Well cementation method and well cementation fluid with adjustable thickening time

Abstract

The invention belongs to the technical field of oil field exploitation well cementation, and particularly relates to a well cementation method and well cementation fluid with adjustable thickening time. The method comprises the following steps: injecting a cementing fluid with adjustable thickening time into an oil well casing; the cementing fluid with adjustable thickening time is prepared by mixing a slow-release sodium silicate activator, sinking beads, slag, fly ash and water and uniformly stirring. The slow-release sodium silicate activator is prepared by the following steps: adding absolute ethyl alcohol into calcium chloride at normal temperature to prepare a calcium chloride solution, completely dissolving the calcium chloride solution, standing for complete reaction, and carrying out suction filtration to obtain the slow-release sodium silicate activator. Absolute ethyl alcohol is selected as a solvent medium wrapped by sodium silicate, so that formation of a calcium silicate compact layer is facilitated, and the problems of agglomeration and adhesion of calcium silicate wrapped sodium silicate particles can be effectively prevented. The thickening time of the cementing fluid can be effectively adjusted by adjusting the adding amount of the slag, the problem that the thickening time of the cementing fluid excited by sodium silicate at high temperature is difficult to adjust is solved, and the method is easy to adjust, environmentally friendly and low in price.

Description

Technical Field

[0001] The present invention belongs to the technical field of well cementing in oilfield exploitation, and particularly relates to a cementing method and a cementing fluid with adjustable thickening time. Background Art

[0002] In the technical field of oilfield development, most oil wells penetrate through multiple formations. The cementing fluid can block multiple interfaces, ensuring good cementing effect. This characteristic effectively reduces the phenomenon of mutual channeling between oil and gas and water flow, thereby improving the sealing performance and stability of oil wells. According to the geological conditions of the wellhead, well depth, drilling environment, and the desired effects, it is crucial to select the appropriate type of cementing fluid. The application of cementing fluid helps to improve the cementing quality and reduce the damage to the production layer during the cementing process. This contributes to extending the lifespan of oil and gas wells and improving the economic benefits of oil and gas wells.

[0003] Portland cement is a commonly used material for preparing cementing fluid in cementing operations, but it has problems such as high CO2 emissions and poor resistance to CO2 corrosion. Therefore, it is crucial to develop new low-carbon cementing gelling materials. Common alkali activators are sodium hydroxide and sodium silicate. The geopolymer prepared has relatively high strength, but under the action of alkali activators such as sodium hydroxide and sodium silicate, materials such as fly ash and slag dissolve and polymerize rapidly, and it is difficult to control with retarders, resulting in difficult control of the thickening / setting time of the cementing fluid. Regarding the slow release of sodium hydroxide, for example, using sodium oxalate to react with calcium hydroxide to generate sodium hydroxide and using a retarder to delay the reaction rate of sodium oxalate and calcium hydroxide to generate sodium hydroxide is an effective method to achieve the control of thickening time. There is less research on the slow release of sodium silicate at present, and there are still obvious deficiencies. Researchers have achieved the slow release of sodium silicate by encapsulating sodium silicate in an aqueous calcium chloride solution, but sodium silicate is prone to agglomeration and difficult to coat in an aqueous solution, and there will be adhesion phenomena after coating, seriously affecting the coating effect. Some researchers have also used organic polymers such as epoxy resin and ethyl cellulose to coat sodium silicate. Although the coated sodium silicate does not show agglomeration and cohesion phenomena, the preparation process is complex, and it is difficult to control the release rate of the coating for complex downhole conditions. The temperatures selected for the above methods are all room temperature. Through laboratory experiments, it is found that the above methods for coating sodium silicate are difficult to effectively extend the thickening time of the cementing fluid at high temperatures. Therefore, it is particularly important to develop a slow-release sodium silicate-activated cementing fluid suitable for high temperatures with adjustable thickening time. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a cementing method. During oilfield cementing, by injecting a cementing fluid with adjustable thickening time into the oil well casing, the adjustable thickening time is achieved. The technical solution adopted is as follows:

[0005] A cementing method, in which a cementing fluid with adjustable thickening time is injected into an oil well casing to achieve adjustable thickening time during cementing.

[0006] The preparation method of the cementing fluid includes the following steps:

[0007] (1) Preparation of the slow-release sodium silicate activator: At room temperature, take calcium chloride and add anhydrous ethanol to form a calcium chloride solution, mark it as solution A, and after the calcium chloride is completely dissolved, let it stand; add solid sodium silicate to solution A, and after the standing reaction is complete, filter to obtain the slow-release sodium silicate activator;

[0008] (2) Preparation of the cementing fluid: Mix the slow-release sodium silicate activator, sink beads, slag, fly ash and water, and stir evenly to obtain a cementing fluid with adjustable thickening time.

[0009] Preferably, in the step (1), the weight ratio of calcium chloride to anhydrous ethanol is 15:79, and the weight ratio of sodium silicate to calcium chloride is 2:1.

[0010] Preferably, in the step (1), in solution A, after the calcium chloride is completely dissolved, it needs to stand for 3-10 min; more preferably, it stands for 5 min.

[0011] Preferably, in the step (1), when adding solid sodium silicate to solution A, let it stand and react for 1-3 days; more preferably, let it stand and react for 2 days.

[0012] Preferably, in the step (2), the weight ratio of the slow-release sodium silicate activator, slag, sink beads, fly ash and water is 2:0-2:4-5:4-5:5-6.

[0013] Preferably, in the step (2), the solidifying fluid is 120 parts by weight of slow-release sodium silicate, 120 parts by weight of slag, 240 parts by weight of sink beads, 240 parts by weight of fly ash, and 317 parts by weight of water.

[0014] Preferably, in the step (2), the slag used is S95 granulated blast furnace slag, and the specific surface area ≥ 400 m 2 / kg.

[0015] Preferably, in the step (2), the specific surface area of the sink beads is greater than 1500 m 2 / g.

[0016] Preferably, in the step (2), the specific surface area of the fly ash is 400-600 m 2 / kg.

[0017] Another problem solved by the present invention is to provide a cementing fluid with adjustable thickening time used in the cementing method.

[0018] The basic principle of preparing the slow-release sodium silicate of the present invention is to form an insoluble protective outer shell calcium silicate on the surface of sodium silicate through the reaction of calcium chloride with sodium silicate, so as to coat the alkali-activated inner core sodium silicate, thereby prolonging the thickening time of the geopolymer at high temperature. The protective outer shell can play a coating role to achieve the purpose of delaying the release of sodium silicate and meet the needs of the project.

[0019] The present invention selects absolute ethanol as the solvent medium for coating sodium silicate. Its outstanding advantage is that sodium silicate is in a "slightly soluble" state in absolute ethanol. After a small amount of sodium silicate dissolves in absolute ethanol, it reacts with calcium chloride in absolute ethanol to form calcium silicate precipitate, which coats the surface of sodium silicate. Due to the low solubility of sodium silicate in ethanol, even if sodium silicate stands in an ethanol solution containing calcium chloride for 2 days, no excess sodium silicate will precipitate, which is conducive to the formation of a dense calcium silicate layer and can effectively prevent the problem of agglomeration and adhesion of calcium silicate-coated sodium silicate particles.

[0020] The regulation principle of the thickening time is to control the thickening time by changing the addition amount of slag in the cement slurry. The content of calcium ions and silicate ions in the slag is relatively high, which can inhibit or delay the release and decomposition of the protective outer shell calcium silicate and delay the release rate of sodium silicate. By changing the addition amount of slag to change the content of calcium ions and silicate ions in the slurry, the release rate of sodium silicate can be controlled, and then the thickening time of the cement slurry can be regulated.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] A cementing method of the present invention can achieve the regulation of the thickening time by injecting a cement slurry with a controllable thickening time into the oil well casing during oil well cementing. The raw materials used in this method are widely sourced, low in price, low-carbon and environmentally friendly, and easy to regulate the thickening time.

[0023] Using low-modulus anhydrous sodium silicate, which is insoluble in absolute ethanol, effectively prevents the dissolution of the alkali activator sodium silicate, improves the encapsulation rate, and prevents the agglomeration and adhesion of the particles after encapsulation.

[0024] The slow-release sodium silicate has strong heat resistance. At high temperature, it can also effectively adjust the thickening time of the cement slurry and solve the problem that it is difficult to regulate the thickening time of the sodium silicate-activated cement slurry at high temperature. Brief Description of the Drawings

[0025] Figure 1 It is the preparation process and principle diagram of the slow-release sodium silicate of the present invention.

[0026] Figure 2 It is the comparison diagram of the thickening time curves of the cement slurries obtained in Examples 1-3 and Comparative Examples 1-3 of the present invention when thickening at a temperature of 70°C. Detailed Embodiments

[0027] The present invention will be further described below by means of the accompanying drawings and embodiments, but the present invention is not limited to the scope of the described embodiments. Chemical reagents used are purchased routinely without special description. Cementing methods not described in the present invention all adopt conventional methods and processes in the prior art.

[0028] Example 1

[0029] A cementing method, injecting a cementing fluid with adjustable thickening time into an oil well casing; the preparation method of the cementing fluid includes the following steps:

[0030] (1) As Figure 1 shown, preparation of a slow-release sodium silicate activator: Add 60 parts of calcium chloride to 316 parts of absolute ethanol, stir evenly, after standing for 5 min, slowly add 120 parts of sodium silicate, react for 2 d, filter off the solution to obtain a slow-release sodium silicate activator H-1;

[0031] (2) Preparation of the cementing fluid: Mix by mass, 120 parts of slow-release sodium silicate activator H-1, 300 parts of sink beads, 300 parts of fly ash, and 317 parts of water, stir evenly to obtain a cementing fluid G-1.

[0032] Example 2

[0033] A cementing method, injecting a cementing fluid with adjustable thickening time into an oil well casing; the preparation method of the cementing fluid includes the following steps:

[0034] (1) Preparation of a slow-release sodium silicate activator: Add 60 parts of calcium chloride to 316 parts of absolute ethanol, stir evenly, after standing for 5 min, slowly add 120 parts of sodium silicate, react for 2 d, filter off the solution to obtain a slow-release sodium silicate activator H-2;

[0035] (2) Preparation of the cementing fluid: Mix by mass, 120 parts of slow-release sodium silicate activator H-2, 60 parts of slag, 270 parts of sink beads, 270 parts of fly ash, and 317 parts of water, stir evenly to obtain a cementing fluid G-2.

[0036] Example 3

[0037] A cementing method, injecting a cementing fluid with adjustable thickening time into an oil well casing; the preparation method of the cementing fluid includes the following steps:

[0038] (1) Preparation of a slow-release sodium silicate activator: Add 60 parts of calcium chloride to 316 parts of absolute ethanol, stir evenly, after standing for 5 min, slowly add 120 parts of sodium silicate, react for 2 d, filter off the solution to obtain a slow-release sodium silicate activator H-3;

[0039] (2) Preparation of Cementing Fluid: Mix by mass parts, 120 parts of slow-release sodium silicate activator H-3, 120 parts of slag, 240 parts of sink beads, 240 parts of fly ash, and 317 parts of water, and stir evenly to obtain cementing fluid G-3.

[0040] Comparative Example 1

[0041] Mix 300 mass parts of sink beads, 300 mass parts of fly ash, 120 mass parts of sodium silicate, and 317 mass parts of water, and stir evenly to obtain cementing fluid D-1.

[0042] Comparative Example 2

[0043] Mix 270 mass parts of sink beads, 270 mass parts of fly ash, 60 mass parts of slag, 120 mass parts of sodium silicate, and 317 mass parts of water, and stir evenly to obtain cementing fluid D-2.

[0044] Comparative Example 3

[0045] Mix 240 mass parts of sink beads, 240 mass parts of fly ash, 120 mass parts of slag, 120 mass parts of sodium silicate, and 317 mass parts of water, and stir evenly to obtain cementing fluid D-3.

[0046] Test the thickening time of the cementing fluids obtained in Examples 1-3 and Comparative Examples 1-3 at a test temperature of 70°C. The specific experimental results are shown in Table 1.

[0047] Table 1 Comparison of thickening times of cementing fluids obtained in Examples 1-3 and Comparative Examples 1-3

[0048] Cementing fluid Gelation time (min) Cementing fluid D-1 12 Cementing fluid D-2 9 Cementing fluid D-3 6 Cementing fluid G-1 33 Cementing fluid G-2 58 Cementing fluid G-3 270

[0049] The data in Table 1 are the thickening times of the slow-release sodium silicate and sodium silicate used in the method of the present invention to stimulate the cementing fluid at 70°C. The thickening time of the sodium silicate-stimulated cementing fluid D-3 is only 6 minutes. Under the condition of a relatively high addition amount of slag, the thickening time is short, and the polymerization reaction of the cementing fluid is fast. However, the thickening time of the cementing fluid G-3 stimulated by the slow-release sodium silicate can reach 270 minutes, with a long thickening time, good thickening performance, and strong high-temperature resistance.

[0050] In Examples 1-3, the addition amounts of slag were different. Under the condition of a relatively high addition amount of slag, more calcium ions and silicate ions inhibited the release of the slow-release sodium silicate shell, achieving the purpose of extending the thickening time. When the addition amount of slag was 60 parts (about 8% of the mass of 60 parts of sink beads, fly ash, slag, and the slow-release sodium silicate activator), the thickening time of the slow-release sodium silicate-activated cementing fluid G-2 was 58 min. When the addition amount of slag was 0%, the thickening time of the slow-release sodium silicate-activated cementing fluid G-1 was 33 min. Compared with the sodium silicate-activated cementing fluids D-1 and D-2, the thickening time was further extended, indicating the effectiveness of the slow-release sodium silicate in regulating the thickening performance. In the method of the present invention, when preparing the cementing fluid, the upper limit of the addition amount of slag is 20% (i.e., slag accounts for 20% of the total amount of sink beads, fly ash, and slag), which can well meet the requirements of on-site construction. When more slag is added, the thickening time of the cementing fluid becomes longer.

[0051] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions, or substitutions made by those skilled in the art within the substantial scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A cementing method, characterized in that, Inject a cementing fluid with adjustable thickening time into the oil well casing; the preparation method of the cementing fluid comprises the following steps: (1) Preparation of a slow-release sodium silicate activator: At room temperature, take calcium chloride and add anhydrous ethanol to prepare a calcium chloride solution, mark the solution as A, and wait for the calcium chloride to completely dissolve, then let it stand; add solid sodium silicate to solution A, and after the standing reaction is complete, filter to obtain a slow-release sodium silicate activator; (2) Preparation of the cementing fluid: Mix the slow-release sodium silicate activator, sink beads, slag, fly ash and water, and stir evenly to obtain a cementing fluid with adjustable thickening time.

2. The cementing method according to claim 1, characterized in that, In the step (1), the weight ratio of calcium chloride to anhydrous ethanol is 15:79, and the weight ratio of sodium silicate to calcium chloride is 2:

1.

3. The cementing method according to claim 2, characterized in that, In the step (1), in solution A, after the calcium chloride is completely dissolved, it needs to stand for 3-10 minutes.

4. The cementing method according to claim 3, characterized in that, In the step (1), add solid sodium silicate to solution A, and let it stand and react for 1-3 days.

5. A cementing method according to claim 1, characterized in that, In the step (2), the weight ratio of the slow-release sodium silicate activator, slag, sink beads, fly ash and water is 2:0-2:4-5:4-5:5-6.

6. The cementing method according to claim 5, characterized in that, In the step (2), the curing fluid is 120 parts by weight of slow-release sodium silicate, 120 parts of slag, 240 parts of sink beads, 240 parts of fly ash, and 317 parts of water.

7. A cementing method according to claim 1, wherein In step (2), the slag used is S95 granulated blast furnace slag with a specific surface area of ≥ 400 m 2 / kg.

8. A cementing method according to claim 1, characterized in that, In the step (2), the specific surface area of the sinking beads is greater than 1500 m 2 / g.

9. A cementing method according to claim 1, characterized in that, In the step (2), the specific surface area of the fly ash is 400 to 600 m 2 / kg.

10. A cementing fluid with adjustable thickening time used in a cementing method according to any one of claims 1-9.

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