Nano-emulsion flushing agent for oil-based mud as well as preparation method and application of nano-emulsion flushing agent

Abstract

The invention relates to a nano-emulsion flushing agent for oil-based mud as well as a preparation method and application of the nano-emulsion flushing agent. The nano-emulsion flushing agent for the oil-based mud comprises an oil phase, an anionic surfactant, alcohol, polylactic acid powder, a chelating agent, an emulsion and water. According to the nano-emulsion flushing agent for the oil-based mud, the formula of the flushing liquid is designed, efficient cleaning and displacement of the oil-based mud in a high-temperature (more than or equal to 200 DEG C) and high-salinity deep well are achieved through the synergistic effect of all the components, and the flushing liquid has good compatibility with well cementation cement and high-temperature drilling fluid; and the subsequent well cementation operation is prevented from being influenced.

Description

Technical Field

[0001] The invention relates to the field of well completion flushing fluid, and in particular to a nano-emulsion flushing agent for oil-based mud, a preparation method thereof and application thereof. Background Art

[0002] Currently, oil-based drilling fluids are increasingly used in complex formations, and bottomhole temperatures are rising, reaching 200°C or even higher in most deep wells. At such high temperatures, oil-based drilling fluid systems are highly incompatible with high-temperature cement slurries, reducing the fluidity of the cement slurry and the bond between the wellbore and casing, severely impacting subsequent cementing results. Therefore, prior to cementing operations, a wash fluid must be injected between the drilling fluid and cement slurry to clean and dilute the drilling fluid, ensuring cementing quality and construction safety.

[0003] For example, CN106367050A discloses an ultra-high-temperature-resistant flushing fluid for high-density oil-based drilling fluid and its preparation method. The flushing fluid comprises coconut oil fatty acid diethanolamide, alkylbenzenesulfonic acid triethanolamine salt, ethylene glycol monobutyl ether, maleic acid and acrylic acid copolymer, and water. This flushing fluid is simple to prepare and boasts a flushing efficiency exceeding 90% for high-density oil-based drilling fluid. It also exhibits strong high-temperature resistance, with stable performance at 190°C, and good compatibility with cement slurry and oil-based drilling fluids. However, its flushing effect on low-density drilling fluids is less effective.

[0004] CN115725284A discloses a flushing agent and its use. The flushing agent comprises dodecylbenzenesulfonic acid, polyoxyethylene nonyl ether, polyoxyethylene fatty alcohol ether, ethylenediaminetetraacetic acid, tributyl phosphate, sodium polyacrylate, and water. While the flushing agent can withstand temperatures exceeding 200°C, it has a low flushing efficiency of only over 70% for oily mud.

[0005] CN104910885A discloses a highly efficient anionic-nonionic composite rinsing fluid and its preparation method. The fluid comprises polyoxyethylene sorbitan fatty acid ester, sodium sulfate of polyoxyethylene fatty alcohol ether, polyoxyethylene nonylphenol ether, sodium tripolyphosphate, and water. The rinsing fluid has a wide operating temperature range and is adaptable to high-temperature and high-salt environments. It also has good cleaning effects at low temperatures. However, the rinsing fluid has a rinsing efficiency of only 86.9% at 190°C.

[0006] It can be seen that although the above-mentioned oil-based mud flushing fluid has a certain flushing effect on oil-based mud, its application range is narrow and its high-temperature resistance is poor, which limits its application scope. Most completion pre-flushing fluids are effective under low temperature conditions, but their stability and flushing efficiency are very low under ultra-high temperature environments. Therefore, there is an urgent need for a completion pre-flushing fluid that can be used as a supporting fluid for ultra-high temperature and high-salinity deep wells. Summary of the Invention

[0007] In view of the problems existing in the prior art, the object of the present invention is to provide a nanoemulsion flushing agent for oil-based mud and its preparation method and use, so as to solve the problem that the current nanoemulsion flushing agent for oil-based mud has poor cleaning effect in high temperature and high salinity environment.

[0008] To achieve this object, the present invention adopts the following technical solutions:

[0009] In a first aspect, the present invention provides a nanoemulsion flushing agent for oil-based mud, wherein the nanoemulsion flushing agent for oil-based mud comprises: an oil phase, an anionic surfactant, alcohol, polylactic acid powder, a chelating agent, an emulsion and water.

[0010] The nanoemulsion flushing agent for oil-based mud provided by the present invention achieves efficient cleaning and displacement of oil-based mud in high-temperature (≥200°C) and high-salinity deep wells by designing the flushing fluid formula and utilizing the synergistic effect between the various components. In addition, the flushing fluid has good compatibility with cementing cement and high-temperature drilling fluid, avoiding affecting subsequent cementing operations.

[0011] As a preferred technical solution of the present invention, the nanoemulsion flushing agent for oil-based mud comprises, by weight: 10-60 parts of oil phase, 1-10 parts of anionic surfactant, 1-5 parts of alcohol, 0.01-1 part of polylactic acid powder, 1-10 parts of chelating agent, 1-10 parts of emulsion, and 4-85 parts of water.

[0012] As a preferred technical solution of the present invention, the oil phase includes one or a combination of at least two of n-octane, n-heptane, n-hexane or cyclohexane.

[0013] As a preferred technical solution of the present invention, the anionic surfactant includes one or a combination of at least two of sodium dedecylbenzenesulfonate, sodium dodecylbenzenesulfonate, sodium tetradecylbenzenesulfonate or sodium dodecylbenzenesulfonate.

[0014] As a preferred technical solution of the present invention, the alcohol includes one or a combination of at least two of n-butanol, n-pentanol or n-hexanol.

[0015] As a preferred technical solution of the present invention, the particle size of the polylactic acid powder is 0.15-0.25 mm.

[0016] As a preferred technical solution of the present invention, the chelating agent includes one or a combination of at least two of ethylenediaminetetraacetic acid, hydroxyethylidene diphosphonic acid or aminotrimethylenephosphonic acid.

[0017] As a preferred technical solution of the present invention, the emulsion includes one or a combination of at least two of sodium polyacrylate, polyacrylamide or xanthan gum.

[0018] In a second aspect, the present invention provides a method for preparing a nanoemulsion flushing agent for oil-based mud as described in the first aspect, the preparation method comprising first mixing an oil phase, an anionic surfactant, alcohol, a chelating agent, an emulsion and water according to a formula, and then adding polylactic acid powder for a second mixing to obtain a nanoemulsion flushing agent for oil-based mud.

[0019] In a third aspect, the present invention provides a use of the nanoemulsion flushing agent for oil-based mud as described in the first aspect, wherein the use is to flush the oil-based mud in a deep well before cementing using the nanoemulsion flushing agent for oil-based mud.

[0020] Compared with the existing technical solutions, the present invention has the following beneficial effects:

[0021] The nanoemulsion flushing agent for oil-based mud provided by this invention is suitable for high-temperature, high-salinity deep wells at 200°C. It can efficiently and quickly clean and displace oil-based drilling fluids. It has a simple preparation process, low production cost, and good compatibility with cement slurry, making it promising for application in high-temperature, high-salinity deep well operations. In high-temperature, high-salinity deep wells at 200°C, the flushing fluid can achieve a flushing efficiency of over 92%. DETAILED DESCRIPTION

[0022] To better illustrate the present invention and facilitate understanding of the technical solutions of the present invention, typical but non-limiting embodiments of the present invention are as follows:

[0023] This embodiment provides a nanoemulsion flushing agent for oil-based mud, comprising: an oil phase, an anionic surfactant, alcohol, polylactic acid powder, a chelating agent, an emulsion, and water.

[0024] Specifically, the composition comprises, by weight: 10-60 parts of oil phase, 1-10 parts of anionic surfactant, 1-5 parts of alcohol, 0.01-1 part of polylactic acid powder, 1-10 parts of chelating agent, 1-10 parts of emulsion, and 4-85 parts of water.

[0025] The oil phase in the nanoemulsion flushing agent for oil-based mud is 10-60 parts by weight, for example, 10 parts, 20 parts, 30 parts, 40 parts, 50 parts or 60 parts, but is not limited to the listed values, and other values ​​not listed within this range are also applicable.

[0026] The anionic surfactant in the nanoemulsion flushing agent for oil-based mud is 1-10 parts by weight, for example, 1 part, 2 parts, 3 parts, 4 parts, 5 parts, 6 parts, 7 parts, 8 parts, 9 parts or 10 parts, but is not limited to the listed values. Other values ​​not listed within this range are also applicable.

[0027] The alcohol content in the nanoemulsion flushing agent for oil-based mud is 1-5 parts by weight, for example, 1 part, 2 parts, 3 parts, 4 parts or 5 parts, but is not limited to the listed values. Other values ​​not listed within the range are also applicable.

[0028] The polylactic acid powder in the nanoemulsion flushing agent for oil-based mud is 0.01-1 parts by weight, for example, it can be 0.01 parts, 0.02 parts, 0.04 parts, 0.06 parts, 0.08 parts, 0.1 parts, 0.2 parts, 0.4 parts, 0.6 parts, 0.8 parts or 1 parts, but is not limited to the listed values. Other values ​​not listed within this range are also applicable.

[0029] The amount of the chelating agent in the nanoemulsion flushing agent for oil-based mud is 1-10 parts by weight, for example, 1 part, 2 parts, 3 parts, 4 parts, 5 parts, 6 parts, 7 parts, 8 parts, 9 parts or 10 parts, but is not limited to the listed values, and other values ​​not listed within the range are also applicable.

[0030] The emulsion in the nanoemulsion flushing agent for oil-based mud is 1-10 parts by weight, for example, it can be 1 part, 2 parts, 3 parts, 4 parts, 5 parts, 6 parts, 7 parts, 8 parts, 9 parts or 10 parts, etc., but is not limited to the listed values. Other values ​​not listed within this range are also applicable.

[0031] The amount of water in the nanoemulsion flushing agent for oil-based mud is 4-86 parts by weight, for example, 4 parts, 5 parts, 10 parts, 15 parts, 20 parts, 25 parts, 30 parts, 35 parts, 40 parts, 45 parts, 50 parts, 55 parts, 60 parts, 65 parts, 70 parts, 75 parts, 80 parts, 85 parts or 86 parts, but is not limited to the listed values, and other values ​​not listed within the range are also applicable.

[0032] Specifically, the oil phase includes one or a combination of at least two of n-octane, n-heptane, n-hexane or cyclohexane.

[0033] Specifically, the anionic surfactant includes one or a combination of at least two of sodium dedecylbenzenesulfonate, sodium dodecylbenzenesulfonate, sodium tetradecylbenzenesulfonate or sodium dodecylbenzenesulfonate.

[0034] Specifically, the alcohol includes one or a combination of at least two of n-butanol, n-pentanol, or n-hexanol.

[0035] Specifically, the particle size of the polylactic acid powder is 0.15-0.25 mm.

[0036] In the present invention, the particle size of the polylactic acid powder is 0.15-0.25 mm, which refers to a uniform particle aggregate within the particle size range or all particle aggregates within a certain range, such as a particle aggregate with a particle size of 0.15 mm, a particle aggregate with a particle size of 0.2 mm, a particle aggregate with a particle size of 0.25 mm, an aggregate of all particles within the particle size range of 0.15-0.2 mm, an aggregate of all particles within the particle size range of 0.15-0.25 mm, an aggregate of all particles within the particle size range of 0.2-0.25 mm, an aggregate of all particles within the particle size range of 0.18-0.22 mm, etc.

[0037] Furthermore, the molecular weight of the polylactic acid can be selected to be 100,000-150,000.

[0038] Specifically, the chelating agent includes one or a combination of at least two of ethylenediaminetetraacetic acid, hydroxyethylidene diphosphonic acid or aminotrimethylenephosphonic acid.

[0039] Specifically, the emulsion includes one or a combination of at least two of sodium polyacrylate, polyacrylamide or xanthan gum.

[0040] Furthermore, the molecular weight of the sodium polyacrylate can be selected to be 500-3000.

[0041] Furthermore, the molecular weight of the polyacrylamide can be selected to be 8 million to 20 million.

[0042] Furthermore, the molecular weight of the xanthan gum can be selected to be 1 million to 2 million.

[0043] Furthermore, this embodiment provides a method for preparing the above-mentioned nanoemulsion flushing agent for oil-based mud, specifically, the oil phase, anionic surfactant, alcohol, chelating agent, emulsion and water are first mixed according to the formula, and then polylactic acid powder is added for a second mixing to obtain the nanoemulsion flushing agent for oil-based mud.

[0044] Specifically, the stirring speed in the first mixing is 600-700 r / min, for example, it can be 600 r / min, 620 r / min, 640 r / min, 660 r / min, 680 r / min or 700 r / min, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0045] Specifically, the first mixing time is 30-45 min, for example, it can be 30 min, 31 min, 32 min, 33 min, 34 min, 35 min, 36 min, 37 min, 38 min, 39 min, 40 min, 41 min, 42 min, 43 min, 44 min or 45 min, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0046] Specifically, the stirring speed in the second mixing is 600-700 r / min, for example, it can be 600 r / min, 620 r / min, 640 r / min, 660 r / min, 680 r / min or 700 r / min, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0047] Specifically, the second mixing is carried out for 5-10 minutes, for example, 5 minutes, 5.5 minutes, 6 minutes, 6.5 minutes, 7 minutes, 7.5 minutes, 8 minutes, 8.5 minutes, 9 minutes or 10 minutes, etc., but is not limited to the listed values, and other values ​​not listed within the range are also applicable.

[0048] Furthermore, this embodiment provides a use of the nanoemulsion flushing agent for oil-based mud, specifically using the nanoemulsion flushing agent for oil-based mud to flush the oil-based mud in a deep well before cementing.

[0049] Specifically, the temperature of the deep well is ≤250°C;

[0050] Specifically, the salinity of the oil-based mud in the deep well is ≤240,000.

[0051] In order to further illustrate the advantages of the nanoemulsion flushing agent for oil-based mud of the present invention, the following specific examples are provided, and the reagents used in the examples are all commercially available reagents.

[0052] Example 1

[0053] This embodiment provides a nanoemulsion flushing agent for oil-based mud. The flushing agent comprises 32g of n-octane, 6g of sodium dodecylbenzenesulfonate, 2g of n-butanol, 4g of ethylenediaminetetraacetic acid, 4.5g of sodium polyacrylate (molecular weight 2000), and 50g of water. After being fully emulsified in an emulsifier, 0.5g of polylactic acid (molecular weight 100,000) is added and stirred until uniform, resulting in the flushing agent. The flushing agent is then mixed with water to form final flushing agents at concentrations of 5%, 10%, 15%, and 20%, respectively.

[0054] Example 2

[0055] This embodiment provides a nanoemulsion flushing agent for oil-based mud. The flushing agent comprises weighing 40g of n-heptane, 1g of sodium decanylbenzenesulfonate, 4g of n-hexanol, 7g of hydroxyethylidene diphosphonic acid, 8g of polyacrylamide (molecular weight 20 million), and 30g of water. After being fully emulsified in an emulsifier, 0.01g of polylactic acid (molecular weight 150,000) is added, stirred, and then stopped to obtain the flushing agent. The flushing agent is then mixed with water to obtain final flushing agents with concentrations of 5%, 10%, 15%, and 20%, respectively.

[0056] Example 3

[0057] This embodiment provides a nanoemulsion flushing agent for oil-based mud. The flushing agent comprises weighing 10g of n-hexane, 10g of sodium tetradecylbenzenesulfonate, 1g of n-pentanol, 1g of ethylenediaminetetraacetic acid, 10g of sodium polyacrylate (molecular weight 500), and 85g of water. After being fully emulsified in an emulsifier, 1g of polylactic acid (molecular weight 120,000) is added and stirred until uniform, resulting in the flushing agent. The flushing agent is then mixed with water to form final flushing agents at concentrations of 5%, 10%, 15%, and 20%, respectively.

[0058] Example 4

[0059] This embodiment provides a nanoemulsion flushing agent for oil-based mud. The flushing agent comprises weighing 60g of n-octane, 3g of sodium lauryl sulfate, 5g of n-butanol, 10g of aminotrimethylenephosphonic acid, 1g of xanthan gum (molecular weight of 1,000,000), and 4g of water. After being fully emulsified in an emulsifier, 0.5g of polylactic acid (molecular weight of 130,000) is added and stirred until uniform, thereby obtaining the flushing agent. The flushing agent is then mixed with water to obtain final flushing agents having concentrations of 5%, 10%, 15%, and 20%, respectively.

[0060] Comparative Example 1

[0061] The only difference from Example 1 is that no emulsifier, ie, sodium polyacrylate, is added to the rinse agent.

[0062] Comparative Example 2

[0063] The only difference from Example 1 is that no polylactic acid powder is added to the flushing agent.

[0064] Comparative Example 3

[0065] The only difference from Example 1 is that sodium dodecylbenzenesulfonate is replaced by an equal amount of Tween 80.

[0066] Comparative Example 4

[0067] The only difference from Example 1 is that ethylenediaminetetraacetic acid is replaced by an equal amount of Tween 80.

[0068] Comparative Example 5

[0069] The only difference from Example 1 is that the polylactic acid powder is replaced by an equal amount of polyvinyl alcohol (polymerization degree or molecular weight is 120,000).

[0070] Test Case

[0071] The nanoemulsion flushing agent for oil-based mud finally configured in Examples 1 to 4 and Comparative Examples 1 to 5 was subjected to performance tests, and high-temperature curing experiments, cleaning efficiency evaluation experiments, temperature resistance experiments, and salt resistance experiments were carried out. The mud used in the test was the high-temperature oil-based mud actually used at the high-temperature drilling site in the Penglai gas field in Yanting County, Mianyang City, Sichuan Province.

[0072] I. High temperature curing experiment

[0073] The specific process involves hot-roll curing the flushing solution according to the drilling fluid curing methods outlined in the national standard GB / T 19139-2012, "Test Methods for Oil Well Cement." After curing, the flushing solution is removed and the next flushing rating test begins. The high-temperature curing test conditions are: 200°C, 100 MPa, and 100 minutes. The primary experimental instrument is a high-temperature roller furnace.

[0074] II. Cleaning efficiency evaluation experiment

[0075] Experimental method: Pour the hot-rolled drilling fluid into the cup of the rotational viscometer, and weigh the mass of the outer cylinder of the viscometer as W; immerse the part below the scale line of the outer cylinder of the rotational viscometer in the drilling fluid, stir at 300r / min for 15min, and allow it to drip for 3min, and weigh the mass of the outer cylinder of the viscometer and the drilling fluid as W1; immerse the outer cylinder of the rotational viscometer stained with drilling fluid in the flushing fluid, flush at 300r / min for 5min, and allow it to drip for 3min, and weigh the mass of the outer cylinder of the rotational viscometer after flushing as W2.

[0076] The flushing rate η was calculated according to formula (1), and three groups of parallel experiments were conducted to obtain the average value. The experimental data results are shown in Table 1.

[0077]

[0078] Where: η is the flushing efficiency;

[0079] W is the mass of the outer cylinder of the rotational viscometer, in grams (g);

[0080] W1 is the mass of the outer cylinder of the rotary viscometer after it is filled with drilling fluid, in grams (g);

[0081] W2 is the mass of the outer cylinder of the rotational viscometer after flushing, in grams (g).

[0082] Examples 1-4 and Comparative Examples 1-5 were each subjected to cleaning efficiency evaluation experiments using a nanoemulsion flushing agent for oil-based mud at a concentration of 15% by mass at a temperature of 200°C. The experimental results are detailed in Table 1. In the table, W is the mass of the outer cylinder of the rotational viscometer; W1 is the mass of the outer cylinder of the rotational viscometer after it is fully saturated with drilling fluid; and W2 is the mass of the outer cylinder of the rotational viscometer after flushing. The flushing efficiency was calculated according to formula (1).

[0083] Table 1

[0084]

[0085] As can be seen from Table 1, the nanoemulsion flushing agent for oil-based mud prepared in Example 1 has a flushing efficiency of 94.29% at 200°C. By comparing the cleaning efficiency with that in the comparative example, it can be seen that there is a synergistic effect between the individual agents in the flushing fluid, and each agent in the flushing fluid has different cleaning effects on different components in the oil-based drilling fluid.

[0086] The nanoemulsion flushing agent for oil-based mud prepared in Example 1 with a mass concentration of 5%, 10%, 15%, and 20% was used to test the flushing efficiency at a temperature of 200°C. The results are shown in Table 2. The test process is the same as the test process of the results in Table 1.

[0087] Table 2

[0088]

[0089] In the table, a mass concentration of 0 means water is used for flushing;

[0090] From Table 2, we can see that the addition of the nanoemulsion flushing agent for oil-based mud of the present invention can significantly improve the cleaning efficiency under high temperature conditions. Adding 5% can increase the well cleaning efficiency to 70%, and when the addition reaches 10%, the flushing efficiency can reach over 90%. This proves that the nanoemulsion flushing agent for oil-based mud of the present invention has good flushing efficiency at different addition amounts. When considering practical application, considering cost, the optimal addition amount should be around 15%, which can achieve both good flushing efficiency and control costs.

[0091] The 15% mass concentration of the nanoemulsion flushing agent for oil-based mud prepared in Examples 1 to 4 and Comparative Examples 1 to 5 was tested for well washing efficiency at temperatures of 120°C, 140°C, 160°C, 180°C, and 200°C. The test results are detailed in Table 3. The test method is the same as the test process of the results in Table 1.

[0092] Table 3

[0093]

[0094] As can be seen from Table 2, the nanoemulsion flushing agent for oil-based mud of the present invention decreases in well washing efficiency as the temperature increases, but the decrease is not obvious. At a temperature of 200°C, it still has a well washing efficiency of more than 92%, which can fully meet the needs of high-temperature deep well washing operations.

[0095] III. Salt resistance test

[0096] NaCl was added to the nanoemulsion flushing agents for oil-based mud with a mass concentration of 15% prepared in Examples 1 to 4 and Comparative Examples 1 to 5 at a temperature of 200°C. The NaCl addition amounts were 0%, 12%, 18%, and 36%, respectively. The experimental results are shown in Table 4.

[0097] Table 4

[0098]

[0099]

[0100] It can be seen from Table 4 that the salt content does not affect the cleaning efficiency of the nanoemulsion flushing agent for oil-based mud of the present invention, indicating that the nanoemulsion flushing agent for oil-based mud has good salt resistance.

[0101] All the nanoemulsion flushing agents for oil-based mud tested indoors were subjected to high-temperature curing at 200° C. for 120 min, proving that the nanoemulsion flushing agent for oil-based mud provided by the present invention has good high-temperature resistance.

[0102] IV. Anti-filtration test

[0103] 500 mL of the 15% mass concentration nanoemulsion flushing agent for oil-based mud prepared in Examples 1 to 4 and Comparative Examples 1 to 5 were respectively placed in a filter loss tester at a temperature of 200° C. The experimental results are detailed in Table 5.

[0104] Table 5

[0105]

[0106]

[0107] As can be seen from Table 5, in Example 1, due to the addition of polylactic acid to the nanoemulsion flushing agent for oil-based mud, the leakage in the first 90 minutes only accounted for 6.8% of the total nanoemulsion flushing agent for oil-based mud, while the sample of Comparative Example 2, which did not add polylactic acid, had a filtration loss of more than 50% of the total nanoemulsion flushing agent for oil-based mud after 120 minutes. This shows that polylactic acid in the nanoemulsion flushing agent formulation for oil-based mud of the present invention can significantly reduce the leakage of the nanoemulsion flushing agent for oil-based mud and restore the permeability of the formation within two hours after the completion of the operation, thereby protecting the reservoir and reducing the pollution to the formation caused by well washing.

[0108] In summary, the nanoemulsion flushing agent for oil-based mud provided by the present invention has good resistance to high temperature and high salt environments, can efficiently and quickly clean and displace oil-based mud in high temperature and high salt environments, and has good compatibility with cementing cement and high-temperature drilling fluid, thereby improving well washing efficiency, enhancing cementing quality, and ensuring construction safety. It has broad prospects in high-temperature deep well cementing cleaning.

[0109] It should be noted that the present invention uses the above-described embodiments to illustrate the detailed structural features of the present invention. However, the present invention is not limited to these detailed structural features, and this does not mean that the present invention must rely on these detailed structural features to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent replacements for selected components, additions of auxiliary components, and selection of specific methods, etc., fall within the scope of protection and disclosure of the present invention.

[0110] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the scope of protection of the present invention.

[0111] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0112] In addition, the various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A nanoemulsion flushing agent for oil-based mud, characterized in that: The nano-emulsion flushing agent for oil-based mud comprises: an oil phase, an anionic surfactant, alcohol, polylactic acid powder, a chelating agent, an emulsion and water.

2. The nanoemulsion flushing agent for oil-based mud according to claim 1, characterized in that: The nano-emulsion flushing agent for oil-based mud comprises, by weight: 10-60 parts of oil phase, 1-10 parts of anionic surfactant, 1-5 parts of alcohol, 0.01-1 parts of polylactic acid powder, 1-10 parts of chelating agent, 1-10 parts of emulsion, and 4-85 parts of water.

3. The nanoemulsion flushing agent for oil-based mud according to claim 1 or 2, characterized in that: The oil phase includes one or a combination of at least two of n-octane, n-heptane, n-hexane or cyclohexane.

4. The nanoemulsion flushing agent for oil-based mud according to any one of claims 1 to 3, characterized in that: The anionic surfactant includes one or a combination of at least two of sodium dodecylbenzene sulfonate, sodium dodecylbenzene sulfonate, sodium tetradecylbenzene sulfonate or sodium dodecylbenzene sulfonate.

5. The nanoemulsion flushing agent for oil-based mud according to any one of claims 1 to 3, characterized in that: The alcohol includes one or a combination of at least two of n-butanol, n-pentanol or n-hexanol.

6. The nanoemulsion flushing agent for oil-based mud according to any one of claims 1 to 3, characterized in that: The particle size of the polylactic acid powder is 0.15-0.25 mm.

7. The nanoemulsion flushing agent for oil-based mud according to any one of claims 1 to 3, characterized in that: The chelating agent includes one or a combination of at least two of ethylenediaminetetraacetic acid, hydroxyethylidene diphosphonic acid or aminotrimethylene phosphonic acid.

8. The nanoemulsion flushing agent for oil-based mud according to any one of claims 1 to 3, characterized in that: The emulsion comprises one or a combination of at least two of sodium polyacrylate, polyacrylamide or xanthan gum.

9. A method for preparing a nanoemulsion flushing agent for oil-based mud according to any one of claims 1 to 8, characterized in that: The preparation method comprises the steps of first mixing an oil phase, anionic surfactant, alcohol, chelating agent, emulsion and water according to a formula, and then adding polylactic acid powder for second mixing to obtain a nanoemulsion flushing agent for oil-based mud.

10. A use of the nanoemulsion flushing agent for oil-based mud according to any one of claims 1 to 8, characterized in that: The application is to use the nano-emulsion flushing agent for oil-based mud to flush the oil-based mud in a deep well before cementing.

Images