Brown coal resin for high-temperature-resistant drilling fluid and preparation method thereof

Abstract

The invention relates to the technical field of oil field drilling, in particular to lignite resin for high-temperature-resistant drilling fluid and a preparation method of the lignite resin. The lignite resin for the high-temperature-resistant drilling fluid is prepared from modified lignite, sodium hydroxide, sodium carbonate, formaldehyde, humic acid, sodium pyrosulfite, lignin, acrylamide, acrylonitrile salt, sodium sulfite and 2-acrylamido-2-methylpropanesulfonic acid. According to the high-temperature-resistant lignite resin, a benzene ring and a nitrogen-containing heterocyclic ring are introduced to construct a synergistic modification system, novel modified lignite is prepared, the temperature resistance and comprehensive performance of the lignite resin are remarkably improved, the resin can still maintain low filter loss at the high temperature of 220 DEG C, meanwhile, a thin and tough mud cake is formed through hydrophobic-hydrophilic balance design, and the high-temperature-resistant lignite resin is prepared. The problem of performance degradation caused by high temperature in deep well and ultra-deep well drilling is effectively solved, and the multifunctional advantages of salt pollution resistance, lubrication, friction reduction and the like are achieved.

Description

Technical Field

[0001] The invention relates to the technical field of oilfield drilling materials, in particular to a lignite resin for high-temperature resistant drilling fluid and a preparation method thereof. Background Art

[0002] Lignite resin, a core fluid loss additive in drilling fluid systems, is primarily a copolymer of nitrohumic acid and sulfomethylphenolic resin. Through the strong hydration of the sulfonic acid groups and the rigid support of the phenolic structure, it exhibits excellent temperature resistance (≤180°C), salt tolerance (≤10% NaCl), and fluid loss reduction properties in freshwater and low- to medium-concentration saline environments. The resulting thin, tough mud cake effectively lubricates drill tools and maintains rheological properties, resulting in its long-standing dominance in the domestic oilfield market. However, as oil and gas exploration extends into deeper formations (such as ultra-deep wells and shale gas horizontal wells in the Tarim Basin) and high-salinity environments (such as carbonate formations in the Middle East), existing treatment agents primarily focus on single-performance enhancements (such as viscosity enhancement or fluid loss reduction), making them incapable of addressing the complex damage of deep formations characterized by high-temperature softening, high-salinity flocculation, and high-solids clogging.

[0003] The existing lignite resins on the market have the following technical defects: 1. Insufficient thermal stability: the main chain of sulfomethylphenolic resin is a CC single bond, which is prone to chain scission and degradation above 180°C, resulting in a system viscosity retention rate of less than 50% (water loss after 16h hot rolling> 30mL); 2. Weak salt pollution resistance: the sulfonic acid group is easily Shielding, hydration film thickness reduced by 30%, causing clay particle flocculation (API filtration loss increased sharply to 25mL / 30min); 3. Failure of dynamic filtration control: Under high temperature and high shear conditions, the resin molecular chain cannot be re-crosslinked after breaking. The addition amount needs to be increased to more than 8% to maintain the filtration loss ≤15mL, but excessive use will lead to a thick mud cake (>4mm), causing the risk of differential pressure sticking.

[0004] In view of this, it is of great significance to prepare a lignite resin for high temperature resistant drilling fluid. Summary of the Invention

[0005] The present application provides a lignite resin for high-temperature resistant drilling fluid and a preparation method thereof. The lignite resin for high-temperature resistant drilling fluid of the present application has a benzene ring-pyridine heterocyclic double-rigid molecular skeleton, and is crosslinked with a nitro humic acid and nano-silica sol system, and has excellent composite performance in deep formation drilling: the 220 DEG C ultra-high temperature thermal stability of the resin can ensure that the molecular chain remains intact in the extreme heat environment, avoiding the viscosity of the system from suddenly dropping and the filtration loss from being out of control due to degradation; under the condition of 25% NaCl high salt, the double electronic shielding layer formed by the benzene ring pi-pi conjugation and the pyridine ring lone pair electron can effectively resist the damage of salt ions to the hydration film, so that the filtration loss is reduced; in the dynamic drilling process, the synergistic toughening effect of the double-rigid unit and the nano-silica can form a dense and elastic mud cake on the well wall, which can not only inhibit the hydration and swelling of shale, but also reduce the torque through the lubricating molecular layer, while significantly reducing the drilling fluid loss, and greatly improving the drilling efficiency and reservoir protection effect of deep and ultra-deep wells.

[0006] The present application provides a preparation method of a lignite resin for high-temperature resistant drilling fluid, comprising the following preparation steps: S1. Extraction: 10-15 parts by weight of modified lignite, 70-80 parts by weight of solvent, 5-7 parts by weight of sodium hydroxide and 0.5-0.8 parts by weight of sodium carbonate are mixed and reacted to obtain a mixed solution.

[0007] S2. Sulfonation: 1-2 parts by weight of formaldehyde, 8-12 parts by weight of humic acid and 1-2 parts by weight of sodium pyrosulfite are added to the mixed solution, and sulfonation reaction is carried out at 137-143 DEG C for 1-1.5 h to obtain a sulfonated solution.

[0008] S3. Synthesis: 9-12 parts by weight of lignin, 5-7 parts by weight of formaldehyde, 1-2 parts by weight of acrylamide, 2-3 parts by weight of acrylonitrile salt, 2-3 parts by weight of sodium sulfite and 1-3 parts by weight of 2-acrylamido-2-methylpropanesulfonic acid are added to the sulfonated solution for synthesis reaction to prepare the lignite resin for high-temperature resistant drilling fluid.

[0009] As a preferred technical solution of the present application, the preparation steps of the modified lignite include: Step one, pretreatment and functional modification: 10-15 parts by weight of lignite is crushed to 200 mesh, mixed with 70-80 parts by weight of deionized water, 5-7 parts by weight of sodium hydroxide and 0.5-0.8 parts by weight of sodium carbonate is added, stirred and mixed at 80 DEG C for 2 h, and filtered to obtain an alkaline lignite suspension.

[0010] Step two, preparation of functional monomer solution: 1 part by weight of modified p-bromostyrene and 0.8 part by weight of modified 2-vinylpyridine are dissolved in 8-10 parts by weight of anhydrous ethanol, 0.1 part by weight of diisobutyl nitrile is added, and pre-polymerization is carried out at 60 DEG C for 1 h to obtain a double-ring conjugated modifier.

[0011] Step three, multi-stage grafting sulfonation: 8-12 parts by weight of humic acid and 1-2 parts by weight of sodium pyrosulfite are sequentially added to the alkaline lignite suspension, and sulfonation reaction is carried out at 100℃ for 2h under nitrogen protection, to generate a lignite intermediate grafted with sulfonic acid groups; when the temperature is reduced to 70℃, the bicyclic conjugate modifier is added dropwise, and 1-3 parts by weight of 2-acrylamido-2-methylpropanesulfonic acid is added at the same time, and grafting reaction is carried out for 3h, to obtain a lignite mixture.

[0012] Step four, high-temperature reinforced crosslinking: formaldehyde is added to the lignite mixture in three batches, and the amount of formaldehyde added in each batch is 2-3 parts by weight; 5-7 parts by weight of lignin is synchronously added; aldehyde-amine polycondensation reaction is carried out at 85℃ for 2-3h; 2-3 parts by weight of acrylonitrile salt and 0.5 parts by weight of nano silicon dioxide are added; a siloxane crosslinking network is constructed by a sol-gel method; high-temperature reaction is maintained at 120℃ for 1h to obtain a modified lignite precursor.

[0013] Step five, post-treatment and structure locking: dilute hydrochloric acid is added to the modified lignite precursor to adjust the pH to 6.5; granular products are obtained by spray drying; the granular products are placed in an oven at 150℃ for heat treatment for 2h to obtain a modified lignite resin.

[0014] As a preferred technical solution of the present application, the modified p-bromostyrene is prepared by the following steps: 10 parts by weight of p-bromostyrene, 2 parts by weight of maleic anhydride, 15 parts by weight of toluene, and 0.1-0.5 parts by weight of 0.1-0.5wt% azobisisobutyronitrile are mixed and then placed in a reaction kettle at 75-85℃ for copolymerization reaction for 6-10 hours to obtain a reaction liquid; 20-30 parts by weight of anhydrous ethanol is added to the reaction liquid for stirring and mixing, filtration, then washed with acetone for 3 times to remove unreacted monomers and small molecule byproducts, and then dried in a vacuum drying oven at 60-80℃ to constant weight after filtration to obtain the modified p-bromostyrene.

[0015] As a preferred technical solution of the present application, the modified 2-vinylpyridine is prepared by the following steps: 10 parts by weight of 2-vinylpyridine, 2 parts by weight of acrylic acid, 15 parts by weight of toluene, and 0.1-0.5 parts by weight of 0.2-0.5wt% azobisisobutyronitrile are mixed and then placed in a reaction kettle at 70-80℃ for copolymerization reaction for 6-10 hours to obtain a reaction liquid; 20-25 parts by weight of petroleum ether is added to the reaction liquid for stirring and mixing, filtration, then washed with anhydrous ethanol for 3 times, and then placed in a vacuum drying oven at 60-80℃ to constant weight after filtration to obtain the modified 2-vinylpyridine.

[0016] As a preferred technical solution of the present application, the mass concentration of sodium hydroxide is 1%.

[0017] Preferably, the nano-silica has a particle size of 20-30 nm.

[0018] Compared with the prior art, the present application has the following advantages: 1. The anti-high-temperature lignite resin of the present application is prepared by doping a heterocycle on the lignite resin. The pyridine ring (C5H5N) of the modified 2-vinylpyridine contains a nitrogen atom, and the lone pair of electrons thereof can form a coordination bond with the active functional groups (such as hydroxyl groups and carboxyl groups) in the lignite, thereby forming a stable six-membered ring transition state. This structure not only inhibits the generation of free radicals at high temperatures (free radicals are the key inducement of oxidative degradation), but also disperses the electric charge through the conjugation effect, thereby improving the salt resistance of the resin by 30% in a 15% salt water environment.

[0019] 2. The anti-high-temperature lignite resin of the present application is prepared by doping a heterocycle on the lignite resin. The pyridine ring (C5H5N) of the modified 2-vinylpyridine contains a nitrogen atom, and the lone pair of electrons thereof can form a coordination bond with the active functional groups (such as hydroxyl groups and carboxyl groups) in the lignite, thereby forming a stable six-membered ring transition state. This structure not only inhibits the generation of free radicals at high temperatures (free radicals are the key inducement of oxidative degradation), but also disperses the electric charge through the conjugation effect, thereby improving the salt resistance of the resin by 30% in a 15% salt water environment.

[0020] 3. The anti-high-temperature lignite resin of the present application is prepared by doping a heterocycle on the lignite resin. The pyridine ring (C5H5N) of the modified 2-vinylpyridine contains a nitrogen atom, and the lone pair of electrons thereof can form a coordination bond with the active functional groups (such as hydroxyl groups and carboxyl groups) in the lignite, thereby forming a stable six-membered ring transition state. This structure not only inhibits the generation of free radicals at high temperatures (free radicals are the key inducement of oxidative degradation), but also disperses the electric charge through the conjugation effect, thereby improving the salt resistance of the resin by 30% in a 15% salt water environment. DETAILED DESCRIPTION

[0021] The technical solutions in the embodiments of the present application will be clearly and completely described below in combination with the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0022] In this document, reference to“an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the application. The appearances of the phrase“in an embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are they necessarily mutually exclusive of one another. Those skilled in the art will appreciate that the embodiments described herein are illustrative of the application and are not meant to be limiting.

[0023] In order for those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application are described clearly and completely below.

[0024] Lignite resin is a functional polymer material prepared by chemical modification or physical blending process with natural lignite as the core raw material. Its core structure is derived from the unique molecular structure of lignite and the active groups introduced in subsequent processing. Natural lignite as the main body, its molecular chain is rich in polar functional groups such as carboxyl (-COOH), hydroxyl (-OH) and phenolic hydroxyl. These groups not only endow lignite with certain hydrophilicity and reactivity, but also become the key modification site. Through chemical means such as sulfonation, oxidation or graft polymerization, strong polar side chains such as sulfonic acid group (-SO3H) and amide group (-CONH2) can be introduced on the lignite skeleton, forming a network structure with lignite carbon chain as support and polar group as functional unit. For example, sulfonated lignite resin is treated with concentrated sulfuric acid to make sulfonic acid groups uniformly distributed on the molecular chain, which significantly improves its water solubility and ion exchange capacity, thereby playing a role in reducing filtration loss and inhibiting clay hydration in drilling fluid.

[0025] In order to further optimize the performance, formaldehyde, hexamethylene tetramine and other crosslinking agents are added to build a three-dimensional crosslinking network by reacting with hydroxyl or amino groups, thereby enhancing the temperature resistance and mechanical strength of the resin. At the same time, phthalate plasticizers are used to reduce the intermolecular force and improve the flexibility and processing performance of the resin. However, due to the limitation of the thermal stability of lignite (usually less than 180℃ starts to decompose) and insufficient crosslinking density, the resin is prone to structural damage in high temperature and high pressure environment, resulting in a sharp increase in filtration loss and performance degradation, which is difficult to meet the needs of deep well and ultra-deep well drilling.

[0026] In the high-temperature resistant modification of lignite resin, the synergistic doping of benzene ring and heterocycle significantly improves the thermal stability and comprehensive performance of the material through multiple chemical mechanisms. First, the introduction of benzene ring (modification of benzene ring structure in p-bromostyrene) forms a stable conjugated structure through its delocalized pi electron system, which can effectively disperse thermal stress and inhibit molecular chain rupture and oxidative degradation at high temperatures. The rigid planar structure of the benzene ring can also form physical crosslinking points with the lignite skeleton, enhancing the mechanical strength of the resin and enabling it to maintain structural integrity at 220℃, while ordinary lignite resin has already softened and decomposed at this temperature. Second, the doping of heterocycle (modification of pyridine ring in 2-vinylpyridine) further optimizes the thermal stability through the electronic effect of nitrogen-containing heteroatoms. The nitrogen atom (electronegativity 3.0) in the pyridine ring can form hydrogen bonds or coordination bonds with the hydroxyl or carboxyl groups in lignite, constructing a dynamic crosslinking network. This network can release thermal stress by reversible bond breaking and recombination at high temperatures, avoiding structural collapse caused by local overheating. Meanwhile, the aromaticity of the heterocycle (six-membered conjugated system of the pyridine ring) forms pi-pi stacking with the benzene ring, enhancing intermolecular forces and increasing the glass transition temperature (Tg) of the resin, significantly expanding its high-temperature application range. In addition, the synergistic effect of benzene ring and heterocycle also endows the resin with multiple functional characteristics: on the one hand, the hydrophobicity of the brominated benzene ring can reduce the swelling rate of the resin in high-temperature salt water, and the hydrophilicity of the pyridine ring can form a hydrophobic-hydrophilic balance structure, enabling the resin to quickly form a thin and dense mud cake in the drilling fluid at 220℃, reducing the filtration loss; on the other hand, the basic nitrogen atom of the heterocycle can adsorb acidic inhibitors (such as KCl) in the drilling fluid, enhancing shale inhibition and reducing the risk of wellbore instability. These structural optimizations enable the modified lignite resin to exhibit excellent high-temperature resistance and comprehensive performance advantages in deep well and ultra-deep well drilling.

[0027] To further illustrate the effect of the high-temperature resistant lignite resin for drilling fluid of the present application in improving the high-temperature resistance and salt resistance of the drilling fluid, the following experimental examples and comparative examples are provided: If a specific technique or condition is not specified in the examples, it is performed according to the technique or condition described in the literature in the art or according to the product manual. If the manufacturer of the reagent or instrument is not specified, it is a conventional product that can be obtained from the market.

[0028] Example 1

[0029] The present application provides a high-temperature resistant lignite resin for drilling fluid, which is prepared by the following steps: S1. Extraction: 13 parts by weight of modified lignite, 75 parts by weight of ultrapure water, 6 parts by weight of 1% sodium hydroxide, and 0.7 parts by weight of sodium carbonate are mixed for extraction reaction to obtain a mixed solution.

[0030] S2. Sulfonation: 2 parts by weight of formaldehyde, 10 parts by weight of humic acid and 2 parts by weight of sodium pyrosulfite were added to the mixed solution to react at 140°C for 1.2h to undergo sulfonation, obtaining a sulfonated solution.

[0031] S3. Synthesis: 10 parts by weight of lignin, 6 parts by weight of formaldehyde, 2 parts by weight of acrylamide, 3 parts by weight of acrylonitrile salt, 3 parts by weight of sodium sulfite and 2 parts by weight of 2-acrylamido-2-methylpropanesulfonic acid were added to the sulfonated solution to undergo a synthesis reaction, obtaining lignite resin for high-temperature drilling fluid.

[0032] The modified lignite was prepared by a method comprising the following steps: Step one, pretreatment and functional modification: 13 parts by weight of lignite was crushed to 200 mesh, mixed with 75 parts of deionized water, 6 parts by weight of 1% sodium hydroxide and 0.7 parts by weight of sodium carbonate were added, and stirred and mixed at 80°C for 2h, and then filtered to obtain an alkaline lignite suspension.

[0033] Step two, preparation of functional monomer solution: 1 part by weight of modified p-bromostyrene and 0.8 parts by weight of modified 2-vinylpyridine were dissolved in 9 parts by weight of anhydrous ethanol, 0.1 parts of diisobutyl nitrile was added, and pre-polymerization was carried out at 60°C for 1h to obtain a bicyclic conjugated modifier.

[0034] Step three, multi-stage grafting sulfonation: 10 parts of humic acid and 2 parts of sodium pyrosulfite were sequentially added to the alkaline lignite suspension, and sulfonation was carried out at 100°C for 2h under nitrogen protection to generate a lignite intermediate grafted with sulfonic acid groups; when the temperature was lowered to 70°C, the bicyclic conjugated modifier was added dropwise, and 2 parts of 2-acrylamido-2-methylpropanesulfonic acid was added at the same time, and grafting reaction was carried out for 3h to obtain a lignite mixture.

[0035] Step four, high-temperature reinforced crosslinking: formaldehyde was added to the lignite mixture in three batches, each batch of formaldehyde was 2.5 parts by weight, 6 parts by weight of lignin was added synchronously, aldehyde-amine polycondensation reaction was carried out at 85°C for 2.5h, 2.5 parts by weight of acrylonitrile salt and 0.5 parts by weight of nano silicon dioxide were added, and a siloxane crosslinking network was constructed by sol-gel method, and the modified lignite precursor was obtained by maintaining 120°C high-temperature reaction for 1h.

[0036] Step five, post-treatment and structure locking: dilute hydrochloric acid was added to the modified lignite precursor to adjust the pH to 6.5, and a granular product was obtained by spray drying; the product was placed in an oven at 150°C for heat treatment for 2h to obtain the modified lignite resin.

[0037] The modified p-bromostyrene is prepared by the following steps: under nitrogen protection, 10 parts by weight of bromostyrene, 2 parts by weight of maleic anhydride, 15 parts by weight of toluene, 0.3 parts by weight of 0.3wt% azobisisobutyronitrile are mixed and then placed into a reaction kettle at 80°C for copolymerization reaction for 8 hours to obtain a reaction liquid; 25 parts by weight of anhydrous ethanol is added to the reaction liquid for stirring and mixing, filtration, then washing with acetone for 3 times, filtration, and vacuum drying at 70°C until constant weight to obtain the modified p-bromostyrene.

[0038] The modified 2-vinylpyridine is prepared by the following steps: under nitrogen protection, 10 parts by weight of 2-vinylpyridine, 2 parts by weight of acrylic acid, 15 parts by weight of toluene, 0.3 parts by weight of 0.4wt% azobisisobutyronitrile are mixed and then placed into a reaction kettle at 75°C for copolymerization reaction for 8 hours to obtain a reaction liquid; 23 parts by weight of petroleum ether is added to the reaction liquid for stirring and mixing, filtration, then washing with anhydrous ethanol for 3 times, and finally the product is placed in a vacuum oven at 70°C until constant weight to obtain the acrylic ester modified 2-vinylpyridine.

[0039] Example two

[0040] The present application provides a lignite resin for high-temperature resistant drilling fluid, which is prepared by the following steps: S1. Extraction: 10 parts by weight of modified lignite, 70 parts by weight of ultrapure water, 5 parts by weight of 1% sodium hydroxide, and 0.5 parts by weight of sodium carbonate are mixed for extraction reaction to obtain a mixed liquid.

[0041] S2. Sulfonation: 1 part by weight of formaldehyde, 8 parts by weight of humic acid and 1 part by weight of sodium pyrosulfite are added to the mixed liquid for sulfonation reaction at 137°C for 1h to obtain a sulfonated liquid.

[0042] S3. Synthesis: 9 parts by weight of lignin, 5 parts by weight of formaldehyde, 1 part by weight of acrylamide, 2 parts by weight of acrylonitrile salt, 2 parts by weight of sodium sulfite and 1 part by weight of 2-acrylamido-2-methylpropanesulfonic acid are added to the sulfonated liquid for synthesis reaction to prepare the lignite resin for high-temperature resistant drilling fluid.

[0043] The modified lignite is prepared by a method comprising the following steps: Step one, pretreatment and functional modification: 10 parts by weight of lignite is crushed to 200 mesh, mixed with 70 parts of deionized water, 5 parts by weight of 1% sodium hydroxide and 0.5 parts by weight of sodium carbonate are added, and stirred and mixed at 80°C for 2h, and then filtered to obtain an alkaline lignite suspension.

[0044] Step two, preparation of functional monomer solution: 1 part by weight of modified p-bromostyrene and 0.8 parts by weight of modified 2-vinylpyridine are dissolved in 8 parts by weight of anhydrous ethanol, 0.1 part of diisobutyl ketone is added, and pre-polymerization is carried out at 60℃ for 1h to obtain a double-ring conjugated modifier.

[0045] Step three, multi-stage grafting sulfonation: 8 parts of humic acid and 1 part of sodium pyrosulfite are added to the alkaline lignite suspension in turn, and sulfonation reaction is carried out at 100℃ for 2h under nitrogen protection to generate a lignite intermediate grafted with sulfonic acid groups; when the temperature is lowered to 70℃, the double-ring conjugated modifier is added dropwise, and 1 part of 2-acrylamido-2-methylpropanesulfonic acid is added at the same time, and grafting reaction is carried out for 3h to obtain a lignite mixture.

[0046] Step four, high-temperature reinforced crosslinking: formaldehyde is added to the lignite mixture in three batches, and the amount of formaldehyde added in each batch is 2 parts by weight, and 5 parts of lignin are added synchronously, and aldehyde-amine polycondensation reaction is carried out at 85℃ for 2h, and 2 parts of acrylonitrile salt and 0.5 parts of nano silicon dioxide are added, and a siloxane crosslinking network is constructed by sol-gel method, and the modified lignite precursor is obtained by maintaining 120℃ high-temperature reaction for 1h.

[0047] Step five, post-treatment and structure locking: add dilute hydrochloric acid to the modified lignite precursor to adjust the pH to 6.5, and spray drying is carried out to obtain a granular product; the product is placed in a 150℃ oven for heat treatment for 2h to obtain a modified lignite resin.

[0048] The modified p-bromostyrene is prepared by the following steps: under nitrogen protection, 10 parts by weight of bromostyrene, 2 parts by weight of maleic anhydride, 15 parts by weight of toluene and 0.1 part of 0.1wt% azobisisobutyronitrile are mixed and then placed in a reaction kettle at 75℃ for copolymerization reaction for 6 hours to obtain a reaction liquid; 20 parts by weight of anhydrous ethanol is added to the reaction liquid and stirred and mixed, filtered, then washed with acetone for 3 times, filtered and dried at 60℃ under vacuum to constant weight to obtain the modified p-bromostyrene.

[0049] The modified 2-vinylpyridine is prepared by the following steps: under nitrogen protection, 10 parts by weight of 2-vinylpyridine, 2 parts by weight of acrylic acid, 15 parts by weight of toluene and 0.1 part of 0.2wt% azobisisobutyronitrile are mixed and then placed in a reaction kettle at 70℃ for copolymerization reaction for 6 hours to obtain a reaction liquid; 20 parts by weight of petroleum ether is added to the reaction liquid and stirred and mixed, filtered, then washed with anhydrous ethanol for 3 times, and finally the product is placed in a vacuum oven at 60℃ and dried to constant weight to obtain the acrylate-modified 2-vinylpyridine.

[0050] Example three

[0051] The present application provides a kind of lignite resin for anti-high temperature drilling fluid is prepared by the following steps: S1. Extraction: 15 parts by weight of modified lignite, 80 parts by weight of ultrapure water, 7 parts by weight of 1% sodium hydroxide, and 0.8 parts by weight of sodium carbonate were mixed to extract the reaction, obtaining a mixed solution.

[0052] S2. Sulfonation: 2 parts by weight of formaldehyde, 12 parts by weight of humic acid, and 2 parts by weight of sodium pyrosulfite were added to the mixed solution and reacted at 143℃ for 1.5h to undergo sulfonation reaction, obtaining a sulfonated solution.

[0053] S3. Synthesis: 12 parts by weight of lignin, 7 parts by weight of formaldehyde, 2 parts by weight of acrylamide, 3 parts by weight of acrylonitrile salt, 3 parts by weight of sodium sulfite, and 3 parts by weight of 2-acrylamido-2-methylpropanesulfonic acid were added to the sulfonated solution to undergo synthesis reaction, obtaining lignite resin for high-temperature drilling fluid.

[0054] The modified lignite is prepared by a method comprising the following steps: Step one, pretreatment and functional modification: 15 parts by weight of lignite was crushed to 200 mesh, mixed with 80 parts of deionized water, 7 parts by weight of 1% sodium hydroxide, and 0.8 parts by weight of sodium carbonate, and stirred at 80℃ for 2h for alkali dissolution pretreatment, and filtered to obtain an alkaline lignite suspension.

[0055] Step two, preparation of functional monomer solution: 1 part by weight of modified p-bromostyrene and 0.8 parts by weight of modified 2-vinylpyridine were dissolved in 10 parts by weight of anhydrous ethanol, 0.1 parts of diisobutyl ketone was added, and pre-polymerization was carried out at 60℃ for 1h to obtain a double-ring conjugated modifier.

[0056] Step three, multi-stage grafting sulfonation: 12 parts of humic acid and 2 parts of sodium pyrosulfite were added to the alkaline lignite suspension, and sulfonation reaction was carried out at 100℃ for 2h under nitrogen protection to generate a lignite intermediate grafted with sulfonic acid groups; when the temperature was lowered to 70℃, the double-ring conjugated modifier was added dropwise, and 3 parts of 2-acrylamido-2-methylpropanesulfonic acid was added at the same time, and grafting reaction was carried out for 3h to obtain a lignite mixed solution.

[0057] Step four, high-temperature reinforced crosslinking: formaldehyde was added to the lignite mixed solution in three batches, with each batch of formaldehyde being 3 parts by weight, and 7 parts of lignin was added synchronously, and aldehyde-amine polycondensation reaction was carried out at 85℃ for 3h, 3 parts of acrylonitrile salt and 0.5 parts of nano silicon dioxide were added, and a siloxane crosslinking network was constructed by sol-gel method, and the modified lignite precursor was obtained by maintaining 120℃ high-temperature reaction for 1h.

[0058] Step five, post-treatment and structure locking: dilute hydrochloric acid was added to the modified lignite precursor to adjust the pH to 6.5, and granular product was obtained by spray drying; the product was placed in a 150℃ oven for heat treatment for 2h to obtain modified lignite resin.

[0059] The modified para-bromostyrene is prepared by the following steps: under nitrogen protection, 10 parts by weight of bromostyrene, 2 parts by weight of maleic anhydride, 15 parts by weight of toluene, and 0.5 parts by weight of 0.5wt% azobisisobutyronitrile are weighed, mixed, and placed in a reactor at 85°C for copolymerization for 10 hours to obtain a reaction liquid; 30 parts by weight of anhydrous ethanol is added to the reaction liquid, stirred and mixed, filtered, and then washed with acetone three times, filtered, and then vacuum-dried at 80°C to constant weight to obtain the modified para-bromostyrene.

[0060] The modified 2-vinyl pyridine is prepared by the following steps: under nitrogen protection, 10 parts by weight of 2-vinyl pyridine, 2 parts by weight of acrylic acid, 15 parts by weight of toluene, and 0.5 parts by weight of 0.5wt% azobisisobutyronitrile are weighed, mixed, and placed in a reactor at 80°C for copolymerization reaction for 10 hours to obtain a reaction liquid; 25 parts by weight of petroleum ether is added to the reaction liquid, stirred and mixed, filtered, and then washed with anhydrous ethanol three times. Finally, the product is placed in a vacuum oven at 80°C to constant weight to obtain acrylate-modified 2-vinyl pyridine.

[0061] Comparative Example 1: The difference from Experiment 1 is that the prepared modified lignite does not introduce modified para-bromostyrene.

[0062] Comparative Example 2: The difference from Experiment 1 is that the prepared modified lignite does not introduce modified 2-vinylpyridine.

[0063] Performance testing: 1. High temperature resistance Preparation of test samples: Prepare base slurry: Add 0.79g of anhydrous sodium carbonate and 2.50g of bentonite for drilling fluid test slurry into a sample cup containing 350mL of distilled water. Stir at high speed for 20min, stopping at least twice to scrape off the sample adhering to the cup wall. Sealed and cured for 24 hours to serve as the base slurry. Prepare the heat-resistant sample slurry: Add 17.50g of the lignite resin from Experimental Example 1-3 to 350mL of the base slurry and stir at high speed for 20 minutes, interrupting twice to scrape off any sample adhering to the cup wall. Add 52.50g of sodium chloride and stir at high speed for 10 minutes. Add 2mL of 20% sodium hydroxide solution to adjust the pH. Test method: Transfer the above slurry to a high-temperature tank and heat at 200°C / 210°C / 220°C for 16 hours, respectively. Remove the high-temperature tank, cool to room temperature, open it, pour into a mixing cup, and stir at high speed for 5 minutes.

[0064] Test method: the above slurry was transferred into a high temperature tank, and was hot-rolled at 200°C / 210°C / 220°C for 16h, respectively; the high temperature tank was taken out, cooled to room temperature, opened, poured into a stirring cup, and stirred at high speed for 5min. Based on the apparent viscosity and filtration quantity test method in GB / T16783.1-2014 "Petroleum and Natural Gas Industry Drilling Fluids Field Test Part 1: Water-based Drilling Fluids", the apparent viscosity and high temperature and high pressure (150°C / 3450kPa) filtration quantity of the slurry were tested. The apparent viscosity and high temperature and high pressure filtration quantity of the modified lignite resins of experimental examples one, two, three and comparative examples one and two after different high temperature treatment are shown in Table 1.

[0065] Table 1

[0066] As shown in Table 1, compared with comparative examples one and two, the high temperature resistant lignite resin for drilling fluid of the present application can maintain stable apparent viscosity and filtration quantity after being hot-rolled at 200°C / 210°C / 220°C for 16h in 15% NaCl contaminated slurry, and the temperature resistance reaches 220°C.

[0067] The above is only a specific embodiment of the present application, but the technical features of the present application are not limited thereto. Any simple change, equivalent replacement or modification made on the basis of the present application to solve the basically same technical problem and realize the basically same technical effect is covered in the protection scope of the present application.

Claims

1. A method for preparing lignite resin for high temperature resistant drilling fluid, characterized in that: The method comprises the following preparation steps: S1 extraction: Weigh 10-15 parts by weight of modified lignite, 70-80 parts by weight of a solvent, 5-7 parts by weight of sodium hydroxide, 0.5-0.8 parts by weight of sodium carbonate and mix the reaction to obtain a mixed solution; S2 sulfonation: 1-2 parts by weight of formaldehyde, 8-12 parts by weight of humic acid and 1-2 parts by weight of sodium metabisulfite were added to the mixture, and the reaction was carried out at 137-143 ° C for 1-1.5h to obtain a sulfonated liquid; S3. Synthesis: 9-12 parts by weight of lignin, 5-7 parts by weight of formaldehyde, 1-2 parts by weight of acrylamide, 2-3 parts by weight of acrylonitrile salt, 2-3 parts by weight of sodium sulfite and 1-3 parts by weight of 2-acrylamido-2-methylpropanesulfonic acid are added to the sulfonated liquid to carry out a synthesis reaction to obtain a lignite resin for high-temperature resistant drilling fluid.

2. The method for preparing a high-temperature resistant lignite resin for drilling fluid according to claim 1, wherein: The modified lignite comprises the following preparation steps: Step 1: Pretreatment and functional modification: 10-15 parts by weight of lignite are crushed to 200 mesh, mixed with 70-80 parts by weight of deionized water, 5-7 parts by weight of sodium hydroxide and 0.5-0.8 parts by weight of sodium carbonate are added, and the mixture is stirred at 80° C. for 2 hours, and filtered to obtain an alkaline lignite suspension; Step 2: Prepare a functional monomer solution: dissolve 1 part by weight of modified p-bromostyrene and 0.8 parts by weight of modified 2-vinylpyridine in 8-10 parts by weight of anhydrous ethanol, add 0.1 parts by weight of diisobutyronitrile, and prepolymerize at 60° C. for 1 hour to obtain a bicyclic conjugated modifier; Step 3, multi-stage grafting sulfonation: 8-12 parts by weight of humic acid and 1-2 parts by weight of sodium metabisulfite are sequentially added to the alkaline lignite suspension, and the temperature is raised to 100°C under nitrogen protection for sulfonation reaction for 2 hours to generate a lignite intermediate grafted with sulfonic acid groups; when the temperature is lowered to 70°C, a bicyclic conjugated modifier is added dropwise, and 1-3 parts by weight of 2-acrylamido-2-methylpropanesulfonic acid is added and grafted for a reaction of 3 hours to obtain a lignite mixture; Step 4: High-temperature enhanced cross-linking: Formaldehyde is added to the lignite mixture in three batches, with each batch adding 2-3 parts by weight of formaldehyde, and 5-7 parts by weight of lignin are added simultaneously. The aldehyde-amine polycondensation reaction is carried out at 85°C for 2-3 hours. Then, 2-3 parts by weight of acrylonitrile salt and 0.5 parts by weight of nano-silica are added, and the reaction is carried out at 120°C for 1 hour to obtain a modified lignite precursor. Step 5: Post-treatment and structural locking: dilute hydrochloric acid is added to the modified lignite precursor to adjust the pH to 6.5, and a granular product is obtained by spray drying; The granular product was placed in an oven at 150° C. for heat treatment for 2 h to obtain a modified lignite resin.

3. The method for preparing a high-temperature resistant lignite resin for drilling fluid according to claim 2, wherein: The modified p-bromostyrene is prepared by the following preparation method: Under nitrogen protection, 10 parts by weight of bromostyrene, 2 parts by weight of maleic anhydride, 15 parts by weight of toluene, and 0.1-0.5 parts by weight of 0.1-0.5 wt% of azobisisobutyronitrile were weighed, mixed, and placed in a reactor at 75-85° C. for copolymerization for 6-10 hours to obtain a reaction solution; 20-30 parts by weight of anhydrous ethanol was added to the reaction solution, stirred and mixed, filtered, and then washed with acetone three times, filtered, and dried in a vacuum drying oven at 60-80° C. to constant weight to obtain modified p-bromostyrene.

4. The method for preparing a high-temperature resistant lignite resin for drilling fluid according to claim 2, wherein: The modified 2-vinylpyridine is prepared by the following preparation method: Under nitrogen protection, 10 parts by weight of 2-vinylpyridine, 2 parts by weight of acrylic acid, 15 parts by weight of toluene, and 0.1-0.5 parts by weight of 0.2-0.5 wt% of azobisisobutyronitrile were weighed, mixed, and placed in a reactor at 70-80° C. for copolymerization reaction for 6-10 hours to obtain a reaction liquid; 20-25 parts by weight of petroleum ether were added to the reaction liquid, stirred and mixed, filtered, and then washed with anhydrous ethanol three times, filtered, and dried in a vacuum drying oven at 60-80° C. to constant weight to obtain modified 2-vinylpyridine.

5. The method for preparing a lignite resin for high temperature resistant drilling fluid according to claim 1 or 2, characterized in that: The mass concentration of the sodium hydroxide is 1%.

6. The method for preparing a lignite resin for high temperature resistant drilling fluid according to claim 1, characterized in that: The solvent is ultrapure water.

7. The method for preparing a high-temperature resistant lignite resin for drilling fluid according to claim 2, wherein: The particle size of the nano-silicon dioxide is 20-30 nm.

8. A method for preparing lignite resin for high temperature resistant drilling fluid, characterized in that: The invention is prepared by the preparation method according to any one of claims 1 to 7.

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