CN110157403A - A low-permeability oil displacement agent - Google Patents

Abstract

The present invention provides a kind of low-permeability oil deposit oil displacement agents.The low-permeability oil deposit oil displacement agent is compounded by the trimethylammonium bromide cationic surfactant of the pure and mild C12-C18 of modified poly ethylene；Modified polyvinylalcohol is 1:9-9:1 with the mass ratio that compounds of the trimethylammonium bromide cationic surfactant of C12-C18.The low-permeability oil deposit oil displacement agent has good oil displacement efficiency.

Description

A low-permeability oil displacement agent

technical field

The invention relates to an oil-displacement composition, in particular to an oil-displacement composition suitable for low-permeability reservoirs, and belongs to the technical field of reservoir exploitation.

Background technique

Since the 21st century, with the rapid growth of the national economy, the demand for oil in countries around the world has risen sharply. Complex oil reservoirs represented by low-permeability and ultra-low-permeability reservoirs have become an important part of my country's oil resource output replacement, and will be an important resource base for my country's oil industry to increase reserves and production for a considerable period of time in the future.

Low permeability reservoirs are currently facing many problems. Compared with medium and high permeability reservoirs, the development effect of low permeability oilfields is quite different. Most low-permeability reservoirs in my country are developed by waterflooding. However, due to low porosity and low permeability, the phenomenon of high water injection pressure and "no injection or production" is common in the development process, which ultimately leads to low oil recovery. In addition, some oilfields in my country are located in the northwest region, and water resources are scarce, which is not conducive to the implementation of water flooding development.

Surfactants have a series of properties such as low interfacial tension, emulsifying crude oil, and changing wettability, which can effectively reduce pressure and increase injection, start the remaining oil in low-permeability matrix, and play a huge role in the development of ultra-low permeability and low permeability reservoirs. application prospects. According to statistics, 80% of the world's crude oil is produced in the form of emulsion. In recent years, laboratory research and field practice have shown that in low-permeability reservoirs, the contribution rate of surfactant emulsification to recovery is greater than that of its interface. Contribution rate of activity to recovery factor.

At present, the surfactants with good emulsifying effect in field application are OP series and petroleum sulfonate series. However, they have the disadvantages of polluting the environment and poor temperature resistance.

Therefore, it is necessary to provide a low-permeability reservoir with excellent emulsifying performance at a low viscosity, which can spontaneously form a relatively low-permeability reservoir. Stable emulsion, a self-emulsification flooding system that further improves the recovery of low-permeability reservoirs.

Contents of the invention

In order to solve the above technical problems, the object of the present invention is to provide a surfactant oil displacement agent with good oil displacement effect.

In order to achieve the above-mentioned technical purpose, the present invention provides a kind of low permeability reservoir (permeability is less than 50mD) oil displacement agent, this low permeability reservoir oil displacement agent is made of modified polyvinyl alcohol and C12-C18 trimethyl bromide Ammonium cationic surfactant is compounded; wherein, the compounding mass ratio of modified polyvinyl alcohol and C12-C18 trimethylammonium bromide cationic surfactant is 1:9-9:1.

In the low-permeability reservoir oil displacement agent of the present invention, the modified polyvinyl alcohol used is to hydrophobically modify the polyvinyl alcohol itself without hydrophobic properties, to construct a kind of polyvinyl alcohol with both hydrophilic groups and hydrophobic groups. polymeric surfactants. The polymer surfactant obtained by modification has a small dosage, high molecular weight and good performance of dispersing oil droplets. More economically friendly.

The macromolecular surfactant adopted in the low-permeability reservoir oil displacement agent of the present invention is modified polyvinyl alcohol, and through the synergistic effect of modified polyvinyl alcohol and C12-C18 trimethylammonium bromide cationic surfactant, the The obtained compound has self-emulsifying oil displacement performance and can be emulsified spontaneously without external force.

In a specific embodiment of the present invention, the compounding mass ratio of the trimethylammonium bromide cationic surfactant of modified polyvinyl alcohol and C12-C18 is 1:9, 3:7, 5:5, 7:3 or 9:1.

In a specific embodiment of the present invention, the C12-C18 trimethylammonium bromide cationic surfactant used is cetyltrimethylammonium bromide.

That is, the low-permeability reservoir oil displacement agent is compounded by modified polyvinyl alcohol and cetyl trimethyl ammonium bromide; wherein, the modified polyvinyl alcohol and cetyl trimethyl ammonium bromide The compounding mass ratio can be 1:9-9:1.

In a specific embodiment of the present invention, the molecular weight of the modified polyvinyl alcohol used is 2000-3000. The modified polyvinyl alcohol with this molecular weight has better oil drop dispersing performance and emulsifying performance. For example, the molecular weight of the modified polyvinyl alcohol used can be 2200.

In a specific embodiment of the present invention, the modified polyvinyl alcohol has both hydrophobic groups and hydrophilic groups.

In a specific embodiment of the present invention, the modified polyvinyl alcohol is obtained by hydrophobically modifying polyvinyl alcohol with a modifier.

For example, the modifier used may be hexadecane bromide or 2,3-epoxypropyltrimethylammonium chloride.

Preferably, the modifier used is hexadecane bromide. That is, the modified polyvinyl alcohol is obtained by modifying polyvinyl alcohol with hexadecane bromide. The structural formula of this modified polyvinyl alcohol is as shown in the following formula:

Wherein, an integer of x≥1, an integer of y≥1, an integer of m≥1, an integer of n≥1, 40≤x+y+m+n≤70.

In a specific embodiment of the present invention, the amount of modifier used is 12.5%-17.5% of the mass of polyvinyl alcohol. For example, the amount of modifier used is 13%, 14%, 15%, 16% and 17% of the mass of polyvinyl alcohol.

In a specific embodiment of the present invention, modified polyvinyl alcohol is prepared through the following steps:

Mix the modifying agent with polyvinyl alcohol at 55°C-75°C, and react for 40h-50h (preferably 48h) to obtain modified polyvinyl alcohol.

In the low-permeability reservoir oil displacement agent of the present invention, C12-C18 trimethylammonium bromide cationic surfactant is compounded with modified polyvinyl alcohol. CTAB is a common chemical reagent in oilfield field and laboratory research, and there is enough research support for its application in the petroleum field. In addition, CTAB has a 16-carbon chain structure similar to the hydrophobic part of modified polyvinyl alcohol, so it has a certain synergistic effect, which is conducive to the occurrence of spontaneous emulsification.

When the oil displacement agent for low-permeability oil reservoirs of the present invention is specifically used for emulsifying low-permeability oil reservoirs, it can be implemented according to the conventional implementation methods of oil displacement agents in the field. Wherein, the addition amount of the low-permeability reservoir oil displacement agent is 3000mg/L.

The low-permeability reservoir oil displacement agent of the present invention can be prepared through the following steps:

Add modified polyvinyl alcohol and C12-C18 trimethylammonium bromide cationic surfactant to the simulated formation water, mix and stir for 30 minutes, and let stand to obtain a low-permeability reservoir oil displacement agent.

The low-permeability reservoir oil-displacing agent of the invention has wide sources of raw materials and is cheap, and can spontaneously form an emulsified oil-displacement system with the low-permeability reservoir.

The physical simulation oil displacement effect of the low-permeability reservoir oil displacement agent of the present invention is good, and the oil recovery rate can be further improved after conventional water flooding of the low-permeability rock core, and the recovery rate can be increased by about 60%.

The low-permeability reservoir oil displacement agent of the present invention is a self-emulsification oil displacement system, which can be emulsified spontaneously without external force, and provides a basis for screening suitable methods for enhancing oil recovery in oil fields.

Description of drawings

Fig. 1 is the variation curve of the interfacial tension of the low-permeability reservoir oil-displacing agent in Example 1 as a function of the compounding ratio.

Detailed ways

In order to have a clearer understanding of the technical features, purposes and beneficial effects of the present invention, the technical solution of the present invention is described in detail below, but it should not be construed as limiting the scope of implementation of the present invention.

Example 1

This embodiment provides a self-emulsifying oil displacement agent for low permeability reservoirs, which is prepared through the following steps:

Use simulated formation water to prepare self-emulsification oil displacement system, the total concentration is 3000mg/L, among which, the concentration of modified PVA-1570 (molecular weight is 2200) (obtained from bromide cetane modified polyvinyl alcohol) is 2100mg/L , the CTAB (cetyltrimethylammonium bromide) concentration was 900mg/L, stirred for 30min, and left to stand to obtain a self-emulsifying polymer composite oil displacement agent.

A surface tension test was performed on the above-mentioned oil displacing agent of this embodiment. The instrument uses TX-500C interfacial tensiometer, the oil phase is degassed and dehydrated crude oil from an oilfield, and the water phase is the actual formation water of the oilfield. The test temperature is 45°C, and the oil-water interfacial tension is measured under the condition of 5000 rpm. The results showed that when the compounding mass ratio was 7:3, the system had self-emulsifying properties, and the emulsion stability was good.

It can be seen from Figure 1 that the compound system of modified PVA-1570 and CTAB reaches a state of low interfacial tension (≤10 ^-2 mN/m) when the mass ratio is 9:1 and 7:3 respectively.

The performance test of the oil displacement agent of this embodiment is shown in Table 1.

Table 1

It can be seen from Table 1 that although the self-emulsifying system is a compound system of polymer surfactant, the viscosity of the system is extremely low, which is close to the viscosity of water. Excessively high viscosity will make it difficult for chemical agents to displace in low-permeability reservoirs, resulting in formation plugging and other phenomena. The low viscosity of the system is more conducive to its application in enhanced oil recovery of low permeability reservoirs.

The self-emulsification flooding system was used to carry out the core displacement experiment, the core length was 10.0cm, the permeability was 15mD, the saturated water was 18mL, and the post-saturated oil was 10mL. After water flooding-chemical flooding-water flooding, the recovery factors are shown in Table 2.

Table 2

It can be seen from Table 2 that the self-emulsifying oil displacement agent has low interfacial tension, high emulsion stability time, and spontaneously emulsifies with crude oil, improving the oil-water mixing ability. It can be seen that the self-emulsifying oil displacement agent of this example can significantly increase the recovery factor. First, carry out water flooding on the oil-bearing low-permeability core, and the recovery rate is 41%, and then carry out self-emulsification flooding (that is, tertiary oil recovery). At this time, the recovery rate can be increased by 12%, and then the secondary water flooding is carried out to increase the recovery rate 3%. The total recovery rate is 56%.

When the amount of oil displacing agent used in this example is 3000mg/L, when the NaCl concentration is 10000-20000mg/L, the spontaneous emulsification effect is the best, and the oil sample can spontaneously enter the water phase immediately after adding, forming an emulsion. The emulsion has strong stability, and it still maintains a good emulsifying effect after standing for 30 minutes.

Put the oil displacing agent solution of this example into a test tube with a pipette gun, and let it stand in a thermostat at 45° C. for 2 hours. Finally, take out the test tube, use a pipette gun to take crude oil at a constant temperature of 45°C (water-oil ratio 9:1), add crude oil dropwise at a distance of 1 cm from the test tube, and observe the change of the solution in the test tube after the crude oil is added dropwise. The oil droplets spontaneously entered the water phase to form an emulsion, which indicated that the emulsifier had spontaneous emulsifying properties.

The above examples illustrate that the oil displacement agent for low-permeability reservoirs of the present invention has a better effect of enhancing oil recovery for low-permeability reservoirs. In addition, it can be clearly seen that the produced fluid exists in the form of emulsion during the displacement process, thereby expanding its application range and providing a new idea for using polymer surfactants in low-permeability reservoirs for tertiary oil recovery.

Claims (10)

1. a kind of low-permeability oil deposit oil displacement agent, which is characterized in that the low-permeability oil deposit oil displacement agent is pure and mild by modified poly ethylene The trimethylammonium bromide cationic surfactant of C12-C18 compounds；Wherein, the modified polyvinylalcohol and C12-C18 Trimethylammonium bromide cationic surfactant compounding mass ratio be 1:9-9:1.

2. low-permeability oil deposit oil displacement agent according to claim 1, which is characterized in that the pure and mild C12- of modified poly ethylene The compounding mass ratio of the trimethylammonium bromide cationic surfactant of C18 is 1:9,3:7,5:5,7:3 or 9:1.

3. low-permeability oil deposit oil displacement agent according to claim 1 or 2, which is characterized in that the front three bromide of the C12-C18 Change ammonium cationic surfactant is cetyl trimethylammonium bromide.

4. low-permeability oil deposit oil displacement agent according to claim 1, which is characterized in that the molecular weight of the modified polyvinylalcohol For 2000-3000.

5. low-permeability oil deposit oil displacement agent according to claim 1, which is characterized in that the modified polyvinylalcohol has hydrophobic Group and hydrophilic radical.

6. low-permeability oil deposit oil displacement agent according to claim 1 or 5, which is characterized in that the modified polyvinylalcohol be by Modifying agent carries out what hydrophobically modified obtained to polyvinyl alcohol.

7. low-permeability oil deposit oil displacement agent according to claim 6, which is characterized in that the modifying agent be bromohexadecane or 2,3- epoxypropyltrimethylchloride chloride；

Preferably, the modifying agent is bromohexadecane.

8. low-permeability oil deposit oil displacement agent according to claim 6, which is characterized in that the dosage of the modifying agent is polyethylene The 12.5%-17.5% of the quality of alcohol；

Preferably, the dosage of the modifying agent is the 15% of the quality of polyvinyl alcohol.

9. according to the described in any item low-permeability oil deposit oil displacement agents of claim 6-8, which is characterized in that the modified polyvinylalcohol Through the following steps that be prepared:

At 55 DEG C -75 DEG C, by modifying agent and polyvinyl alcohol, 40h-50h is reacted, the modified polyvinylalcohol is obtained.

10. the application of the described in any item low-permeability oil deposit oil displacement agents of claim 1-9, which is characterized in that the low-permeability oil deposit When oil displacement agent is used to emulsify low-permeability oil deposit, additive amount 3000mg/L.