CN114920899A

CN114920899A - Efficient thickening liquid carbon dioxide thickener and preparation method thereof

Info

Publication number: CN114920899A
Application number: CN202210631690.5A
Authority: CN
Inventors: 袁彦峰; 逯瑞晓; 王甜; 刘小江; 田兵兵; 付亨; 加永飞
Original assignee: Yanan Shuang Feng Group Co ltd
Current assignee: Yanan Shuang Feng Group Co ltd
Priority date: 2022-06-06
Filing date: 2022-06-06
Publication date: 2022-08-19

Abstract

The invention relates to a thickening agent, in particular to a liquid carbon dioxide thickening agent with high-efficiency thickening property and a preparation method thereof. The method comprises the following steps: synthesizing small molecular cyclic siloxane into poly cyclic siloxane through polymerization, adding perfluoro caprylic ethyl carbamate tert-butyl ester into a mixed solution of poly cyclic siloxane and difluoroacetic acid, reacting for 3-6h at normal temperature, adding an alkaline solution into the solution for neutralization, extracting the mixed solution for 4-6 times by using trichloromethane, drying, removing a filtering solvent, adding toluene diisocyanate into the product, and reacting at room temperature to obtain a crude product. The obtained crude product is washed for a plurality of times by using a mixed solvent of ethyl acetate and benzene, dried and filtered, and finally the product is obtained. The thickening agent prepared by the method has high synthesis yield, and meanwhile, the polycyclosiloxane has an excellent three-dimensional network structure and excellent high-temperature resistance, and the prepared thickening agent also has high-temperature resistance.

Description

Efficient viscosity-increasing liquid carbon dioxide thickener and preparation method thereof

Technical Field

The invention relates to a thickening agent, in particular to a liquid carbon dioxide thickening agent with high-efficiency thickening property and a preparation method thereof.

Background

Unconventional oil and gas resources refer to hydrocarbon resources different from conventional oil and gas resources such as reservoir formation mechanism, storage state, distribution rule, exploration and development method and the like, and mainly comprise compact oil, shale oil, compact gas, shale gas, coal bed gas and the like, while the total amount of the unconventional oil and gas resources in China is about 2 times of that of the conventional oil and gas resources. Most unconventional oil and gas reservoirs are low-porosity and low-permeability, have strong heterogeneity and poor physical properties, and can show strong water sensitivity, so that the most effective method for developing unconventional oil and gas resources is fracturing transformation at present. And the conventional fracturing fluid is used to possibly cause a water locking phenomenon and a water sensitivity phenomenon of a reservoir, so that the reservoir is damaged. The anhydrous unconventional fracturing fluid has the characteristics of small damage to a reservoir stratum, good flowback performance, high compatibility with the reservoir stratum, good temperature resistance and shear resistance and the like. Therefore, it is extremely important to develop a fracturing fluid system suitable for fracturing and increasing the production of unconventional oil and gas resources.

In recent years, liquid or supercritical CO ₂ As a new fracturing medium, it has become the focus of current world research. Experiments have shown that liquid or supercritical CO is used ₂ Fracturing stimulation operations on unconventional hydrocarbon reservoirs are an effective and feasible approach. However, liquid or supercritical CO ₂ Lower viscosity, resulting in CO ₂ The effect is not good whether the method is used for carrying sand or used for oil displacement. However, its viscosity is a very important parameter for fracturing fluids when CO is present ₂ In the supercritical state, the viscosity is only 10 ^-2 mPa.S. When CO is present ₂ When the fracturing fluid is used for field construction, the CO is in a liquid state ₂ Has a low viscosityThe problems of poor sand carrying capacity, large filtration loss of the carbon dioxide fracturing fluid and the like are caused, and the development of the carbon dioxide fracturing fluid towards the direction of improving the recovery ratio is seriously influenced. Thus, for existing liquid CO ₂ The defects of low viscosity, poor sand carrying capacity, poor oil displacement effect and the like are overcome, and the finding of a liquid carbon dioxide thickening agent with high-efficiency thickening property and a preparation method thereof are very important.

According to the invention, micromolecular cyclosiloxane is synthesized into poly-cyclosiloxane through polymerization reaction, the synthesized polyepoxysilane has an excellent three-dimensional network structure, and then the polyepoxysilane is further prepared into the thickening agent. The prepared thickening agent achieves excellent thickening effect on the premise of small using amount, and the sand carrying capacity of liquid carbon dioxide is enhanced. Meanwhile, after the polyepoxy silane and the catalyst are mixed, the prepared thickening agent has excellent high temperature resistance and salt resistance.

Disclosure of Invention

Aiming at the defects of the prior art, the invention aims to prepare the high-efficiency thickening liquid carbon dioxide thickener which has the characteristics of high viscosity, strong sand carrying capacity, good dissolving effect and the like.

The first aspect of the invention provides a high-efficiency thickening liquid carbon dioxide thickener, and the preparation method comprises the following steps:

the preparation method comprises the steps of loading 6mL of difluoroacetic acid and 12mL of polycyclic siloxane into a three-neck flask with a condenser tube, weighing 1.2g of perfluorooctanoic acid ethyl carbamate tert-butyl ester, adding the perfluorooctanoic acid ethyl carbamate tert-butyl ester into a mixed solution of trifluoroacetic acid and dichloromethane, reacting at normal temperature for 3-6 hours, neutralizing by adding an alkaline solution into the solution, extracting the mixed solution with trichloromethane for 4-6 times, drying, removing a filtering solvent, finally adding toluene diisocyanate into a product, and reacting at room temperature to obtain a crude product. The obtained crude product is washed for a plurality of times by using a mixed solvent of ethyl acetate and benzene, and is dried and filtered to finally obtain the product.

Wherein the polycyclic siloxane is synthesized by small molecule cyclic siloxane through polymerization reaction.

The catalyst solution is toluene diisocyanate.

The second aspect of the invention provides a preparation method of the thickening agent, which comprises the following steps:

mixing polyepoxy silane, perfluoro ethyl caprylate tert-butyl carbamate and a catalyst according to a certain mass, and reacting the components in a liquid carbon dioxide medium, wherein the reaction conditions comprise that: the reaction time is 2-10h at room temperature.

Wherein the weight of the polyepoxy silane, the perfluoro caprylic acid ethyl ester carbamic acid tert-butyl ester and the catalyst is 0.6-2.4g, 2-12mL and 4-18mL,

preferably: the weight of the polyepoxy silane, the perfluoro caprylic acid ethyl carbamate and the catalyst is 1.2g, 6mL and 12 mL.

Preferably: the reaction temperature is room temperature, and the reaction time is 3-6 h.

Preferably: after the reaction is finished, washing the mixture for a plurality of times by using a mixed solvent of ethyl acetate and benzene, and filtering.

Compared with the prior art, the invention has the following beneficial effects:

1. the thickener main body prepared by the invention has an excellent three-dimensional network structure, so that the thickener has better high temperature resistance.

2. The thickening agent prepared by the invention has the characteristics of high viscosity, strong sand carrying capacity, good dissolving effect, crack resistance and the like.

3. The method has the advantages of simple operation, mild preparation conditions and low production cost.

4. The thickener prepared by the invention has excellent high temperature resistance.

Drawings

FIG. 1 is a reaction equation of the thickener prepared according to the present invention.

FIG. 2 is an infrared spectrum of a thickener prepared according to the present invention.

FIG. 3 is a carbon nuclear magnetic resonance spectrum of the thickener prepared by the invention.

FIG. 4 is a thermogravimetric analysis curve of the thickener of example 1 of the present invention.

FIG. 5 is a bar graph of sand carrying capacity compared to pure liquid carbon dioxide for examples 1-5.

FIG. 6 is a plot of viscosity at different shear rates for example 1 and comparative examples 1-3.

FIG. 7 is a schematic diagram of the mechanism of action of the thickener of example 1.

Detailed Description

The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention. It is to be noted that the features in the following embodiments and examples may be combined with each other without conflict.

Preparation of thickener body

Example 1

1.2g of perfluoro ethyl octanoate tert-butyl carbamate was weighed, added to a mixed solution of 6mL of difluoroacetic acid and 12mL of polycyclosiloxane, reacted at room temperature for 3 hours, and saturated NaHCO was added to the solution ₃ Neutralizing the solution, extracting the mixed solution with chloroform for 4 times, and collecting anhydrous Na ₂ SO ₄ After drying and removing the solvent by distillation under reduced pressure, toluene diisocyanate was added to the product and reacted at room temperature to obtain a crude product. And washing the crude product for multiple times by using a mixed solvent of ethyl acetate and benzene, and filtering to obtain the final product.

FIG. 1 is a main reaction equation for the preparation of a thickener. The main principle is as follows: a tert-butyloxycarbonyl (Boc) amino protecting group is a type of amino protecting group that is relatively sensitive to acids, and thus, a difluoroacetic acid solution is used to remove the Boc amino protecting group. The main products of the solution after the Boc amino protective group is removed are isobutene and CO ₂ . And isocyanates can react with reactive hydrogen-containing groups, such as hydroxyl, amino, and the like. The reaction of amino groups with isocyanates is also a relatively common reaction for the preparation of polyurethanes. Isocyanate reacts with amino to generate carbamido compound, and the reaction has higher reactivity than that of isocyanate and other active hydrogen, and primary amine reacts with isocyanate more quickly and has quite large activity. The thickeners are prepared herein by adding trifluoroacetic acid (TFA) to t-butyl perfluorooctanoate carbamate to remove the Boc protecting group and reacting with diisocyanate at room temperature.

FIG. 2 is an infrared spectrum of the thickener prepared in example 1. Wherein the wave number is 1769.03cm ^-1 The peak is the characteristic absorption peak of stretching vibration of carbonyl C ═ O in the ester, the wave number is 1200.38cm ^-1 And 1136.98cm ^-1 Respectively shows the symmetric and asymmetric absorption peaks of the stretching vibration characteristic of C-O-C in the ester, the wave number is 1679.46cm ^-1 The wave number is 1537.74cm ^-1 Is the absorption peak of the stretching vibration characteristic of N-C-N in carbamido with wave number of 810.23cm ^-1 To 1349.94cm ^-1 The characteristic absorption peak of the stretching vibration of C-F appears. And at wave number 2230cm ^-1 This is the characteristic absorption peak of the isocyanate functional group, which is not present in IR spectrum 2, and it is evident that the isocyanate has reacted completely.

Example 2

0.8g of perfluorooctanoic acid ethyl ester carbamic acid tert-butyl ester is weighed, added into a mixed solution of 6mL of difluoroacetic acid and 12mL of polycyclosiloxane, reacted for 6 hours at normal temperature, and saturated NaHCO is added to the solution ₃ Neutralizing the solution, extracting the mixed solution with chloroform for 6 times, and extracting with anhydrous Na ₂ SO ₄ After drying, the solvent was removed by distillation under reduced pressure, toluene diisocyanate was added to the product, and the reaction was carried out at room temperature to obtain a crude product. And washing the crude product for multiple times by using a mixed solvent of ethyl acetate and benzene, and filtering to obtain the final product.

Example 3

1.0g of perfluorooctanoic acid ethyl ester carbamic acid tert-butyl ester is weighed, added into a mixed solution of 6mL of difluoroacetic acid and 12mL of polycyclosiloxane, reacted for 6 hours at normal temperature, and saturated NaHCO is added to the solution ₃ Neutralizing the solution, extracting the mixed solution with chloroform for 6 times, and extracting with anhydrous Na ₂ SO ₄ After drying and removing the solvent by distillation under reduced pressure, toluene diisocyanate was added to the product and reacted at room temperature to obtain a crude product. Then using the mixed solvent of ethyl acetate and benzeneThe crude product was washed several times and filtered to obtain the final product.

Example 4

1.2g of t-butyl perfluorooctanoate ethyl carbamate was weighed, added to a mixed solution of 8mL of difluoroacetic acid and 12mL of polycyclosiloxane, reacted at room temperature for 6 hours, and saturated NaHCO was added to the solution ₃ Neutralizing the solution, extracting the mixed solution with chloroform for 4 times, and collecting anhydrous Na ₂ SO ₄ After drying and removing the solvent by distillation under reduced pressure, toluene diisocyanate was added to the product and reacted at room temperature to obtain a crude product. And washing the crude product for multiple times by using a mixed solvent of ethyl acetate and benzene, and filtering to obtain the final product.

Example 5

1.2g of perfluoro ethyl octanoate tert-butyl carbamate was weighed, added to a mixed solution of 6mL of difluoroacetic acid and 12mL of polycyclosiloxane, reacted at room temperature for 5 hours, and saturated NaHCO was added to the solution ₃ Neutralizing the solution, extracting the mixed solution with chloroform for 5 times, and extracting with anhydrous Na ₂ SO ₄ After drying, the solvent was removed by distillation under reduced pressure, toluene diisocyanate was added to the product, and the reaction was carried out at room temperature to obtain a crude product. And washing the crude product for multiple times by using a mixed solvent of ethyl acetate and benzene, and filtering to obtain the final product.

Example 6

1.2g of t-butyl perfluorooctanoate ethyl carbamate was weighed, added to a mixed solution of 8mL of difluoroacetic acid and 10mL of polycyclosiloxane, reacted at room temperature for 5 hours, and saturated NaHCO was added to the solution ₃ Neutralizing the solution, extracting the mixed solution with chloroform for 5 times, and extracting with anhydrous Na ₂ SO ₄ After drying, the solvent was removed by distillation under reduced pressure, toluene diisocyanate was added to the product, and the reaction was carried out at room temperature to obtain a crude product. And washing the crude product for multiple times by using a mixed solvent of ethyl acetate and benzene, and filtering to obtain the final product.

Comparative example 1

The thickener was prepared as described in example 1, except that no polyepoxide silane and no difluoroacetic acid were added.

Comparative example 2

As described in example 1, except that difluoroacetic acid was not added to the thickener prepared.

Comparative example 3

The thickener was prepared as described in example 1, except that no polyepoxy silane was added.

Thermal stability testing

Thickeners as CO ₂ The most important component of the fracturing fluid system directly influences the performance of the fracturing fluid system, and the performance of the fracturing fluid system is related to whether the fracturing fluid system can be applied to fracturing transformation or not. With the development of the oil and gas resource exploration and development technology, the depth of a stratum where oil and gas resources are located is larger and larger, and the thickening agent is required to have enough thermal stability and not to generate a thermal degradation phenomenon when the thickening agent is at the temperature of the stratum. Whether the thickener can increase CO ₂ Viscosity of (2), thickening agent in CO ₂ The solubility of the thickener in CO is a key factor to be considered ₂ When the solubility is better, this means that there are enough thickener molecular interactions for CO ₂ The thickening effect is also obvious. If the thickener is soluble in the condensate or formation water, it can contaminate the condensate or formation water with the thickener, making subsequent handling and flowback of the thickener difficult.

FIG. 3 is a thermogravimetric analysis curve of the thickener of example 1 prepared by the present invention, and it can be seen from the graph that the temperature at which thermal degradation of the prepared thickener occurs is about 250 ℃, which is a temperature that completely meets the needs of domestic oil and gas reservoirs.

Dissolution Performance test

Whether the thickener can increase CO ₂ Viscosity of (2) thickening agent in CO ₂ The solubility of the thickener in CO is a key factor to be considered ₂ The better solubility in (C) means that there are enough thickener molecular interactions for CO ₂ The thickening effect is also obvious, and the CO can be obviously promoted ₂ Viscosity of (3), thickening agent in CO ₂ Has good solubility inBad, affecting the subsequent CO ₂ Viscosity of (2). Meanwhile, if the thickener can be dissolved in condensate or formation water, the thickener can pollute the condensate or the formation water, and causes difficulty in subsequent treatment and flowback of the thickener, and if the thickener can be dissolved in CO to the maximum extent ₂ Subsequent contamination can also be reduced.

The invention mainly determines the CO content of the prepared thickening agent ₂ Of (2) is dissolved. The experimental solubilities and the theoretically calculated solubilities of the thickeners at different temperatures (303.15-363.15K) and dissolution pressures (6.0-14.0MPa) are shown in tables 1-3. It can be seen that the thickener is in CO ₂ Has better dissolving performance in the medium

TABLE 1 CO at 303.15K ₂ Solubility of medium thickeners under different pressures

TABLE 2 CO at 333.15K ₂ Solubility of medium thickeners at different pressures

TABLE 3 CO at 363.15K ₂ Solubility of medium thickeners at different pressures

Sand carrying performance detection

The sand carrying performance of the fracturing fluid directly influences the fracturing construction effect, the sand carrying performance of the fracturing fluid can influence whether a propping agent can achieve the supporting and flow guiding capacity of the propping agent on a fracture in the fracture, and if the sand carrying performance of the fracturing fluid is poor, the propping agent is easy to settle, cannot expand the fracture and is easy to quickly settle to the bottom of a well to generate risks of sand blocking, sand blockage and the like, so the sand carrying performance of the fracturing fluid is taken as an important standard for evaluating the performance of the fracturing fluid.

The quality of the prepared thickener is judged by measuring the quality of sand of the carbon dioxide suspensoid. The thickening agents prepared in the examples were dissolved in carbon dioxide to prepare equal mass fractions of carbon dioxide liquid containing the thickening agents, and the sand carrying capacity of the thickening agents shown in table 1 was obtained by comparing the sand carrying capacity of pure liquid carbon dioxide.

Fig. 5 is a bar graph of sand carrying capacity of examples 1-6 compared to comparative examples 1, 2, 3. As can be seen from table 4 and fig. 5, the thickener prepared by the present invention has excellent sand-carrying ability. The reason may be that the small-molecule cyclic siloxane has a three-dimensional network structure through polymerization reaction to synthesize the polycyclosiloxane. The polyepoxy silane with the structure has better thickening effect on carbon dioxide, so that the liquid carbon dioxide has higher viscosity and better sand carrying capacity. In addition, the sand carrying performance of the embodiment added with the polyepoxy silane and the difluoroacetic acid is far better than that of the comparative example only added with the polyepoxy silane or the difluoroacetic acid, probably because the polyepoxy silane and the difluoroacetic acid have a certain synergistic effect, so that the sand carrying effect of the thickening agent is more excellent.

TABLE 4

	Multiple (compared to liquid carbon dioxide)
		Example 1	200.2±13.2
Example 2	190.3±16.2
		Example 3	160.6±12.3
Example 4	155.8±15.1
		Example 5	90.8±21.3
Example 6	85.7±29.2
		Comparative example 1	75.7±8.1
Comparative example 2	155.9±9.8
		Comparative example 3	95.7±12.9

Shear resistance test

The shear resistance of the fracturing fluid is an important performance index. Because the fracturing fluid is inevitably subjected to mechanical shearing at different shearing speeds at positions such as a shaft oil pipe, an annular space, a perforation hole and the like in the construction process, the fracturing fluid can cause damage to aggregates of the fracturing fluid or polymer molecular chains in the micromolecular polymer fracturing fluid, and the apparent viscosity in the fracturing process is rapidly reduced, so that the shearing resistance of the fracturing fluid is a very important evaluation index for ensuring the success of fracturing construction. The invention tested the viscosity of example 1 versus the comparative example at different shear rates.

Through experiments, we study the mixing of the shear rate to the fracturing fluidAnd (3) influence rule of system viscosity. Thickening agent in CO ₂ The space network structure is formed through the action of hydrogen bonds, and meanwhile, the hydrophilic group in the thickener molecule is subjected to CO ₂ Increase intermolecular forces, and thus CO ₂ The viscosity of (3) is increased. Pure CO ₂ The properties of the fluid are close to those of Newtonian fluids, and therefore CO is essentially negligible ₂ The viscosity of the fluid is influenced by shearing action, namely the viscosity of a mixed system of the fracturing fluid is changed mainly by the thickening agent in CO ₂ Change in spatial configuration of (a).

As can be seen from fig. 6, the viscosity of the thickener prepared in example 1 is much better than the thickeners prepared in comparative examples 1 to 3. This shows that the addition of the polyepoxy silane and the difluoroacetic acid to the thickener prepared according to the invention has a certain synergistic effect. In addition, the shear rate is less than 200S ^-1 When the viscosity of the thickener prepared in example 1 is substantially unchanged, but when the shear rate is more than 200S ^-1 In time, the viscosity of the thickener prepared in example 1 was gradually decreased. The reason may be that when the shear rate is less than 200S ^-1 The thickener prepared by the invention has an excellent three-dimensional network structure, and the structure has a certain repairing effect, but when the shear rate is more than 200S ^-1 When the shear rate is too high, under the action of shear force, the hydrogen bond action among the thickener molecules is destroyed, so that the three-dimensional network structure of the thickener is destroyed, and the viscosity of the thickener is reduced. This also proves from another point of view that the addition of the polyepoxy silane and the difluoroacetic acid makes the effect of the thickener more excellent, and the synergistic effect between the two makes the three-dimensional network structure more stable.

The thickening agent prepared by the invention has excellent effects in the aspects of high temperature resistance, good solubility, sand carrying capacity, shear resistance and the like. The small molecular cyclic siloxane is synthesized into the poly cyclic siloxane through polymerization reaction, has a three-dimensional network structure and has good high temperature resistance. The liquid carbon dioxide is further prepared into a thickening agent, so that an excellent thickening effect is achieved on the premise of less using amount, and the sand carrying capacity of the liquid carbon dioxide is enhanced.

Finally, it should be noted that: the above-mentioned embodiments only express the specific embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the present invention. It should be noted that various changes and modifications can be made by those skilled in the art without departing from the spirit of the invention, and these changes and modifications are all within the scope of the invention.

Claims

1. A preparation method of a liquid carbon dioxide thickening agent with high-efficiency thickening property is characterized by comprising the following steps:

s1, synthesizing the small molecular cyclic siloxane into poly cyclic siloxane through a polymerization reaction;

s2, adding perfluoro ethyl caprylate tert-butyl carbamate into the mixed solution of poly cyclic siloxane and difluoroacetic acid, and reacting for 3-6h at normal temperature;

s3, adding an alkaline solution into the solution for neutralization, extracting the mixed solution with chloroform for 4-6 times, drying, and removing the filtering solvent;

s4, finally adding toluene diisocyanate into the product, and reacting at room temperature to obtain a crude product;

and S5, washing the crude product for multiple times by using the mixed solvent, drying and filtering to obtain the final product.

2. The method for preparing the highly effective thickening liquid carbon dioxide thickener according to claim 1, wherein the method comprises the steps of: the polycyclosiloxane in the step S1 is synthesized by polymerization of small molecule cyclic siloxane.

3. The method for preparing the highly effective thickening liquid carbon dioxide thickener according to claim 2, wherein the method comprises the steps of: the preparation method of the perfluoro ethyl caprylate tert-butyl carbamate in the step S2 comprises the following steps: adding a proper amount of perfluorooctanoic acid into a three-neck flask with a condenser pipe, adding thionyl chloride, using N, N-dimethylformamide as a catalyst, heating to 80 ℃, stirring for reaction for 3 hours, taking a lower-layer white precipitate in the solution, evaporating to remove the thionyl chloride to obtain perfluorooctanoyl chloride, then adding hydroxyethyl carbamic acid tert-butyl ester into the perfluorooctanoyl chloride, heating to 60 ℃ to obtain a crude product, adding anhydrous ether, mixing with a NaOH solution, layering the solution, extracting to obtain a precipitate, and washing with distilled water for multiple times to obtain perfluorooctanoic acid ethyl ester tert-butyl carbamate.

4. The method of preparing a highly effective thickening liquid carbon dioxide thickener according to claim 3, wherein the method comprises the steps of: the method for filtering the solvent in the step S3 is as follows: washing with anhydrous ethanol for several times, and adding anhydrous Na ₂ SO ₄ Dried, and then the solvent was distilled off by ethanol under reduced pressure.

5. The method of preparing the highly effective thickening liquid carbon dioxide thickener according to claim 4, wherein the method comprises the steps of: the basic solution described in step S3 is typically saturated NaHCO ₃ Or sodium hydroxide, etc.

6. The method for preparing the highly effective thickening liquid carbon dioxide thickener according to claim 4, wherein the method comprises the steps of: the toluene diisocyanate described in step S4 may also be replaced by 1, 6-hexamethylene diisocyanate.

7. The method of preparing a highly effective thickening liquid carbon dioxide thickener according to claim 5, wherein: the mixed solvent described in step S5 is a mixed solvent of ethyl acetate and benzene or ethanol and benzene.

8. The method of preparing a highly effective thickening liquid carbon dioxide thickener according to claim 7, wherein: the mass of the polyepoxy silane, the perfluoro caprylic acid ethyl carbamate and the difluoroacetic acid is 0.6-2.4g, 2-12mL and 4-18mL, and the mass is preferably 1.2g, 8mL and 12 mL.

9. A highly effective thickening liquid carbon dioxide thickener prepared by the process according to any of claims 1 to 8.