Strongly-adsorptive hyperbranched fluid loss reducing agent resisting 240℃ and saturated salt conditions for water-based drilling fluid, preparation method therefor, and use thereof

Abstract

Disclosed are a strongly-adsorptive hyperbranched fluid loss reducing agent resisting 240°C and saturated salt conditions for a water-based drilling fluid, a preparation method therefor, and the use thereof. The fluid loss reducing agent comprises a first structural unit, a second structural unit, a third structural unit, a fourth structural unit, a fifth structural unit, and a sixth structural unit, wherein the first structural unit is provided by an anionic hydration enhancement monomer, the second structural unit is provided by a cationic positively-charged adsorption monomer, the third structural unit is provided by a main chain monomer, the fourth structural unit is provided by a cyclic monomer, the fifth structural unit is provided by a polyether monomer, and the sixth structural unit is provided by a hyperbranched structural monomer. The fluid loss reducing agent can enable drilling fluids to keep good rheologic properties and fluid loss reducing performance even under 240°C and saturated salt conditions and achieve long-term stability.

Description

Strongly adsorbed hyperbranched fluid loss additive for 240℃ saturated salt water-based drilling fluid and preparation method and application thereof TECHNICAL FIELD

[0001] The present application relates to the technical field of drilling, in particular to a fluid loss additive and a preparation method and application thereof, more particularly to a strongly adsorbed hyperbranched fluid loss additive for 240℃ saturated salt water-based drilling fluid and a preparation method and application thereof. BACKGROUND

[0002] Drilling fluid is a key technology to ensure safe and efficient exploration and development of ultra-deep and super-deep oil and gas, and its performance determines the safety, efficiency and success of drilling. However, ultra-deep drilling fluid faces unprecedented major challenges: ultra-high temperature (≥200℃), ultra-high pressure (≥140MPa), ultra-high salt (≥200000mg / L), and ultra-high stress (≥160MPa). These difficulties make it difficult to control the stability of drilling fluid performance, which can easily lead to accidents such as well collapse, well leakage, and blowout. The cost of ultra-deep and super-deep wells is relatively high, and once an accident occurs, it will cause huge economic losses, and even evolve into a disastrous accident of "well destruction and human death". The most critical factor to stabilize the performance of drilling fluid is the fluid loss additive, but there is currently a lack of drilling fluid fluid loss additives that can resist ultra-high temperature, ultra-high pressure, and saturated salt (36% NaCl), especially those that can resist 240℃ saturated salt. Therefore, it is urgent to develop a drilling fluid fluid loss additive that can resist ultra-high temperature, ultra-high pressure, and saturated salt.

[0003] Patent application CN115850578A discloses a polymer fluid loss additive that can resist temperatures up to 240℃, but only 4% salt, which cannot maintain good performance under saturated salt conditions. Patent application CN114989351A discloses a low molecular weight fluid loss additive that can resist up to saturated salt, but the ester monomer in it is prone to high-temperature degradation, and the polymer can only resist temperatures up to 200℃. Patent applications CN114716607A and CN106366243A both disclose new zwitterionic copolymer fluid loss additives, in which the cationic groups can enhance the adsorption capacity of the polymer at high temperatures, and the strong hydration groups can enhance the salt resistance of the polymer, but their K + , Ca 2+ performance cannot meet the requirements of deep formations, and their high-temperature and high-pressure filtration performance is poor.

[0004] SUMMARY

[0005] The purpose of this invention is to overcome the problem that existing water-based drilling fluid filtration reducers cannot simultaneously withstand ultra-high temperature, ultra-high pressure, and saturated salt conditions. This invention provides a highly adsorbent, hyperbranched filtration reducer for use in 240°C saturated salt-based drilling fluids, along with its preparation method and application. The filtration reducer provided by this invention maintains good performance under 240°C and saturated salt conditions and remains stable for extended periods (greater than 10 days), providing technical support for ultra-deep oil and gas drilling.

[0006] To achieve the above objectives, the present invention provides a filtration loss reducing agent, which includes:

[0007] The first structural unit is provided by anionic hydration-enhanced monomers;

[0008] The second structural unit is provided by a cationic positively charged adsorption monomer;

[0009] The third structural unit is provided by the main chain monomer;

[0010] The fourth structural unit is provided by a ring-shaped monomer;

[0011] The fifth structural unit is provided by the polyether monomer;

[0012] The sixth structural unit is provided by the hyperbranched structural monolith;

[0013] The main chain monomer is N,N-dimethylacrylamide and / or N,N-diethylacrylamide, and the weight-average molecular weight of the filtration loss reducer is 200,000 to 800,000.

[0014] Preferably, the weight ratio of the first structural unit, the second structural unit, the third structural unit, the fourth structural unit, the fifth structural unit, and the sixth structural unit is (10-60):(5-40):(5-40):(2-20):(5-40):1, and more preferably (20-30):(10-20):(10-20):(5-10):(10-20):1.

[0015] Preferably, the anionic hydration-enhancing monomer is at least one selected from 2-acrylamido-2-methylpropanesulfonic acid, sodium p-styrenesulfonate, sodium allyl sulfonate, and sodium methpropylene sulfonate.

[0016] Preferably, the cationic positively charged adsorbent monomer is at least one of dimethylaminopropylmethacrylamide, dimethyldiallylammonium chloride, and acryloyloxyethyltrimethylammonium chloride.

[0017] Preferably, the main chain monomer is a combination of N,N-dimethylacrylamide and N,N-diethylacrylamide, and the weight ratio of N,N-dimethylacrylamide to N,N-diethylacrylamide is 1:0.1-1, preferably 1:0.3-0.5.

[0018] Preferably, the cyclic monomer is at least one selected from N-vinylpyrrolidone, 1-vinylimidazolium, 4-vinylpyridine, and 4-acryloylmorpholine.

[0019] Preferably, the polyether monomer is at least one selected from modified alkylene-based polyoxyethylene ether, hydroxybutyl polyoxyethylene ether, 4-hydroxybutyl vinyl ether polyoxyethylene ether, and ethylene glycol monovinyl polyoxyethylene ether.

[0020] Preferably, the molecular weight of the polyether monomer is 1500-4000.

[0021] Preferably, the structural formula of the hyperbranched monomer is shown in formula (I).

[0022] A second aspect of the present invention provides a method for preparing a filtration loss reducing agent, the method comprising:

[0023] Under an inert atmosphere, anionic hydration-enhancing monomers, cationic positively charged adsorption monomers, main-chain monomers, cyclic monomers, and polyether monomers undergo a single reaction in the presence of a first initiator.

[0024] The product obtained after the first reaction is reacted with the hyperbranched monomer in the presence of a second initiator in a second reaction.

[0025] The main chain monomer is N,N-dimethylacrylamide and / or N,N-diethylacrylamide.

[0026] Preferably, the weight ratio of the anionic hydration-enhancing monomer, the cationic positively charged adsorption monomer, the main chain monomer, the cyclic monomer, the polyether monomer, and the hyperbranched monomer is (10-60):(5-40):(5-40):(2-20):(5-40):1, and more preferably (20-30):(10-20):(10-20):(5-10):(10-20):1.

[0027] Preferably, the anionic hydration-enhancing monomer is at least one selected from 2-acrylamido-2-methylpropanesulfonic acid, sodium p-styrenesulfonate, sodium allyl sulfonate, and sodium methpropylene sulfonate.

[0028] Preferably, the cationic positively charged adsorbent monomer is at least one of dimethylaminopropylmethacrylamide, dimethyldiallylammonium chloride, and acryloyloxyethyltrimethylammonium chloride.

[0029] Preferably, the main chain monomer is a combination of N,N-dimethylacrylamide and N,N-diethylacrylamide, and the weight ratio of N,N-dimethylacrylamide to N,N-diethylacrylamide is 1:0.1-1, preferably 1:0.3-0.5.

[0030] Preferably, the cyclic monomer is at least one selected from N-vinylpyrrolidone, 1-vinylimidazolium, 4-vinylpyridine, and 4-acryloylmorpholine.

[0031] Preferably, the polyether monomer is at least one selected from modified alkylene-based polyoxyethylene ether, hydroxybutyl polyoxyethylene ether, 4-hydroxybutyl vinyl ether polyoxyethylene ether, and ethylene glycol monovinyl polyoxyethylene ether.

[0032] Preferably, the molecular weight of the polyether monomer is 1500-4000.

[0033] Preferably, the structural formula of the hyperbranched monomer is shown in formula (I).

[0034] Preferably, the first initiator is a combination of persulfate and reducing agent, and the weight ratio of the persulfate to the reducing agent is 1:0.1-0.5.

[0035] Preferably, the persulfate is at least one selected from ammonium persulfate, potassium persulfate, and sodium persulfate.

[0036] Preferably, the reducing agent is at least one selected from sodium bisulfite, ammonium bisulfite, and potassium bisulfite.

[0037] Preferably, the second initiator is a combination of azobisisobutyramidine hydrochloride and a reducing agent, and the weight ratio of the azobisisobutyramidine hydrochloride to the reducing agent is 1:0.1-0.5.

[0038] Preferably, the reducing agent is at least one selected from sodium bisulfite, ammonium bisulfite, and potassium bisulfite.

[0039] Preferably, the temperature of the secondary reaction is 5-25°C higher than the temperature of the primary reaction.

[0040] Preferably, the temperature of the primary reaction is 65-75°C, and the temperature of the secondary reaction is 80-90°C.

[0041] A third aspect of the present invention provides a drilling fluid containing the aforementioned filtration loss reducer.

[0042] The filtration loss reducer according to the present invention is obtained by copolymerization of anionic hydration-enhancing monomers, cationic positively charged adsorption monomers, main-chain monomers, cyclic monomers, polyether monomers and hyperbranched monomers. When used in water-based drilling fluids, it can maintain good drilling fluid rheology and filtration loss reduction properties at 240°C and under saturated salt conditions, and remain stable for a long time. The cationic structure can strongly adsorb onto negatively charged clay surfaces, while the anionic structure can strongly adsorb onto positively charged clay end faces. Desorption is difficult under ultra-high temperature conditions. The hyperbranched monomer structure enables the polymer to form a three-dimensional broom-like hyperbranched polymer. The polyether monomer can react with hydroxyl groups on the clay surface through its own alkyl ether structure to form multiple CO chemical bonds, which are more stable than other chemical bonds, hydrogen bonds, electrostatic interactions, etc. The unique three-dimensional broom-like hyperbranched molecular chain has a stronger adsorption capacity than other micro-crosslinked structures and hydrophobic associative structures, and is also more rigid and has greater steric hindrance. This ensures the long-term structural stability of the polymer under ultra-high temperature conditions and effectively resists the strong double-layer compression effect of high-valence salt ions on the molecular chain. This allows the polymer to efficiently maintain the spatial extension state of the molecular chain under ultra-high temperature and saturated salt conditions, resulting in a thicker hydration film. The polymer exhibits stable performance under ultra-high temperature and ultra-high pressure saturated salt conditions, effectively reducing filtration loss.

[0043] With the commencement of exploration and development of deep wells at depths of 10,000 meters, the ultra-high temperature and saturated salt environment at these depths present significant challenges to drilling fluid fluid loss control agents. The fluid loss control agent of this invention directly addresses the practical engineering needs of deep well drilling at 10,000 meters, exhibiting excellent fluid loss control performance under ultra-high temperature and high salinity conditions of 240°C saturated salt, and demonstrating long-term stability. This provides efficient technical support for deep well drilling at 10,000 meters and fills the gap in products containing fluid loss control agents resistant to 240°C saturated salt. Furthermore, the fluid loss control agent of this invention exhibits good compatibility with other oilfield chemical treatment agents and can be used as a viscosifier in fracturing fluids and a fluid loss control agent in cementing fluids. Detailed Implementation

[0044] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0045] The filtration loss reducer of this invention comprises a first structural unit, a second structural unit, a third structural unit, a fourth structural unit, a fifth structural unit, and a sixth structural unit. The first structural unit is provided by an anionic hydration-enhancing monomer, the second structural unit is provided by a cationic positively charged adsorption monomer, the third structural unit is provided by a main-chain monomer, the fourth structural unit is provided by a cyclic monomer, the fifth structural unit is provided by a polyether monomer, and the sixth structural unit is provided by a hyperbranched monomer. According to this invention, by combining the six types of structural units, the filtration loss reducer, when used in water-based drilling fluids, maintains good drilling fluid rheological and filtration performance at 240°C under saturated salt conditions and remains stable for a long period.

[0046] In the filtration loss reducing agent of the present invention, the weight ratio of the first structural unit, the second structural unit, the third structural unit, the fourth structural unit, the fifth structural unit and the sixth structural unit can be (10-60):(5-40):(5-40):(2-20):(5-40):1, preferably (12-55):(6-35):(6-35):(3-18):(6-35):1, more preferably (15-50):(7-30):(7-30):(4-15):(7-30):1, further preferably (18-40):(8-25):(8-25):(5-12):(8-25):1, and even more preferably (20-30):(10-20):(10-20):(5-10):(10-20):1. When the proportion of the six structural units in the filtration loss reducer is within the above-mentioned range (especially the preferred range), the filtration loss reducer has better filtration loss reduction performance.

[0047] In this invention, the weight-average molecular weight of the filtration loss reducing agent is 200,000 to 800,000, preferably 300,000 to 700,000, and more preferably 350,000 to 650,000. In this document, the weight-average molecular weight of the filtration loss reducing agent is obtained by gel permeation chromatography.

[0048] In this invention, the main chain monomer is N,N-dimethylacrylamide and / or N,N-diethylacrylamide. Preferably, the main chain monomer is a combination of N,N-dimethylacrylamide and N,N-diethylacrylamide, and the weight ratio of N,N-dimethylacrylamide to N,N-diethylacrylamide is 1:0.1-1, preferably 1:0.2-0.8, more preferably 1:0.3-0.7, and even more preferably 1:0.3-0.5. Under these preferred conditions, the filtration loss reducing agent has better filtration loss reducing performance.

[0049] In this invention, preferably, the anionic hydration-enhancing monomer is at least one selected from 2-acrylamido-2-methylpropanesulfonic acid, sodium p-styrene sulfonate, sodium allyl sulfonate, and sodium methpropylene sulfonate. When the anionic hydration-enhancing monomer is selected from the above-mentioned preferred monomer examples, the filtration loss reducing agent has better filtration loss reducing performance.

[0050] In this invention, preferably, the cationic positively charged adsorbent is at least one selected from dimethylaminopropylmethacrylamide, dimethyldiallylammonium chloride, and acryloyloxyethyltrimethylammonium chloride. When the cationic positively charged adsorbent is selected from the above-mentioned preferred monomer examples, the filtration loss reducing agent has better filtration loss reducing performance.

[0051] In this invention, preferably, the cyclic monomer is at least one selected from N-vinylpyrrolidone, 1-vinylimidazolium, 4-vinylpyridine, and 4-acryloylmorpholine. When the cyclic monomer is selected from the above-mentioned preferred monomer examples, the filtration loss reducing agent has better filtration loss reducing performance.

[0052] In this invention, preferably, the polyether monomer is at least one selected from modified alkylene-based polyoxyethylene ether, hydroxybutyl polyoxyethylene ether, 4-hydroxybutyl vinyl ether polyoxyethylene ether, and ethylene glycol monovinyl polyoxyethylene ether. When the polyether monomer is selected from the above-mentioned preferred monomer examples, the filtration loss reducing agent has better filtration loss reducing performance. The molecular weight of the polyether monomer can be 1000-10000, preferably 1500-6000, more preferably 1500-4000, and even more preferably 1800-3000.

[0053] In this invention, preferably, the hyperbranched structural monomer has the structural formula shown in formula (I).

[0054] When the hyperbranched monomer is selected from the monomer shown in formula (I) above, the filtration loss reducing agent has significantly better filtration loss reducing performance.

[0055] In some embodiments, the monomers forming the filtration loss reducing agent are 2-acrylamido-2-methylpropanesulfonic acid, dimethylaminopropylmethacrylamide, a main-chain monomer, modified alkylene polyoxyethylene ether, 1-vinylimidazolium, and a monomer shown in formula (I), wherein the main-chain monomer is a combination of N,N-dimethylacrylamide and N,N-diethylacrylamide, and the ratio of N,N-dimethylacrylamide to N,N-diethylacrylamide is 1:0.3-0.5. The filtration loss reducing agent formed according to this embodiment has significantly higher filtration loss reducing performance.

[0056] In other embodiments, the monomers forming the filtration loss reducing agent are sodium p-styrene sulfonate, dimethyl diallyl ammonium chloride, a main-chain monomer, hydroxybutyl polyoxyethylene ether, 4-acryloylmorpholine, and a monomer shown in formula (I), wherein the main-chain monomer is a combination of N,N-dimethylacrylamide and N,N-diethylacrylamide, and the ratio of N,N-dimethylacrylamide to N,N-diethylacrylamide is 1:0.3-0.5. The filtration loss reducing agent formed according to this embodiment has significantly higher filtration loss reducing performance.

[0057] In other embodiments, the monomers forming the filtration loss reducing agent are sodium allyl sulfonate, acryloyloxyethyltrimethylammonium chloride, a main-chain monomer, 4-hydroxybutyl vinyl ether polyoxyethylene ether, N-vinylpyrrolidone, and a monomer of formula (I), wherein the main-chain monomer is a combination of N,N-dimethylacrylamide and N,N-diethylacrylamide, and the ratio of N,N-dimethylacrylamide to N,N-diethylacrylamide is 1:0.3-0.5. The filtration loss reducing agent formed according to this embodiment has significantly higher filtration loss reducing performance.

[0058] In other embodiments, the monomers forming the filtration loss reducing agent are sodium methacrylate sulfonate, dimethyl diallyl ammonium chloride, a main-chain monomer, ethylene glycol monovinyl polyoxyethylene ether, 4-vinylpyridine, and a monomer shown in formula (I), wherein the main-chain monomer is a combination of N,N-dimethylacrylamide and N,N-diethylacrylamide, and the ratio of N,N-dimethylacrylamide to N,N-diethylacrylamide is 1:0.3-0.5. The filtration loss reducing agent formed according to this embodiment has significantly higher filtration loss reducing performance.

[0059] The filtration loss reducing agent of the present invention can be prepared by conventional polymerization methods. In some embodiments, the preparation method of the filtration loss reducing agent includes:

[0060] Under an inert atmosphere, anionic hydration-enhancing monomers, cationic positively charged adsorption monomers, main-chain monomers, cyclic monomers, and polyether monomers undergo a single reaction in the presence of a first initiator.

[0061] The product obtained after the first reaction is reacted with the hyperbranched monomer in the presence of a second initiator in a second reaction.

[0062] In the method described in this invention, the weight ratio of the anionic hydration-enhancing monomer, the cationic positively charged adsorption monomer, the main-chain monomer, the cyclic monomer, the polyether monomer, and the hyperbranched monomer can be (10-60):(5-40):(5-40):(2-20):(5-40):1, preferably (12-55):(6-35):(6-35):(3-18). The ratio is (6-35):1, more preferably (15-50):(7-30):(7-30):(4-15):(7-30):1, further preferably (18-40):(8-25):(8-25):(5-12):(8-25):1, and even more preferably (20-30):(10-20):(10-20):(5-10):(10-20):1. The filtration loss reducing agent prepared according to the above ratio range (especially the preferred range) has better filtration loss reducing performance.

[0063] In the method described in this invention, the conditions of the primary reaction and the secondary reaction are such that the weight-average molecular weight of the prepared filtration loss reducer is 200,000 to 800,000, preferably 300,000 to 700,000, and more preferably 350,000 to 650,000.

[0064] In a preferred embodiment, the temperature of the secondary reaction is 5-25°C higher than the temperature of the primary reaction, preferably 8-20°C, and more preferably 10-18°C higher. Even more preferably, the temperature of the primary reaction is 65-75°C, and the temperature of the secondary reaction is 80-90°C.

[0065] In the method described in this invention, preferably, the duration of the primary reaction is 4-6 hours, and the duration of the secondary reaction is 2-4 hours.

[0066] In the method described in this invention, the main-chain monomer is N,N-dimethylacrylamide and / or N,N-diethylacrylamide. Preferably, the main-chain monomer is a combination of N,N-dimethylacrylamide and N,N-diethylacrylamide, and the weight ratio of N,N-dimethylacrylamide to N,N-diethylacrylamide is 1:0.1-1, preferably 1:0.2-0.8, more preferably 1:0.3-0.7, and even more preferably 1:0.3-0.5. Under the above preferred conditions, the prepared filtration loss reducing agent has better filtration loss reducing performance.

[0067] In the method described in this invention, preferably, the anionic hydration-enhancing monomer is at least one selected from 2-acrylamido-2-methylpropanesulfonic acid, sodium p-styrene sulfonate, sodium allyl sulfonate, and sodium methpropylene sulfonate. When the anionic hydration-enhancing monomer is selected from the above-mentioned preferred monomer examples, the prepared filtration loss reducing agent has better filtration loss reducing performance.

[0068] In the method described in this invention, preferably, the cationic positively charged adsorbent is at least one selected from dimethylaminopropylmethacrylamide, dimethyldiallylammonium chloride, and acryloyloxyethyltrimethylammonium chloride. When the cationic positively charged adsorbent is selected from the above-mentioned preferred monomer examples, the prepared filtration loss reducing agent has better filtration loss reducing performance.

[0069] In the method described in this invention, preferably, the cyclic monomer is at least one selected from N-vinylpyrrolidone, 1-vinylimidazolium, 4-vinylpyridine, and 4-acryloylmorpholine. When the cyclic monomer is selected from the above-mentioned preferred monomer examples, the prepared filtration loss reducing agent has better filtration loss reducing performance.

[0070] In the method described in this invention, preferably, the polyether monomer is at least one selected from modified alkylene-based polyoxyethylene ether, hydroxybutyl polyoxyethylene ether, 4-hydroxybutyl vinyl ether polyoxyethylene ether, and ethylene glycol monovinyl polyoxyethylene ether. When the polyether monomer is selected from the above-mentioned preferred monomer examples, the prepared filtration loss reducing agent has better filtration loss reducing performance. The molecular weight of the polyether monomer can be 1000-10000, preferably 1500-6000, more preferably 1500-4000, and even more preferably 1800-3000.

[0071] In this invention, preferably, the hyperbranched structural monomer has the structural formula shown in formula (I).

[0072] When the hyperbranched monomer is selected from the monomer shown in formula (I) above, the prepared filtration loss reducer has significantly better filtration loss reduction performance.

[0073] In this invention, the hyperbranched monomer shown in formula (I) can be obtained by esterification of N-methyl-N-(N,N-dimethylaminoethyl)ethanolamine and maleic anhydride, as shown in the following reaction formula.

[0074] In some embodiments, the monomers used to prepare the filtration loss reducing agent are 2-acrylamido-2-methylpropanesulfonic acid, dimethylaminopropylmethacrylamide, a main-chain monomer, modified alkylene-based polyoxyethylene ether, 1-vinylimidazolium, and a monomer shown in formula (I), wherein the main-chain monomer is a combination of N,N-dimethylacrylamide and N,N-diethylacrylamide, and the ratio of N,N-dimethylacrylamide to N,N-diethylacrylamide is 1:0.3-0.5. The filtration loss reducing agent prepared according to this embodiment has significantly higher filtration loss reducing performance.

[0075] In other embodiments, the monomers used to prepare the filtration loss reducing agent are sodium p-styrene sulfonate, dimethyl diallyl ammonium chloride, a main-chain monomer, hydroxybutyl polyoxyethylene ether, 4-acryloylmorpholine, and a monomer shown in formula (I), wherein the main-chain monomer is a combination of N,N-dimethylacrylamide and N,N-diethylacrylamide, and the ratio of N,N-dimethylacrylamide to N,N-diethylacrylamide is 1:0.3-0.5. The filtration loss reducing agent prepared according to this embodiment has significantly higher filtration loss reducing performance.

[0076] In other embodiments, the monomers used to prepare the filtration loss reducing agent are sodium allyl sulfonate, acryloyloxyethyltrimethylammonium chloride, a main-chain monomer, 4-hydroxybutyl vinyl ether polyoxyethylene ether, N-vinylpyrrolidone, and the monomer shown in formula (I), wherein the main-chain monomer is a combination of N,N-dimethylacrylamide and N,N-diethylacrylamide, and the ratio of N,N-dimethylacrylamide to N,N-diethylacrylamide is 1:0.3-0.5. The filtration loss reducing agent prepared according to this embodiment has significantly higher filtration loss reducing performance.

[0077] In other embodiments, the monomers used to prepare the filtration loss reducing agent are sodium methacrylate sulfonate, dimethyl diallyl ammonium chloride, a main-chain monomer, ethylene glycol monovinyl polyoxyethylene ether, 4-vinylpyridine, and a monomer shown in formula (I), wherein the main-chain monomer is a combination of N,N-dimethylacrylamide and N,N-diethylacrylamide, and the ratio of N,N-dimethylacrylamide to N,N-diethylacrylamide is 1:0.3-0.5. The filtration loss reducing agent prepared according to this embodiment has significantly higher filtration loss reducing performance.

[0078] In the method described in this invention, the primary reaction is carried out in the presence of a first initiator, which is preferably a combination of a persulfate and a reducing agent. More preferably, in the first initiator, the weight ratio of the persulfate to the reducing agent is 1:0.1-0.5, preferably 1:0.2-0.4, and more preferably 1:0.2-0.3. The persulfate can be at least one selected from ammonium persulfate, potassium persulfate, and sodium persulfate. The reducing agent can be at least one selected from sodium bisulfite, ammonium bisulfite, and potassium bisulfite.

[0079] In the method described in this invention, the secondary reaction is carried out in the presence of a second initiator, which is preferably a combination of azobisisobutyramidine hydrochloride and a reducing agent. More preferably, the weight ratio of the azobisisobutyramidine hydrochloride to the reducing agent is 1:0.1-0.5, preferably 1:0.2-0.4, and more preferably 1:0.2-0.3. The reducing agent is at least one selected from sodium bisulfite, ammonium bisulfite, and potassium bisulfite.

[0080] In a preferred embodiment, the method for preparing the filtration loss reducing agent includes:

[0081] (1) Disperse the anionic hydration-enhancing monomer in water. If the solution is acidic, adjust the pH to 5-7 using an alkaline solution (such as NaOH solution).

[0082] (2) Add the main chain monomer, cationic positively adsorbed monomer, polyether monomer and cyclic monomer in sequence, stir and mix, then heat to 65-75℃, purge with nitrogen (or inert gas) for 10-30 min, add the first initiator, and react at a constant temperature for 4-6 h.

[0083] (3) Continue heating to 80-90℃, add hyperbranched monomer and second initiator, and continue the reaction for 2-4 hours;

[0084] (4) After the reaction is completed, the reaction product is washed with acetone 3-5 times, dried at 80-100℃ for 8-12h, and then pulverized to obtain a white or light yellow powder, which is the filtration loss reducer of the present invention suitable for use as a water-based drilling fluid filtration loss reducer.

[0085] In the method described in this invention, the weight ratio of water to the hyperbranched monomer can be 60-400:1, preferably 80-200:1.

[0086] In the method described in this invention, the weight ratio of the first initiator to the hyperbranched monomer can be 0.05-0.6:1, preferably 0.1-0.5:1.

[0087] In the method described in this invention, the weight ratio of the second initiator to the hyperbranched monomer can be 0.025-0.2:1, preferably 0.05-0.1:1.

[0088] The drilling fluid of this invention contains a filtration loss reducer, which is the filtration loss reducer provided by this invention. The drilling fluid according to this invention can maintain good rheological and filtration loss reduction properties under ultra-high temperature (e.g., 240°C) and saturated salt conditions, and remains stable for a long time.

[0089] The following examples further illustrate the strong adsorption hyperbranched filtration loss reducing agent for 240℃ saturated brine-based drilling fluids described in this invention, its preparation method, and its application. These examples are implemented based on the technical solution of this invention, providing detailed implementation methods and specific operating procedures; however, the scope of protection of this invention is not limited to the following examples.

[0090] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods in the art. Unless otherwise specified, the experimental materials used in the following embodiments are commercially available.

[0091] The following examples and comparative examples used 2-acrylamido-2-methylpropanesulfonic acid, sodium p-styrene sulfonate, sodium allyl sulfonate, sodium methpropylene sulfonate, dimethylaminopropylmethacrylamide, dimethyldiallylammonium chloride, acryloyloxyethyltrimethylammonium chloride, N,N-dimethylacrylamide, N,N-diethylacrylamide, N-vinylpyrrolidone, 1-vinylimidazolium, 4-vinylpyridine, 4-acryloylmorpholine, N-methyl-N-(N,N-dimethylaminoethyl)ethanolamine, maleic anhydride, N,N,N',N'-tetramethylethylenediamine, ammonium persulfate, potassium persulfate, azobisisobutyramidine hydrochloride, and sodium bisulfite, all of which were purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0092] The hyperbranched monomer TME was prepared by esterification of analytically pure N-methyl-N-(N,N-dimethylaminoethyl)ethanolamine and maleic anhydride.

[0093] Modified alkylene-based polyoxyethylene ether (PCB7230-1800), hydroxybutyl polyoxyethylene ether (PSV7630-2000), 4-hydroxybutyl vinyl ether polyoxyethylene ether (VPEG-1800), and ethylene glycol monovinyl polyoxyethylene ether (EPEG-2000) were all purchased from Wuhan Shanjiang Chemical Technology Co., Ltd. The number after the "-" indicates the molecular weight.

[0094] Sodium-based bentonite was purchased from Shandong Huawai Bentonite Co., Ltd.

[0095] The filtration loss reducer DSP 1, sulfonated asphalt FF-1, amino polyol AP-1, sulfonated methyl phenolic resin SMP-2, sulfonated lignite SMC, sulfonated lignite phenolic resin SPNH, lubricant RH-3, and plugging agent NP-1 were all purchased from Shandong Deshunyuan Petroleum Technology Co., Ltd.

[0096] The high-temperature cementing fluid loss reducing agent HT-1 was purchased from Chengdu Chuanfeng Chemical Engineering Co., Ltd.

[0097] In the examples, the weight-average molecular weight of the filtration loss reducer was obtained by gel permeation chromatography.

[0098] Example 1

[0099] The main chain monomers used in this embodiment are N,N-dimethylacrylamide and N,N-diethylacrylamide mixed at a mass ratio of 1:0.4.

[0100] (1) Add 20g of 2-acrylamido-2-methylpropanesulfonic acid to 130g of water and stir until fully dispersed. Adjust the pH value to 6 using a 50wt% NaOH solution.

[0101] (2) Add 10g of main chain monomer, 15g of dimethylaminopropylmethacrylamide, 15g of polyether monomer PCB7230-1800 and 8g of 1-vinylimidazole in sequence, stir until fully dispersed, and transfer the liquid to a three-necked flask;

[0102] (3) Heat to 65℃, purge with nitrogen for 20 min, then add 0.25 g ammonium persulfate and 0.05 g sodium bisulfite to initiate the reaction, and purge with nitrogen at a constant temperature for 5 h;

[0103] (4) Continue heating to 85°C, connect the flask to the condenser, add 0.8g of hyperbranched monomer TME, 0.05g of azobisisobutyramidine hydrochloride and 0.02g of sodium bisulfite, and continue the reaction for 3h;

[0104] (5) After the reaction is completed, the reaction product is washed three times with acetone, dried in an oven at 90°C for 10 hours and then pulverized. The resulting light yellow powder is the filtration loss reducer A1 of the present invention, with a weight-average molecular weight of 490,000.

[0105] Example 2

[0106] The main chain monomers used in this embodiment are N,N-dimethylacrylamide and N,N-diethylacrylamide mixed at a mass ratio of 1:0.3.

[0107] (1) Add 30g of sodium styrene sulfonate to 180g of water and stir until fully dispersed;

[0108] (2) Add 15g of main chain monomer, 20g of dimethyl diallyl ammonium chloride, 20g of polyether monomer PSV7630-2000 and 9g of 4-acryloylmorpholine in sequence, stir until fully dispersed, and transfer the liquid to a three-necked flask;

[0109] (3) Heat to 70℃, purge with nitrogen for 20 min, then add 0.3 g ammonium persulfate and 0.1 g sodium bisulfite to initiate the reaction, and purge with nitrogen at a constant temperature for 6 h;

[0110] (4) Continue heating to 90°C, connect the flask to the condenser, add 1g of hyperbranched monomer TME, 0.06g of azobisisobutyramidine hydrochloride and 0.02g of sodium bisulfite, and continue the reaction for 4h;

[0111] (5) After the reaction is completed, the reaction product is washed three times with acetone, dried in an oven at 90°C for 10 hours and then pulverized. The resulting white powder is the filtration loss reducer A2 of the present invention, with a weight-average molecular weight of 410,000.

[0112] Example 3

[0113] The main chain monomers used in this embodiment are N,N-dimethylacrylamide and N,N-diethylacrylamide mixed at a mass ratio of 1:0.4.

[0114] (1) Add 30g of sodium allyl sulfonate to 160g of water and stir until fully dispersed;

[0115] (2) Add 20g of main chain monomer, 10g of acryloyloxyethyltrimethylammonium chloride, 15g of polyether monomer VPEG-1800 and 6g of N-vinylpyrrolidone in sequence, stir until fully dispersed, and transfer the liquid to a three-necked flask;

[0116] (3) Heat to 70℃, purge with nitrogen for 20 min, then add 0.25 g potassium persulfate and 0.15 g sodium bisulfite to initiate the reaction, and purge with nitrogen at a constant temperature for 5 h;

[0117] (4) Continue heating to 80°C, connect the flask to the condenser, add 2g of hyperbranched monomer TME, 0.08g of azobisisobutyramidine hydrochloride and 0.02g of sodium bisulfite, and continue the reaction for 2h;

[0118] (5) After the reaction is completed, the reaction product is washed three times with acetone, dried in an oven at 90°C for 10 hours and then pulverized. The resulting white powder is the filtration loss reducer A3 of the present invention, with a weight-average molecular weight of 580,000.

[0119] Example 4

[0120] The main chain monomers used in this embodiment are N,N-dimethylacrylamide and N,N-diethylacrylamide mixed at a mass ratio of 1:0.5.

[0121] (1) Add 25g of sodium methyl allyl sulfonate to 190g of water and stir until fully dispersed;

[0122] (2) Add 10g of main chain monomer, 10g of dimethyl diallyl ammonium chloride, 10g of dimethylaminopropyl methacrylamide, 20g of polyether monomer EPEG-2000 and 8g of 4-vinylpyridine in sequence, stir until fully dispersed, and transfer the liquid to a three-necked flask;

[0123] (3) Heat to 75℃, purge with nitrogen for 20 min, then add 0.35 g potassium persulfate and 0.15 g sodium bisulfite to initiate the reaction, and purge with nitrogen at a constant temperature for 6 h;

[0124] (4) Continue heating to 85°C, connect the flask to the condenser, add 1g of hyperbranched monomer TME, 0.04g of azobisisobutyramidine hydrochloride and 0.01g of sodium bisulfite, and continue the reaction for 2h.

[0125] (5) After the reaction is completed, the reaction product is washed three times with acetone, dried in an oven at 90°C for 10 hours and then pulverized. The resulting light yellow powder is the filtration loss reducer A4 of the present invention, with a weight-average molecular weight of 360,000.

[0126] Comparative Example 1

[0127] The filtration loss reducer was prepared according to the method of Example 1, except that no anionic hydration-enhancing monomer (i.e., 2-acrylamido-2-methylpropanesulfonic acid) was added, resulting in filtration loss reducer D1.

[0128] Comparative Example 2

[0129] The filtration loss reducer was prepared according to the method of Example 1, except that no cationic positively charged adsorbent monomer (i.e., dimethylaminopropylmethacrylamide) was added, resulting in filtration loss reducer D2.

[0130] Comparative Example 3

[0131] The filtration loss reducer was prepared according to the method in Example 1, except that the polyether monomer PCB7230-1800 was not added, resulting in filtration loss reducer D3.

[0132] Comparative Example 4

[0133] The filtration loss reducer was prepared according to the method of Example 1, except that no cyclic monomer (i.e., 1-vinylimidazole) was added, resulting in filtration loss reducer D4.

[0134] Comparative Example 5

[0135] The filtration loss reducer was prepared according to the method of Example 1, except that no main chain monomer was added, resulting in filtration loss reducer D5.

[0136] Comparative Example 6

[0137] The filtration loss reducer was prepared according to the method in Example 1, except that the hyperbranched monomer TME was not added, resulting in filtration loss reducer D6.

[0138] Comparative Example 7

[0139] The filtration loss reducer was prepared according to the method of Example 1, except that the hyperbranched monomer TME in step (4) was replaced with an equal mass of N,N,N',N'-tetramethylethylenediamine, to obtain filtration loss reducer D7.

[0140] Comparative Example 8

[0141] The filtration loss reducer was prepared according to the method of Example 1, except that sodium bisulfite was not added in steps (3) and (4) to obtain filtration loss reducer D8.

[0142] Comparative Example 9

[0143] The filtration loss reducer was prepared according to the method of Example 1, except that the temperature was not increased in step (4), and the reaction temperature was kept at 65°C to obtain filtration loss reducer D9.

[0144] Application Example 1

[0145] (1) Preparation of drilling fluid F1: Add 4 parts by weight of sodium-based bentonite to 100 parts by weight of water, stir for 20 min, let stand at room temperature for 24 h, stir for another 20 min, add 3 parts by weight of filtration loss reducer A1, stir for 20 min, and obtain drilling fluid F1.

[0146] (2) Preparation of drilling fluid F2: Add 4 parts by weight of sodium-based bentonite to 100 parts by weight of water, stir for 20 min, let stand at room temperature for 24 h, stir for another 20 min, add 3 parts by weight of filtration loss reducer A2, stir for 20 min, and obtain drilling fluid F2.

[0147] (3) Preparation of drilling fluid F3: Add 4 parts by weight of sodium bentonite to 100 parts by weight of water, stir for 20 min, let stand at room temperature for 24 h, stir for another 20 min, add 3 parts by weight of filtration loss reducer A3, stir for 20 min, and obtain drilling fluid F3.

[0148] (4) Preparation of drilling fluid F4: Add 4 parts by weight of sodium-based bentonite to 100 parts by weight of water, stir for 20 min, let stand at room temperature for 24 h, stir for another 20 min, add 3 parts by weight of filtration loss reducer A4, stir for 20 min, and obtain drilling fluid F4.

[0149] Application Comparative Example 1

[0150] (1) Preparation of drilling fluid DF0: Add 4 parts by weight of sodium-based bentonite to 100 parts by weight of water, stir for 20 min, let stand at room temperature for 24 h, stir for another 20 min, add 3 parts by weight of commercially available filtration loss reducer DSP-1, stir for 20 min, and obtain drilling fluid DF0.

[0151] (2) Preparation of drilling fluid DF1: Add 4 parts by weight of sodium bentonite to 100 parts by weight of water, stir for 20 min, let stand at room temperature for 24 h, stir for another 20 min, add 3 parts by weight of filtration loss reducer D1, stir for 20 min, and obtain drilling fluid DF1.

[0152] (3) Preparation of drilling fluid DF2: Add 4 parts by weight of sodium-based bentonite to 100 parts by weight of water, stir for 20 min, let stand at room temperature for 24 h, stir for another 20 min, add 3 parts by weight of filtration loss reducer D2, stir for 20 min, and obtain drilling fluid DF2.

[0153] (4) Preparation of drilling fluid DF3: Add 4 parts by weight of sodium bentonite to 100 parts by weight of water, stir for 20 min, let stand at room temperature for 24 h, stir for another 20 min, add 3 parts by weight of filtration loss reducer D3, stir for 20 min, and obtain drilling fluid DF3.

[0154] (5) Preparation of drilling fluid DF4: Add 4 parts by weight of sodium bentonite to 100 parts by weight of water, stir for 20 min, let stand at room temperature for 24 h, stir for another 20 min, add 3 parts by weight of filtration loss reducer D4, stir for 20 min, and obtain drilling fluid DF4.

[0155] (6) Preparation of drilling fluid DF5: Add 4 parts by weight of sodium bentonite to 100 parts by weight of water, stir for 20 min, let stand at room temperature for 24 h, stir for another 20 min, add 3 parts by weight of filtration loss reducer D5, stir for 20 min, and obtain drilling fluid DF5.

[0156] (7) Preparation of drilling fluid DF6: Add 4 parts by weight of sodium bentonite to 100 parts by weight of water, stir for 20 min, let stand at room temperature for 24 h, stir for another 20 min, add 3 parts by weight of filtration loss reducer D6, stir for 20 min, and obtain drilling fluid DF6.

[0157] (8) Preparation of drilling fluid DF7: Add 4 parts by weight of sodium bentonite to 100 parts by weight of water, stir for 20 min, let stand at room temperature for 24 h, stir for another 20 min, add 3 parts by weight of filtration loss reducer D7, stir for 20 min, and obtain drilling fluid DF7.

[0158] (9) Preparation of drilling fluid DF8: Add 4 parts by weight of sodium bentonite to 100 parts by weight of water, stir for 20 min, let stand at room temperature for 24 h, stir for another 20 min, add 3 parts by weight of filtration loss reducer D8, stir for 20 min, and obtain drilling fluid DF8.

[0159] (10) Preparation of drilling fluid DF9: Add 4 parts by weight of sodium bentonite to 100 parts by weight of water, stir for 20 min, let stand at room temperature for 24 h, stir for another 20 min, add 3 parts by weight of filtration loss reducer D9, stir for 20 min, and obtain drilling fluid DF9.

[0160] Application Example 2

[0161] (1) Preparation of drilling fluid T1: Add 4 parts by weight of sodium bentonite to 100 parts by weight of water, stir for 20 min, let stand at room temperature for 24 h, stir for another 20 min, add 3 parts by weight of filtration loss reducer A1, 3 parts by weight of sulfonated asphalt FF-1 and 3 parts by weight of lubricant RH-3, stir for 20 min to obtain drilling fluid T1.

[0162] (2) Preparation of drilling fluid T2: Add 4 parts by weight of sodium bentonite to 100 parts by weight of water, stir for 20 min, let stand at room temperature for 24 h, stir for another 20 min, add 3 parts by weight of filtration loss reducer A1, 2 parts by weight of sulfonated methyl phenolic resin SMP-2, 2 parts by weight of sulfonated lignite SMC and 1 part by weight of sulfonated lignite phenolic resin SPNH, stir for 20 min to obtain drilling fluid T2.

[0163] (3) Preparation of drilling fluid T3: Add 4 parts by weight of sodium bentonite to 100 parts by weight of water, stir for 20 min, let stand at room temperature for 24 h, stir for another 20 min, add 3 parts by weight of filtration loss reducer A1, 3 parts by weight of plugging agent NP-1 and 2 parts by weight of amino polyol AP-1, stir for 20 min to obtain drilling fluid T3.

[0164] (4) Preparation of drilling fluid T4: Add 4 parts by weight of sodium bentonite to 100 parts by weight of water, stir for 20 min, let stand at room temperature for 24 h, stir for another 20 min, add 3 parts by weight of filtration loss reducer A1, 3 parts by weight of sulfonated asphalt FF-1, 3 parts by weight of lubricant RH-3, 3 parts by weight of plugging agent NP-1 and 2 parts by weight of amino polyol AP-1, stir for 20 min to obtain drilling fluid T4.

[0165] Application Comparative Example 2

[0166] The filter loss reducer A1 used in the preparation of drilling fluids T1-T4 in Application Example 2 was replaced with an equal weight of filter loss reducer DSP-1, and comparative drilling fluids DT1-DT4 were prepared respectively.

[0167] Test Example 1

[0168] Four groups of drilling fluids, F1-F4 and DF0-DF9, were taken in 400 mL each. After stirring at 8000 rpm for 20 min, 36 wt% NaCl, 5 wt% CaCl2, 10 wt% KCl, and a compound salt (15 wt% NaCl + 7 wt% KCl + 5 wt% CaCl2) were added respectively. After stirring for another 20 min, the mixture was transferred to a stainless steel aging tank and kept at 240℃ for 16 hours. After aging, the mixture was cooled to room temperature and stirred at 8000 rpm for 20 min. The apparent viscosity (AV, mPa·s), plastic viscosity (PV, mPa·s), dynamic shear force (YP, Pa), and API filtration loss (FL) of the above drilling fluids were determined according to the petroleum and natural gas industry standard GB / T 16783.1-2014 "Field Testing of Drilling Fluids for Petroleum and Natural Gas Industry - Part 1: Water-based Drilling Fluids". API and high temperature and high pressure filtration loss FL HTHP 240℃ The results are shown in Table 1-4.

[0169] Table 1: Drilling fluid performance test (36wt% NaCl)

[0170] Table 2: Drilling fluid performance test (5wt% CaCl2)

[0171] Table 3: Drilling fluid performance test (10wt% KCl)

[0172] Table 4: Drilling Fluid Performance Tests (Compound Salt)

[0173] As can be seen from the data in Tables 1-4, the filtration loss reducer of the present invention has a significantly better filtration loss reduction effect. The filtration loss reducer of the present invention can achieve good filtration loss reduction effects under conditions of 240℃ high temperature, 36wt% NaCl, 5wt% CaCl2, and 10wt% KCl, which can meet the needs of ultra-deep and extra-deep drilling.

[0174] Test Example 2

[0175] 400 mL of drilling fluid F1-F4 was taken respectively, stirred at 8000 rpm for 20 min, and then rolled at 240℃ for 1 day, 3 days, 5 days, 7 days, and 10 days. After aging, it was cooled to room temperature and taken out, and stirred at 8000 rpm for 20 min. The apparent viscosity (AV, mPa.s), plastic viscosity (PV, mPa.s), dynamic shear force (YP, Pa), and API filtration loss (FL) of the above drilling fluids were determined according to the petroleum and natural gas industry standard GB / T 16783.1-2014 "Field Testing of Drilling Fluids for Petroleum and Natural Gas Industry - Part 1: Water-based Drilling Fluids". API and high temperature and high pressure filtration loss FL HTHP 240℃ The results are shown in Table 5.

[0176] Table 5: Drilling Fluid Performance Tests (Long-Term Aging)

[0177] As shown in Table 5, the drilling fluid with the filtration loss reducer of the present invention exhibits a decrease in viscosity after prolonged aging, but still maintains good rheological properties and retains a low filtration loss. After aging at 240℃ for 10 days, the high-temperature and high-pressure filtration loss of the drilling fluid is less than 25 mL, demonstrating the ultra-long-term stability of the filtration loss reducer of the present invention, which can effectively reduce filtration loss for an extended period in field applications.

[0178] Test Example 3

[0179] 400 mL of drilling fluids T1-T4 and DT1-DT4 were taken separately, stirred at 8000 rpm for 20 min, and then placed into a stainless steel aging tank. The tank was kept at 240℃ and rolled for 16 hours. After aging, the fluids were cooled to room temperature and then stirred at 8000 rpm for 20 min. The apparent viscosity (AV, mPa·s), plastic viscosity (PV, mPa·s), dynamic shear force (YP, Pa), and API filtration loss (FL) of the above drilling fluids were determined according to the petroleum and natural gas industry standard GB / T 16783.1-2014 "Field Testing of Drilling Fluids for Petroleum and Natural Gas Industry - Part 1: Water-based Drilling Fluids". API and high temperature and high pressure filtration loss FL HTHP 240℃ The results are shown in Table 6.

[0180] Table 6: Drilling Fluid Performance Tests

[0181] As shown in Table 6, the fluid loss reducer of this invention exhibits good compatibility with common commercially available drilling fluid treatment agents such as sulfonated asphalt FF-1, lubricant RH-3, and plugging agent NP-1. When used in combination, they can synergistically enhance each other's effects, providing convenience for configuring drilling fluid systems and demonstrating the good compatibility and universality of this fluid loss reducer. In contrast, the commercially available fluid loss reducer DSP-1, besides being weaker in performance than the fluid loss reducer of this invention, also has poor compatibility with some treatment agents, and its performance is further reduced when used together.

[0182] Test Example 4

[0183] The effectiveness of the fluid loss reducer of the present invention as a fluid loss reducer in cementing fluids was tested.

[0184] According to the relevant provisions of the petroleum and natural gas industry standard SY / T5504.2-2013 "Evaluation Method of Oil Well Cement Admixtures Part 2: Fluid Loss Reducing Agents" and the national standard GB / T19139-2012 "Test Methods for Oil Well Cement", the performance of fluid loss reducing agents A1-A4 prepared in Examples 1-4 and the commercially available high-temperature cementing fluid loss reducing agent HT-1 was evaluated. Initial consistency, API fluid loss, and free fluid were measured at a test temperature of 240℃ and an addition amount of 5 wt% to the cement slurry. The results are shown in Table 7.

[0185] Table 7: Cementing Fluid Loss Test

[0186] As can be seen from the data in Table 7, the fluid loss reducer of the present invention can also play a good role when used as a cementing fluid loss reducer. Under ultra-high temperature conditions of 240℃, it can keep the cementing cement at a low initial consistency, with an API fluid loss of less than 26mL and no free fluid precipitation. Its performance is significantly better than the commercially available high temperature cementing fluid loss reducer HT-1.

[0187] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A fluid loss additive characterized in that, The filtrate reducer comprises: a first structural unit provided by an anionic hydration-enhancing monomer; a second structural unit provided by a cationic positive adsorption monomer; a third structural unit provided by a main chain monomer; a fourth structural unit provided by a cyclic monomer; a fifth structural unit provided by a polyether monomer; a sixth structural unit provided by a hyperbranched structure monomer; wherein the main chain monomer is N,N-dimethyl acrylamide and / or N,N-diethyl acrylamide, and the weight average molecular weight of the filtrate reducer is 200,000 to 800,000.

2. The fluid loss additive of claim 1, wherein, The weight ratio of the first structural unit, the second structural unit, the third structural unit, the fourth structural unit, the fifth structural unit and the sixth structural unit is (10-60):(5-40):(5-40):(2-20):(5-40):1, preferably (20-30):(10-20):(10-20):(5-10):(10-20):

1.

3. The fluid loss additive of claim 1 or 2, wherein, The anionic hydration-enhancing monomer is at least one of 2-acrylamido-2-methylpropanesulfonic acid, sodium p-styrenesulfonate, sodium allylsulfonate and sodium methacrylsulfonate.

4. The fluid loss additive of claim 1 or 2, wherein, The cationic positive adsorption monomer is at least one of dimethylaminopropyl methacrylamide, dimethyldiallylammonium chloride and acryloyloxyethyl trimethyl ammonium chloride.

5. The fluid loss additive of claims 1 or 2, wherein, The main chain monomer is a combination of N,N-dimethyl acrylamide and N,N-diethyl acrylamide, and the weight ratio of N,N-dimethyl acrylamide to N,N-diethyl acrylamide is 1:0.1-1, preferably 1:0.3-0.

5.

6. The fluid loss additive of claims 1 or 2, wherein, The cyclic monomer is at least one of N-vinylpyrrolidone, 1-vinylimidazole, 4-vinylpyridine and 4-acryloylmorpholine.

7. The fluid loss additive of claims 1 or 2, wherein, The polyether monomer is at least one of modified alkylene alkylene polyoxyethylene ether, hydroxybutyl polyoxyethylene ether, 4-hydroxybutyl vinyl ether polyoxyethylene ether and ethylene glycol monovinyl polyoxyethylene ether. Preferably, the molecular weight of the polyether monomer is 1500-4000.

8. The fluid loss additive of claims 1 or 2, wherein, The structural formula of the hyperbranched structure monomer is shown as formula (I), 9. A method for preparing a fluid loss additive, characterized by, The method comprises: under an inert atmosphere, subjecting an anionic hydration-enhancing monomer, a cationic positive adsorption monomer, a main chain monomer, a cyclic monomer and a polyether monomer to a first reaction in the presence of a first initiator; subjecting the product obtained after the first reaction to a second reaction in the presence of a second initiator; wherein the main chain monomer is N,N-dimethyl acrylamide and / or N,N-diethyl acrylamide.

10. The method of claim 9, wherein, The weight ratio of the anionic hydration-enhancing monomer, the cationic positive adsorption monomer, the main chain monomer, the cyclic monomer, the polyether monomer and the hyperbranched structure monomer is (10-60):(5-40):(5-40):(2-20):(5-40):1, preferably (20-30):(10-20):(10-20):(5-10):(10-20):

1.

11. The method according to claim 9 or 10, characterized in that, The anionic hydration-enhancing monomer is at least one of 2-acrylamido-2-methylpropanesulfonic acid, sodium p-styrenesulfonate, sodium allylsulfonate and sodium methacrylsulfonate.

12. The method according to claim 9 or 10, characterized in that, The cationic positive adsorption monomer is at least one of dimethylaminopropyl methacrylamide, dimethyldiallylammonium chloride and acryloyloxyethyl trimethyl ammonium chloride.

13. The method of claim 9 or 10, wherein, The main chain monomer is a combination of N,N-dimethyl acrylamide and N,N-diethyl acrylamide, and the weight ratio of N,N-dimethyl acrylamide to N,N-diethyl acrylamide is 1:0.1-1, preferably 1:0.3-0.

5.

14. The method of claim 9 or 10, wherein, The cyclic monomer is at least one of N-vinyl pyrrolidone, 1-vinylimidazole, 4-vinyl pyridine and 4-acryloyl morpholine.

15. The method of claim 9 or 10, wherein, The polyether monomer is at least one of modified alkylene alkenyl polyoxyethylene ether, hydroxybutyl polyoxyethylene ether, 4-hydroxybutyl vinyl ether polyoxyethylene ether and ethylene glycol monovinyl polyoxyethylene ether. Preferably, the molecular weight of the polyether monomer is 1500-4000.

16. The method of claim 9 or 10, wherein, The structural formula of the hyperbranched structural monomer is shown as formula (I), 17. The method of claim 9 or 10, wherein, The first initiator is a combination of persulfate and reducing agent, and the weight ratio of the persulfate to the reducing agent is 1:0.1-0.5; Preferably, the persulfate is at least one of ammonium persulfate, potassium persulfate and sodium persulfate; Preferably, the reducing agent is at least one of sodium bisulfite, ammonium bisulfite and potassium bisulfite.

18. The method of claim 9 or 10, wherein, The second initiator is a combination of azobisdimethylamidinium hydrochloride and reducing agent, and the weight ratio of the azobisdimethylamidinium hydrochloride to the reducing agent is 1:0.1-0.5; Preferably, the reducing agent is at least one of sodium bisulfite, ammonium bisulfite and potassium bisulfite.

19. The method of claim 9 or 10, wherein, The temperature of the secondary reaction is 5-25℃ higher than that of the primary reaction; Preferably, the temperature of the primary reaction is 65-75℃, and the temperature of the secondary reaction is 80-90℃.

20. A drilling fluid, characterized by, The drilling fluid contains the filtrate reducer according to any one of claims 1-8.

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