Oil-based spacer fluid for leaking stoppage of cement paste as well as preparation method and application of oil-based spacer fluid

Abstract

The invention relates to an oil-based spacer fluid for cement paste leaking stoppage and a preparation method and application thereof, and belongs to the technical field of oil and gas exploitation. The spacer fluid comprises an acrylamide polymer and an oil-based liquid, wherein the acrylamide polymer is formed by polymerizing acrylamide, 2-acrylamide-2-methylpropanesulfonic acid and acrylic acid; according to the present invention, the water-in-oil polymer is prepared by compounding the acrylamide polymer and the oil-based liquid, the viscosity is adjustable, the acrylamide polymer is the hydrophilic chain-like high-molecular compound, and the acrylamide polymer in the water-in-oil liquid cannot completely extend so as to intuitively show that the product has advantages of low viscosity in the oil-based liquid, pumpability, good rheological property and the like during the site construction; when the hydrophilic high-molecular compound is mixed with a water-based liquid, molecular chains of the hydrophilic high-molecular compound fully extend along with the increase of the mixing amount of the water-based liquid, a net structure is formed among the molecular chains, and the adhesive cutting is exponentially increased, so that the requirement of isolating cement paste during plugging of a large karst cave and a large crack can be met.

Description

Technical Field

[0001] This application relates to the technical field of oil and gas exploitation, and particularly to an oil-based spacer fluid for plugging cement slurry, a preparation method thereof, and an application thereof. Background Art

[0002] During the drilling process of oil and gas wells, the loss phenomenon, especially the lost circulation caused by large karst caves and large fractures, seriously affects the drilling efficiency. For the lost circulation caused by large karst caves and large fractures, cement slurry is generally used for plugging operations. Before injecting the cement slurry into the karst cave, a high-viscosity spacer fluid for isolation needs to be injected underground. This spacer fluid mainly bears the liquid column pressure from the cement slurry and the drilling fluid, ensures that the cement slurry stays and solidifies at the opening of the karst cave, and after the cement slurry solidifies, it can generate a high enough strength to build a blocking wall at the opening of the hole to block the hole, thereby achieving the purpose of plugging.

[0003] However, in on-site construction, the high-viscosity spacer fluid mainly consists of high-concentration bentonite slurry or dripping drilling fluid. These two types of spacer fluids are extremely easy to be diluted by formation water, and cannot achieve the function of isolating and plugging the cement slurry, resulting in the loss of cement slurry along large karst caves and large fractures, and causing the failure of plugging. Summary of the Invention

[0004] This application provides an oil-based spacer fluid for plugging cement slurry, a preparation method thereof, and an application thereof to improve the anti-dilution property of the spacer fluid.

[0005] In a first aspect, this application provides an oil-based spacer fluid for plugging cement slurry, where the spacer fluid includes an acrylamide polymer and an oil-based liquid, and the acrylamide polymer is polymerized from acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and acrylic acid.

[0006] As an optional implementation manner, the molecular weight of the acrylamide polymer is 4.0×10 6 ~1.0×10 7 .

[0007] As an optional implementation manner, the oil-based liquid includes at least one of methyl silicone oil, white oil, and 9-alkenyl-12-hydroxyoctadecanoic acid.

[0008] In a second aspect, this application provides a preparation method of an oil-based spacer fluid for plugging cement slurry, and the method includes:

[0009] Obtaining raw materials, where the raw materials include acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, acrylic acid, oil-based liquid, emulsifier, initiator, and stabilizer;

[0010] Dissolving the acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and acrylic acid in a solvent to obtain a mixed solution;

[0011] Mix the above-mentioned mixed solution, oil-based liquid and emulsifier to obtain an emulsified solution;

[0012] Prepare the initiator into a solution to obtain an initiator solution;

[0013] Mix and react the emulsified solution and the initiator solution to polymerize acrylamide, 2-acrylamido-2-methylpropanesulfonic acid and acrylic acid to form an acrylamide-based polymer, and then add the stabilizer to obtain an isolation fluid.

[0014] As an alternative embodiment, the raw materials include, by weight: 7-10 parts of acrylamide, 3-5 parts of 2-acrylamido-2-methylpropanesulfonic acid, 5-8 parts of acrylic acid, 80-85 parts of oil-based liquid, 3-5 parts of emulsifier, 0.5-1 part of initiator and 2-4 parts of stabilizer.

[0015] As an alternative embodiment, the raw materials include, by weight: 8-9 parts of acrylamide, 3.5-4.5 parts of 2-acrylamido-2-methylpropanesulfonic acid, 6-7 parts of acrylic acid, 81-84 parts of oil-based liquid, 3.5-4.5 parts of emulsifier, 0.7-0.8 part of initiator and 2.5-3.5 parts of stabilizer.

[0016] As an alternative embodiment, the pH value of the mixed solution is 8-9.

[0017] As an alternative embodiment, the temperature of the mixing reaction is 80-90 °C; and / or

[0018] The time of the mixing reaction is 3.5-4 h.

[0019] As an alternative embodiment, the initiator includes potassium persulfate; and / or

[0020] The emulsifier includes sorbitan monooleate; and / or

[0021] The stabilizer includes at least one of silicon dioxide, calcium silicate and magnesium oxide.

[0022] In a third aspect, the present application provides an application of an oil-based isolation fluid for plugging cement slurry. The isolation fluid is the isolation fluid described in the first aspect or the isolation fluid prepared by the preparation method described in the second aspect. The application includes using the isolation fluid for plugging cement slurry in oil and gas well drilling.

[0023] The above technical solutions provided by the embodiments of the present application have the following advantages compared with the prior art:

[0024] The spacer fluid provided by the embodiments of the present application is prepared by compounding acrylamide polymers and oil-based liquids, achieving adjustable viscosity. The acrylamide polymer is a hydrophilic chain-shaped polymer compound. In the water-in-oil liquid, due to the inability of the molecular chains to fully stretch, the product intuitively shows low viscosity in the oil-based liquid, and has advantages such as pumpability and good rheology in on-site construction. When it is mixed with the water-based liquid, as the amount of the water-based liquid mixed in increases, the molecular chains of the hydrophilic polymer compound fully stretch, and a network structure is formed between the molecular chains, and the viscosity and shear rate increase exponentially. Therefore, it can meet the requirements of isolating cement slurry when plugging large karst caves and large fractures. As a cement slurry spacer fluid, it thickens when encountering water, and the thickening is controllable and has strong anti-dilution properties; under the condition of 150 °C and aging for 72 h, the apparent viscosity does not decrease significantly, and it has good high-temperature resistance; in addition, the spacer fluid has good compatibility with the cement slurry, and no flash setting phenomenon of the cement slurry will occur after full mixing. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The accompanying drawings here are incorporated into the specification and constitute a part of this specification, showing embodiments consistent with the present application, and are used together with the specification to explain the principles of the present application.

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0027] Figure 1 It is a schematic flow chart of the method provided by the embodiments of the present application;

[0028] Figure 2 It is a graph showing the change in apparent viscosity after the spacer fluid provided by the embodiments of the present application is mixed with different water-based drilling fluids;

[0029] Figure 3 It is a graph showing the change in apparent viscosity with the increase in temperature after the spacer fluid provided by the embodiments of the present application is mixed with potassium chloride polysulfonate drilling fluid. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are some, but not all, of the embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present application.

[0031] Unless otherwise specified, all kinds of raw materials, reagents, instruments, equipment, etc. used in this application can be obtained through market purchase or can be prepared by existing methods.

[0032] The loss phenomenon during the drilling process of oil and gas wells, especially the lost circulation caused by large karst caves and large fractures, seriously affects the drilling efficiency. For the lost circulation caused by large karst caves and large fractures, cement slurry is generally used for plugging operations. Before injecting the cement slurry into the karst cave, a high-viscosity isolation and supporting liquid for isolation needs to be injected downhole. This isolation liquid mainly bears the liquid column pressure from the cement slurry and the drilling fluid, ensures that the cement slurry stays and solidifies at the opening of the karst cave, and after the cement slurry solidifies, it can generate a high enough strength to build a blocking wall at the hole of the leak, seal the hole, and thus achieve the purpose of plugging.

[0033] However, in on-site construction, the high-viscosity isolation liquid mainly consists of high-concentration bentonite slurry or dripping drilling fluid. These two kinds of isolation liquids are extremely easy to be diluted by formation water, and cannot achieve the effect of isolating and plugging the cement slurry, resulting in the loss of the cement slurry along large karst caves and large fractures, and causing the failure of plugging.

[0034] Therefore, the inventor intends to provide an isolation liquid with high anti-dilution property to cooperate with the cement slurry to achieve the plugging of oil and gas wells.

[0035] The embodiment of the present application provides an oil-based isolation liquid for plugging with cement slurry. The isolation liquid includes an acrylamide polymer and an oil-based liquid. The acrylamide polymer is polymerized from acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and acrylic acid.

[0036] The acrylamide polymer is a hydrophilic chain-shaped macromolecular compound. In the oil-based liquid, its molecular chain cannot be fully extended, and intuitively, the product has a low viscosity in the oil-based liquid. In on-site construction, it has advantages such as being pumpable and having good rheology. When this isolation liquid is mixed with a water-based liquid, as the mixing amount of the water-based liquid increases, the molecular chains of the hydrophilic macromolecular compound are fully extended, and a network structure is formed between the molecular chains. Intuitively, after the isolation liquid is mixed with the water-based liquid, the viscosity and shear force increase exponentially, so it can meet the requirements of isolating the cement slurry when plugging large karst caves and large fractures.

[0037] In some embodiments, the molecular weight of the acrylamide polymer is 4.0×10 6 ~1.0×10 7 .

[0038] In some embodiments, the oil-based liquid includes at least one of methyl silicone oil, white oil, and 9-alkenyl-12-hydroxystearic acid.

[0039] Figure 1 It is a schematic flow chart of the method provided by the embodiment of the present application; as Figure 1As shown, based on a general inventive concept, an embodiment of the present application further provides a preparation method of an oil-based isolation fluid for plugging cement slurry leakage, and the method includes:

[0040] S1. Obtain raw materials, where the raw materials include acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, acrylic acid, an oil-based liquid, an emulsifier, an initiator, and a stabilizer;

[0041] In some embodiments, the raw materials include, by weight: 7-10 parts of acrylamide, 3-5 parts of 2-acrylamido-2-methylpropanesulfonic acid, 5-8 parts of acrylic acid, 80-85 parts of an oil-based liquid, 3-5 parts of an emulsifier, 0.5-1 part of an initiator, and 2-4 parts of a stabilizer.

[0042] Further, the raw materials include, by weight: 8-9 parts of acrylamide, 3.5-4.5 parts of 2-acrylamido-2-methylpropanesulfonic acid, 6-7 parts of acrylic acid, 81-84 parts of an oil-based liquid, 3.5-4.5 parts of an emulsifier, 0.7-0.8 part of an initiator, and 2.5-3.5 parts of a stabilizer.

[0043] In some embodiments, the initiator includes potassium persulfate; the emulsifier includes sorbitan monooleate (also known as SP80 or Span 80); the stabilizer includes at least one of silica, calcium silicate, and magnesium oxide.

[0044] S2. Dissolve the acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and acrylic acid in a solvent to obtain a mixed solution;

[0045] In some embodiments, the pH value of the mixed solution is 8-9.

[0046] Specifically, in this embodiment, 8-10 parts by weight of acrylamide, 3-5 parts by weight of 2-acrylamido-2-methylpropanesulfonic acid, and 5-8 parts by weight of acrylic acid are dissolved in water, and a 1-1.5 wt% sodium hydroxide solution is added dropwise to adjust the pH of the solution to 8-9 to prepare a mixed solution.

[0047] S3. Mix the mixed solution, the oil-based liquid, and the emulsifier to obtain an emulsified solution;

[0048] Specifically, in this embodiment, 80-85 parts by weight of an oil-based liquid are added to a four-necked flask, the mixed solution is added to the four-necked flask, and 3-5 parts by weight of an emulsifier are added while stirring and nitrogen is filled to obtain an emulsified solution.

[0049] S4. Prepare the initiator into a solution to obtain an initiator solution;

[0050] Specifically, in this embodiment, 0.5-1 part by weight of an initiator for polymerizing monomers is dissolved in water to prepare an initiator solution.

[0051] S5. Mix the emulsified solution and the initiator solution for a reaction to polymerize acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and acrylic acid to form an acrylamide-based polymer, and then add the stabilizer to obtain the spacer fluid.

[0052] In some embodiments, the temperature of the mixing reaction is 80-90 °C; the time of the mixing reaction is 3.5-4 h.

[0053] Specifically, in this embodiment, continue to stir the emulsified solution and heat it in a water bath to 80-90 °C, then slowly dropwise add the initiator solution to the mixed solution, continue to pass nitrogen and stir for 3.5-4 h, stop the reaction, cool to room temperature, and then mix in 2-4 parts by weight of the stabilizer. The resulting white viscous liquid is the oil-based spacer fluid for cement slurry plugging.

[0054] This method is synthesized by the inverse emulsion polymerization method. By compounding with an oil-based system, a cement slurry spacer fluid with adjustable viscosity that can meet the needs of on-site construction is obtained; and this oil-based spacer fluid for cement slurry plugging thickens when encountering water as a cement slurry spacer fluid, and the thickening is controllable and has strong anti-dilution properties; at 150 °C for 72 h of aging, the apparent viscosity does not decrease significantly, and it has good temperature resistance; in addition, this spacer fluid has good compatibility with the cement slurry, and no flash setting phenomenon of the cement slurry will occur after sufficient mixing. The normal temperature flow performance and high temperature flow performance of the mixed slurry both have the characteristics of being pumpable, and can meet the requirements of on-site construction.

[0055] Based on a general inventive concept, the embodiments of the present application further provide an application of an oil-based spacer fluid for cement slurry plugging. The spacer fluid is the spacer fluid provided above or the spacer fluid prepared by the preparation method provided above. The application includes using the spacer fluid for cement slurry plugging in oil and gas well drilling.

[0056] This application is implemented based on the above spacer fluid or method. The specific content of the spacer fluid or method can be referred to the above embodiments. Since this application adopts some or all of the technical solutions of the above embodiments, it at least has all the beneficial effects brought by the technical solutions of the above embodiments, and will not be elaborated one by one here.

[0057] The following further elaborates the present application in combination with specific embodiments. It should be understood that these embodiments are only used to illustrate the present application and not to limit the scope of the present application. The experimental methods without specific conditions noted in the following embodiments are usually determined according to national standards. If there is no corresponding national standard, they are carried out according to general international standards, conventional conditions, or conditions recommended by the manufacturer.

[0058] Example 1

[0059] A preparation method of an oil-based isolation fluid for plugging cement slurry, the method comprising:

[0060] Dissolve 8 g of acrylamide, 3 g of 2-acrylamido-2-methylpropanesulfonic acid and 5 g of acrylic acid in 50 mL of water, and dropwise add 1 wt% sodium hydroxide solution to adjust the pH of the solution to 9 to obtain aqueous solution I; dissolve 1 g of potassium persulfate in 20 ml of water to prepare aqueous solution II; add 100 mL of white oil to a four-necked flask, and add solution I to the four-necked flask. Under stirring conditions, add 3 g of SP-80 and purge with nitrogen to remove oxygen; after heating the mixed solution in a water bath to 80 °C, slowly add solution II dropwise into the four-necked flask, continue to purge with nitrogen and stir for 4 h, then stop the reaction. Cool the solution to room temperature, and then mix in 3 g of silicon dioxide. The obtained white viscous liquid is the oil-based isolation fluid for plugging cement slurry.

[0061] Example 2

[0062] A preparation method of an oil-based isolation fluid for plugging cement slurry, the method comprising:

[0063] Dissolve 10 g of acrylamide, 5 g of 2-acrylamido-2-methylpropanesulfonic acid and 8 g of acrylic acid in 80 mL of water, and dropwise add 1.5 wt% sodium hydroxide solution to adjust the pH of the solution to 9 to obtain aqueous solution I; dissolve 0.5 g of potassium persulfate in 20 g of water to prepare aqueous solution II; add 110 mL of white oil to a four-necked flask, and add solution I to the four-necked flask. Under stirring conditions, add 3 g of SP-80 and purge with nitrogen to remove oxygen; after heating the mixed solution in a water bath to 90 °C, slowly add solution II dropwise into the four-necked flask, continue to purge with nitrogen and stir for 4 h, then stop the reaction. Cool the solution to room temperature, and then mix in 3 g of magnesium oxide. The obtained white viscous liquid is the oil-based isolation fluid for plugging cement slurry.

[0064] Example 3

[0065] A preparation method of an oil-based isolation fluid for plugging cement slurry, the method comprising:

[0066] Dissolve 9 g of acrylamide, 4 g of 2-acrylamido-2-methylpropanesulfonic acid and 6 g of acrylic acid in 80 mL of water, and dropwise add 1 wt% sodium hydroxide solution to adjust the pH of the solution to 8 to obtain aqueous solution I; dissolve 0.5 g of potassium persulfate in 20 g of water to prepare aqueous solution II; add 100 mL of white oil to a four-necked flask, and add solution I to the four-necked flask. Under stirring conditions, add 3 g of SP-80 and purge with nitrogen to remove oxygen; after heating the mixed solution in a water bath to 90 °C, slowly add solution II dropwise into the four-necked flask, continue to purge with nitrogen and stir for 3.5 h, then stop the reaction. Cool the solution to room temperature, and then mix in 3 g of magnesium oxide. The obtained white viscous liquid is the oil-based isolation fluid for plugging cement slurry.

[0067] Comparative Example 1

[0068] A preparation method of a high-concentration bentonite isolation fluid, the method comprising:

[0069] Take 40 g of sodium bentonite for drilling fluid, 4 g of sodium carbonate, and 1 g of sodium hydroxide, dissolve them in 400 ml of water, and stir for 2 hours to make them evenly mixed. Let it stand for 24 hours. After the soil slurry is fully hydrated and dispersed, stir evenly. The obtained yellow viscous liquid is the high-concentration bentonite isolation fluid.

[0070] Comparative Example 2

[0071] A preparation method of a trickle bentonite isolation fluid, the method comprising:

[0072] Take 40 g of sodium bentonite for drilling fluid, 4 g of sodium carbonate, and 1 g of sodium hydroxide, dissolve them in 400 ml of water, and stir for 2 hours to make them evenly mixed. Let it stand for 24 hours. After the soil slurry is fully hydrated and dispersed, stir evenly. Add 4 g of sodium carboxymethylcellulose to the drilling fluid and stir at high speed. The obtained yellow gel-like viscous liquid is the trickle bentonite isolation fluid.

[0073] Mix the isolation fluids provided in Examples 1 to 3 and Comparative Examples 1 to 2 as cement slurry isolation fluids with different amounts of added clear water, and use an NDJ-1 type viscometer with a large viscosity range to measure the apparent viscosity of the mixed isolation fluid; among them, the test conditions: No. 2 rotor, rotation speed: 100 r / min; the test results are shown in Table 1.

[0074]

[0075] It can be seen from Table 1 that the larger the volume ratio of clear water to the isolation fluid provided in the examples of the present application, that is, the greater the content of clear water mixed with the isolation fluid, the greater the apparent viscosity. When the volume ratio of clear water to the isolation fluid is 8:1, the apparent viscosity is still as high as 113 mPa·s, having strong anti-dilution property. In addition, it can also be seen from Table 1 that the oil-based isolation fluid for plugging cement slurry as an isolation fluid not only thickens when encountering water and is difficult to control, but also the shear force after the isolation fluid thickens when encountering water can be adjusted.

[0076] The spacer fluid comes into contact with water-based liquids such as formation water and drilling fluid, and there is thickening to varying degrees after contact. The magnitude of the viscosity and shear force of the liquid phase after thickening is the key to whether the cement can stay at the wellhead. The higher the viscosity and shear force, the higher the success rate of plugging. Therefore, it is necessary to conduct a compatibility experiment between the spacer fluid and water-based drilling fluid. The oil-based spacer fluid for cement slurry plugging prepared in Example 1 is used as the cement slurry spacer fluid to conduct a compatibility experiment with water-based drilling fluid. For water-based drilling fluid, fresh water, 6% bentonite drilling fluid, potassium chloride polysulfonate drilling fluid, and composite salt drilling fluid (composite salt formula: fresh water + 7% potassium chloride + 50% formate + 3% white asphalt + 3% polyalcohol + 0.5% xanthan gum) are respectively selected to test the compatibility and apparent viscosity after mixing the spacer fluid with conventional drilling fluid. The test results are shown in Figure 2 . As Figure 2 shown, as the mixing ratio of the spacer fluid with fresh water or water-based drilling fluid increases, the viscosity of the spacer fluid increases exponentially. When the mixing amount of the spacer fluid is about 100%, the initial shear of the spacer fluid reaches the peak value. As the mixing amount of the water-based drilling fluid increases, the viscosity of the spacer fluid decreases slowly. When the mixing amount of the water-based drilling fluid is 8:1, the apparent viscosity of the spacer fluid still reaches about 100 mPa·s.

[0077] The high-temperature resistance performance of the spacer fluid is the key to the success or failure of plugging solution cavities. Under high-temperature conditions, once the spacer fluid loses its viscosity and shear force, it cannot play the role of isolating the cement slurry, resulting in plugging failure. Therefore, it is necessary to conduct a high-temperature stability test on the spacer fluid. The oil-based spacer fluid for cement slurry plugging prepared in Example 1 is used as the isolating agent and mixed with potassium chloride polysulfonate drilling fluid at a volume ratio of 1:2, and the change in apparent viscosity at 60°C, 90°C, 120°C, 150°C, and 200°C is tested. Its change trend is shown in Figure 3 .

[0078] From Figure 3 it can be seen that after the spacer fluid is mixed with 200% potassium chloride polysulfonate drilling fluid, the apparent viscosity of the mixed liquid is as high as 326 mPa·s. When aged at 60°C, 90°C, and 120°C for 72 hours, the apparent viscosity of the mixed liquid does not decrease significantly. When the aging temperature is 200°C, the viscosity of the spacer fluid decreases significantly, indicating that the high-temperature resistance of the spacer fluid is 150°C.

[0079] During the construction process of cement slurry plugging solution cavities, the spacer fluid will also come into direct contact with the cement slurry. To ensure the construction quality and avoid the occurrence of complex situations such as "flagpole insertion", it is necessary to conduct a compatibility evaluation between the spacer fluid and the cement slurry. The oil-based spacer fluid for cement slurry plugging prepared in Example 1 is used as the isolating agent and mixed with the cement slurry, and its rheological properties, thickening time, strength and other properties are tested. The test results are shown in Table 2.

[0080] Test conditions: test temperature is 100°C, 40 MPa; the cement slurry formula is: 800 g of cement + 352 g of clear water + 0.5% dispersant + 0.2% retarder + 1.3% fluid loss reducer.

[0081] Table 2 Compatibility Evaluation Table of Spacer Fluid and Cement Slurry

[0082]

[0083]

[0084] It can be seen from Table 2 that as the mixing amount of the spacer fluid increases, the thickening time curve of the cement slurry first decreases and then increases. After mixing 70% cement slurry with 30% spacer fluid, the thickening time of the cement slurry is shortened to 53 min, but it will not cause "flash setting" of the cement slurry to affect the construction safety, and both the normal temperature flow performance and high temperature flow performance of the mixed slurry have the characteristics of being pumpable, which can meet the on-site construction requirements.

[0085] The various embodiments of the present application may exist in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be construed as a rigid limitation on the scope of the present application; therefore, it should be considered that the described range description has specifically disclosed all possible sub-ranges and single values within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, which applies regardless of the range. Additionally, whenever a numerical range is indicated herein, it means including any cited number (fraction or integer) within the indicated range.

[0086] In this application, unless otherwise stated, the orientation terms such as "upper" and "lower" specifically refer to the drawing directions in the accompanying drawings. Additionally, in the description of this application's specification, terms such as "including" and "comprising" mean "including but not limited to". In this text, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. In this text, "and / or" describes the association relationship of associated objects, indicating that three relationships can exist. For example, A and / or B can mean: A exists alone, A and B exist simultaneously, or B exists alone. Here, A and B can be singular or plural. In this text, "at least one" means one or more, and "multiple" means two or more. "At least one kind", "at least one (item) of the following" or similar expressions refer to any combination of these items, including any combination of single item (s) or plural items (s). For example, "at least one (item) of a, b, or c", or, "at least one (item) of a, b, and c" can both mean: a, b, c, a - b (i.e., a and b), a - c, b - c, or a - b - c, where a, b, and c can be single or multiple respectively.

[0087] The above description is only the specific implementation manners of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application will not be limited to these embodiments shown herein, but rather will conform to the broadest scope consistent with the principles and novel features claimed herein.

Claims

1. An oil-based isolation fluid for plugging leaks in cement slurry, Characterized in that, The isolation fluid comprises an acrylamide polymer and an oil-based liquid, and the acrylamide polymer is polymerized from acrylamide, 2-acrylamido-2-methylpropanesulfonic acid and acrylic acid.

2. The oil-based isolation fluid for plugging leaks in cement slurry according to claim 1, Characterized in that, The molecular weight of the acrylamide polymer is 4.0×10 6 ~1.0×10 7 .

3. The oil-based isolation fluid for plugging leaks in cement slurry according to claim 1, Characterized in that, The oil-based liquid comprises at least one of methyl silicone oil, white oil and 9-alkenyl-12-hydroxystearic acid.

4. A preparation method of an oil-based isolation fluid for plugging leaks in cement slurry, Characterized in that, The method comprises: Obtaining raw materials, which include acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, acrylic acid, an oil-based liquid, an emulsifier, an initiator and a stabilizer; Dissolving the acrylamide, 2-acrylamido-2-methylpropanesulfonic acid and acrylic acid in a solvent to obtain a mixed solution; Mixing the mixed solution, the oil-based liquid and the emulsifier to obtain an emulsified solution; Preparing the initiator into a solution to obtain an initiator solution; Mixing and reacting the emulsified solution and the initiator solution to polymerize acrylamide, 2-acrylamido-2-methylpropanesulfonic acid and acrylic acid to form an acrylamide polymer, and then adding the stabilizer to obtain the isolation fluid.

5. The preparation method of the oil-based isolation fluid for plugging leaks in cement slurry according to claim 4, Characterized in that, The raw materials include, by weight: 7-10 parts of acrylamide, 3-5 parts of 2-acrylamido-2-methylpropanesulfonic acid, 5-8 parts of acrylic acid, 80-85 parts of an oil-based liquid, 3-5 parts of an emulsifier, 0.5-1 part of an initiator and 2-4 parts of a stabilizer.

6. The preparation method of the oil-based isolation fluid for plugging leaks in cement slurry according to claim 5, Characterized in that, The raw materials include, by weight: 8-9 parts of acrylamide, 3.5-4.5 parts of 2-acrylamido-2-methylpropanesulfonic acid, 6-7 parts of acrylic acid, 81-84 parts of an oil-based liquid, 3.5-4.5 parts of an emulsifier, 0.7-0.8 part of an initiator and 2.5-3.5 parts of a stabilizer.

7. The preparation method of the oil-based isolation fluid for plugging leaks in cement slurry according to claim 4, Characterized in that, The pH value of the mixed solution is 8-9.

8. The preparation method of the oil-based isolation fluid for plugging leaks in cement slurry according to claim 4, Characterized in that, The temperature of the mixing reaction is 80-90 °C; and / or The time of the mixing reaction is 3.5-4 h.

9. The preparation method of the oil-based isolation fluid for plugging leaks in cement slurry according to claim 4, Characterized in that, The initiator includes potassium persulfate; and / or The emulsifier includes sorbitan monooleate; and / or The stabilizer includes at least one of silicon dioxide, calcium silicate and magnesium oxide.

10. An application of an oil-based isolation fluid for plugging leaks in cement slurry, Characterized in that, The isolation fluid is the isolation fluid described in any one of claims 1 to 3 or the isolation fluid prepared by the preparation method described in any one of claims 4 to 9, and the application includes using the isolation fluid for plugging leaks in cement slurry for oil and gas well drilling.

Images