[Oil Displacement Agents] Preparation Methods of Fatty Amine Polyester Ether Surfactants and Their Composite Ionic Oil Displacement Agents

Technical Field

This invention pertains to oilfield chemicals, and in particular relates to a method for preparing a fatty amine polyester ether surfactant and its composite ionic oil displacement agent.

Background Technology

Ternary composite flooding systems ( polymer + surfactant + alkali ) are an important development technology in the field of chemical flooding in oilfields. A series of pilot field tests have been conducted in Daqing Oilfield, effectively improving crude oil recovery rates. However, some problems have arisen with the large-scale industrial application of ternary composite flooding. In particular, the use of alkali can cause the dispersion and migration of formation clay, leading to a decrease in formation permeability. It also brings a series of problems such as complex on-site construction processes, reduced production well production capacity, reservoir and wellbore scaling, and shortened pump inspection cycles. The presence of alkali also significantly reduces polymer viscosity, and more importantly, reduces the viscoelasticity of the polymer. Unfavorable mobility ratios can lead to viscous fingering, greatly reducing the swept volume and resulting in oil recovery losses. Simultaneously, the presence of alkali can cause severe emulsification of the produced fluid, not only affecting well productivity but also significantly increasing the difficulty and cost of demulsification and dehydration in the surface system and wastewater treatment. These adverse factors severely restrict the further application of ternary composite flooding technology.

To avoid these adverse factors, the development and promotion of alkali-free binary composite oil displacement systems ( polymer + surfactant ) is imperative. Binary composite oil displacement systems enhance oil recovery by relying on the viscoelasticity of polymers and the ultra-low interfacial tension of surfactants without the addition of alkali. Due to the absence of alkali, the viscoelasticity of the system increases significantly. According to capillary number theory, when the interfacial tension is below the order of 10⁻² mN/m , the oil recovery effect is still no less than that of ternary composite flooding. However, precisely because of the absence of alkali, the interfacial tension between crude oil and water often fails to meet requirements, thus affecting the oil displacement effect. Therefore, the development of surfactants with high interfacial activity, temperature and salt resistance, and low adsorption loss is of great significance. Simultaneously, with increasing environmental protection requirements, the research and application of green and environmentally friendly surfactants have received more attention. Furthermore, optimizing production processes and formulations to reduce the production cost of surfactants is also key to improving the economic benefits and promoting the application of binary composite flooding technology.

Currently, in tertiary oil recovery chemical flooding technology, the commonly used nonionic surfactants in binary composite flooding systems mainly include fatty alcohol polyoxyethylene ethers, fatty amine polyoxyethylene ethers, alkylphenol polyoxyethylene ethers, fatty acid polyoxyethylene esters, Pluronic series ( polyoxyethylene – polyoxypropylene block copolymers ) , and other polyoxyethylene ether nonionic surfactants, as well as composite flooding agents that combine polyoxyethylene ether nonionic surfactants with other types of surfactants.

Polyoxyethylene ether nonionic surfactants are synthesized by ring-opening polymerization of ethylene oxide with compounds containing active hydrogen ( such as fatty alcohols, alkylphenols, and fatty amines ) . For example, patent publication number CN111423572A , “A method for preparing octadecyl fatty amine polyoxyethylene ether,” uses octadecyl fatty amine and ethylene oxide as the main raw materials. However, ethylene oxide is flammable, explosive, toxic, and irritating, leading to high costs for transportation, storage, and use. Long-term exposure can also harm human health. Furthermore, the ring-opening polymerization of ethylene oxide requires high pressure resistance and airtightness of equipment, and the process is relatively complex. These problems not only increase production costs and operational difficulty but also limit its application in chemical displacement oil technology.

Furthermore, composite oil displacement agents that combine polyoxyethylene ether nonionic surfactants with other types of surfactants, such as patent publication number CN113583648A “A fatty amine polyoxyethylene ether surfactant for enhancing oil recovery and its preparation method,” are prepared by compounding fatty amine polyoxyethylene ether nonionic surfactants, sodium petroleum sulfonate, and industrial sodium chloride. On the one hand, the fatty amine polyoxyethylene ether nonionic surfactant in this patented technology’s formulation has a relatively high final cost due to its synthesis method. On the other hand, the patented technology’s formulation contains a high concentration of Na+ and Cl- ions, which easily form a strong electrolyte environment, accelerating the electrochemical corrosion of metal equipment and pipelines. In addition, this patented technology product needs to be used in combination with alkali to achieve ultra-low interfacial tension and application in composite oil displacement systems. Therefore, it is evident that the cost-effectiveness advantage of this patented technology still has certain shortcomings.

In summary, superior performance, environmental friendliness, and low cost are key to the development of binary composite flooding surfactant technology. Furthermore, the synergistic properties of surfactants with polymer systems, high interfacial activity, temperature and salt resistance, and low adsorption loss are of great practical significance for the application of tertiary oil recovery chemical flooding technology.

Summary of the Invention

The present invention aims to overcome the shortcomings of the prior art and provides a method for preparing a fatty amine polyester ether surfactant and its composite ionic oil displacement agent.

Preparation method:

Example 1

The fatty amine polyester ether surfactant of the present invention is a nonionic surfactant, and its structural formula is as follows:

In the above structural formula:

m represents the degree of polymerization of the carbonate group in the fatty amine polyester ether surfactant molecule, and m is any integer from 1 to 10 ;

n represents the degree of polymerization of the ethoxy group in the fatty amine polyester ether surfactant molecule, and n is any integer from 1 to 10 ;

The sum of m+n is any integer from 2 to 20 ;

R represents the C12-18 alkyl group in the fatty amine polyester ether surfactant molecule .

Example 2

The fatty amine polyester ether surfactant of Example 1 can be prepared by the following method: 94.33 kg (350 mol ) of octadecyl primary amine and 3.22 kg of potassium hydroxide catalyst are added to a reactor, and stirring is started until homogeneous. When the reactor temperature is raised to 80 °C , 308 kg (3500 mol ) of ethylene carbonate is added dropwise, and the reactor temperature is controlled between 80-100 °C during the dropwise addition. After the dropwise addition is completed, the reactor temperature is raised to 145-150 ° C for ring-opening polymerization for 8-10 hours. After the reaction is completed, the temperature is lowered to 20-30 ° C to obtain the octadecylamine polyester ether surfactant (AEC1810) of Example 2 , with a molar ratio of octadecyl primary amine to ethylene carbonate of 1:10 .

Example 5

The preparation method of the composite ionic oil displacement agent of the present invention is as follows: 100 kg of ethylene glycol monobutyl ether (EDG), 550 kg of water , 150 kg of the octadecylamine polyester ether surfactant (AEC1810) prepared in Example 2 , and 150 kg of naphthenic acid amide polyether ester sulfonate anionic surfactant are added sequentially to a stainless steel reactor. Stirring is started and the mixture is dissolved for 30 minutes. After the solution is homogenized, 50 kg of octadecyltrimethylammonium sulfate cationic surfactant is added to the reactor , and stirring is continued for another 30 minutes. After the solution is homogenized, the composite ionic oil displacement agent product of Example 5 is obtained .

Performance evaluation:

1. Evaluation of interfacial tension in binary systems with different surfactant concentrations

Following the determination method in section 6.3 of Q/SY1583-2013 , dehydrated crude oil from the South 7-1 Joint Station of the Ninth Operating Area of Daqing Oilfield No. 2 Oil Production Plant, and 25 million molecular weight polyacrylamide for oil displacement from Daqing Refining & Chemical Company, binary system solutions with oil displacement agent concentrations of 0.05 %, 0.1 %, 0.2 %, 0.3 %, 0.4 %, and 0.5 %, and a polyacrylamide concentration of 1000 ppm were prepared using simulated brine from Examples 5 , 6 , 7 , and Comparative Example 1 , respectively. The interfacial tension between the oil displacement agent solutions of different concentrations and the crude oil was measured using a TX-500C rotating drop interfacial tensiometer at 45 ℃ and a rotation speed of 5000 rpm . The results are shown in the table below:

sample	project	Surfactant concentration (%)
		0.05	0.1	0.2	0.3	0.1	0.5
Example 5		2.12	1.65	1.79	1.03	2.59	2.71

As shown in the table above, the binary oil displacement systems composed of composite ionic oil displacement agents and naphthenic acid amide polyether sulfonate oil displacement agents, respectively, and polyacrylamide, can maintain an ultra-low interfacial tension of < 1 × 10⁻² mN/m within a wide effective concentration range of 0.05 % to 0.5 % . However, the interfacial tension values between the composite ionic oil displacement agent solutions of different concentrations and crude oil are even lower and more stable, indicating that the interfacial tension of the composite ionic oil displacement agent is superior to that of the naphthenic acid amide polyether sulfonate anionic oil displacement agent.

2. Evaluation of viscosity and interfacial tension stability of binary systems

Following the determination method in section 6.9 of Q/SY1583-2013 , under a polyacrylamide concentration of 1000 ppm , binary solutions with an oil displacement agent concentration of 0.2 % were prepared for Examples 5 , 6 , 7 , and Comparative Example 1. These solutions were placed in an oven at 45 ℃ under anaerobic conditions and left for 0 , 1 , 3 , 7 , 15 , 30 , and 60 days , respectively . The viscosity of the binary solutions was measured, and the interfacial tension between the binary solutions and crude oil was also measured. The results are shown in the table below:

sample	project	Stability evaluation
		0 days	1 day	3 days	7 days	15 days	30 days	60 days
Example 5	Viscosity (mPa.s)	45.7	45.7	44.9	44.0	42.5	41.3	38.9
	Interfacial tension (X10mN/m)	1.83	1.79	2.41	3.41	4.62	6.3	7.94

As shown in the table above, the binary displacement systems composed of composite ionic displacement agents, naphthenic acid amide polyether ester sulfonate displacement agents, and polyacrylamide, respectively, maintain an ultra-low interfacial tension of < 1 × 10⁻² mN/m within 60 days , and the viscosity retention rate remains at a relatively high level. This fully meets the ultra-low interfacial tension requirements of Q/SY1583-2013 standard, which stipulates a viscosity retention rate ≥ 90 % and an interfacial tension of < 1 × 10⁻² mN/m within 30 days .

3. Evaluation of the salt resistance performance of the binary system

Sodium chloride solutions with different salinities were prepared using distilled water. Under conditions of 1000 ppm polyacrylamide concentration, binary systems with an oil displacement agent concentration of 0.2 % were prepared using water with different salinities for Examples 5 , 6 , 7 , and Comparative Example 1. The interfacial tension between these solutions and crude oil was measured at 45 °C and a rotation speed of 5000 rpm . The results are shown in the table below:

sample	project	NaCl concentration (mg/L)
		1000	2000	3000	4000	5000	6000	7000	8000
Example 5		1.79	1.56	1.59	1.65	1.79	2.87	3.13	3.53

As shown in the table above, the binary oil displacement systems composed of the composite ionic oil displacement agent and the naphthenic acid amide polyether ester sulfonate oil displacement agent, respectively, and polyacrylamide, maintain an ultra-low interfacial tension of <1 × 10⁻² mN/m within a salinity range of 1000–8000 mg / L , exhibiting good salt resistance. However, the salt resistance of the composite ionic oil displacement agent is significantly better than that of the naphthenic acid amide polyether ester sulfonate anionic oil displacement agent. This is because the nonionic hydrophilic groups in the fatty amine polyester ether surfactant molecules of the composite ionic oil displacement agent are less likely to become ineffective due to charge neutralization or changes in ion concentration in high-salt solutions, thus resulting in superior salt resistance.

4. Hard water resistance test of binary system

Simulated hard water solutions containing Ca²⁺ and Mg²⁺ at different concentrations were prepared using distilled water. Under conditions of 1000 ppm polymer concentration, binary systems with an oil displacement agent concentration of 0.2 % were prepared by mixing these Ca²⁺ and Mg²⁺ solutions from Examples 5 , 6 , 7 , and Comparative Example 1. The interfacial tension between these solutions and crude oil was measured at 45 °C and a rotation speed of 5000 rpm . The results are shown in the table below.

sample	project	Ca²⁺ + Mg²⁺ concentration (mg/L )
		10	20	30	40	50
Example 5		1.72	1.86	1.97	2.07	2.20

As shown in the table above, the binary oil displacement systems composed of the composite ionic oil displacement agent and the naphthenic acid amide polyether sulfonate oil displacement agent, respectively, and polyacrylamide , maintain an ultra-low interfacial tension of < 1 × 10⁻² mN/m within the Ca²⁺–Mg²⁺ concentration range of 10–50 mg/L , exhibiting good resistance to hard water. However, the composite ionic oil displacement agent demonstrates significantly better resistance to hard water than the naphthenic acid amide polyether sulfonate anionic oil displacement agent.

5. Multiple adsorption experiments of binary systems

Following the determination method in section 6.4 of Q/SY1583-2013 , solutions of the oil displacement agent with a concentration of 0.2 % were prepared for Examples 5 , 6 , 7 , and Comparative Example 1. The solutions were then shaken at a solid-liquid ratio of 1:9 (oil sand to oil displacement agent solution) for 12 hours at 45 °C and a shaking frequency of 90 times /min . The interfacial tension after oil sand adsorption was measured. The same experimental conditions were then repeated with the adsorbed oil displacement agent solution, and the interfacial tension values were measured after four adsorption cycles. The results are shown in the table below.

sample	project	Interfacial tension ( X10⁻³ mN/m)
		Before adsorption	Primary adsorption	Secondary adsorption	Triple adsorption	Four adsorptions
Example 5	Interfacial tension	1.63	1.93	2.13	2.73	5.78

As shown in the table above, the binary displacement system composed of naphthenic acid amide polyether sulfonate oil displacement agent and polyacrylamide in Comparative Example 1 exhibited an interfacial tension > 1 × 10⁻² mN/m after the fourth adsorption experiment . In contrast, the binary displacement system composed of the composite ionic oil displacement agent and polyacrylamide maintained an interfacial tension < 1 × 10⁻² mN/m after four adsorption experiments . These experimental results further demonstrate that the anti-adsorption capacity of the composite ionic oil displacement agent is significantly improved compared to that of the naphthenic acid amide polyether sulfonate oil displacement agent.

6. Binary system oil displacement experiment

the binary system (S surfactant + P polymer ) on artificial rock cores was tested according to the test method in Chapter 9 of the standard SY/T6424-2014 “Performance Test Method of Composite Oil Displacement System” .

1 ) Experimental conditions

(1) Core: A homogeneous artificial physical core was used, with core dimensions of 4.0cm × 4.0cm × 30cm .

(2) Experimental water: The water used for water flooding and binary system was Daqing Oilfield standard simulated brine. (3) Chemical agents used in the experiment: The polymer used was Daqing Refining & Chemical Company’s 25 million molecular weight polyacrylamide for oil displacement, and the oil displacement agent used was the product prepared in Examples 5 , 6 , 7 and Comparative Example 1 of this invention .

(4) Experimental oil: Dehydrated crude oil from the South 7-1 Joint Station of the Ninth Operating Area of Daqing Oilfield No. 2 Oil Production Plant ;

(5) Experimental temperature: All experiments were conducted at 45 ℃;

(6) Injection rate: 20 mL/h .

2. Oil displacement experiment results data

sample	Core marking	Oil saturation (%)	Water drive miningYield (%)	Dual-drive enhances oil recovery (%)	Total recovery rate(%)	Binary system formulation and dosage
Example 5	2505126-1	55.75	51.57	28.69	80.26	Binary system (S/0.3% + P/1500ppm + simulated saline) 0.3pv

20 % after waterflooding in a binary system experiment using artificial cores. The composite ionic oil displacement agents in Examples 5 , 6 , and 7 achieved an average oil recovery rate increase of over 28.20 % after waterflooding . The composite ionic oil displacement agent significantly improved the oil recovery rate compared to the naphthenic acid amide polyether ester sulfonate anionic oil displacement agent.

The experimental data above show that the composite ionic displacement agent outperforms the single naphthenic acid amide polyether sulfonate anionic displacement agent in terms of overall performance, interfacial tension stability, salt resistance, hard water resistance, anti-adsorption performance, and binary system oil displacement performance. Specifically, the octadecyltrimethylammonium sulfate cationic surfactant and octadecylamine polyester ether surfactant in the composite ionic displacement agent do not undergo charge binding or precipitation reactions with Ca2+ and Mg2+ ions, thus significantly improving hard water resistance. In particular, the octadecylamine polyester ether surfactant is nonionic, containing no ionic groups in its molecule; the solubility and performance of its nonionic hydrophilic groups are less affected by salt concentration, resulting in superior salt resistance.