CN115678518A - Environment-friendly high-temperature-resistant saturated saline water high-density polymer drilling fluid system and preparation method and application thereof - Google Patents
Environment-friendly high-temperature-resistant saturated saline water high-density polymer drilling fluid system and preparation method and application thereof Download PDFInfo
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Abstract
The invention provides an environment-friendly high-temperature saturated brine resistant 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 polyalcohol, 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, plugging and lubricating properties, and meets the environment-friendly requirement of environment-sensitive areas because a sulfonated material is not used.
Description
Technical Field
The invention relates to an environment-friendly high-temperature-resistant saturated brine high-density polymer drilling fluid system, a preparation method and application thereof, belonging to the field of oilfield chemistry in the petroleum industry.
Background
With the gradual shortage of middle and shallow layer oil and gas resources, deep layer and ultra-deep layer oil and gas drilling becomes an important way and direction for obtaining more oil and gas resources. But the deep stratum has high bottom temperature and pressure and complex geological conditions (most of which are salt rock layers and salt-paste layers), and provides great challenges for the performance of the drilling fluid. If the drilling fluid can not meet the performance requirements, complex conditions or safety accidents such as well collapse, drilling sticking, lost circulation, blowout and the like can be caused, and the safety and the efficiency of drilling are severely restricted.
Technical difficulties of deep formation drilling fluids include: first, the bottom hole temperature is high, which places high demands on the temperature resistance of the drilling fluid. Second, the bottom hole pressure is high and the drilling fluid needs to have a sufficiently high density to balance the formation pressure. Thirdly, drilling in a salt rock layer or a salt-gypsum layer has high requirements on the salt resistance of the drilling fluid. Oil-based drilling fluids or saturated brine drilling fluids are often used to prevent the dissolution of salts. At present, sulfonated materials are usually used for controlling the high-temperature high-pressure filtration loss and plugging formation micro-pores in the high-temperature saturated brine drilling fluid. In China, the commonly used sulfonated materials are mainly: sulfonated asphalt, sulfonated lignite, sulfomethyl phenolic resin, sulfonated tannin extract and sulfonated tannin. In high temperature water-based drilling fluids, sulfonated materials are added in amounts of even up to 6-15% in order to control fluid loss. In recent years, in view of environmental reasons, use of sulfonated materials is gradually being restricted in some areas. Therefore, the high temperature saturated salt water drilling fluid without using sulfonated materials is becoming the focus and difficulty of research in the drilling engineering community. Especially under the condition of high density, the rheological and fluid loss performance of the drilling fluid system is difficult to regulate and control. In addition, under the conditions of three high (high temperature, high salt and high density), the lubricating property of the drilling fluid system needs to be considered.
The polymer drilling fluid using the synthetic polymer as a key material has huge research and application prospects. How to develop the high temperature and salt resistant treating agent is the key to the construction of an environment-friendly high temperature and salt resistant drilling fluid system, and in the aspect of the molecular structure design of the treating agent, the current research mainly comprises the steps of introducing a cationic monomer, a monomer containing a ring structure or a hydrophobic monomer and the like into the molecular structure of a polymer to improve the temperature and salt resistance of the polymer. In terms of polymer fluid loss additives, dristm and Driscal D, high temperature resistant polymer fluid loss additives from the company zustan, are excellent products in the industry, and various documents report that 2-acrylamide-2-methylpropanesulfonic Acid (AMPS) is a very critical monomer for the synthesis of high temperature resistant polymer fluid loss additives, such as: chinese patent documents CN104531104A and CN105176499A both use AMPS as a key synthetic raw material to prepare the high temperature resistant and salt resistant filtrate reducer; in the field of environmental protection type high temperature resistant and salt resistant blocking agent, the use of polymer particles mainly made of styrene has been studied more and more, for example: chinese patent document CN111138594A discloses a modified polystyrene resin material with a cross-linked structure, which has excellent filtration loss reduction, plugging and anti-collapse properties, and has good temperature resistance, and can realize effective plugging and anti-collapse on high-temperature stratum. Besides using the environment-friendly materials with high temperature resistance and salt resistance, how to improve the temperature resistance 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 resistance and salt resistance 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 tackifying filtrate reducer, has insufficient temperature 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 a sulfonated material to regulate and control the filtration performance of the drilling fluid, and the sulfonated material has the problems of high toxicity and difficult degradation although having the temperature resistance, and is gradually abandoned in an environment sensitive area; (3) Under the condition of high density, the performance requirement of the treating agent is further improved in order to regulate and control the rheological property of a drilling fluid system, and the existing treating agent is difficult to meet the requirement.
At present, the construction of the existing drilling fluid system mainly has the problems that the temperature resistance and the environment protection cannot be considered at the same time, and the high-temperature-resistant high-density saturated brine drilling fluid without using a sulfonated material is lacked, so that the drilling of deep ultra-deep oil and gas is difficult to meet. Therefore, the development of a high-temperature-resistant high-density saturated brine drilling fluid system without using a sulfonated material has important significance for ensuring the drilling of deep ultra-deep oil and gas.
Disclosure of Invention
Aiming at the defects of the prior art, particularly the problem that the temperature resistance and the environment protection cannot be considered at the same time in the construction of the current environment-friendly high temperature resistant salt-resistant drilling fluid system, 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 disclosed by the invention can resist high temperature of 200 ℃ and saturated salt, has good rheological, plugging and lubricating properties, and meets the environment-friendly requirement of environment-sensitive areas.
The technical scheme adopted by the invention is as follows:
an environment-friendly high-temperature-resistant saturated saline water 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 polyalcohol, 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 fluid loss additive is prepared according to 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 adjusting 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, drying and crushing the obtained product to obtain the high-temperature-resistant salt-resistant filtrate reducer; 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, hexadecyl 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 hexadecyl dimethyl allyl ammonium chloride, the dodecyl dimethyl allyl ammonium chloride and the tetradecyl dimethyl allyl ammonium chloride are respectively shown as the following formulas I-IV:
preferably, the vinyl monomer with a ring structure is one of N-vinyl pyrrolidone, styrene and sodium styrene sulfonate.
Preferably, the mass ratio of the N, N-dimethylacrylamide, 2-acrylamide-2-methylpropanesulfonic Acid (AMPS), the hydrophobic association cationic monomer and the vinyl monomer with a ring structure is 20-30.
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), the hydrophobically associating cationic monomer and the vinyl monomer with a ring structure; the mass ratio of the emulsifier to the volume of water is 0.1-0.2g.
Preferably, the pH value of the system is adjusted to 7.0-8.0 by using 30-40% of 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), the hydrophobically associating cationic monomer and the 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-methacryloxypropyltrimethoxysilane (KH 570), vinyltrimethoxysilane (KH-171) or vinyltris (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 percent of the total mass of N, N-dimethylacrylamide, 2-acrylamide-2-methylpropanesulfonic Acid (AMPS), hydrophobically associating cationic monomer and vinyl monomer with a ring structure, and the mass is more preferably 0.009-0.015 percent;
further preferably, the nano-cross-linking 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 cross-linking agent; the mass ratio of the nano-silica to the toluene is 3-6 g/100mL; the mass ratio of the nano silicon dioxide to the silane coupling agent is 1.02-0.05.
According to the invention, the alkalinity regulator is preferably one of sodium hydroxide, potassium hydroxide, sodium bicarbonate and sodium carbonate.
Preferably, according to the invention, the polymeric alcohol is a polymeric glycerol having an average molecular weight of 250 to 350.
According to the invention, the flexible plugging agent is preferably a high-temperature-resistant polymer microsphere nano plugging agent which is prepared according to Chinese patent document CN 111499790A.
According to the invention, the polymer brush lubricant is preferably polyacrylate with high grafting degree and excellent temperature resistance, which is prepared by polymerization of acrylate monomer composition; it is prepared according to 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-resistant saturated brine high-density polymer drilling fluid system also comprises a density regulator, wherein the density regulator is barite, the addition amount of the barite is only required for weighting the drilling fluid system to the required density, and the density of the barite is 4.2-4.3g/cm 3 (ii) a The density of the environment-friendly high-temperature-resistant saturated saline water high-density polymer drilling fluid system is 1.5-2.2g/cm 3 。
According to the invention, the preparation method of the environment-friendly high-temperature-resistant saturated brine high-density polymer drilling fluid system comprises the following steps:
firstly, adding bentonite and attapulgite into water, adding an alkalinity regulator, and stirring the mixture for 24 hours under the condition of 300r/min to prepare base slurry; adding a high-temperature-resistant salt-resistant fluid loss additive, polyalcohol, a flexible plugging agent, a polymer brush lubricant, sodium chloride and formate into the base slurry, and stirring at a high speed for 20min after adding each raw material; the rotating speed of the high-speed stirring is 5000r/min.
According to the preferable preparation method of the environment-friendly high-temperature-resistant saturated brine high-density polymer drilling fluid system, the preparation method further comprises the following steps: after the formate is added, the density regulator is added, and the mixture is stirred for 20min at the rotating speed of 5000r/min.
According to the invention, the environment-friendly high-temperature-resistant saturated saline water high-density polymer drilling fluid system is applied to deep ultra-deep oil and gas drilling.
The principle of the invention is as follows:
(1) In the aspect of processing agent development, in order to improve the high-temperature resistance and salt resistance of the polymer fluid loss additive, on the basis of the conventional technical means, the technical means adopted in the synthesis process mainly comprises three points: firstly, a weak crosslinking structure is introduced into a molecular structure 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 type, the addition amount and the addition time of a nano crosslinking agent have important influences 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 salt resistance of the polymer is improved by utilizing the reverse polyelectrolyte effect of the zwitterionic polymer, and the gel protection effect is provided through adsorption with the negative charge on the clay surface; thirdly, the cationic monomer simultaneously carries a hydrophobic group, the synthesized product can further improve the temperature and salt resistance through hydrophobic association, and meanwhile, the introduction of the cyclic monomer further improves the temperature resistance. Therefore, the inventor of the present application conducts a large number of experiments to determine the addition amount and the addition timing of the specific cross-linking agent of the present invention, and the performance of the obtained fluid loss additive is poor if the cross-linking agent is added too early or too late; meanwhile, a large amount of monomers and the proportion are screened, and finally, the specific monomer combination and the proportion among different monomers are selected to obtain the temperature-resistant and salt-resistant filtrate reducer with excellent performance.
(2) In the aspect of system construction, high-temperature and high-pressure rheological property and high-temperature and high-pressure filtration loss regulation are the most central technical difficulties in the construction of a high-temperature saturated salt resistant polymer water-based drilling fluid system. Under the condition of high density, the drilling fluid has good rheological property; the drilling fluid loss under the conditions of high temperature and high pressure is in a proper range. In order to realize the difficulty, the following technical countermeasures are designed:
firstly, the formate is utilized to improve the temperature resistance of the polymer treating agent, and the organic acid radical anion of the formate can remove dissolved oxygen in water so as to prevent the polymer treating agent of the invention from degrading.
Secondly, bentonite and high temperature resistant and salt resistant clay are compounded for use. When the content of bentonite in the drilling fluid is more than a certain value, the drilling fluid loses fluidity at high temperature, which is called high-temperature gelation. The prevention of high-temperature gelation of the drilling fluid is a key technology of high-temperature resistant drilling fluid, and the high-temperature gelation can be inhibited by reducing the content of bentonite and using a dispersing agent or a diluent at present. The invention controls the bentonite content of the drilling fluid in a lower range to prevent high-temperature gelation. The attapulgite has strong inertia, can not be flocculated by electrolyte in saline water, and has high temperature resistance. Because the attapulgite slurrying rate is low, and the influence on the rheological property is small, the clay of the drilling fluid system is compounded by the attapulgite and the bentonite, so that the clay is resistant to temperature and salt and has a certain slurrying rate.
Thirdly, the plugging performance of the 'synergistic effect' enhanced system regulates the high-temperature and high-pressure filtration loss. The high-temperature and high-pressure filtration loss control is the biggest difficulty in constructing the high-temperature and high-density resistant polymer saturated brine drilling fluid, and the difficulty in obtaining low filtration loss is high under the condition that the drilling fluid has good rheological property. The invention uses two ways to improve the plugging performance 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, and the effects of film forming, plugging and filtration reduction can be achieved.
In addition, the high-temperature-resistant and salt-resistant fluid loss additive is used for reducing the fluid loss, and the fluid loss additive and three polymer treatment agents of the flexible nano plugging agent and the polymer are cooperatively used for improving the high-temperature and high-pressure fluid loss performance of the drilling fluid system.
The invention has the advantages that:
1. the filtrate reducer of the invention introduces weak cross-linking structure to limit molecular chain movement, thus improving the temperature resistance of the polymer, and simultaneously ensuring lower cross-linking density to ensure that the polymer can still be dissolved in water; an anionic group (sulfonic acid group) and a cationic group (quaternary ammonium salt group) are simultaneously introduced into the molecular structure of the fluid loss additive, the salt resistance of the polymer is improved by utilizing the reverse polyelectrolyte effect of the zwitterionic polymer, and the cationic monomer simultaneously has a hydrophobic group, so that the synthesized product can further improve the temperature and salt resistance through the hydrophobic association effect. Therefore, the filtrate reducer has excellent temperature resistance and salt resistance, and can remarkably reduce the filtrate loss under the conditions of high temperature and high pressure compared with other filtrate reducers when added into a drilling fluid system.
2. The environment-friendly high-temperature-resistant saturated salt-resistant high-density polymer system has excellent performance, the temperature resistance can reach 200 ℃, the sedimentation stability is good after the high-temperature standing for 5 days, the rolling recovery rate of rock debris easy to hydrate is close to that of oil-based drilling fluid, and the polymer system has good rheological, plugging and lubricating properties.
3. The environment-friendly high-temperature-resistant saturated salt-resistant high-density polymer system disclosed by the invention does not use a sulfonated material, and meets the environment-friendly requirement of an environment-sensitive area.
Detailed Description
The present invention will be described in detail with reference to examples, which are intended to illustrate only some, but not all, embodiments of the present invention. The experimental technical methods and scientific terms used in the examples have the same meanings as commonly understood by a person of ordinary skill in the art without specific descriptions. The involved experimental consumables and reagents are generally available from commercial sources if no special remarks exist.
The bentonite, the attapulgite, the polyalcohol and the barite used in the examples are provided by Shandong Shunyuan oil science and technology Limited; the used polymeric alcohol is polymeric glycerol with an average molecular weight of 250-350.
The flexible plugging 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 particle size of the nanosilica used in the preparation examples was 20nm.
Preparation example 1 (filtrate reducer)
A preparation method of a high-temperature-resistant salt-resistant filtrate reducer comprises the following steps:
(1) Preparing a nano cross-linking agent:
will 5Adding g of nano silicon dioxide into 100mL of toluene, stirring and dispersing for 10 minutes at 2000r/min, then adding 0.15g of silane coupling agent gamma-methacryloxypropyltrimethoxysilane (KH 570) into the nano silicon dioxide toluene mixture, and reacting for 2 hours at 75 ℃; after the reaction is finished, naturally cooling to room temperature, performing suction filtration, drying the obtained solid at 70 ℃ to constant weight 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-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 an aqueous solution of sodium hydroxide with the mass fraction of 40%; reacting in nitrogen environment, heating to 60 deg.C, adding 0.2g ammonium persulfate initiator, reacting at 60 deg.C for 1 hr, adding 0.01g nanometer cross-linking agent KH570-SiO 2 Continuing the reaction for 5 hours; and after the reaction is finished, cooling to room temperature, drying the obtained product at 80 ℃ to constant weight, and crushing to obtain the high-temperature-resistant salt-resistant filtrate reducer.
Preparation example 2 (filtrate reducer)
A preparation method of a high-temperature-resistant salt-resistant filtrate reducer comprises the following steps:
(1) Preparing a nano cross-linking agent: same as preparation example 1 step (1)
(2) The preparation method is characterized by utilizing an aqueous solution polymerization method, 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 Span20 are dissolved in 150mL of water, and the pH value of the system is adjusted to 7.0 by using a sodium hydroxide aqueous solution with the mass fraction of 40%; reacting in nitrogen environment, heating to 60 deg.C, adding 0.2g ammonium persulfate initiator, reacting at 60 deg.C for 1 hr, adding 0.01g nanometer cross-linking agent KH570-SiO 2 Continuing the reaction for 5 hours; and after the reaction is finished, cooling to room temperature, drying the obtained product at 80 ℃ to constant weight, and crushing to obtain the high-temperature-resistant salt-resistant filtrate reducer.
Preparation example 3 (filtrate reducer)
A preparation method of a high-temperature-resistant salt-resistant filtrate reducer comprises the following steps:
(1) Preparing a nano cross-linking agent:
adding 5g of nano-silica into 100mL of toluene, stirring and dispersing for 10 minutes at 2000r/min, then adding 0.15g of silane coupling agent vinyltrimethoxysilane (KH 171) into the nano-silica toluene mixture, and reacting for 2 hours at 75 ℃; after the reaction is finished, naturally cooling to room temperature, performing suction filtration, drying the obtained solid at 70 ℃ to constant weight 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 carboxymethyloctadecyl methyldiallylammonium 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 sodium hydroxide aqueous solution with the mass fraction of 40%; reacting in nitrogen environment, heating to 60 deg.C, adding 0.2g ammonium persulfate initiator, reacting at 60 deg.C for 1 hr, and adding 0.01g nanometer cross-linking agent KH171-SiO 2 Continuing the reaction for 5 hours; and after the reaction is finished, cooling to room temperature, drying the obtained product at 80 ℃ to constant weight, and crushing to obtain the high-temperature-resistant salt-resistant filtrate reducer.
Preparation example 4 (filtrate reducer)
A preparation method of a high-temperature-resistant salt-resistant filtrate reducer comprises the following steps:
(1) Preparing a nano cross-linking agent: same as preparation example 3 step (1)
(2) 30g of N, N-dimethylacrylamide, 40g of 2-acrylamide-2-methylpropanesulfonic acid AMPS,5g of carboxymethyloctadecylmethyldiallylammonium chloride, 15g N-vinylpyrrolidone and 0.2g of an emulsifier Span20 are dissolved in 150mL of water, and the pH of the system is adjusted to 7.0 by using a 40% by mass aqueous sodium hydroxide solution; reacting in nitrogen environment, heating to 60 deg.C, adding 0.2g ammonium persulfate initiator, reacting at 60 deg.C for 1 hr, and adding 0.01g nanometer cross-linking agent KH171-SiO 2 Continuing the reaction for 5 hours; and after the reaction is finished, cooling to room temperature, drying the obtained product at 80 ℃ to constant weight, and crushing to obtain the high-temperature-resistant salt-resistant filtrate reducer.
COMPARATIVE PREPARATION EXAMPLE 1 (filtrate reducer)
A polymer fluid loss additive was prepared as described in preparative example 1, except that: no nanocrosslinker was added.
Comparative preparation example 2 (filtrate reducer)
A polymer fluid loss additive was prepared as described in preparative example 1, except that: dodecyl dimethyl allyl ammonium chloride was not added.
COMPARATIVE PREPARATION EXAMPLE 3 (filtrate reducer)
A polymer fluid loss additive was prepared as described in preparative example 1, except that: the dodecyl dimethyl allyl ammonium chloride in the reaction is changed into dimethyl diallyl ammonium chloride.
COMPARATIVE PREPARATION EXAMPLE 4 (filtrate reducer)
A polymer fluid loss additive was prepared as described in preparative example 1, except that: no N-vinylpyrrolidone was added.
Comparative preparation example 5 (filtrate reducer)
A polymer fluid loss additive was prepared as described in preparative example 1, except that: 0.05g of nano-crosslinking agent was added.
COMPARATIVE PREPARATION EXAMPLE 6 (filtrate reducer)
A polymer fluid loss additive was prepared as described in preparative example 1, except that: 0.002g of crosslinking agent was added.
COMPARATIVE PREPARATION EXAMPLE 7 (filtrate reducer)
A polymer fluid loss additive was prepared as described in preparative example 1, except that: 50g of N, N-dimethylacrylamide was added.
COMPARATIVE PREPARATION EXAMPLE 8 (filtrate reducer)
A polymer fluid loss additive was prepared as described in preparative example 1, except that: the nano cross-linking agent is replaced by N, N-dimethyl bisacrylamide.
Test example 1 evaluation of fluid loss additive Properties
The performance evaluation of the fluid loss additives prepared in preparation examples 1 to 4 and comparative preparation examples 1 to 8 was carried out by the following specific steps:
preparing saturated saline water base slurry: slowly adding 16g of bentonite into 400mL of distilled water while stirring, and then curing for 24 hours at room temperature to prepare bentonite-based slurry; 146g (36.5%) of NaCl was added to 400mL of each bentonite-based slurry, and the mixture was stirred at 5000r/min for 20min to obtain a saturated brine-based slurry.
2% of the fluid loss additive prepared in preparation examples 1-4 and comparative preparation examples 1-8 (namely 8g of the fluid loss additive is added into 400mL of saturated saline base slurry) is added into 400mL of saturated saline base slurry respectively, the mixture is stirred for 20min under the condition of 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 (American Petroleum and mineral) fluid loss of the drilling fluid are evaluated according to GB/T16783.1-2014 part 1 water-based drilling fluid field test. Transferring the prepared drilling fluid into a roller heating furnace at 200 ℃, aging at high temperature for 16h, and measuring rheological property parameters of the drilling fluid such as apparent viscosity, plastic viscosity, dynamic shear force and the like and API (American Petroleum institute) filtration loss of the drilling fluid. The results are shown in Table 1.
TABLE 1 evaluation results of fluid loss additive Properties
It can be seen from table 1 that both the pre-aging examples and comparative examples significantly increased the viscosity and significantly reduced the fluid loss of the saturated brine-based slurries. And the sample of the embodiment has better tackifying and fluid loss reducing effects. After aging at 200 ℃, the viscosity of the drilling fluid samples of the examples and comparative examples were significantly reduced due to the effect of high temperature aging. However, the API filtration loss of the samples in the examples is slightly increased compared with that before aging, and is less than 5mL, and the samples still have good effect. The viscosity of the drilling fluid is smaller due to the fact that no cross-linking agent is arranged in the comparative preparation example 1, the viscosity is reduced seriously after aging, but the fluid loss is still smaller than 10mL, and the cross-linking agent mainly plays a role in increasing the cross-linking degree of the fluid loss additive and improving the viscosity to resist high-temperature thermal decomposition, and has small influence on the fluid loss property. In comparative preparation example 2, because the filtrate reducer does not contain the hydrophobic association cationic monomer, the molecular chain of the filtrate reducer does not have a hydrophobic association structure and a reverse polyelectrolyte effect (the molecular chain contains anions and cations), so that the salt resistance of the drilling fluid is poor, and the drilling fluid filtration loss before and after high-temperature aging is large. In comparison with preparation example 3, the hydrophobic association cationic monomer is replaced by a common cationic monomer, so that the filtrate reducer with the reverse polyelectrolyte effect can still maintain higher viscosity and lower filtrate loss in the saturated saline drilling fluid, which indicates that the reverse polyelectrolyte effect of the molecular chain of the filtrate reducer has a dominant effect on improving the temperature and salt resistance of the filtrate reducer and the hydrophobic association effect is secondary. The comparative preparation example 4 does not contain the vinyl monomer with the ring structure, the ring structure has good rigidity, although the vinyl monomer with the ring structure has larger steric hindrance, the temperature resistance of the polymer can be obviously improved, the vinyl monomer with the ring structure is removed, the molecular weight flexibility of the polymer can be increased, so the drilling fluid has higher viscosity and shearing force before aging, but the viscosity and the shearing force are obviously reduced due to poorer temperature resistance after aging, the performance of the drilling fluid is unstable, and the filtration loss is also obviously increased. Comparative preparation example 5 excessive addition of the crosslinking agent causes deterioration in solubility of the product in water by transitional crosslinking, insufficient viscosity, reduced interaction with clay, and increased fluid loss. Comparative preparation example 6 in which the amount of the crosslinking agent added was too small, resulted in good solubility of the product in water and excessive viscosity, but poor temperature resistance. In comparative preparation example 7, the proportion of the N, N-dimethylacrylamide monomer is too large, the product has a high easily polymerizable molecular weight, but the content of the temperature-resistant and salt-resistant monomer is relatively reduced, so that the viscosity before aging is large, the viscosity after aging is obviously reduced, and the fluid loss performance is insufficient. In comparative preparation example 8, the nano cross-linking agent was replaced with N, N-dimethyl bisacrylamide, and the cross-linking agent was easily broken at high temperature, and the obtained fluid loss additive was superior in performance.
In conclusion, the fluid loss additive prepared by the preparation example of the invention has excellent fluid loss performance, the performance of the obtained drilling fluid system is obviously superior to that of the fluid loss additive prepared by a comparative example when the fluid loss additive is applied to prepare the drilling fluid system, and the fluid loss additive prepared by the preparation example 1 is selected to prepare the drilling fluid system for description.
The high temperature resistant, salt resistant fluid loss additives used in the following examples and comparative examples (except comparative example 6) were the high temperature resistant, salt resistant fluid loss additives prepared in preparative example 1.
Example 1 (drilling fluid System)
An environment-friendly high-temperature-resistant saturated saline water 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 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 the weight is increased by using barite until the density of a drilling fluid system is 2.2g/cm 3 。
The preparation method of the environment-friendly high-temperature-resistant saturated brine high-density polymer drilling fluid system comprises the following steps:
firstly, adding bentonite and attapulgite 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 and salt-resistant filtrate reducer, polyalcohol, 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 20min after adding each raw material; the high-speed stirring speed is 5000r/min, and the obtained density is 2.2g/cm 3 An environment-friendly high-temperature-resistant saturated saline water 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 the weight is increased by using barite until the density of a drilling fluid system is 2.2g/cm 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 saline water 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 and 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 the weight is increased by using barite until the density of a drilling fluid system is 2.2g/cm 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 as described in example 1, except that: 3 parts of bentonite were used instead of 2 parts of bentonite and 1 part of attapulgite.
COMPARATIVE EXAMPLE 2 drilling fluid System
A polymer drilling fluid system as described in example 1, except that: no flexible blocking agent is added.
COMPARATIVE EXAMPLE 3 drilling fluid System
A polymer drilling fluid system as described in example 1, except that: 3 parts lubricant methyl oleate was used instead of 3 parts polymer brush lubricant.
COMPARATIVE EXAMPLE 4 drilling fluid System
A polymer drilling fluid system 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 as described in example 1, except that: no lubricant was added.
COMPARATIVE EXAMPLE 6 drilling fluid System
A polymer drilling fluid system as described in example 1, except that: the high-temperature-resistant and salt-resistant fluid loss additive is the fluid loss additive 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) Evaluation of rheological fluid loss Properties
Rheological performance parameters such as apparent viscosity, plastic viscosity, dynamic shear force and the like of a prepared drilling fluid system and API (American Petroleum institute) filtration loss of the drilling fluid are evaluated according to GB/T16783.1-2014 part 1 water-based drilling fluid of the oil and gas industrial drilling fluid field test. And transferring the drilling fluid system into a stainless steel high-temperature aging tank, aging for 16h at 200 ℃, and then measuring the rheological parameters of the drilling fluid system, the API (American Petroleum institute) filtration loss of the drilling fluid system and the high-temperature high-pressure filtration loss at 200 ℃. The results are shown in Table 2.
(2) Suspension stability
And (3) putting the drilling fluid system into an aging tank, aging for different times at 200 ℃, removing a small amount of semitransparent liquid on the upper layer, and respectively pumping and transferring the drilling fluid on the upper half part and the drilling fluid on the lower half part of the aging tank into two high-stirring cups by using a wide-range injector. After the upper drilling fluid and the lower drilling fluid are uniformly stirred, the density rho of the upper drilling fluid is respectively tested by using a densimeter for drilling fluid t And density ρ of the lower drilling fluid b And calculating the static sedimentation factor of the drilling fluid according to the formula (1). 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 plugging Properties
The PPA high-temperature high-pressure permeability plugging tester is used for testing the filtration loss of a system on ceramic sand trays with different apertures, the apertures of the ceramic sand trays are 3 microns, 5 microns and 10 microns, and the testing condition is 200 ℃. The sand disc loss equals 30min filtrate volume multiplied by 2. The results are shown in Table 4.
(4) Evaluation of suppression Properties
Weighing 20g of dry rock easy to hydrate with the size of 6-10 meshes, and adding the rock into a prepared drilling fluid system. The drilling fluid is aged for 16 hours in a rolling way at 200 ℃, the drilling fluid is filtered through a 40-mesh sieve and is fully washed by clear water, after the rock left by sieving is dried for 4 hours in a drying oven at 105 ℃, the mass of the rock is weighed, the rolling recovery rate of the drilling fluid system to the mud shale easy to hydrate is calculated, and a comparison experiment is carried out with the oil-based drilling fluid with the same density. The results are shown in Table 5.
(5) Lubricating performance
The extreme pressure lubricating agent is used for measuring the extreme pressure lubricating coefficient of the drilling fluid system after aging at 200 ℃, and the extreme pressure lubricating coefficient is compared with the oil-based drilling fluid with the same density. And (3) testing conditions are as follows: the rotating speed is 60 rpm, and the torsion is 16.95 N.m. The results are shown in Table 6.
The formula of the oil-based drilling fluid comprises: 240mL 5# white oil +60mL CaCl with mass fraction of 30% 2 Aqueous solution, 3g of organic soil Geltone II, 4.5g of emulsifier FACTANT, 10g of emulsifier EZ-MUL, 2.5g of phospholipid wetting agent, 9.0g of calcium oxide and barite (the density of the oil-based drilling fluid after the barite is added is 2.2 g/cm) 3 ) Oil-based drilling fluid treatments are available from Haributton.
(6) Environmental protection Performance test
According to the requirements for comprehensive utilization of solid waste in oil and gas field drilling and pollution control (DB 65T 3997-2017) of local standard of Uygur autonomous area in Xinjiang, 50g of rock debris is added into 350mL of the drilling fluid system of example 1, and the content of pollutants in drill cuttings after the drilling fluid is polluted is tested. The results are shown in Table 7.
Measurement results
TABLE 2 evaluation of rheological fluid loss properties of environment-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 comparative examples had good fluid loss reduction before aging. After aging, the viscosity of the drilling fluid in the embodiments 1, 2 and 3 is slightly reduced, the API (American Petroleum institute) filtration loss is small, and the high-temperature high-pressure filtration loss is less than 15mL, which shows that the drilling fluid systems in the embodiments have good temperature resistance, salt resistance and filtration loss reduction performance. The highest fluid loss additive content in example 3 results in the highest viscosity and the lowest fluid loss, indicating that the fluid loss additive has the greatest effect on the drilling fluid system. In example 2, the content of the attapulgite is higher than that in example 1, so that the viscosity and the shear force are slightly higher, the filtration loss is slightly lower, and the attapulgite also has certain temperature and salt resistance effects. Comparative example 1 does not contain attapulgite, and the content of bentonite is too high, so that the viscosity shear force is obviously reduced after aging, the filtration loss is increased rapidly, the performance of the drilling fluid system is greatly influenced by the content of a soil phase, and the salt resistance of the bentonite is poor, so the requirement of the salt resistance cannot be met. Comparative example 2 lacks a flexible plugging agent, so although viscosity change is not large after aging, lack of a plugging material causes rapid increase of high-temperature and high-pressure filtration loss, which indicates that the nano plugging agent has a large influence on a 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 and reducing the fluid loss can be achieved through self-adaptive pores. Comparative example 3 the conventional lubricant methyl oleate was used instead of the polymer brush lubricant, whereas the polymer brush lubricant, in addition to its effect on the lubricity of the system, also has good temperature and salt resistance properties due to its unique molecular structure. The disruption of the "synergistic" action 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 is an oil phase and also has a certain fluid loss reducing effect, so that comparative example 5 has slightly inferior fluid loss properties without adding the lubricant. The fluid loss additive of comparative example 6 was not a product of a crosslinked structure, and therefore, the temperature resistance was poor and the fluid loss after high-temperature aging was high.
TABLE 3 evaluation of suspension stability of drilling fluid system
Sedimentation stability is a key property of drilling fluids. If the settling stability is poor, the heavy material settling may cause sticking, well kick and even more serious accidents. It can be seen from table 3 that with long-term high-temperature aging, the sedimentation coefficient of the drilling fluid is larger and larger, which indicates that the shearing force and viscosity of the drilling fluid are also gradually reduced, and the internal structure of the drilling fluid is gradually damaged. The sedimentation coefficient of the samples of example 1, example 2 and example 3 is less than 0.52 even after 96 hours of high-temperature aging. It is shown that the samples of the examples have good high temperature resistance. The settlement coefficients of the comparative samples are all larger than 0.52 after aging for 96 hours, which shows that the drilling fluid can not bear high temperature for a long time, and the temperature resistance is poor, especially under the condition of containing high salt. And the settlement factor of the comparative example 1 is as high as 0.53, which indicates that the grid structure in the drilling fluid is seriously damaged, and the shearing force and the rock carrying property of the drilling fluid are seriously insufficient. As can be seen from comparative examples 1 to 3, 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 and high-pressure plugging performance of drilling fluid system
As can be seen from table 4, since the pore diameter of the sand table is larger than that of the high-temperature high-pressure filter paper, the filter loss of the sand table is higher than that of the high-temperature high-pressure filter paper under the same conditions. The main technical strategy for constructing a high-temperature-resistant polymer saturated salt water drilling fluid system is to reduce the filtration loss of the drilling fluid at high temperature and high pressure by improving the plugging performance of the drilling fluid. The invention improves the plugging performance of the drilling fluid by the synergistic combined action of the flexible nano plugging agent and the cloud point effect of the polymeric alcohol. The sand pan filtration losses at 10 μm for the example samples were all less than 30mL. Comparative example 1 since only bentonite having poor salt resistance was contained, the internal network structure of the drilling fluid was destroyed under high temperature and high salt conditions, resulting in a large fluid loss. Comparative example 2 has a larger sand disc fluid loss at 10 μm compared to comparative example 3 due to the absence of the nano-plugging agent or the change in the kind of lubricant. The comparative example result shows that the nano plugging agent is crucial 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 drilling fluid system inhibition performance by rolling recovery
| Sample(s) | 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 for inhibiting the hydration expansion of clay minerals and stabilizing a borehole wall stratum. The oil-based drilling fluid has excellent inhibition performance because the external phase is an oil phase and clay minerals are basically not expanded in the oil, and the rolling recovery rate of the system is as high as 98.6%. The rolling recovery rate of the embodiment is similar to that of an oil-based drilling fluid system and is higher than 95%, which shows that the drilling fluid system has excellent inhibition performance. The attapulgite has a micro filamentous structure, and can be coated on the surface of the rock to prevent the rock from being hydrated, so that the rolling recovery rate of the comparative example 1 is reduced. The nano plugging agent can be adsorbed on the surface of rock to block the pores of the rock and prevent water from invading, so that the hydration collapse of the rock is reduced, and the rolling recovery rate of the comparative example 2 which lacks the nano plugging agent is obviously reduced. The comb-type polymer lubricant can be 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 is decreased. The experimental results show that the good inhibition performance of the drilling fluid system is also the result of the synergistic effect of the components. The nano plugging agent in the drilling fluid system can be adsorbed on the surface of rock to block the pores of the rock and prevent the invasion of water; the comb-type polymer lubricant can be adsorbed on the rock surface to change the wettability of the surface, so that the resistance of water invading the rock pores is increased; the attapulgite has a microscopic filamentous structure and can be coated on the surface of the rock to prevent the rock from being hydrated and broken; the high-temperature-resistant salt-resistant fluid loss additive of the zwitterionic polymer has a hydrophobic structure and cationic groups, and hydration of clay minerals is inhibited to a certain extent.
TABLE 6 evaluation of lubricating properties of drilling fluid systems
| Sample (I) | 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 have similar properties although the lubricity is not as good as that of the oil-based drilling fluid, which indicates that the comb polymer has good lubricating property in the high-temperature high-density saturated brine drilling fluid and the lubricating property of the drilling fluid is good. Comparative example 1 due to the lack of attapulgite, bentonite is easily compressed and agglomerated under high temperature and high salt conditions, resulting in a decrease in lubricating properties. The comparative example 2 lacks the nano plugging agent, and the microscopic spherical shape of the nano plugging agent also has a certain promotion effect on improving the lubricant of the drilling fluid. The methyl oleate in the comparative example 3 has weak temperature resistance, and the drilling fluid has larger friction resistance after aging. The conventional lubricant has the problems of thermal degradation and poor dispersibility in high-temperature high-salt high-density drilling fluid, so that the lubricating property is insufficient. A significant reduction in lubricity can be seen due to the absence of comb polymer. The lubricating properties of comparative example 4 are close to those of the examples. Comparative example 5 no lubricant was added and the coefficient of friction was much greater than the examples. Comparative example 6 lubricating performance was close to that of the examples.
TABLE 7 contaminant content of drill cuttings after drilling fluid contamination
| Item | 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 |
| Water content (%) | ≤60 | 8.1 |
As can be seen from Table 7, in the examples, after the samples were contaminated, the indexes of the contaminant contents of the drill cuttings all meet the requirements of the local standard "pollution control requirements for comprehensive utilization of solid wastes for drilling oil and gas fields" (DB 65T 3997-2017) in Uygur autonomous area of Xinjiang.
Comprehensive analysis shows that the amphoteric ionic polymer high-temperature-resistant salt-resistant fluid loss additive with the micro-crosslinking structure has good temperature and salt resistance, and is a foundation for ensuring that the environment-friendly high-temperature-resistant saturated brine high-density drilling fluid has good fluid 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 polyalcohol cloud point effect act together to improve the plugging property of a drilling fluid system, and the comb-type polymer lubricant ensures the lubricity of the drilling fluid system under the high-temperature condition. Besides, the attapulgite and the comb polymer lubricant have a certain promotion effect on the inhibition performance, and the comb polymer lubricant and the flexible nano plugging agent have a certain promotion effect on the fluid loss performance. Generally, the good performance of the environment-friendly high-temperature-resistant saturated brine high-density drilling fluid is the result of high-efficiency action and synergistic interaction of all components in the system, and the environment-friendly requirement of certain environment-sensitive areas is met due to the fact that no sulfonated material is used.
Claims (10)
1. An environment-friendly high-temperature-resistant saturated saline water high-density polymer drilling fluid system 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 polyalcohol, 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.
2. The environment-friendly high temperature resistant saturated brine high density polymer drilling fluid system of claim 1, wherein the high temperature resistant salt resistant fluid loss additive is prepared by the following method:
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 adjusting the pH 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, drying and crushing the obtained product to obtain the high-temperature-resistant salt-resistant filtrate reducer; the high-temperature-resistant and salt-resistant filtrate reducer is a zwitterionic polymer with a micro-crosslinking structure.
3. The environment-friendly high temperature resistant saturated brine high density polymer drilling fluid system according to claim 2, wherein the hydrophobically associating cationic monomer is one of carboxymethyl octadecyl methyl diallyl ammonium chloride, hexadecyl 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 styrene sulfonate;
preferably, the mass ratio of the N, N-dimethylacrylamide, the 2-acrylamide-2-methylpropanesulfonic acid, the hydrophobic association cationic monomer and the vinyl monomer with the ring structure is 20-30.
4. The environment-friendly high temperature resistant saturated brine high density polymer drilling fluid system of claim 2, 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, hydrophobically associating cationic monomer, vinyl monomer with ring structure; the mass ratio of the emulsifier to the volume of water is 0.1-0.2g;
adjusting the pH value of the system to 7.0-8.0 by using 30-40% of sodium hydroxide aqueous solution by mass fraction;
the initiator is ammonium persulfate or potassium persulfate; the initiator is 0.1-0.3% of the total mass of N, N-dimethylacrylamide, 2-acrylamide-2-methylpropanesulfonic acid, the hydrophobic association cationic monomer and the vinyl monomer with the ring structure.
5. The environment-friendly high temperature-resistant saturated brine high density polymer drilling fluid system as claimed in claim 2, wherein the nano-cross-linking agent is nano-silica modified by silane coupling agent, the silane coupling agent is gamma-methacryloxypropyltrimethoxysilane, vinyltrimethoxysilane or vinyltris (b-methoxyethoxy) silane, and the nano-silica has a particle size of 10-30nm; the mass of the nano cross-linking agent is 0.005-0.025%, preferably 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.
6. The environment-friendly high temperature saturated brine resistant high density polymer drilling fluid system of claim 2 or 5, wherein the nano cross-linking agent is prepared according to 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 cross-linking agent; the mass ratio of the nano-silica to the toluene is 3-6 g/100mL; the mass ratio of the nano silicon dioxide to the silane coupling agent is 1.02-0.05.
7. The environment-friendly high temperature saturated brine high density polymer drilling fluid system of claim 1, wherein the alkalinity regulator is one of sodium hydroxide, potassium hydroxide, sodium bicarbonate, 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.
8. The environment-friendly high temperature saturated brine resistant high density polymer drilling fluid system of claim 1, further comprising a density modifier, wherein the density modifier is barite, and the barite is added in an amount that causes the drilling fluid system to be weighted to a desired density.
9. The preparation method of the environment-friendly high temperature saturated brine resistant high density polymer drilling fluid system of claim 1, comprising the steps of:
firstly, adding bentonite and attapulgite into water, adding an alkalinity regulator, and stirring the mixture for 24 hours under the condition of 300r/min to prepare base slurry; adding a high-temperature-resistant salt-resistant fluid loss additive, polyalcohol, a flexible plugging agent, a polymer brush lubricant, sodium chloride and formate into the base slurry, and stirring at a high speed for 20min after adding each raw material; the rotating speed of the high-speed stirring is 5000r/min;
preferably, the preparation method of the environment-friendly high-temperature-resistant saturated brine high-density polymer drilling fluid system further comprises the following steps: after the formate is added, the density regulator is added, and the mixture is stirred for 20min at the rotating speed of 5000r/min.
10. The use of the environmentally friendly high temperature resistant saturated brine high density polymer drilling fluid system of claim 1 in deep ultra deep oil and gas drilling.
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