A polycyclic anti-sulfur ion type polyacrylamide oil displacement agent and its preparation method

Technical Field

This invention belongs to the field of oilfield oil recovery additives technology, specifically relating to a polycyclic anti-sulfur ion type polyacrylamide oil displacement agent and its preparation method.

Background Technology

In tertiary oil recovery, polymer flooding is a crucial technology for enhancing oilfield recovery. With most oilfields in my country entering a high water-cut stage, the development of tertiary oil recovery technology is of great significance to reservoir recovery. Oilfield wastewater contains large amounts of salt and reactive substances, placing increasingly stringent requirements on the performance indicators of polymers during formulation and injection into wells. In particular, sulfides are difficult to control, leading to generally low injected viscosity. Furthermore, many studies have shown that sulfur has a far greater impact on polymer viscosity than other elements. Sulfides and their ions can chemically react with functional groups on polymer molecular chains, inducing chain breakage and degradation. Their effect on reducing solution viscosity is significantly higher than that of most other elements or ions. This chemical degradation is particularly prominent in reservoirs with high sulfur content and is one of the important reasons for the decline in polymer flooding efficiency.

Besides sulfides, high temperature and high salinity environments are also key factors affecting the performance of polyacrylamide polymers. Although ordinary polyacrylamide and partially hydrolyzed polyacrylamide have good water solubility and certain thickening ability, their molecular chains contain a large number of carboxylic acid groups, which are prone to coiling at high temperatures. Furthermore, the small molecule electrolytes commonly found in oilfield wastewater can shield the electrostatic repulsion between carboxylic acid ions, significantly reducing the hydrodynamic volume of the molecular chain and causing a sharp drop in solution viscosity. This makes it difficult for ordinary polyacrylamide products to be used in oil reservoirs with high sulfur content, high temperature, and high salinity.

Therefore, developing a polyacrylamide polymer that is suitable for high-sulfur environments, high-temperature resistant, and adaptable to high salinity is of great significance for improving the recovery rate of oil reservoirs with high sulfur content.

Summary of the Invention

To address one or more technical problems existing in the prior art, this invention provides a polycyclic sulfide-resistant polyacrylamide-based oil displacement agent and its preparation method. The polycyclic sulfide-resistant polyacrylamide-based oil displacement agent prepared by this invention exhibits excellent sulfide ion resistance in complex underground high-temperature and high-salt environments.

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

The polycyclic sulfide-resistant polyacrylamide oil displacement agent prepared by this invention not only has the advantages of good temperature and sulfur resistance, but also has the advantage that its viscosity increases with increasing temperature in high sulfur environments. The polycyclic sulfide-resistant polyacrylamide oil displacement agent of this invention exhibits excellent sulfur ion resistance in high temperature and high salt complex environments.

This invention introduces a polycyclic, temperature- and sulfur-resistant monomer, generated by the reaction of 3- methoxy -4- hydroxybenzaldehyde unsaturated glycidyl ether with aniline, for copolymerization. This allows the introduction of a rigid polycyclic structure and polar groups containing hydroxyl and methoxy groups into the polyacrylamide molecular chain. The cyclic structure exhibits greater rigidity and stability under high temperature, high salinity, and high sulfur environments, making it less prone to degradation. This polycyclic modified polyacrylamide molecular chain is less susceptible to curling and degradation, resulting in enhanced temperature resistance, salt resistance, sulfur resistance, and stability. Furthermore, compared to ordinary polyacrylamide, the polyacrylamide modified by this invention exhibits superior performance under high temperature, high salinity, and high sulfur environments. In this environment, the molecular chains are more extended, and intramolecular and intermolecular associations are more likely to occur, improving the steric and thermal stability of the polyacrylamide molecular chain structure. On the other hand, the polycyclic aromatic structure can form a shielding effect with sulfur ions through steric hindrance, and the polar groups can also form weak interactions with sulfur ions or other anions, reducing their destructive effect on the polymer chain, thereby improving the viscosity retention and sulfur ion resistance in high-temperature, high-salt, and high-sulfur environments. At the same time, this structure may promote hydrophobic association between molecular chains under heating conditions, enabling the oil displacement agent to exhibit the unique property of increasing viscosity with increasing temperature in high-sulfur environments.

Preparation method:

Example 1

Preparation of polycyclic, temperature- and sulfur-resistant elemental monomers:

One part by weight of 3- methoxy -4- hydroxybenzaldehyde and ethanol were added to a flask equipped with a stirrer, burette, reflux condenser, and thermometer. The mixture was then heated to 50 °C until fully dissolved, yielding a first mixture. 0.8 parts by weight of levulinic acid, 0.05 parts by weight of pyrrolidine, and 0.1 parts by weight of glacial acetic acid were dissolved in ethanol to obtain a second mixture. This second mixture was then slowly added dropwise to the first mixture. The reaction was carried out at 100 °C for 5 hours , followed by vacuum distillation and drying to obtain the unsaturated monomer of 3- methoxy -4- hydroxybenzaldehyde. The mass ratio of ethanol in the first mixture to that in the second mixture was 1:1 . After adding the second mixture dropwise to the first mixture, the system contained 60% ethanol by mass. One part by weight of 3- methoxy -4- hydroxybenzaldehyde unsaturated monomer and 0.8 parts by weight of epichlorohydrin were added to a flask equipped with a stirrer, burette, reflux condenser, and thermometer and mixed thoroughly to obtain a third mixture. Then, 0.01 parts by weight of benzyltriethylammonium chloride were slowly added dropwise to the third mixture, and the mixture was reacted at 70 °C for 2 h to obtain 3- methoxy -4- hydroxybenzaldehyde unsaturated glycidyl ether. Finally, one part by weight of 3- methoxy -4- hydroxybenzaldehyde unsaturated glycidyl ether and 0.25 parts by weight of aniline were dissolved in dimethyl sulfoxide and reacted at 30 °C for 3 h . After vacuum distillation and drying, a polycyclic, heat- and sulfur-resistant elemental monomer was finally obtained. The mass of dimethyl sulfoxide used was 60% of the mass of the system formed by 3- methoxy -4- hydroxybenzaldehyde unsaturated glycidyl ether, aniline, and dimethyl sulfoxide .

Preparation of polycyclic anti-sulfide polyacrylamide oil displacement agents:

Ten parts by weight of polycyclic heat- and sulfur-resistant elemental monomers, 150 parts by weight of acrylamide, 80 parts by weight of 2- acrylamido -2- methylpropanesulfonic acid, 5 parts by weight of N- dodecylacrylamide, 5 parts by weight of nonylphenol polyoxyethylene ether, 1 part by weight of ethylenediaminetetraacetic acid, 5 parts by weight of N, N-methylenebisacrylamide, 5 parts by weight of sodium dodecylbenzenesulfonate, and 744 parts by weight of deionized water were added to a beaker and mixed thoroughly to obtain a mixed system. The temperature and pH of the mixed system were then adjusted to 5 °C and 7.1 , respectively , and poured into a reaction vessel. N2 was purged for 30 minutes to remove oxygen. Then, under N2 protection, 0.003 parts by weight of initiator and 0.005 parts by weight of chain transfer agent were added . The reaction system solution was purged with nitrogen (N2) until viscous and then sealed. After the reaction was completed, the colloid was taken out and subjected to granulation, drying, grinding, and sieving in sequence to finally obtain a polycyclic sulfur-resistant polyacrylamide-based oil displacement agent.

Performance evaluation:

The present invention evaluates the performance of polyacrylamide-based oil displacement agents prepared in various embodiments and comparative examples.

Using a 1000 ppm sodium chloride aqueous solution as the solvent and the polyacrylamide-based oil displacement agents prepared in each example and comparative example as the solute, a polymer mother liquor with a concentration of 5 g/L was prepared . The concentration of the polymer mother liquor was diluted to 1500 ppm , and the polymer viscosity was measured using a Brookfield DV- Ⅲ viscometer with rotor No. 0 selected , rotation speed 6 r/min , and temperature 45 ℃. The results are shown in Table 1 and are recorded as brine viscosity. At the same time, the concentration of the prepared polymer mother liquor was diluted to 1500 ppm in the same manner, and sodium sulfide was added to make the sulfur ion S2- concentration in the polymer mother liquor reach 5 mg/L . The viscosity of the polymer mother liquor was measured and recorded as S2- containing brine viscosity. The results are shown in Table 1. Wherein, viscosity retention rate = S2- brine viscosity / brine viscosity × 100% .

Table 1

Example	Apparent viscosity (mPa.s)
	Salt water viscosity	S2- Brine viscosity​	Viscosity retention rate (%)
Example 1	120	105	87.5

Table 1 , the symbol ” – ” indicates that the performance metric was not tested.

The present invention also investigated the effects of temperature and sulfur-containing elements on the prepared polyacrylamide-based oil displacement agents, and the effects of salinity and sulfur-containing elements on the polyacrylamide-based oil displacement agents prepared in Examples 1-6 . The results are shown in Table 2 .

In investigating the effects of temperature and sulfur-containing brine on polyacrylamide-based oil displacement agents, brine with a salinity of 100,000 was used to prepare brine solutions with a concentration of 2000 mg/L for the polyacrylamide-based oil displacement agents prepared in each example . Sodium sulfide was then added to the brine solution to achieve a sulfur ion (S2-) concentration of 5 mg/L . The viscosity of the S2– containing brine solution was then tested at temperatures of 65 ℃, 75 ℃, and 85 ℃, with a shear rate of 170 s⁻¹ . The results are shown in Table 2 .

In this invention, the brine with a mineralization of 100,000 is prepared from sodium chloride, calcium chloride, magnesium chloride, and deionized water, resulting in a total Ca2+ and Mg2+ ion concentration of 3500 mg/L (Ca2+ and Mg2+ ion concentration ratio of 1:1) and a total ion concentration of 100,000 mg/L . The brine with a mineralization of 200,000 is prepared from sodium chloride, calcium chloride, magnesium chloride, and deionized water, resulting in a total Ca2+ and Mg2+ ion concentration of 15,000 mg/L (Ca2+ and Mg2+ ion concentration ratio of 1:1) and a total ion concentration of 200,000 mg/L .

Table 2

Example	Apparent viscosity (mPa.s)
	S2- Brine viscosity(65℃, 100,000)Mineralization	S2- Brine viscosity(65℃, 100,000)Mineralization	S2- Brine viscosity(75℃, 100,000)Mineralization	S2- Brine viscosity(85℃, 100,000)Mineralization
Example 1	83	70	91	103