A method for preparing a nano-admixture for cement and its application in anti-corrosion cement slurry for cementing carbon dioxide injection and production wells.

Abstract

This invention discloses a method for preparing a nano-admixture for cement, comprising the following steps: (1) adding dimethyl sulfate and dichloromethane sequentially to amino carbon nanotubes, mixing, and stirring at room temperature for 20-30 min to obtain a mixed solution; (2) adding potassium phosphate to the mixed solution, stirring at 35-40℃ for 1.5-2 h, filtering, removing dichloromethane by rotary evaporation, rinsing the obtained solid with deionized water, and drying to obtain the nano-admixture for cement. Simultaneously, this invention also discloses the application of the nano-admixture for cement in anti-corrosion cement slurry for carbon dioxide injection-production wells. The nano-admixture for cement can fill the internal micropores of cement stone, having a filling and plugging effect, thereby improving the density of the cement stone; and by reacting chemically with carbon dioxide present in oil and gas wells, it further improves the corrosion resistance of the cement stone.

Description

Technical Field

[0001] This invention belongs to the field of cementing technology, specifically relating to a method for preparing a nano-admixture for cement and its application in anti-corrosion cement slurry for cementing carbon dioxide injection and production wells. Background Technology

[0002] Achieving carbon peaking and carbon neutrality mainly involves two aspects: controlling carbon emissions and increasing carbon sinks through the development of carbon capture and storage (CCS) technologies. Injecting carbon dioxide into the formation via wellbore for oil displacement or storage is a crucial aspect of CCS technology. In this technology, the wellbore is primarily sealed with cement slurry, which is one of the main barriers preventing carbon dioxide escape. However, the cement used in the cement slurry is silicate cement, which reacts with carbon dioxide in a wet environment, reducing the strength of the cement stone, damaging the cement sheath structure, and creating upward channels. Therefore, the cement slurry used in injection and production wells during carbon dioxide displacement or storage must possess a certain degree of resistance to carbon dioxide corrosion.

[0003] Research has shown that adding admixtures with certain anti-corrosion functions to oil well cement is an effective way to improve the corrosion resistance of cement slurry. Currently, publicly available admixtures for carbon dioxide corrosion resistance in oil well cement mainly include fly ash, resin, latex, and microsilica. These admixtures (or additives) can improve the carbon dioxide corrosion resistance of cement stone under specific working conditions, but they also have certain limitations. For example, granular materials have a significant impact on the strength of cement stone, and the dosage of resin or latex is large and costly. On the other hand, 90% of the cement pores after hydration are nanoscale, and the lack of sufficient consideration and utilization of nanoscale pores to improve carbon dioxide corrosion resistance is one of the main technological bottlenecks in this field. To address this issue, nano-silica is added to oil well cement as an admixture to improve the corrosion resistance of cement stone. Its core mechanism of action is pore filling and nucleation, increasing the Si / Ca ratio and density of hydration products, thereby improving the carbon dioxide corrosion resistance of cement stone, demonstrating the superiority of nanomaterials in this technological field. However, nano-silica primarily improves corrosion resistance by increasing the density of cement stone, without specifically modifying the cement stone based on the characteristics of carbon dioxide. Therefore, its resistance to carbon dioxide corrosion needs further enhancement. Furthermore, carbon dioxide injection-production wells often involve water-gas alternation, causing the wellbore to experience periodic alternating stresses, requiring the cement stone to possess strong tensile strength. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method for preparing a nano-admixture for cement, and also provides the application of the nano-admixture for cement in anti-corrosion cement slurry for carbon dioxide injection and production wells, which has a good anti-carbon dioxide corrosion effect.

[0005] A method for preparing a nano-admixture for cement includes the following steps:

[0006] (1) Add dimethyl sulfate and dichloromethane sequentially to amino carbon nanotubes, mix, and stir at room temperature for 20-30 min to obtain a mixed solution;

[0007] (2) Add potassium phosphate to the mixed solution, stir at 35-40℃ for 1.5-2h, filter, remove dichloromethane by rotary evaporation, wash the obtained solid with deionized water, dry, and obtain the nano-admixture for cement.

[0008] Preferably, the proportions of the raw materials are as follows: the mass ratio of the amino carbon nanotubes, dimethyl sulfate, dichloromethane, and potassium phosphate is 1:(1-1.5):(45-56):(1-1.5).

[0009] More preferably, the proportions of the raw materials are as follows: the mass ratio of amino carbon nanotubes, dimethyl sulfate, dichloromethane, and potassium phosphate is 1:1.2:50:1.2.

[0010] Preferably, the drying conditions are drying at 105-110°C to constant weight.

[0011] A corrosion-resistant cement slurry for cementing carbon dioxide injection and production wells is composed of the following raw materials in parts by weight: 100 parts oil well cement, 2.0-4.0 parts fluid loss reducer, 1.0-2.0 parts gas channeling inhibitor, 0.02-0.05 parts cement nano-admixture, 0.5-0.6 parts defoamer, and 40-50 parts water; wherein the cement nano-admixture is prepared by the preparation method of the cement nano-admixture of the present invention.

[0012] Preferably, the oil well cement is Grade G oil well cement;

[0013] Preferably, the water loss reducing agent is a modified acrylamide copolymer water loss reducing agent or a polyvinyl alcohol water loss reducing agent.

[0014] Preferably, the defoamer is an organosilicon defoamer, a mineral oil defoamer, or a modified silicone polyether defoamer.

[0015] Preferably, the anti-gas channeling agent is an aluminum powder-based anti-gas channeling agent or a polymer-based anti-gas channeling agent.

[0016] The method for preparing the anti-corrosion cement slurry for cementing carbon dioxide injection and production wells includes the following steps:

[0017] (1) Take oil well cement, fluid loss reducer and gas channeling inhibitor and mix them to obtain a mixture;

[0018] (2) Take water, cement nano-admixture and defoamer, mix them, and ultrasonically treat them at 350W power for 25-30 minutes to obtain a mixed solution;

[0019] (3) The mixture is added to the mixture within 10-15s under the stirring condition of 4500r / min, and then stirred for 50-60s at 8000r / min to obtain anti-corrosion cement slurry for cementing carbon dioxide injection and production wells.

[0020] Advantages of this invention:

[0021] (1) The cement nano admixture provided by the present invention is a nano admixture that can fill the internal micropores of cement stone and has the function of filling and plugging pores, thereby improving the density of cement stone;

[0022] (2) The cement nano-admixture provided by the present invention is an amine-modified carbon nanotube. By reacting chemically with carbon dioxide present in oil and gas wells, it can dilute the concentration of carbon dioxide on the one hand, and the generated product can further fill smaller pores on the other hand, thereby improving the corrosion resistance of cement stone.

[0023] (3) The nano-admixture of the present invention can be better dispersed in cement slurry, better exert its high strength characteristics, and improve the mechanical properties of cement slurry. Implementation

[0024] Example 1

[0025] A method for preparing a nano-admixture for cement includes the following steps:

[0026] (1) Add 1.2 parts of dimethyl sulfate and 50 parts of dichloromethane to 1 part of amino carbon nanotubes, mix, and stir at room temperature for 20 min to obtain a mixed solution;

[0027] (2) Add 1.2 parts of potassium phosphate to the mixed solution, stir at 35°C for 2 hours, filter, remove dichloromethane by rotary evaporation, wash the obtained solid with deionized water, and dry at 105°C to constant weight to obtain a nano-admixture for cement.

[0028] Example 2

[0029] A method for preparing a nano-admixture for cement includes the following steps:

[0030] (1) Add 1 part dimethyl sulfate and 45 parts dichloromethane to 1 part amino carbon nanotubes, mix, and stir at room temperature for 30 min to obtain a mixed solution;

[0031] (2) Add 1 part of potassium phosphate to the mixed solution, stir at 40°C for 1.5 h, filter, remove dichloromethane by rotary evaporation, wash the obtained solid with deionized water, dry at 110°C to constant weight, and obtain the nano-admixture for cement.

[0032] Example 3

[0033] A method for preparing a nano-admixture for cement includes the following steps:

[0034] (1) Add 1.5 parts of dimethyl sulfate and 56 parts of dichloromethane to 1 part of amino carbon nanotubes, mix, and stir at room temperature for 30 min to obtain a mixed solution;

[0035] (2) Add 1.5 parts of potassium phosphate to the mixed solution, stir at 40°C for 1.5 h, filter, remove dichloromethane by rotary evaporation, wash the obtained solid with deionized water, and dry at 110°C to constant weight to obtain a nano-admixture for cement.

[0036] Example 4

[0037] The anti-corrosion cement slurry for cementing carbon dioxide injection and production wells is composed of the following raw materials in parts by weight: 100 parts of G-grade oil well cement, 3.0 parts of fluid loss reducer, 1.5 parts of gas channeling inhibitor, 0.04 parts of cement nano-admixture, 0.5 parts of defoamer, and 46 parts of water.

[0038] The water loss reducing agent is of type HT-1 and is a modified acrylamide copolymer;

[0039] The anti-gas channeling agent is model KQ-T, and is an aluminum powder-based anti-gas channeling agent;

[0040] The defoamer is model KS-66 and is an organosilicon defoamer;

[0041] The nano-admixture for cement is prepared by the preparation method described in claim 1.

[0042] The anti-corrosion cement slurry for cementing carbon dioxide injection and production wells is prepared by the following method:

[0043] (1) Take oil well cement, fluid loss reducer and gas channeling inhibitor and mix them to obtain a mixture;

[0044] (2) Take water, cement nano-admixture and defoamer, mix them, and ultrasonically treat them at 350W power for 25 minutes to obtain a mixed solution;

[0045] (3) The mixture is added to the mixture within 10s under the stirring condition of 4500r / min, and then stirred for 50s at 8000r / min to obtain anti-corrosion cement slurry for cementing carbon dioxide injection and production wells.

[0046] Example 5

[0047] The anti-corrosion cement slurry for cementing carbon dioxide injection and production wells is composed of the following raw materials in parts by weight: 100 parts of G-grade oil well cement, 2.0 parts of fluid loss reducer, 1.0 part of gas channeling inhibitor, 0.02 parts of cement nano-admixture, 0.6 parts of defoamer, and 40 parts of water.

[0048] The water loss reducing agent is of type HT-1 and is a modified acrylamide copolymer;

[0049] The anti-gas channeling agent is designated as OD-348, and is a polymer-based anti-gas channeling agent.

[0050] The defoamer is designated as WBA, and is a mineral oil-based defoamer.

[0051] The nano-admixture for cement is prepared by the preparation method described in claim 1.

[0052] The anti-corrosion cement slurry for cementing carbon dioxide injection and production wells is prepared by the following method:

[0053] (1) Take oil well cement, fluid loss reducer and gas channeling inhibitor and mix them to obtain a mixture;

[0054] (2) Take water, cement nano-admixture and defoamer, mix them, and ultrasonically treat them at 350W power for 30min to obtain a mixed solution;

[0055] (3) The mixture is added to the solution within 15s under the stirring condition of 4500r / min, and then stirred for 60s at 8000r / min to obtain anti-corrosion cement slurry for cementing carbon dioxide injection and production wells.

[0056] Example 6

[0057] The anti-corrosion cement slurry for cementing carbon dioxide injection and production wells is composed of the following raw materials in parts by weight: 100 parts of G-grade oil well cement, 4.0 parts of fluid loss reducer, 2.0 parts of gas channeling inhibitor, 0.05 parts of cement nano-admixture, 0.5 parts of defoamer, and 50 parts of water.

[0058] The water loss reducing agent is designated as LT-2 and is a polyvinyl alcohol-based water loss reducing agent.

[0059] The anti-gas channeling agent is model DG-29, which is an aluminum powder-based anti-gas channeling agent;

[0060] The defoamer is designated as KB-202 and is a mineral oil-based defoamer.

[0061] The cement nano-admixture is prepared by the preparation method described in claim 3;

[0062] The rest is the same as in Example 4.

[0063] Comparative Example 1

[0064] No cement-grade nano-admixtures were added; otherwise, the process was the same as in Example 4.

[0065] Comparative Example 2

[0066] Amino carbon nanotubes were used to replace the nano-admixtures used in cement, and the rest was the same as in Example 4.

[0067] Comparative Example 3

[0068] Carbon nanotubes were used to replace the nano-admixtures used in cement, and the rest was the same as in Example 4.

[0069] I. Mechanical property testing

[0070] The above-mentioned cement slurry was pressurized and cured using a DFC-0720 pressurized curing kettle. Based on the downhole conditions during cementing of different cement slurry systems, the curing conditions for Example 4, Comparative Example 1, Comparative Example 2, and Comparative Example 3 were set to 70℃×20.8MPa×72h. The compressive strength curing mold was 50mm×50mm×50mm, and the flexural strength curing mold was 40mm×40mm×160mm.

[0071] The compressive strength and flexural strength of the cement stone were tested separately. The compressive strength test method was based on GB / T 19139-2012 "Test Methods for Cement in Oil Wells", and the flexural strength test method was based on GB / T 17671-2021 "Test Methods for Strength of Cement Mortar (ISO Method)". The instruments used were a YJ-2000 compression testing machine and a DKZ-5000 flexural testing machine, respectively. The test results are shown in Table 1.

[0072] Table 1. Test results of mechanical properties of cement grout system

[0073]

[0074] As shown in Table 1, the admixture provided by this invention can enhance the compressive and flexural strength of cement stone in cement slurry. Compared with Comparative Example 1 without nano-admixtures, the increases are 31.6% and 40.9%, respectively. Compared with amino carbon nanotubes (Comparative Example 2), the compressive and flexural strengths of the embodiments of this invention are also improved to a certain extent, especially the flexural strength, which is increased by 24.0%. When carbon nanotubes are added (Comparative Example 3), its strength is slightly higher than that of Comparative Example 1, but much lower than that of Example 4. Analysis suggests that this is mainly because, compared with carbon nanotubes and amino carbon nanotubes, the nano-admixture of this invention can be better dispersed in the cement slurry, better exerting its high-strength characteristics, increasing the density of the carbon nanotube cement slurry, and making the cement slurry more mechanically robust. When subjected to external force, the pull-out energy consumption of the material with a longer aspect ratio is higher, which macroscopically manifests as an increase in flexural strength.

[0075] II. Carbon Dioxide Corrosion Resistance Testing

[0076] First, a 25mm diameter cylindrical cement stone sample with a length of 25mm was drilled from a 50mm×50mm×50mm block cement stone sample (the cement stone formed during the mechanical property testing). Then, a carbon dioxide corrosion experiment was conducted on the cement stone samples of different systems using an XWL-18 high-temperature and high-pressure carbon dioxide reactor. The temperature and pressure conditions were 70℃×15MPa, and the corrosion time was 28 days. After the corrosion experiment, the porosity, compressive strength, and corrosion depth were measured and compared with those of cement stone cured under the same formula and temperature / pressure water bath. The results are shown in Table 2.

[0077] Table 2 Corrosion test results

[0078]

[0079] As shown in Table 2, in the cement slurry system, in Comparative Example 1 without additives, the corrosion depth of the cement stone was deeper, and the strength degradation rate was as high as 65.06%. However, in the cement slurry system of this invention (Example 4), the corrosion depth was less than 1.5 mm, and the strength degradation rate was less than 5%. The inventors analyzed that this result was due to the following two aspects: First, the additives of this invention fill the internal micropores of the cement stone, having a filling and plugging effect, thereby improving the compactness of the cement stone; second, when carbon dioxide invades the cement stone matrix, it can react with carbon dioxide to generate insoluble quaternary ammonium salts. On the one hand, this can block the generated pores, compensating for some of the strength loss; on the other hand, the generated insoluble quaternary ammonium salts slow down the dissolving effect of carbon dioxide on the cement slurry. Therefore, the porosity change after corrosion is not significant, and the strength reduction rate is also low. In comparison, amino-carbon nanotube cement slurry (Comparative Example 2) and carbon nanotube cement slurry have similar mechanisms of action to existing corrosion inhibitors. They only delay carbon dioxide intrusion by filling pores to increase density. Their effect is relatively limited under high temperature and high pressure environments, and the strength reduction rate still exceeds 20%. The porosity after corrosion also increases significantly.

Claims

1. A method for preparing a nano-admixture for cement, characterized in that: Includes the following steps: (1) Add dimethyl sulfate and dichloromethane sequentially to amino carbon nanotubes, mix, and stir at room temperature for 20-30 min to obtain a mixed solution; (2) Add potassium phosphate to the mixed solution, stir at 35-40℃ for 1.5-2h, filter, remove dichloromethane by rotary evaporation, wash the obtained solid with deionized water, dry, and obtain the nano-admixture for cement.

2. The method for preparing a nano-admixture for cement according to claim 1, characterized in that: The mass ratio of amino carbon nanotubes, dimethyl sulfate, dichloromethane, and potassium phosphate is 1:(1-1.5):(45-56):(1-1.5).

3. The method for preparing a nano-admixture for cement according to claim 2, characterized in that: The mass ratio of amino carbon nanotubes, dimethyl sulfate, dichloromethane, and potassium phosphate is 1:1.2:50:1.

2.

4. The method for preparing a nano-admixture for cement according to claim 2, characterized in that: The drying conditions are as follows: drying at 105-110°C to constant weight.

5. A corrosion-resistant cement slurry for cementing carbon dioxide injection and production wells, characterized in that: It is composed of the following raw materials in parts by weight: 100 parts oil well cement, 2.0-4.0 parts fluid loss reducer, 1.0-2.0 parts anti-gas channeling agent, 0.02-0.05 parts cement nano-admixture, 0.5-0.6 parts defoamer, and 40-50 parts water; wherein the cement nano-admixture is prepared by the preparation method described in any one of claims 1-4.

6. The anti-corrosion cement slurry for cementing carbon dioxide injection and production wells according to claim 5, characterized in that: The oil well cement is Grade G oil well cement.

7. The anti-corrosion cement slurry for cementing carbon dioxide injection and production wells according to claim 6, characterized in that: The water loss reducing agent is a modified acrylamide copolymer water loss reducing agent or a polyvinyl alcohol water loss reducing agent.

8. The anti-corrosion cement slurry for cementing carbon dioxide injection and production wells according to claim 7, characterized in that: The defoamer is an organosilicon defoamer or a mineral oil defoamer.

9. The anti-corrosion cement slurry for cementing carbon dioxide injection and production wells according to claim 8, characterized in that: The anti-gas channeling agent is an aluminum powder-based anti-gas channeling agent or a polymer-based anti-gas channeling agent.

10. The method for preparing the anti-corrosion cement slurry for cementing carbon dioxide injection and production wells as described in claim 5, characterized in that: Includes the following steps: (1) Take oil well cement, fluid loss reducer and gas channeling inhibitor and mix them to obtain a mixture; (2) Take water, cement nano-admixture and defoamer, mix them, and ultrasonically treat them at 350W power for 25-30 minutes to obtain a mixed solution; (3) The mixture is added to the mixture within 10-15s under the stirring condition of 4500r / min, and then stirred for 50-60s at 8000r / min to obtain anti-corrosion cement slurry for cementing carbon dioxide injection and production wells.

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