What is a demulsifier?

Demulsifier is a type of chemical agent specifically used in oilfield crude oil dehydration processes to separate oil-water emulsions formed after crude oil is extracted from the formation. It works by breaking the stability of the oil-water interface, promoting the aggregation and separation of water droplets in the emulsion, thereby achieving the purpose of crude oil dehydration. Among various demulsifiers, polyether demulsifiers are the most widely used in oilfields, which can be synthesized with different initiators such as amines, polyhydric alcohols and resins. To meet the requirements of rapid and continuous dehydration in oilfields, polyether demulsifiers often need to be modified (e.g., cross-linked modification with toluene diisocyanate) to improve their dehydration performance, such as increasing dehydration speed, increasing the volume of separated water and improving the clarity of separated water.

Introduction

After crude oil is extracted from the formation, dehydration treatment is required first, and chemical demulsification is the most commonly used dehydration method in oilfields at present. Among them, polyether demulsifiers are the most widely used demulsifiers in oilfields. At present, the commonly used polyether demulsifiers include polyether demulsifiers using amines (such as diethylenetriamine, tetraethylenepentamine and polyethylenepolyamine, etc.) as initiators, polyether demulsifiers using polyhydric alcohols (such as stearyl alcohol, propylene glycol and glycerol, etc.) as initiators, and polyether demulsifiers using resins (such as phenolic resin, phenolamine resin, etc.) as initiators. However, traditional polyether demulsifiers cannot fully meet the field needs. Most traditional polyether demulsifiers have slow dehydration speed and cannot adapt to the requirements of rapid and continuous dehydration in oilfields. Therefore, most polyether demulsifiers need to be modified and compounded to improve their dehydration performance.

This paper developed a new type of initiator. Polyol was modified with epichlorohydrin to synthesize condensed polyol. The synthetic product has more functional groups. Using this as the initiator, a series of condensed polyol polyether demulsifiers were synthesized by changing the dosage of the initiator and the ratio of ethylene oxide and propylene oxide. In application, it was found that this type of polyether demulsifier has good dehydration effect on heavy oil, and combines the characteristics of clear water quality after demulsification of polyether demulsifiers using alcohols as initiators. To improve the dehydration performance of this polyether demulsifier, toluene diisocyanate was used to modify the polyether in this paper. The modified demulsifier was applied in field tests and achieved good results.

1 Experiment

1.2 Experimental Methods

1.2.1 Synthesis of Initiator

Glycerol and epichlorohydrin were put into a three-necked flask and mixed. 50% potassium hydroxide solution was added dropwise at 60 °C. After dropping for 30 min, the temperature was raised to 80 °C for reaction for 4 h, and then cooled and filtered to obtain the condensed polyol initiator.

1.2.2 Synthesis of Polyether Demulsifier

Using condensed polyol as initiator and potassium hydroxide as catalyst, ring-opening polymerization was carried out with ethylene oxide and propylene oxide at a temperature of 130-140 °C and a pressure of 0.2-0.4 MPa to synthesize block polyether demulsifiers with different initiator contents and different m(EO)/m(PO) values.

1.2.3 Synthesis of Modified Polyether Demulsifier

The synthesized polyether demulsifier was mixed with solvent xylene to prepare a solution with a mass fraction of 60%. Toluene diisocyanate accounting for 1.8% of the polyether mass was added, and the reaction was carried out at 65 °C for 3 h. After the reaction, the temperature was lowered to obtain the modified polyether demulsifier.

1.3 Sample Evaluation and Laboratory Verification

The bottle test method was used in the experiment. The produced liquid taken from an oilfield site was stirred evenly to form an oil-water emulsion. 80 mL of the oil-water emulsion was added to a 100 mL dehydration bottle, placed in a constant temperature water bath and preheated to the test temperature of 70 °C for 10 min. A certain concentration of demulsifier was added, and the dehydration bottle was shaken 100 times to mix the agent with the sample. The change of water content in the bottle within 60 min was observed and recorded, and divided into different grades according to the clarity of the water.

The demulsification performance of the demulsifier was evaluated with reference to the industry standard Test Method for Application Performance of Crude Oil Demulsifiers (Bottle Test Method) (SY/T 5281—2000).

1.4 Process Discussion and Result Verification

The demulsification performance of polyether demulsifiers with different initiator contents and different m(EO)/m(PO) values was evaluated, and the results are shown in Table 1.

Initiator/PO Feed Ratio	PO/EO Feed Ratio	Volume of Separated Water (mL)	Water Quality Grade of Separated Water	Demulsification Effect Evaluation
1:39	3:1	42	Grade 3	General
1:39	5:1	45	Grade 2	Good
1:69	3:1	47	Grade 2	Good
1:69	5:1	50	Grade 1	Excellent
1:99	3:1	48	Grade 1	Excellent
1:99	5:1	46	Grade 2	Good

According to the experimental results, when the initiator/PO feed ratio of the demulsifier was 1:69 and the PO/EO feed ratio was 5:1, both the volume of separated water and the color of separated water were good.

The above demulsifiers were cross-linked with 1.8% toluene diisocyanate, and the modified products were GlE3931E, GlE3951E, GlE6931E, GlE6951E, GlE9931E and GlE9951E. The dehydration performance of the cross-linked condensed polyol polyether demulsifiers was verified, and the results are shown in Table 2.

Modified Product Model	Dehydration Rate (mL/min)	Volume of Separated Water (mL)	Clarity of Separated Water	Comprehensive Performance Score
GlE3931E	0.72	45	Slightly turbid	78
GlE3951E	0.78	48	Slightly turbid	82
GlE6931E	0.83	51	Clear	86
GlE6951E	0.85	53	Clear	88
GlE9931E	0.92	55	Crystal clear	95
GlE9951E	0.88	52	Clear	90

It can be seen from Table 2 that the dehydration performance of the cross-linked condensed polyol polyether demulsifiers was improved to a certain extent, that is, the dehydration speed was faster and the dehydration volume was higher. It can be seen that after the condensed polyol polyether demulsifier was cross-linked, the number of branched chains increased, the relative molecular mass increased, and the adsorption capacity at the oil-water interface was enhanced. Among them, GlE9931E had the best demulsification performance.

1.5 Product Characterization

The infrared characterization of the synthesized GlE9931E was carried out, and the results are shown in Figure 1. It can be seen from Figure 1 that the peak at 1735 cm⁻¹ was the stretching vibration peak of the —C=O group on the carbamate group generated by the reaction, the peak at 3320 cm⁻¹ was the stretching vibration peak of the —NH group on the carbamate group, and the peak at 1555 cm⁻¹ was the bending vibration peak of the —NH group on the carbamate group.

The peaks at 1030 cm⁻¹ and 950 cm⁻¹ were the asymmetric and symmetric stretching vibration peaks of the ester group C—O bond, respectively. The peak at 1383 cm⁻¹ was the symmetric deformation vibration absorption peak of —CH₃, and the peak at 1459 cm⁻¹ was the in-plane bending vibration absorption peak of —CH₂—. The characteristic absorption peak of —OH was around 3486 cm⁻¹, indicating that part of the polyether was not cross-linked. There was no characteristic absorption peak of —NCO at 2280-2260 cm⁻¹, indicating that toluene diisocyanate had reacted with polyether.

2 Field Test of Demulsifier

The test demulsifier GlE9931E was injected into the primary/secondary separators at 60/100 mg·L⁻¹ respectively, and the water content of crude oil at the outlets of the primary/secondary separators and the electric dehydrator (external transportation) was monitored. The test process was as follows: blank data were collected; after 10 h, the test demulsifier GlE9931E was switched in, and the injection volume was maintained at 60/100 mg·L⁻¹; after 48 h of detection, the injection volume was reduced to 50/80 mg·L⁻¹, and the monitoring was continued for 48 h; the injection volume was reduced to 40/60 mg·L⁻¹, and the monitoring was continued. The experimental process is shown in Figure 2.

During the test period, at the same injection volume, the average water content in the oil at the outlet of the primary separator decreased from 41% to 27%, and the average water content in the oil at the outlet of the secondary separator decreased from 21% to 14%, with a reduction ratio of more than 30%; the water content of crude oil entering the electric dehydrator decreased significantly, and the electric dehydration treatment pressure decreased. It can be seen from Figure 1 that when the injection concentration was reduced to 40/60 mg·L⁻¹, the water content at the outlet was basically equivalent to that when the on-site agent in use was injected at 60/100 mg·L⁻¹.

It can be seen that when the demulsifier GlE9931E was injected, the water content of crude oil in the primary/secondary separators decreased significantly, indicating that the demulsification effect of the test agent was better than that of the agent in use.

The average oil content at the water phase outlets of each separator is shown in Table 3.

Equipment Name	Injection Concentration (mg·L⁻¹)	Average Oil Content at Water Phase Outlet (mg·L⁻¹)	Change Rate Compared with On-site Agent in Use (%)
Primary Separator	60	85	-28.3
Primary Separator	50	92	-22.5
Primary Separator	40	105	-13.1
Secondary Separator	100	68	-31.7
Secondary Separator	80	75	-25.5
Secondary Separator	60	88	-14.6
Electric Dehydrator	60/100	32	-36.0
Electric Dehydrator	50/80	38	-24.0
Electric Dehydrator	40/60	45	-10.0

When the injection concentration of GlE9931E was 40/60 mg·L⁻¹, the oil content at the water phase outlets of each separator and the electric dehydrator decreased.

It can be seen from Table 3 that the oil content at the water phase outlets of each separator and the electric dehydrator decreased during the test period, which was consistent with the characteristics of clear water quality after dehydration of the condensed polyol polyether demulsifier.

2 Conclusions

1) A series of diblock polyethers were synthesized by copolymerization of condensed polyol as initiator with ethylene oxide and propylene oxide. The demulsification performance of polyether demulsifiers with different initiator contents and different m(EO)/m(PO) values was evaluated, and it was found that GlE6951 had the best demulsification effect. After cross-linking the synthesized polyether demulsifier with toluene diisocyanate, it was found that GlE9931E had the best demulsification performance.

2) Field test results showed that when the injection concentration of GlE9931E was 40/60 mg·L⁻¹, the water content at the outlet of the primary and secondary separators was equivalent to that when the injection concentration of the agent in use was 60/100 mg·L⁻¹, indicating that this type of demulsifier could well adapt to the field process.