CN115678518B - Environment-friendly high-temperature-resistant saturated brine high-density polymer drilling fluid and preparation and application thereof - Google Patents
Environment-friendly high-temperature-resistant saturated brine high-density polymer drilling fluid and preparation and application thereof Download PDFInfo
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Abstract
The invention provides an environment-friendly high-temperature-resistant saturated brine high-density polymer drilling fluid system, and a preparation method and application thereof. The environment-friendly high-temperature-resistant saturated brine high-density polymer drilling fluid system comprises the following raw materials in parts by mass: 100 parts of water, 1-2 parts of bentonite, 1-2 parts of attapulgite, 0.1-0.4 part of alkalinity regulator, 2-3 parts of high temperature resistant and salt resistant filtrate reducer, 2-3 parts of polymeric alcohol, 1-4 parts of flexible plugging agent, 2-5 parts of polymer brush lubricant, 36.5 parts of sodium chloride and 3-8 parts of formate. The environment-friendly high-density drilling fluid system can resist high temperature of 200 ℃ and saturated salt, has good rheological property, plugging property and lubricating property, and meets the environment-friendly requirement of an environment-sensitive area because no sulfonated material is used.
Description
Technical Field
The invention relates to an environment-friendly high-temperature-saturation-resistant brine high-density polymer drilling fluid system and a preparation method and application thereof, belonging to the field of oilfield chemistry in petroleum industry.
Background
With the gradual shortage of middle and shallow hydrocarbon resources, deep ultra-deep hydrocarbon drilling has become an important way and direction to acquire more hydrocarbon resources. But deep stratum has high bottom hole temperature pressure and complex geological conditions (salt rock layers and salt paste layers are mostly existing), and the deep stratum has great challenges on the performance of drilling fluid. If the drilling fluid can not meet the performance requirements, complex situations or safety accidents such as well collapse, drill sticking, well leakage, blowout and the like can be caused, and the drilling safety and efficiency are seriously restricted.
Technical difficulties of deep formation drilling fluids include: first, the bottom hole temperature is high, and the temperature resistance requirement on the drilling fluid is high. Second, the bottom hole pressure is high and the drilling fluid needs to have a high enough density to balance the formation pressure. Thirdly, drilling a salt rock stratum or a salt paste layer, and has high requirement on the salt resistance of drilling fluid. Oil-based drilling fluids or saturated brine drilling fluids are typically used to prevent dissolution of the salt. At present, a high-temperature-resistant saturated brine drilling fluid generally uses a sulfonated material to control high-temperature high-pressure filtration loss and seal micro-pores of a stratum. In China, common sulfonated materials mainly include: sulfonated asphalt, sulfonated lignite, sulfomethyl phenolic resin, sulfonated tannin extract and sulfonated tannin. In high temperature water-based drilling fluids, the amount of sulphonated material added is even as high as 6-15% in order to control the fluid loss. In recent years, some areas have gradually begun to restrict the use of sulfonated materials for environmental reasons. Therefore, high temperature resistant saturated brine drilling fluids that do not use sulfonated materials are becoming an important and difficult point of research in the drilling engineering community. Especially under the high-density condition, the rheological and filtration properties of the drilling fluid system are more difficult to regulate. In addition, under the condition of three highs (high temperature, high salt and high density), the lubricating performance of the drilling fluid system also needs to be emphasized.
The polymer drilling fluid using the synthetic polymer as a key material has great research and application prospects. How to develop a high-temperature-resistant and salt-resistant treating agent is a key for constructing an environment-friendly high-temperature-resistant and salt-resistant drilling fluid system, and in terms of the molecular structure design of the treating agent, the current research mainly comprises introducing a cationic monomer, a ring-containing structural monomer or a hydrophobic monomer and the like into the molecular structure of a polymer to improve the temperature resistance and salt resistance of the polymer. In terms of polymer fluid loss additives, the high temperature resistant fluid loss additives, drasetemp and Dracal D, of the Stant company are excellent products in the industry, and with respect to the synthesis of high temperature resistant polymer fluid loss additives, a number of documents report that 2-acrylamido-2-methylpropanesulfonic Acid (AMPS) is a very critical monomer, such as: both Chinese patent documents CN104531104A and CN105176499A use AMPS as a key synthetic raw material to prepare high temperature and salt resistant filtrate loss reducer; in the aspect of environment-friendly high temperature resistant and salt resistant plugging agents, the use of polymer particles mainly made of styrene has been increasingly studied, for example: chinese patent document CN111138594A discloses a modified polystyrene resin material with a cross-linked structure, which has excellent filtration loss reduction, blocking and collapse prevention performances, and has better temperature resistance, and can realize effective blocking and collapse prevention of a high-temperature stratum. In addition to using environment-friendly materials resistant to high temperature and salt, how to improve the temperature and salt resistance of the drilling fluid system by utilizing the synergistic effect of various materials is another key for constructing the environment-friendly high temperature and salt resistant drilling fluid system.
The construction of the existing drilling fluid system mainly has the following technical problems: (1) The existing environment-friendly drilling fluid system uses natural polymers and modified materials thereof as a viscosity-increasing filtrate reducer, has insufficient temperature resistance and salt resistance, is easy to degrade and lose efficacy under high temperature conditions, and cannot meet the drilling requirement of deep high-temperature stratum; (2) The existing high-temperature-resistant water-based drilling fluid system mostly uses sulfonated materials to regulate and control the filtration performance of the drilling fluid, and the sulfonated materials have the problems of high toxicity and difficult degradation although having the temperature resistance, and are gradually abandoned in an environment-sensitive area; (3) Under the high-density condition, in order to regulate the rheological property of the drilling fluid system, the performance requirement of the treating agent is further improved, and the existing treating agent is difficult to meet the requirement.
At present, the construction of the existing drilling fluid system mainly has the problem that the temperature resistance and the environmental protection cannot be achieved, the high-temperature-resistant high-density saturated brine drilling fluid without using sulfonated materials is lacking, and the drilling of deep ultra-deep oil and gas is difficult to meet. Therefore, the development of the high-temperature-resistant high-density saturated brine drilling fluid system without using sulfonated materials has important significance for guaranteeing the drilling of deep and ultra-deep oil and gas.
Disclosure of Invention
Aiming at the defects of the prior art, in particular to the problems that the construction of the current environment-friendly high-temperature-resistant and salt-resistant drilling fluid system has temperature resistance and environment protection cannot be achieved, the invention provides an environment-friendly high-temperature-resistant saturated brine high-density polymer drilling fluid system, and a preparation method and application thereof. The environment-friendly high-density drilling fluid system can resist high temperature of 200 ℃ and saturated salt, has good rheological property, plugging property and lubricating property, and meets the environment-friendly requirement of an environment-sensitive area.
The technical scheme adopted by the invention is as follows:
an environment-friendly high-temperature-resistant saturated brine high-density polymer drilling fluid system comprises the following raw materials in parts by mass: 100 parts of water, 1-2 parts of bentonite, 1-2 parts of attapulgite, 0.1-0.4 part of alkalinity regulator, 2-3 parts of high temperature resistant and salt resistant filtrate reducer, 2-3 parts of polymeric alcohol, 1-4 parts of flexible plugging agent, 2-5 parts of polymer brush lubricant, 36.5 parts of sodium chloride and 3-8 parts of formate.
According to the invention, the high-temperature-resistant and salt-resistant filtrate reducer is prepared by the following method:
dissolving N, N-dimethylacrylamide, 2-acrylamide-2-methylpropanesulfonic Acid (AMPS), a hydrophobic association cationic monomer, a vinyl monomer with a ring structure and an emulsifier in water, and regulating the pH value of the system to 7.0-8.0; heating to 60-70 ℃ in a nitrogen environment, adding an initiator, reacting for 0.5-1 hour at 60-70 ℃, adding a nano cross-linking agent, and continuing to react for 3-5 hours; after the reaction is finished, the obtained product is dried and crushed, and the high-temperature-resistant salt-resistant filtrate reducer is obtained; the high-temperature-resistant and salt-resistant filtrate reducer is a zwitterionic polymer with a micro-crosslinking structure.
Preferably, the hydrophobic association cationic monomer is one of carboxymethyl octadecyl methyl diallyl ammonium chloride, cetyl dimethyl allyl ammonium chloride, dodecyl dimethyl allyl ammonium chloride and tetradecyl dimethyl allyl ammonium chloride; the structural formulas of the carboxymethyl octadecyl methyl diallyl ammonium chloride, the cetyl dimethyl allyl ammonium chloride, the dodecyl dimethyl allyl ammonium chloride and the tetradecyl dimethyl allyl ammonium chloride are shown in the following formulas I-IV respectively:
preferably, the vinyl monomer with the ring structure is one of N-vinyl pyrrolidone, styrene and sodium styrenesulfonate.
Preferably, the mass ratio of the N, N-dimethylacrylamide, the 2-acrylamide-2-methylpropanesulfonic Acid (AMPS), the hydrophobically associating cationic monomer and the vinyl monomer with a ring structure is 20-30:40-55:5-10:12-25.
Preferably, the emulsifier is Span20, and the mass of the emulsifier is 0.1-0.3% of the total mass of N, N-dimethylacrylamide, 2-acrylamide-2-methylpropanesulfonic Acid (AMPS), hydrophobic association cationic monomer and vinyl monomer with a ring structure; the ratio of the mass of the emulsifier to the volume of water is 0.1-0.2 g/100 mL.
Preferably, the pH of the system is adjusted to 7.0-8.0 by using 30-40% sodium hydroxide aqueous solution by mass fraction.
Preferably, the initiator is ammonium persulfate or potassium persulfate; the mass of the initiator is 0.1-0.3% of the total mass of N, N-dimethylacrylamide, 2-acrylamide-2-methylpropanesulfonic Acid (AMPS), hydrophobic association cationic monomer and vinyl monomer with a ring structure.
Preferably, the nano cross-linking agent is nano silicon dioxide modified by a silane coupling agent, the silane coupling agent is gamma-methacryloxypropyl trimethoxy silane (KH 570), vinyl trimethoxy silane (KH-171) or vinyl tri (b-methoxyethoxy) silane, and the particle size of the nano silicon dioxide is 10-30nm; the mass of the nano cross-linking agent is 0.005-0.025% of the total mass of N, N-dimethylacrylamide, 2-acrylamide-2-methylpropanesulfonic Acid (AMPS), hydrophobic association cationic monomer and vinyl monomer with a ring structure, and more preferably 0.009-0.015%;
further preferably, the nano-crosslinking agent is prepared by the following method:
adding nano silicon dioxide into toluene, stirring and dispersing uniformly, then adding a silane coupling agent, and reacting for 1-3h at 70-80 ℃; after the reaction is finished, filtering and drying to obtain a modified nano silicon dioxide crosslinking agent; the ratio of the mass of the nano silicon dioxide to the volume of toluene is 3-6 g/100 mL; the mass ratio of the nano silicon dioxide to the silane coupling agent is 1:0.02-0.05.
According to the invention, preferably, the alkalinity regulator is one of sodium hydroxide, potassium hydroxide, sodium bicarbonate and sodium carbonate.
According to a preferred aspect of the present invention, the polymeric alcohol is a polymeric glycerol having an average molecular weight of 250-350.
According to the invention, the flexible blocking agent is preferably a high temperature resistant polymer microsphere nano blocking agent, which is prepared according to Chinese patent document CN 111499790A.
According to the invention, the polymer brush lubricant is polyacrylate with high grafting degree, which is prepared by polymerization of an acrylate monomer composition and has excellent temperature resistance; it is prepared according to the Chinese patent document CN 114805670A.
According to the invention, the formate is preferably one or a combination of more than two of sodium formate, potassium formate and cesium formate.
According to the invention, the environment-friendly high-temperature-saturation-resistant brine high-density polymer drilling fluid system also comprises a density regulator, wherein the density regulator is a heavy crystalThe addition amount of stone and barite can weight the drilling fluid system to the required density, and the density of the barite is 4.2-4.3g/cm 3 The method comprises the steps of carrying out a first treatment on the surface of the The density of the environment-friendly high-temperature-saturation-resistant brine high-density polymer drilling fluid system is 1.5-2.2g/cm 3 。
According to the application, the preparation method of the environment-friendly high-temperature-resistant saturated brine high-density polymer drilling fluid system comprises the following steps:
firstly, bentonite and attapulgite are added into water, an alkalinity regulator is added, and the mixture is stirred for 24 hours under the condition of 300r/min to prepare base slurry; adding a high-temperature-resistant salt-resistant filtrate reducer, a polymeric alcohol, a flexible plugging agent, a polymer brush lubricant, sodium chloride and formate into the base slurry, and stirring at a high speed for 20 minutes after each raw material is added; the rotating speed of the high-speed stirring is 5000r/min.
According to the application, the preparation method of the environment-friendly high-temperature-saturation-resistant brine high-density polymer drilling fluid system further comprises the following steps: after the formate is added, a density regulator is added, and stirring is carried out for 20min at a rotation speed of 5000r/min.
According to the application, the environment-friendly high-temperature-resistant saturated brine high-density polymer drilling fluid system is applied to deep ultra-deep oil and gas drilling.
The principle of the application is as follows:
(1) In the aspect of development of the treating agent, in order to improve the high temperature resistance and salt resistance of the polymer filtrate reducer, on the basis of conventional technical means, the technical means adopted in the synthesis process mainly have three points: firstly, in a molecular structure, a weak crosslinking structure is introduced to limit molecular chain movement so as to improve the temperature resistance of the polymer, and meanwhile, a lower crosslinking density is ensured so that the polymer can still be dissolved in water, so that the types, the addition amount and the addition timing of the nano crosslinking agent have important influence on the filtrate reducer; secondly, an anionic group (sulfonic acid group) and a cationic group (quaternary ammonium salt group) are simultaneously introduced into the molecular structure, the anti-polyelectrolyte effect of the zwitterionic polymer is utilized to improve the salt resistance of the polymer, and the gel protection effect is provided through the adsorption of negative charges on the surface of clay; thirdly, the cationic monomer is provided with a hydrophobic group, so that the synthesized product can further improve the temperature resistance and salt resistance through hydrophobic association, and meanwhile, the temperature resistance is further improved through the introduction of the annular monomer. Therefore, the inventor of the present application carries out a large number of experiments to determine the addition amount and the addition time of the specific cross-linking agent, and the cross-linking agent is added too early or too late, so that the performance of the obtained filtrate reducer is poor; meanwhile, a large number of monomers and proportions of the monomers are screened, and the specific monomer combination and the proportions of different monomers are finally selected, so that the temperature-resistant salt-resistant filtrate reducer with excellent performance is obtained.
(2) In the aspect of system construction, high-temperature high-pressure rheological property and high-temperature high-pressure filtration loss regulation and control are the most core technical difficulties in constructing a high-temperature-resistant saturated salt polymer water-based drilling fluid system. Under the high-density condition, the drilling fluid has good rheological property; under the high-temperature and high-pressure conditions, the filtration loss of the drilling fluid is required to be in a proper range. In order to achieve the above-mentioned difficulty, the following technical countermeasures are designed:
first, formate is used to improve the temperature resistance of the polymer-based treatment agent, mainly because the organic acid radical anion of formate can remove dissolved oxygen in water, thereby preventing the degradation of the polymer-based treatment agent of the invention.
And secondly, the bentonite and the high-temperature-resistant and salt-resistant clay are used in a compounding way. When the bentonite content in the drilling fluid is greater than a certain value, the drilling fluid loses fluidity at high temperature, which is called high-temperature gelation. Preventing high temperature gelation of drilling fluids is a key technology for high temperature resistant drilling fluids, and currently, the bentonite content is reduced, and the high Wen Jiaoning can be inhibited by using dispersing agents or diluents. The invention controls the bentonite content of the drilling fluid in a lower range to prevent high Wen Jiaoning. The attapulgite has strong inertia, can not be flocculated by electrolyte in salt water, and has high temperature resistance. Because the attapulgite clay has low pulping rate and small influence on rheological property, the attapulgite clay and bentonite are compounded to serve as clay of a drilling fluid system, so that the clay has temperature resistance, salt resistance and certain pulping rate.
Third, the 'synergistic effect' enhances the plugging performance of the system to regulate and control the high-temperature high-pressure filtration loss. The high-temperature high-pressure filtration loss regulation is the biggest difficulty in constructing high-temperature high-density polymer saturated brine drilling fluid, and the difficulty in obtaining lower filtration loss is high under the condition that good rheological property of the drilling fluid is ensured. The invention uses the combined action of two ways to improve the plugging performance so as to reduce the filtration loss. The flexible nano plugging agent is used for improving the quality of mud cakes and reducing the high-temperature high-pressure filtration loss; by utilizing the cloud point effect of the polymeric alcohol, when the temperature is higher than the cloud point of the polymeric alcohol, the polymeric alcohol is separated out from the drilling fluid and is adhered to a drilling tool and a well wall, so that the functions of film forming, plugging and fluid loss reduction can be achieved.
In addition, the high-temperature-resistant salt-resistant filtrate reducer is utilized to reduce the filtrate loss, and the filtrate loss is synergistic with the three polymer treatment agents, namely the flexible nanometer plugging agent and the polymer, so that the high-temperature high-pressure filtrate loss performance of the drilling fluid system is improved.
The invention has the following advantages:
1. the filtrate reducer provided by the invention has the advantages that the weak crosslinking structure is introduced to limit molecular chain movement so as to improve the temperature resistance of the polymer, and meanwhile, the lower crosslinking density is ensured so that the polymer can still be dissolved in water; the molecular structure of the filtrate reducer is simultaneously introduced with an anionic group (sulfonic acid group) and a cationic group (quaternary ammonium salt group), the anti-polyelectrolyte effect of the zwitterionic polymer is utilized to improve the salt resistance of the polymer, and the cationic monomer is simultaneously provided with a hydrophobic group, so that the synthesized product can further improve the temperature resistance and the salt resistance through hydrophobic association. Therefore, the fluid loss additive has excellent temperature resistance and salt resistance, and when the fluid loss additive is added into a drilling fluid system, compared with other fluid loss additives, the fluid loss additive can remarkably reduce the fluid loss under high temperature and high pressure conditions.
2. The environment-friendly high-temperature-resistant saturated salt-resistant high-density polymer system has excellent performance, high temperature resistance up to 200 ℃, high-temperature standing for 5 days, good sedimentation stability, and good rheological, plugging and lubricating properties, and the rolling recovery rate of easily-hydrated rock debris is similar to that of oil-based drilling fluid.
3. The environment-friendly high-temperature-resistant saturated salt-resistant high-density polymer system does not use sulfonated materials, and meets the environment-friendly requirement of an environment-sensitive area.
Detailed Description
The following detailed description of embodiments of the invention further provides for the implementation of embodiments of the invention, some of which are described below, but not all of which are described in detail below. Experimental technical methods and scientific terms used in the examples have the same meaning as commonly understood by one of ordinary skill unless otherwise indicated. The experimental consumables and reagents involved, as without any special remarks, are commercially available in general.
Bentonite, attapulgite, polyalcohol and barite used in the examples are provided by Shandong cis-source oil technology Co., ltd; the polyalcohol is polyglycerol with average molecular weight of 250-350.
The flexible blocking agent used in the examples was prepared according to chinese patent document CN111499790a, example 1;
The polymer brush lubricant used was prepared according to chinese patent document CN114805670a example 1.
The nanosilica used in the preparation example had a particle size of 20nm.
Preparation example 1 (fluid loss additive)
A preparation method of a high-temperature-resistant salt-resistant filtrate reducer comprises the following steps:
(1) Preparation of the nano cross-linking agent:
5g of nano silicon dioxide is added into 100mL of toluene, stirred and dispersed for 10 minutes at 2000r/min, then 0.15g of silane coupling agent gamma-methacryloxypropyl trimethoxy silane (KH 570) is added into the mixture of nano silicon dioxide and toluene, and the mixture is reacted for 2 hours at 75 ℃; after the reaction is completed, naturally filtering the mixture at room temperature, and drying the obtained solid to constant weight at 70 ℃ to obtain the nano cross-linking agent KH570-SiO 2 。
(2) 25g of N, N-dimethylacrylamide, 40g of 2-acrylamide-2-methylpropanesulfonic acid AMPS,7g of dodecyl dimethyl allyl ammonium chloride, 18g N-vinyl pyrrolidone and 0.2g of emulsifier Span 20 are dissolved in 150mL of water, and the pH of the system is adjusted to 7.0 by using a 40% sodium hydroxide aqueous solution in mass fraction; reacting in nitrogen environment, adding 0.2g ammonium persulfate initiator when heating to 60 ℃, reacting for 1 hour at 60 ℃, and adding 0.01g nanometer cross-linking agent Coupling agent KH570-SiO 2 The reaction was continued for 5 hours; after the reaction is completed, cooling to room temperature, drying the obtained product to constant weight at 80 ℃, and crushing to obtain the high-temperature-resistant salt-resistant filtrate reducer.
Preparation example 2 (fluid loss additive)
A preparation method of a high-temperature-resistant salt-resistant filtrate reducer comprises the following steps:
(1) Preparation of the nano cross-linking agent: step (1) of preparation example 1
(2) Prepared by aqueous solution polymerization, 23g of N, N-dimethylacrylamide, 45g of 2-acrylamide-2-methylpropanesulfonic acid AMPS,5g of dodecyl dimethyl allyl ammonium chloride, 17g of sodium styrene sulfonate and 0.2g of emulsifier Span 20 are dissolved in 150mL of water, and the pH of the system is adjusted to 7.0 by using 40% by mass of aqueous sodium hydroxide solution; reacting in nitrogen environment, adding 0.2g ammonium persulfate initiator when heating to 60 ℃, reacting for 1 hour at 60 ℃, and adding 0.01g nano cross-linking agent KH570-SiO 2 The reaction was continued for 5 hours; after the reaction is completed, cooling to room temperature, drying the obtained product to constant weight at 80 ℃, and crushing to obtain the high-temperature-resistant salt-resistant filtrate reducer.
Preparation example 3 (fluid loss additive)
A preparation method of a high-temperature-resistant salt-resistant filtrate reducer comprises the following steps:
(1) Preparation of the nano cross-linking agent:
5g of nano silicon dioxide is added into 100mL of toluene, stirred and dispersed for 10 minutes at 2000r/min, then 0.15g of silane coupling agent vinyl trimethoxy silane (KH 171) is added into the nano silicon dioxide toluene mixture, and the mixture is reacted for 2 hours at 75 ℃; after the reaction is completed, naturally filtering the mixture at room temperature, and drying the obtained solid to constant weight at 70 ℃ to obtain the nano cross-linking agent KH171-SiO 2 。
(2) 27g of N, N-dimethylacrylamide, 52g of 2-acrylamide-2-methylpropanesulfonic acid AMPS,5g of carboxymethyl octadecyl methyl diallyl ammonium chloride, 18g of sodium styrene sulfonate and 0.2g of emulsifier Span20 are dissolved in 150mL of water, and the pH of the system is adjusted to 7.0 by using a 40% sodium hydroxide aqueous solution in mass fraction; reacting in nitrogen environment, heating to 60 DEG CAdding 0.2g ammonium persulfate initiator, reacting at 60 ℃ for 1 hour, and then adding 0.01g nano cross-linking agent KH171-SiO 2 The reaction was continued for 5 hours; after the reaction is completed, cooling to room temperature, drying the obtained product to constant weight at 80 ℃, and crushing to obtain the high-temperature-resistant salt-resistant filtrate reducer.
Preparation example 4 (fluid loss additive)
A preparation method of a high-temperature-resistant salt-resistant filtrate reducer comprises the following steps:
(1) Preparation of the nano cross-linking agent: step (1) of preparation example 3
(2) 30g of N, N-dimethylacrylamide, 40g of 2-acrylamide-2-methylpropanesulfonic acid AMPS,5g of carboxymethyl octadecyl methyl diallyl ammonium chloride, 15. 15g N-vinylpyrrolidone and 0.2g of emulsifier Span20 are dissolved in 150mL of water, and the pH of the system is adjusted to 7.0 by using a 40% mass fraction of sodium hydroxide aqueous solution; reacting in nitrogen environment, adding 0.2g ammonium persulfate initiator when heating to 60 ℃, reacting for 1 hour at 60 ℃, and adding 0.01g nano cross-linking agent KH171-SiO 2 The reaction was continued for 5 hours; after the reaction is completed, cooling to room temperature, drying the obtained product to constant weight at 80 ℃, and crushing to obtain the high-temperature-resistant salt-resistant filtrate reducer.
Comparative preparation 1 (fluid loss additive)
The preparation method of the polymer filtrate reducer is as described in preparation example 1, except that: no nano-crosslinker was added.
Comparative preparation 2 (fluid loss additive)
The preparation method of the polymer filtrate reducer is as described in preparation example 1, except that: no dodecyl dimethyl allyl ammonium chloride was added.
Comparative preparation 3 (fluid loss additive)
The preparation method of the polymer filtrate reducer is as described in preparation example 1, except that: the dodecyldimethylallylammonium chloride in the reaction is exchanged for dimethyldiallylammonium chloride.
Comparative preparation 4 (fluid loss additive)
The preparation method of the polymer filtrate reducer is as described in preparation example 1, except that: n-vinylpyrrolidone was not added.
Comparative preparation 5 (fluid loss additive)
The preparation method of the polymer filtrate reducer is as described in preparation example 1, except that: the nano-crosslinking agent is added at 0.05g.
Comparative preparation 6 (fluid loss additive)
The preparation method of the polymer filtrate reducer is as described in preparation example 1, except that: the crosslinker was added at 0.002g.
Comparative preparation 7 (fluid loss additive)
The preparation method of the polymer filtrate reducer is as described in preparation example 1, except that: 50g of N, N-dimethylacrylamide are added.
Comparative preparation 8 (fluid loss additive)
The preparation method of the polymer filtrate reducer is as described in preparation example 1, except that: the nano-crosslinking agent is replaced by N, N-dimethyl bisacrylamide.
Test example 1 evaluation of fluid loss additive Performance
The fluid loss additives prepared in preparation examples 1 to 4 and comparative examples 1 to 8 were subjected to performance evaluation as follows:
preparing saturated brine-based slurry: slowly adding 16g of bentonite into 400mL of distilled water under stirring, and curing for 24h at room temperature to prepare bentonite-based slurry; 146g (36.5%) NaCl was added to 400mL of bentonite slurry, and the mixture was stirred at 5000r/min for 20min to obtain a saturated brine-based slurry.
2% of the filtrate reducer prepared in preparation examples 1-4 and comparative preparation examples 1-8 are respectively added into 400mL of saturated brine-based slurry (namely, 8g of filtrate reducer is added into 400mL of saturated brine-based slurry), stirring is carried out for 20min at 3000r/min, and rheological performance parameters such as apparent viscosity, plastic viscosity, dynamic shear force and the like of the prepared drilling fluid and API (application program interface) filtrate loss of the drilling fluid are evaluated according to GB/T16783.1-2014 oil and gas industry drilling fluid field test part 1 water-based drilling fluid. And (3) transferring the prepared drilling fluid into a roller heating furnace at 200 ℃, aging for 16 hours at high temperature, and measuring rheological performance parameters such as apparent viscosity, plastic viscosity, dynamic shear force and the like of the drilling fluid and API (application program interface) fluid loss of the drilling fluid again. The experimental results are shown in Table 1.
Table 1 results of evaluation of fluid loss additive properties
It can be seen from table 1 that both the pre-aging examples and the comparative examples significantly increase the viscosity of the saturated brine-based slurry and significantly reduce its fluid loss. And the sample of the embodiment has better viscosity increasing and fluid loss reducing effects. After 200 ℃ aging, the viscosity of the drilling fluid samples of the examples and comparative examples was significantly reduced due to the effect of high temperature aging. However, the API filtration loss of the sample of the embodiment is less than that of the sample before aging, and the API filtration loss is less than 5mL, and the sample still has good action and effect. The comparative preparation example 1 has the advantages that the viscosity of the drilling fluid is smaller due to the fact that the cross-linking agent is not used, the viscosity is seriously reduced after aging, but the fluid loss is still smaller than 10mL, so that the cross-linking agent mainly plays a role in increasing the cross-linking degree of the fluid loss agent, improving the viscosity to resist pyrolysis and having less influence on the fluid loss. In comparative preparation example 2, the molecular chain of the filtrate reducer does not have a hydrophobic association structure and an inverse polyelectrolyte effect (the molecular chain contains anions and cations simultaneously) due to the fact that the filtrate reducer does not contain hydrophobic association cationic monomers, so that the salt resistance of the drilling fluid is poor, and the filtrate loss of the drilling fluid is large before and after high-temperature aging. Comparative preparation 3 changes the hydrophobic association cationic monomer into the common cationic monomer, and can see that the filtrate reducer with the anti-polyelectrolyte effect can still maintain higher viscosity and lower filtrate loss in saturated brine drilling fluid, which shows that the anti-polyelectrolyte effect of the molecular chain of the filtrate reducer plays a dominant role in improving the temperature resistance and salt resistance of the filtrate reducer, and the hydrophobic association is secondary. The comparative preparation example 4 does not contain vinyl monomer with ring structure, the ring structure has good rigidity, but has larger steric hindrance, but can obviously improve the temperature resistance of the polymer, and removing the vinyl monomer with ring structure can increase the molecular weight flexibility of the polymer, so the drilling fluid has higher viscosity and shear force before aging, but the viscosity and shear force are obviously reduced due to poor temperature resistance after aging, the drilling fluid performance is unstable, and the fluid loss is obviously increased. The cross-linking agent of comparative preparation 5 is excessively added to cause poor solubility of the product in water, insufficient viscosity, reduced interaction with clay and increased fluid loss. Comparative preparation 6 the amount of crosslinking agent added is too small, resulting in good solubility of the product in water, too high viscosity, but poor temperature resistance. In comparative preparation example 7, the ratio of N, N-dimethylacrylamide monomer is too large, the product is easy to polymerize and has large molecular weight, but the monomer content of temperature resistance and salt resistance is relatively reduced, the viscosity is larger before aging, the viscosity is obviously reduced after aging, and the filtration performance is insufficient. In comparative preparation 8, the nano-crosslinker was replaced with N, N-dimethyl bisacrylamide, and the crosslinker was prone to chain scission at high temperature, resulting in a filtrate reducer with comparable performance.
In summary, it can be seen that the fluid loss additive prepared in the preparation example of the present invention has excellent fluid loss performance, and when the fluid loss additive is applied to preparing a drilling fluid system, the performance of the obtained drilling fluid system is obviously better than that of the fluid loss additive prepared in the comparative example, and the fluid loss additive prepared in the preparation example 1 is selected to prepare the drilling fluid system for illustration.
The high temperature and salt-resistant fluid loss additives used in the following examples and comparative examples (except comparative example 6) were the high temperature and salt-resistant fluid loss additives prepared in preparation example 1.
Example 1 (drilling fluid System)
An environment-friendly high-temperature-resistant saturated brine high-density polymer drilling fluid system comprises the following raw materials in parts by mass: 100 parts of water, 2 parts of bentonite, 1 part of attapulgite, 0.1 part of sodium hydroxide, 2 parts of high temperature-resistant salt-resistant filtrate reducer, 2 parts of polymeric alcohol, 3 parts of flexible plugging agent, 3 parts of polymer brush lubricant, 36.5 parts of sodium chloride and 5 parts of potassium formate, and weighting until the density of a drilling fluid system is 2.2g/cm by using barite 3 。
The preparation method of the environment-friendly high-temperature-resistant saturated brine high-density polymer drilling fluid system comprises the following steps:
firstly, bentonite andadding attapulgite together into water, adding sodium hydroxide, and stirring the mixture for 24 hours under the condition of 300r/min to prepare base slurry; sequentially adding a high-temperature-resistant salt-resistant filtrate reducer, a polymeric alcohol, a flexible plugging agent, a polymer brush lubricant, sodium chloride, potassium formate and barite into the base slurry, and stirring at a high speed for 20 minutes after each raw material is added; the rotation speed of the high-speed stirring is 5000r/min, and the density is 2.2g/cm 3 An environment-friendly high-temperature-resistant saturated brine high-density polymer drilling fluid system.
Example 2 (drilling fluid System)
An environment-friendly high-temperature-resistant saturated brine high-density polymer drilling fluid system comprises the following raw materials in parts by mass: 100 parts of water, 2 parts of bentonite, 2 parts of attapulgite, 0.1 part of sodium hydroxide, 2 parts of high temperature-resistant salt-resistant filtrate reducer, 2 parts of polyalcohol, 3 parts of flexible plugging agent, 3 parts of polymer brush lubricant, 36.5 parts of sodium chloride and 5 parts of potassium formate, and weighting until the density of a drilling fluid system is 2.2g/cm by using barite 3 。
The preparation method of the environment-friendly high-temperature-resistant saturated brine high-density polymer drilling fluid system is as described in example 1.
Example 3 (drilling fluid System)
An environment-friendly high-temperature-resistant saturated brine high-density polymer drilling fluid system comprises the following raw materials in parts by mass: 100 parts of water, 2 parts of bentonite, 1 part of attapulgite, 0.1 part of sodium hydroxide, 3 parts of high temperature-resistant salt-resistant filtrate reducer, 2 parts of polyalcohol, 3 parts of flexible plugging agent, 3 parts of polymer brush lubricant, 36.5 parts of sodium chloride and 5 parts of potassium formate, and weighting until the density of a drilling fluid system is 2.2g/cm by using barite 3 。
The preparation method of the environment-friendly high-temperature-resistant saturated brine high-density polymer drilling fluid system is as described in example 1.
Comparative example 1 (drilling fluid System)
A polymer drilling fluid system was as described in example 1, except that: 3 parts of bentonite are used instead of 2 parts of bentonite and 1 part of attapulgite.
Comparative example 2 (drilling fluid System)
A polymer drilling fluid system was as described in example 1, except that: no flexible blocking agent was added.
Comparative example 3 (drilling fluid System)
A polymer drilling fluid system was as described in example 1, except that: instead of 3 parts of the polymer brush lubricant, 3 parts of the lubricant methyl oleate was used.
Comparative example 4 (drilling fluid System)
A polymer drilling fluid system was as described in example 1, except that: instead of 3 parts of flexible blocking agent, 3 parts of ultrafine calcium carbonate (particle size 6 μm) were used.
Comparative example 5 (drilling fluid System)
A polymer drilling fluid system was as described in example 1, except that: no lubricant is added.
Comparative example 6 (drilling fluid System)
A polymer drilling fluid system was as described in example 1, except that: the high temperature resistant and salt resistant filtrate reducer is the filtrate reducer prepared in comparative preparation example 1.
Test example 2
The polymer drilling fluid systems prepared in examples 1-3 and comparative examples 1-6 were evaluated for the following properties:
(1) Rheological fluid loss evaluation
The apparent viscosity, plastic viscosity, dynamic shear force and other rheological performance parameters of the prepared drilling fluid system and the API fluid loss of the drilling fluid are evaluated according to GB/T16783.1-2014 oil and gas industry drilling fluid field test part 1 water-based drilling fluid. The drilling fluid system is transferred into a stainless steel high-temperature aging tank, and after aging for 16 hours at 200 ℃, the rheological parameters of the drilling fluid system, the API filtration capacity of the drilling fluid system and the high-temperature high-pressure filtration capacity at 200 ℃ are measured again. The experimental results are shown in Table 2.
(2) Suspension stability
Placing the drilling fluid system into an aging tank, aging at 200deg.C for different times, removing small amount of semitransparent fluid on the upper layer, and respectively extracting and transferring the drilling fluid on the upper half and the lower half of the aging tank to two by using a large-range injectorIn a high stirring cup. After the upper drilling fluid and the lower drilling fluid are uniformly stirred, the density ρ of the upper drilling fluid is respectively tested by using the density points for the drilling fluids t And density ρ of the lower drilling fluid b And (3) calculating the static sedimentation factor of the drilling fluid according to the formula (1). The results of the suspension stability measurements are shown in Table 3.
Wherein SF-sedimentation factor, dimensionless;
ρ t upper drilling fluid density, g/cm 3 ；
ρ b Lower drilling fluid density, g/cm 3 。
(3) Evaluation of blocking Property
The PPA high-temperature high-pressure permeability plugging tester is used for testing the filtration loss of a system to ceramic sand discs with different apertures, wherein the apertures of the ceramic sand discs are 3 mu m, 5 mu m and 10 mu m, and the testing condition is 200 ℃. The sand disc filtrate loss is equal to 30min filtrate volume times 2. The experimental results are shown in Table 4.
(4) Inhibition performance evaluation
Weighing 20g of dry easily-hydratable rock with the size of 6-10 meshes, and adding the rock into a prepared drilling fluid system. The drilling fluid is rolled and aged for 16 hours at 200 ℃, the drilling fluid is filtered through a 40-mesh sieve, clean water is used for fully flushing, the quality of the sieved rock is weighed after the sieved rock is dried in an oven at 105 ℃ for 4 hours, the rolling recovery rate of the drilling fluid system to the easy-to-hydrate shale is calculated, and a comparison experiment is carried out with the oil-based drilling fluid with the same density. The experimental results are shown in Table 5.
(5) Lubricating property
And (3) measuring the extreme pressure lubrication coefficient of the drilling fluid system after aging at 200 ℃ by using the extreme pressure lubricant, and comparing with the oil-based drilling fluid with the same density. Test conditions: the rotation speed is 60 rpm, and the torsion force is 16.95 N.m. The experimental results are shown in Table 6.
The formula of the oil-based drilling fluid is as follows: 240mL of 5# white oil plus 60mL of CaCl with mass fraction of 30% 2 Aqueous solution +3g organic soil Geltone II +4.5g emulsifier FACTANT +10g emulsifier EZ-MUL +2.5g phospholipid wetting agent +9.0g calcium oxide +barite (oil-based drilling fluid density after adding barite is 2.2 g/cm) 3 ) Oil-based drilling fluid treatments were all from harributone.
(6) Environmental protection performance test
According to Xinjiang Uygur autonomous region local standard comprehensive utilization pollution control requirement of drilling solid waste of oil and gas field (DB 65T 3997-2017), 50g of rock cuttings are added into 350mL of the drilling fluid system of example 1, and the pollutant content of drilling cuttings after drilling fluid pollution is tested. The experimental results are shown in Table 7.
Measurement results
Table 2 evaluation of rheological fluid loss properties of environmentally friendly high temperature resistant saturated brine high density drilling fluid system
As can be seen from Table 2, the drilling fluid systems of the examples and the comparative examples have good fluid loss performance before aging. The viscosity of the drilling fluid system of the embodiment 1, the embodiment 2 and the embodiment 3 is slightly reduced after aging, the API filtrate loss is small, the high-temperature high-pressure filtrate loss is less than 15mL, and the drilling fluid system of the embodiment has good temperature resistance, salt resistance and filtrate loss reduction performance. In example 3, the highest filtrate reducer content resulted in the highest viscosity and the lowest filtrate loss, indicating that the filtrate reducer had the greatest effect on the drilling fluid system. Example 2 because the attapulgite content is higher than example 1, the viscosity and shear force are also slightly higher, and the fluid loss is slightly smaller, which indicates that the attapulgite also has a certain temperature and salt resistance effect. In comparative example 1, the viscosity shear force is obviously reduced after aging due to the fact that the bentonite is not provided with attapulgite, the fluid loss is sharply increased, the performance of a drilling fluid system is greatly influenced by the soil phase content, and the salt resistance of the bentonite is poor, so that the requirement of the salt resistance cannot be met. Comparative example 2 lacks a flexible plugging agent, so that the lack of plugging material causes a rapid increase in high temperature and high pressure fluid loss despite a small change in viscosity after aging, indicating that the nano plugging agent has a similar greater effect on the drilling fluid system. The superfine calcium used in comparative example 4 is difficult to deform, and the flexible plugging agent is easy to deform, so that the effect of plugging the filtrate loss can be achieved through the self-adaptive hole and seam. Comparative example 3 a conventional lubricant methyl oleate was used instead of the polymer brush lubricant, and the polymer brush lubricant has good temperature and salt resistance characteristics due to its unique molecular structure, in addition to the effect on the lubricity of the system. The disruption of the "synergy" between the polymer treatments (fluid loss additives, plugging agents and brush polymers) is also responsible for the increased fluid loss of the drilling fluid system. The lubricant has a certain effect of reducing the filtration of the oil phase, so that the filtration performance of comparative example 5 is slightly poorer without adding the lubricant. The fluid loss additive of comparative example 6 is not a crosslinked structure product, and therefore has poor temperature resistance and high fluid loss after aging at high temperature.
Table 3 evaluation of suspension stability of drilling fluid system
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Sedimentation stability is a critical property of drilling fluids. If the sedimentation stability is not good, the sedimentation of the weighting material may cause stuck drilling and kick accidents or even more serious accidents. It can be seen from table 3 that the sedimentation coefficient of the drilling fluid is larger and larger with the long-time aging at high temperature, which means that the shear force and viscosity of the drilling fluid are also gradually reduced, and the internal structure of the drilling fluid is gradually destroyed. Example 1, example 2, example 3 had a sedimentation coefficient of less than 0.52 even after 96 hours of high temperature aging. The example samples are illustrated to have good resistance to high temperatures. The sedimentation coefficients of the comparative samples after 96 hours aging are all larger than 0.52, which indicates that the drilling fluid cannot bear high temperature for a long time and has poor temperature resistance, especially under the condition of high salt content. While the sedimentation factor of comparative example 1 is as high as 0.53, which indicates that the grid structure inside the drilling fluid is severely damaged, and the shear force and the rock carrying property of the drilling fluid are severely insufficient. It can be seen from comparative examples 1-3 that the polymer brush lubricant, the nano plugging agent, and the attapulgite have an important effect on maintaining the shear force of the drilling fluid.
Table 4 evaluation of high temperature high pressure plugging properties of drilling fluid systems
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As can be seen from table 4, since the pore size of the sand disc is larger than that of the high temperature and high pressure filter paper, the sand disc fluid loss is higher than that of the high temperature and high pressure filter paper under the same conditions. The method for reducing the fluid loss of the drilling fluid at high temperature and high pressure by improving the plugging performance of the drilling fluid is a main technical countermeasure for constructing the high-temperature-resistant polymer saturated brine drilling fluid system. The invention improves the plugging performance of the drilling fluid by the combined action of the flexible nanometer plugging agent and the cloud point effect of the polymer alcohol. The samples of the examples all had a sand disc fluid loss at 10 μm of less than 30mL. Comparative example 1 only contains bentonite with poor salt resistance, and the internal network structure of the drilling fluid is destroyed under the high-temperature and high-salt condition, so that the fluid loss is large. Comparative example 2 has a larger sand disc fluid loss at 10 μm than comparative example 3 due to the lack of nano plugging agent or the change of lubricant type. The comparative example results show that the nano plugging agent is critical to the plugging performance of the drilling fluid, and the attapulgite indirectly improves the plugging performance of the drilling fluid by maintaining the space network structure of the drilling fluid.
TABLE 5 evaluation of Rolling recovery of inhibition Performance of drilling fluids
| Sample of | Rolling recovery/% |
| Clean water | 13.2 |
| Oil-based drilling fluid | 98.6 |
| Example 1 | 95.5 |
| Example 2 | 95.8 |
| Example 3 | 96.3 |
| Comparative example 1 | 91.2 |
| Comparative example 2 | 89.7 |
| Comparative example 3 | 93.4 |
| Comparative example 4 | 94.7 |
| Comparative example 5 | 90.3 |
| Comparative example 6 | 94.8 |
The hydration inhibition performance of the drilling fluid is important to inhibit hydration expansion of clay minerals and stabilize a borehole wall stratum. Because the external phase of the oil-based drilling fluid is an oil phase, clay minerals do not basically expand in the oil, so that the oil-based drilling fluid has excellent inhibition performance, and the rolling recovery rate of the system is up to 98.6%. The rolling recovery rates of the examples are similar to those of oil-based drilling fluid systems and are all higher than 95%, which indicates that the drilling fluid systems have excellent inhibition performance. The attapulgite clay has a micro-filiform structure and can be coated on the surface of the rock to prevent the rock from hydration, so that the rolling recovery rate of the comparative example 1 is reduced. The nano plugging agent can be adsorbed on the surface of the rock to block the rock pores and prevent water invasion, so that hydration collapse of the rock is reduced, and the rolling recovery rate of the nano plugging agent in comparative example 2 is remarkably reduced. The comb-type polymer lubricant was adsorbed on the rock surface to change the wettability of the surface thereof, thereby increasing the resistance of water intrusion into the rock pores, so that the rolling recovery rate of comparative example 3 was lowered. The experimental results demonstrate that the good inhibition properties of the drilling fluid system are also a result of the "synergistic effect" of the components. The nano plugging agent in the drilling fluid system can be adsorbed on the surface of the rock to block the rock pores, so that the invasion of water is prevented; and the comb-shaped polymer lubricant can be adsorbed on the rock surface to change the wettability of the surface of the rock, so that the resistance of water invasion into rock pores is increased; the attapulgite has a micro-filiform structure and can be coated on the surface of the rock to prevent the rock from hydration collapse; the zwitterionic polymer high-temperature-resistant salt-resistant filtrate reducer has a hydrophobic structure and cationic groups, so that hydration of clay minerals is inhibited to a certain extent.
Table 6 evaluation of lubricating Properties of drilling fluid systems
| Sample of | Extreme pressure lubrication coefficient |
| Oil-based drilling fluid | 0.087 |
| Example 1 | 0.129 |
| Example 2 | 0.125 |
| Example 3 | 0.122 |
| Comparative example 1 | 0.138 |
| Comparative example 2 | 0.147 |
| Comparative example 3 | 0.228 |
| Comparative example 4 | 0.132 |
| Comparative example 5 | 0.452 |
| Comparative example 6 | 0.135 |
As can be seen from table 6, the samples of the examples, while not as lubricious as the oil-based drilling fluid, perform quite similar, indicating that the comb polymer has good lubricity in the high temperature, high density saturated brine drilling fluid and the drilling fluid has good lubricity. Comparative example 1 bentonite was easily compressed and agglomerated under high temperature and high salt conditions due to the lack of attapulgite, resulting in a reduction in lubricating properties. In comparative example 2, the absence of the nano plugging agent, the microscopic sphere shape of the nano plugging agent, also has a certain promoting effect on improving the lubricant of the drilling fluid. The methyl oleate in comparative example 3 has weak temperature resistance, and the drilling fluid has larger friction resistance after aging. In the high-temperature high-salt high-density drilling fluid, the conventional lubricant has the problems of thermal degradation and poor dispersibility, so that the lubricating performance is insufficient. Due to the lack of comb polymer, a significant reduction in lubrication performance can be seen. The lubricating properties of comparative example 4 were similar to those of the examples. Comparative example 5 was free of added lubricant and had a coefficient of friction much greater than that of each example. Comparative example 6 has lubricating properties close to those of the examples.
TABLE 7 pollutant content of cuttings after drilling fluid contamination
| Project | Standard requirements | Actual value |
| pH | 2.0-12.5 | 9.5 |
| Hexavalent chromium (mg/kg) | ≤13 | 0 |
| Copper (mg/kg) | ≤600 | 5.2 |
| Zinc (mg/kg) | ≤1500 | 10.0 |
| Nickel (mg/kg) | ≤150 | 9.6 |
| Lead (mg/kg) | ≤600 | 0.8 |
| Arsenic (mg/kg) | ≤20 | 0 |
| Benzo (a) pyrene mg/kg | ≤0.7 | 0 |
| Oil content (%) | ≤2 | 0.14 |
| COD(mg/L) | ≤150 | 35.2 |
| Moisture content (%) | ≤60 | 8.1 |
As can be seen from Table 7, after the sample of the example is polluted, the pollutant content indexes of the drill cuttings all meet the requirements of Xinjiang Uygur autonomous region local standard comprehensive utilization pollution control requirement of drilling solid waste of oil and gas field (DB 65T 3997-2017).
Comprehensive analysis, the zwitterionic polymer high-temperature-resistant salt-resistant filtrate reducer with the micro-crosslinking structure has good temperature resistance and salt resistance, and is a basis for ensuring that the environment-friendly high-temperature-resistant saturated brine high-density drilling fluid has good filtrate loss performance. The formate is utilized to improve the temperature resistance of the polymer treating agent, the attapulgite and bentonite are compounded to ensure the high-temperature rheological property of the drilling fluid, the flexible nano plugging agent and the polymeric alcohol cloud point effect act together to improve the plugging property of the drilling fluid system, and the comb-shaped polymer lubricant ensures the lubricity of the drilling fluid system under the high-temperature condition. Besides, the attapulgite and the comb-shaped polymer lubricant have certain promotion effect on the inhibition performance, and the comb-shaped polymer lubricant and the flexible nano plugging agent have certain promotion effect on the filtration performance. In general, the good performance of the environment-friendly high-temperature-saturation-resistant brine high-density drilling fluid is the result of the high-efficiency action and the synergistic effect of all components in the system, and the environment-friendly requirement of certain environment-sensitive areas is met because no sulfonated material is used.
Claims (10)
1. The environment-friendly high-temperature-resistant saturated brine high-density polymer drilling fluid is characterized by comprising the following raw materials in parts by mass: 100 parts of water, 1-2 parts of bentonite, 1-2 parts of attapulgite, 0.1-0.4 part of alkalinity regulator, 2-3 parts of high temperature resistant and salt resistant filtrate reducer, 2-3 parts of polymeric alcohol, 1-4 parts of flexible plugging agent, 2-5 parts of polymer brush lubricant, 36.5 parts of sodium chloride and 3-8 parts of formate;
the high-temperature-resistant salt-resistant filtrate reducer is prepared by the following steps:
dissolving N, N-dimethylacrylamide, 2-acrylamide-2-methylpropanesulfonic acid, a hydrophobic association cationic monomer, a vinyl monomer with a ring structure and an emulsifier in water, and regulating the pH value of the system to 7.0-8.0; heating to 60-70 ℃ in a nitrogen environment, adding an initiator, reacting for 0.5-1 hour at 60-70 ℃, adding a nano cross-linking agent, and continuing to react for 3-5 hours; after the reaction is finished, the obtained product is dried and crushed, and the high-temperature-resistant salt-resistant filtrate reducer is obtained; the high-temperature-resistant and salt-resistant filtrate reducer is a zwitterionic polymer with a micro-crosslinking structure; the hydrophobic association cationic monomer is one of carboxymethyl octadecyl methyl diallyl ammonium chloride, cetyl dimethyl allyl ammonium chloride, dodecyl dimethyl allyl ammonium chloride and tetradecyl dimethyl allyl ammonium chloride; the vinyl monomer with the ring structure is one of N-vinyl pyrrolidone, styrene and sodium styrenesulfonate; the mass ratio of the N, N-dimethylacrylamide to the 2-acrylamide-2-methylpropanesulfonic acid to the hydrophobically associating cationic monomer to the vinyl monomer with the ring structure is 20-30:40-55:5-10:12-25;
The nano cross-linking agent is nano silicon dioxide modified by a silane coupling agent, the silane coupling agent is gamma-methacryloxypropyl trimethoxy silane, vinyl trimethoxy silane or vinyl tri (b-methoxyethoxy) silane, and the particle size of the nano silicon dioxide is 10-30nm.
2. The environment-friendly high-temperature-resistant saturated brine high-density polymer drilling fluid according to claim 1, wherein the emulsifier is Span20, and the mass of the emulsifier is 0.1-0.3% of the total mass of N, N-dimethylacrylamide, 2-acrylamide-2-methylpropanesulfonic acid, hydrophobic association cationic monomer and vinyl monomer with a ring structure; the ratio of the mass of the emulsifier to the volume of water is 0.1-0.2g to 100mL;
adjusting the pH value of the system to 7.0-8.0 by using 30-40% sodium hydroxide aqueous solution by mass fraction;
the initiator is ammonium persulfate or potassium persulfate; the mass of the initiator is 0.1-0.3% of the total mass of N, N-dimethylacrylamide, 2-acrylamide-2-methylpropanesulfonic acid, hydrophobic association cationic monomer and vinyl monomer with a ring structure.
3. The environment-friendly high-temperature-saturation-resistant brine high-density polymer drilling fluid according to claim 1, wherein the mass of the nano cross-linking agent is 0.005-0.025% of the total mass of N, N-dimethylacrylamide, 2-acrylamide-2-methylpropanesulfonic acid, hydrophobic association cationic monomer and vinyl monomer with a ring structure.
4. The environment-friendly high-temperature-saturation-resistant brine high-density polymer drilling fluid according to claim 1, wherein the mass of the nano cross-linking agent is 0.009-0.015% of the total mass of N, N-dimethylacrylamide, 2-acrylamide-2-methylpropanesulfonic acid, hydrophobic association cationic monomer and vinyl monomer with a ring structure.
5. The environment-friendly high-temperature-resistant saturated brine high-density polymer drilling fluid according to claim 1, wherein the nano-crosslinking agent is prepared by the following method:
adding nano silicon dioxide into toluene, stirring and dispersing uniformly, then adding a silane coupling agent, and reacting for 1-3h at 70-80 ℃; after the reaction is finished, filtering and drying to obtain a modified nano silicon dioxide crosslinking agent; the ratio of the mass of the nano silicon dioxide to the volume of toluene is 3-6 g/100 mL; the mass ratio of the nano silicon dioxide to the silane coupling agent is 1:0.02-0.05.
6. The environmentally-friendly high-temperature-resistant saturated brine high-density polymer drilling fluid according to claim 1, wherein the alkalinity regulator is one of sodium hydroxide, potassium hydroxide, sodium bicarbonate and sodium carbonate; the polymeric alcohol is polymeric glycerol, and the average molecular weight of the polymeric glycerol is 250-350; the formate is one or the combination of more than two of sodium formate, potassium formate and cesium formate.
7. The environmentally friendly high temperature resistant saturated brine high density polymer drilling fluid of claim 1, further comprising a density modifier, wherein the density modifier is a barite, and wherein the amount of barite is such that the drilling fluid is weighted to a desired density.
8. The method for preparing the environment-friendly high-temperature-resistant saturated brine high-density polymer drilling fluid according to claim 1, which comprises the following steps:
firstly, bentonite and attapulgite are added into water, an alkalinity regulator is added, and the mixture is stirred for 24 hours under the condition of 300r/min to prepare base slurry; adding a high-temperature-resistant salt-resistant filtrate reducer, a polymeric alcohol, a flexible plugging agent, a polymer brush lubricant, sodium chloride and formate into the base slurry, and stirring at a high speed for 20 minutes after each raw material is added; the rotating speed of the high-speed stirring is 5000r/min.
9. The method for preparing the environment-friendly high-temperature-resistant saturated brine high-density polymer drilling fluid according to claim 8, which is characterized by further comprising the following steps: after the formate is added, a density regulator is added, and stirring is carried out for 20min at a rotation speed of 5000r/min.
10. The use of the environmentally friendly high temperature saturation brine resistant high density polymer drilling fluid of claim 1 in deep ultra deep oil and gas drilling.
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