A nano-composite paraffin emulsion plugging agent applicable to coalbed methane drilling

Abstract

The present invention provides a nano-composite paraffin emulsion plugging agent applicable to coalbed methane drilling, belonging to the technical field of oilfield chemistry in petroleum drilling engineering. By introducing rigid materials and nano-particles that enhance the adsorption and cementing properties into the paraffin emulsion, the present invention forms a composite plugging system to improve the mechanical strength and adsorption and cementing properties of the plugging agent. The nano-composite paraffin emulsion plugging agent provided by the present invention has characteristics such as low-temperature adaptability for coalbed methane wells, plugging and anti-collapse properties for coal rocks, low friction, abrasion resistance, non-toxic and environmentally friendly, etc.

Description

Technical Field

[0001] The present invention relates to the technical field of oil drilling engineering and oilfield chemistry, and particularly relates to a nano-composite paraffin emulsion plugging agent suitable for coalbed methane drilling. Background Technique

[0002] During the drilling process of coalbed methane wells, due to the well-developed microfractures in the coal-rock formation and the strong brittleness of the formation, the stability of the wellbore faces a severe challenge. During the drilling fluid circulation process, the brittleness of the formation makes it vulnerable to external disturbances, leading to wellbore instability or collapse, and thus causing complex downhole problems such as lost circulation and stuck pipe. Many existing plugging technologies and materials, especially nano-plugging agents, mainly target brittle shale formations with well-developed microfractures, while the research and application of plugging technologies for coal-rock formations are relatively few. The unique pore structure and brittle characteristics of coal-rock make it difficult for conventional shale plugging agents to be effectively adapted and applied to coalbed methane wells.

[0003] Nano paraffin emulsion has certain advantages in the process of plugging coalbed methane wells. The low melting point of paraffin enables it to fully exert the plugging effect in the low-temperature environment of coalbed methane wells. Especially under the action of pressure difference, the paraffin emulsion can deform and squeeze into the micropores and microfractures of coal-rock, thereby forming a physical plug and enhancing the stability of the wellbore. This characteristic makes the application of nano paraffin emulsion in coalbed methane wells have good adaptability. However, paraffin emulsion still has certain limitations as a plugging material in application, such as poor rigidity and insufficient strength, resulting in an unsatisfactory plugging effect under high pressure difference conditions. At the same time, its adsorption capacity with the formation is weak, further affecting the durability and reliability of plugging. Summary of the Invention

[0004] To overcome the problems of insufficient adsorption, weak cementation, and poor adaptability to coal-rock formations existing in conventional nano paraffin emulsion plugging agents, the present invention provides a nano-composite paraffin emulsion plugging agent suitable for coalbed methane drilling. This nano-composite paraffin emulsion plugging agent has characteristics such as low-temperature adaptability to coalbed methane wells, coal-rock plugging and anti-collapse properties, low friction, anti-wear, non-toxic and environmentally friendly.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] One of the technical solutions of the present invention, a preparation method of a nano-composite paraffin emulsion plugging agent suitable for coalbed methane drilling, includes the following steps:

[0007] After mixing the emulsifier and water evenly, an aqueous phase is obtained. After melting the paraffin, an oil phase is obtained. The aqueous phase is added to the oil phase to obtain a nano paraffin emulsion;

[0008] Mix the sodium hydroxide solution and nano-chitin and carry out a deacetylation reaction to obtain deacetylated nano-chitin;

[0009] Mix the silane coupling agent with an ethanol solution and then carry out a hydrolysis reaction to obtain a hydrolyzed solution of the silane coupling agent;

[0010] Add the deacetylated nano-chitin to the hydrolyzed solution of the silane coupling agent and carry out a hydrothermal reaction to obtain Intermediate Product I;

[0011] Mix water, acrylic acid, acrylamide and dimethyldiallylammonium chloride evenly and adjust the pH to alkaline to obtain a monomer mixture;

[0012] Add Intermediate Product I to the monomer mixture and carry out a polymerization reaction under the condition of an initiator to obtain Intermediate Product II;

[0013] Mix Intermediate Product II evenly with the nano paraffin emulsion and a suspending agent to obtain the nano composite paraffin emulsion plugging agent.

[0014] The second technical solution of the present invention is a nano composite paraffin emulsion plugging agent suitable for coalbed methane drilling prepared by the above preparation method.

[0015] The third technical solution of the present invention is an application of the above nano composite paraffin emulsion plugging agent suitable for coalbed methane drilling in plugging coalbed methane wells.

[0016] The present invention discloses the following technical effects:

[0017] Nano paraffin emulsion itself has a certain plugging effect. Utilizing the low melting point characteristic of paraffin, it can match the low-temperature characteristics of coalbed methane wells and deform and squeeze into micropores and microfractures under the action of pressure difference to form a plug. However, there are still problems such as poor rigidity, insufficient strength, and insufficient adsorption capacity. The present invention introduces a functionalized rigid nano-core and combines it with a paraffin flexible shell to provide a nano-composite paraffin emulsion plugging agent, which takes into account the deformation ability, adsorption characteristics, and rigidity, and makes up for the deficiencies of nano paraffin emulsion. On the one hand, the nano-composite paraffin emulsion plugging agent can utilize the deformation ability of the paraffin shell to squeeze into the formation microfractures and micropores under the action of pressure difference, and form a tight plugging layer by flexible lapping and stacking at low temperature. When the temperature is higher than the melting point of paraffin, it will also release the functionalized rigid nano-core therein, which plays a role in cementing the surrounding coal rock to improve the compressive strength. The main raw material of this functionalized rigid nano-core is selected from nano-chitin, which is of natural biomass origin, non-toxic and environmentally friendly, and has a nano-size effect, which is beneficial to plugging micropores. However, the original nano-chitin has low solubility in water and limited dispersibility. In the present invention, partial deacetylation is carried out to expose some amino groups, which is beneficial to increasing the electrostatic repulsion force between chitin molecular chains, improving its dispersibility and reactivity; and grafting branches with hydrophilic and strongly adsorbing functional groups such as carboxyl, amide, and cationic ammonium onto the partially deacetylated nano-chitin through a silane coupling agent to improve the functionality of the rigid nano-core; especially the adsorption characteristics, on the one hand, originate from the physical interactions (such as electrostatic interactions or hydrogen bond interactions) between carboxyl, amide, and cationic ammonium and formation rocks, and on the other hand, originate from the chemical interactions between the silanol groups in the silane coupling agent and the silanol groups in the formation rocks, as well as the cementation reaction with minerals such as calcium, magnesium, iron, and aluminum in coal rock. These interactions synergistically strengthen the cementation effect between the plugging agent and the wellbore rock, thus significantly improving the wellbore stability of the coal rock formation. At the same time, the amino, carboxyl, amide, and cationic ammonium contained in the plugging agent also endow it with excellent clay hydration inhibition, and have a significant inhibitory effect on the mud contained in the mudstone or coal gangue in the coal-mud interlayer. In addition, the nano-composite paraffin emulsion plugging agent provided by the present invention also has good lubricity, which is attributed to its good adsorption characteristics, and can form a lubricating film on the surface of the friction pair, thus effectively reducing the friction coefficient; it can also use the functionalized rigid nano-core to repair micro-scratches, thereby reducing wear. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required to be used in the embodiments. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0019] Figure 1Particle size distribution diagram of the nano-composite paraffin emulsion plugging agent prepared in Example 1;

[0020] Figure 2 Particle size distribution diagram of the nano-composite paraffin emulsion plugging agent prepared in Example 2;

[0021] Figure 3 Particle size distribution diagram of the nano-composite paraffin emulsion plugging agent prepared in Example 3;

[0022] Figure 4 Particle size distribution diagram of the nano-composite paraffin emulsion plugging agent prepared in Example 4. Detailed implementation manners

[0023] Now, various exemplary implementation manners of the present invention will be described in detail. This detailed description should not be considered as a limitation to the present invention, but should be understood as a more detailed description of certain aspects, characteristics and implementation schemes of the present invention.

[0024] It should be understood that the terms described in the present invention are only for describing specific implementation manners and are not used to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0025] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0026] Without departing from the scope or spirit of the present invention, various improvements and changes can be made to the specific implementation manners of the specification of the present invention, which are obvious to those skilled in the art. Other implementation manners obtained from the specification of the present invention are obvious to those skilled in the art. The specification and examples of the present invention are only exemplary.

[0027] Regarding the use of "comprising", "including", "having", "containing", etc. in this article, they are all open-ended terms, that is, they are meant to include but not limited to.

[0028] In order to overcome the deficiencies of poor rigidity, insufficient strength, and weak adsorption capacity between the nano-paraffin emulsion and the formation, which reduce the plugging effect, the research direction of the present invention focuses on the development of a composite nano-plugging agent. By introducing a rigid material and nano-particles that enhance the adsorption and cementing properties into the paraffin emulsion, a composite plugging system is formed to improve the mechanical strength and adsorption and cementing properties of the plugging agent, making it more suitable for the special formation environment of coalbed methane wells, thereby reducing the occurrence of downhole complex situations.

[0029] The first aspect of the present invention provides a preparation method of a nano-composite paraffin emulsion plugging agent suitable for coalbed methane drilling, comprising the following steps:

[0030] After mixing the emulsifier and water evenly, an aqueous phase is obtained. After melting the paraffin, an oil phase is obtained. The aqueous phase is added to the oil phase to obtain a nano-paraffin emulsion;

[0031] Mix the sodium hydroxide solution and nano-chitin and carry out a deacetylation reaction to obtain deacetylated nano-chitin;

[0032] Mix the silane coupling agent with an ethanol solution and carry out a hydrolysis reaction to obtain a silane coupling agent hydrolysis solution;

[0033] Add the deacetylated nano-chitin to the silane coupling agent hydrolysis solution and carry out a hydrothermal reaction to obtain Intermediate Product I;

[0034] Mix water, acrylic acid, acrylamide, and dimethyldiallylammonium chloride evenly and adjust the pH to alkaline to obtain a monomer mixture;

[0035] Add the Intermediate Product I to the monomer mixture and carry out a polymerization reaction under the condition of an initiator to obtain Intermediate Product II;

[0036] Mix the Intermediate Product II with the nano-paraffin emulsion and a suspending agent evenly to obtain the nano-composite paraffin emulsion plugging agent.

[0037] In some embodiments of the present invention, after mixing the emulsifier and water evenly, an aqueous phase is obtained, specifically: after mixing the emulsifier and water, stir at 55-65 °C for 30-60 min to ensure that the emulsifier and water are fully mixed evenly; in the present invention, adding the aqueous phase to the oil phase to obtain a nano-paraffin emulsion, specifically: under stirring conditions, slowly add the aqueous phase to the oil phase and continuously stir at 80-90 °C for 10-20 min to obtain a nano-paraffin emulsion.

[0038] In some embodiments of the present invention, the emulsifier is a mixture of Span and Tween; the mass ratio of the emulsifier, water, and paraffin is (20-30):(120-140):(30-60).

[0039] In some embodiments of the present invention, the emulsifier is a mixture of Span 40 and Tween 21 with a mass ratio of 1:1 (HLB = 10.0), a mixture of Span 60 and Tween 40 with a mass ratio of 1:1 (HLB = 10.2), or a mixture of Span 65 and Tween 20 with a mass ratio of 45:55 (HLB = 10.1); the paraffin wax is 52# paraffin wax, 54# paraffin wax, 56# paraffin wax, 58# paraffin wax, 60# paraffin wax or 62# paraffin wax.

[0040] In some embodiments of the present invention, sodium hydroxide solution and nano-chitin are mixed and then subjected to a deacetylation reaction to obtain deacetylated nano-chitin. Specifically: after nano-chitin is mixed with sodium hydroxide solution, the deacetylation reaction is carried out at 85 - 95 °C. After the reaction for 1 - 2 h, it is cooled to room temperature, and then after centrifugation, washing with deionized water, ethanol dehydration and freeze-drying, deacetylated nano-chitin is obtained; the mass concentration of the sodium hydroxide solution is 30% - 40%; the mass ratio of the nano-chitin, sodium hydroxide solution to the paraffin wax is (10 - 20):(100 - 150):(30 - 60).

[0041] In the application of the drilling fluid plugging agent, the complete deacetylation of chitin not only has a long reaction time and high cost, but also leads to a decrease in crystallinity and a weakening of the hydrogen bond interaction between molecular chains, weakening the strength of the plugging layer and making it difficult to resist the high pressure difference in the wellbore cracks, ultimately reducing the plugging effect. Therefore, in the present invention, by limiting the reaction temperature, time, concentration of sodium hydroxide solution and the mass ratio of nano-chitin to sodium hydroxide solution, partial deacetylation reaction of nano-chitin occurs, promoting the exposure of some amino groups on its molecular chain, increasing the electrostatic repulsion between molecules, improving the dispersibility of the material, and enhancing the reaction activity and stability. At the same time, the remaining partial acetyl group structure endows the material with appropriate crystallinity and rigidity, thus forming a plugging layer with higher strength and better stability, which is beneficial to the stability of the coal seam wellbore.

[0042] In some embodiments of the present invention, the average particle size of the nano-chitin is 10 - 50 nm.

[0043] In some embodiments of the present invention, the silane coupling agent is vinyltriethoxysilane, dimethylethenyl ethoxysilane or vinyltris(2-methoxyethoxy)silane; the mass ratio of the silane coupling agent to the paraffin wax is (3 - 5):(30 - 60); the mass fraction of the ethanol solution is 90%; the temperature of the hydrolysis reaction is 50 - 60 °C and the time is 3 - 5 h.

[0044] In some embodiments of the present invention, the temperature of the hydrothermal reaction is 70 - 80 °C and the time is 16 - 20 h. After the hydrothermal reaction is completed, it further includes the steps of cooling the reaction system to room temperature, centrifuging to collect the precipitate, and washing and drying the precipitate.

[0045] In some embodiments of the present invention, the mass ratio of paraffin wax, acrylic acid, acrylamide, and dimethyldiallylammonium chloride is (30 - 60)∶(3 - 5)∶(2 - 4)∶(5 - 10); when water, acrylic acid, acrylamide, and dimethyldiallylammonium chloride are mixed evenly, the mass ratio of the water used and acrylic acid is 100∶(3 - 5); the pH is 7 - 8. The present invention has no special requirements for the alkali solution used to adjust the pH, and the conventional technical means of those skilled in the art can be selected, for example: 0.1mol / L NaOH solution.

[0046] In some embodiments of the present invention, the intermediate product I is added to the monomer mixture, and a polymerization reaction is carried out under the condition of an initiator. Specifically: under stirring conditions, intermediate product I is added to the monomer mixture, nitrogen is passed through to remove oxygen, the temperature is raised to 70 - 80°C, and an initiator is added to initiate the polymerization reaction, which lasts for 2 - 3h; after the polymerization reaction is completed, it further includes the steps of cooling the reaction system to room temperature, centrifuging to collect the precipitate, washing the precipitate with a precipitant, vacuum drying, and grinding.

[0047] In some embodiments of the present invention, the initiator is potassium persulfate and / or ammonium persulfate; the mass ratio of the initiator to acrylic acid is (0.1 - 0.3)∶(3 - 5).

[0048] In some embodiments of the present invention, by mass, the suspending agent is a mixture of 40 - 60 parts of xanthan gum, 20 - 30 parts of guar gum, and 20 - 30 parts of alginate; the mass ratio of the suspending agent to paraffin wax is (0.10 - 0.16)∶(30 - 60). Xanthan gum, guar gum, and alginate are all biopolysaccharide polymers, which have good low-temperature water solubility and suspension stability, and can improve the anti-settling stability of the nano-composite paraffin emulsion plugging agent.

[0049] The second aspect of the present invention provides a nano-composite paraffin emulsion plugging agent for coalbed methane drilling prepared by the above preparation method.

[0050] The nano-composite paraffin emulsion plugging agent provided by the present invention has a particle size range of 45 - 737nm, has a wide distribution at the nano-scale, can achieve the plugging of nano-pores or cracks step by step through particle size matching, and also has significant anti-collapse, inhibition, and lubrication properties, and is environmentally friendly to the ecological environment.

[0051] The third aspect of the present invention provides an application of the above nano-composite paraffin emulsion plugging agent for coalbed methane drilling in plugging coalbed methane wells.

[0052] The technical solutions of the present invention, unless otherwise specified, are all conventional solutions in the art. The reagents or raw materials used, unless otherwise specified, are all purchased from commercial channels or have been made public.

[0053] To better understand the present invention, the content of the present invention will be further clarified below in conjunction with embodiments. However, the content of the present invention is not limited to the following embodiments only.

[0054] In the embodiments, "parts" all represent "parts by mass". Example 1

[0055] A nano-composite paraffin emulsion plugging agent suitable for coalbed methane drilling, and its preparation method steps are as follows:

[0056] 1. Add 120 parts of deionized water and 20 parts of emulsifier (a mixture of Span 40 and Tween 21 with a mass ratio of 1:1 (HLB = 10.0)) to a beaker, place it on a magnetic heating stirrer and heat up to 55 °C, stir for 30 min to obtain an aqueous phase; then add 30 parts of 52# paraffin to a three-necked flask, heat it in a water bath to 65 °C, and stir for 10 min to obtain an oil phase; then, under stirring conditions, slowly add the aqueous phase to the three-necked flask containing the oil phase, raise the temperature to 80 °C, and continuously stir for 10 min to obtain a nano-paraffin emulsion;

[0057] 2. Add 10 parts of nano-chitin (average particle size of 10 nm) to a polytetrafluoroethylene beaker containing 100 parts of a 30% sodium hydroxide solution by mass fraction, place it on a magnetic heating stirrer and heat up to 85 °C for partial deacetylation reaction. After reacting for 1 h, cool to room temperature, and obtain partially deacetylated nano-chitin after centrifugation, washing with deionized water, dehydration with ethanol, and freeze-drying;

[0058] 3. Add 3 parts of vinyltriethoxysilane and 150 parts of a 90% ethanol solution by mass fraction to a four-necked flask, slowly heat up to 50 °C under stirring conditions, and carry out a hydrolysis reaction for 3 h to obtain a silane coupling agent hydrolysis solution; then slowly add the partially deacetylated nano-chitin prepared in step 2 thereto, continuously stir and heat up to 70 °C, stop heating after reacting for 16 h, and cool to room temperature; obtain a precipitate by centrifugation, wash it with absolute ethanol, and then obtain intermediate product I after vacuum drying;

[0059] 4. Add 100 parts of deionized water, 3 parts of acrylic acid, 2 parts of acrylamide, and 5 parts of dimethyldiallylammonium chloride to another four-necked flask, adjust the pH to 7 with a 0.1 mol / L NaOH solution, and stir for 20 min to obtain a monomer mixture; then add intermediate product I thereto under stirring conditions, purge with nitrogen to remove oxygen, heat up to 70 °C, and add 0.1 part of potassium persulfate to initiate a polymerization reaction. After continuously reacting for 2 h, cool to room temperature, and obtain intermediate product II after centrifugation, washing, vacuum drying, and grinding;

[0060] 5. During the stirring process, the intermediate product II was slowly added to a three-necked flask containing the nano paraffin emulsion, and then 0.10 part of the suspending agent was added. After stirring for 30 min, a nano-composite paraffin emulsion plugging agent was obtained.

[0061] Among them, by mass parts, the suspending agent is a mixture of 40 parts of xanthan gum, 20 parts of guar gum, and 20 parts of alginate.

[0062] The particle size distribution of the nano-composite paraffin emulsion plugging agent prepared in this example is as Figure 1 shown, with a particle size range of 45 - 622 nm and an average particle size of 195 nm. Example 2

[0063] A nano-composite paraffin emulsion plugging agent suitable for coalbed methane drilling, and its preparation method steps are as follows:

[0064] 1. Add 140 parts of deionized water and 30 parts of an emulsifier (a mixture of Span 60 and Tween 40 with a mass ratio of 1:1 (HLB = 10.2)) to a beaker, place it on a magnetic heating stirrer and heat up to 65 °C, stir for 60 min to obtain an aqueous phase; then add 60 parts of 62# paraffin to a three-necked flask, heat it in a water bath to 75 °C, and stir for 20 min to obtain an oil phase; then, under stirring conditions, slowly add the aqueous phase to the three-necked flask containing the oil phase, raise the temperature to 90 °C, and continuously stir for 20 min to obtain a nano paraffin emulsion;

[0065] 2. Add 20 parts of nano chitin (average particle size of 50 nm) to a polytetrafluoroethylene beaker containing 150 parts of a 40% sodium hydroxide solution by mass fraction, place it on a magnetic heating stirrer and heat up to 95 °C for partial deacetylation reaction. After reacting for 2 h, cool it to room temperature, and after centrifugation, washing with deionized water, ethanol dehydration, and freeze-drying, obtain partially deacetylated nano chitin;

[0066] 3. Add 5 parts of vinyltris(2-methoxyethoxy)silane and 200 parts of a 90% ethanol solution by mass fraction to a four-necked flask, slowly heat up to 60 °C under stirring conditions, and carry out a hydrolysis reaction for 5 h to obtain a silane coupling agent hydrolysis solution; then slowly add the partially deacetylated nano chitin prepared in step 2 thereto, continuously stir and heat up to 80 °C, stop heating after reacting for 20 h, and cool it to room temperature; obtain the precipitate by centrifugation, wash it with absolute ethanol, and then vacuum dry it to obtain intermediate product I;

[0067] 4. In another four-necked flask, add 100 parts of deionized water, 5 parts of acrylic acid, 4 parts of acrylamide, and 10 parts of dimethyldiallylammonium chloride. Then, adjust the pH to 8 with 0.1 mol / L NaOH solution, and stir for 30 min to obtain a monomer mixture. Subsequently, add Intermediate Product I thereto under stirring conditions, remove oxygen by passing nitrogen, raise the temperature to 80 °C, and add 0.3 parts of ammonium persulfate to initiate the polymerization reaction. After 3 h, cool to room temperature, and obtain Intermediate Product II after centrifugation, washing, vacuum drying, and grinding.

[0068] 5. During stirring, slowly add Intermediate Product II to a three-necked flask containing nano paraffin emulsion, and then add 0.16 parts of suspending agent. After stirring for 60 min, a nano composite paraffin emulsion plugging agent is obtained.

[0069] Among them, by mass, the suspending agent is a mixture of 60 parts of xanthan gum, 20 parts of guar gum, and 20 parts of alginate.

[0070] The particle size distribution of the nano composite paraffin emulsion plugging agent prepared in this example is as Figure 2 shown, with a particle size range of 65 - 705 nm and an average particle size of 344 nm. Example 3

[0071] A nano composite paraffin emulsion plugging agent suitable for coalbed methane drilling, and its preparation method steps are as follows:

[0072] 1. Add 130 parts of deionized water and 25 parts of emulsifier (a mixture of Span 65 and Tween 20 with a mass ratio of 45:55 (HLB = 10.1)) to a beaker, place it on a magnetic heating stirrer, heat up to 60 °C, and stir for 45 min to obtain an aqueous phase. Then, add 45 parts of 56# paraffin to a three-necked flask, heat it in a water bath to 70 °C, and stir for 15 min to obtain an oil phase. Then, under stirring conditions, slowly add the aqueous phase to the three-necked flask containing the oil phase, raise the temperature to 85 °C, and continuously stir for 15 min to obtain a nano paraffin emulsion.

[0073] 2. Add 15 parts of nano chitin (with an average particle size of 30 nm) to a polytetrafluoroethylene beaker containing 125 parts of 35% sodium hydroxide solution by mass, place it on a magnetic heating stirrer, heat up to 90 °C for partial deacetylation reaction. After 1.5 h of reaction, cool to room temperature, and obtain partially deacetylated nano chitin after centrifugation, washing with deionized water, ethanol dehydration, and freeze drying.

[0074] 3. Add 4 parts of dimethylethenyl ethoxysilane and 175 parts of 90% ethanol solution into a four-necked flask. Slowly heat it to 55°C under stirring conditions and carry out hydrolysis reaction for 4 h to obtain a hydrolyzate of the silane coupling agent. Then slowly add a part of the deacetylated nano-chitin prepared in step 2 thereto, continuously stir and heat it to 75°C. After reacting for 18 h, stop heating and cool it to room temperature. Obtain the precipitate by centrifugation, wash it with absolute ethanol, and then obtain intermediate product I through vacuum drying;

[0075] 4. Add 100 parts of deionized water, 4 parts of acrylic acid, 3 parts of acrylamide and 7.5 parts of dimethyldiallylammonium chloride into another four-necked flask, and adjust the pH to 7.5 with 0.1 mol / L NaOH solution, stir for 25 min to obtain a monomer mixture. Then add intermediate product I thereto under stirring conditions, purge with nitrogen to remove oxygen, heat it to 75°C, and add 0.2 part of initiator to initiate the polymerization reaction. After 2.5 h, cool it to room temperature. After centrifugation, washing, vacuum drying and grinding, obtain intermediate product II;

[0076] 5. Slowly add intermediate product II into a three-necked flask containing nano-paraffin emulsion during stirring, then add 0.13 part of suspending agent, and stir for 45 min to obtain a nano-composite paraffin emulsion plugging agent.

[0077] Among them, by mass, the initiator is a mixture of 50 parts of potassium persulfate and 50 parts of ammonium persulfate;

[0078] By mass, the suspending agent is a mixture of 50 parts of xanthan gum, 25 parts of guar gum and 25 parts of alginate.

[0079] The particle size distribution of the nano-composite paraffin emulsion plugging agent prepared in this example is as Figure 3 shown, with a particle size range of 54 - 737 nm and an average particle size of 323 nm. Example 4

[0080] A nano-composite paraffin emulsion plugging agent applicable to coalbed methane drilling, and its preparation method steps are as follows:

[0081] 1. Add 140 parts of deionized water and 20 parts of emulsifier (a mixture of Span 60 and Tween 40 with a mass ratio of 1:1 (HLB = 10.2)) into a beaker, place it on a magnetic heating stirrer and heat it to 62°C, stir for 50 min to obtain an aqueous phase. Then add 45 parts of 58# paraffin into a three-necked flask, heat it to 68°C in a water bath, stir for 16 min to obtain an oil phase. Then, under stirring conditions, slowly add the aqueous phase into the three-necked flask containing the oil phase, raise the temperature to 88°C, and continuously stir for 17 min to obtain a nano-paraffin emulsion;

[0082] 2. Add 16 parts of nano-chitin (average particle size of 20 nm) into a PTFE beaker containing 120 parts of sodium hydroxide solution with a mass fraction of 33%, place it on a magnetic heating stirrer, heat up to 93 °C for partial deacetylation reaction. After reacting for 1.3 h, cool it to room temperature, and obtain partially deacetylated nano-chitin after centrifugation, washing with deionized water, dehydration with ethanol and freeze-drying;

[0083] 3. Add 3 parts of vinyltriethoxysilane and 160 parts of ethanol solution with a mass fraction of 90% into a four-necked flask, slowly heat up to 56 °C under stirring conditions, and carry out hydrolysis reaction for 3.5 h to obtain a silane coupling agent hydrolysis solution; then slowly add the partially deacetylated nano-chitin prepared in step 2 thereto, continuously stir and heat up to 77 °C, stop heating after reacting for 18 h, and cool it to room temperature; obtain the precipitate by centrifugation, wash it with absolute ethanol, and then obtain intermediate product I after vacuum drying;

[0084] 4. Add 100 parts of deionized water, 5 parts of acrylic acid, 3 parts of acrylamide and 8 parts of dimethyldiallylammonium chloride into another four-necked flask, adjust the pH to 8 with 0.1 mol / L NaOH solution, and stir for 28 min to obtain a monomer mixture; then add intermediate product I thereto under stirring conditions, purge with nitrogen to remove oxygen, heat up to 73 °C, and add 0.15 parts of initiator to initiate the polymerization reaction. After 3 h, cool it to room temperature, and obtain intermediate product II after centrifugation, washing, vacuum drying and grinding;

[0085] 5. Slowly add intermediate product II to a three-necked flask containing nano-paraffin emulsion during stirring, then add 0.15 parts of suspending agent, and stir for 40 min to obtain a nano-composite paraffin emulsion plugging agent.

[0086] Among them, by mass, the initiator is a mixture of 30 parts of potassium persulfate and 70 parts of ammonium persulfate;

[0087] By mass, the suspending agent is a mixture of 45 parts of xanthan gum, 30 parts of guar gum and 25 parts of alginate.

[0088] The particle size distribution of the nano-composite paraffin emulsion plugging agent prepared in this example is as Figure 4 shown, the particle size range is 52 - 567 nm, and the average particle size is 234 nm. Comparative Example 1

[0089] 130 parts of deionized water and 25 parts of emulsifier (a mixture of Span 65 and Tween 20 with a mass ratio of 45:55 (HLB = 10.1)) were added to a beaker, and the temperature was raised to 60 °C on a magnetic heating stirrer and stirred for 45 min to obtain an aqueous phase; then 45 parts of paraffin wax #56 were added to a three-necked flask, heated in a water bath to 70 °C, and stirred for 15 min to obtain an oil phase; then, under stirring conditions, the aqueous phase was slowly added to the three-necked flask containing the oil phase, the temperature was raised to 85 °C, and stirring was continued for 15 min to obtain a nano paraffin emulsion. (That is, the nano paraffin emulsion provided in this comparative example is the nano paraffin emulsion prepared in step 1 of Example 3).

[0090] Effect verification:

[0091] The nano composite paraffin emulsion plugging agents obtained in Examples 1-4 above and the nano paraffin emulsion obtained in Comparative Example 1 were added to the following drilling fluid for performance evaluation. The performance tests were carried out according to the test methods in GB / T 16783.1-2014 "Petroleum and natural gas industries - Field testing of drilling fluids - Part 1: Water-based drilling fluids", GB / T 29170-2012 "Petroleum and natural gas industries - Laboratory testing of drilling fluids", and SY / T 7467—2020 "Technical specification for evaluation of environmental protection performance of drilling fluids". The results are shown in Tables 1-3 (in Tables 1-3, "%" represents the mass percentage of the plugging agent of the example or comparative example in the drilling fluid).

[0092] Drilling fluid formula: Fresh water + 3% bentonite + 0.3% sodium hydroxide + 0.3% sodium carbonate + 5% potassium chloride + 0.3% zwitterionic polymer strong coating agent + 0.3% high-viscosity carboxymethyl cellulose + 3% lignite resin + barite weighted to a density of 1.20 g / cm 3 。

[0093] Table 1 Influence of nano composite paraffin emulsion plugging agent on rheological properties of drilling fluid

[0094] ,

[0095] Table 2 Influence of nano composite paraffin emulsion plugging agent on plugging and anti-collapse properties of drilling fluid

[0096] ,

[0097] Table 3 Influence of nano composite paraffin emulsion plugging agent on lubricating properties of drilling fluid

[0098] ,

[0099] Note: T: Aging temperature of base mud or drilling fluid, °C

[0100] t: Rolling aging time of drilling fluid, h

[0101] PV: Plastic viscosity of drilling fluid, mPa·s

[0102] YP: Yield point of drilling fluid, Pa

[0103] API: Medium pressure filtration loss of drilling fluid (0.7 MPa, room temperature, 30 min), mL

[0104] HTHP: High temperature and high pressure filtration loss of drilling fluid (3.5 MPa, T, 30 min), mL

[0105] CF: Extreme pressure friction coefficient, dimensionless

[0106] ΔCF: Reduction rate of extreme pressure friction coefficient, %

[0107] δ: HTHP mud cake thickness (3.5 MPa, T, 30 min), mm

[0108] θ: Clear water filtration loss of HTHP mud cake (3.5 MPa, T, 30 min), mL

[0109] η: Retention rate of coal rock strength (3.5 MPa, T, 72 h), %

[0110] γ: Shale swelling rate, %

[0111] It can be seen from the data of Examples 1 - 4 and Comparative Example 1 in Table 1 that the 1% nano - composite paraffin emulsion plugging agent has basically no effect on the rheology of the drilling fluid. When its dosage is increased to 3%, the viscosity of the drilling fluid increases slightly, but the overall change is small. The nano - paraffin emulsion also has little effect on the rheology of the drilling fluid. However, due to the increase in the liquid phase content, the viscosity of the drilling fluid shows a downward trend. In contrast, the functionalized nano - chitin core contained in the nano - composite paraffin emulsion plugging agent compensates for this part of the viscosity loss.

[0112] From the data of Examples 1 to 4 and Comparative Example 1 in Table 2, it can be seen that the filtration loss of the blank drilling fluid is relatively large, the mud cake is relatively thick, the clear water filtration loss of the mud cake is large, the compactness is insufficient, and at the same time, there is almost no strengthening effect on coal rock, the anti-collapse property is poor, and the shale expansion rate is relatively large, and the inhibition is insufficient; while the 1% nano-composite paraffin emulsion plugging agent has a significant filtration loss reduction effect, the mud cake thickness and the clear water filtration loss of the mud cake decrease significantly, indicating that the compactness of the mud cake is improved. At the same time, it plays a cementing role on coal rock, the strength is significantly improved, and the inhibition is strengthened, and the shale expansion rate is significantly reduced; when its dosage is increased to 3%, all aspects of performance are further improved, the reduction rates of API and HTHP filtration loss are both > 50%, the reduction rate of HTHP mud cake thickness is > 45%, the reduction rate of HTHP mud cake clear water filtration loss is > 65%, the retention rate of coal rock strength is > 35%, and the reduction rate of shale expansion is > 70%, and the plugging, anti-collapse and inhibition effects are significant; in contrast, the nano-paraffin emulsion has a small improvement in the plugging and inhibition performance of the drilling fluid, and there is almost no improvement in improving the coal rock strength, and the anti-collapse effect is not good.

[0113] From the data of Examples 1 to 4 and Comparative Example 1 in Table 3, it can be seen that the extreme pressure friction coefficient of the blank drilling fluid is relatively large and the lubricity is poor; the addition of the nano-composite paraffin emulsion plugging agent can significantly reduce the friction coefficient and improve the lubricity; although the nano-paraffin emulsion also has the ability to improve lubrication, the effect is significantly inferior to that of the nano-composite paraffin emulsion plugging agent under the same dosage.

[0114] In summary, the nano-composite paraffin emulsion plugging agent applicable to coalbed methane drilling of the present invention has significant effects in plugging, anti-collapse, inhibition and lubrication, which is beneficial to stabilizing the coal rock wellbore and ensuring the safe and efficient drilling operation of coalbed methane wells.

[0115] The above are only the preferred embodiments of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A preparation method of a nano-composite paraffin emulsion plugging agent applicable to coalbed methane drilling, characterized in that, It includes the following steps: After uniformly mixing an emulsifier and water, an aqueous phase is obtained. After melting paraffin wax, an oil phase is obtained. The aqueous phase is added to the oil phase to obtain a nano paraffin wax emulsion; Sodium hydroxide solution and nano chitin are mixed and then subjected to a deacetylation reaction to obtain deacetylated nano chitin; A silane coupling agent is mixed with an ethanol solution and then subjected to a hydrolysis reaction to obtain a silane coupling agent hydrolysis solution; The deacetylated nano chitin is added to the silane coupling agent hydrolysis solution, and a hydrothermal reaction is carried out to obtain Intermediate Product I; Water, acrylic acid, acrylamide and dimethyldiallylammonium chloride are mixed uniformly and the pH is adjusted to be alkaline to obtain a monomer mixture; The Intermediate Product I is added to the monomer mixture, and a polymerization reaction is carried out under the condition of an initiator to obtain Intermediate Product II; after the polymerization reaction is completed, it further includes the steps of cooling the reaction system to room temperature, collecting the precipitate by centrifugation, washing the precipitate, vacuum drying and grinding; The Intermediate Product II is mixed uniformly with the nano paraffin wax emulsion and a suspending agent to obtain the nano composite paraffin wax emulsion plugging agent; The mass concentration of the sodium hydroxide solution is 30% - 40%; the mass ratio of the nano chitin, sodium hydroxide solution to the paraffin wax is (10 - 20)∶(100 - 150)∶(30 - 60); the reaction temperature of the deacetylation reaction is 85 - 95°C, and the reaction time is 1 - 2 h; The silane coupling agent is vinyltriethoxysilane, dimethylethenyethoxysilane or vinyltris(2 - methoxyethoxy)silane; the mass ratio of the silane coupling agent to the paraffin wax is (3 - 5)∶(30 - 60); the temperature of the hydrolysis reaction is 50 - 60°C, and the time is 3 - 5 h; The emulsifier is a mixture of Span and Tween; the mass ratio of the emulsifier, water, and paraffin wax is (20 - 30)∶(120 - 140)∶(30 - 60); The mass ratio of the paraffin wax, acrylic acid, acrylamide and dimethyldiallylammonium chloride is (30 - 60)∶(3 - 5)∶(2 - 4)∶(5 - 10); the pH is 7 - 8; By mass fraction, the suspending agent is a mixture of 40 - 60 parts of xanthan gum, 20 - 30 parts of guar gum and 20 - 30 parts of alginate; the mass ratio of the suspending agent to the paraffin wax is (0.10 - 0.16)∶(30 - 60).

2. The preparation method of the nano-composite paraffin emulsion plugging agent applicable to coalbed methane drilling according to claim 1, characterized in that, The temperature of the hydrothermal reaction is 70 - 80°C, and the time is 16 - 20 h.

3. The preparation method of the nano-composite paraffin emulsion plugging agent applicable to coalbed methane drilling according to claim 1, characterized in that, The initiator is potassium persulfate and / or ammonium persulfate; the temperature of the polymerization reaction is 70 - 80°C, and the time is 2 - 3 h.

4. A nano composite paraffin wax emulsion plugging agent suitable for coalbed methane drilling prepared by the preparation method according to any one of claims 1 - 3.

5. Application of the nano composite paraffin wax emulsion plugging agent suitable for coalbed methane drilling according to claim 4 in plugging coalbed methane wells.

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