Application of synergistic composition in inhibition of wellbore blockage and drilling fluid

Abstract

The invention relates to the field of well drilling, and discloses application of a synergistic composition in inhibition of wellbore blockage and a drilling fluid. The synergistic composition comprises a first inhibitor and a second inhibitor, the first inhibitor comprises an alcohol and a salt; the second inhibitor comprises polyvinylpyrrolidone, polyether amine and a compound with a structure as shown in a formula I; wherein R is alkyl of C2-C6, and n is an integer of 1-6. The synergistic composition contains the specific first inhibitor and the second inhibitor, the first inhibitor and the second inhibitor can synergistically inhibit generation of new substances in a shaft, shaft blockage is effectively inhibited, and the synergistic composition has good environmental protection performance and meets the environmental protection index requirement of a first-grade sea area. The comprehensive technical performance meets the technical requirements of sea area natural gas hydrate drilling engineering.

Description

Technical Field

[0001] This invention relates to the field of drilling, and more specifically to the application of an synergistic composition in inhibiting wellbore blockage and drilling fluid. Background Technology

[0002] As oil and gas exploration and development progresses, polar regions are becoming increasingly attractive targets for extraction. Due to the effects of climate change, polar glaciers are melting, meaning that oil and gas resources previously covered by thick ice sheets are now more easily accessible for extraction.

[0003] Cryogenic drilling fluid technology for polar regions is one of the key technologies developed under challenging environments. The frigid climates, freezing conditions, and unique geological environments of the Arctic and Antarctic require drilling fluids with high cold resistance, stability, and environmental friendliness. In the Arctic, the abundant untapped oil resources make the demand for cryogenic drilling fluids particularly urgent. Antarctica, as the last undeveloped continent on Earth, possesses rich resource potential and scientific research value, making cryogenic drilling fluid technology a crucial link in scientific exploration. Traditional water-based drilling fluids are prone to freezing at the ultra-low temperatures of polar regions, while oil-based drilling fluids, although able to address the cold resistance issue to some extent, pose a significant challenge due to their environmental pollution. Therefore, researchers are dedicated to developing novel cryogenic drilling fluid systems to meet the challenges of polar regions.

[0004] In recent years, significant progress has been made in cryogenic drilling fluid technology for polar regions. Researchers have successfully improved the stability and rheological properties of drilling fluids in extremely low-temperature environments by adjusting the formulation and adding special additives. Related research has also been conducted on issues such as wellbore blockage and preventing wellbore instability, with some results achieved. However, despite these advancements, many challenges and problems remain. For example, the ultra-low temperature environment in polar regions increases the likelihood of new material formation in the wellbore; therefore, preventing the formation of new materials that lead to wellbore blockage is a major technical challenge for drilling fluids. Simultaneously, the fragility of the polar ecosystem places stringent requirements on the environmental performance of drilling fluids. Further improvements and research are needed in the environmental friendliness of drilling fluids, as well as their requirements for wellbore blockage and stability, to meet the needs of polar resource development and scientific exploration. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of wellbore clogging, poor rheological properties, and non-compliance with environmental protection requirements when drilling fluids are applied in low-temperature marine environments. This invention provides an synergistic composition for inhibiting wellbore clogging in drilling fluids. The synergistic composition contains specific first and second inhibitors, which work synergistically to improve the rheological properties of the composition when added to the drilling fluid in low-temperature marine environments, effectively inhibiting wellbore clogging while maintaining low-temperature resistance.

[0006] To achieve the above objectives, a first aspect of the present invention provides the application of an synergistic composition in suppressing wellbore blockage, wherein the synergistic composition comprises a first inhibitor and a second inhibitor;

[0007] The first inhibitor comprises an alcohol and a salt;

[0008] The second inhibitor comprises polyvinylpyrrolidone, polyetheramine, and a compound with the structure shown in Formula I;

[0009]

[0010] Where R is a C2-C6 alkyl group and n is an integer from 1 to 6.

[0011] A second aspect of the present invention provides a drilling fluid, wherein the drilling fluid comprises 15-20 wt% of an synergistic composition, 1-5 wt% of bentonite, 0.4-0.6 wt% of a viscosifier, 2.5-2.9 wt% of a filtration loss reducer and 77.5-86 wt% of water;

[0012] The synergistic composition is the composition described in the first aspect of the present invention.

[0013] Through the above technical solution, the synergistic composition provided by the present invention achieves the following beneficial effects in suppressing wellbore blockage and drilling fluid: the synergistic composition contains specific first inhibitor and second inhibitor, which, when added to drilling fluid, can work synergistically, making it suitable for drilling operations in low-temperature sea areas with a water depth of 2000m, and has good rheological stability. At the same time, it can effectively suppress wellbore blockage and has excellent environmental performance. Attached Figure Description

[0014] Figure 1 It is a pressure curve of drilling fluid inhibiting hydrate formation. Detailed Implementation

[0015] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0016] The first aspect of the present invention provides the application of an synergistic composition in suppressing wellbore blockage, wherein the synergistic composition comprises a first inhibitor and a second inhibitor;

[0017] The first inhibitor comprises an alcohol and a salt;

[0018] The second inhibitor comprises polyvinylpyrrolidone, polyetheramine, and a compound with the structure shown in Formula I;

[0019]

[0020] Where R is a C2-C6 alkyl group and n is an integer from 1 to 6.

[0021] In this invention, the first inhibitor and the second inhibitor in the composition have a synergistic effect. When added to drilling fluid and applied to low-temperature sea areas, they exhibit excellent low-temperature resistance and can improve the effect of inhibiting wellbore blockage.

[0022] Furthermore, the inventors unexpectedly discovered in extensive research that when polyvinylpyrrolidone, polyetheramine, and compounds with the structure shown in Formula I are used in combination in the second inhibitor, the synergistic effect with the first inhibitor can be further enhanced.

[0023] According to a preferred embodiment of the present invention, the mass ratio of the first inhibitor to the second inhibitor is 10-100:1.

[0024] In this invention, when the mass ratio of the first inhibitor and the second inhibitor meets the above-mentioned range, the composition can be used as a drilling fluid to ensure excellent cuttings carrying and suspending capabilities and well washing effect, while ensuring safety during operations in low-temperature sea areas and further suppressing wellbore blockage.

[0025] Furthermore, the mass ratio of the first inhibitor to the second inhibitor is 14-40:1.

[0026] According to the present invention, in the first inhibitor, the alcohol is selected from at least one of low-carbon monohydric alcohols, low-carbon polyhydric alcohols, and low-carbon polymeric alcohols.

[0027] According to a specific embodiment of the present invention, the low-carbon monohydric alcohol is selected from at least one of methanol, ethanol and propanol.

[0028] According to a specific embodiment of the present invention, the low-carbon polyol is selected from at least one of ethylene glycol, propylene glycol, and butanediol.

[0029] According to a specific embodiment of the present invention, the low-carbon polymeric alcohol is polyethylene glycol (PEG).

[0030] According to the present invention, the salt is selected from chlorides.

[0031] According to a preferred embodiment of the present invention, the salt is selected from at least one of sodium chloride, potassium chloride and calcium chloride.

[0032] Furthermore, the inventors discovered that when the first inhibitor is polyethylene glycol and sodium chloride, the two can work synergistically to prolong the induction time of blockages in the wellbore, thereby inhibiting wellbore blockage.

[0033] According to the present invention, in the first inhibitor, the mass ratio of alcohol to salt is 1:1.2-5.

[0034] In this invention, the mass ratio of alcohol to salt meets the above-mentioned range, which can further improve the inhibition of wellbore blockage.

[0035] Furthermore, in the first inhibitor, the mass ratio of alcohol to salt is 1:2-3.

[0036] According to the present invention, in the second inhibitor, the mass ratio of polyvinylpyrrolidone, polyetheramine and the compound with the structure shown in Formula I is 1-5:0.8-2:1.

[0037] In this invention, the mass ratio of polyvinylpyrrolidone, polyetheramine, and the compound with the structure shown in Formula I satisfies the above-mentioned range, and can synergistically enhance the effect with the first inhibitor to improve the inhibition of wellbore blockage.

[0038] Furthermore, in the second inhibitor, the mass ratio of polyvinylpyrrolidone, polyetheramine, and the compound with the structure shown in Formula I is 1.8-2:0.8-1.5:1;

[0039] According to a preferred embodiment of the present invention, in the compound with the structure shown in Formula I, R is a C2-C4 alkyl group and n is an integer from 1 to 4.

[0040] According to the present invention, the molecular weight of the polyvinylpyrrolidone is 8,000-700,000.

[0041] In this invention, the molecular weight of the polyvinylpyrrolidone (PVP) satisfies the aforementioned range, which enhances the synergistic effect between the second inhibitor containing PPVP and the aforementioned first inhibitor. According to a preferred embodiment of the invention, the PPVP is PVP-K90.

[0042] According to the present invention, the molecular weight of polyetheramine is 230-2000.

[0043] According to a preferred embodiment of the present invention, the polyetheramine is selected from at least one of polyetheramine D230, polyetheramine D400, polyetheramine D2000 and polyetheramine D4000, and more preferably polyetheramine D230.

[0044] According to the present invention, the thickener is selected from at least one of modified cellulose, plant gums and biopolymers.

[0045] In this invention, the inventors unexpectedly discovered that when the thickener is selected from biopolymers, the composition containing the thickener can have excellent environmental performance, and at the same time, it can enhance the synergistic effect of the composition with other components when it is added to the drilling fluid described later, further inhibiting wellbore blockage.

[0046] According to some embodiments of the present invention, the modified cellulose is carboxymethyl cellulose and / or carboxyethyl cellulose.

[0047] According to the present invention, the plant gum is selected from at least one of guar gum, guar gum, bay leaf powder and azurite powder.

[0048] According to the present invention, the biopolymer is selected from xanthan gum (XG) and / or water-soluble starch.

[0049] In this invention, the inventors discovered during their research that when the thickener in the composition system described in this invention is xanthan gum, it can enhance the synergistic effect with the first inhibitor and the second inhibitor, making the viscosity of the composition suitable. At the same time, since the dynamic plasticity ratio of xanthan gum is more suitable for the application scenario of this invention, it can better handle rock cuttings and purify boreholes, and has low filtration loss, excellent rheological properties, and can improve the hydration inhibition ability of mudstone and shale.

[0050] During drilling, under the influence of pressure differential, water in the drilling fluid inevitably seeps into the reservoir through the wellbore. As water enters the formation, clay particles in the drilling fluid adhere to the wellbore, forming a "filter cake." Because the filter cake is relatively dense, it prevents further water loss from the drilling fluid and protects the wellbore. However, excessive water loss during filter cake formation, an overly thick filter cake, and fine clay particles entering the formation with the water can all affect normal drilling and damage the formation. Therefore, low filtration loss is required during drilling to reduce the leakage of drilling fluid and harmful substances into the formation. However, excessively low filtration loss increases costs and reduces drilling speed. Therefore, it is crucial to select appropriate filtration loss reducers to minimize the impact on the formation. Extensive research by the inventors has revealed that the filtration loss reducer is selected from at least one of low-viscosity sodium carboxymethyl cellulose (LV-CMC), high-viscosity sodium carboxymethyl cellulose (HV-CMC), and potassium humate (KHM). The solution is more adaptable to the present invention. When added to drilling fluid, it can further synergistically ensure the effective construction of drilling operations. At the same time, it can also synergistically work with the first inhibitor and the second inhibitor to inhibit wellbore blockage.

[0051] In this invention, from the perspective of environmental protection such as non-toxicity, non-pollution, and non-interference from fluorescent labeling, the filtration loss reducing agent is preferably low-viscosity sodium carboxymethyl cellulose.

[0052] According to the present invention, the composition further comprises 0.5-2 wt% nano-silica.

[0053] In this invention, the inventors discovered through extensive research that when nano-silica is added to the composition, the rheological properties of the composition are enhanced, making the rheological properties unaffected by temperature and pressure. At the same time, when the composition containing nano-silica is added to the drilling fluid, the drilling efficiency is improved, and the filtration loss and formation damage are reduced during drilling operations.

[0054] Furthermore, when the content of the nano-silica meets the above range, wellbore blockage can be further suppressed.

[0055] According to the present invention, the particle size of the nano-silica is 1-100 nm.

[0056] In this invention, the particle size of the nano-silica meets the above-mentioned range, which enables the components in the composition to be highly dispersed, which is beneficial to maintaining the stability of the rheological properties of the composition and reducing wellbore blockage.

[0057] Furthermore, the particle size of the nano-silica is 10-20 nm.

[0058] A second aspect of the present invention provides a drilling fluid, wherein the drilling fluid comprises 15-20 wt% of an synergistic composition, 1-5 wt% of bentonite, 0.4-0.6 wt% of a viscosifier, 2.5-2.9 wt% of a filtration loss reducer and 77.5-86 wt% of water;

[0059] The synergistic composition is the composition described in the first aspect of the present invention.

[0060] In this invention, the drilling fluid comprises the composition described in the first aspect of the invention, which can synergistically enhance the effects of other components in the drilling fluid. When used to suppress wellbore blockage, the drilling fluid can improve the suppression of wellbore blockage and can withstand low-temperature environments of at least -20°C.

[0061] According to the present invention, the half-effective concentration EC of the drilling fluid 50 Value > 2.8 × 10 4 mg / L, LC50 50 Value > 6 × 10 4 mg / L.

[0062] In this invention, the half-lethal concentration and half-effective concentration are drug safety indicators. Generally, the higher the value, the safer and more environmentally friendly the drug is.

[0063] In this invention, the apparent viscosity of the drilling fluid is 30-40 mPa·s, preferably 34-37 mPa·s.

[0064] In this invention, the drilling fluid is an ultra-low temperature drilling fluid system suitable for polar natural gas hydrate formations. The drilling fluid, comprising the composition described in the first aspect, enables it to possess excellent environmental performance and effectively inhibits wellbore blockage in low-temperature marine environments. In this invention, the drilling fluid is an ultra-low temperature drilling fluid system suitable for polar natural gas hydrate formations.

[0065] According to a particularly preferred embodiment of the present invention, the drilling fluid comprises: 14.5-19 wt% of a first inhibitor, 0.5-1 wt% of a second inhibitor, 3-4 wt% of bentonite, 0.4-0.6 wt% of XG, 2.5-2.9 wt% of LV-CMC, and 1.8-2 wt% of nano-silica, with the balance made up with water. The first inhibitor contains an alcohol to salt ratio of 1:2-3, and the second inhibitor contains polyvinylpyrrolidone, polyetheramine, and a compound of formula I in a mass ratio of 1.8-2:0.8-1:1, where the compound of formula I is ethylene glycol butyl ether.

[0066] The present invention will be described in detail below through embodiments.

[0067] In the following examples, the half-effective concentration EC of the drilling fluid is... 50 The value was determined by the Microtox luminescent bacteria method;

[0068] The LC50 value of drilling fluid was determined by the still water biotoxicity test method for artesian worms (GB T18420.2-2009).

[0069] Rheological stability was determined by the following methods:

[0070] The smaller the difference ΔP between the two measurements of the equivalent circulating density of drilling fluid at 4℃ and 25℃, the better the rheological stability.

[0071] Wellbore blockage is determined using the following methods:

[0072] Drilling fluid was added to the reactor of the wellbore blockage inhibition performance test device, and high-pressure methane gas was introduced. Under constant low temperature (4℃), closed conditions, and stirring at 300 r / min, the inhibition performance of the inhibitor was evaluated by monitoring the pressure change inside the reactor and weighing the mass m of the new substance generated in the system (the new substance is a blocky substance, which is the main source of wellbore blockage). The smaller the pressure change and the less new substance is generated, the better the wellbore blockage performance.

[0073] Example 1

[0074] Water-based drilling fluid S1 was prepared by mixing 10g NaCl, 4.2g PEG, 4g bentonite, 0.4g polyvinylpyrrolidone (PVP-K90_, molecular weight 130000), 0.2g polyetheramine D230, 0.2g ethylene glycol butyl ether, 0.5g XG, 2.5g LV-CMC, 2g nano silica (particle size 15nm) and 76g water evenly.

[0075] The mass ratio of alcohol to salt is 1:2.4, the mass ratio of 0.4g polyvinylpyrrolidone, 0.2g polyetheramine, and 0.2g ethylene glycol butyl ether is 2:1:1, and the mass ratio of the first inhibitor to the second inhibitor is 17.8:1.

[0076] The apparent viscosity and half-effective concentration EC of the water-based drilling fluid S1 were determined. 50 Value, LC50 50 The rheological stability ΔP, the mass m of the new substance generated by the water-based drilling fluid S1 in the water wellbore blockage inhibition performance experiment, and the pressure change in the reactor during the test were tested and recorded. The results are shown in Table 1.

[0077] Example 2

[0078] The method is the same as in Example 1, except that the NaCl content is 9.8 g and the PEG content is 4.4 g, resulting in a mass ratio of alcohol to salt of 1:2.2.

[0079] Example 3

[0080] The method is the same as in Example 1, except that the content of NaCl is 9.5g, the content of PEG is 4.7g, and there are 0.3g of polyvinylpyrrolidone, 0.3g of polyetheramine, and 0.3g of ethylene glycol butyl ether.

[0081] Example 4

[0082] The method is the same as in Example 1, except that the amount of NaCl used is 14.2g and the amount of PEG used is 5g.

[0083] Example 5

[0084] The method is the same as in Example 1, except that the amount of NaCl used is 8g and the amount of PEG used is 6.2g.

[0085] Example 6

[0086] The method is the same as in Example 1, except that the amount of polyvinylpyrrolidone is 0.5g, the amount of polyetheramine is 0.15g, and the amount of ethylene glycol butyl ether is 0.15g, so that the mass ratio is 3.3:1:1.

[0087] Example 7

[0088] The method is the same as in Example 1, except that in the first inhibitor, NaCl is replaced with an equal amount of CaCl2.

[0089] Example 8

[0090] The method is the same as in Example 1, except that XG is replaced with an equal amount of guar gum.

[0091] Example 9

[0092] The method is the same as in Example 1, except that the amount of polyvinylpyrrolidone is 1g, the amount of polyetheramine is 0.2g, and the amount of ethylene glycol butyl ether is 0.2g, so that the mass ratio of the first inhibitor to the second inhibitor is 10:1.

[0093] Example 10

[0094] The method is the same as in Example 1, except that the amount of polyvinylpyrrolidone is 0.8g, the amount of polyetheramine is 0.1g, and the amount of ethylene glycol butyl ether is 0.1g, so that the mass ratio of polyvinylpyrrolidone:polyetheramine:ethylene glycol butyl ether is 8:1:1.

[0095] Comparative Example 1

[0096] The method is the same as in Example 1, except that the second inhibitor does not contain polyetheramine and compounds with the structure shown in Formula I, and the content of polyvinylpyrrolidone is 0.8g.

[0097] Comparative Example 2

[0098] The method of Example 1 was followed, except that the amount of PEG used was 10g and the amount of water was 70.2g, resulting in an amount of 20.8g of the synergistic composition.

[0099] Comparative Example 3

[0100] The method is the same as in Example 1, except that it does not contain NaCl and PEG, and the amount of polyvinylpyrrolidone used is 7.5g, the amount of polyetheramine used is 3.75g, and the amount of ethylene glycol butyl ether used is 3.75g.

[0101] Comparative Example 4

[0102] The method is the same as in Example 1, except that it does not contain polyvinylpyrrolidone, polyetheramine and ethylene glycol butyl ether, the amount of NaCl used is 10g and the amount of PEG used is 5g.

[0103] Comparative Example 5

[0104] The method is the same as in Example 1, except that it does not contain NaCl and the amount of PEG used is 14.2g.

[0105] Table 1

[0106]

[0107]

[0108] P.S.: The initial pressure inside the vessel is 15 MPa.

[0109] As can be seen from the results in Table 1, Examples 1-10 that meet the requirements of the present invention have good rheological properties and can effectively suppress the formation of new materials in the wellbore, and have good low-temperature rheological properties.

[0110] Furthermore, embodiments 1-3 that satisfy the preferred embodiments of the present invention achieve significantly better technical effects. The drilling fluids configured in embodiments 1-3 have excellent rheological stability (Δρ<0.004), a new material generation amount of <1g, and a pressure change in the wellbore of no more than 1.8MPa, thus exhibiting excellent wellbore blockage suppression effect.

[0111] To further illustrate the excellent rheological stability of the composition provided by this invention as a drilling fluid, taking Example 1 as an example, the equivalent circulating density ρ1 of the water-based drilling fluid S1 at 4°C and the equivalent circulating density ρ2 at 25°C were tested. It was found that the difference between ρ2 and ρ1 was only 0.004 g / cm³. 3 This indicates excellent low-temperature rheological stability.

[0112] Inhibiting wellbore blockage stability: Taking Example 1 as an example, water-based drilling fluid S1 was added to the reactor, and high-pressure methane gas was introduced. The reactor was continuously tested for 20 hours under constant low temperature (4°C), initial pressure (15 MPa), closed system, and stirring at 300 r / min. The results are as follows: Figure 1 As shown, the pressure curve of the test fluid is stable, and no new substances are generated on the stirring rod or in the reaction vessel, indicating that the wellbore blockage suppression stability is excellent.

[0113] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. The application of a synergistic composition in suppressing wellbore blockage, characterized in that, The synergistic composition includes a first inhibitor and a second inhibitor; The first inhibitor comprises an alcohol and a salt; The second inhibitor comprises polyvinylpyrrolidone, polyetheramine, and a compound with the structure shown in Formula I; Where R is a C2-C6 alkyl group and n is an integer from 1 to 6.

2. The application according to claim 1, wherein, The mass ratio of the first inhibitor to the second inhibitor is 10-100:1, preferably 14-40:

1.

3. The application according to claim 1 or 2, wherein, In the first inhibitor, the alcohol is selected from at least one of low-carbon monohydric alcohols, low-carbon polyhydric alcohols, and low-carbon polymeric alcohols; Preferably, the low-carbon monohydric alcohol is selected from at least one of methanol, ethanol, and propanol; Preferably, the low-carbon polyol is selected from at least one of ethylene glycol, propylene glycol, and butanediol; Preferably, the low-carbon polymeric alcohol is polyethylene glycol; And / or, the salt is a chloride; Preferably, the salt is selected from at least one of sodium chloride, potassium chloride, and calcium chloride; And / or, in the first inhibitor, the mass ratio of alcohol to salt is 1:1.2-5, preferably 1:2-3.

4. The application according to claim 1 or 2, wherein, In the second inhibitor, the mass ratio of polyvinylpyrrolidone, polyetheramine, and the compound with the structure shown in Formula I is 1-5:0.8-2:1, preferably 1.8-2:0.8-1.5:1; And / or, in the compounds with the structure shown in Formula I, R is a C2-C4 alkyl group and n is an integer from 1 to 4.

5. The application according to claim 4, wherein, The molecular weight of the polyvinylpyrrolidone is 8,000-700,000; And / or, the molecular weight of polyetheramine is 230-2000; Preferably, the polyetheramine is selected from at least one of polyetheramine D230, polyetheramine D400, polyetheramine D2000 and polyetheramine D4000.

6. The application according to claim 1 or 2, wherein, The thickener is selected from at least one of modified cellulose, plant gums and biopolymers; Preferably, the modified cellulose is carboxymethyl cellulose and / or carboxyethyl cellulose; Preferably, the plant gum is selected from at least one of guar gum, guar gum, geranium powder, and azurite powder; Preferably, the biopolymer is selected from xanthan gum and / or water-soluble starch.

7. The application according to claim 1 or 2, wherein, The filtration loss reducing agent is selected from at least one of low-viscosity sodium carboxymethyl cellulose, high-viscosity sodium carboxymethyl cellulose, and potassium humate.

8. The application according to claim 1 or 2, wherein, The composition also includes 0.5-2 wt% nano-silica; And / or, the particle size of the nano-silica is 1-100 nm, preferably 10-20 nm.

9. A drilling fluid, characterized in that, The drilling fluid contains 15-20 wt% of an synergistic composition, 1-5 wt% of bentonite, 0.4-0.6 wt% of a viscosifier, 2.5-2.9 wt% of a filtration loss reducer, and 77.5-86 wt% of water. The synergistic composition is the composition according to any one of claims 1-8.

10. The drilling fluid according to claim 9, wherein, The half-effective concentration EC of the drilling fluid 50 Value > 2.8 × 10 4 mg / L, LC50 50 Value > 6 × 10 4 mg / L.

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