Waterproof coating for temporary plugging agent coating, preparation method thereof and temporary plugging agent

Abstract

The application discloses a waterproof coating for temporary plugging agent coating, a preparation method of the waterproof coating and a temporary plugging agent. The preparation method of the waterproof coating for temporary plugging agent coating comprises the following steps: polyvinyl alcohol, glycolic acid and lactic acid are subjected to polycondensation reaction in the presence of a solution system and a catalyst to form a coating base resin; and phosphoric acid degradation plasticizer, a diluent and fumed silica are further added into the coating base resin. The coating base resin is synthesized by esterification of polyvinyl alcohol, lactic acid and glycolic acid, and no large hydrophobic group is protected around the ester bond, so that the ester bond is easy to hydrolyze, and therefore the coating prepared from the coating base resin has good degradation and dissolution performance. The phosphoric acid degradation plasticizer is further added into the coating base resin, and the diluent and the fumed silica are further added into the coating base resin, so that the prepared coating has good coating performance and coating strength. The temporary plugging agent with the waterproof coating does not become sticky in a short time in cold water, has less dissolution in the construction process, and can be quickly dissolved after construction.

Description

Technical Field

[0001] This invention relates to the field of oil and gas production enhancement technology, and more specifically, to a waterproof coating for applying a temporary plugging agent, its preparation method, and the temporary plugging agent. Background Technology

[0002] Currently, temporary plugging and redirection fracturing technology has become an important technical approach for increasing oil and gas field production. This technology involves adding a temporary plugging agent to the working fluid or sand-mixing truck during fracturing operations to temporarily seal old fractures, sand-filled fractures, or certain perforations. Changes in fracture pressure and fracture propagation pressure force the fluid to redirect, thus creating new fractures. By using a temporary plugging agent, the orientation of the repeated fracturing fracture deviates from the original fracture, thereby connecting reservoirs with low or no utilization. Temporary plugging and redirection fracturing technology can not only increase oil and gas production but also, to some extent, change the direction of water drive and improve the utilization rate of injected water. Therefore, an ideal temporary plugging agent should be one with a controllable dissolution rate (dissolving rapidly after the temporary plugging operation), good strength, not dissolving prematurely in cold water, and not becoming sticky (if the material becomes sticky upon contact with water, it will cause the temporary plugging agent to clump together, affecting pumping and downhole sealing effectiveness).

[0003] Common temporary plugging agents can be classified into dissolving materials and degradable materials according to their plugging failure mechanism. Dissolving materials refer to a type of temporary plugging agent that can dissolve in water under specific conditions, forming a temporary plugging agent solution that causes the plugging to fail. The disadvantage of this type of temporary plugging agent is that the dissolution is uncontrollable. In cold water, there is often a very serious premature dissolution and swelling phenomenon, resulting in poor plugging effect of the temporary plugging particles.

[0004] Degradable temporary plugging agents refer to those whose large molecules can undergo chain breakage and degradation into smaller molecules under specific water conditions, eventually dissolving in water and thus rendering the plugging ineffective. Typical examples include polyglycolic acid and polylactic acid, but these materials are generally only suitable for high-temperature wells. Currently, the temporary plugging agents widely used in low-temperature oil and gas fields with well temperatures of 30-60℃ are mostly dissolving temporary plugging agents (commonly including polyacrylamide, polyethylene oxide, water-soluble polyacrylic acid, etc.). These products immediately swell and become sticky upon contact with water, causing a decrease in the strength of the temporary plugging agent and poor application results. There are also a small number of specially copolymerized modified polyacrylamides that can remain non-sticky in cold water and exhibit good solubility only above 50℃, but these products often require special customization, are not economical, and do not solve the problem of swelling and subsequent strength reduction upon contact with cold water. Therefore, there is an urgent need to develop a temporary plugging agent with the following properties: it does not become sticky in cold water (it does not become sticky for at least 30 minutes, which is conducive to pumping the material into the well; it does not swell significantly, which is conducive to ensuring the strength of the temporary plugging agent); it dissolves less during construction (it must ensure a construction pressure bearing time of at least 2 hours and the dissolution rate does not exceed 10%); and it can dissolve quickly after construction (the material can dissolve within 12 hours).

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a waterproof coating for temporary plugging agent application, a method for preparing the same, and the temporary plugging agent, in order to improve the above-mentioned technical problems.

[0007] This invention is implemented as follows:

[0008] In a first aspect, the present invention provides a method for preparing a waterproof coating for temporary plugging agent application, comprising:

[0009] Polyvinyl alcohol, glycolic acid, and lactic acid are subjected to a polycondensation reaction in a solution system and in the presence of a catalyst to obtain the coating matrix resin.

[0010] Add phosphoric acid-degradable plasticizer, diluent, and fumed silica to the coating matrix resin and mix thoroughly.

[0011] Secondly, the present invention also provides a waterproof coating for temporary plugging agent application, which is prepared by the above-described preparation method.

[0012] Thirdly, the present invention also provides a temporary plugging agent, the surface of which is coated with the above-mentioned waterproof coating for applying the temporary plugging agent.

[0013] Fourthly, the present invention also provides a method for preparing the above-mentioned temporary plugging agent, which includes: adding the temporary plugging agent matrix to the above-mentioned waterproof coating for temporary plugging agent coating and mixing and drying;

[0014] Optionally, the mass ratio of the waterproof coating used for applying the temporary plugging agent to the substrate of the temporary plugging agent is 5 to 7:94.

[0015] This invention offers the following advantages: A coating matrix resin is formed by the condensation of three water-soluble monomers—polyvinyl alcohol, lactic acid, and glycolic acid—through an esterification reaction. Since these three raw materials are linked by ester bonds, and these bonds lack large hydrophobic groups for protection, they are easily hydrolyzed. Therefore, coatings prepared using this matrix resin exhibit excellent degradation and dissolution properties. Furthermore, an easily hydrolyzable phosphoric acid-degradable plasticizer is added to the matrix resin, along with a diluent and fumed silica to improve coating performance, resulting in a coating with excellent coating properties and strength. Therefore, this waterproof coating features controllable waterproofing time, high waterproofing efficiency, and the ability to fully degrade or dissolve in the formation environment, without damaging formation oil and gas channels after use.

[0016] Furthermore, the temporary sealant formed by coating with this waterproof coating has the characteristics of not becoming sticky in cold water for a short time, dissolving less during construction, and dissolving quickly after construction. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 The image shows the infrared spectrum of the coating matrix resin synthesized in Example 1 of this invention. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0020] The following is a detailed description of a waterproof coating for temporary plugging agent application, its preparation method, and the temporary plugging agent proposed in this invention.

[0021] To address the problems of poor economic efficiency, swelling, stickiness, and reduced strength of commonly used temporary plugging agents in low-temperature oil and gas fields, the inventors, through extensive research and practice, proposed a method to coat the surface of existing low-temperature temporary plugging agents with a waterproof coating. This coating aims to prevent the plugging agent from becoming sticky in cold water (at least within 30 minutes, facilitating pumping); to prevent significant swelling, thus maintaining the strength of the plugging agent; to minimize dissolution during application (ensuring at least 2 hours of pressure resistance with a dissolution rate not exceeding 10%); and to allow for rapid dissolution after application (within 12 hours). Furthermore, the waterproof coating itself possesses good dissolution or degradation properties, ensuring minimal damage to the formation after application. The specific solution is as follows:

[0022] Some embodiments of the present invention provide a method for preparing a waterproof coating for temporary plugging, comprising: subjecting polyvinyl alcohol, glycolic acid, and lactic acid to a polycondensation reaction in a solution system and in the presence of a catalyst to obtain a coating matrix resin; adding a phosphoric acid-degradable plasticizer, a diluent, and fumed silica to the coating matrix resin, and mixing them uniformly.

[0023] By first designing a coating matrix resin that is easily degradable and has good solubility, a coating matrix resin is formed by the condensation of three water-soluble monomers—polyvinyl alcohol, lactic acid, and glycolic acid—through an esterification reaction. Since these three raw materials are linked by ester bonds without large hydrophobic groups protecting them, the resulting ester bonds are easily hydrolyzed. Then, an easily hydrolyzable phosphoric acid-degradable plasticizer is added to the coating matrix resin, along with a diluent and fumed silica to improve coating performance. This results in a coating with excellent coating properties and strength. Therefore, this waterproof coating features controllable waterproofing time, high waterproofing efficiency, and the ability to fully degrade or dissolve in the formation environment, without damaging the formation's oil and gas channels after use.

[0024] Specifically, some embodiments of the present invention provide a method for preparing a waterproof coating for temporary plugging agent application, which specifically includes:

[0025] S1. Polyvinyl alcohol, glycolic acid and lactic acid are subjected to a polycondensation reaction in a solution system and in the presence of a catalyst to obtain the coating matrix resin.

[0026] Specifically, in some embodiments, polyvinyl alcohol, glycolic acid, and lactic acid react in water, or polyvinyl alcohol, glycolic acid, lactic acid, and water are heated in a reaction vessel to carry out the reaction.

[0027] To achieve optimal degradation and solubility properties of the coating matrix resin obtained through polycondensation, the proportions and selection of raw materials need to be optimized during the polycondensation process. Specifically, in some embodiments, the mass ratio of polyvinyl alcohol to the total mass of glycolic acid and lactic acid is 1:1 to 1:2; for example, the mass ratio of polyvinyl alcohol to the total mass of glycolic acid and lactic acid can be selected as 1:1, 1:1.2, 1:1.3, 1:1.5, 1:1.7, 1:1.8, or 1:2, etc.

[0028] In some embodiments, the mass ratio of glycolic acid to lactic acid is 2:3 to 3:2, for example, 2:3, 1:1 or 3:2.

[0029] In some embodiments, the amount of water used is 1 to 3 times the mass of polyvinyl alcohol, for example, 1, 2 or 3 times, preferably 2 times.

[0030] In some embodiments, the catalyst includes, but is not limited to, boron phosphate. The amount of catalyst used is 0.3% to 0.6% of the mass of polyvinyl alcohol, for example, the amount of catalyst can be specifically selected as 0.3%, 0.4%, 0.5%, or 0.6% of the mass of polyvinyl alcohol.

[0031] In some embodiments, the degree of polymerization of polyvinyl alcohol is 300-500, and the degree of alcoholysis of polyvinyl alcohol is 87-89, preferably 88.

[0032] Furthermore, the polycondensation reaction yields a coating matrix resin comprising:

[0033] S1.1 In the presence of a catalyst, polyvinyl alcohol, lactic acid and glycolic acid are first prepolymerized in water.

[0034] Specifically, in some embodiments, the pre-polymerization temperature is 100℃~130℃, and the pre-polymerization reaction time is 4h~8h. During the pre-polymerization process, the vacuum degree is maintained at -0.06MPa~-0.08MPa, preferably -0.07MPa, and the pre-polymerization reaction is carried out under stirring conditions at a stirring speed of 100rpm~200rpm.

[0035] Prepolymerization primarily aims to achieve thorough mixing of the individual materials at the molecular level and remove moisture, allowing most of the hydroxyl and carboxyl groups in the system to undergo esterification. The temperature and vacuum during prepolymerization must not be too high, as excessively high temperatures and vacuums will remove unreacted monomers.

[0036] S1.2. The product after prepolymerization is heated and subjected to a secondary polymerization reaction.

[0037] Specifically, in some embodiments, the temperature of the secondary polycondensation reaction is 150℃~190℃, and the reaction time is 5h~10h. During the secondary polycondensation process, the vacuum level is continuously maintained at 100pa~200pa, and the reaction is carried out under stirring conditions at a stirring speed of 50rpm~200rpm.

[0038] The condensation reaction of lactic acid, glycolic acid and polyvinyl alcohol is mainly achieved through the esterification reaction of hydroxyl and carboxyl groups. However, to allow these two functional groups to fully react and form ester bonds, a high temperature and high vacuum environment is required to remove the water produced in the reaction, thereby promoting the esterification reaction. Therefore, after the pre-condensation polymerization completes the condensation reaction of most of the raw materials, the temperature is increased to allow the remaining raw materials to undergo a further full esterification reaction, thereby obtaining a coating matrix resin with better performance.

[0039] S2. Add phosphoric acid-degradable plasticizer, diluent and fumed silica to the coating matrix resin, and mix thoroughly in a mixing tank.

[0040] Specifically, in some embodiments, the mass ratio of the coating matrix resin, phosphoric acid degradable plasticizer, diluent, and fumed silica is 100:20–40:50–100:1–3. An appropriate amount of phosphoric acid degradable plasticizer can improve the toughness and coating performance of the coating; furthermore, due to its easy hydrolysis, the phosphoric acid degradable plasticizer can promote coating degradation. The higher the amount of ethyl acetate diluent, the lower the viscosity of the coating, which is beneficial for forming a thinner coating. In addition, adding a small amount of fumed silica helps to improve the coating's coatability and strength.

[0041] In some embodiments, the phosphoric acid-degradable plasticizer includes, but is not limited to, tributyl phosphite, and the diluent includes, but is not limited to, ethyl acetate.

[0042] Some embodiments of the present invention also provide a waterproof coating for temporary plugging agent application, which is prepared by the preparation method of any of the above embodiments.

[0043] Furthermore, some embodiments of the present invention also provide a temporary plugging agent, the surface of which is coated with the aforementioned waterproof coating for applying the temporary plugging agent. The base material of the temporary plugging agent can be a commonly used low-temperature temporary plugging agent, such as polyacrylamide particles.

[0044] By coating the surface of a conventional low-temperature temporary plugging agent with the above-mentioned waterproof coating, it is possible to achieve the following: it does not become sticky in cold water (it does not become sticky for at least 30 minutes, which is conducive to pumping the material into the well; it does not cause significant swelling, which is conducive to ensuring the strength of the temporary plugging agent); it dissolves less during construction (at least 2 hours of pressure-bearing time must be guaranteed, and the dissolution rate does not exceed 10%); it dissolves quickly after construction (the material can dissolve within 12 hours); and the waterproof coating has the characteristics of reasonable and controllable waterproofing time, high waterproofing efficiency, and the coating itself can be fully degraded or dissolved in the formation environment, and will not damage the formation oil and gas channels after use.

[0045] Some embodiments of the present invention also provide a method for preparing the above-mentioned temporary plugging agent, wherein the temporary plugging agent matrix is ​​added to the above-mentioned waterproof coating for temporary plugging agent coating and mixed and dried.

[0046] In some embodiments, the mass ratio of the waterproof coating used for applying the temporary plugging agent to the temporary plugging agent matrix is ​​5 to 7:94.

[0047] Specifically, the operation can be as follows: take a temporary plugging agent (e.g., polyacrylamide granules) according to the ratio, add it to the waterproof coating, put it into a rotary dryer, and perform surface coating treatment at 80°C, normal pressure, and a rotation speed of 60 r / min for 1 hour to obtain the coated temporary plugging agent.

[0048] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0049] Example 1

[0050] This embodiment provides a method for preparing a waterproof coating for temporary plugging agent application, which specifically includes:

[0051] 500g of polyvinyl alcohol (brand name 0588), 250g of lactic acid, 250g of glycolic acid, and 1000g of water were added to a 3L polymerization reactor in the specified proportions. The vacuum was maintained at -0.07MPa, and a pre-condensation reaction was carried out at a stirring speed of 100 rpm in the presence of a catalyst (boron phosphate, 0.4% of the total mass of polyvinyl alcohol added, i.e., 2g, at a pre-condensation temperature of 120℃) for 8 hours to obtain a prepolymer. Then, the prepolymer was subjected to a condensation reaction at a stirring speed of 50 rpm (with a condensation temperature of 150℃, a reaction time of 10 hours, and a vacuum of 100 Pa absolute pressure) to prepare the coating matrix resin.

[0052] Subsequently, 200g of the coating matrix resin, 60g of tributyl phosphite, 160g of ethyl acetate, and 4g of fumed silica were thoroughly mixed and homogenized in a 1L stirred tank at a stirring speed of 100r / min for 30min to prepare a waterproof coating for temporary sealing.

[0053] Example 2

[0054] This embodiment provides a method for preparing a waterproof coating for temporary plugging agent application, which specifically includes:

[0055] 500g of polyvinyl alcohol (brand name 0588), 250g of lactic acid, 250g of glycolic acid, and 1000g of water were added to a 3L polymerization reactor in the specified proportions. The vacuum was maintained at -0.07MPa, and a pre-condensation reaction was carried out at a stirring speed of 100 rpm in the presence of a catalyst (boron phosphate, 0.4% of the total mass of polyvinyl alcohol added, i.e., 2g, at a pre-condensation temperature of 120℃) for 8 hours to obtain a prepolymer. Then, the prepolymer was subjected to a condensation reaction at a stirring speed of 50 rpm (with a condensation temperature of 150℃, a reaction time of 10 hours, and a vacuum of 100 Pa absolute pressure) to prepare the coating matrix resin.

[0056] Subsequently, 200g of the coating matrix resin, 60g of tributyl phosphite, 160g of ethyl acetate, and 4g of fumed silica were thoroughly mixed and homogenized in a 1L stirred tank at a stirring speed of 100r / min for 30min to prepare a waterproof coating for temporary sealing.

[0057] Example 3

[0058] This embodiment provides a method for preparing a waterproof coating for temporary plugging agent application, which specifically includes:

[0059] 500g of polyvinyl alcohol (brand name 0388), 360g of lactic acid, 240g of glycolic acid, and 1000g of water were added to a 3L polymerization reactor in the specified proportions. The vacuum was maintained at -0.07MPa, and a pre-condensation reaction was carried out at a stirring speed of 200 rpm in the presence of a catalyst (boron phosphate, 0.4% of the total mass of polyvinyl alcohol added, i.e., 2g, at a pre-condensation temperature of 120℃) for 8 hours to obtain a prepolymer. Then, the prepolymer was subjected to a condensation reaction at a stirring speed of 100 rpm (with a condensation temperature of 190℃, a reaction time of 5 hours, and a vacuum of 120 Pa absolute pressure) to prepare the coating matrix resin.

[0060] Subsequently, 200g of the coating matrix resin, 60g of tributyl phosphite, 160g of ethyl acetate, and 4g of fumed silica were thoroughly mixed and homogenized in a 1L stirred tank at a stirring speed of 100r / min for 30min to prepare a waterproof coating for temporary sealing.

[0061] Example 4

[0062] This embodiment provides a method for preparing a waterproof coating for temporary plugging agent application, which specifically includes:

[0063] 500g of polyvinyl alcohol (brand name 0388), 500g of lactic acid, 500g of glycolic acid, and 1000g of water were added to a 3L polymerization reactor in the specified proportions. The vacuum was maintained at -0.07MPa, and a pre-condensation reaction was carried out under stirring speed of 200 rpm and in the presence of a catalyst (boron phosphate, 0.4% of the total mass of polyvinyl alcohol added, i.e., 2g, pre-condensation temperature 130℃) for 4 hours to obtain a pre-condensed polymer. Then, under stirring speed of 200 rpm, the pre-condensed polymer underwent a condensation reaction (condensation temperature 180℃, reaction time 8 hours, vacuum degree 200 Pa absolute pressure) to prepare the coating matrix resin.

[0064] Subsequently, 200g of the coating matrix resin, 60g of tributyl phosphite, 160g of ethyl acetate, and 4g of fumed silica were thoroughly mixed and homogenized in a 1L stirred tank at a stirring speed of 100r / min for 30min to prepare a waterproof coating for temporary sealing.

[0065] Example 5

[0066] This embodiment provides a method for preparing a waterproof coating for temporary plugging agent application, which specifically includes:

[0067] 500g of polyvinyl alcohol (brand name 0388), 400g of lactic acid, 400g of glycolic acid, and 1000g of water were added to a 3L polymerization reactor in the specified proportions. The vacuum was maintained at -0.07MPa, and a pre-condensation reaction was carried out under stirring speed of 150 rpm and in the presence of a catalyst (boron phosphate, 0.4% of the total mass of polyvinyl alcohol added, i.e., 2g, pre-condensation temperature 120℃) for 8 hours to obtain a prepolymer. Then, under stirring speed of 100 rpm, the prepolymer underwent a condensation reaction (condensation temperature 150℃, reaction time 10 hours, vacuum degree 120 Pa absolute pressure) to prepare the coating matrix resin.

[0068] Subsequently, 200g of the coating matrix resin, 60g of tributyl phosphite, 160g of ethyl acetate, and 4g of fumed silica were thoroughly mixed and homogenized in a 1L stirred tank at a stirring speed of 100r / min for 30min to prepare a waterproof coating for temporary sealing.

[0069] Example 6

[0070] This embodiment provides a method for preparing a waterproof coating for temporary plugging agent application, which specifically includes:

[0071] 500g of polyvinyl alcohol (brand name 0388), 240g of lactic acid, 360g of glycolic acid, and 1000g of water were added to a 3L polymerization reactor in the specified proportions. The vacuum was maintained at -0.07MPa, and a pre-condensation reaction was carried out at a stirring speed of 150 rpm in the presence of a catalyst (boron phosphate, 0.3% of the total mass of polyvinyl alcohol added, i.e., 1.5g, at a pre-condensation temperature of 120℃) for 8 hours to obtain a prepolymer. Then, the prepolymer was subjected to a condensation reaction at a stirring speed of 100 rpm (with a condensation temperature of 150℃, a reaction time of 10 hours, and a vacuum of 120 Pa absolute pressure) to prepare the coating matrix resin.

[0072] Subsequently, 200g of the coating matrix resin, 60g of tributyl phosphite, 160g of ethyl acetate, and 4g of fumed silica were thoroughly mixed and homogenized in a 1L stirred tank at a stirring speed of 100r / min for 30min to prepare a waterproof coating for temporary sealing.

[0073] Example 7

[0074] This embodiment provides a method for preparing a waterproof coating for temporary plugging agent application, which specifically includes:

[0075] 500g of polyvinyl alcohol (brand name 0588), 400g of lactic acid, 400g of glycolic acid, and 1000g of water were added to a 3L polymerization reactor in the specified proportions. The vacuum was maintained at -0.07MPa, and a pre-condensation reaction was carried out at a stirring speed of 150 rpm in the presence of a catalyst (boron phosphate, 0.4% of the total mass of polyvinyl alcohol added, i.e., 2g, at a pre-condensation temperature of 120℃) for 8 hours to obtain a prepolymer. Then, the prepolymer was subjected to a condensation reaction at a stirring speed of 100 rpm (with a condensation temperature of 150℃, a reaction time of 10 hours, and a vacuum of 120 Pa absolute pressure) to prepare the coating matrix resin.

[0076] Subsequently, 200g of the coating matrix resin, 60g of tributyl phosphite, 160g of ethyl acetate, and 4g of fumed silica were thoroughly mixed and homogenized in a 1L stirred tank at a stirring speed of 100r / min for 30min to prepare a waterproof coating for temporary sealing.

[0077] Example 8

[0078] This embodiment provides a method for preparing a waterproof coating for temporary plugging agent application, which specifically includes:

[0079] 500g of polyvinyl alcohol (brand name 0388), 400g of lactic acid, 400g of glycolic acid, and 1000g of water were added to a 3L polymerization reactor in the specified proportions. The vacuum was maintained at -0.07MPa, and a pre-condensation reaction was carried out at a stirring speed of 200 rpm in the presence of a catalyst (boron phosphate, 0.6% of the total mass of polyvinyl alcohol added, i.e., 3g, at a pre-condensation temperature of 100℃) for 8 hours to obtain a prepolymer. Then, the prepolymer was subjected to a condensation reaction at a stirring speed of 100 rpm (with a condensation temperature of 170℃, a reaction time of 7 hours, and a vacuum of 160 Pa absolute pressure) to prepare the coating matrix resin.

[0080] Subsequently, 200g of the coating matrix resin, 40g of tributyl phosphite, 200g of ethyl acetate, and 6g of fumed silica were thoroughly mixed and homogenized in a 1L stirred tank at a stirring speed of 120r / min for 30min to prepare a waterproof coating for temporary sealing.

[0081] Example 9

[0082] This embodiment provides a method for preparing a waterproof coating for temporary plugging agent application, which specifically includes:

[0083] 500g of polyvinyl alcohol (brand name 0388), 400g of lactic acid, 400g of glycolic acid, and 1000g of water were added to a 3L polymerization reactor in the specified proportions. The vacuum was maintained at -0.07MPa, and a pre-condensation reaction was carried out under stirring speed of 150 rpm and in the presence of a catalyst (boron phosphate, 0.4% of the total mass of polyvinyl alcohol added, i.e., 2g, pre-condensation temperature 120℃) for 8 hours to obtain a prepolymer. Then, under stirring speed of 100 rpm, the prepolymer underwent a condensation reaction (condensation temperature 150℃, reaction time 10 hours, vacuum degree 120 Pa absolute pressure) to prepare the coating matrix resin.

[0084] Subsequently, 200g of the coating matrix resin, 80g of tributyl phosphite, 160g of ethyl acetate, and 4g of fumed silica were thoroughly mixed and homogenized in a 1L stirred tank at a stirring speed of 100r / min for 30min to prepare a waterproof coating for temporary sealing.

[0085] Example 10

[0086] This embodiment provides a method for preparing a waterproof coating for temporary plugging agent application, which specifically includes:

[0087] 500g of polyvinyl alcohol (brand name 0588), 400g of lactic acid, 400g of glycolic acid, and 1500g of water were added to a 3L polymerization reactor in the specified proportions. The vacuum was maintained at -0.07MPa, and a pre-condensation reaction was carried out at a stirring speed of 150 rpm in the presence of a catalyst (boron phosphate, 0.4% of the total mass of polyvinyl alcohol added, i.e., 2g, at a pre-condensation temperature of 120℃) for 8 hours to obtain a prepolymer. Then, the prepolymer was subjected to a condensation reaction at a stirring speed of 100 rpm (with a condensation temperature of 150℃, a reaction time of 10 hours, and a vacuum of 120 Pa absolute pressure) to prepare the coating matrix resin.

[0088] Subsequently, 200g of the coating matrix resin, 80g of tributyl phosphite, 200g of ethyl acetate, and 2g of fumed silica were thoroughly mixed and homogenized in a 1L stirred tank at a stirring speed of 100r / min for 30min to prepare a waterproof coating for temporary sealing.

[0089] Example 11

[0090] This embodiment provides a method for preparing a waterproof coating for temporary plugging agent application, which specifically includes:

[0091] 500g of polyvinyl alcohol (brand name 0388), 400g of lactic acid, 400g of glycolic acid, and 1000g of water were added to a 3L polymerization reactor in the specified proportions. The vacuum was maintained at -0.07MPa, and a pre-condensation reaction was carried out under stirring speed of 150 rpm and in the presence of a catalyst (boron phosphate, 0.4% of the total mass of polyvinyl alcohol added, i.e., 2g, pre-condensation temperature 120℃) for 8 hours to obtain a prepolymer. Then, under stirring speed of 100 rpm, the prepolymer underwent a condensation reaction (condensation temperature 150℃, reaction time 10 hours, vacuum degree 120 Pa absolute pressure) to prepare the coating matrix resin.

[0092] Subsequently, 200g of the coating matrix resin, 40g of tributyl phosphite, 200g of ethyl acetate, and 4g of fumed silica were thoroughly mixed and homogenized in a 1L stirred tank at a stirring speed of 100r / min for 30min to prepare a waterproof coating for temporary sealing.

[0093] Example 12

[0094] This embodiment provides a method for preparing a waterproof coating for temporary plugging agent application, which specifically includes:

[0095] 500g of polyvinyl alcohol (brand name 0399), 400g of lactic acid, 400g of glycolic acid, and 1000g of water were added to a 3L polymerization reactor in the specified proportions. The vacuum was maintained at -0.07MPa, and a pre-condensation reaction was carried out at a stirring speed of 150 rpm in the presence of a catalyst (boron phosphate, 0.4% of the total mass of polyvinyl alcohol added, i.e., 2g, at a pre-condensation temperature of 120℃) for 8 hours to obtain a prepolymer. Then, the prepolymer was subjected to a condensation reaction at a stirring speed of 100 rpm (with a condensation temperature of 150℃, a reaction time of 10 hours, and a vacuum of 120 Pa absolute pressure) to prepare the coating matrix resin.

[0096] Subsequently, 200g of the coating matrix resin, 60g of tributyl phosphite, 160g of ethyl acetate, and 4g of fumed silica were thoroughly mixed and homogenized in a 1L stirred tank at a stirring speed of 100r / min for 30min to prepare a waterproof coating for temporary sealing.

[0097] Example 13

[0098] This embodiment provides a method for preparing a waterproof coating for temporary plugging agent application, which specifically includes:

[0099] 500g of polyvinyl alcohol (brand name 1788), 400g of lactic acid, 400g of glycolic acid, and 1000g of water were added to a 3L polymerization reactor in the specified proportions. The vacuum was maintained at -0.07MPa, and a pre-condensation reaction was carried out at a stirring speed of 150 rpm in the presence of a catalyst (boron phosphate, 0.4% of the total mass of polyvinyl alcohol added, i.e., 2g, at a pre-condensation temperature of 120℃) for 8 hours to obtain a prepolymer. Then, the prepolymer was subjected to a condensation reaction at a stirring speed of 100 rpm (with a condensation temperature of 150℃, a reaction time of 10 hours, and a vacuum of 120 Pa absolute pressure) to prepare the coating matrix resin.

[0100] Subsequently, 200g of the coating matrix resin, 60g of tributyl phosphite, 160g of ethyl acetate, and 4g of fumed silica were thoroughly mixed and homogenized in a 1L stirred tank at a stirring speed of 100r / min for 30min to prepare a waterproof coating for temporary sealing.

[0101] Example 14 (Catalyst: Zinc acetate, a common esterification catalyst)

[0102] This embodiment provides a method for preparing a waterproof coating for temporary plugging agent application, which specifically includes:

[0103] 500g of polyvinyl alcohol (brand name 0388), 400g of lactic acid, 400g of glycolic acid, and 1000g of water were added to a 3L polymerization reactor in the specified proportions. The vacuum was maintained at -0.07MPa, and a pre-condensation reaction was carried out at a stirring speed of 150 rpm in the presence of a catalyst (zinc acetate, 0.4% of the total mass of polyvinyl alcohol added, i.e., 2g, pre-condensation temperature 120℃) for 8 hours to obtain a pre-condensed polymer. Then, the pre-condensed polymer was subjected to a condensation reaction at a stirring speed of 100 rpm (condensation temperature 150℃, reaction time 10 hours, vacuum degree 120 Pa absolute pressure) to prepare the coating matrix resin.

[0104] Subsequently, 200g of the coating matrix resin, 60g of tributyl phosphite, 160g of ethyl acetate, and 4g of fumed silica were thoroughly mixed and homogenized in a 1L stirred tank at a stirring speed of 100r / min for 30min to prepare a waterproof coating for temporary sealing.

[0105] Comparative Example 1

[0106] This comparative example provides a method for preparing a waterproof coating for temporary plugging agent application, which specifically includes:

[0107] 500g of polyvinyl alcohol (brand name 1788), 800g of glycolic acid, and 1000g of water were added to a 3L polymerization reactor in a specific ratio. The vacuum was maintained at -0.07MPa, and a pre-polymerization reaction was carried out at a stirring speed of 150 rpm in the presence of a catalyst (boron phosphate, 0.4% of the total mass of polyvinyl alcohol added, i.e., 2g, at a pre-polymerization temperature of 120℃) for 8 hours to obtain a prepolymer. Then, the prepolymer was subjected to a polycondensation reaction at a stirring speed of 100 rpm (polymerization temperature 150℃, reaction time 10 hours, vacuum degree 120 Pa absolute pressure) to prepare a blocky coating matrix resin.

[0108] Subsequently, 200g of the coating matrix resin was mixed with 60g of tributyl phosphite, 160g of ethyl acetate, and 4g of fumed silica in a 1L stirred tank at a stirring speed of 100r / min. It was found that the coating matrix resin could not be dissolved, making it impossible to conduct subsequent coating tests.

[0109] Comparative Example 2 (without tributyl phosphite)

[0110] This comparative example provides a method for preparing a waterproof coating for temporary plugging agent application, specifically comprising: adding 500g of polyvinyl alcohol (brand name 0388), 400g of lactic acid, 400g of glycolic acid, and 1000g of water to a 3L polymerization reactor in proportion; maintaining a vacuum of -0.07MPa; and carrying out a pre-condensation reaction (the catalyst is boron phosphate, with an amount of 0.4% of the total mass of polyvinyl alcohol added, i.e., 2g, and a pre-condensation temperature of 120℃) at a stirring speed of 150 rpm for 8 hours to obtain a pre-condensed polymer. Then, under stirring conditions of 100 rpm, the pre-condensed polymer is subjected to a condensation reaction (with a condensation temperature of 150℃, a reaction time of 10 hours, and a vacuum of 120 Pa) to prepare the coating matrix resin.

[0111] Subsequently, 200g of the coating matrix resin, 160g of ethyl acetate, and 4g of fumed silica were thoroughly mixed and homogenized in a 1L stirred tank at a stirring speed of 100r / min for 30min to prepare a waterproof coating for temporary sealing.

[0112] Comparative Example 3 (without fumed silica)

[0113] This comparative example provides a method for preparing a waterproof coating for temporary plugging agent application, which specifically includes:

[0114] 500g of polyvinyl alcohol (brand name 0388), 400g of lactic acid, 400g of glycolic acid, and 1000g of water were added to a 3L polymerization reactor in the specified proportions. The vacuum was maintained at -0.07MPa, and a pre-condensation reaction was carried out under stirring speed of 150 rpm and in the presence of a catalyst (boron phosphate, 0.4% of the total mass of polyvinyl alcohol added, i.e., 2g, pre-condensation temperature 120℃) for 8 hours to obtain a prepolymer. Then, under stirring speed of 100 rpm, the prepolymer underwent a condensation reaction (condensation temperature 150℃, reaction time 10 hours, vacuum degree 120 Pa absolute pressure) to prepare the coating matrix resin.

[0115] Subsequently, 200g of the coating matrix resin, 60g of tributyl phosphite, and 160g of ethyl acetate were thoroughly mixed and homogenized in a 1L stirred tank at a stirring speed of 100r / min for 30min to prepare a waterproof coating for temporary sealing.

[0116] Comparative Example 4 (without glycolic acid)

[0117] This comparative example provides a method for preparing a waterproof coating for temporary plugging agent application, which specifically includes:

[0118] 500g of polyvinyl alcohol (brand name 0388), 800g of lactic acid, and 1000g of water were added to a 3L polymerization reactor in the specified proportions. The vacuum was maintained at -0.07MPa, and a pre-condensation reaction was carried out under stirring speed of 150 rpm and in the presence of a catalyst (boron phosphate catalyst, 0.4% of the total mass of polyvinyl alcohol added, i.e., 2g; pre-condensation temperature: 120℃) for 8 hours to obtain a pre-condensed polymer. Then, under stirring speed of 100 rpm, the pre-condensed polymer underwent a condensation reaction (condensation temperature: 150℃; reaction time: 10 hours; vacuum: 120 Pa) to prepare the coating matrix resin.

[0119] Subsequently, 200g of the coating matrix resin, 60g of tributyl phosphite, 160g of ethyl acetate, and 4g of silica were mixed and homogenized in a 1L stirred tank at a stirring speed of 100r / min for 30min to prepare a waterproof coating for temporary sealing.

[0120] Comparative Example 5

[0121] This comparative example provides a temporary plugging agent, polyacrylamide, without any coating treatment.

[0122] Test case

[0123] The coating base resin synthesized in Example 1 was subjected to infrared spectroscopy detection, and the results are as follows: Figure 1 As shown.

[0124] The waterproof coating for the temporary plugging agent obtained in Examples 1-14 and Comparative Examples 1-4 was applied to the temporary plugging agent using the following method:

[0125] Take 940g of temporary plugging agent matrix (polyacrylamide particles), add 60g of waterproof coating to be evaluated, put it into a rotary dryer, and perform surface coating treatment at 80℃, normal pressure, and a rotation speed of 60r / min for 1 hour to obtain the coated temporary plugging agent.

[0126] Then, the temporary plugging agents obtained by coating the temporary plugging agent matrix with the waterproof coating obtained by Examples 1-14 and Comparative Examples 1-4, as well as the uncoated temporary plugging agent of Comparative Example 5, were subjected to the following tests: pressure resistance test, water solubility test at 30°C for 30 minutes, stickiness test, and standard solubility test at different temperatures.

[0127] It should be noted that the waterproof coating for the temporary plugging agent in the embodiments of the present invention needs to be applied to the surface of the temporary plugging agent according to the above method, and then a series of tests such as pressure resistance and solubility are performed on the coated temporary plugging agent to effectively evaluate the performance of the waterproof coating. Therefore, unless otherwise specified, the temporary plugging agent used in the pressure resistance test, water solubility (30℃, 30min) determination, tackiness judgment, and standard solubility test at different temperatures in the experimental examples of the present invention are all temporary plugging agents obtained after coating.

[0128] Specifically, the test method for the pressure resistance (plugging strength) of the temporary plugging agent is as follows:

[0129] (1) Preparation of guar gum base solution: Measure 1000mL of distilled water and pour it into the sample cup of the Wu Yin mixer. Add 4.0g of hydroxypropyl guar gum, set the Wu Yin mixer to "fast speed" and adjust the voltage to 55V. Stir for 5min, pour into a beaker, and add 3.0g of sodium carbonate. Pour the solution into a wide-mouth bottle, cover, and place in a 30℃ water bath for 4h.

[0130] (2) Preparation of temporary plugging solution: Measure 1000mL of the guar gum base solution prepared in (1) with a graduated cylinder and place it in a beaker. Add the temporary plugging agent to the guar gum base solution according to the dosage of 200g / L. After mixing and stirring evenly, add 0.5% organic boron crosslinking agent to form a gel containing the temporary plugging agent for later use.

[0131] (3) Set the outlet width of the wedge-shaped steel core slotted plate to 1 mm, insert the core holder, connect the holder to the intermediate container, and heat the core holder to the selected evaluation temperature (30℃ or 60℃). Then, place the gel containing the temporary plugging agent into the 1000 mL intermediate container. Open the connecting valve of the intermediate container, start the horizontal flow pump, set the horizontal flow pump displacement to 40 mL / min, and the pressure limit to 5 MPa, and conduct the displacement experiment. Observe and record the pressure rise after temporary plugging. If the pressure rise after temporary plugging reaches 5 MPa and remains stable for 1 hour or more, the temporary plugging agent is considered qualified.

[0132] (4) Based on the experiment in step (3), continue to increase the displacement of the horizontal flow pump. Gradually increase the displacement from 40 mL / min to 100 mL / min to carry out the displacement experiment. Within the rated maximum pressure range of the horizontal flow pump, observe and record the displacement pressure rise after temporary plugging. When the pressure rises to a certain value, the pressure drops rapidly. The maximum pressure at this time is the pressure bearing capacity of the temporary plugging agent under the crack width condition.

[0133] The water solubility of the temporary plugging agent at 30℃ for 30 minutes and the determination of its viscosity are as follows:

[0134] The temperature of the constant temperature drying oven was set to 105℃. The experimental filter paper was dried to constant weight and recorded as m1 (accurate to 0.0001g). 20g (accurate to 0.0001g) of temporary plugging agent was weighed using an electronic balance and recorded as m2. It was added to a wide-mouth bottle containing 200mL of distilled water and stirred evenly. The wide-mouth bottle was placed in a water bath at a constant temperature of 30℃. After 30 minutes, the temporary plugging agent was gently stirred with a glass rod. If the temporary plugging agent clumps together and cannot be dispersed, it indicates that the temporary plugging agent has a problem of becoming sticky in cold water (conversely, if the temporary plugging agent can be dispersed by gently stirring with a glass rod, it indicates that the temporary plugging agent does not have a problem of becoming sticky in cold water). Then, the sample was removed and filtered through filter paper. The filter paper and sample were then placed in an oven at 105℃ and dried to constant weight and recorded as m3.

[0135] The water solubility ω1 of the temporary plugging agent at 30℃ and 30min is calculated according to formula (1):

[0136]

[0137] In the formula:

[0138] ω1—Water solubility at 30℃ for 30 minutes, %;

[0139] m1 — Mass of filter paper, g;

[0140] m2 — Mass of temporary plugging agent, g;

[0141] m3 — Total mass of the dissolved temporary plugging agent and filter paper, in grams.

[0142] The standard solubility tests at different temperatures are as follows:

[0143] ① Set the temperature of the constant temperature drying oven to 105℃ and dry the experimental filter paper to constant weight, recording it as m4 (accurate to 0.0001g). ② Weigh 2g (accurate to 0.0001g) of temporary plugging agent using an electronic balance, recording it as m5, and add it to a wide-mouth bottle containing 200mL of distilled water, stirring well. Then place the wide-mouth bottle in an oven, setting the oven temperature to the selected evaluation temperature (30 or 60℃), and maintain the temperature for 72 hours before stopping heating. ③ Open the wide-mouth bottle, filter the sample using rapid qualitative filter paper, and then place the filter paper and sample in an oven at 105℃ to dry to constant weight, recording it as m6. Calculate the solubility using the following formula:

[0144]

[0145] It should be noted that in the above examples, comparative examples, and experimental examples, the polyacrylamide particles (irregular particles with a particle size of 5-80 mesh, model S2060) used were purchased from Zhejiang Shenyao Petrochemical Technology Co., Ltd.; glycolic acid was purchased from Suzhou Guren Nanomaterials Co., Ltd.; and all other reagents were commercially available. The four polyvinyl alcohols with grades 0388 (88% degree of hydrolysis, 300% degree of polymerization), 0399 (99% degree of hydrolysis, 300% degree of polymerization), 0588 (88% degree of hydrolysis, 500% degree of polymerization), and 1788 (88% degree of hydrolysis, 1700% degree of polymerization) were all purchased from Sinopec Sichuan Chemical Co., Ltd. Unless otherwise specified, the amounts of reagents used in the examples, comparative examples, and experimental examples of this invention have been converted to 100% concentration.

[0146] The instrument used for testing the pressure-bearing capacity of the temporary plugging agent in the experimental examples of this invention was a DV-IV type temporary plugging agent pressure-bearing capacity evaluation instrument manufactured by Jiangsu Huaan Scientific Instrument Co., Ltd. The rotary dryer used for coating the surface of the temporary plugging agent was an SZG-2 type rotary dryer testing machine manufactured by Changzhou Jiacheng Drying Equipment Co., Ltd. The 3L reactor used in the embodiments and comparative examples of this invention was an X-3L12 type anchor reactor manufactured by Weihai Xingyu Chemical Machinery Co., Ltd. The 1L stirred tank used in the embodiments and comparative examples of this invention was an X-1L5 type stirred tank manufactured by Weihai Xingyu Chemical Machinery Co., Ltd. All other instruments and equipment were commercially available.

[0147] The results of the pressure-bearing capacity test of the temporary plugging agent, the water solubility determination and viscousness judgment of the temporary plugging agent at 30℃ and 30min, and the standard solubility test at different temperatures are shown in Table 1.

[0148] Table 1. Performance Evaluation Results of Waterproof Coatings

[0149]

[0150]

[0151]

[0152] Note: The performance of waterproof coatings is evaluated by testing the performance of temporary plugs after the waterproof coating is applied to the surface of the temporary plug; " / " indicates that testing was not possible or not performed.

[0153] In summary, the waterproof coating for temporary plugging agent application provided by the embodiments of the present invention has the following advantages:

[0154] (1) A coating matrix resin is formed by condensing three water-soluble monomers—polyvinyl alcohol, lactic acid, and glycolic acid—through an esterification reaction under heating and vacuum. Since these three raw materials are bonded by ester bonds, and there are no large hydrophobic groups around the ester bonds for protection, the formed ester bonds are easily hydrolyzed. Coatings prepared with this coating matrix resin have good degradation and solubility properties.

[0155] (2) Tributyl phosphite, which is easily hydrolyzed, was added to the coating matrix resin as a plasticizer, along with ethyl acetate as a diluent and fumed silica to improve coating performance. The prepared coating has good coating performance and coating strength.

[0156] (3) In response to the short-term waterproofing requirements of temporary plugging agents used in oil and gas development, the prepared temporary plugging agent professional waterproof coating has the characteristics of reasonable and controllable waterproofing time, high waterproofing efficiency, and the coating itself can be fully degraded or dissolved in the formation environment. After use, it will not cause damage to the formation oil and gas channels.

[0157] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a waterproof coating for temporary plugging agent application, characterized in that, It includes: polycondensation reaction of polyvinyl alcohol, glycolic acid and lactic acid in solution system and in the presence of catalyst to obtain coating matrix resin; adding phosphoric acid degradable plasticizer, diluent and fumed silica to coating matrix resin and mixing them evenly; The mass ratio of the polyvinyl alcohol to the total mass of the glycolic acid and the lactic acid is 1:1 to 1:2; the mass ratio of the glycolic acid to the lactic acid is 2:3 to 3:2; the polyvinyl alcohol, glycolic acid and lactic acid react in water, and the amount of water is 1 to 3 times the mass of the polyvinyl alcohol. The phosphoric acid-degradable plasticizer is tributyl phosphite; The catalyst is boron phosphate; the amount of the catalyst used is 0.3% to 0.6% of the mass of polyvinyl alcohol. The degree of polymerization of the polyvinyl alcohol is 300-500; the degree of alcoholysis of the polyvinyl alcohol is 87-89.

2. The method for preparing a waterproof coating for temporary plugging agent application according to claim 1, characterized in that, The mass ratio of the coating matrix resin, the phosphoric acid degradable plasticizer, the diluent, and the fumed silica is 100:20-40:50-100:1-3; the diluent is ethyl acetate.

3. The method for preparing the waterproof coating for temporary plugging agent application according to claim 1, characterized in that, The polycondensation reaction to obtain the coating matrix resin involves pre-polymerizing polyvinyl alcohol, lactic acid, and glycolic acid in water in the presence of a catalyst, followed by a secondary polycondensation reaction after heating.

4. The method for preparing the waterproof coating for temporary plugging agent application according to claim 3, characterized in that, The pre-polymerization temperature is 100℃~130℃, and the pre-polymerization reaction time is 4h~8h; the secondary polymerization reaction temperature is 150℃~190℃, and the secondary polymerization reaction time is 5h~10h; and / or, during the pre-polymerization process, the vacuum degree is continuously maintained at -0.06MPa~-0.08MPa, and the pre-polymerization reaction is carried out under stirring conditions with a stirring speed of 100rpm~200rpm; and / or, during the secondary polymerization process, the vacuum degree is continuously controlled to be maintained at 100pa~200pa, and the secondary polymerization reaction is carried out under stirring conditions with a stirring speed of 50rpm~200rpm.

5. A waterproof coating for applying a temporary plugging agent, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 4.

6. A temporary plugging agent, characterized in that, Its surface is coated with a waterproof coating for temporary plugging agent as described in claim 5.

7. A method for preparing a temporary plugging agent, characterized in that, It includes: The temporary plugging agent matrix is ​​added to the waterproof coating for temporary plugging agent coating as described in claim 6 and mixed and dried; the mass ratio of the waterproof coating for temporary plugging agent coating to the temporary plugging agent matrix is ​​5-7:94.

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