.76 and 0.5363, has a free liquid content of just 0.1%, and reduces water loss to 108 mL. Moreover, latex had certain retarding properties. The compressive strength and flexural strength of the latex cement composite were increased by 13.47% and 33.64% compared with the blank cement composite. A long-term CO2 corrosion experiment also showed that latex significantly increased the cement composite’s resilience to corrosion, lowering the blank cement composite’s growth rate of permeability from 46.88% to 19.41% and its compressive strength drop rate from 27.39% to 11.74%. Through the use of XRD and SEM, the latex’s anti-corrosion mechanism, hydration products, and microstructure were examined. In addition to forming a continuous network structure with the hydrated calcium silicate and other gels, the latex can form a latex film to attach and fill the hydration products. This slows down the rate of CO2 corrosion of the hydration products, enhancing the cement composite’s resistance to corrosion. CO2-resistant toughened latex can effectively solve the CO2 corrosion problem of the cementing cement ring in shale reservoirs.

1. Introduction

The current research gradually focuses on the development of unconventional oil and gas resources, particularly the development of shale oil resources [1,2], as a result of the growing demand for oil and gas resources in social development and the significantly declining amount of exploitable conventional reservoir resources. At present, shale reservoirs frequently used formation fracturing techniques to boost output. However, the fracturing pressure of conventional fracturing methods decreased rapidly, and the pressure cannot be transferred to the tight formation, resulting in the formation of fractures and the limited production effect in shale reservoirs. Thus, more CO2-fracturing technology was employed for the development of unconventional oil reserves like shale reservoirs. CO2 may go from a gas to a supercritical state and persist steadily in an environment where the temperature and pressure are both higher than 31.1 °C and 7.38 MPa. CO2 may go from a gas to a supercritical state and persist steadily in an environment where the temperature and pressure were both higher than 31.1 °C and 7.38 MPa. Supercritical CO2 had both the flow characteristics of liquid and the flow resistance of gas, so that CO2 can effectively spread the micro pores and channels in the formation under the push of fracturing pressure. And supercritical CO2 can continue to exert osmotic pressure on the micro pores, so as to achieve the purpose of efficient fracturing, so as to improve the production of shale oil. On the basis of CO2 fracturing, CO2 can also be used for CO2 huff and huff, CO2 flooding, and other stimulation methods to promote the development and utilization of shale reservoirs [3,4,5].
Due to the influence of the anisotropic strength properties of shale [6,7,8], it was easy to cause formation instability with organic rich shales, which required improving the cementing quality. We minimize the impact of shale instability and guarantee the integrity of the wellbore in shale reservoirs. Meanwhile, utilizing CO2 can promote the development rate of the shale reservoir, but it will also increase the corrosion of CO2 on the cement ring. CO2 corrosion usually occurred in the formation with a high CO2 content, and the development of CO2 injection into the oil well created the corresponding conditions for CO2 corrosion on the cement ring. The hydration products created by cement will cause the CO2 in the formation to undergo a number of chemical corrosion processes, including leaching, decalcification, carbonization, and dissolution. The CO2 in the supercritical state, which was more likely to corrode through the pores or cracks of the cement ring, will erode the alkaline substances in the cement ring through a series of chemical corrosion reactions that include leaching, decalcification, carbonization, and dissolution with the hydration products formed by the cement [9,10]. The complete CO2 oxidation of the cement ring resulted in the loss of the cement ring’s suspending effect on the cementing casing and the formation fluid’s cross-flow, which posed a risk of working fluid pollution, formation damage, and the corrosion of the pipes [11,12]. Consequently, in order to lessen the damage caused by CO2 corrosion and increase the service life of shale oil wells, efficient measures to increase the corrosion resistance of cement rings must be taken.
Numerous studies have demonstrated that the present focus on developing shale reservoirs mostly concentrates on using CO2 for development and stimulation [13,14,15,16], with little regard for the corrosion risks that CO2 poses to oil wells. Therefore, in order to prevent more CO2-corrosion-related damage to oil wells, prompt action must be taken to address the issue of CO2 corrosion on cementing cement ring. At present, the corrosion resistance of cement was mainly improved by improving the composition of the cement system, increasing the density of the cement composite and providing a protective layer for the cement composite. Among them, the more effective measures were adding cement admixtures, anti-corrosion materials, anti-corrosion admixtures, or anti-corrosion coatings to the cement slurry system. Morandeau et al. [17] studied the effect of fly ash on the corrosion resistance of the cement composite, and the experiment showed that the decline in the compressive strength of the cement composite could be effectively slowed down when the amount of fly ash was more than 30%. Gong et al. [18] used calcium aluminate cement to improve the integrity of cement rings in a CO2 environment. Compared with ordinary Portland cement, calcium aluminate cement can better cope with CO2 corrosion in the formation, and the corrosion rate of calcium aluminate cement is slower. Peng et al. [19] modified the traditional oil-based epoxy resin with a high-temperature-resistant monomer to obtain an anticorrosive epoxy resin, which greatly improved the anticorrosive performance of the epoxy resin in the oil well cement. Zhang et al. [20] solved the problem of the poor dispersion and low stability of epoxy resin in the cement slurry, and this resin can effectively improve the compressive strength of the cement composite after curing and the decline in compressive strength after CO2 corrosion. Wang et al. [21] found that adding a small amount of styrene–butadiene latex to the cement slurry can effectively improve the mechanical properties of the cement composite, and found that the influence of latex on the cement composite formed a continuous structure with the polymer film formed by latex and cement hydration products. Wang et al. [22] synthesized modified polyacrylate latex with methyl methacrylate and butyl acrylate. This latex can gradually hydrolyze the ester group of the molecular chain into a carboxylic group in an alkaline environment, and better Ca(OH)2 can be cemented to form a network structure. Faruk et al. [23] compared the performance of styrene–butadiene latex and styrene–propyl latex in the process of CO2 corrosion. Styrene–butadiene latex has a stronger performance in improving the cement slurry, and styrene–butadiene latex has a stronger polymer-film-forming performance and stronger carbonization resistance, which is more suitable for improving the corrosion resistance of the cement composite.
By comparing various methods to improve the corrosion resistance of the cement ring, styrene–butadiene latex was an excellent material to improve the corrosion resistance of the cementing cement ring. It can not only improve the corrosion resistance of the cementing cement ring, but also improve the strength and toughness of the cement ring, reduce the damage of the cement ring during the fracturing development of the shale reservoir, and reduce the strength decline of the cement ring. However, there has not been enough research carried out on styrene–butadiene latex to address CO2 corrosion in the cement rings as of yet. Therefore, a new kind of CO2-resistant toughened latex was synthesized and analyzed using liquid polybutadiene, styrene, 2-acrylamide-2-methylpropanesulfonic acid, and maleic anhydride. The research examined the effect of latex on the performance of the cement slurry system, the improvement of the anti-CO2 corrosion performance of the system and the anti-corrosion mechanism of latex. The improvement effect of CO2-corrosion-resistant toughened rubber latex on the corrosion resistance of the cement ring was deeply explored, and the CO2 corrosion harm caused by CO2 exploitation in the shale reservoir was solved.

2. Experiments

2.1. Materials and Equipment

The materials and equipment were shown in Table 1 and Table 2. The chemical composition of G class oil well cement was shown in Table 3. All of these were commercial products and used without further purification.

2.2. Experimental Methods

2.2.1. Synthesis and Property Analysis of CO2-Resistant Latex

In order to guarantee that the produced latex had high qualities and particle size, seed emulsion polymerization was used to create CO2-corrosion-resistant latex, and the semi-continuous technique of latex monomer addition was used [24]. Figure 1 and Figure 2 depicted the synthesis reaction and the process of experimentation. The synthesis steps were as follows: after thoroughly mixing LPB, St, and SDS into nuclear emulsion A, and MA, AMPS, and APS into shell monomer solution B, they were each given a 30 min stir. After that, the flask was filled with the required amounts of nuclear emulsion A and shell monomer solution B, and it was heated to 75 °C in the oil bath. Initiate the agitator and set the stirring rate to 250 rpm. Inject nitrogen continually and let it react for one hour to make the seed emulsion. Following the preparation of the seed emulsion, the leftover solution A and solution B were added to the constant-pressure falling funnel, respectively, and allowed to react steadily for two hours. The CO2-resistant toughened latex was obtained by allowing the reaction to proceed for three hours after the drop was introduced.
The research began with an examination of the CO2-resistant toughened latex’s molecular structure, temperature resistance, and particle size distribution. FTIR was used to measure the infrared spectrum of latex at 4000–400 cm−1. The particle size distribution of latex was analyzed by DLS. The temperature stability of latex was analyzed by TGA. The core-shell structure and particle size of latex particles were observed by TEM. EDX was used to observe the elemental changes of cement.
The latex’s mechanical stability, salt resistance stability, freeze–thaw stability, and physical characteristics were next analyzed. The apparent viscosity of latex was determined by a rotary viscometer. The quality change of latex before and after complete drying was measured by drying method to obtained the solid content of latex. The mechanical stability experiment was to stir the latex at 3000 rpm for 5 min, and then carry out constant-pressure pumping and filtering, so that the latex particles generated by mechanical agitation are attached to the filter paper. When the mass fraction of the mass change of the filter paper to the total mass of the original latex was less than 0.2%, the mechanical stability of the latex was good. The salt stability test was conducted by adding saturated CaCl2, NaCl, and MgCl2 solutions to the latex drops. If the latex did not break or flocculate, the salt stability of the latex is good [25]. Similarly, the freeze–thaw stability experiment was a freeze–thaw cycle in which the latex is frozen at −20 °C for 18 h, and then thawed naturally at 25 °C for 6 h. The cycle was carried out until the latex cannot recover its initial state, and the number of 7 cycles was recorded. When the number of cycles was greater than 4 times, the freeze–thaw stability was good [26].

2.2.2. Experiment on the Effect of Latex on the Properties of Cement Slurry

In order to explore the effect of CO2-resistant toughened latex on the system, the formula of the cement slurry was designed as shown in Table 4. The prepared cement blocks were compressive strength test molds (diameter 25 mm × height 50 mm) and flexural strength test molds (length 40 mm × width 40 mm × height 100 mm), and the preparation process of cement slurry and cement blocks was carried out according to the American Petroleum Institute (API). Concurrently, the effect of the amount of latex on the rheology, stability, and thickening process of cement slurry, as well as the physical strength and microstructure of cement were investigated.

2.2.3. CO2 Corrosion Test of Latex Cement Composite

The compressive strength test mold was prepared according to the specified process of API, and was cured in a water bath environment of 90 °C and 15 MPa for 7 days. Following the curing period, the cement composite was moved to a high-temperature and high-pressure CO2-curing kettle, and the CO2 corrosion test was conducted in accordance with the procedure depicted in Figure 3. In order to investigate the enhancement effect of the CO2-resistant toughened latex on the corrosion resistance of the system and the anti-corrosion mechanism of the latex, the cement should be corroded at 90 °C and 15 MPa for 60 days in the CO2 liquid-phase corrosion environment. After 0, 20, 40, and 60 days of CO2 corrosion, the physical properties and physical composition of different cement composite were analyzed to explore the improvement effect of CO2-resistant toughened latex on the corrosion resistance of the system and the anti-corrosion mechanism of the latex. The formula of cement slurry was shown in Table 5.

3. Results and Discussion

3.1. Structure and Properties of CO2-Resistant Toughened Latex

3.1.1. FTIR Analysis

According to the infrared spectrum test results in Figure 4, it can be found that the strong absorption peak at 3416 cm−1 came from the N-H bond connected with C=O in AMPS. The absorption peak at 3060 cm−1 was the -CH absorption peak of olefin. The absorption peak at 3026 cm−1 was produced by C-H connected to the benzene ring. The absorption peak at 2924 cm−1 was -CH2. The absorption peak at 1719 cm−1 was the stretching vibration peak of -COOH in maleic anhydride. The absorption peak at 1640 cm−1 was the characteristic peak of the AMPS amide bond. The absorption peaks at 1551 cm−1, 1493 cm−1, 1453 cm−1, and 1391 cm−1 were the stretching vibration peaks of the conjugated system formed by the benzene ring and maleic anhydride. The absorption peaks at 1186 cm−1 and 1055 cm−1 were the symmetric and asymmetric stretching vibration peaks of the sulfonic acid group S=O in AMPS. The absorption peaks at 697 cm−1 and 623 cm−1 were the stretching vibration peaks of the benzene ring single substitution. It can be seen that the synthesized latex contained all the characteristic structures of the reaction monomer, and the CO2-corrosion-resistant toughened latex was successfully synthesized.

3.1.2. DLS Analysis

Figure 5 illustrated the particle size distribution of the latex. CO2-resistant toughened latex had a particle size distribution ranging from 50 nm to 500 nm, with a predominant distribution between 160 nm and 220 nm. The latex’s average particle size was 208.5 nm, which suggested that it had large-enough particles to accomplish the desired result.

3.1.3. TGA Analysis

Figure 6 illustrated the thermogravimetric spectrum of the CO2-resistant toughened latex. It can be seen that, when the temperature of the thermal analysis was less than 25 °C, a small amount of decomposition occurs in the latex, and its mass fraction was reduced by 6.4%. In this process, the decomposition occurred mainly in the copolymer attached to the main chain of the latex or the part with a low polymerization degree. When the temperature exceeded 300 °C, a large amount of latex decomposition occurred, and the main thing that occurred in this process was the break and decomposition of the main chain of latex molecules, which made the latex decompose rapidly until the temperature reached 460 °C, and the quality of latex was lost by 81.4%. When the temperature exceeded 460 °C, the decomposition of benzene ring mainly occurred, and the mass loss was small. The results showed that the CO2-resistant toughened latex had a high-molecular-weight stability and it was not easy to break and decompose molecular chains at 300 °C, which indicated that the CO2-resistant toughened latex had good temperature stability.

3.1.4. TEM Analysis

The transmission electron microscopy of the CO2-corrosion-resistant toughened latex’s particle structure was displayed in Figure 7. The preceding figure showed that the particle size distribution was focused and that the majority of latex particles may be kept in the 160–200 nm range. The figure demonstrated the clear core-shell structure of the latex and the uniform dispersion of the latex particles in the solution.

3.1.5. Performance Analysis of Latex

The physical characteristics and stability of both the regular styrene–butadiene latex and CO2-resistant toughened latex were ascertained through a series of studies. Table 6 displayed the physical characteristics of CO2-resistant toughened latex. The latex had the same physical characteristics as traditional styrene–butadiene latex and showed a strong long-term stability.
Table 7 showed the chemical composition of the CO2-resistant toughened latex, in which PB and St were the core structure of the latex, and the higher content can ensure the good rigidity and mechanical stability of the latex. AMPS and MA as the shell structure of the latex can further improve the temperature resistance and film-forming ability of the latex; SDS can promote the stability of the latex; and NaCl and APS were the raw materials of the latex synthesis (Table 8).
Figure 8, Table 8 and Table 9 demonstrated that the CO2-resistant toughened latex can withstand multiple freeze–thaw cycles, high temperatures, high speed shear, saturated salt water, and other extreme environments without experiencing aberrant behaviors like flocculation. The findings demonstrated that, in terms of mechanical stability, temperature stability, salt stability, and freeze–thaw stability, CO2-resistant toughened latex performed better than regular styrene–butadiene latex.

3.2. Effect of Latex on Properties of Cement Slurry and Cement Composite

3.2.1. Effect of Latex on the Properties of Cement Slurry

According to the results of the effect of the latex addition on the rheological properties of the latex cement in Figure 9, it can be seen that, with the increase in the latex addition, the fluidity index kept increasing, and the consistency index also decreased accordingly. A higher dispersion of the cement slurry [27,28] indicated that latex particles can fill between cement particles and act as ball-bearing lubrication [29]. When the amount of latex is 8%, the cement slurry was 0.76 and 0.5363, indicating that the latex can promote the rheology of the cement slurry.
Table 10 illustrated that, with the increase in the amount of CO2-corrosion-resistant toughened latex, the free liquid content, the upper and lower density difference of the cement slurry, and the API water loss all showed a downward trend. When the amount of latex added was 8%, the latex significantly enhanced the cement slurry’s stability. The cement slurry’s free liquid content was currently barely 0.1%, and the difference in density between its top and lower portions is only 0.01 g·cm−3. Concurrently, the cement slurry’s water loss decreases to 108 mL from 1150 mL. The results demonstrate that latex may successfully lower the system’s water loss. Additionally, latex particles can swiftly spread throughout cement slurry, squeeze out and fill any spaces left by cement particles, and encourage the production of filter cakes. In the meantime, the cement particle surface protection layer creation can help lessen cement particle water loss. As a result, it significantly affects the cement slurry stability and water loss reduction.
The pressurization thickening experiment in Figure 10 showed that the thickening curve of the cement slurry was closer to “right angle thickening” and more stable than that of blank cement following the addition of the CO2-resistant toughened latex. Indicating that CO2-resistant toughened latex can still preserve latex properties over time in high-temperature and high-pressure environments and support the rheological stability of the cement slurry, an increase in the latex content had no discernible impact on the thickening time or consistency. Table 11 showed that the initial and final setting times of the latex cement rose as the latex dose increased. This suggested that latex slowed the hydration of cement, and that the inhibition effect increases as the latex dosage increased. The application of latex particles to the surface of cement particles created a protective film that delayed the hydration reaction time of the cement and had a retarding effect by preventing the cement in the film from coming into contact with water during the hydration induction period and by lowering the reaction’s hydration heat [30]. The degree of the latex effect is determined by its charge characteristics and functional group [31]. The anionic functional group on the CO2-resistant toughened latex’s molecular chain gave it a significant adsorption capacity, and lengthened the initial and final setting times.

3.2.2. Effect of Latex on Properties of Cement Composite

Figure 11 illustrated how the compressive and flexural strengths of the latex cement exhibit a tendency of first increasing, and then dropping as the curing time increases. The impact of the latex addition on cement strength likewise exhibited this similar trend. The maximum compressive strength of the latex cement composite was 27.81 MPa, or 13.47% greater than the blank cement composite, when the latex content was 4%. When the amount of latex was 8%, the flexural strength of the latex cement was up to 4.33 MPa, which was 33.64% higher than that of the blank cement, indicating that the latex can be fully dispersed in the cement slurry and form a latex film, and the latex film formed by the latex particles can cover and fill the surface and space of the hydration product. Together with the hydration products, the continuous spatial network structure was formed [32], thereby increasing the physical strength of the cement composite. At the same time, the latex film formed by latex had a lower rigidity and greater flexibility, and had a better improvement effect on the cement composite flexural strength. In addition, because of the requirements of cementing construction, the influence of bubbles produced by emulsifiers in latex cannot be completely eliminated, which led to a decrease in the strength of the cement composite due to the excessive addition of latex.
Figure 12 illustrated the permeability of various cement composites decreased steadily as the curing time increases. The cement’s permeability initially rose, and then fell as the amount of latex increases. This demonstrated that the latex can successfully close up remaining holes in the cement composite and raise its density. Simultaneously, the continuous latex coating might lessen the cement permeability by preventing the infiltration of extraneous fluids and strengthening the link between various hydration products.

3.3. Corrosion Resistance Analysis of CO2-Resistant Toughened Latex

3.3.1. Effect of Latex on Physical Properties of Cement

As illustrated in Figure 13, as the corrosion time increased, the cement’s compressive strength kept decreasing while its permeability gradually increased and changes more quickly over time. The cement can be less susceptible to CO2 corrosion with the use of CO2-resistant toughened latex. After 60 days of CO2 corrosion, the compressive strength of the blank cement system decreased by 27.39% and the permeability increased by 46.88%. However, when the amount of latex was 8%, the compressive strength and permeability of the blank cement system only changed by 11.74% and 19.41%. This demonstrated that the latex film formed by the latex and the filling effect of latex particles effectively protected the hydration products [33], hindered the intrusion of CO2 into the interior of the cement composite, improved the corrosion resistance of the cement composite, and, thus, slowed the decline in the strength of the cement composite and the increase in permeability.
The surfaces of the cement composite after 60 days of CO2 liquid-phase corrosion are shown in Figure 14. The surfaces of L0 and L12 were seriously corroded, and numerous corrosion holes and corrosion product CaCO3 were formed, among which the corrosion damage of the blank cement was the most serious, which further led to the acceleration of the CO2 corrosion rate. However, only a small amount of corrosion occurred on the surface of L4 and L8, and there was no obvious corrosion phenomenon. As Figure 15 illustrates, the corrosion depth of CO2 on cement tended to rise with increasing corrosion time. The addition of latex can decrease the corrosion depth of CO2, with the lowest corrosion depth occurring at an 8% latex addition. These all demonstrated that the CO2-resistant toughened latex’s continuous network structure and latex film successfully impeded the eroding effect of CO2 into the cement composite and the corrosion consumption of alkaline materials. Additionally, Figure 16 showed that the section of the blank cement composite stained by phenolphthalide was continuously reduced as the corrosion time increased. This meant that the non-corroded part of the cement composite gradually decreased until only the central portion remained uncorroded [34], indicating that the CO2 corrosion of the blank cement composite was extremely serious. The addition of the CO2-resistant toughened latex can effectively slow down the corrosion rate of CO2.

3.3.2. Effect of Latex on Microstructure of Cement

As per Figure 17, which depicted the physical property change process of the composite and cement, uncorroded cement had a high concentration of amorphous hydrated calcium silicate and Ca(OH)2. The concentrations of the hydrated produced Ca(OH)2 and hydrated calcium silicate will steadily decline as CO2 corrosion advances and eventually change into carbonated products like calcite CaCO3 and arachite CaCO3 [35]. The consumption of Ca(OH)2 and the subsequent conversion to CaCO3 in the latter stages of corrosion further indicated that significant corrosion was occurring inside the cement composite. In this process, the addition of latex promoted the production of hydration products to a certain extent, and slowed down the corrosion of Ca(OH)2 and the hydrated calcium silicate, indicating that the latex film formed by latex effectively protected the hydration products, blocked the residual pores of cement hydration, reduced the corrosive contact between CO2 and the hydration products, and improved the corrosion resistance of the cement composite.
According to the microstructure of the cement composite in Figure 18, it can be found that the cement composite that had been etched for 0 days is still in the hydration reaction. From photo a1, it can be found that there are flake Ca(OH)2 crystals on the cement composite matrix, needle-etched composite, hydrated calcium silicate clusters gathered and on the surface, and cement clinker particles that have not been completely hydrated. Because of the latex membrane structure, the cement composite matrix that was applied with latex were smoother and more complete, as shown in photo a2. The latex film also connected the hydration products to produce a more complete cement. The formation of hydrated calcium silicate and Ca(OH)2 was completed by the cement composite with the extension of the corrosion period, producing a more complete form [36]. Simultaneously, the surface of the b1, c1, and d1 cement composite matrix showed signs of corrosion carbonization, and, over time, loose free calcium silicate was progressively created [37,38]. As the corrosion deepens, it was converted into tiny carbonization product CaCO3 particles [39], which caused the strength of the cement composite to rapidly decrease. As compared to the blank cement, the latex cement composite produced far less loose hydrated calcium silicate and carbonization products, and, even after 60 days of corrosion, microcracks will not form on the matrix surface, which suggested that the CO2-resistant toughened latex can effectively slow down CO2 corrosion and increase the cement composite’s resistance to corrosion.
Figure 19 and Table 12 illustrated that the element composition of the blank cement composite was notably lower in Ca than that of the latex cement composite, with a greater substitution of O. The degree of cement deterioration increased with decreasing calcium concentration [40]. Latex was better at preventing cement from corroding from CO2 and can effectively slow down the loss of calcium in cement.

3.3.3. Corrosion Resistance Mechanism of CO2-Resistant Toughened Latex

Figure 20 depicted the latex action process on the cement matrix surface. The protective impact of the latex coating and the cementation and filling action of the hydration products were primarily responsible for the system’s increased anti-corrosion performance. The latex can more easily disperse on the surface of the cement particles due to its nanoscale particle size. It can also create a continuous latex film in the pores of the cement particles and the surface of the hydration products, which encouraged the development of a continuous network structure between the latex and the hydration products. An improved cement composite density was achieved by covering the pores with a latex film and particles, which inhibited the corrosive medium’s penetration and rate of corrosion. Eventually, the cement composite’s ability to withstand corrosion was improved.

4. Conclusions

In this paper, the CO2-resistant toughened latex was created using seed emulsion polymerization, using styrene and polybutadiene as the core materials and maleic anhydride, 2-acrylamide, and 2-methylpropanesulfonic acid as the shell materials. Latex had an apparent viscosity of 36.8 mPa ·s, a solid content of 32.2%, and a size distribution that was mostly between 160 and 220 nm. Corrosion-resistant latex had a good mechanical stability, temperature stability, salt stability, and freeze–thaw stability, which was better than ordinary styrene–butadiene latex. In addition to increasing the cement slurry’s rheology and stability, latex may also strengthen the cement composite’s compressive, flexural, and permeability properties. It can also extend the cement slurry’s initial and final setting times and slow down coagulation. When the amount of latex was 8%, the fluidity index of cement slurry was 0.76, the consistency index was 0.5363, the free liquid content was only 0.1%, and the water loss was reduced to 108 mL. The compressive strength and flexural strength of the latex cement composite were increased by 13.47% and 33.64% compared with the blank cement composite.
Then, the corrosion resistance of latex was studied. The findings demonstrated that latex may successfully reduce CO2 corrosion’s rate and effect. At an 8% latex addition, the cement’s corrosion resistance was significantly increased, the cement’s compressive strength drop rate was lowered from 27.39% to 11.74%, and the permeability growth rate was lowered from 46.88% to 19.41%.
Lastly, the mechanism of resistance to CO2 corrosion and the change in the latex microstructure during corrosion were examined using XRD and SEM. The film formation and filling effect of latex on hydration products were further analyzed. Latex increased cement’s density and reduced the hydration products’ corrosion consumption, demonstrating that latex increased cement’s resistance to corrosion. According to the experimental findings, the CO2-resistant toughened latex can significantly improve the physical strength and CO2 corrosion resistance of the cement, and significantly reduce the influence of CO2 corrosion on the compressive strength, permeability, and hydration products of the cement. The CO2-resistant toughened latex can effectively solve the CO2 corrosion problem of the cementing cement ring and avoid the impact of CO2 corrosion in shale reservoirs.

Author Contributions

C.J.: writing—original draft, writing—review and editing, and investigation. X.Z. and Y.Z.: data curation, formal analysis, writing—original draft, and writing—review and editing. L.T., Y.L., Z.Z. and H.Z.: conceptualization, funding acquisition, project administration, resources, and methodology. All authors have read and agreed to the published version of the manuscript.

Funding

The research was funded by the Opening Project of Oil & Gas Field Applied Chemistry Key Laboratory of Sichuan Province, grant number No. YQKF202109, Sichuan Province Science and Technology Project (MZGC20230089).

Data Availability Statement

The data are contained within the article.

Conflicts of Interest

Author Lei Tang was employed by the company Sichuan Ruidong Technology Co., Ltd. Author Yuhao Liu was employed by the company CNPC Chuanqing Drilling Engineering Company Limited. Author Zhijun Zhao was employed by the company CNPC Xibu Drilling Engineering Company Ltd., Jundong Drilling Company. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

References

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Figure 1. Synthesis formula of CO2-resistant toughened latex.
Figure 1. Synthesis formula of CO2-resistant toughened latex.
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Figure 2. Experimental flow chart of synthetic latex.
Figure 2. Experimental flow chart of synthetic latex.
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Figure 3. Experimental flow chart of CO2 corrosion cement ((a). Corrosion device components, and (b). Corrosion device schematic diagram).
Figure 3. Experimental flow chart of CO2 corrosion cement ((a). Corrosion device components, and (b). Corrosion device schematic diagram).
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Figure 4. FTIR spectrum of CO2-resistant toughened latex.
Figure 4. FTIR spectrum of CO2-resistant toughened latex.
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Figure 5. Size distribution of CO2-resistant toughened latex.
Figure 5. Size distribution of CO2-resistant toughened latex.
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Figure 6. Thermogravimetric spectrum of CO2-resistant toughened latex.
Figure 6. Thermogravimetric spectrum of CO2-resistant toughened latex.
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Figure 7. TEM image of CO2-resistant toughened latex ((a). 100 nm, (b). 200 nm, and (c). 500 nm).
Figure 7. TEM image of CO2-resistant toughened latex ((a). 100 nm, (b). 200 nm, and (c). 500 nm).
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Figure 8. Flow state of latex after repeated freezing and thawing.
Figure 8. Flow state of latex after repeated freezing and thawing.
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Figure 9. Effect of latex addition on rheological properties of cement slurry.
Figure 9. Effect of latex addition on rheological properties of cement slurry.
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Figure 10. Effect of latex addition on thickening curve.
Figure 10. Effect of latex addition on thickening curve.
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Figure 11. Effect of latex addition on compressive strength and flexural strength of cement.
Figure 11. Effect of latex addition on compressive strength and flexural strength of cement.
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Figure 12. Effect of latex addition on permeability of cement.
Figure 12. Effect of latex addition on permeability of cement.
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Figure 13. Compressive strength and permeability of cement composite with time.
Figure 13. Compressive strength and permeability of cement composite with time.
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Figure 14. Corrosion diagram of cement surface ((a). L0 cement composite, (b). L4 cement composite, (c). L8 cement composite, and (d). L12 cement composite).
Figure 14. Corrosion diagram of cement surface ((a). L0 cement composite, (b). L4 cement composite, (c). L8 cement composite, and (d). L12 cement composite).
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Figure 15. Corrosion depth of cement composite with time.
Figure 15. Corrosion depth of cement composite with time.
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Figure 16. The change of corrosion depth of L0 cement composite with time ((a). 0 d, (b). 20 d, (c). 40 d, and (d). 60 d).
Figure 16. The change of corrosion depth of L0 cement composite with time ((a). 0 d, (b). 20 d, (c). 40 d, and (d). 60 d).
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Figure 17. XRD pattern of cement composite after corrosion.
Figure 17. XRD pattern of cement composite after corrosion.
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Figure 18. SEM pattern of cement composite after corrosion ((a1). L0 corrosion for 0 days, (a2). L8 corrosion for 0 days, (b1). L0 corrosion for 20 days, (b2). L8 corrosion for 20 days, (c1). L0 corrosion for 40 days, (c2). L8 corrosion for 40 days, (d1). L0 corrosion for 60 days, and (d2). L8 corrosion for 60 days).
Figure 18. SEM pattern of cement composite after corrosion ((a1). L0 corrosion for 0 days, (a2). L8 corrosion for 0 days, (b1). L0 corrosion for 20 days, (b2). L8 corrosion for 20 days, (c1). L0 corrosion for 40 days, (c2). L8 corrosion for 40 days, (d1). L0 corrosion for 60 days, and (d2). L8 corrosion for 60 days).
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Figure 19. EDX of hydration products of cement composite.
Figure 19. EDX of hydration products of cement composite.
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Figure 20. Schematic diagram of latex’s anti-corrosion mechanism.
Figure 20. Schematic diagram of latex’s anti-corrosion mechanism.
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Table 1. Materials and related information.
Table 1. Materials and related information.
MaterialsChemical PurityManufacturer
Liquid polybutadiene (PB)Average Mn 1530–2070Chengdu Huaxia Chemical Reagent Co., Ltd.
Styrene (St)CPChengdu Colon Chemical Co., Ltd.
2-acrylamide-2-methylpropanesulfonic acid (AMPS)ARChengdu Huaxia Chemical Reagent Co., Ltd.
Maleic anhydride (MA)ARShanghai Maclin Biochemical Technology Co., Ltd.
Sodium dodecyl sulfate (SDS)ARChengdu Colon Chemical Co., Ltd.
Ammonium persulfate (APS)GRChengdu Colon Chemical Co., Ltd.
Sodium hydroxide (NaOH)GRChengdu Colon Chemical Co., Ltd.
Calcium chloride (CaCl2)GRChengdu Colon Chemical Co., Ltd.
Sodium chloride (NaCl)GRChengdu Colon Chemical Co., Ltd.
Magnesium chloride (MgCl2)GRChengdu Colon Chemical Co., Ltd.
G class oil well cementTechnical gradeJiahua Special Cement Co., Ltd.
Micro-siliconTechnical gradeSichuan Zhengrong Industrial Co., Ltd.
Fluid loss additiveTechnical gradeTianjin Boxing Engineering Technology Co., Ltd.
DispersantTechnical gradeWeihui Chemical Co., Ltd.
DefoamerTechnical gradeClient supply
Pure waterPrimary purified waterTianjin development zone ruier environmental protection Technology Co., Ltd.
Carbon dioxide99.999Chengdu Xindu District Zhengrong gas Co., Ltd.
Nitrogen99.999Chengdu Xindu District Zhengrong gas Co., Ltd.
PhenolphthaleinPh Eur., 98%Shijiazhuang Simo Technology Co., Ltd.
Table 2. Experimental equipment.
Table 2. Experimental equipment.
EquipmentManufacturer
Stainless steel masherShanghai Jingke Industrial Co., Ltd.
WQF-520 infrared spectrometerBeijing Ruili Analytical Instrument Co., Ltd.
Talos F200S G2 S transmission electron microscopeThermo Fisher Technologies Ltd.
Zeta potential and nano-size analyzerMalvern Panalytical Instruments Ltd.
TGA 2 thermogravimetric analyzerMettler Toledo International Trading Co. Ltd.
NDJ-79 rotational viscometerShanghai Fangrui Instrument Co., Ltd., China
X-ray diffractometerDutch Panaco Company
Quanta 650 Field Emission Scanning Electron MicroscopeFEI Czech Republic S. r. o
High-temperature and high-pressure CO2-curing kettleSelf-innovate
Cement stone strength test moldSelf-innovate
Hydraulic servo drive control universal testing machineMets Industrial Systems (China) Co., Ltd.
Energy-Dispersive X-ray SpectroscopyShimadzu Corporation of Japan
Laboratory ultrapure water equipmentShijiazhuang Simo Technology Co., Ltd.
Table 3. Chemical composition of G class oil well cement, wt%.
Table 3. Chemical composition of G class oil well cement, wt%.
SiO2Al2O3Fe2O3MgOCaOK2ONa2OSO3Others
22.313.604.761.2964.060.411.480.961.13
Table 4. Composition ratio of cement slurry, g.
Table 4. Composition ratio of cement slurry, g.
SampleCementMicro-SiliconFluid Loss AdditiveDispersantLatexDefoamerWater
1600240003264
26002400243264
36002400483264
46002400723264
Table 5. Composition ratio of cement slurry in CO2 corrosion, g.
Table 5. Composition ratio of cement slurry in CO2 corrosion, g.
SampleCementMicro-SiliconFluid Loss AdditiveDispersantLatexDefoamerWater
L06002418303264
L460024183243264
L860024183483264
L1260024183723264
Table 6. Physical properties of CO2-resistant toughened.
Table 6. Physical properties of CO2-resistant toughened.
Physical PropertiesParameter
AppearanceMilky solution
pH7~8
Solid content32.2
Apparent viscosity, mPa·s36.8
Free water content (20 °C ± 2 °C, 1 MPa), %0
Long-term stabilityNo latex particles were produced
Table 7. Chemical composition of CO2-resistant toughened latex, molar ratio.
Table 7. Chemical composition of CO2-resistant toughened latex, molar ratio.
PBStAMPSMASDSNaClAPS
48.9973110100.0010.0010.001
Table 8. Comparison of salt stability between CO2-resistant toughened latex and ordinary latex.
Table 8. Comparison of salt stability between CO2-resistant toughened latex and ordinary latex.
Types of LatexNaClCaCl2MaCl2
CO2-resistant toughened latexNo flocculeNo flocculeNo floccule
Ordinary latexNo flocculeFloccule 0.23 gFloccule 0.31 g
Table 9. Comparison of stability between CO2-resistant toughened latex and ordinary latex.
Table 9. Comparison of stability between CO2-resistant toughened latex and ordinary latex.
Test ItemCO2-Resistant Toughened LatexOrdinary Latex
Mechanical stabilityMass change 0.1%Mass change 0.6%
Temperature stabilityDecomposition temperature > 309 °CDecomposition temperature > 200 °C
Salt stabilityNo flocculeFloccule 0.31 g
Freeze–thaw stabilityFreeze–thaw index ≥ 5Freeze–thaw index ≤ 1
Table 10. Effect of latex addition on the stability of cement slurry.
Table 10. Effect of latex addition on the stability of cement slurry.
Amount of Latex Added/%Free Liquid Content/%Density Difference of Cement Paste/g·cm−3API Water Loss/mL
03.50.091150
40.60.03320
80.10.01108
120056
Table 11. Effect of latex on the setting time of cement slurry.
Table 11. Effect of latex on the setting time of cement slurry.
Amount of Latex Added/%Initial Setting Time/minFinal Setting Time/min
0172213
4217272
8278343
12349391
Table 12. EDX analysis result on hydration products of cement composite.
Table 12. EDX analysis result on hydration products of cement composite.
Symbol of ElementL0L8
Weight PercentAtom PercentWeight PercentAtom Percent
O60.0677.1346.9967.40
Ca29.1414.9444.0225.21
Si9.657.067.636.23
Cl0.050.030.030.02
Al1.100.831.341.14
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Jiang, C.; Zheng, X.; Zhu, Y.; Tang, L.; Liu, Y.; Zhao, Z.; Zhang, H. Preparation and Application of CO2-Resistant Latex in Shale Reservoir Cementing. Processes 2024, 12, 945. https://doi.org/10.3390/pr12050945

AMA Style

Jiang C, Zheng X, Zhu Y, Tang L, Liu Y, Zhao Z, Zhang H. Preparation and Application of CO2-Resistant Latex in Shale Reservoir Cementing. Processes. 2024; 12(5):945. https://doi.org/10.3390/pr12050945

Chicago/Turabian Style

Jiang, Chunyuan, Xuecheng Zheng, Yuanqiang Zhu, Lei Tang, Yuhao Liu, Zhijun Zhao, and Hongyu Zhang. 2024. "Preparation and Application of CO2-Resistant Latex in Shale Reservoir Cementing" Processes 12, no. 5: 945. https://doi.org/10.3390/pr12050945

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