CN114437679B

CN114437679B - Water-based drilling fluid and preparation method and application thereof

Info

Publication number: CN114437679B
Application number: CN202011194045.9A
Authority: CN
Inventors: 王晨; 睢文云; 杨国兴; 赵凯强; 杨超; 尹泽群; 贾未鸣; 周成华
Original assignee: China Petroleum and Chemical Corp; Sinopec Dalian Research Institute of Petroleum and Petrochemicals
Current assignee: Sinopec Dalian Petrochemical Research Institute Co ltd; China Petroleum and Chemical Corp
Priority date: 2020-10-30
Filing date: 2020-10-30
Publication date: 2023-04-07
Anticipated expiration: 2040-10-30
Also published as: CN114437679A

Abstract

The invention discloses a water-based drilling fluid and a preparation method and application thereof. And mixing the components to obtain the water-based drilling fluid. Also provides an application of the drilling fluid in the reservoir development process. The water-based drilling fluid provided by the invention has the advantages of simple composition, high use efficiency, environmental friendliness and the like.

Description

Water-based drilling fluid and preparation method and application thereof

Technical Field

The invention belongs to the technical field of oilfield chemicals, and particularly relates to a drilling fluid and a preparation method thereof.

Background

The drilling fluid process technology is an important component of oil and gas development, plays an important role in the drilling and completion construction, and development of a high-performance water-based drilling fluid system is always the research focus in the drilling and completion field. In the research and development and application process of the drilling fluid system, the drilling fluid system matched with the characteristics of the oil-gas field in each area is developed and is the basic direction of the drilling fluid technology development. At present, the development of a drilling fluid system usually focuses on the temperature resistance of the system so as to meet the application requirements of the drilling fluid technology in domestic deep wells, ultra-deep wells or other unconventional wells, for example, patent CN 109735314A develops an organic-inorganic silicate temperature-resistant drilling fluid system, and the system still has good inhibition and anti-collapse properties in a high-temperature environment, but the salt resistance of the system is slightly less focused. The Chuannan oil and gas field has the characteristic of high bittern, and the common water-based drilling fluid system is often difficult to exert excellent performance in the high bittern environment, so that the salt resistance of the system needs to be further improved to adapt to the application requirement of the system in the high bittern environment.

In addition to the application performance, the environmental protection performance of the drilling fluid system is getting more and more attention, because the corresponding environmental protection regulations in China are continuously perfected, and the environmental protection situation of the oil field site is increasingly severe. In some areas with high environmental sensitivity, such as near water oil fields, the requirement of environmental protection on a drilling fluid system is put forward and improved. In addition to the current strict environmental protection requirement, the background of low oil price is gradually forcing the environmental protection performance of the drilling fluid system to be improved. The well drilling liquid system has the advantages of high investment on processing equipment of the waste drilling liquid, high processing cost, good compatibility, convenient application, high efficiency and environmental protection, and has wide application space in the future, and the profit of oil products is seriously influenced in the low oil price era. In recent years, the development of domestic environment-friendly water-based drilling fluid systems is relatively fast, but because of late start, the salt resistance and the environment-friendly performance of the drilling fluid systems are still a certain gap from foreign companies. The starch material has wide domestic sources and low price, and has recognized environmental protection, degradability, salt resistance and pollution resistance. At present, a plurality of published articles and patents are used for researching the application performance of the nano starch microspheres in a plurality of fields such as medical treatment, packaging, paper making and the like, for example, the patent CN 104785179A discloses a method for preparing the nano starch microspheres, the method prepares the nano starch microspheres with controllable grain diameter and high purity in an energy-saving and environment-friendly way through freezing, melting, dialysis and filtration, and the method has huge application potential in the field of biological medicine. In the field of oilfield chemicals, the development of environment-friendly drilling aids and the formation of drilling fluid systems around the drilling aids by using starch as a raw material are a new direction for the development of environment-friendly salt-resistant drilling fluid systems.

Disclosure of Invention

Aiming at the problems in the prior art, the invention aims to provide a water-based drilling fluid and a preparation method and application thereof, wherein the drilling fluid has the advantages of simple composition, high use efficiency, environmental friendliness and the like.

The invention provides a drilling fluid, which comprises water, bentonite, a nano-starch microsphere oil-gas layer protective agent, a viscosity reducer, a wall fixing agent, a polyether polyol coating agent and a fluid loss additive, and comprises the following components in parts by weight: 100 parts of water, 1-6 parts of bentonite, preferably 2-4 parts, 0.5-5 parts of nano starch microsphere oil-gas layer protective agent, preferably 1-3 parts, 0.5-5 parts of modified starch fluid loss additive, preferably 1-3 parts, 0.2-4 parts of polyether polyol coating agent, preferably 0.4-2 parts, 0.5-4 parts of wall-fixing agent, preferably 1-3 parts of viscosity reducer, preferably 0.05-0.5 parts, and preferably 0.2-0.4 parts.

In the drilling fluid, the nano-starch microsphere oil-gas layer protective agent comprises water, starch, a solvent, sodium trimetaphosphate, a monomer, an initiator, a stabilizer, a zwitterionic surfactant, a cross-linking agent and an inorganic salt solution, and the dosage of the raw materials is as follows in parts by weight: 200 parts of deionized water, 1-25 parts of starch, 100-500 parts of solvent and 37.5-100 parts of sodium trimetaphosphate solution, wherein the solute sodium trimetaphosphate accounts for 0.5-12.5 parts, 0.2-10 parts of monomer, 0.001-0.2 part of initiator, 10-60 parts of stabilizer, 0.1-10 parts of zwitterionic surfactant, 0.1-15 parts of cross-linking agent and 3-75 parts of inorganic salt solution, and the solute inorganic salt accounts for 0.1-15 parts; preferably 200 parts of deionized water, 5-15 parts of starch, 200-400 parts of solvent, 50-75 parts of sodium trimetaphosphate solution, wherein the solute sodium trimetaphosphate accounts for 2.5-10 parts, 0.5-6 parts of monomer, 0.003-0.06 part of initiator, 30-50 parts of stabilizer, 1-4.5 parts of zwitterionic surfactant, 0.5-9 parts of cross-linking agent and 15-45 parts of inorganic salt solution, and the solute of inorganic salt accounts for 0.75-9 parts.

In the drilling fluid, the bentonite is drilling-grade bentonite, and the drilling-grade bentonite can be any one of commercially available drilling-grade bentonite meeting the GB/T5005-2010 standard.

In the drilling fluid, the wall fixing agent is an inorganic wall fixing agent, and specifically, the wall fixing agent may be any one or two selected from nano calcium carbonate and nano silica.

In the drilling fluid, the polyether polyol coating agent is a block copolyether containing a terminal hydroxyl group or a terminal alkoxy group, and the polyether polyol can be any one or more of three-segment polyether polyols or any one or two of two-segment polyether polyols. When the polyether polyol is a three-stage polyether polyol, the polyether polyol may be specifically a PEP polyether polyol having a Propylene Oxide (PO) structural unit at both ends and an Ethylene Oxide (EO) structural unit in the middle, or an EPE polyether polyol having an Ethylene Oxide (EO) structural unit at both ends and a Propylene Oxide (PO) structural unit in the middle. The PEP and the EPE have the structural formulas shown as (1) and (2), wherein a, b and c are all non-zero integers and satisfy the condition that (a + b + c) is more than or equal to 25 and less than or equal to 125, and preferably 75 and less than or equal to (a + b + c) and less than or equal to 100; when the polyether polyol is a two-stage polyether polyol, the polyether polyol can be specifically EP polyether polyol in a structural form of an Ethylene Oxide (EO) -Propylene Oxide (PO) structural unit, and can also be PE polyether polyol in a structural form of a Propylene Oxide (PO) -Ethylene Oxide (EO) structural unit, the structural formulas of EP and PE are shown as (3) and (4), wherein x and y are non-zero integers, and the requirement that x + y is not less than 25 and not more than 100 is met, and preferably not less than 50 and not more than (x + y) is not more than 75.

（1）

（2）

（3）

（4）

In the drilling fluid, the filtrate reducer is a modified starch filtrate reducer, specifically, the filtrate reducer can be one or more of zwitterionic modified starch and nonionic modified starch, and preferably is zwitterionic modified starch. When the modified starch fluid loss additive is a zwitterionic modified starch, the modified starch fluid loss additive can be one or more of DMAPS (methacryloyloxyethyl-N, N-dimethyl propane sulfonate) grafted starch, DAPS (N, N-dimethyl allyl amine propane sulfonate) grafted starch, VPPS (4-vinylpyridine propane sulfonate) grafted starch, MAPS (N-methyl diallyl propane sulfonate) grafted starch and MABS (N-methyl diallyl butane sulfonate) grafted starch; when the modified starch fluid loss additive is nonionic modified starch, the modified starch fluid loss additive can be specifically one or more of NVP (N-vinyl pyrrolidone) grafted starch, AN (acrylonitrile) grafted starch, NVF (vinyl formamide) grafted starch and NVA (vinyl acetamide) grafted starch. The modified starch fluid loss additive can be prepared by adopting a commercially available product or a method disclosed in the prior journal and patent literature, such as the methods disclosed in the patents CN 104926995A and CN 104926996A previously disclosed by the applicant.

In the drilling fluid, the viscosity reducer is an amphoteric series monomer oligomer viscosity reducer, such as any one or two of commercially available zwitterionic vinyl monomer oligomer viscosity reducers XY-27 and XY-28.

In the drilling fluid, the nano starch microsphere oil-gas layer protective agent is prepared by the following method, and the preparation method comprises the following steps:

s1, heating a mixed solution of starch and water to boiling, keeping for a period of time, and then cooling;

s2, slowly adding a solvent into the material obtained in the step S1, and standing after the solvent is added;

s3, further separating, washing and drying the lower-layer insoluble substance after the S2 is stood to obtain nano-starch crystals;

s4, adding the nano-starch crystals into a sodium trimetaphosphate solution, uniformly mixing, standing, heating, maintaining, and further separating, washing and drying to obtain esterified nano-starch crystals;

s5, heating a solution obtained by mixing the esterified nano-starch crystals with water to boil, and keeping for a period of time;

and S6, adding a zwitterionic surfactant and a stabilizer into the feed liquid obtained in the step S5, fully and uniformly mixing, then slowly adding an inorganic salt solution and a cross-linking agent, and further performing centrifugal separation, washing and drying after reaction.

In the preparation method of the nano-starch microsphere oil-gas layer protective agent, the starch in the step S1 is one or more of mung bean starch, cassava starch, sweet potato starch, wheat starch, water caltrop starch, lotus root starch and corn starch, and preferably corn starch and/or potato starch.

In the preparation method of the nano-starch microsphere oil-gas layer protective agent, the boiling treatment time in the step S1 is 15-60 min, preferably 20-40 min.

In the preparation method of the nano-starch microsphere oil-gas layer protective agent, the temperature is reduced to 10-50 ℃ in the step S1, and preferably 20-40 ℃.

In the preparation method of the nano-starch microsphere oil-gas layer protective agent, the solvent in the step S2 is an organic solvent, specifically, the solvent may be one or more of ethanol, methanol, benzyl alcohol, acetone, cyclohexanone, acetophenone, toluene, ethylbenzene and chlorobenzene, preferably ethanol and/or acetone, and more preferably ethanol.

In the preparation method of the nano-starch microsphere oil-gas layer protective agent, the separation in the step S3 is centrifugal separation; the washing is carried out by using an ethanol solvent under stirring, wherein the ethanol solvent is excessive; the drying is carried out for 2 to 8 hours at the temperature of between 20 and 50 ℃.

In the preparation method of the nano-starch microsphere oil-gas layer protective agent, the standing and dipping time in the step S4 is 0.5-4 h, preferably 1-3 h.

In the preparation method of the nano-starch microsphere oil-gas layer protective agent, the curing treatment temperature in the step S4 is 20-60 ℃, and the treatment time is 0.5-3 h, preferably 1-2.5 h.

In the preparation method of the nano-starch microsphere oil-gas layer protective agent, the boiling treatment time in the step S5 is 5-45 min, preferably 10-30 min.

In the preparation method of the nano-starch microsphere oil-gas layer protective agent, the stabilizing agent in the step S6 is one or more of polyalcohol, alcohol amine, polyvinylpyrrolidone and tween; specifically, the surfactant can be one or more of polyethylene glycol 400, polyethylene glycol 600, polyethylene glycol 1000, polyethylene glycol 2000, polyethylene glycol 4000, polyethylene glycol 6000, polyethylene glycol 10000, polyethylene glycol 20000, diglycerol, triglycerol, glycerol, diethylene glycol, triethanolamine, triisopropanolamine, N-methyldiethanolamine, polyvinylpyrrolidone K12, polyvinylpyrrolidone K30, polyvinylpyrrolidone K60, tween 20, tween 40, tween 60 and Tween 80.

In the preparation method of the nano-starch microsphere oil-gas layer protective agent, in the step S6, the cross-linking agent is an organic cross-linking agent and is one or more of epichlorohydrin, phosphorus oxychloride, formaldehyde, glyoxal and glutaraldehyde, and preferably epichlorohydrin.

In the preparation method of the nano-starch microsphere oil and gas layer protective agent, in step S6, the zwitterionic surfactant is a betaine zwitterionic surfactant, and the zwitterionic surfactant may specifically be one or more of dimethyl dodecyl carboxymethyl ammonium salt, dimethyl dodecyl carboxyethyl ammonium salt, dimethyl hexadecyl carboxymethyl ammonium salt, dimethyl octadecyl carboxymethyl ammonium salt, dimethyl dodecyl sulfopropyl ammonium salt, dimethyl hexadecyl sulfoethyl ammonium salt, dimethyl octadecyl sulfobutyl ammonium salt, dimethyl (3-hydroxy dodecyl) sulfopropyl ammonium salt, dimethyl (6-aminotetradecyl) sulfoethyl ammonium salt, dimethyl dodecyl methyl ammonium phosphate, dimethyl dodecyl ethyl ammonium phosphate, dimethyl tetradecyl methyl ammonium phosphate, dimethyl hexadecyl methyl ammonium phosphate, and dimethyl octadecyl methyl ammonium phosphate.

In the preparation method of the nano-starch microsphere oil-gas layer protective agent, the reaction time in the step S6 is 2-8 hours, preferably 3-6 hours.

In the preparation method of the nano-starch microsphere oil-gas layer protective agent, the inorganic salt in step S6 is a soluble inorganic salt, the inorganic salt is one or more of sodium salt, potassium salt, ammonium salt, calcium salt and magnesium salt, and when the inorganic salt is sodium salt, the inorganic salt is specifically one or more of sodium chloride, sodium bromide, sodium sulfate, sodium sulfite, sodium carbonate, sodium bicarbonate, sodium nitrate, sodium phosphate, sodium hydrogen phosphate and sodium silicate; when the inorganic salt is potassium salt, it is specifically one or more of potassium chloride, potassium bromide, potassium sulfate, potassium sulfite, potassium carbonate, potassium bicarbonate, potassium nitrate, potassium phosphate, potassium hydrogen phosphate and potassium silicate; when the inorganic salt is ammonium salt, the inorganic salt is one or more of ammonium chloride, ammonium bromide and ammonium nitrate; when the inorganic salt is a calcium salt, it is specifically calcium chloride or calcium bromide; when the inorganic salt is a magnesium salt, the inorganic salt is specifically one or more of magnesium chloride, magnesium bromide, magnesium sulfate and magnesium nitrate.

In the preparation method of the nano-starch microsphere oil-gas layer protective agent, a step S501 is also arranged between the step S5 and the step S6, a monomer is added into the feed liquid obtained in the step S5, and an initiator is added to react for 3 to 6 hours after the monomers are fully dissolved and mixed; the monomer can be one or more of cationic monomer, anionic monomer, zwitterionic monomer and nonionic monomer. The initiator is one or more of potassium persulfate, sodium persulfate and ammonium persulfate.

In the preparation method of the nano-starch microsphere oil-gas layer protective agent, the zwitterion monomer can be one or more of DMAPS (methacryloyloxyethyl-N, N-dimethyl propanesulfonate), DAPS (N, N-dimethyl allyl amine propanesulfonate), VPPS (4-vinylpyridine propanesulfonate), MAPS (N-methyl diallyl propanesulfonate) and MABS (N-methyl diallyl butanesulfonate). The cationic monomer is one or more of DMC (methacryloyloxyethyl trimethyl ammonium chloride), DAC (acryloyloxyethyl trimethyl ammonium chloride), DBC (acryloyloxyethyl dimethyl benzyl ammonium chloride), DMDAAC (dimethyl diallyl ammonium chloride) and DEDAAC (diethyl diallyl ammonium chloride). The anionic monomer is one or more of AA (acrylic acid), AMPS (2-methyl-2-acrylamidopropanesulfonic acid), FA (fumaric acid), SSS (sodium allylsulfonate) and AOIAS (sodium 2-acryloyloxyisopentene sulfonate). The non-ionic monomer is one or more of NVP (N-vinyl pyrrolidone), AN (acrylonitrile), NVF (vinyl formamide) and NVA (vinyl acetamide).

In the preparation method of the nano-starch microsphere oil-gas layer protective agent, the water, the starch, the solvent, the sodium trimetaphosphate, the monomer, the initiator, the stabilizer, the zwitterionic surfactant, the cross-linking agent and the inorganic salt solution are calculated according to the parts by weight: 200 parts of deionized water, 1-25 parts of starch, 100-500 parts of solvent and 37.5-100 parts of sodium trimetaphosphate solution, wherein the solute sodium trimetaphosphate accounts for 0.5-12.5 parts, 0.2-10 parts of monomer, 0.001-0.2 part of initiator, 10-60 parts of stabilizer, 0.1-10 parts of zwitterionic surfactant, 0.1-15 parts of cross-linking agent and 3-75 parts of inorganic salt solution, and the solute inorganic salt accounts for 0.1-15 parts; preferably 200 parts of deionized water, 5-15 parts of starch, 200-400 parts of solvent, 50-75 parts of sodium trimetaphosphate solution, wherein the solute sodium trimetaphosphate accounts for 2.5-10 parts, 0.5-6 parts of monomer, 0.003-0.06 part of initiator, 30-50 parts of stabilizer, 1-4.5 parts of zwitterionic surfactant, 0.5-9 parts of cross-linking agent and 15-45 parts of inorganic salt solution, and the solute of inorganic salt accounts for 0.75-9 parts.

The particle size controllable range of the nano-starch microsphere hydrocarbon reservoir protective agent obtained by the preparation method of the nano-starch microsphere hydrocarbon reservoir protective agent is 25-1000 nm, the distribution of the nano-starch microsphere hydrocarbon reservoir protective agent in the particle size interval is more than or equal to 99%, and the distribution mode is polydisperse distribution. Meanwhile, the nano-starch microsphere oil-gas layer protective agent also has the following typical particle size distribution characteristics: d10 is more than or equal to 200nm and more than or equal to 60nm, D50 is more than or equal to 400nm and more than or equal to 200nm, D90 is more than or equal to 400nm, namely the distribution of the starch microspheres in the interval of 60 nm-600 nm is more than or equal to 80%.

The second aspect of the invention provides a preparation method of the drilling fluid, which comprises the steps of mixing water, bentonite, a nano-starch microsphere oil-gas reservoir protective agent, a viscosity reducer, a wall fixing agent, a polyether polyol coating agent and a filtrate reducer, and uniformly mixing to obtain the drilling fluid.

In a third aspect, the invention provides the use of the drilling fluid in a reservoir development process.

Compared with the prior art, the drilling fluid, the preparation method and the application thereof have the following advantages:

(1) The drilling fluid is prepared by compounding nano-scale starch microspheres serving as an oil-gas layer protective agent, water-soluble modified starch serving as a filtrate reducer and other environment-friendly functional single agents. The whole system has the characteristics of high efficiency and environmental protection. The starch-based drilling fluid system is prepared by aiming at a hard and brittle shale reservoir stratum which has a nano pore throat and micro cracks and is easy to cause borehole wall instability. The nano-scale crosslinked starch microsphere oil-gas layer protective agent can be used for carrying out pressure-bearing deformation plugging on nano-scale pore throats or microcracks of a shale oil-gas layer to form compact mud cakes, and the modified starch filtrate reducer and the inorganic nano-scale wall fixing agent are matched to further reduce water loss, prevent a large amount of filtrate from permeating into a stratum and form a high-efficiency pressure-bearing temporary plugging zone in a region close to a well wall; the polyether polyol can effectively inhibit the clay in the well wall from hydrating and dispersing, and further prevent the clay shale from destabilizing, reducing and collapsing; the viscosity of the system can be controlled by adding the viscosity reducer, so that the drilling fluid is prevented from being obviously thickened after various single agents are added, and meanwhile, the synergistic inhibition effect can be achieved.

(2) The drilling fluid provided by the invention takes the strong-salt-resistance zwitterionic or nonionic polymer as a functional component, so that the salt resistance of the system is obviously improved, the serious influence of inorganic salt on the polymer molecular conformation and the coil size is avoided, the compatibility of single agents with excellent performance is improved, and the synergistic interaction of different components is enhanced.

(3) The particle size of the nano starch microsphere oil-gas layer protective agent is polydispersed and distributed between 25nm and 1000nm, and the structure is different from that of nano starch crystals which are not crosslinked or are only surface-crosslinked in the prior art; the grain size is different from that of micron-sized or monodisperse nano-sized cross-linked starch microspheres in the prior art. The method solves the technical problem that the nano starch is difficult to prepare by using the micron starch raw material, and the starch is a polymer of an anhydrous glucose unit and has a certain particle size, and the particle size of starch of different biological sources is between about 1 mu m and 100 mu m, so that the method for preparing the nano starch microspheres by using the starch as the raw material is difficult and serious. The nano-scale crosslinked starch microspheres also have the characteristics of good sphericity and high strength, can be extruded into micropores of a shale reservoir stratum in application, form a pressure-bearing temporary plugging zone in the reservoir stratum close to a well wall, and reduce the water loss of drilling fluid.

(4) In the preparation method of the nano-starch microsphere oil-gas layer protective agent, a novel composite crosslinking technology is adopted, wherein, firstly, nano-starch crystals are saturated and adsorbed with sodium trimetaphosphate through dipping, and in the maintenance process, hydroxyl in the crystal grains and the sodium trimetaphosphate are esterified and crosslinked to complete internal bridging; on the basis, the organic cross-linking agent epichlorohydrin is used for etherification cross-linking with the hydroxyl on the surface of the nano starch crystal by a dispersion polymerization method to finish surface curing. Through the combination of inorganic-organic cross-linking agents, and the mode of internal bridging and surface curing which are carried out successively, the nano-starch microsphere hydrocarbon reservoir protective agent has higher strength compared with the micron-starch microsphere hydrocarbon reservoir protective agent only with surface cross-linking, can generate limited deformation in application, and can bear and block in a near-wellbore area without excessively deforming to move deep into a reservoir, thereby really achieving the rigidity and flexibility.

(5) The preparation method of the nano-starch microsphere oil-gas layer protective agent comprises a two-stage boiling treatment technology. The first-order boiling treatment bombards micron-sized starch particles under the dual action of heat and bubbles, quickly and efficiently strips out nano-starch crystals, and well-dispersed nano-starch grains can be obtained in subsequent poor solvent precipitation. The second-order boiling treatment is that after esterification crosslinking, sodium trimetaphosphate adsorbed on the surface of the crystal grain can be bridged on the surface in the esterification crosslinking process, so that the nano starch crystal is slightly bonded and the hydroxyl active site of subsequent etherification crosslinking is reduced, the weak ester bond on the surface of the crystal grain can be opened by the second-order boiling treatment, and the influence of the esterification crosslinking on the dispersibility of the crystal grain and the subsequent etherification crosslinking efficiency is eliminated. The two-stage boiling treatment technology ensures the dispersibility of the nano starch crystal before surface curing and protects the successive proceeding of inorganic-organic crosslinking.

(6) In the preparation method of the nano-starch microsphere oil-gas layer protective agent, the nano-starch microsphere oil-gas layer protective agent is prepared by a dispersion polymerization method, and nano-starch crystals containing an internal cross-linking structure are uniformly suspended in a water phase under the action of mechanical stirring, a stabilizing agent and a zwitterionic surfactant to complete surface cross-linking. The reaction process has the advantages of easy heat transfer and control, continuous production and environment-friendly process.

Detailed Description

The starch microspheres of the present invention, and the method and use of the starch microspheres are further described by the following specific examples, which should not be construed as limiting the invention.

The particle size of the starch microsphere is measured by a Malvern Nano-ZS particle size analyzer, and the measuring method is wet measurement.

The ratios of materials presented in all the following examples and comparative examples are mass parts ratios of materials.

Example 1

Weighing 5 parts of wheat starch, adding the wheat starch into 100 parts of deionized water, boiling for 20min, cooling the feed liquid to 20 ℃, dropwise adding 200 parts of toluene into the feed liquid, standing after dropwise addition to obtain a bottom insoluble substance, centrifuging, stirring, washing, and drying at 25 ℃ for 2.5h to obtain the nano-starch crystal. Weighing 2.5 parts of sodium trimetaphosphate to prepare 50 parts of solution, adding the nano starch crystal into the solution, uniformly mixing, standing, soaking for 1h, curing the solution for 1h at 25 ℃, centrifuging, stirring, washing, and drying for 2h at 25 ℃ to obtain the esterified nano starch crystal. Mixing the esterified nano-starch crystals with 100 parts of deionized water, heating the obtained solution to boiling, keeping the temperature for 15min, then cooling the feed liquid to 20 ℃, adding 30 parts of a stabilizer (polyethylene glycol 600: polyethylene glycol 20000= 5) and 1 part of dimethyldodecylsulfopropyl ammonium salt into the feed liquid, and fully and uniformly mixing the materials. Weighing 0.75 part of potassium chloride at 30 ℃ to prepare 15 parts of inorganic salt solution, simultaneously dripping 0.5 part of glutaraldehyde into the feed liquid at the same temperature, continuously reacting for 3 hours after dripping is finished, and obtaining white powdery nanoscale crosslinked starch microspheres through centrifugation, washing and drying. The cumulative distribution of the starch microspheres in each particle size interval is as follows: (d.ltoreq.25 nm): 1.99 percent; (d.ltoreq.50 nm): 5.76 percent; (d.ltoreq.125 nm): 21.22 percent; (d.ltoreq.250 nm): 39.30 percent; (d.ltoreq.500 nm): 86.32 percent; (d ≦ 1000 nm): 99.25 percent. Typical particle size distribution characteristics are: d10=81nm; d50=327nm; d90=519nm.

Weighing 4 parts of bentonite, adding the bentonite into 100 parts of water to prepare bentonite-based slurry, sequentially adding 1 part of nano-starch microsphere oil-gas layer protective agent, 3 parts of DMAPS modified starch filtrate reducer, 0.4 part of PEP polyether polyol coating agent, 3 parts of nano calcium carbonate wall-fixing agent and 0.4 part of XY-27 viscosity reducer into the prepared bentonite-based slurry, and fully mixing at normal temperature to prepare the starch-based environment-friendly drilling fluid treating agent system A.

Example 2

Weighing 15 parts of corn starch, adding the corn starch into 100 parts of deionized water, boiling for 40min, cooling the feed liquid to 40 ℃, dropwise adding 400 parts of methanol into the feed liquid, standing after dropwise adding to obtain a bottom insoluble substance, centrifuging, stirring, washing, and drying at 45 ℃ for 4.5h to obtain the nano-starch crystal. Weighing 10 parts of sodium trimetaphosphate to prepare 75 parts of solution, adding the nano-starch crystal into the solution, uniformly mixing, standing, soaking for 3 hours, maintaining the solution at 55 ℃ for 2.5 hours, centrifuging, stirring, washing, and drying at 45 ℃ for 7 hours to obtain the esterified nano-starch crystal. Mixing the esterified nano-starch crystals with 100 parts of deionized water, heating the obtained solution to boiling, keeping the temperature for 30min, then cooling the feed liquid to 40 ℃, adding 50 parts of polyethylene glycol 2000 and 4.5 parts of dimethyl hexadecyl sulfoethyl ammonium salt into the feed liquid, and fully and uniformly mixing. Weighing 9 parts of sodium chloride at 55 ℃ to prepare 45 parts of inorganic salt solution, simultaneously dripping the solution and 9 parts of glyoxal into the feed liquid at the same temperature, continuously reacting for 6 hours after the dripping is finished, and centrifuging, washing and drying to obtain white powdery nanoscale crosslinked starch microspheres. The starch microspheres are distributed in each particle size interval in an accumulated way as follows: (d.ltoreq.25 nm): 0.76 percent; (d.ltoreq.50 nm): 3.09%; (d.ltoreq.125 nm): 13.17 percent; (d.ltoreq.250 nm): 33.43 percent; (d.ltoreq.500 nm): 78.22 percent; (d.ltoreq.1000 nm): 99.09 percent. Typical particle size distribution characteristics are: d10=101nm; d50=368nm; d90=579nm.

Weighing 2 parts of bentonite, adding the bentonite into 100 parts of water to prepare bentonite-based slurry, sequentially adding 3 parts of nano-starch microsphere oil-gas layer protective agent, 1 part of MAPS modified starch fluid loss additive, 2 parts of EPE polyether polyol coating agent, 1 part of nano-silica wall-fixing agent and 0.2 part of XY-28 viscosity reducer into the prepared bentonite-based slurry, and fully mixing at normal temperature to prepare the starch-based environment-friendly drilling fluid treating agent system B.

Example 3

Weighing 1 part of water chestnut starch, adding the water chestnut starch into 100 parts of deionized water, boiling for 15min, cooling the feed liquid to 10 ℃, dropwise adding 100 parts of ethanol into the feed liquid, standing after dropwise adding to obtain a bottom insoluble substance, centrifuging, stirring, washing, and drying at 20 ℃ for 2h to obtain the nano-starch crystal. Weighing 0.5 part of sodium trimetaphosphate to prepare 37.5 parts of solution, adding the nano-starch crystal into the solution, uniformly mixing, standing, soaking for 0.5h, curing the solution at 20 ℃ for 0.5h, centrifuging, stirring, washing, and drying at 20 ℃ for 2h to obtain the esterified nano-starch crystal. Mixing the esterified nano-starch crystals with 100 parts of deionized water, heating the obtained solution to boiling, keeping the temperature for 5min, then cooling the feed liquid to 10 ℃, adding 10 parts of triethanolamine and 0.1 part of dimethyl octadecyl sulfobutyl ammonium salt into the feed liquid, and fully and uniformly mixing. Weighing 0.15 parts of inorganic salt (potassium chloride: sodium chloride =4: 1) at 30 ℃ to prepare 3 parts of inorganic salt solution, simultaneously dripping the inorganic salt solution and 0.1 part of formaldehyde into the feed liquid at the same temperature, continuously reacting for 2 hours after the dripping is finished, and centrifuging, washing and drying to obtain the white powdery nanoscale crosslinked starch microspheres. The cumulative distribution of the starch microspheres in each particle size interval is as follows: (d.ltoreq.25 nm): 2.68 percent; (d.ltoreq.50 nm): 7.02 percent; (d.ltoreq.125 nm): 26.42 percent; (d.ltoreq.250 nm): 53.17 percent; (d is less than or equal to 500 nm): 89.88 percent; (d.ltoreq.1000 nm): 99.66 percent. Typical particle size distribution characteristics are: d10=73nm; d50=249nm; d90=505nm.

Weighing 6 parts of bentonite, adding the bentonite into 100 parts of water to prepare bentonite-based slurry, sequentially adding 0.5 part of nano-starch microsphere oil-gas layer protective agent, 5 parts of NVP modified starch filtrate reducer, 0.2 part of EP polyether polyol coating agent, 4 parts of superfine calcium carbonate wall-fixing agent and 0.05 part of XY-27 viscosity reducer into the prepared bentonite-based slurry, and fully mixing at normal temperature to prepare the starch-based environment-friendly drilling fluid treating agent system C.

Example 4

Weighing 25 parts of mung bean starch, adding the mung bean starch into 100 parts of deionized water, boiling for 60min, cooling the feed liquid to 50 ℃, dropwise adding 500 parts of acetone into the feed liquid, standing after dropwise addition to obtain a bottom insoluble substance, centrifuging, stirring, washing, and drying at 50 ℃ for 8h to obtain the nano-starch crystals. Weighing 12.5 parts of sodium trimetaphosphate to prepare 100 parts of solution, adding the nano-starch crystal into the solution, uniformly mixing, standing, soaking for 4 hours, curing the solution at 60 ℃ for 3 hours, centrifuging, stirring, washing, and drying at 50 ℃ for 8 hours to obtain the esterified nano-starch crystal. Mixing the esterified nano-starch crystal with 100 parts of deionized water, heating the obtained solution to boil, keeping the temperature for 45min, cooling the feed liquid to 50 ℃, adding 60 parts of isopropanol and 10 parts of dimethyl (3-hydroxydodecyl) sulfopropyl ammonium salt into the feed liquid, and fully and uniformly mixing. Weighing 15 parts of inorganic salt (potassium chloride: calcium chloride = 14) at 60 ℃ to prepare 75 parts of inorganic salt solution, simultaneously dripping the inorganic salt solution and 15 parts of epichlorohydrin into the feed liquid at the same temperature, continuously reacting for 8 hours after dripping is finished, and obtaining white powdery nanoscale crosslinked starch microspheres through centrifugation, washing and drying. The cumulative distribution of the starch microspheres in each particle size interval is as follows: (d.ltoreq.25 nm): 0.09%; (d.ltoreq.50 nm): 2.25 percent; (d. Ltoreq.125 nm): 8.37 percent; (d.ltoreq.250 nm): 32.13 percent; (d.ltoreq.500 nm): 64.22 percent; (d.ltoreq.1000 nm): 99.05 percent. Typical particle size distribution characteristics are: d10=142nm; d50=382nm; d90=594nm.

Weighing 1 part of bentonite, adding the bentonite into 100 parts of water to prepare bentonite-based slurry, adding 5 parts of nano-starch microsphere oil-gas layer protective agent, 0.5 part of NVF modified starch filtrate reducer, 4 parts of PE polyether polyol coating agent, 0.5 part of wall fixing agent (nano calcium carbonate: nano silica = 1.

Example 5

Weighing 6 parts of starch (sweet potato: cassava = 1) and adding the starch into 100 parts of deionized water, boiling for 30min, cooling the feed liquid to 35 ℃, dropwise adding 250 parts of chlorobenzene into the feed liquid, standing after the dropwise addition to obtain a bottom insoluble substance, centrifuging, stirring and washing, and drying at 25 ℃ for 2.5h to obtain the nano-starch crystal. Weighing 6.6 parts of sodium trimetaphosphate to prepare 66 parts of solution, adding the nano-starch crystal into the solution, uniformly mixing, standing, soaking for 1.5h, maintaining the solution at 25 ℃ for 1.5h, centrifuging, stirring, washing, and drying at 25 ℃ for 2.5h to obtain the esterified nano-starch crystal. Mixing esterified nano-starch crystal with 100 parts of deionized water, heating the obtained solution to boil, keeping the temperature for 15min, cooling the feed liquid to 35 ℃, adding 35 parts of tween-60 and 1.5 parts of dimethyl dodecyl carboxymethyl ammonium salt into the feed liquid, and fully and uniformly mixing. Weighing 1.75 parts of magnesium chloride at the same temperature to prepare 17.5 parts of inorganic salt solution, simultaneously dripping the inorganic salt solution and 8.5 parts of cross-linking agent (epichlorohydrin: glyoxal =4: 1) into the feed liquid, continuously reacting for 3.5h after the dripping is finished, and centrifuging, washing and drying to obtain the white powdery nano-scale cross-linked starch microspheres. The starch microspheres are distributed in each particle size interval in an accumulated way as follows: (d.ltoreq.25 nm): 1.44 percent; (d.ltoreq.50 nm): 4.13 percent; (d.ltoreq.125 nm): 16.22 percent; (d is less than or equal to 250 nm): 35.32 percent; (d.ltoreq.500 nm): 80.78 percent; (d.ltoreq.1000 nm): 99.11 percent. Typical particle size distribution characteristics are: d10=93nm; d50=369nm; d90=549nm.

Weighing 3 parts of bentonite, adding the bentonite into 100 parts of water to prepare bentonite-based slurry, adding 2.5 parts of a nano-starch microsphere oil-gas layer protective agent, 2.5 parts of a modified starch fluid loss additive (NVP: MAPS =1 = 4), 1.5 parts of a polyether polyol coating agent (PEP: EPE = 2.

Example 6

Weighing 7.5 parts of starch (water caltrop: cassava = 4) and adding the starch into 100 parts of deionized water, boiling for 35min, then cooling the feed liquid to 30 ℃, dropwise adding 270 parts of solvent (methanol: ethanol =1 = 2) into the feed liquid, standing after the dropwise addition is finished to obtain a bottom insoluble substance, centrifuging, stirring and washing, and drying at 27 ℃ for 3.5h to obtain the nano-starch crystal. Weighing 5.5 parts of sodium trimetaphosphate to prepare 52 parts of solution, adding the nano starch crystal into the solution, uniformly mixing, standing, soaking for 2 hours, curing the solution at 30 ℃ for 2 hours, centrifuging, stirring, washing, and drying at 30 ℃ for 3 hours to obtain the esterified nano starch crystal. Mixing the esterified nano-starch crystal with 100 parts of deionized water, heating the obtained solution to boiling, keeping for 25min, then cooling the feed liquid to 62 ℃, adding 10 parts of DAC into the feed liquid at the same temperature, fully dissolving and mixing, then adding 0.2 part of initiator (sodium persulfate: ammonium persulfate = 1). 40 parts of polyvinylpyrrolidone K30 and 3 parts of dimethyl hexadecyl carboxymethyl ammonium salt are added into the feed liquid and fully and uniformly mixed. Weighing 2 parts of inorganic salt (sodium carbonate: sodium chloride = 1) at 52 ℃ to prepare 20 parts of inorganic salt solution, simultaneously dripping 7.5 parts of phosphorus oxychloride into the feed liquid at the same temperature, continuously reacting for 3 hours after the dripping is finished, and obtaining white powdery nanoscale crosslinked starch microspheres through centrifugation, washing and drying. The cumulative distribution of the starch microspheres in each particle size interval is as follows: (d. Ltoreq.25 nm): 0.54 percent; (d.ltoreq.50 nm): 2.03 percent; (d. Ltoreq.125 nm): 12.23 percent; (d.ltoreq.250 nm): 28.43 percent; (d.ltoreq.500 nm): 70.38 percent; (d.ltoreq.1000 nm): 99.10 percent. Typical particle size distribution characteristics are: d10=105nm; d50=390nm; d90=589nm.

Weighing 1.8 parts of bentonite, adding the bentonite into 100 parts of water to prepare bentonite-based slurry, sequentially adding 3.6 parts of nano-starch microsphere oil-gas layer protective agent, 1.8 parts of MABS modified starch fluid loss additive, 2.2 parts of polyether polyol coating agent (EP: PE = 1.

Example 7

Weighing 12.5 parts of starch (mung bean: sweet potato = 3) and adding the starch into 100 parts of deionized water, boiling for 45min, cooling the feed liquid to 45 ℃, dropwise adding 330 parts of solvent (ethanol: acetone = 10) into the feed liquid, standing after the dropwise addition to obtain a bottom insoluble substance, centrifuging, stirring and washing, and drying at 44 ℃ for 4h to obtain the nano-starch crystal. Weighing 6 parts of sodium trimetaphosphate to prepare 54 parts of solution, adding the nano-starch crystal into the solution, uniformly mixing, standing, soaking for 2.5h, maintaining the solution at 56 ℃ for 1.5h, centrifuging, stirring, washing, and drying at 44 ℃ for 6h to obtain the esterified nano-starch crystal. Mixing the esterified nano-starch crystals with 100 parts of deionized water, heating the obtained solution to boil, keeping the temperature for 45min, cooling the feed liquid to 66 ℃, adding 0.5 part of NVF into the feed liquid at the same temperature, fully dissolving and mixing, adding 0.003 part of potassium persulfate, and reacting for 6h. To the feed solution, 48 parts of a stabilizer (polyethylene glycol 600: glycerol = 2) and 4 parts of methyldodecylphosphate ammonium salt were added, and mixed thoroughly. Weighing 6 parts of inorganic salt (sodium sulfate: potassium carbonate = 2) at 44 ℃ to prepare 36 parts of inorganic salt solution, simultaneously dripping 7.5 parts of glutaraldehyde into the feed liquid at the same temperature, continuously reacting for 6 hours after dripping is finished, and centrifuging, washing and drying to obtain white powdery nanoscale crosslinked starch microspheres. The cumulative distribution of the starch microspheres in each particle size interval is as follows: (d.ltoreq.25 nm): 0.76 percent; (d.ltoreq.50 nm): 3.53 percent; (d.ltoreq.125 nm): 15.11 percent; (d.ltoreq.250 nm): 31.26 percent; (d.ltoreq.500 nm): 76.29 percent; (d.ltoreq.1000 nm): 99.08 percent. Typical particle size distribution characteristics are: d10=92nm; d50=362nm; d90=556nm.

Weighing 3.6 parts of bentonite, adding the bentonite into 100 parts of water to prepare bentonite-based slurry, sequentially adding 1.8 parts of nano-starch microsphere oil-gas layer protective agent, 4.4 parts of VPPS modified starch fluid loss additive, 0.8 part of polyether polyol coating agent (EP: PE =1: 3), 2.5 parts of nano-silica wall-fixing agent and 0.45 part of XY-28 into the prepared bentonite-based slurry, and fully mixing at normal temperature to prepare a starch-based environment-friendly drilling fluid treating agent system G.

Example 8

Weighing 8 parts of sweet potato starch, adding the sweet potato starch into 100 parts of deionized water, boiling for 50min, cooling the feed liquid to 38 ℃, dropwise adding 250 parts of acetone into the feed liquid, standing after dropwise adding to obtain a bottom insoluble substance, centrifuging, stirring, washing, and drying at 36 ℃ for 6h to obtain the nano-starch crystal. Weighing 5 parts of sodium trimetaphosphate to prepare 65 parts of solution, adding the nano-starch crystal into the solution, uniformly mixing, standing, soaking for 2 hours, maintaining the solution at 33 ℃ for 2 hours, centrifuging, stirring, washing, and drying at 36 ℃ for 4 hours to obtain the esterified nano-starch crystal. Mixing the esterified nano-starch crystals with 100 parts of deionized water, heating the obtained solution to boiling, keeping the temperature for 55min, cooling the feed liquid to 72 ℃, adding 6 parts of AMPS into the feed liquid at the same temperature, fully dissolving and mixing, adding 0.06 part of potassium persulfate, and reacting for 5h. To the feed liquid, 33 parts of triisopropanolamine and 3.6 parts of a zwitterionic surfactant (dimethyldodecylcarboxymethylammonium salt: dimethyldodecylcarboxyethylammonium salt = 1) were added and mixed thoroughly and uniformly. Weighing 5 parts of inorganic salt (sodium sulfate: sodium chloride = 4) at 36 ℃ to prepare 25 parts of inorganic salt solution, simultaneously dripping the inorganic salt solution and 5.5 parts of cross-linking agent (glutaraldehyde: epichlorohydrin = 6). The cumulative distribution of the starch microspheres in each particle size interval is as follows: (d. Ltoreq.25 nm): 0.33 percent; (d.ltoreq.50 nm): 1.88 percent; (d. Ltoreq.125 nm): 11.05 percent; (d.ltoreq.250 nm): 25.24 percent; (d is less than or equal to 500 nm): 64.68 percent; (d.ltoreq.1000 nm): 99.12 percent. Typical particle size distribution characteristics are: d10=115nm; d50=387nm; d90=584nm.

Weighing 5.5 parts of bentonite, adding the bentonite into 100 parts of water to prepare bentonite-based slurry, adding 3.5 parts of a nano-starch microsphere oil-gas layer protective agent, 2.8 parts of a modified starch fluid loss additive (NVP: MABS =3, 4), 2.6 parts of a polyether polyol coating agent (PEP: EPE = 6), 3.8 parts of a nano-silica wall-fixing agent, 0.25 parts of a viscosity reducer (XY-27 XY-28= 3) into the prepared bentonite-based slurry in sequence, fully mixing the components, and preparing the starch-based drilling fluid treating agent system H at normal temperature.

Example 9

Weighing 7 parts of cassava starch, adding the cassava starch into 100 parts of deionized water, boiling for 38min, cooling the feed liquid to 38 ℃, dropwise adding 225 parts of solvent (chlorobenzene: acetone = 1. Weighing 7 parts of sodium trimetaphosphate to prepare 49 parts of solution, adding the nano starch crystal into the solution, uniformly mixing, standing, soaking for 2.5 hours, curing the solution at 49 ℃ for 1.5 hours, centrifuging, stirring, washing, and drying at 27 ℃ for 7 hours to obtain the esterified nano starch crystal. Mixing the esterified nano-starch crystals with 100 parts of deionized water, heating the obtained solution to boiling, keeping the temperature for 37min, cooling the feed liquid to 75 ℃, adding 0.2 part of VPPS into the feed liquid at the same temperature, fully dissolving and mixing, adding 0.001 part of ammonium persulfate, and reacting for 5 hours. To the feed solution were added 37 parts of polyvinylpyrrolidone K60, 2.2 parts of a zwitterionic surfactant (dimethyldodecylcarboxymethyl ammonium salt: dimethylhexadecylsulfoethyl ammonium salt = 1), and thoroughly mixed uniformly. Weighing 3 parts of inorganic salt (potassium carbonate: sodium carbonate = 1) at 47 ℃ to prepare 30 parts of inorganic salt solution, dripping the inorganic salt solution and 2.5 parts of cross-linking agent (phosphorus oxychloride: epichlorohydrin =1 = 4) into the feed liquid at the same time, continuing to react for 4.5h after the dripping is finished, and obtaining the white powdery nanoscale cross-linked starch microspheres through centrifugation, washing and drying. The cumulative distribution of the starch microspheres in each particle size interval is as follows: (d.ltoreq.25 nm): 0.88 percent; (d.ltoreq.50 nm): 4.02 percent; (d.ltoreq.125 nm): 12.87 percent; (d.ltoreq.250 nm): 36.19 percent; (d.ltoreq.500 nm): 79.40 percent; (d.ltoreq.1000 nm): 99.17 percent. Typical particle size distribution characteristics are: d10=107nm; d50=370nm; d90=565nm.

Weighing 5.2 parts of bentonite, adding the bentonite into 100 parts of water to prepare bentonite-based slurry, adding 3.7 parts of nano-starch microsphere oil-gas layer protective agent and 2.9 parts of AN modified starch filtrate reducer, 1.3 parts of PEP polyether polyol coating agent, 3.1 parts of nano-silica wall-fixing agent and 0.65 part of viscosity reducer (XY-27.

Comparative example 1

Weighing 5 parts of wheat starch, adding the wheat starch into 100 parts of deionized water, fully and uniformly mixing, dropwise adding 200 parts of toluene into the feed liquid, standing after dropwise adding to obtain a bottom insoluble substance, centrifuging, stirring and washing, and drying at 25 ℃ for 2.5 hours to obtain the nano starch crystal. Mixing the nano-starch crystal and 100 parts of deionized water, adding 30 parts of stabilizer (polyethylene glycol 600: polyethylene glycol 20000= 5) and 1 part of dimethyl dodecyl sulfopropyl ammonium salt into the feed liquid at 20 ℃, and fully and uniformly mixing. Weighing 0.75 part of potassium chloride at 30 ℃ to prepare 15 parts of inorganic salt solution, simultaneously dripping 0.5 part of glutaraldehyde into the feed liquid at the same temperature, continuously reacting for 3 hours after dripping is finished, and obtaining white powdery nanoscale crosslinked starch microspheres through centrifugation, washing and drying. The starch microspheres are distributed in each particle size interval in an accumulated way as follows: (d.ltoreq.25 nm): 0.00 percent; (d.ltoreq.50 nm): 0.21 percent; (d.ltoreq.125 nm): 1.74 percent; (d.ltoreq.250 nm): 4.22 percent; (d.ltoreq.500 nm): 18.52 percent; (d.ltoreq.1000 nm): 55.31 percent. Typical particle size distribution characteristics are: d10=323nm; d50=898nm; d90=2023nm.

Weighing 4 parts of bentonite, adding the bentonite into 100 parts of water to prepare bentonite-based slurry, sequentially adding 1 part of nano-starch microsphere oil-gas layer protective agent, 3 parts of DMAPS modified starch filtrate reducer, 0.4 part of PEP polyether polyol coating agent, 3 parts of nano calcium carbonate wall-fixing agent and 0.4 part of XY-27 viscosity reducer into the prepared bentonite-based slurry, and fully mixing at normal temperature to prepare the starch-based environment-friendly drilling fluid treating agent system A1.

Comparative example 2

Weighing 5 parts of wheat starch, adding the wheat starch into 100 parts of deionized water, boiling for 20min, cooling the feed liquid to 20 ℃, dropwise adding 200 parts of toluene into the feed liquid, standing after dropwise addition to obtain a bottom insoluble substance, centrifuging, stirring, washing, and drying at 25 ℃ for 2.5h to obtain the nano-starch crystal. Weighing 2.5 parts of sodium trimetaphosphate to prepare 50 parts of solution, adding the nano-starch crystal into the solution, uniformly mixing, standing, soaking for 1h, maintaining the solution at 25 ℃ for 1h, centrifuging, stirring, washing, and drying at 25 ℃ for 2h to obtain the esterified nano-starch crystal. The esterified nano-starch crystals are mixed with 100 parts of deionized water, 30 parts of a stabilizer (polyethylene glycol 600: polyethylene glycol 20000= 5) and 1 part of dimethyldodecylsulfopropyl ammonium salt are added into the feed liquid at 20 ℃, and the mixture is mixed uniformly. Weighing 0.75 part of potassium chloride at 30 ℃ to prepare 15 parts of inorganic salt solution, simultaneously dripping 0.5 part of glutaraldehyde into the feed liquid at the same temperature, continuously reacting for 3 hours after dripping is finished, and obtaining white powdery nanoscale crosslinked starch microspheres through centrifugation, washing and drying. The cumulative distribution of the starch microspheres in each particle size interval is as follows: (d.ltoreq.25 nm): 0.26 percent; (d.ltoreq.50 nm): 2.28 percent; (d.ltoreq.125 nm): 5.96 percent; (d is less than or equal to 250 nm): 20.05 percent; (d.ltoreq.500 nm): 51.78%; (d.ltoreq.1000 nm): 91.09 percent. Typical particle size distribution characteristics are: d10=178nm; d50=489nm; d90=799nm.

Weighing 4 parts of bentonite, adding the bentonite into 100 parts of water to prepare bentonite-based slurry, sequentially adding 1 part of nano-starch microsphere oil-gas layer protective agent, 3 parts of DMAPS modified starch fluid loss additive, 0.4 part of PEP polyether polyol coating agent, 3 parts of nano calcium carbonate wall-fixing agent and 0.4 part of XY-27 viscosity reducer into the prepared bentonite-based slurry, and fully mixing at normal temperature to prepare the starch-based environment-friendly drilling fluid treating agent system A2.

Comparative example 3

Weighing 5 parts of wheat starch, adding the wheat starch into 100 parts of deionized water, fully and uniformly mixing, dropwise adding 200 parts of toluene into the feed liquid, standing after dropwise adding to obtain a bottom insoluble substance, centrifuging, stirring and washing, and drying at 25 ℃ for 2.5 hours to obtain the nano starch crystal. Weighing 2.5 parts of sodium trimetaphosphate to prepare 50 parts of solution, adding the nano-starch crystal into the solution, uniformly mixing, standing, soaking for 1h, maintaining the solution at 25 ℃ for 1h, centrifuging, stirring, washing, and drying at 25 ℃ for 2h to obtain the esterified nano-starch crystal. Mixing the esterified nano-starch crystal with 100 parts of deionized water, heating the obtained solution to boiling, keeping the temperature for 15min, cooling the feed liquid to 20 ℃, adding 30 parts of a stabilizer (polyethylene glycol 600: polyethylene glycol 20000= 5) and 1 part of dimethyl dodecyl sulfopropyl ammonium salt into the feed liquid, and fully and uniformly mixing the materials. Weighing 0.75 part of potassium chloride at 30 ℃ to prepare 15 parts of inorganic salt solution, simultaneously dripping 0.5 part of glutaraldehyde into the feed liquid at the same temperature, continuously reacting for 3 hours after dripping is finished, and obtaining white powdery nanoscale crosslinked starch microspheres through centrifugation, washing and drying. The cumulative distribution of the starch microspheres in each particle size interval is as follows: (d.ltoreq.25 nm): 0.00 percent; (d.ltoreq.50 nm): 1.57 percent; (d. Ltoreq.125 nm): 3.89 percent; (d.ltoreq.250 nm): 16.14 percent; (d is less than or equal to 500 nm): 45.22 percent; (d.ltoreq.1000 nm): 92.03 percent. Typical particle size distribution characteristics are: d10=201nm; d50=542nm; d90=987nm.

Weighing 4 parts of bentonite, adding the bentonite into 100 parts of water to prepare bentonite-based slurry, sequentially adding 1 part of nano-starch microsphere oil-gas layer protective agent, 3 parts of DMAPS modified starch fluid loss additive, 0.4 part of PEP polyether polyol coating agent, 3 parts of nano calcium carbonate wall-fixing agent and 0.4 part of XY-27 viscosity reducer into the prepared bentonite-based slurry, and fully mixing at normal temperature to prepare the starch-based environment-friendly drilling fluid treating agent system A3.

Comparative example 4

Weighing 5 parts of wheat starch, adding the wheat starch into 100 parts of deionized water, boiling for 20min, cooling the feed liquid to 20 ℃, dropwise adding 200 parts of toluene into the feed liquid, standing after dropwise addition to obtain a bottom insoluble substance, centrifuging, stirring, washing, and drying at 25 ℃ for 2.5h to obtain the nano-starch crystal. Mixing the nano-starch crystals with 100 parts of deionized water, heating the obtained solution to boil, keeping the temperature for 15min, then cooling the feed liquid to 20 ℃, adding 30 parts of a stabilizer (polyethylene glycol 600: polyethylene glycol 20000= 5) and 1 part of dimethyl dodecyl sulfopropyl ammonium salt into the feed liquid, and fully and uniformly mixing the components. Weighing 0.75 part of potassium chloride at 30 ℃ to prepare 15 parts of inorganic salt solution, simultaneously dripping 0.5 part of glutaraldehyde into the feed liquid at the same temperature, continuously reacting for 3 hours after dripping is finished, and obtaining white powdery nanoscale crosslinked starch microspheres through centrifugation, washing and drying. The cumulative distribution of the starch microspheres in each particle size interval is as follows: (d. Ltoreq.25 nm): 0.83 percent; (d.ltoreq.50 nm): 2.02 percent; (d.ltoreq.125 nm): 10.98 percent; (d.ltoreq.250 nm): 30.14 percent; (d.ltoreq.500 nm): 59.19 percent; (d ≦ 1000 nm): 95.18 percent. Typical particle size distribution characteristics are: d10=118nm; d50=472nm; d90=736nm.

Weighing 4 parts of bentonite, adding the bentonite into 100 parts of water to prepare bentonite-based slurry, sequentially adding 1 part of nano-starch microsphere oil-gas layer protective agent, 3 parts of DMAPS modified starch fluid loss additive, 0.4 part of PEP polyether polyol coating agent, 3 parts of nano calcium carbonate wall-fixing agent and 0.4 part of XY-27 viscosity reducer into the prepared bentonite-based slurry, and fully mixing at normal temperature to prepare the starch-based environment-friendly drilling fluid treating agent system A4.

Comparative example 5

Weighing 5 parts of wheat starch, adding the wheat starch into 100 parts of deionized water, boiling for 20min, cooling the feed liquid to 20 ℃, dropwise adding 200 parts of toluene into the feed liquid, standing after dropwise addition to obtain a bottom insoluble substance, centrifuging, stirring, washing, and drying at 25 ℃ for 2.5h to obtain the nano-starch crystal. Weighing 2.5 parts of sodium trimetaphosphate to prepare 50 parts of solution, adding the nano-starch crystal into the solution, uniformly mixing, standing, soaking for 1h, maintaining the solution at 25 ℃ for 1h, centrifuging, stirring, washing, and drying at 25 ℃ for 2h to obtain the esterified nano-starch crystal. Mixing the esterified nano-starch crystals with 100 parts of deionized water, heating the obtained solution to boiling, keeping the temperature for 15min, then cooling the feed liquid to 20 ℃, adding 30 parts of a stabilizer (polyethylene glycol 600: polyethylene glycol 20000= 5) and 1 part of dimethyldodecylsulfopropyl ammonium salt into the feed liquid, and fully and uniformly mixing the materials. Weighing 0.75 part of potassium chloride at 30 ℃ to prepare 15 parts of inorganic salt solution, simultaneously dripping 0.5 part of glutaraldehyde into the feed liquid at the same temperature, continuously reacting for 3 hours after dripping is finished, and obtaining white powdery nanoscale crosslinked starch microspheres through centrifugation, washing and drying. The cumulative distribution of the starch microspheres in each particle size interval is as follows: (d.ltoreq.25 nm): 1.99 percent; (d.ltoreq.50 nm): 5.76 percent; (d.ltoreq.125 nm): 21.22 percent; (d.ltoreq.250 nm): 39.30 percent; (d is less than or equal to 500 nm): 86.32 percent; (d.ltoreq.1000 nm): 99.25 percent. Typical particle size distribution characteristics are: d10=81nm; d50=327nm; d90=519nm.

Weighing 4 parts of bentonite, adding the bentonite into 100 parts of water to prepare bentonite base slurry, sequentially adding 1 part of nano starch microsphere oil-gas layer protective agent, 3 parts of sulfomethyl phenolic resin filtrate reducer, 0.4 part of PEP polyether polyol coating agent, 3 parts of non-fluorescent sulfonated asphalt wall-fixing agent and 0.4 part of iron-chromium lignosulfonate viscosity reducer into the prepared bentonite base slurry, and fully mixing at normal temperature to prepare the starch-based environment-friendly drilling fluid treating agent system A5.

Performance evaluation:

1. young's modulus test

And (3) measuring the compression Young modulus of the nano-scale crosslinked starch microspheres by adopting an AFM force curve technology so as to evaluate the crosslinking strength of the nano-scale starch microspheres.

The instrumentation used in the evaluation process included: a JSM-6360LA scanning electron microscope used for observing the appearance and the particle size of a sample; the VeecoDimension-V atomic force microscope is used for carrying out AFM force curve measurement on the microspheres, the used probe is an NSG-10 type monocrystalline silicon probe, the curvature radius is about 10nm, and the elastic coefficient range is 3.1-37.6N/m; nanoScope Analysis software was used to fit the force curve data and calculate the young's modulus of the samples. The experimental steps are as follows:

(1) Substrate pretreatment: and preparing the starch microsphere single-layer film by using a silicon wafer (roughness RMS value less than 0.4 nm) as a rigid substrate. The silicon wafer is ultrasonically cleaned for 30min by ethanol, and then the silicon wafer is subjected to hydrophilic treatment for 1h at 80 ℃ by a mixed solution of hydrogen peroxide solution (30%) and concentrated sulfuric acid (98%) in a volume ratio of 1.

(2) Sample pretreatment: weighing 1 part of starch microspheres, fully and uniformly mixing and dispersing in 100 parts of ethanol solution to prepare starch microsphere suspension with the mass fraction of 1%, carrying out ultrasonic treatment on the suspension at room temperature for 5min, then titrating the suspension on the surface of a silicon wafer, and airing the silicon wafer to be tested.

(3) The force-displacement curve of the sample was tested and recorded at 25 ℃ and 40% relative humidity, the effective force curve data was analyzed and fitted, and the young's modulus of the sample was calculated from the Hertz's model, with the specific results shown in table 1.

TABLE 1 results of the experiment

The results show that when the samples of examples 1-9 are adopted, the Young modulus of the microsphere is greater than 1.6GPa, the largest Young modulus can reach (2.55 +/-0.39) GPa, the ratio of the stress to the strain of the microsphere is larger, and the strength of the nano crosslinked starch microsphere is higher. When the samples of comparative examples 1-4 are adopted, the Young modulus of the microspheres is small, the ratio of stress to strain is small, and particularly, the Young modulus of the microspheres is as low as (0.55 +/-0.38) and (0.72 +/-0.42) in comparative examples 1 and 4 which are not internally crosslinked, which indicates that the strength of the nano crosslinked starch microspheres is weak.

2. Starch microsphere plugging performance test

The plugging performance of the starch microspheres in a mineralization dispersion system is evaluated by adopting a constant-pressure microporous (nanoscale) filter membrane, the microporous filter membrane can be taken as a section of the pore throat of a shale reservoir, the plugging effect of the microspheres on the pore throat is simulated, and the method has the advantages of accuracy and convenience and is suitable for rapid evaluation in laboratories and on sites. Based on the method, the microporous filter membrane is used for replacing filter paper, and a microsphere emulsion filtration experiment is carried out under 0.1MPa, so that the blocking condition of microspheres to the pore throat of the reservoir can be simulated.

The instruments used in the evaluation procedure included: medium pressure filtration loss instrument, stirrer, settling kettle, roller furnace and evaluation tank. Experimental materials: the examples and comparative examples were emulsion (solid content 30%), nylon filter (hydrophilic type, membrane diameter 90mm, pore diameter 0.4 μm), filter paper for drilling fluid (diameter 90 mm).

The experimental steps are as follows:

(1) Preparing a dispersion system: preparing a dispersion system with the microsphere concentration of 20% and the mineralization degree of 5000mg/L by using deionized water, starch microspheres and sodium chloride, putting the system into a precipitation kettle, aging for 12 hours at 120 ℃, and standing the system to room temperature after aging is finished.

(2) Nuclear track membrane plugging experiment: the nylon filter membrane was placed at the bottom of the filtration analyzer evaluation tank and clamped tightly, 100ml of the uniformly stirred microsphere dispersion was added to the tank, the evaluation tank was sealed, and the time of the entire filtration loss of the microsphere emulsion dispersion was recorded at a pressure of 0.1 MPa.

The fluid loss time of the starch microsphere dispersion after aging was h, and the results are shown in Table 2.

TABLE 2 results of the experiment

From the above results, it can be seen that when the samples of examples 1 to 9 were used, the total fluid loss time of the microsphere emulsion was greater than 160min, indicating that the plugging effect was good and the fluid loss reduction effect was significant. When the samples of comparative examples 1-4 were used, the total fluid loss time of the microspheres was less than 25min, indicating that the effect was not good.

3. Testing of water loss reducing performance of drilling fluid system

The water loss reduction performance of the starch-based drilling fluid systems obtained in the above examples 1 to 9 and comparative examples 1 to 4 was evaluated by a sand bed plugging experiment. An experimental instrument: a drilling fluid sand bed filtration loss instrument and a stirrer. Experimental materials: example samples, comparative samples and 20-40 mesh sand samples.

The experimental steps are as follows:

(1) Manufacturing a sand bed: adding 20-40 mesh sand into the cylinder at 350mm, and shaking up;

(2) Adding 400mL of samples of the examples and the comparative examples, fixing the samples on an instrument frame, and sealing an upper channel and a lower channel;

(3) And opening an air source, adjusting the pressure to 0.69mPa, simultaneously opening an upper switch and a lower switch, and measuring the condition that the drilling fluid invades the sand bed in the half-hour process.

The experimental results are as follows:

filtration loss FL after 30min of adding the samples of the examples and the comparative examples ₁ And the drilling fluid is basically stable after invading the sand bed to the depth D. After a stable mud cake is formed, the drilling fluid is discharged after pressure relief, clear water is added to the position of 400mL, and the filtration loss FL after 30min of pressurization (0.69 mPa) measurement is carried out ₂ The results are shown in Table 3.

4. Testing temperature resistance and salt resistance of drilling fluid system

And (3) evaluating the salt resistance of the drilling fluid systems obtained in the examples and the comparative examples by using a medium-temperature medium-pressure filtration loss instrument. An experimental instrument: medium temperature and medium pressure filtration loss instrument, stirrer, deposition kettle and rolling heating furnace. Experimental materials: examples, comparative examples, sodium chloride, calcium chloride.

The experimental steps are as follows:

(1) And slurry preparation: the CaCl is cut at the rate of drilling fluid +15% NaCl ₂ + 2% of the example sample or the comparative example formulation material.

(2) And high-temperature aging of the drilling fluid: and (2) measuring 350ml of the drilling fluid obtained in the step (1), and filling into a settling kettle. And then placing the precipitation kettle into a roller type heating furnace, and aging the drilling fluid added with the compound material for 16 hours at the temperature of 180 ℃.

(3) And evaluating the temperature resistance and salt resistance: and cooling the aged drilling fluid to room temperature, pouring the drilling fluid into an evaluation tank, and then installing the evaluation tank on a medium-temperature medium-pressure filtration loss instrument. And opening an air source, adjusting the pressure to 0.69mPa, then opening an air inlet switch, and measuring the water loss amount of the drilling fluid in the half-hour process.

The experimental results are as follows:

evaluation of fluid loss of drilling fluid FL 30min after the start of the experiment ₃ The results are shown in Table 1.

TABLE 3 results of the experiment

According to the results, when the drilling fluid prepared by the scheme of the embodiment is adopted, the filtration loss of clear water in 0.69mPa pressure within 30min is obviously lower than that of the comparative sample, and the plugging effect is good. In addition, when the drilling fluid prepared by the comparative example scheme is adopted, the invasion depth of the drilling fluid in 0.69mPa pressure within 30min can reach 305mm at most, which indicates that the effect is poor. Therefore, the starch-based drilling fluid adopting the nano starch microspheres as the plugging material has good plugging and filtrate loss reducing performances.

In the evaluation of temperature resistance and salt resistance, when the sample of the embodiment is adopted, the filtration loss of the drilling fluid in 0.69mPa pressure within 30min is lower than that of the embodiment under the same condition, which shows that the drilling fluid still has good plugging performance and excellent temperature resistance and salt resistance after aging at 180 ℃ and under high-salt conditions. When the sample of the comparative example is adopted, the filtration loss of the drilling fluid can reach 5ml at the maximum within 30min under the pressure of 0.69mPa, and the effect is relatively poor.

5. Environmental performance test of drilling fluid system

The environmental protection performance of the drilling fluid systems of the examples and the comparative examples was evaluated according to the drilling fluid environmental protection performance evaluation indexes and evaluation methods in table 4, and the results are shown in table 5.

TABLE 4 evaluation index and evaluation method for environmental protection performance of drilling fluid

TABLE 5 results of the experiment

According to the results, when the drilling fluid prepared by the schemes of the examples and the comparative examples 1 to 4 is adopted, the heavy metal content of the drilling fluid is ppb level, and the heavy metal content is dozens of times lower than that of the conventional drilling fluid; the biological toxicity is far more than 30000, and the discharge standard is reached; and in terms of biodegradability, drilling fluid BOD ₅ /COD _cr Far more than 10 percent, and belongs to the environment-friendly degradable category. And in the comparative example 5, the heavy metal content of the starch-based polysulfonate drilling fluid formed by compounding the nano starch microspheres with the sulfonated material is far higher than that of the starch-based polysulfonate drilling fluid in the examples and the comparative examples 1 to 4, the biotoxicity is 19000, the actual nontoxic standard can only be achieved, the emission standard (not less than 30000) cannot be achieved, and the biodegradability cannot reach the standard value, which indicates that the comprehensive environmental protection performance of the starch-based polysulfonate drilling fluid is poor.

Claims

1. The drilling fluid comprises water, bentonite, a nano starch microsphere oil-gas layer protective agent, a viscosity reducer, a wall fixing agent, a polyether polyol coating agent and a fluid loss additive, and comprises the following components in parts by weight: 100 parts of water, 1-6 parts of bentonite, 0.5-5 parts of nano starch microsphere oil-gas layer protective agent, 0.5-5 parts of modified starch fluid loss additive, 0.2-4 parts of polyether polyol coating agent, 0.5-4 parts of wall-fixing agent and 0.05-0.5 part of viscosity reducer; the nano-starch microsphere oil-gas layer protective agent comprises raw materials of water, starch, a solvent, sodium trimetaphosphate, a monomer, an initiator, a stabilizer, a zwitterionic surfactant, a cross-linking agent and an inorganic salt solution, and the raw materials are counted by weight: 200 parts of deionized water, 1-25 parts of starch, 100-500 parts of solvent and 37.5-100 parts of sodium trimetaphosphate solution, wherein the solute sodium trimetaphosphate accounts for 0.5-12.5 parts, 0.2-10 parts of monomer, 0.001-0.2 part of initiator, 10-60 parts of stabilizer, 0.1-10 parts of zwitterionic surfactant, 0.1-15 parts of cross-linking agent and 3-75 parts of inorganic salt solution, and the solute inorganic salt accounts for 0.1-15 parts;

the preparation method of the nano starch microsphere oil-gas layer protective agent comprises the following steps:

2. The drilling fluid of claim 1, wherein: the drilling fluid comprises water, bentonite, a nano-starch microsphere oil-gas layer protective agent, a viscosity reducer, a wall fixing agent, a polyether polyol coating agent and a fluid loss additive, and comprises the following components in parts by weight: 100 parts of water, 2-4 parts of bentonite, 1-3 parts of nano starch microsphere oil-gas layer protective agent, 1-3 parts of modified starch fluid loss additive, 0.4-2 parts of polyether polyol coating agent, 1-3 parts of wall fixing agent and 0.2-0.4 part of viscosity reducer.

3. The drilling fluid of claim 1, wherein: the nano-starch microsphere oil-gas layer protective agent comprises raw materials of water, starch, a solvent, sodium trimetaphosphate, a monomer, an initiator, a stabilizer, a zwitterionic surfactant, a cross-linking agent and an inorganic salt solution, wherein the raw materials comprise the following components in parts by weight: 200 parts of deionized water, 5-15 parts of starch, 200-400 parts of solvent, 50-75 parts of sodium trimetaphosphate solution, wherein the solute sodium trimetaphosphate accounts for 2.5-10 parts, 0.5-6 parts of monomer, 0.003-0.06 part of initiator, 30-50 parts of stabilizer, 1-4.5 parts of zwitterionic surfactant, 0.5-9 parts of cross-linking agent and 15-45 parts of inorganic salt solution, and the solute of inorganic salt accounts for 0.75-9 parts.

4. The drilling fluid of claim 1, wherein: the wall-fixing agent is an inorganic wall-fixing agent.

5. The drilling fluid according to claim 1 or 4, wherein: the wall-fixing agent is selected from one or two of nano calcium carbonate and nano silicon dioxide.

6. The drilling fluid of claim 1, wherein: the polyether polyol coating agent is block copolyether containing terminal hydroxyl or terminal alkoxy.

7. The drilling fluid of claim 1, wherein: the polyether polyol is any one or more of three-stage polyether polyol or any one or two of two-stage polyether polyol.

8. The drilling fluid of claim 7, wherein: when the polyether polyol is a three-section polyether polyol, the polyether polyol is PEP polyether polyol with two ends provided with a Propylene Oxide (PO) structural unit and the middle provided with an Ethylene Oxide (EO) structural unit, or EPE polyether polyol with two ends provided with an Ethylene Oxide (EO) structural unit and the middle provided with a Propylene Oxide (PO) structural unit, the structural formulas of the PEP polyether polyol and the EPE polyether polyol are shown as (1) and (2), wherein a, b and c are non-zero integers and meet the condition that (a + b + c) is more than or equal to 25 and less than or equal to 125; when the polyether polyol is a two-stage polyether polyol, the polyether polyol is EP polyether polyol in a structural unit form of Ethylene Oxide (EO) -Propylene Oxide (PO) or PE polyether polyol in a structural unit form of Propylene Oxide (PO) -Ethylene Oxide (EO), the structural formulas of the EP polyether polyol and the PE polyether polyol are shown as (3) and (4), wherein x and y are non-zero integers and satisfy the condition that x + y is not less than 25 and not more than 100;

（1）；

（2）；

（3）；

（4）。

9. the drilling fluid of claim 8, wherein: a. b and c are non-zero integers, and satisfy that (a + b + c) is more than or equal to 75 and less than or equal to 100; x and y are non-zero integers, and satisfy that (x + y) is more than or equal to 50 and less than or equal to 75.

10. The drilling fluid of claim 1, wherein: the filtrate reducer is a modified starch filtrate reducer.

11. Drilling fluid according to claim 1 or 10, wherein: the fluid loss additive is one or more of zwitterion modified starch and nonionic modified starch.

12. The drilling fluid according to claim 1 or 10, wherein: the filtrate reducer is zwitterionic modified starch.

13. The drilling fluid of claim 11, wherein: when the modified starch fluid loss additive is zwitterion modified starch, the modified starch fluid loss additive is one or more of methacryloyloxyethyl-N, N-dimethyl propane sulfonate grafted starch, N-dimethyl allyl amine propane sulfonate grafted starch, 4-vinyl pyridine propane sulfonate grafted starch, N-methyl diallyl propane sulfonate grafted starch and N-methyl diallyl butane sulfonate grafted starch; when the modified starch fluid loss additive is nonionic modified starch, the modified starch fluid loss additive is one or more of N-vinyl pyrrolidone grafted starch, acrylonitrile grafted starch, vinyl formamide grafted starch and vinyl acetamide grafted starch.

14. The drilling fluid of claim 1, wherein: the viscosity reducer is an amphoteric series monomer oligomer viscosity reducer.

15. The drilling fluid according to claim 1 or 14, wherein: the viscosity reducer is any one or two of zwitter ion vinyl monomer oligomer viscosity reducer XY-27 and XY-28.

16. The drilling fluid of claim 1, wherein: in the step S1, the starch is one or more of mung bean starch, cassava starch, sweet potato starch, wheat starch, water caltrop starch, lotus root starch and corn starch.

17. The drilling fluid according to claim 1 or 16, wherein: in step S1, the starch is corn starch and/or potato starch.

18. The drilling fluid of claim 1, wherein: in step S1, the temperature is reduced to 10-50 ℃.

19. The drilling fluid according to claim 1 or 18, wherein: in the step S1, the temperature is reduced to 20-40 ℃.

20. The drilling fluid of claim 1, wherein: the solvent in step S2 is an organic solvent.

21. The drilling fluid according to claim 1 or 20, wherein: in the step S2, the solvent is one or more of ethanol, methanol, benzyl alcohol, acetone, cyclohexanone, acetophenone, toluene, ethylbenzene and chlorobenzene.

22. The drilling fluid according to claim 1 or 20, wherein: the solvent in step S2 is ethanol and/or acetone.

23. The drilling fluid according to claim 1 or 20, wherein: in the step S2, the solvent is ethanol.

24. The drilling fluid of claim 1, wherein: the separation in step S3 is centrifugal separation; the washing is carried out by using an ethanol solvent under stirring, wherein the ethanol solvent is excessive; the drying is carried out for 2 to 8 hours at the temperature of between 20 and 50 ℃.

25. The drilling fluid of claim 1, wherein: in the step S4, the curing temperature is 20-60 ℃.

26. The drilling fluid of claim 1, wherein: and in the step S6, the stabilizer is one or more of polyalcohol, alcohol amine, polyvinylpyrrolidone and tween.

27. The drilling fluid according to claim 1 or 26, wherein: in the step S6, the stabilizer is one or more of polyethylene glycol 400, polyethylene glycol 600, polyethylene glycol 1000, polyethylene glycol 2000, polyethylene glycol 4000, polyethylene glycol 6000, polyethylene glycol 10000, polyethylene glycol 20000, diglycerol, triglycerol, glycerol, diethylene glycol, triethanolamine, triisopropanolamine, N-methyldiethanolamine, polyvinylpyrrolidone K12, polyvinylpyrrolidone K30, polyvinylpyrrolidone K60, tween 20, tween 40, tween 60 and Tween 80.

28. The drilling fluid of claim 1, wherein: in the step S6, the cross-linking agent is an organic cross-linking agent and is one or more of epichlorohydrin, phosphorus oxychloride, formaldehyde, glyoxal and glutaraldehyde.

29. The drilling fluid according to claim 1 or 28, wherein: in the step S6, the cross-linking agent is epoxy chloropropane.

30. The drilling fluid of claim 1, wherein: in step S6, the zwitterionic surfactant is a betaine zwitterionic surfactant.

31. The drilling fluid according to claim 1 or 30, wherein: in the step S6, the zwitterionic surfactant is one or more of dimethyldodecylcarboxymethyl ammonium salt, dimethyldodecylcarboxyethyl ammonium salt, dimethylhexadecylcarboxymethyl ammonium salt, dimethyloctadecyl carboxymethyl ammonium salt, dimethyldodecylsulfopropyl ammonium salt, dimethylhexadecylsulfoethyl ammonium salt, dimethyloctadecyl sulfobutyl ammonium salt, dimethyl (3-hydroxydodecyl) sulfopropyl ammonium salt, dimethyl (6-aminotetradecyl) sulfoethyl ammonium salt, dimethyldodecyl methyl ammonium phosphate, dimethyldodecyl ethyl ammonium phosphate, dimethyltetradecyl methyl ammonium phosphate, dimethylhexadecyl methyl ammonium phosphate and dimethyloctadecyl methyl ammonium phosphate.

32. The drilling fluid of claim 1, wherein: in the step S6, the inorganic salt is soluble inorganic salt and is one or more of sodium salt, potassium salt, ammonium salt, calcium salt and magnesium salt.

33. The drilling fluid of claim 32, wherein: when the inorganic salt is sodium salt, the inorganic salt is one or more of sodium chloride, sodium bromide, sodium sulfate, sodium sulfite, sodium carbonate, sodium bicarbonate, sodium nitrate, sodium phosphate, sodium hydrogen phosphate and sodium silicate; when the inorganic salt is potassium salt, the inorganic salt is one or more of potassium chloride, potassium bromide, potassium sulfate, potassium sulfite, potassium carbonate, potassium bicarbonate, potassium nitrate, potassium phosphate, potassium hydrogen phosphate and potassium silicate; when the inorganic salt is ammonium salt, the inorganic salt is one or more of ammonium chloride, ammonium bromide and ammonium nitrate; when the inorganic salt is calcium salt, calcium chloride or calcium bromide; when the inorganic salt is magnesium salt, the inorganic salt is one or more of magnesium chloride, magnesium bromide, magnesium sulfate and magnesium nitrate.

34. The drilling fluid of claim 1, wherein: step S501 is also arranged between the step S5 and the step S6, the monomer is added into the feed liquid obtained in the step S5, and the mixture is fully dissolved and mixed, and then the initiator is added to react for 3 to 6h; the monomer is one or more of a cationic monomer, an anionic monomer, a zwitterionic monomer and a nonionic monomer.

35. The drilling fluid of claim 34, wherein: the initiator is one or more of potassium persulfate, sodium persulfate and ammonium persulfate.

36. The preparation method of the drilling fluid as claimed in any one of claims 1 to 35, wherein the preparation method comprises the steps of mixing water, bentonite, a nano-starch microsphere hydrocarbon reservoir protective agent, a viscosity reducer, a wall fixing agent, a polyether polyol coating agent and a fluid loss additive, and uniformly mixing to obtain the drilling fluid.

37. Use of a drilling fluid according to any one of claims 1 to 35 in a reservoir development process.