Nano-emulsion flushing agent for water-based mud and application of nano-emulsion flushing agent

Abstract

The invention relates to a nano-emulsion flushing agent for water-based mud and application of the nano-emulsion flushing agent, and aims at solving the problems that in the prior art, a flushing agent for the water-based mud is poor in stability and low in cleaning efficiency under the conditions that the temperature is larger than or equal to 180 DEG C and the mud salinity is high. The nano-emulsion flushing agent for the water-based mud is prepared from an acidic nano-emulsion, an emulsion, polylactic acid and inorganic salt, the acidic nano-emulsion comprises a nonionic surfactant, a solvent, alcohol, a chelating agent and water. According to the flushing agent provided by the invention, the salt resistance and high temperature resistance of the flushing agent are improved by utilizing the synergistic strengthening effect of the components in the flushing agent, and meanwhile, the flushing agent can efficiently and quickly clean and displace a water-based drilling fluid, is good in compatibility with cement paste, and has a wide application prospect in high-temperature and high-salt deep well operation.

Description

Technical Field

[0001] The invention relates to the field of cementing pre-flushing fluid wells, and in particular to a nano-emulsion flushing agent for water-based mud and application thereof. Background Art

[0002] At present, the exploration and development of oil and gas resources is constantly exploring deeper strata, and the temperature at the bottom of the well is getting higher and higher. The temperature of most deep wells has reached above 180℃. Under such high temperature, the long-term circulation of the mud in the water drilling fluid system will form a thick virtual mud cake on the well wall and casing. The virtual mud cake will seriously affect the bonding quality between the well wall, casing wall and cement slurry, and seriously affect the subsequent cementing quality. Therefore, before the cementing operation, it is necessary to inject a section of well washing fluid between the drilling fluid and cement slurry to clean and dilute the virtual mud cake to ensure the cementing quality and construction safety.

[0003] For example, CN105001842A discloses a weighted well-washing fluid for cementing, which is prepared from 100 weight parts of water, 10-1000 weight parts of weighting agent, 1-10 weight parts of surfactant, 0.1-5 weight parts of sodium lignin and 0-10 weight parts of retarder. The weighted well-washing fluid for cementing: the density of the well-washing fluid can reach 1.8g / cm 3 It can effectively balance the formation pressure in high-pressure layer cementing operations; it can improve the interface bonding strength between cement slurry and casing; and it has good high temperature resistance, and can be used in temperatures up to 180°C, but its cleaning efficiency for water-based drilling fluid is low, only about 88%.

[0004] CN115637139A discloses a multi-faceted quartz sand cementing and washing fluid and a preparation method thereof, comprising water, a suspending agent, and multi-faceted quartz sand. The washing fluid has a wide temperature range of use, can adjust density, and has good compatibility with cement slurry and drilling fluid. However, the washing efficiency of the washing fluid for relatively low-density drilling fluid is only 60%, and the washing efficiency for low-density drilling fluid is very low.

[0005] However, although the above-mentioned water-based mud flushing fluid has a certain flushing effect on water-based mud, its application scope is narrow and its use range is relatively limited. Most cementing pre-flushing fluids have good effects 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 cementing pre-flushing fluid that can be used as a supporting ultra-high temperature and high-salt deep well. Summary of the invention

[0006] In view of the problems existing in the prior art, the object of the present invention is to provide a nanoemulsion flushing agent for water-based mud and its use, so as to solve the problems of poor stability and low cleaning efficiency of the flushing agent for water-based mud in the prior art when the temperature is ≥180°C and the mud salinity is high.

[0007] To achieve this object, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a nanoemulsion flushing agent for water-based mud, the nanoemulsion flushing agent for water-based mud comprising: an acidic nanoemulsion, an emulsion, polylactic acid and an inorganic salt;

[0009] The acidic nanoemulsion comprises: a nonionic surfactant, a solvent, an alcohol, a chelating agent and water.

[0010] The flushing agent provided by the present invention improves the salt and high temperature resistance of the flushing agent by utilizing the synergistic reinforcement effect among the components in the flushing agent. At the same time, it can efficiently and quickly clean and displace water-based drilling fluid, has good compatibility with cement slurry, and has broad application prospects in high-temperature and high-salt deep well operations.

[0011] As a preferred technical solution of the present invention, the nanoemulsion flushing agent for water-based mud comprises, by weight:

[0012] 20-50 parts of acidic nanoemulsion, 1-10 parts of emulsion, 0.1-1 parts of polylactic acid and 20-50 parts of inorganic salt.

[0013] As a preferred technical solution of the present invention, the acidic nanoemulsion comprises, by weight: 10-40 parts of nonionic surfactant, 10-60 parts of solvent, 1-50 parts of alcohol, 1-50 parts of chelating agent and 1-100 parts of water.

[0014] 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.

[0015] As a preferred technical solution of the present invention, the inorganic salt is a soluble inorganic salt.

[0016] As a preferred technical solution of the present invention, the nonionic surfactant in the acidic nanoemulsion includes polyoxyethylene ether;

[0017] Preferably, the solvent in the acidic nanoemulsion includes one or a combination of at least two of xylene, toluene or acetone;

[0018] Preferably, the alcohol in the acidic nanoemulsion comprises one or a combination of at least two of isopropanol, n-propanol or n-butanol.

[0019] As a preferred technical solution of the present invention, the nanoemulsion flushing agent for water-based mud also includes a soaking aid.

[0020] In the present invention, by further introducing a soaking aid, more efficient cleaning can be achieved for difficult-to-clean water-based mud, and the flushing effect can be further improved.

[0021] As a preferred technical solution of the present invention, the soaking aid comprises 1-10% of alkali and 0.01-1% of oxidant in terms of mass percentage, and the balance is water.

[0022] As a preferred technical solution of the present invention, the alkali used in the soaking aid is a soluble alkali;

[0023] Preferably, the oxidant used in the soaking aid includes one or a combination of at least two of potassium chlorate, ammonium persulfate, hydrogen peroxide or sodium peroxide.

[0024] In a second aspect, the present invention provides the use of the nanoemulsion flushing agent for water-based mud as described in the first aspect, and the use comprises: flushing the wellbore with the nanoemulsion flushing agent for water-based mud.

[0025] Compared with the prior art solutions, the present invention has the following beneficial effects:

[0026] The acidic nanoemulsion well-washing fluid combination provided by the present invention has good resistance to high temperature (temperature ≥180°C) and high-salt environment (water mineralization ≥200,000), and can efficiently and quickly wash and displace water-based mud in high-temperature and high-salt environments. At the same time, it can also reduce the loss of well-washing fluid during the well-washing process, improve the well-washing efficiency, enhance the cementing quality, and ensure the safety of construction, and has broad prospects in high-temperature deep well cementing cleaning. DETAILED DESCRIPTION

[0027] To better illustrate the present invention and facilitate understanding of the technical solution of the present invention, typical but non-limiting embodiments of the present invention are as follows:

[0028] The present invention provides a nanoemulsion flushing agent for water-based mud, the nanoemulsion flushing agent for water-based mud comprising: acidic nanoemulsion, emulsion, polylactic acid and inorganic salt;

[0029] The acidic nanoemulsion comprises: a nonionic surfactant, a solvent, an alcohol, a chelating agent and water.

[0030] During use, the nanoemulsion flushing agent for water-based mud can further adjust the mass concentration of the solution by using water, so that corresponding adjustments can be made according to different needs.

[0031] Specifically, the nanoemulsion flushing agent for water-based mud comprises, by weight: 20-50 parts of acidic nanoemulsion, 1-10 parts of emulsion, 0.1-1 parts of polylactic acid and 20-50 parts of inorganic salt.

[0032] Among them, the acidic nanoemulsion in the nanoemulsion flushing agent for water-based mud is 20-50 parts by weight, for example, it can be 20 parts, 25 parts, 30 parts, 35 parts, 40 parts, 45 parts or 50 parts, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0033] Among them, the emulsion in the nanoemulsion flushing agent for water-based mud is 1-10 parts by weight, for example, it can be 1 part, 2 parts, 4 parts, 6 parts, 8 parts or 10 parts, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0034] Among them, the polylactic acid in the nanoemulsion flushing agent for water-based mud is 0.1-1 part by weight, for example, it can be 0.1 part, 0.2 part, 0.4 part, 0.6 part, 0.8 part or 1 part, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0035] Among them, the inorganic salt in the nanoemulsion flushing agent for water-based mud is 20-50 parts by weight, for example, it can be 20 parts, 25 parts, 30 parts, 35 parts, 40 parts, 45 parts or 50 parts, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0036] Specifically, the acidic nanoemulsion comprises, by weight: 10-40 parts of a nonionic surfactant, 10-60 parts of a solvent, 1-50 parts of an alcohol, 1-50 parts of a chelating agent and 1-100 parts of water.

[0037] The nonionic surfactant in the acidic nanoemulsion is 10-40 parts by weight, for example, 10 parts, 15 parts, 20 parts, 25 parts, 30 parts, 35 parts or 40 parts, but is not limited to the listed values, and other values ​​not listed within the range are also applicable.

[0038] The acidic nanoemulsion contains 10-60 parts by weight of solvent, for example, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55 or 60 parts, but is not limited to the listed values, and other values ​​not listed within the range are also applicable.

[0039] The alcohol in the acidic nanoemulsion is 1-50 parts by weight, for example, 1 part, 5 parts, 10 parts, 15 parts, 20 parts, 25 parts, 30 parts, 35 parts, 40 parts, 45 parts or 50 parts, but is not limited to the listed values, and other values ​​not listed within the range are also applicable.

[0040] The chelating agent in the acidic nanoemulsion is 1-50 parts by weight, for example, 1 part, 5 parts, 10 parts, 15 parts, 20 parts, 25 parts, 30 parts, 35 parts, 40 parts, 45 parts or 50 parts, but is not limited to the listed values, and other values ​​not listed within the range are also applicable.

[0041] The amount of water in the acidic nanoemulsion is 1-100 parts by weight, for example, 1 part, 1 part, 10 parts, 20 parts, 30 parts, 40 parts, 50 parts, 60 parts, 70 parts, 80 parts, 90 parts or 100 parts, but is not limited to the listed values, and other values ​​not listed within the range are also applicable.

[0042] Specifically, the emulsion includes one or a combination of at least two of sodium polyacrylate, polyacrylamide or xanthan gum.

[0043] Wherein, the molecular weight of the sodium polyacrylate used can be selected to be 500-3000.

[0044] The molecular weight of the polyacrylamide used can be selected to be 8 million to 20 million.

[0045] The molecular weight of the xanthan gum used can be selected to be 1 million to 2 million.

[0046] Specifically, the polylactic acid is in the form of particles under a -200 mesh sieve, and the molecular weight can be selected to be 100,000-150,000.

[0047] Specifically, the inorganic salt is a soluble inorganic salt, including sodium salt and / or potassium salt, such as sodium chloride, potassium chloride, sodium bromide or potassium bromide, etc., and any one or a combination of at least two of them can be selected.

[0048] Specifically, the nonionic surfactant in the acidic nanoemulsion includes polyoxyethylene ether, specifically long-chain fatty alcohol polyoxyethylene ether and / or alkylphenol polyoxyethylene ether, etc., and any one or a combination of at least two of them may be selected.

[0049] Among them, the molecular weight of the polyoxyethylene ether can be selected to be 1000-2000.

[0050] Specifically, the solvent in the acidic nanoemulsion includes xylene, toluene, acetone and other commonly used organic solvents in the art, and one or a combination of at least two of them can be selected.

[0051] Specifically, the alcohol in the acidic nanoemulsion includes isopropanol, n-propanol, n-butanol and other alcohols commonly used in the art, and one or a combination of at least two of them may be selected.

[0052] Specifically, the chelating agent in the acidic nanoemulsion includes hydroxyethylidene diphosphonic acid and / or aminotrimethylene phosphonic acid and other commonly used chelating agents in the art.

[0053] Furthermore, the nanoemulsion flushing agent for water-based mud also includes a soaking aid, and the soaking aid used includes 1-10% of alkali and 0.01-1% of oxidant in terms of mass percentage, and the balance is water.

[0054] The alkali content of the soaking aid used is 1-10% by mass, for example, it can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%, etc., but is not limited to the listed values, and other values ​​not listed within the range are also applicable.

[0055] Among them, the oxidant in the soaking aid is 0.01-1% by mass, for example, it can be 0.01%, 0.02%, 0.04%, 0.06%, 0.08%, 0.1%, 0.2%, 0.4%, 0.6%, 0.8% or 1%, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0056] The base can be a soluble base, such as sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate and other reagents commonly used in the art that can make the solution alkaline. One or a combination of at least two of them can be selected.

[0057] The oxidant may be potassium chlorate, ammonium persulfate, hydrogen peroxide, sodium peroxide or other commonly used oxidants in the art, and any one or a combination of at least two of them may be selected.

[0058] Furthermore, the present embodiment provides a method for preparing the aforementioned nanoemulsion flushing agent for water-based mud, which specifically includes mixing and emulsifying a solvent, a nonionic surfactant, an alcohol, a chelating agent and water according to a formula to obtain an acidic nanoemulsion; then adding an emulsion and polylactic acid powder to the acidic nanoemulsion, and obtaining the nanoemulsion flushing agent for water-based mud by mixing and stirring.

[0059] In the present invention, the water used in the process of preparing the flushing agent can be tap water, deionized water, factory purified return water, etc., which does not affect the function of the flushing agent of the present invention.

[0060] Furthermore, the present embodiment provides a use of the aforementioned water-based mud nanoemulsion flushing agent, specifically comprising: flushing the wellbore with the water-based mud nanoemulsion flushing agent;

[0061] Alternatively, the wellbore is soaked with a soaking aid, and then a nanoemulsion flushing agent of a water-based mud is added for flushing. The end point of the cleaning is when there is no solid phase in the flushing fluid circulation.

[0062] In order to further illustrate the beneficial effects of the nanoemulsion flushing agent for water-based mud provided by the present invention, the following practical implementation examples are provided. The mud used in the implementation process is the high-temperature resistant water-based organosilicon mud actually used in the high-temperature drilling site of Pengshen 6 Well in Penglai Gas Field, Yanting County, Mianyang City, Sichuan Province. All reagents used are commercially available agents.

[0063] Example 1

[0064] This embodiment provides a nanoemulsion flushing agent for water-based mud and a well soaking aid thereof:

[0065] Well soaking aid: weigh 5g sodium carbonate, 0.1g potassium chlorate, and 94g water, stir and dissolve thoroughly to obtain well soaking liquid.

[0066] Nanoemulsion flushing agent for water-based mud: Weigh 26g of xylene, 26g of polyoxyethylene ether (molecular weight 1123.5), 26g of isopropanol, 22g of hydroxyethylidene diphosphonic acid and 50g of water, place them in an emulsifier and stop after sufficient emulsification to finally obtain an acidic nanoemulsion, add 0.7g of sodium polyacrylate (molecular weight 500), 0.5g of -200 mesh polylactic acid powder (molecular weight 120,000) and 30g of sodium chloride, and then mix them with water to make flushing agents with concentrations of 5%, 10%, 15% and 20% respectively.

[0067] During the test, the wellbore was first soaked with a well soaking agent for 1 hour, then cleaned with a nanoemulsion flushing agent of a water-based mud and a well washing test was performed.

[0068] Example 2

[0069] This embodiment provides a nanoemulsion flushing agent for water-based mud and a well soaking aid thereof:

[0070] Well soaking aid: weigh 5g potassium carbonate, 0.1g ammonium persulfate, and 94g water, stir and dissolve thoroughly to obtain the well soaking liquid.

[0071] Nanoemulsion flushing agent for water-based mud: Weigh 10g of toluene, 40g of polyoxyethylene ether (molecular weight 1123.5), 3g of isobutanol, 1g of aminotrimethylene phosphonic acid and 60g of water, place them in an emulsifier and stop after sufficient emulsification to finally obtain an acidic nanoemulsion, then add 0.1g of -200 mesh polylactic acid (molecular weight 140,000), 10g of polyacrylamide (molecular weight 8 million) and 20g of potassium chloride, and then mix with water to make flushing agents with concentrations of 5%, 10%, 15% and 20%.

[0072] During the test, the wellbore was first soaked with a well soaking agent for 1 hour, then cleaned with a nanoemulsion flushing agent of a water-based mud and a well washing test was performed.

[0073] Example 3

[0074] This embodiment provides a nanoemulsion flushing agent for water-based mud and a well soaking aid thereof:

[0075] Well soaking aid: weigh 10g potassium carbonate, 1g ammonium persulfate, and 89g water, stir and dissolve thoroughly to obtain the well soaking liquid.

[0076] Nanoemulsion flushing agent for water-based mud: Weigh 60g of toluene, 10g of polyoxyethylene ether (molecular weight of 1200), 50g of isobutanol, 50g of aminotrimethylene phosphonic acid and 40g of water, place them in an emulsifier and stop after sufficient emulsification, and finally obtain an acidic nanoemulsion, then add 1g of -200 mesh polylactic acid (molecular weight of 150,000), 1g of polyacrylamide (molecular weight of 20 million) and 50g of potassium chloride, and then mix with water to make flushing agents with concentrations of 5%, 10%, 15% and 20%.

[0077] During the test, the wellbore was first soaked with a well soaking agent for 1 hour, then cleaned with a nanoemulsion flushing agent of a water-based mud and a well washing test was performed.

[0078] Example 4

[0079] This embodiment provides a nanoemulsion flushing agent for water-based mud:

[0080] Nanoemulsion flushing agent for water-based mud: Weigh 20g of xylene, 30g of polyoxyethylene ether (molecular weight 1123.5), 30g of propanol, 10g of ethylidene diphosphonic acid and 50g of water, place them in an emulsifier and stop after sufficient emulsification, and finally obtain an acidic nanoemulsion. Then add 2g of sodium polyacrylate (molecular weight 3000), 0.5g of -200 mesh polylactic acid (molecular weight 100,000) and 30g of sodium bromide, and then mix with water to make flushing agents with concentrations of 5%, 10%, 15% and 20%.

[0081] During the test, the nanoemulsion flushing agent of the water-based mud of the present invention is directly injected to perform a well flushing test.

[0082] Example 5

[0083] This embodiment provides a nanoemulsion flushing agent for water-based mud:

[0084] Nanoemulsion flushing agent for water-based mud: Weigh 30g of xylene, 26g of polyoxyethylene ether (molecular weight of 1500), 26g of propanol, 22g of ethylidene diphosphonic acid and 45.5g of water, place them in an emulsifier and stop after sufficient emulsification to finally obtain an acidic nanoemulsion, then add 7g of sodium polyacrylate (molecular weight of 1000), 0.8g of -200 polylactic acid (molecular weight of 130,000) and 35g of sodium bromide, and then mix with water to make flushing agents with concentrations of 5%, 10%, 15% and 20%.

[0085] During the test, the nanoemulsion flushing agent of the water-based mud of the present invention is directly injected to perform a well flushing test.

[0086] Example 6

[0087] This embodiment provides a nanoemulsion flushing agent for water-based mud:

[0088] Nanoemulsion flushing agent for water-based mud: Weigh 25g of xylene, 29g of polyoxyethylene ether (molecular weight of 1500), 35g of propanol, 22g of ethylidene diphosphonic acid and 55.5g of water, place them in an emulsifier and stop after sufficient emulsification to finally obtain an acidic nanoemulsion, then add 4g of sodium polyacrylate (molecular weight of 2000), 0.2g of -200 polylactic acid (molecular weight of 10 million) and 44g of sodium bromide, and then mix with water to make flushing agents with concentrations of 5%, 10%, 15% and 20%.

[0089] During the test, the nanoemulsion flushing agent of the water-based mud of the present invention is directly injected to perform a well flushing test.

[0090] Comparative Example 1

[0091] The only difference from Example 1 is that no polylactic acid is added to the nanoemulsion flushing agent for water-based mud.

[0092] Comparative Example 2

[0093] The only difference from Example 1 is that the polylactic acid in the nanoemulsion flushing agent for water-based mud is replaced by an equal amount of carboxymethyl hydroxyethyl cellulose.

[0094] Comparative Example 3

[0095] The only difference from Example 1 is that the polylactic acid in the nanoemulsion flushing agent for water-based mud is replaced by an equal amount of xanthan gum.

[0096] Comparative Example 4

[0097] The only difference from Example 1 is that the sodium chloride in the nanoemulsion flushing agent for water-based mud is replaced by an equal amount of sodium silicate.

[0098] Comparative Example 5

[0099] The only difference from Example 1 is that no chelating agent is added to the nanoemulsion flushing agent for water-based mud.

[0100] Comparative Example 6

[0101] The only difference from Example 1 is that no sodium polyacrylate is added to the nanoemulsion flushing agent for water-based mud.

[0102] Test Case

[0103] The performance tests were conducted on the well washing fluids finally prepared in Examples 1-6 and Comparative Examples 1-6, including high temperature maintenance experiments, cleaning efficiency evaluation experiments, temperature resistance experiments, and salt resistance experiments.

[0104] I. High temperature curing experiment:

[0105] The specific process is: hot rolling curing of the flushing agent solution is carried out according to the drilling fluid curing method in the national standard GB / T 19139-2012 "Test Methods for Oil Well Cement", and then the next flushing rating experiment is started after curing. The experimental conditions of the high temperature curing experiment are: temperature of 200℃, pressure of 100MPa, and time of 100min; the main experimental instrument is: high temperature roller furnace.

[0106] II. Cleaning efficiency evaluation experiment:

[0107] 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 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 into the well washing fluid, rinse at 300r / min for 5min, and drip for 3min, and weigh the mass of the outer cylinder of the rotational viscometer after washing as W2.

[0108] The flushing rate η was calculated according to formula (1), and three groups of parallel experiments were performed to obtain the average value. The experimental data results are shown in Table 1.

[0109]

[0110] Where: η is the flushing efficiency;

[0111] W is the mass of the outer cylinder of the rotational viscometer, in grams (g);

[0112] W1 is the mass of the outer cylinder of the rotary viscometer after it is filled with drilling fluid, in grams (g);

[0113] W2 is the mass of the outer cylinder of the rotational viscometer after flushing, in grams (g).

[0114] According to the cleaning process of Examples 1-6 and Comparative Examples 1-6, a cleaning efficiency evaluation experiment was carried out using a nanoemulsion flushing agent of a water-based mud with a mass concentration of 15% at a temperature of 200°C. In Examples 1-3, a well soaking aid was first used for soaking and then a water-based mud nanoemulsion flushing agent was used for flushing. Examples 4-6 directly used a water-based mud nanoemulsion flushing agent for flushing. The comparative example had the same process as that of Example 1. The experimental results are shown 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 being stained with drilling fluid; W2 is the mass of the outer cylinder of the rotational viscometer after flushing. The flushing efficiency is calculated according to formula (1).

[0115] Table 1

[0116]

[0117]

[0118] As can be seen from Table 1, the nanoemulsion flushing agent for water-based mud prepared in Example 1 has a flushing efficiency of more than 95% at a temperature of 200°C. By comparing the cleaning efficiency with that in the comparative example, the individual flushing agents have a synergistic effect, and the various agents in the flushing agent have different cleaning effects on different components in the drilling fluid.

[0119] The nanoemulsion flushing agent for water-based mud with a mother liquor mass concentration of 5%, 10%, 15%, and 20% (specifically adjusted by controlling the water content in the emulsion) configured in Example 1 was taken to test the flushing efficiency at a temperature of 200°C, wherein the well was firstly soaked with a well soaking aid and then flushed with the nanoemulsion flushing agent for water-based mud. The experimental results are shown in Table 2. The test method is the same as the test process of the data in Table 1.

[0120] Table 2

[0121]

[0122]

[0123] From Table 2, we can see that adding the nanoemulsion flushing agent for water-based mud of the present invention can significantly improve the cleaning efficiency of the flushing agent under high temperature environment. The mass concentration of 5% can increase the well washing efficiency to 78%, and the mass concentration of more than 10% can reach a flushing efficiency of more than 90%, proving that the flushing agent of the present invention has good flushing efficiency at different addition amounts. When considering practical application, considering the cost, the optimal addition amount should be about 15%, which can not only obtain good flushing efficiency, but also control costs.

[0124] The nanoemulsion flushing agent for water-based mud with a mass concentration of 15% configured in Examples 1-6 and Comparative Examples 1-6 was used for well washing efficiency tests at temperatures of 120°C, 140°C, 160°C, 180°C, and 200°C, respectively. Examples 1-3 first used a well-soaking aid to soak the well and then used a nanoemulsion flushing agent for water-based mud for flushing. Examples 4-6 directly used a nanoemulsion flushing agent for water-based mud for flushing. The comparative example had the same process as Example 1. The test results are detailed in Table 3, and the test method is the same as Table 1.

[0125] Table 3

[0126]

[0127]

[0128] It can be seen from Table 3 that the nanoemulsion flushing agent for water-based mud of the present invention decreases with increasing temperature, but the decrease is not obvious. At 200°C, it still has a well washing efficiency of more than 95%, which fully meets the needs of high-temperature deep well washing operations.

[0129] III. Salt resistance test:

[0130] NaCl was added to the nanoemulsion flushing agent for water-based mud with a mass concentration of 15% prepared in Examples 1-6 and Comparative Examples 1-6 at a temperature of 200°C, and the amounts of NaCl added were 0%, 12%, 18%, and 36%, respectively. Among them, Examples 1-3 first used a well soaking aid to soak the well and then used the nanoemulsion flushing agent for water-based mud for flushing. Examples 4-6 directly used the nanoemulsion flushing agent for water-based mud for flushing. The comparative example had the same process as Example 1. The test results are detailed in Table 4.

[0131] Table 4

[0132]

[0133]

[0134] It can be seen from Table 4 that the salt content does not affect the cleaning efficiency of the nanoemulsion flushing agent for water-based mud of the present invention, indicating that the nanoemulsion flushing agent for water-based mud provided by the present invention has good salt resistance.

[0135] All the well-flushing fluids tested in the above-mentioned indoor tests were subjected to high-temperature curing at 200° C. for 120 minutes, which proves that the nanoemulsion flushing agent for water-based mud provided by the present invention has good high-temperature resistance.

[0136] IV. Anti-filtration test: 500 mL of the nanoemulsion flushing agent for water-based mud with a mass concentration of 15% configured in Examples 1-6 and Comparative Examples 1-6 were respectively placed in a filter loss meter with the temperature set to 200°C, that is, only the nanoemulsion flushing agent for water-based mud in Examples 1-6 and Comparative Examples 1-6 were used for testing. The experimental data are detailed in Table 5.

[0137] Table 5

[0138]

[0139]

[0140] From Table 5, we can see that the leakage in the first 90 minutes of Example 1 only accounts for 6.8% of the total nanoemulsion flushing agent used for water-based mud, and the temporary plugging effect gradually disappears after 90 minutes, while the sample without adding polylactic acid has exceeded 50% of the nanoemulsion flushing agent used for water-based mud in the 120-minute filtration loss. This shows that adding polylactic acid to the flushing agent of the present invention can significantly reduce the leakage of the nanoemulsion flushing agent used for water-based mud, and can restore the permeability of the formation within two hours after the construction is completed, thereby protecting the reservoir and reducing the pollution of the formation by well washing.

[0141] In summary, the nanoemulsion flushing agent for water-based mud provided by the present invention achieves the improvement of the salt and high temperature resistance of the flushing agent by utilizing the synergistic strengthening effect among the components in the flushing agent. At the same time, it can efficiently and quickly clean and displace water-based drilling fluid, has good compatibility with cement slurry, and has broad application prospects in high-temperature and high-salt deep well operations.

[0142] It is stated that the present invention illustrates the detailed structural features of the present invention through the above embodiments, but the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must rely on the above detailed structural features to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of the components selected by the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

[0143] 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, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0144] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0145] In addition, 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 water-based mud, characterized in that: The nanoemulsion flushing agent for water-based mud comprises: acidic nanoemulsion, emulsion, polylactic acid and inorganic salt; The acidic nanoemulsion comprises: a nonionic surfactant, a solvent, an alcohol, a chelating agent and water.

2. The nanoemulsion flushing agent for water-based mud according to claim 1, characterized in that: The nanoemulsion flushing agent for water-based mud comprises, by weight: 20-50 parts of acidic nanoemulsion, 1-10 parts of emulsion, 0.1-1 parts of polylactic acid and 20-50 parts of inorganic salt.

3. The nanoemulsion flushing agent for water-based mud according to claim 1 or 2, characterized in that: The acidic nanoemulsion comprises, by weight: 10-40 parts of a nonionic surfactant, 10-60 parts of a solvent, 1-50 parts of an alcohol, 1-50 parts of a chelating agent and 1-100 parts of water.

4. The nanoemulsion flushing agent for water-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.

5. The nanoemulsion flushing agent for water-based mud according to any one of claims 1 to 4, characterized in that: The inorganic salt is a soluble inorganic salt.

6. The nanoemulsion flushing agent for water-based mud according to any one of claims 1 to 5, characterized in that: The nonionic surfactant in the acidic nanoemulsion includes polyoxyethylene ether; Preferably, the solvent in the acidic nanoemulsion includes one or a combination of at least two of xylene, toluene or acetone; Preferably, the alcohol in the acidic nanoemulsion comprises one or a combination of at least two of isopropanol, n-propanol or n-butanol.

7. The nanoemulsion flushing agent for water-based mud according to any one of claims 1 to 6, characterized in that: The nanoemulsion flushing agent for water-based mud also includes a soaking aid.

8. The nanoemulsion flushing agent for water-based mud according to claim 7, characterized in that: The soaking aid comprises 1-10% of alkali and 0.01-1% of oxidant in terms of mass percentage, and the balance is water.

9. The nanoemulsion flushing agent for water-based mud according to claim 7 or 8, characterized in that: The alkali used in the soaking aid is a soluble alkali; Preferably, the oxidant used in the soaking aid includes one or a combination of at least two of potassium chlorate, ammonium persulfate, hydrogen peroxide or sodium peroxide.

10. A use of the nanoemulsion flushing agent for water-based mud according to any one of claims 1 to 9, characterized in that: The application includes: using a nano-emulsion flushing agent of water-based mud to flush the wellbore.

Images