An oil-resistant foam stabilizer and a preparation method thereof, and a high-oil-content microfoam fluid and a preparation method thereof

Abstract

The application provides an anti-oil foam stabilizer and a preparation method thereof, and a high-oil-content microfoam fluid and a preparation method thereof. The anti-oil foam stabilizer comprises an emulsifier, a viscoelastic polymer and modified starch. The viscoelastic polymer is an organic polymer with an elastic modulus to viscous modulus ratio of 1<10; and the modified starch is prepared by etherification of starch under alkaline conditions. The anti-oil foam stabilizer added into the microfoam fluid can greatly improve the anti-oil pollution capacity of the microfoam fluid, changes the conventional oil pollution into oil performance promotion, improves the oil content capacity limit of the microfoam fluid technology, and improves the stability of the microfoam fluid.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of drilling engineering low-density leak-proof plugging technology, and particularly relates to an oil-resistant foam stabilizer and a preparation method thereof, and a high-oil-content micro-foam fluid and a preparation method thereof, which can greatly improve the oil pollution resistance of the micro-foam fluid and provide technical support for low-density drilling in a low-pressure leakage formation with serious oil leakage. BACKGROUND

[0002] The micro-foam fluid is formed by using a surfactant to reduce the gas / liquid surface tension, by a multi-layer liquid film to wrap a gas core to form an independent sphere, and by a bubble group to exist in the system in a single suspension or a partially interconnected manner, thereby forming a micro-foam system. As a low-density drilling fluid technology, the micro-foam fluid can reduce the density of the drilling fluid, reduce the pressure difference between the liquid column and the formation pore pressure, reduce the leakage amount, and realize low-density drilling while drilling in a leakage formation. 3 The micro-foam fluid is mainly applied to fractured limestone formations, clastic rock and ancient buried hill carbonate rock, igneous rock and other formations. The technology has been applied to more than 100 wells of high-deviation wells, horizontal wells and underbalanced pressure drilling in Shengli Oilfield, and has successfully solved the problem of serious leakage in low-pressure formations of the ancient buried hill in Shengli Oilfield, and has achieved remarkable economic and social benefits.

[0003] Although the technology has obvious advantages in underbalanced drilling, it also has obvious disadvantages, one of which is poor resistance to crude oil pollution and sensitivity to lubricants. If a serious oil leakage formation is drilled or a large amount of lubricant is added in horizontal well drilling, the stability of the micro-foam fluid will be dramatically deteriorated, and even completely defoamed, thereby increasing the density, leaking the formation and causing downhole complex accidents.

[0004] Chinese patent CN 201410451339.3 discloses an anti-high-temperature micro-foam drilling fluid, which is composed of modified attapulgite 10-15 parts, sodium alpha-alkyl sulfonate 4-6 parts, nano-titanium dioxide 0.5-2 parts, tea saponin 1-3 parts, nano-molybdenum disulfide 0.2-0.5 parts, nano-zirconium dioxide 0.4-0.7 parts, filtration reducer 3-5 parts, shale inhibitor 1-2 parts, and water 100-130 parts. The temperature resistance can reach 130℃, the half-life period is 27.6 minutes, the foaming volume decreases from 521 mL to 370 mL in 10% kerosene, the density decreases obviously, and the half-life period of the system is short and the stability is poor.

[0005] Drilling Fluids and Completion Fluids, No. 25, 2008, introduces an experimental study on an anti-high-temperature seawater micro-foam drilling fluid. The micro-foam drilling fluid prepared in the paper has a density of 0.6-0.95 g / cm 3LNW was introduced to improve the temperature stability of the seawater micro-foam drilling fluid, which can reach 150℃ and the long-term stability can reach 7 days. However, after adding 5% of crude oil, the density of the drilling fluid increases from 0.70 to 0.72 and the half-life decreases from 5 days to about 24 hours. The density of the drilling fluid changes little, but the stability of the micro-foam film decreases dramatically, which may cause hidden troubles in the field safety.

[0006] A high-lubricating micro-foam drilling fluid and a preparation method thereof are provided in Chinese patent CN201610753824.5. The high-lubricating micro-foam drilling fluid is composed of base slurry, lubricant and additive. The base slurry is prepared from 8-12 parts of bentonite, 0.2-0.3 parts of alkali and 100-140 parts of water. The additive is prepared from 5-10 parts of tackifier, 1-5 parts of aluminum oxide, 1-5 parts of polyquaternary sodium, 10-15 parts of sulfonate, 2-6 parts of carboxymethyl cellulose, 0.5-1 part of nano titanium chloride, 0.5-1 part of viscosity reducer and 0.1-0.5 part of sodium dodecyl sulfate. The lubricant is aliphatic succinic acid, and the amount of the lubricant is 5-10 parts by weight. The lubricant is aliphatic succinic acid, and the inclusion capacity is 10%. The density of the drilling fluid is 0.53-0.62 g / cm 3 , the half-life is 16-17 hours, and the lubrication coefficient is 0.13. The technology provided in the patent is suitable for a specific lubricant product and does not have broad spectrum. The half-life is short, the drilling fluid does not have temperature resistance, the lubrication coefficient is high, and the drilling fluid is not suitable for deep well high-temperature environment, directional wells or horizontal wells with high lubrication performance requirements, and the content of bentonite is extremely high, which is not conducive to oil and gas layer protection.

[0007] A high-oil micro-foam drilling fluid is provided in Chinese patent CN201310078767.1. The content of each component is 100 parts of water, 2.5-3 parts of bentonite, 0.10-0.15 parts of sodium carbonate, 0.10-0.15 parts of pH value regulator, 0.20-0.25 parts of anti-sloughing agent (polyacrylamide potassium salt), 0.4-0.5 parts of filtration loss reducer (hydrolyzed polyacrylonitrile sodium salt), 1.5-2.0 parts of anti-sloughing agent (sulfonated asphalt), 0.8-1.0 parts of high-temperature resistant filtration loss reducer (sulfonated phenolic resin), 0.10-0.15 parts of flow pattern regulator (XC), and 47-113 parts of oil (light crude oil) and 3-4 parts of oil-water compatible foaming agent DRfoam-Ⅱ. The oil content is 30.15%-50.4%, and the density is 0.322-0.399 g / cm 3, half-life of 4-8h. This patent significantly improves the capacity limit of microfoam on light crude oil, but at the same time leads to very low microfoam density, short half-life, and high requirements for key foaming agents - must be oil-water compatible foaming agent, which will cause the foaming agent to preferentially adsorb at the oil-water interface, and the amount of adsorption at the gas-liquid interface will be greatly reduced, thereby sharply reducing the stability of the foam in the oil. In addition, the use of such oil-water compatible foaming agents or oil-based foaming agents has low industrialization degree and does not have on-site implementation.

[0008] Chinese patent CN201310012264.4 provides a high oil-water ratio oil-in-water recyclable microfoam drilling fluid composition, which comprises foaming agent: 0.5%-8wt%; oil: 55%-90wt%; bentonite: 0.5%-8wt%; tackifier: 0.15-1wt%; fluid loss additive: 0.55%-8wt%; diluent: 0.2%-3wt%; shale inhibitor: 0-8wt%; weighting agent: 1.05g / cm 3 ~2.2g / cm 3 according to the added amount; the balance is water phase; this drilling fluid composition can form an oil-in-water recyclable microfoam drilling fluid in a water-based drilling fluid and under conditions containing different added amounts (0-80%) of oil (kerosene, diesel or light crude oil), which has good lubricity, low fluid loss, leak-proof effect, is not flammable and safe during drilling, and has good temperature resistance. The tackifier is a biopolymer, acrylic-acrylamide copolymer, cellulose natural high molecular polymer, the fluid loss additive is lignite resin, phenolic resin, asphalt, acrylic polymer, modified starch, modified cellulose, the diluent is zwitterionic or lignin polymer, and the shale inhibitor is sodium chloride, potassium chloride, quaternary ammonium salt. The oil content reaches 80%, and the density is as low as 1.05g / cm 3 , and as high as 2.2g / cm 3 without any foam characteristic index - half-life performance index. The core of this patent is to expand the drilling fluid density range under the condition of weighting, which in fact does not form a foam system, but prevents the drilling fluid from being invaded by gas, forms a stable drilling fluid system, and wraps the gas core in the system in the form of foam to prevent complex accidents caused by large changes in drilling fluid performance.

[0009] In summary, the current micro-foam drilling fluid contains a large amount of bentonite, cellulose polymer, or a large amount of barite, which has a certain adsorption effect on oil and fat, but the capacity limit of oil or lubricant using these conventional treatment agents is 5% to 10%, the quality and stability of the micro-foam are reduced after being contaminated by oil and fat, the half-life is shortened, and the density is increased. Or use special oil-water compatible foaming agent to increase the oil content of the water-based micro-foam system, although the oil capacity of the micro-foam drilling fluid reaches 30% to 80%, the half-life is short, the foam quality is seriously attenuated, and the density is higher than the water density, becoming an oil-in-water drilling fluid, which does not have the effect of low-density drilling fluid. At the same time, the clay solid content of the system is very high, which causes great damage to the permeability of oil and gas layers. SUMMARY

[0010] In view of the above problems existing in the prior art, the present application provides an oil-resistant foam stabilizer which can greatly improve the oil pollution resistance of the micro-foam fluid, change the conventional oil and fat pollution into performance promotion of oil and fat, increase the oil capacity limit of the micro-foam fluid, and improve the stability of the micro-foam fluid. The present application also provides a preparation method of an oil-resistant foam stabilizer, a high-oil micro-foam fluid, and a preparation method thereof.

[0011] The first aspect of the present application provides an oil-resistant foam stabilizer, which comprises an emulsifier, a viscoelastic polymer, and modified starch.

[0012] According to some embodiments of the present application, the viscoelastic polymer is an organic polymer with an elastic modulus G' to viscous modulus G" ratio of 1

[0013] According to some embodiments of the present application, the modified starch is prepared by etherification of starch under alkaline conditions.

[0014] According to some embodiments of the present application, the weight parts include:

[0015] The emulsifier is 0.5 to 2.0 parts, the viscoelastic polymer is 0.1 to 0.3 parts, and the modified starch is 0.2 to 1.0 parts.

[0016] According to some embodiments of the present application, the parts of the emulsifier are 0.5, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, and any value therebetween.

[0017] According to some embodiments of the present application, the parts of the viscoelastic polymer are 0.1, 0.15, 0.2, 0.25, 0.3, and any value therebetween.

[0018] According to some embodiments of the present application, the parts of the modified starch are 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, and any value therebetween.

[0019] According to some embodiments of the present application, the emulsifier is selected from one or more of non-ionic surfactants, polyhydroxy surfactants.

[0020] According to some embodiments of the present application, the non-ionic surfactant comprises one or more of a Span surfactant and / or a Tween surfactant.

[0021] According to some embodiments of the present application, the Span surfactant comprises one or more of SP-20, SP-40, SP-60 and SP-80.

[0022] According to some embodiments of the present application, the Tween surfactant comprises one or more of TW-20, TW-40, TW-60 and TW-85.

[0023] According to some embodiments of the present application, the polyhydroxy surfactant comprises polyvinyl alcohol.

[0024] According to some embodiments of the present application, the polyhydroxy surfactant comprises one or more of polyvinyl alcohol BP05, polyvinyl alcohol 1288, polyvinyl alcohol 1488 and polyvinyl alcohol 1788.

[0025] According to some embodiments of the present application, the viscoelastic polymer comprises one or more of low molecular weight high temperature foam stabilizer TFS, xanthan gum XC and hydroxyethyl cellulose HEC.

[0026] According to some embodiments of the present application, the viscoelastic polymer has a weight average molecular weight of 1 million to 3 million.

[0027] According to some embodiments of the present application, the modified starch comprises one or more of carboxymethyl starch CMS and high temperature resistant starch CMS-K.

[0028] The second aspect of the present application provides a method for preparing the oil-resistant foam stabilizer of the first aspect, comprising the step of mixing the emulsifier, the viscoelastic polymer and the modified starch.

[0029] The third aspect of the present application provides a fluid, comprising a foaming agent, an oil, water and the oil-resistant foam stabilizer of the first aspect or prepared by the method of the second aspect.

[0030] According to some embodiments of the present application, the fluid has a density of 0.6 to 0.99 g / cm 3 .

[0031] According to some embodiments of the present application, the fluid has a half-life of 1 hour or more.

[0032] According to some embodiments of the present application, the half-life of the fluid is greater than 168 hours.

[0033] In the present application, the half-life refers to the time required for the volume of liquid drained from the foam to be half of the total volume of liquid in the foam, or the time required for the volume of the foam to be reduced to half of the volume of the foam before the liquid is drained.

[0034] According to some embodiments of the present application, the oil in the fluid accounts for more than 5 wt% of the total weight of the fluid.

[0035] According to some embodiments of the present application, the oil in the fluid accounts for more than 60 wt% of the total weight of the fluid.

[0036] According to some embodiments of the present application, the fluid comprises, by weight, 100-105 parts of water, 5-60 parts of oil, 0.5-2.0 parts of emulsifier, 0.1-0.3 parts of viscoelastic polymer, 0.2-1.0 parts of modified starch, and 0.3-0.8 parts of foaming agent.

[0037] According to some embodiments of the present application, the foaming agent comprises one or more of anionic foaming agent and non-ionic foaming agent.

[0038] According to some embodiments of the present application, the anionic foaming agent comprises one or more of sodium dodecyl benzene sulfonate (SDBS), sodium dodecyl sulfate (SDS), and sodium alpha-olefin sulfonate (AOS).

[0039] According to some embodiments of the present application, the non-ionic foaming agent comprises one or more of coconut oil diethanolamide, cocamidopropyl dimethyl tertiary amine (PKO), and oleic acid amidopropyl dimethyl tertiary amine (PKO-O).

[0040] The fourth aspect of the present application provides a method for preparing the fluid of the third aspect, comprising mixing the emulsifier, the viscoelastic polymer, the modified starch, the foaming agent, the oil, and the water.

[0041] According to some embodiments of the present application, the method comprises the following steps:

[0042] S1: obtaining an aqueous solution of emulsifier;

[0043] S2: mixing the viscoelastic polymer, the modified starch, and the foaming agent with the aqueous solution of emulsifier to obtain a mixture;

[0044] S3: emulsifying the mixture with the oil and optionally water to obtain the fluid.

[0045] According to some embodiments of the present application, the aqueous solution of step S1 comprises 95-105 parts of water and 0.5-2.0 parts of emulsifier.

[0046] According to some embodiments of the application, the method of obtaining the aqueous solution of emulsifier in step S1 comprises mixing water and emulsifier.

[0047] According to some embodiments of the application, the temperature of mixing in step S1 is 80-100°C.

[0048] According to some embodiments of the application, the method of mixing in step S1 comprises stirring.

[0049] According to some embodiments of the application, the stirring time is 10-20 min.

[0050] According to some embodiments of the application, the method of mixing in step S2 comprises stirring.

[0051] According to some embodiments of the application, the speed of stirring is 800-1200 rpm.

[0052] According to some embodiments of the application, the time of stirring is 2-3 h.

[0053] According to some embodiments of the application, the amount of oil used for emulsification in step S3 is 5-60 parts.

[0054] According to some embodiments of the application, the amount of oil used for emulsification in step S3 is 50-60 parts.

[0055] According to some embodiments of the application, the amount of water used for emulsification in step S3 is 0-5 parts.

[0056] According to some embodiments of the application, the amount of water used for emulsification in step S3 is 1-5 parts.

[0057] According to some embodiments of the application, the method of emulsification in step S3 comprises adding oil and optionally water to the mixture.

[0058] According to some embodiments of the application, the oil is added in two times, i.e. oil is added to the mixture, water is added, and then oil is added.

[0059] According to some embodiments of the application, after the first addition of oil, the mixture is stirred for 20-30 min, and then water is added.

[0060] According to some embodiments of the application, after the second addition of oil, the mixture is stirred for 10-30 min.

[0061] According to some embodiments of the application, 5-10 parts of oil are added in the first addition, and 0-50 parts of oil are added in the second addition.

[0062] According to some embodiments of the present application, 5-10 parts of oil are added for the first time, and 45-50 parts of oil are added for the second time.

[0063] According to some embodiments of the present application, the oil includes one or more of diesel oil, kerosene, white oil, synthetic base oil and crude oil.

[0064] The anti-oil foam stabilizer provided by the present application includes an emulsifier, a viscoelastic polymer and modified starch. The modified starch and the viscoelastic polymer jointly bind free water in the system and adsorb a small amount of oil film. The specific principle is that the viscoelastic polymer enhances the cohesion of the molecules of the micro-foam fluid through a temporary supramolecular network structure, thereby enhancing the strength of the liquid film; the swelling of the modified starch in water enhances the viscosity of the fluid; the extended chain of the modified starch can form an interpenetrating structure with the network structure of the viscoelastic polymer, thereby further promoting the binding effect of the viscoelastic polymer on the free water; and the structure formed by the two under the action of the emulsifier forms a high-quality oil-containing liquid film with a small amount of oil.

[0065] The micro-foam fluid provided by the present application can be emulsified by the emulsifier under high-speed shearing action when a large amount of oil invades from the outside, and the emulsification effect is further improved under the action of the network structure formed by the modified starch and the viscoelastic polymer. The stable micro-foam group is not disturbed, and the oil resistance of the micro-foam fluid is improved to more than 60%, and the half-life is improved from 25h to more than 7d.

[0066] The micro-foam fluid provided by the present application does not need a special oil-water compatible or oil-based foaming agent to improve the oil resistance of the water-based micro-foam fluid, and changes the oil pollution into oil performance promotion. The micro-foam fluid improves the oil capacity limit of the micro-foam fluid, improves the stability of the micro-foam fluid, prolongs the half-life of the foam, and increases the efficiency of the fluid circulation. The micro-foam fluid not only has low density and high oil resistance, but also has excellent inhibition, lubricity and oil and gas layer protection effect comparable to oil-based drilling fluid. It can be applied not only to limestone formation leakage and leakage prevention, but also to safe drilling in shale formation wellbore instability formation.

[0067] The technical idea provided by the present application is novel and has strong adaptability. It can be applied to enhance the oil capacity of the water-based micro-foam fluid, and can also be applied to enhance the oil capacity of the oil-based micro-foam fluid. DETAILED DESCRIPTION

[0068] In order to make the present application easier to understand, the present application will be described in detail below with reference to the embodiments, which are only illustrative and do not limit the scope of application of the present application.

[0069] The test method of the present application is as follows:

[0070] (1) The calculation method of apparent viscosity AV in the present application is: Φ600 / 2

[0071] (2) The calculation method of plastic viscosity PV is: Φ600-Φ300

[0072] (3) The calculation method of dynamic shear YP is: (Φ300-PV) / 2.

[0073] Wherein, Φ600 and Φ300 represent the readings of the viscometer at 600 rpm and 300 rpm, respectively.

[0074] Elastic modulus (G′): G′ represents the elasticity of a viscoelastic fluid, meaning the storage of elastic energy, which can be recovered later. The oscillation frequency of the polymer aqueous solution is 0.01-100 Hz, which is scanned by the AR1500ex type rotary rheometer produced in the United States.

[0075] Viscosity modulus (G″): G〞 is the loss modulus, which reflects the viscosity of the viscoelastic fluid, meaning that the energy used for initial flow is irreversible loss. The oscillation frequency of the polymer aqueous solution is 0.01-100 Hz, which is scanned by the AR1500ex type rotary rheometer produced in the United States.

[0076] In the present application, polyvinyl alcohol 1788 is purchased from Shanghai Yingjia Industrial Development Co., Ltd., with a weight average molecular weight of 1700 and an alcoholysis degree of 85-89%;

[0077] Polyvinyl alcohol 1488 is purchased from Shanghai Yingjia Industrial Development Co., Ltd., with a weight average molecular weight of 1400 and an alcoholysis degree of 85-89%;

[0078] Polyvinyl alcohol 1288 is purchased from Shanghai Yingjia Industrial Development Co., Ltd., with a weight average molecular weight of 1200 and an alcoholysis degree of 85-89%;

[0079] Polyvinyl alcohol BP05 is purchased from Shanghai Yingjia Industrial Development Co., Ltd., with a weight average molecular weight of 17600-26400;

[0080] Xanthan gum (G′ / G″ is 2.66, and the molecular weight is 2.41 million) is purchased from Shengda Cellulose Factory of Shengli Oilfield, and is a biological polymer xanthan gum XC GB / T 5005;

[0081] Low molecular weight high temperature foam stabilizer TFS (G′ / G″ is 4.18, and the molecular weight is 1.26 million) is selected from the low molecular weight high temperature foam stabilizer prepared in Example 2 of Chinese invention patent "Low molecular weight high temperature foam stabilizer and its preparation method", application number 201911401646.X;

[0082] Hydroxyethyl cellulose HEC (G′ / G″ is 1.50) is purchased from Shandong Feicheng Yutian Chemical Co., Ltd., and the weight average molecular weight is 2.5-4.5 million;

[0083] Carboxymethyl starch CMS is purchased from Shandong Deshengyuan Petroleum Technology Co., Ltd., and the weight average molecular weight is 3-5 million;

[0084] High-temperature-resistant starch CMS-K is purchased from Zhengzhou Jingyuan Mud Material Co., Ltd.;

[0085] Sodium dodecyl benzene sulfonate SDBS is purchased from Shandong Yongwang Chemical Co., Ltd., and the CAS number is 25155-30-0;

[0086] Sodium dodecyl sulfate SDS is purchased from Shandong Guohua Chemical Co., Ltd., and the CAS number is 151-21-3;

[0087] Sodium alpha-olefin sulfonate AOS is purchased from Zhongqing Chemical Co., Ltd., and the CAS number is 68439-57-6;

[0088] Cocamidopropyl dimethyl tertiary amine PKO is purchased from Jinan Baoliyuan Chemical Co., Ltd., and the CAS number is 68140-01-2;

[0089] Diesel oil is purchased from Sinopec Sales Co., Ltd. Hubei Jingzhou Petroleum Branch, and the brand is diesel oil 0#, 5# or 10#;

[0090] White oil is purchased from Sinopec Group Asset Management Co., Ltd. Jingmen Branch, and the brand is white oil 3#, 5#, 7#, 10# or 15#;

[0091] Synthetic base oil is purchased from Sinopec Sales Co., Ltd. Hubei Jingzhou Petroleum Branch, and the brand is gas oil synthetic base liquid GTL.

[0092] Example 1

[0093] This example provides a water-based microfoam fluid, and the preparation method is as follows:

[0094] S1: Take 100 parts of water, add 0.5 parts of polyvinyl alcohol 1788, stir while heating to 90℃, keep stirring for 20 min until fully dissolved, and get the water solution of emulsifier after cooling;

[0095] S2: Accurately take 0.1 parts of xanthan gum XC, 0.3 parts of carboxymethyl starch CMS, 0.2 parts of sodium dodecyl benzene sulfonate SDBS and 0.1 parts of sodium dodecyl sulfate SDS, mix well, then add the water solution of emulsifier, and continuously stir for 3 h at 800 rpm speed with a low-speed powerful stirrer to get a mixture;

[0096] S3: 5 parts of diesel oil were added to the mixture at the same stirring speed, 1 part of clean water was added after stirring for 30 min, 5 parts of diesel oil were added again after stirring for 30 min, and a micro-foam fluid with an oil content of 10% was obtained.

[0097] Example 2

[0098] This example provides a water-based micro-foam fluid, and the preparation method is the same as that of Example 1, and the difference is only that S3 is different:

[0099] S3: 5 parts of diesel oil were added to the mixture at the same stirring speed, 1 part of clean water was added after stirring for 30 min, 5 parts of diesel oil were added again after stirring for 30 min, and a micro-foam fluid with an oil content of 10% was obtained.

[0100] Example 3

[0101] This example provides a water-based micro-foam fluid, and the preparation method is the same as that of Example 1, and the difference is only that S3 is different:

[0102] S1: 100 parts of clean water were taken, 0.5 parts of polyvinyl alcohol 1788 were added, and the temperature was increased to 90°C while stirring, and stirring was maintained for 20 min until complete dissolution, and the water-soluble emulsifier solution was obtained after cooling;

[0103] S2: 0.1 parts of xanthan gum XC, 0.3 parts of CMS, 0.2 parts of sodium dodecyl benzene sulfonate SDBS and 0.1 parts of sodium dodecyl sulfate SDS were accurately weighed, and were fully mixed and then added to the water-soluble emulsifier solution, and were continuously stirred at a speed of 800 rpm for 3 h using a low-speed powerful stirrer to obtain a mixture;

[0104] S3: 5 parts of diesel oil were added to the mixture at the same stirring speed, 1 part of clean water was added after stirring for 30 min, 5 parts of diesel oil were added again after stirring for 30 min, and a micro-foam fluid with an oil content of 10% was obtained.

[0105] Example 4

[0106] This example provides a water-based micro-foam fluid, and the preparation method is the same as that of Example 1, and the difference is only that S3 is different:

[0107] S1: 100 parts of clean water were taken, 0.5 parts of polyvinyl alcohol 1788 were added, and the temperature was increased to 90°C while stirring, and stirring was maintained for 20 min until complete dissolution, and the water-soluble emulsifier solution was obtained after cooling;

[0108] S2: accurately take 0.1 parts of xanthan gum XC, 0.3 parts of carboxymethyl starch CMS, 0.2 parts of sodium dodecyl benzene sulfonate SDBS and 0.1 parts of sodium dodecyl sulfate SDS, fully mix and add into the water solution of emulsifier, continuously stir for 3h at 800rpm speed by low speed strong stirrer to obtain a mixture;

[0109] S3: under the same stirring speed, add 5 parts of diesel oil into the mixture, stir for 30min, then add 5 parts of diesel oil, continue to stir for 30min to obtain a micro-foam fluid with 10% oil content.

[0110] Test Example 1

[0111] (1) Density test. YM-7 type liquid density meter with measurement range of 0.1-1.5g / cm 3 was used to test and record the density of the micro-foam fluids prepared in Example 1-Example 4, and the specific data are shown in Table 1.

[0112] (2) Rheological property test. ZNN-D6 type six-speed rotary viscometer was used to test and record the readings of the micro-foam fluids prepared in Example 1, Example 2, Example 3 and Example 4 at Φ600 and Φ300 rotation speeds, and the apparent viscosity, plastic viscosity and dynamic shear force of the micro-foam fluids were calculated, and the specific data are shown in Table 1, AV represents apparent viscosity, PV represents plastic viscosity, and YP represents dynamic shear force.

[0113] (3) Half-life test. The micro-foam fluids prepared in Example 1-Example 4 were poured into a 250mL measuring cylinder, and the time required for the volume of liquid drained from the foam to be half of the total liquid volume when the foam was not drained, or the time required for the volume of the foam to be reduced and settled to be half of the total liquid volume when the foam was not drained, was tested, and the specific data are shown in Table 1.

[0114] (4) Test 4: Lubrication performance test.

[0115] EP extreme pressure lubricator manufactured by OFI Test Equipment Corporation of the United States was used to test the extreme pressure lubrication coefficient of the micro-foam fluids prepared in Example 1-Example 4 under different diesel oil additions, and the test steps were as follows:

[0116] First, the EP extreme pressure lubricator was preheated and operated at 300r / min for 15min. Then, distilled water was used to calibrate the instrument, and the instrument was operated at 60r / min and a torque of 150psi for 5min, and the readings of the instrument were recorded. Finally, the lubrication coefficient of the sample with different oil content was tested, and the test conditions were 60r / min, test torque was 150psi, test time was 5min, and the instrument readings were recorded after 5min, wherein K f represents the extreme pressure lubrication coefficient.

[0117] (5) Test 5: Inhibition test. The shale recovery method is used to test the inhibition of the microfoam fluid. The test steps are as follows:

[0118] ① 50g of dry rock sample of 6-10 mesh (accurate to 0.1g) is taken and loaded into a mud tank containing 350mL of the test liquid, and the lid is screwed tightly;

[0119] ② The mud tank is placed in a roller oven set at a constant temperature, and rolled for 16h.

[0120] ③ After rolling for 16h, the mud tank is taken out and cooled to room temperature. The liquid and rock sample in the tank are all poured onto a 40-mesh sample screen and wet-screened in a tank containing tap water for 1min.

[0121] ④ The 40-mesh screen residue rock sample is placed in a constant-temperature drying oven at 105±3℃ and dried for 4h. After being taken out and cooled, it is left in the air for 24h, and then weighed and recorded as M1 (accurate to 0.1g).

[0122] ⑤ The recovery rate R = M1 / 50 x 100% is calculated.

[0123] The core is selected as the dark gray shale debris with a water recovery rate of 35%-40%, and is soaked in Examples 1-4, respectively, after being rolled at 150℃ for 16h. The shale recovery rate is tested, and the data obtained are shown in Table 1.

[0124] Table 1: Parameters and rheological test data of the microfoam fluid of Examples 1-4

[0125]

[0126] As can be seen from Table 1, the initial density of the microfoam fluid of the present application is 0.61g / cm 3 When the oil content reaches 15%, the change range is very small, and the density is stable. The microfoam quality increases, the half-life period becomes longer, the dynamic plasticity ratio increases, and the suspension stability further increases. Moreover, the lubricating performance is good, and the inhibition of shale is strong.

[0127] Example 5

[0128] The water-based microfoam fluid is provided, and the specific preparation method is as follows:

[0129] S1: 100 parts of water is taken, 0.5 parts of polyvinyl alcohol 1488 is added, and the temperature is increased to 90℃ while stirring, and stirring is maintained for 20min until complete dissolution. After cooling, the water solution of the emulsifier is obtained;

[0130] S2: 0.1 parts of low molecular weight high temperature foam stabilizer TFS, 0.1 parts of hydroxyethyl cellulose HEC, 0.5 parts of carboxymethyl starch CMS, 0.3 parts of sodium a-olefin sulfonate AOS and 0.2 parts of sodium dodecyl sulfate SDS were accurately weighed, mixed thoroughly and then added to the aqueous emulsifier solution, and stirred at a speed of 900 rpm for 3 h using a low-speed high-torque stirrer to obtain a mixture;

[0131] S3: 5 parts of diesel oil were added to the mixture at the same stirring speed, stirred for 30 min, 2 parts of water were added, stirred for 30 min, and then 10 parts of white oil were added to obtain a micro-foam fluid with high oil content.

[0132] Example 6

[0133] This example provides a water-based micro-foam fluid, and the preparation method is the same as that of Example 5, the only difference being that S3 is different:

[0134] S3: 5 parts of diesel oil were added to the mixture at the same stirring speed, stirred for 30 min, 2 parts of water were added, stirred for 30 min, and then 20 parts of white oil were added to obtain a micro-foam fluid with high oil content.

[0135] Example 7

[0136] This example provides a water-based micro-foam fluid, and the preparation method is the same as that of Example 5, the only difference being that no water and no second oil and fat are added in S3, and the specific preparation method is as follows:

[0137] S1: 100 parts of water were taken, 0.5 parts of polyvinyl alcohol 1488 were added, and the temperature was raised to 90°C while stirring, and stirring was maintained for 20 min until complete dissolution, and the aqueous emulsifier solution was obtained after cooling;

[0138] S2: 0.1 parts of low molecular weight high temperature foam stabilizer TFS, 0.1 parts of hydroxyethyl cellulose HEC, 0.5 parts of carboxymethyl starch CMS, 0.3 parts of sodium a-olefin sulfonate AOS and 0.2 parts of sodium dodecyl sulfate SDS were accurately weighed, mixed thoroughly and then added to the aqueous emulsifier solution, and stirred at a speed of 900 rpm for 3 h using a low-speed high-torque stirrer to obtain a mixture;

[0139] S3: 5 parts of diesel oil were added to the mixture at the same stirring speed, stirred for 30 min to obtain a micro-foam fluid with an oil content of 5%.

[0140] Example 8

[0141] This example provides a water-based micro-foam fluid, and the preparation method is the same as that of Example 5, the only difference being that no water is added in S3, and the specific preparation method is as follows:

[0142] S1: take 100 parts of clean water, add 0.5 parts of polyvinyl alcohol 1488, stir while heating to 90℃, keep stirring for 20 min until fully dissolved, and get the water solution of emulsifier after cooling;

[0143] S2: accurately take 0.1 parts of low molecular weight high temperature foam stabilizer TFS, 0.1 parts of hydroxyethyl cellulose HEC, 0.5 parts of carboxymethyl starch CMS, 0.3 parts of alpha-olefin sulfonic acid sodium AOS and 0.2 parts of sodium dodecyl sulfate SDS, fully mix and add to the water solution of emulsifier, continuously stir for 3 h at 900 rpm speed with a low speed strong stirrer, and get the mixture;

[0144] S3: under the same stirring speed, add 5 parts of diesel oil to the mixture, stir for 30 min, then add 5 parts of white oil, continue to stir for 30 min, and get the micro-foam fluid with 10% oil content.

[0145] Test Example 2

[0146] The micro-foam fluid prepared in Examples 5-8 was tested for density, half-life and rheological property by the test method used in Test Example 1, and the test results are shown in Table 2.

[0147] Table 2: Quality and rheological property test data of micro-foam fluid of Examples 5-8

[0148]

[0149] From Table 2, the initial density of the micro-foam fluid of the application is 0.74 g / cm 3 , and when the oil content reaches 25%, the change range is very small, and the density is stable with only a 0.02 g / cm 3 increase in Δρ; the micro-foam quality increases, the half-life becomes longer, the dynamic plasticity ratio increases, and the suspension stability further increases; and the lubrication performance is good, and the shale has strong inhibition.

[0150] Example 9

[0151] This example provides a water-based micro-foam fluid, and the specific preparation method is as follows:

[0152] S1: take 100 parts of clean water, add 1 part of polyvinyl alcohol 1288, stir while heating to 90℃, keep stirring for 20 min until fully dissolved, and get the water solution of emulsifier after cooling;

[0153] S2: 0.1 parts of low molecular weight high temperature foam stabilizer TFS, 0.1 parts of xanthan gum XC, 0.8 parts of high temperature resistant starch CMS-K, 0.3 parts of alpha-olefin sulfonate sodium AOS and 0.2 parts of sodium dodecyl sulfate SDS were accurately weighed, and after being thoroughly mixed, they were added to the aqueous solution of the emulsifier, and stirred at a low speed of 1000 rpm for 3 h to obtain a mixture;

[0154] S3: 5 parts of white oil were added to the mixture at the same stirring speed, and after stirring for 30 min, 3 parts of clean water were added, and after stirring for 30 min, 10 parts of synthetic base oil were added to obtain a micro-foam fluid with high oil content.

[0155] Example 10

[0156] This example provides a water-based micro-foam fluid, and the preparation method is the same as that of Example 9, except that S3 is different:

[0157] S3: 5 parts of white oil were added to the mixture at the same stirring speed, and after stirring for 30 min, 3 parts of clean water were added, and after stirring for 30 min, 20 parts of synthetic base oil were added to obtain a micro-foam fluid with high oil content.

[0158] Example 11

[0159] This example provides a water-based micro-foam fluid, and the preparation method is the same as that of Example 9, except that S3 is different:

[0160] S3: 5 parts of white oil were added to the mixture at the same stirring speed, and after stirring for 30 min, 4 parts of clean water were added, and after stirring for 30 min, 40 parts of synthetic base oil were added to obtain a micro-foam fluid with high oil content.

[0161] Example 12

[0162] This example provides a water-based micro-foam fluid, and the preparation method is the same as that of Example 9, except that S3 is different:

[0163] S3: 5 parts of white oil were added to the mixture at the same stirring speed, and after stirring for 30 min, 4 parts of clean water were added, and after stirring for 30 min, 50 parts of synthetic base oil were added to obtain a micro-foam fluid with high oil content.

[0164] Example 13

[0165] This example provides a water-based micro-foam fluid, and the preparation method is the same as that of Example 9, except that no water and second oil are added in S3, and the specific preparation method is as follows:

[0166] S1: Take 100 parts of clean water, add 1 part of polyvinyl alcohol 1288, stir while heating to 90°C, keep stirring for 20 min until fully dissolved, and get the water solution of emulsifier after cooling;

[0167] S2: Accurately take 0.1 part of low molecular weight high temperature foam stabilizer TFS, 0.1 part of xanthan gum XC, 0.8 part of high temperature resistant starch CMS-K, 0.3 part of α-olefin sulfonic acid sodium AOS and 0.2 part of sodium dodecyl sulfate SDS, fully mix and add to the water solution of emulsifier, continuously stir for 3 h at 1000 rpm speed with a low speed strong stirrer, and get a mixture;

[0168] S3: Under the same stirring speed, add 5 parts of white oil to the mixture, stir for 30 min to get a micro foam fluid containing 5% oil.

[0169] Example 14

[0170] This example provides a water-based micro foam fluid, and the preparation method is the same as that of Example 9, the only difference is that no water is added in S3, and the specific preparation method is as follows:

[0171] S1: Take 100 parts of clean water, add 1 part of polyvinyl alcohol 1288, stir while heating to 90°C, keep stirring for 20 min until fully dissolved, and get the water solution of emulsifier after cooling;

[0172] S2: Accurately take 0.1 part of low molecular weight high temperature foam stabilizer TFS, 0.1 part of xanthan gum XC, 0.8 part of high temperature resistant starch CMS-K, 0.3 part of α-olefin sulfonic acid sodium AOS and 0.2 part of sodium dodecyl sulfate SDS, fully mix and add to the water solution of emulsifier, continuously stir for 3 h at 1000 rpm speed with a low speed strong stirrer, and get a mixture;

[0173] S3: Under the same stirring speed, add 5 parts of white oil to the mixture, stir for 30 min to get a micro foam fluid containing 5% oil.

[0174] Example 15

[0175] This example provides a water-based micro foam fluid, and the preparation method is the same as that of Example 9, the only difference is that no water is added in S3, and the specific preparation method is as follows:

[0176] S1: Take 100 parts of clean water, add 1 part of polyvinyl alcohol 1288, stir while heating to 90°C, keep stirring for 20 min until fully dissolved, and get the water solution of emulsifier after cooling;

[0177] S2: 0.1 parts of low molecular weight high temperature foam stabilizer TFS, 0.1 parts of xanthan gum XC, 0.8 parts of high temperature resistant starch CMS-K, 0.3 parts of alpha-olefin sulfonic acid sodium AOS and 0.2 parts of sodium dodecyl sulfate SDS are accurately weighed, mixed thoroughly and then added to the aqueous emulsifier solution, and stirred at a speed of 1000 rpm for 3 hours with a low-speed strong stirrer to obtain a mixture;

[0178] S3: 5 parts of white oil are added to the mixture at the same stirring speed, stirred for 30 minutes, then 10 parts of synthetic base oil are added, and stirred for another 30 minutes to obtain a micro-foam fluid with an oil content of 15%.

[0179] Test Example 3

[0180] The micro-foam fluids prepared in Examples 9-15 are tested for density, half-life and rheological properties using the test methods used in Test Example 1, and the test results are shown in Table 3.

[0181] Table 3: Parameters and rheological test data of micro-foam fluids of Examples 9-15

[0182]

[0183] As can be seen from Table 3, the initial density of the micro-foam fluid of the present application is 0.82 g / cm 3 When the oil content of the micro-foam fluid of the present application reaches 55%, the density is stable, the micro-foam quality increases, the half-life becomes longer, the dynamic plastic ratio increases, and the suspension stability further increases. Moreover, the lubricating performance is good, and the shale inhibition is strong.

[0184] Example 16

[0185] The present example provides a water-based micro-foam fluid, and the specific preparation method is as follows:

[0186] S1: 100 parts of water are taken, 2 parts of polyvinyl alcohol BP05 are added, and the temperature is raised to 90°C while stirring, and stirring is maintained for 20 minutes until complete dissolution. After cooling, an aqueous emulsifier solution is obtained;

[0187] S2: 0.3 parts of low molecular weight high temperature foam stabilizer TFS, 0.5 parts of carboxymethyl starch CMS, 0.3 parts of high temperature resistant starch CMS-K, 0.5 parts of alpha-olefin sulfonic acid sodium AOS and 0.3 parts of cocamide propyl dimethyl tertiary amine PKO are accurately weighed, mixed thoroughly and then added to the aqueous emulsifier solution, and stirred at a speed of 1000 rpm for 3 hours with a low-speed strong stirrer to obtain a mixture;

[0188] S3: 10 parts of crude oil are added to the mixture at the same stirring speed, stirred for 30 minutes, then 5 parts of water are added, stirred for 30 minutes, then 20 parts of synthetic base oil are added, and a micro-foam fluid with high oil content is obtained.

[0189] Example 17

[0190] This example provides a water-based micro-foam fluid, the preparation method is the same as that of Example 16, and the difference is only that S3 is different:

[0191] S3: Under the same stirring speed, 10 parts of crude oil are added to the mixture, 5 parts of clean water are added after stirring for 30 min, and 30 parts of synthetic base oil are added after stirring for 30 min, to obtain a micro-foam fluid with high oil content.

[0192] Example 18

[0193] This example provides a water-based micro-foam fluid, the preparation method is the same as that of Example 16, and the difference is only that S3 is different:

[0194] S3: Under the same stirring speed, 10 parts of crude oil are added to the mixture, 5 parts of clean water are added after stirring for 30 min, and 50 parts of synthetic base oil are added after stirring for 30 min, to obtain a micro-foam fluid with high oil content.

[0195] Example 19

[0196] This example provides a water-based micro-foam fluid, the preparation method is the same as that of Example 16, and the difference is only that no water and second oil and fat are added in S3, and the specific preparation method is as follows:

[0197] S1: Take 100 parts of clean water, add 2 parts of polyvinyl alcohol BP05, and stir while heating to 90°C, keep stirring for 20 min until fully dissolved, and then cool to obtain an aqueous emulsifier solution;

[0198] S2: Accurately weigh 0.3 parts of low molecular weight high temperature foam stabilizer TFS, 0.5 parts of carboxymethyl starch CMS, 0.3 parts of high temperature resistant starch CMS-K, 0.5 parts of sodium a-olefin sulfonate AOS and 0.3 parts of cocamide propyl dimethyl tertiary amine PKO, mix well and add to the aqueous emulsifier solution, use a low-speed powerful stirrer, stir at a speed of 1000 rpm for 3 h, to obtain a mixture;

[0199] S3: Under the same stirring speed, 10 parts of crude oil are added to the mixture, and after stirring for 30 min, a micro-foam fluid with an oil content of 10% is obtained.

[0200] Example 20

[0201] This example provides a water-based micro-foam fluid, the preparation method is the same as that of Example 16, and the difference is only that no water is added in S3, and the specific preparation method is as follows:

[0202] S1: Take 100 parts of water, add 2 parts of polyvinyl alcohol BP05, stir while heating to 90°C, keep stirring for 20 min to fully dissolve, and get the water solution of emulsifier after cooling;

[0203] S2: Accurately take 0.3 parts of low molecular weight high temperature foam stabilizer TFS, 0.5 parts of carboxymethyl starch CMS, 0.3 parts of high temperature resistant starch CMS-K, 0.5 parts of sodium a-olefin sulfonate AOS and 0.3 parts of cocamide propyl dimethyl tertiary amine PKO, mix well and add to the water solution of emulsifier, use a low speed and powerful stirrer, stir at 1000 rpm for 3 h, get the mixture;

[0204] S3: Under the same stirring speed, add 10 parts of crude oil to the mixture, stir for 30 min, then add 5 parts of synthetic base oil, continue to stir for 30 min to get the oil content of 15% micro foam fluid.

[0205] Comparative Example 1

[0206] This comparative example provides a water-based micro foam fluid, without adding emulsifier, without adding water and second oil in S3, the specific preparation method is as follows:

[0207] S1: Accurately take 0.3 parts of low molecular weight high temperature foam stabilizer TFS, 0.5 parts of carboxymethyl starch CMS, 0.5 parts of high temperature resistant starch CMS-K, 0.3 parts of sodium a-olefin sulfonate AOS and 0.2 parts of cocamide propyl dimethyl tertiary amine PKO, mix well and add to 100 parts of water, use a low speed and powerful stirrer, stir at 1000 rpm for 3 h to get the water solution of emulsifier;

[0208] S2: Under the same stirring speed, add 5 parts of crude oil to the water solution of emulsifier, stir for 30 min to get the oil content of 5% micro foam fluid.

[0209] Comparative Example 2

[0210] This comparative example provides a water-based micro foam fluid, without adding viscoelastic polymer, the rest of water and oil, the specific preparation method is as follows:

[0211] S1: Take 100 parts of water, add 2 parts of polyvinyl alcohol BP05, stir while heating to 90°C, keep stirring for 20 min to fully dissolve, and get the water solution of emulsifier after cooling;

[0212] S2: Accurately take 0.5 parts of carboxymethyl starch CMS, 0.5 parts of high temperature resistant starch CMS-K, 0.3 parts of sodium a-olefin sulfonate AOS and 0.2 parts of cocamide propyl dimethyl tertiary amine PKO, mix well and add to the water solution of emulsifier, use a low speed and powerful stirrer, stir at 800 rpm for 3 h to get the mixture;

[0213] S3: under the same stirring speed, 5 parts of crude oil was added into the mixture, and after stirring for 30 min, a micro-foam fluid with oil content of 5% was obtained.

[0214] Comparative Example 3

[0215] This comparative example provides a water-based micro-foam fluid without adding modified starch, without adding water in S3 and without adding oil and fat for the second time, and the specific preparation method is as follows:

[0216] S1: 100 parts of water was taken, 2 parts of polyvinyl alcohol BP05 was added, and the temperature was increased to 90℃ while stirring, and the stirring was maintained for 20 min until fully dissolved, and after cooling, a water solution of emulsifier was obtained;

[0217] S2: 0.3 parts of low molecular weight high temperature foam stabilizer TFS, 0.3 parts of sodium a-olefin sulfonate AOS and 0.2 parts of cocamide propyl dimethyl tertiary amine PKO were accurately weighed, and after fully mixed, the water solution of emulsifier was added, and a low-speed powerful stirrer was used to continuously stir at a speed of 1000 rpm for 3 h, and a mixture was obtained;

[0218] S3: under the same stirring speed, 5 parts of crude oil was added into the mixture, and after stirring for 30 min, a micro-foam fluid with oil content of 5% was obtained.

[0219] Test Example 4

[0220] The micro-foam fluids prepared in Examples 16-20 and Comparative Examples 1-3 were tested for density, half-life and rheological property by using the test method used in Test Example 1, and the test results are shown in Table 4.

[0221] Table 4: Various parameters and rheological test data of the micro-foam fluids of Examples 16-20 and Comparative Examples

[0222]

[0223]

[0224] Among them, the fluid density of Example 20 is higher than water, the foam content is extremely low or even completely no bubble, and the function of low density and low pressure underbalanced drilling has been lost, so there is no half-life data.

[0225] From Table 4, the initial density of the micro-foam fluid of the present application is 0.92g / cm 3 When the oil content reaches 60%, the change range is extremely small, and Δρ even only decreases by 0.03g / cm 3 The micro-foam quality increases, the half-life becomes longer, the dynamic plastic ratio increases, and the suspension stability further increases; and the lubricating property is good, and the shale has strong inhibition.

[0226] In summary, the present invention adds an oil-resistant stabilizer to the micro-foam fluid, and the prepared micro-foam fluid has greatly improved oil resistance, prolonged half-life, good stability, and the advantages of low density and high oil resistance.

[0227] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, under the technical enlightenment provided by the present invention, as common knowledge in the art, other equivalent variations and improvements can be made, which should also be considered as the scope of protection of the present invention.

Claims

1. An oil-resistant foam stabilizer, characterized in that: including emulsifiers, viscoelastic polymers, and modified starches; The viscoelastic polymer is an organic polymer with a ratio of elastic modulus to viscous modulus of 1 < 10; The modified starch is prepared by etherifying starch under alkaline conditions; Emulsifier 0.5-2.0 parts, viscoelastic polymer 0.1-0.3 parts, modified starch 0.2-1.0 parts; The emulsifier includes polyvinyl alcohol; The viscoelastic polymer is selected from one or more of a low molecular weight high temperature foam stabilizer, xanthan gum and hydroxyethyl cellulose.

2. The oil-resistant foam stabilizer according to claim 1, characterized in that: The emulsifier is selected from one or more of nonionic surfactants and polyhydroxy surfactants; The nonionic surfactant is selected from Span surfactants and / or Tween surfactants.

3. The oil-resistant foam stabilizer according to claim 1, characterized in that: The modified starch is selected from one or more of carboxymethyl starch CMS and high temperature resistant starch CMS-K.

4. The oil-resistant foam stabilizer according to claim 1, characterized in that: The weight average molecular weight of the viscoelastic polymer is 1 million to 3 million.

5. The method for preparing the oil-resistant foam stabilizer according to any one of claims 1 to 4, characterized in that: The method comprises the steps of mixing an emulsifier, a viscoelastic polymer and a modified starch.

6. A fluid, characterized in that The invention comprises a foaming agent, grease, water and an oil-resistant foam stabilizer, wherein the oil-resistant foam stabilizer is the oil-resistant foam stabilizer according to any one of claims 1 to 4 or the oil-resistant foam stabilizer prepared according to claim 5.

7. The fluid according to claim 6, characterized in that The density of the fluid is 0.6~0.99 g / cm 3 ; and / or, the half-life of the fluid is greater than 1 hour; And / or, the oil in the fluid accounts for more than 5 wt% of the total weight of the fluid.

8. The fluid according to claim 7, characterized in that The half-life of the fluid is more than 168 hours; And / or, the oil in the fluid accounts for more than 60 wt% of the total weight of the fluid.

9. The fluid according to claim 6, characterized in that In parts by weight, the fluid includes 100-105 parts of water, 5-60 parts of oil, 0.5-2.0 parts of emulsifier, 0.1-0.3 parts of viscoelastic polymer, 0.2-1.0 parts of modified starch, and 0.3-0.8 parts of foaming agent.

10. The fluid according to claim 6, characterized in that The foaming agent is selected from one or more of anionic foaming agents and nonionic foaming agents; The anionic foaming agent is selected from one or more of sodium dodecylbenzenesulfonate, sodium lauryl sulfate and sodium α-olefinsulfonate; The nonionic foaming agent is selected from one or more of coconut oil diethanolamide, cocamidopropyl dimethyl tertiary amine and oleamidopropyl dimethyl tertiary amine.

11. The method for preparing a fluid according to any one of claims 6 to 10, characterized in that: The preparation method comprises the steps of mixing an emulsifier, a viscoelastic polymer, modified starch, a foaming agent, oil and water.

12. The preparation method according to claim 11, characterized in that The following steps are involved: S1: obtaining an aqueous solution of an emulsifier; S2: mixing a viscoelastic polymer, a modified starch, a foaming agent, and an aqueous solution of the emulsifier to obtain a mixture; S3: emulsifying the mixture with oil, fat, and optionally water to obtain the fluid; The aqueous solution in step S1 comprises 95 to 105 parts by weight of water and 0.5 to 2.0 parts by weight of an emulsifier; The method of obtaining an aqueous solution of an emulsifier in step S1 comprises the steps of mixing water and an emulsifier, wherein the mixing temperature is preferably 80-100°C; In step S3, the mixture is 1 to 4 parts by weight; the oil is 5 to 60 parts by weight; and the water is 0 to 5 parts by weight.

13. The preparation method according to claim 12, characterized in that In step S3, the amount of oil is 50-60 parts by weight; the amount of water is 1-5 parts by weight.

14. The preparation method according to claim 12 or 13, characterized in that: In step S3, the emulsification method is to add oil and optional water to the mixture.

15. The preparation method according to claim 14, characterized in that The oil is divided into oil ester I and oil ester II, which are added to the mixture twice; The amount of oil I is 5 to 10 parts by weight, and the amount of oil II is 0 to 50 parts by weight.

16. The preparation method according to claim 15, characterized in that First add Grease I to the mixture, then add water, and then add Grease II.

17. The preparation method according to claim 15, characterized in that The amount of oil I is 5 to 10 parts by weight, and the amount of oil II is 45 to 50 parts by weight.

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