CN115584256B

CN115584256B - High-temperature-resistant high-salt cleanup additive for acidizing and fracturing and preparation method thereof

Info

Publication number: CN115584256B
Application number: CN202211593722.3A
Authority: CN
Inventors: 罗斌; 曹学军; 李晖; 陈科; 张朝举; 唐祖兵; 颜磊; 王明贵; 张明江; 牛会娟
Original assignee: Sinopec Southwest Petroleum Engineering Co ltd; Sinopec Southwest Petroleum Engineering Co Ltd Downhole Operation Branch
Current assignee: Sinopec Southwest Petroleum Engineering Co ltd; Sinopec Southwest Petroleum Engineering Co Ltd Downhole Operation Branch
Priority date: 2022-12-13
Filing date: 2022-12-13
Publication date: 2023-04-18
Anticipated expiration: 2042-12-13
Also published as: CN115584256A

Abstract

The invention discloses a high-temperature-resistant high-salt cleanup additive for acidizing and fracturing and a preparation method thereof, and belongs to the technical field of oilfield chemistry. The cleanup additive comprises, by weight, 12-23 parts of fatty acid methyl ester polyoxyethylene ether, 5-9 parts of castor oil polyoxyethylene ether, 4-9 parts of an anionic surfactant, 0.1-1.5 parts of an inorganic salt, 5-13 parts of a cosolvent, 25-35 parts of an oil phase and water, wherein the weight ratio of the oil phase to the water is 1.1-1.5. The invention has lower surface tension and interfacial tension, and can improve the wettability of the core, so that the water contact angle of the core is closer to 90 degrees, the water lock effect of a contact reservoir is more favorable, and the flowback rate of fracturing fluid is increased; the oil-water well drilling fluid also has good temperature resistance and salt tolerance, can resist the temperature of more than 120 ℃, can resist 80000mg/L salt, and can be suitable for high-temperature and high-salinity oil reservoirs; meanwhile, the compound has higher discharge assisting rate and better storage stability.

Description

High-temperature-resistant high-salt cleanup additive for acidizing and fracturing and preparation method thereof

Technical Field

The invention relates to the technical field of oilfield chemistry, in particular to a high-temperature-resistant high-salt cleanup additive for acidizing and fracturing and a preparation method thereof.

Background

With the gradual development of oil and gas fields at home and abroad, the exploitation target has gradually shifted to low-permeability and ultra-low permeability oil and gas reservoirs. For low-permeability and ultra-low permeability oil and gas reservoirs, fracturing modification technology of the reservoir is an important production increasing measure. After fracturing a reservoir, the fractured liquid phase usually needs to be quickly drained back to the ground by means of the fracturing fluid and the pressure of the reservoir, but in most cases, the drainage rate of the fracturing fluid is low due to the retention effect of capillary force. The fracturing fluid retained in the stratum can cause serious water lock damage to the reservoir, so that the yield of oil gas is reduced, and therefore, a cleanup additive for promoting the flowback of the fracturing fluid needs to be added into the fracturing fluid to increase the flowback rate of the fracturing fluid and reduce the retention amount of the fracturing fluid, so that the damage of fracturing to the reservoir is reduced, and the productivity is increased.

In the prior art, a plurality of surfactants are usually combined to prepare a cleanup additive, for example, chinese patent CN111519036A discloses a cleanup additive for fracturing fluid and a preparation method thereof, wherein an amide type nonionic surfactant, a polyoxyethylene type nonionic surfactant, an emulsifier, a fluorocarbon surfactant, low molecular alcohol and the like are adopted to prepare the cleanup additive, and the cleanup additive has lower interfacial tension and better compatibility and can be used for cleanup of the fracturing fluid; chinese patent CN106281287A discloses an environmentally friendly fluorine-free cleanup additive and a preparation method thereof, wherein the cleanup additive is prepared by arranging an anionic surfactant, a nonionic surfactant, a cationic surfactant and a solvent, and has a low interfacial tension and a small amount. However, in the above patent documents, only the interfacial tension is used as an index of the drainage performance, but the drainage performance of the drainage aid is not only related to the interfacial tension but also to the core wettability after the addition of the drainage aid, and these drainage aids do not have the temperature resistance and salt tolerance and are difficult to be applied to a high-temperature and high-salt reservoir (a reservoir having a temperature of more than 80 ℃ and a salt content of more than 20000 mg/L).

Disclosure of Invention

In view of the above technical problems, an object of the present invention is to provide a high temperature and high salt resistant cleanup additive for acid fracturing, which has lower surface tension and interfacial tension, and can improve wettability of a reservoir, so that a water contact angle of the reservoir is closer to 90 °, and a water lock effect of the reservoir can be effectively removed, so that the cleanup additive has better cleanup performance, and meanwhile, the cleanup additive can be applied to a high temperature and high salt reservoir, and has a wider application range.

The invention adopts the following technical scheme that:

a high-temperature-resistant high-salt cleanup additive for acidizing and fracturing comprises the following components in parts by weight: 12-23 parts of fatty acid methyl ester polyoxyethylene ether, 5-9 parts of castor oil polyoxyethylene ether, 4-9 parts of an anionic surfactant, 0.1-1.5 parts of an inorganic salt, 5-13 parts of a cosolvent, 25-35 parts of an oil phase and water, wherein the weight ratio of the oil phase to the water is 1.1-1.5.

In the fatty acid methyl ester polyoxyethylene ether, the carbon chain length of fatty acid methyl ester is 10-20, and the polymerization degree of polyoxyethylene is 6-10.

The castor oil polyoxyethylene ether is EL-20.

The anionic surfactant is one or more of alkyl sulfonate and alkyl sulfate.

The inorganic salt is one or more of sodium nitrate and potassium nitrate, and the cosolvent is a small molecular alcohol.

The oil phase is one or more of mineral oil or vegetable oil.

The oil phase is one or more of white oil, diesel oil and limonene.

The invention also aims to provide a preparation method of the high-temperature-resistant high-salt cleanup additive for acid fracturing, which comprises the following steps: mixing fatty acid methyl ester polyoxyethylene ether, castor oil polyoxyethylene ether, anionic surfactant, inorganic salt, cosolvent, oil phase and water, stirring at a rotating speed of 500-1000 r/min for at least 2min, and stirring at a rotating speed of 100-200 r/min for 10min to obtain the product.

In one embodiment of the present invention, the stirring is performed at 40 to 60 ℃.

The invention also aims to provide a preparation method of the high-temperature-resistant high-salt cleanup additive for acid fracturing, which comprises the following steps: adding fatty acid methyl ester polyoxyethylene ether, castor oil polyoxyethylene ether, anionic surfactant, inorganic salt and cosolvent into water, dropwise adding the oil phase into the water solution at the rotating speed of 100-200 r/min, and stirring for at least 10min after dropwise adding.

In one embodiment of the present invention, the stirring operation is performed at a rotation speed of 40 to 60 ℃.

The beneficial technical effects of the invention are as follows: the high-temperature-resistant high-salt cleanup additive for acidizing and fracturing and the preparation method thereof have lower surface tension and interface tension, and can improve the wettability of the core, so that the water contact angle of the core approaches to 90 degrees, the water lock effect of a reservoir is relieved, and the flowback rate of fracturing fluid is increased; meanwhile, the high-temperature-resistant and high-salt-resistant cleanup additive for acid fracturing and the preparation method thereof have good temperature resistance and salt tolerance, the temperature resistance of the cleanup additive can reach more than 120 ℃, and the cleanup additive can resist 80000mg/L of salt and is suitable for high-temperature and high-salt oil reservoirs; it has higher discharge aiding rate and better storage stability; meanwhile, compared with gemini surfactants commonly used in the prior art, the raw materials adopted in the invention have lower cost and wider source range, and are more environment-friendly compared with fluorocarbon surfactants.

Detailed Description

The technical solutions of the present invention will be described in detail below in order to clearly understand the technical features, objects, and advantages of the present invention, but the present invention is not limited to the practical scope of the present invention.

The weight ratio of oil phase to water is preferably 1.1 to 1.5, and if there is more oil phase, water-in-oil emulsion is easily formed, and if there is more water, the emulsion concentration is insufficient.

In the invention, three surfactants are used as main agents of the whole cleanup additive, and the three surfactants can generate synergistic action under certain conditions, so that the prepared cleanup additive has more excellent properties.

Wherein, the structural formula of the fatty acid methyl ester polyoxyethylene ether is shown as follows. Compared with the rest of conventional nonionic surfactants, the surfactant has a cloud point generally greater than 98 ℃, and has better temperature resistance. Meanwhile, the fatty acid methyl ester polyoxyethylene ether has better environmental protection performance and is easy to decompose under certain conditions. Meanwhile, the surfactant is used as the surfactant with the highest addition amount, the addition amount of other surfactants can be reduced, the environmental protection performance of the whole cleanup additive is improved, and the fatty acid methyl ester polyoxyethylene ether also has the advantage of lower cost.

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Wherein R is an initial carbon chain, and n is the polymerization degree of ethylene oxide.

For fatty acid methyl ester polyoxyethylene ether, the carbon chain length and the polymerization degree of the ethylene oxide have great influence on the comprehensive performance of the fatty acid methyl ester polyoxyethylene ether, and generally, the fatty acid methyl ester polyoxyethylene ether commonly used in the market at present can be applied to the invention. However, in view of the effect, cost and ease of use, the starting carbon chain R is a saturated or unsaturated hydrocarbon group having a carbon chain length of 10 to 20, and n is usually 6 to 10. In a preferred embodiment, R can be a linear saturated hydrocarbyl group having a carbon chain length of 13, a linear unsaturated hydrocarbyl group having a carbon chain length of 15 (i.e., the corresponding R group in the fatty acid methyl ester polyoxyethylene ether made from methyl palmitoleate), a linear saturated hydrocarbyl group having a carbon chain length of 18; n is 7 to 9.

As for the castor oil polyoxyethylene ether, the inventor finds that when the fatty acid methyl ester polyoxyethylene ether is compounded and used under certain conditions, the acid resistance and the salt resistance of the whole system can be improved, and meanwhile, the contact angle is also improved to a certain extent. In the invention, the adopted castor oil polyoxyethylene ether is EL-20, and the castor oil polyoxyethylene ether with the polymerization degree and the fatty acid methyl ester polyoxyethylene ether can achieve better technical effect after being compounded.

The anionic surfactant adopted in the invention has strong temperature resistance and salt tolerance, and after the anionic surfactant is compounded with fatty acid methyl ester polyoxyethylene ether and castor oil polyoxyethylene ether, the temperature resistance and salt tolerance of the system are improved to a certain extent, and the core contact angle of the anionic surfactant can be greatly improved. In the present invention, conventional anionic surfactants such as carboxylic acid-based anionic surfactants, sulfuric acid-based anionic surfactants, and sulfonic acid-based surfactants can achieve the object, but one or more of alkylsulfonic acid salts and alkylsulfuric acid salts are preferred, and one of sodium dodecylsulfate and sodium dodecylsulfate is particularly preferred.

In the invention, a small amount of inorganic salt is added into the whole system, because the small amount of inorganic salt can increase the stability of the microemulsion to a certain extent and prolong the storage time of the whole microemulsion system. In general, these inorganic salts may be salts of any soluble monovalent metal ions, but sodium nitrate and potassium nitrate are preferable in terms of cost and influence on pipelines.

The cosolvent adopted in the invention is a cosolvent which needs to be added in the conventional cleanup additive, and specifically is a small molecular alcohol, such as ethanol, isopropanol and the like.

In the invention, the oil phase is used for generating microemulsion, and the oil phase is preferably one or more of white oil, diesel oil and limonene, and more preferably a combination of white oil and limonene in a mass ratio of 1.

The first method is to mix all the raw materials and stir at a rotating speed of 500-1000 r/min for at least 2min, for example, the rotating speed can be 500r/min, 1000r/min and 800r/min, and the mixture is stirred at a rotating speed of 100-200 r/min for 10min, for example, the rotating speed can be 100r/min, 200r/min and 150r/min. The second method comprises adding all the raw materials except oil phase into water, adding oil phase into the water solution at 100-200 r/min (such as 100r/min, 200r/min, 150 r/min), and stirring for at least 10 min. Meanwhile, when stirring, if the temperature is raised to 40-60 ℃, the microemulsion is more favorably formed.

The two preparation methods described above have different advantages: the first method requires less time for the whole preparation process, and since all the materials are mixed together, the operation is relatively simple and the requirement on the production equipment is lower. For the second method, since it needs to drop the oil phase into the aqueous solution, it takes a long time, and at the same time, it needs to add corresponding dropping equipment, such as head tank, valve, flowmeter, etc., so that the production cost is relatively high, but the particle size distribution of the finally prepared microemulsion is narrower, the whole product is more uniform, and the requirement for the stirrer is lower.

The skilled person can choose any of the above methods to produce the cleanup additive according to the present invention according to actual needs.

In the following examples, methyl palmitoleate polyoxyethylene ether-8 indicates that the polymerization degree of polyoxyethylene ether in methyl palmitoleate polyoxyethylene ether is 8, and this specification applies to the remaining polyoxyethylene ether polymer.

In the following examples, all the raw materials were commercial products and were commercially available unless otherwise specified.

Example 1

Taking 20g of methyl palmitoleate polyoxyethylene ether-8, 7g of castor oil polyoxyethylene ether EL-20 (the polymerization degree of polyoxyethylene is 20), 8g of sodium dodecyl sulfate, 0.2g of potassium nitrate and 10g of ethanol, adding the mixture into 40g of water, continuously stirring to uniformly mix the mixture, adjusting the rotating speed of a stirrer to 200r/min, dropwise adding a mixture of 30g of white oil and limonene with the mass ratio of 1.

Example 2

And (2) adding 20g of methyl palmitoleate polyoxyethylene ether-8, 7g of castor oil polyoxyethylene ether EL-20, 8g of sodium dodecyl sulfate, 0.2g of potassium nitrate, 10g of ethanol, 30g of a mixture of white oil and limonene with the mass ratio of 1.

Example 3

The difference between the embodiment and the embodiment 1 is that the used fatty acid methyl ester polyoxyethylene ether is replaced by tridecyl acid methyl ester polyoxyethylene ether-8, the potassium nitrate is replaced by sodium nitrate, and the rest are the same, so that the cleanup additive Z3 is finally prepared.

Example 4

The difference between this example and example 1 is that sodium dodecyl sulfate used was replaced by sodium dodecyl sulfate, and the rest were the same, and the cleanup additive Z4 was finally prepared.

Example 5

The difference between this example and example 1 is that the mixture of white oil and limonene of 1 is changed to diesel oil, and the rest is the same, and the cleanup additive Z5 is finally prepared.

Example 6

The difference between the embodiment and the embodiment 1 is that 12g of methyl palmitoleate polyoxyethylene ether-8, 9g of castor oil polyoxyethylene ether EL-20, 5g of sodium lauryl sulfate and the balance of the same are adopted, and the cleanup additive Z6 is finally prepared.

Example 7

The difference between this example and example 1 is that 1.5g of potassium nitrate, 35g of a mixture of white oil and limonene in a mass ratio of 1, and 38.5g of water were used, and the rest were the same, thereby finally obtaining a cleanup additive Z7.

Example 8

The difference between this example and example 1 is that the castor oil polyoxyethylene ether used is castor oil polyoxyethylene ether EL-10 (the degree of polymerization of polyoxyethylene is 10), and the rest is the same, and the cleanup additive Z8 is finally prepared.

Example 9

The difference between the sample and the sample 1 is that 23g of methyl palmitoleate polyoxyethylene ether-8, 6g of castor oil polyoxyethylene ether EL-20, 4g of sodium dodecyl sulfate and 13g of ethanol are added, and the rest are the same, so that the cleanup additive Z9 is finally prepared.

Example 10

The difference between this example and example 1 is that the amount of ethanol added is 7g, the amount of water is 40g, the oil phase is white oil and the amount of the white oil added is 34g, and the rest is the same, and the cleanup additive Z10 is finally prepared.

Example 11

In the embodiment, 15g of methyl palmitoleate polyoxyethylene ether-8, 5g of castor oil polyoxyethylene ether EL-20, 9g of sodium dodecyl sulfate, 1.0g of potassium nitrate and 5g of ethanol are taken, added into 37.5g of water, continuously stirred to be uniformly mixed, the rotating speed of a stirrer is adjusted to 200r/min, 25g of a mixture of white oil and diesel oil with the mass ratio of 1 is dropwise added into the mixed solution, and after the dropwise addition is finished, the mixture is continuously stirred at room temperature for 15min to obtain the cleanup additive Z11.

Comparative example 1

The comparative example is different from example 2 in that the rotation speed of the stirrer is kept at 200r/min, and the rest is the same, and finally the cleanup additive D1 is prepared.

Comparative example 2

This comparative example was different from example 1 in that sodium lauryl sulfate was not contained and the rest was the same, and a cleanup additive D2 was finally obtained.

Comparative example 3

The comparative example differs from example 1 in that no castor oil polyoxyethylene ether EL-20 was included, the oil was included, and the remainder was the same, and a cleanup additive D3 was finally obtained.

Comparative example 4

The difference between the comparative example and the example 1 is that the cleanup additive D4 is finally prepared by adjusting the amount of methyl palmitoleate polyoxyethylene ether-8 to 8g, the amount of castor oil polyoxyethylene ether EL-20 to 20g, and the rest are the same.

To further illustrate the technical effect of the high temperature and high salt resistant cleanup additive for acid fracturing in the above examples, the performance thereof was tested.

1. Surface tension, interfacial tension and contact angle

The high-temperature-resistant and high-salt cleanup additive for acidizing and fracturing obtained in examples 1 to 11 and the cleanup additive prepared in comparative examples 1 to 4 were prepared into an aqueous solution with a mass concentration of 0.3%, and the surface tension and the interfacial tension were measured according to the method in "evaluation method of cleanup additive performance for acidizing and fracturing SYT 5755-2016". Wherein the measurement temperature is 25 ℃, the interfacial tension is the interfacial tension with kerosene, the contact angle of the cleanup additive on a mica sheet is also tested, and the contact angle of distilled water on the mica sheet is 27 degrees. The final measurement results are shown in table 1.

TABLE 1 surface tension, interfacial tension and contact Angle measurements

Sample(s)	Surface tension mN/m	Interfacial tension mN/m	Contact angle °
				Z1	17.4	0.0038	87
Z2	19.3	0.0043	86
				Z3	18.5	0.0042	84
Z4	19.1	0.0037	85
				Z5	17.8	0.0038	85
Z6	18.5	0.0040	85
				Z7	17.8	0.0046	84
Z8	22.4	0.049	73
				Z9	21.3	0.0083	79
Z10	20.8	0.0065	80
				Z11	21.4	0.0056	81
D1	30.7	0.052	48
				D2	22.9	0.051	43
D3	24.9	0.078	67
				D4	28.6	0.14	59

As can be seen from table 1, the high temperature and high salt resistant cleanup additives for acid fracturing prepared in examples 1 to 11 have a surface tension in the range of 17 to 22.4mN/m and an interfacial tension of less than 0.05mN/m even when they are prepared as aqueous solutions having a mass concentration of 0.3%; meanwhile, the contact angle of the rock-wetting agent can reach 87 degrees at most, which shows that the rock-wetting agent can effectively improve the wettability of the rock. The above data demonstrate that the high temperature and high salt resistant cleanup additive for acid fracturing of examples 1-11 can effectively release the formation water lock and promote the flowback of the fracturing fluid.

Comparing the result of example 2 with the result of comparative example 1, it is demonstrated that the stirring speed has a great influence on the preparation of the high temperature and high salt resistant cleanup additive for acid fracturing.

Comparing the results of example 1 with those of comparative example 2, it is demonstrated that sodium dodecyl sulfate has a greater contribution to improving the contact angle of the high temperature and high salt resistant cleanup additive for acid fracturing.

Comparing the results of example 1 with those of comparative example 3, it is shown that castor oil polyoxyethylene ether EL-20 helps to improve the contact angle of the high temperature and high salt resistant cleanup additive for acid fracturing, and also helps to improve the interfacial tension of the high temperature and high salt resistant cleanup additive for acid fracturing.

The results of example 1 and comparative example 4 were compared to illustrate that the amounts added between the components have a greater effect on the performance of the cleanup additive.

The high-temperature-resistant high-salt cleanup additive for acid fracturing of examples 1 to 11 was placed in a polytetrafluoroethylene reaction kettle, and the thermal stability test was performed according to the method of "evaluation method of cleanup additive for acid fracturing of SYT 5755-2016", the test temperature was 120 ℃, and the final test results are shown in Table 2.

TABLE 2 surface tension and interfacial tension after aging

Sample (I)	Surface tension mN/m	Interfacial tension mN/m
			Z1	21.5	0.0075
Z2	22.7	0.0083
			Z3	22.9	0.0091
Z4	23.2	0.0077
			Z5	21.9	0.0080
Z6	22.4	0.0083
			Z7	23.5	0.0098
Z8	25.8	0.094
			Z9	25.3	0.018
Z10	24.8	0.014
			Z11	26.3	0.013

As can be seen from Table 2, even after aging the high temperature and high salt resistant cleanup additive for acid fracturing at 120 ℃ for 24h, the cleanup additive still has lower surface tension and interfacial tension, indicating that the cleanup additive has better thermal stability.

80000mg/L of sodium chloride water solution is used as preparation water, the high-temperature-resistant high-salt cleanup additive for acid fracturing in the embodiments 1-11 is prepared into a solution with the concentration of 0.3%, the surface tension and the interfacial tension of the solution are measured, a certain crude oil in a Bohai oilfield is added when the interfacial tension is measured, and the final test result is shown in Table 3.

Table 3 results of salt tolerance test

Sample (I)	Surface tension mN/m	Interfacial tension mN/m
			Z1	25.3	0.014
Z2	26.8	0.018
			Z3	26.2	0.016
Z4	25.7	0.017
			Z5	25.9	0.016
Z6	26.9	0.023
			Z7	26.5	0.029
Z8	28.6	0.175
			Z9	27.4	0.143
Z10	27.2	0.127
			Z11	26.9	0.106

As can be seen from table 3, the high temperature and high salt resistant cleanup additive for acid fracturing of examples 1 to 11 has good salt resistance.

2. Particle size test

The high-temperature-resistant high-salt cleanup additive for acid fracturing obtained in examples 1 to 11 and the cleanup additive obtained in comparative example 1 were measured by a laser particle sizer, and the final measurement results are shown in table 4.

TABLE 4 particle size testing

Sample(s)

Z1

Z2

Z3

Z4

Z5

Z6

Particle size nm

30～70

20～150

25～70

30～70

30～80

Sample(s)

Z7

Z8

Z9

Z10

Z11

D1

Particle size nm

25～80

30～70

25~75

25~80

25~110

80~1200

From table 4, it can be seen that the final particle size distribution range of the microemulsion prepared by dropping the oil phase is smaller, while the particle size distribution range of the microemulsion prepared by the one-pot method is wider, but still belongs to the nanometer level. For comparative example 1, the minimum dimension is 80nm, and the maximum particle size can reach micron level, which shows that the stirring speed has an important influence on the preparation of the cleanup additive.

3. Drainage aid rate

The flowback rates of the high-temperature-resistant high-salt discharge assistant for acid fracturing obtained in examples 1 to 11 and the discharge assistants in comparative examples 1 to 4 were measured according to the device and method of 6.8.1 in "evaluation method of performance of discharge assistant for fracture acidizing by SYT 5755-2016", and each discharge assistant was prepared as an aqueous solution of 0.3% by weight during measurement, and the final test results are shown in table 5.

TABLE 5 test results of drainage aid rate

Sample (I)	The discharge aiding rate%
		Z1	46.2
Z2	44.1
		Z3	45.9
Z4	42.7
		Z5	43.6
Z6	41.8
		Z7	41.9
Z8	38.7
		Z9	40.3
Z10	41.9
		Z11	40.7
D1	23.2
		D2	34.4
D3	30.7
		D4	29.5

As can be seen from table 5, the high temperature and high salt resistant cleanup additive for acid fracturing in examples 1 to 11 has a high cleanup rate up to 46% or more; meanwhile, the results of comparative example 1, comparative example 2, comparative example 3 and comparative example 4 are respectively compared with the result of example 1, which shows that the rotation speed of the stirrer, the anionic surfactant, the castor oil polyoxyethylene ether and the proportion of each component have great influence on the performance of the high-temperature-resistant high-salt cleanup additive for acid fracturing.

4. Stability test

The high-temperature and high-salt resistant cleanup additive for acid fracturing in example 1 is stored at 30 ℃, sampled and analyzed every 20 days, and when the ratio of any index of surface tension, interfacial tension and particle size to the initial value is greater than 1.1, the storage time is the stable storage time, and the final test result is: when the storage time was 260 days, the interfacial tension was 0.042mN/m. The high-temperature and high-salt resistant cleanup additive for acid fracturing in example 1 can be stored stably for 260 days at least and has very stable performance.

In the prior art, the stability of the emulsion is measured, and whether the emulsion is layered or not is taken as a basis for the stability of the emulsion, but the inventor finds that the basis is unreasonable: before the microemulsion is layered, the performance of the whole microemulsion system is rapidly reduced, and after the system is layered, the performance of the system, particularly the reduction range of individual indexes reaches over 50 percent, so the judgment is based on the fact that the change of the performance is not considered.

In conclusion, the high-temperature-resistant high-salt cleanup additive for acid fracturing prepared in the embodiments 1 to 11 has lower surface tension and interface tension, can adjust the contact angle to be more than 87 degrees at the highest, can effectively remove the water lock of the reservoir, promotes the flowback of the fracturing fluid, and minimizes the damage of the fracturing fluid to the reservoir; meanwhile, the high-temperature resistant high-salinity stratum material has better temperature resistance and salt tolerance, can resist the temperature of 120 ℃, and can resist 80000mg/L salt, which indicates that the high-temperature resistant high-salinity stratum material can be used for a high-temperature high-salinity stratum; the compound fertilizer also has high discharge aiding rate which can reach more than 46% at most and has good storage stability.

5. Environment-friendly test

The degradability of the polymer can be expressed by biochemical property (BOD 5/CODcr), the high-temperature-resistant high-salt cleanup additive for acid fracturing in example 1 and example 6 is demulsified by a demulsifier, the BOD5 of the polymer is measured by an inoculation and dilution method according to standard HJ/T505-2009, the CODcr is measured by a potassium dichromate method according to standard YJ/T377-2007, the ratio of the high-temperature-resistant high-salt cleanup additive for acid fracturing in example 1 is measured to be 0.42, and the ratio of the high-temperature-resistant high-salt cleanup additive for acid fracturing in example 6 is measured to be 0.40, which indicates that the polymer is easy to degrade.

While the invention has been described with reference to specific preferred embodiments, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. The high-temperature-resistant high-salt cleanup additive for acidizing and fracturing is characterized by comprising the following components in parts by weight: 12-23 parts of fatty acid methyl ester polyoxyethylene ether, 5-9 parts of castor oil polyoxyethylene ether, 4-9 parts of an anionic surfactant, 0.1-1.5 parts of an inorganic salt, 5-13 parts of a cosolvent, 25-35 parts of an oil phase and water, wherein the weight ratio of the oil phase to the water is 1.1-1.5; the fatty acid methyl ester polyoxyethylene ether is methyl palmitoleate polyoxyethylene ether-8 or tridecyl acid methyl ester polyoxyethylene ether-8, the castor oil polyoxyethylene ether is castor oil polyoxyethylene ether EL-20 or castor oil polyoxyethylene ether EL-10, and the anionic surfactant is sodium dodecyl sulfate or sodium dodecyl sulfate.

2. The high-temperature-resistant high-salt cleanup additive for acid fracturing as claimed in claim 1, wherein the inorganic salt is one or more of sodium nitrate and potassium nitrate, and the cosolvent is a small-molecule alcohol.

3. The high-temperature-resistant high-salt cleanup additive for acid fracturing as recited in claim 1, wherein the oil phase is one or more of mineral oil and vegetable oil.

4. The high-temperature-resistant high-salt cleanup additive for acid fracturing as recited in claim 3, wherein the oil phase is one or more of white oil, diesel oil, and limonene.

5. The preparation method of the high-temperature and high-salt resistant cleanup additive for acid fracturing as claimed in any one of claims 1 to 4, comprising the steps of: mixing fatty acid methyl ester polyoxyethylene ether, castor oil polyoxyethylene ether, an anionic surfactant, inorganic salt, a cosolvent, an oil phase and water, stirring at a rotating speed of 500-1000 r/min for at least 2min, and stirring at a rotating speed of 100-200 r/min for 10min to obtain the castor oil polyoxyethylene ether-modified castor oil; or adding fatty acid methyl ester polyoxyethylene ether, castor oil polyoxyethylene ether, anionic surfactant, inorganic salt and cosolvent into water, dripping the oil phase into the water solution at the rotating speed of 100-200 r/min, and stirring for at least 10min after dripping.