Ionic liquid-surfactant oil displacement system and preparation method and application thereof

Abstract

The present invention belongs to the field of oilfield chemical technology, and relates to an ionic liquid-surfactant flooding system and a preparation method and application thereof. The ionic liquid-surfactant flooding system of the present invention comprises, by weight percentage, 0.75-1.20wt% of ionic liquid, 0.30-0.60wt% of surfactant, and the rest is formation water. The ionic liquid-surfactant flooding system of the present invention has good temperature and salt resistance, can stably exist for about 35 days in formation water at 300°C and a salinity of 35000mg / L, and is suitable for the exploitation of heavy oil steam injection reservoirs.

Description

Technical Field

[0001] The invention belongs to the technical field of oilfield chemistry and relates to an ionic liquid-surfactant oil displacement system and a preparation method and application thereof. Background Art

[0002] Oil is known as the blood of industry and is an important strategic material. Its demand is increasing, while crude oil reserves are decreasing. Therefore, how to improve oil recovery has become a hot topic in today's research. Secondary oil recovery is the main method of oil reservoir exploitation today, but with the continuous deepening of secondary oil recovery, the exploitation capacity of some oil fields has approached or even reached its limit, and the original displacement method has gradually become ineffective, resulting in a significant reduction in crude oil recovery. Therefore, how to improve the efficiency of tertiary oil recovery after secondary oil recovery and recover the crude oil remaining underground is the key to improving recovery.

[0003] In recent years, surfactant flooding has become one of the effective methods for improving crude oil recovery as a highly potential tertiary oil recovery method due to its good oil recovery effect and wide application. At present, surfactant flooding agents mainly include cationic surfactants, anionic surfactants, nonionic surfactants and amphoteric surfactants. Although surfactant flooding has made great progress in the research of improving oil recovery, there are still many problems in the displacement process. Since the temperature of heavy oil steam injection development is as high as 300℃, and the salinity of formation water in heavy oil reservoirs is usually high, the stability of surfactants is poor under high temperature and high salt, and the surface activity decreases during the oil recovery process, which greatly reduces the oil recovery efficiency. For reservoirs with low permeability and non-uniform porosity, traditional surfactant flooding cannot effectively increase the viscosity of the displacement phase, resulting in a low sweep coefficient during the displacement process and the recovery rate cannot be greatly improved. In addition, surfactants are easily adsorbed, stagnant and interact with multivalent ions in the formation, resulting in poor oil recovery effect; and the surfactant molecules have long alkane chains and poor solubility, and organic solvents need to be added as co-solvents. Most organic solvents are not only volatile and cause environmental pollution, but also flammable.

[0004] The problems existing in the above-mentioned surfactant flooding process have brought a series of difficulties to the actual production and application of oil fields. Therefore, it is of great significance to seek a new temperature-resistant and salt-resistant oil recovery system suitable for thermal recovery. Summary of the invention

[0005] The purpose of the present invention is to provide an ionic liquid-surfactant oil displacement system and a preparation method and application thereof in view of the defects of the prior art.

[0006] Specifically, the ionic liquid-surfactant flooding system of the present invention comprises, by weight percentage, 0.75-1.20 wt % of ionic liquid, 0.30-0.60 wt % of surfactant, and the remainder being formation water.

[0007] The above-mentioned ionic liquid-surfactant flooding system comprises, by weight percentage, 0.75-1.20wt% of ionic liquid, 0.30-0.60wt% of surfactant, and the rest being formation water.

[0008] In the above-mentioned ionic liquid-surfactant flooding system, the ionic liquid is an alkyl imidazole ionic liquid, and its molecular structure is generally expressed as follows:

[0009]

[0010] Wherein, n=12, 14 or 16.

[0011] In the above-mentioned ionic liquid-surfactant flooding system, the surfactant is a cationic surfactant.

[0012] In the above-mentioned ionic liquid-surfactant flooding system, the cationic surfactant is one of dodecyltrimethylammonium chloride and hexadecyltrimethylammonium chloride.

[0013] In the above-mentioned ionic liquid-surfactant flooding system, the cationic surfactant is hexadecyltrimethylammonium chloride.

[0014] In the above-mentioned ionic liquid-surfactant flooding system, the formation water has a salinity of 20,000-40,000 mg / L and a calcium ion content of 1,500-4,000 mg / L.

[0015] In the above-mentioned ionic liquid-surfactant flooding system, the formation water has a salinity of 35000 mg / L and a calcium ion content of 2000 mg / L.

[0016] On the other hand, the present invention provides a method for preparing the above-mentioned ionic liquid-surfactant oil recovery system, comprising: weighing a formula amount of ionic liquid and surfactant, dissolving the surfactant with formation water at room temperature, and then mixing the surfactant evenly with the ionic liquid to obtain the ionic liquid-surfactant oil recovery system.

[0017] In yet another aspect, the present invention also provides the use of the above-mentioned ionic liquid-surfactant flooding system in tertiary oil recovery in oil fields.

[0018] The technical solution of the present invention has the following beneficial effects:

[0019] (1) The ionic liquid-surfactant flooding system of the present invention has good temperature and salt resistance and can stably exist for about 35 days in formation water at 300°C and a salinity of 35,000 mg / L, and is suitable for the exploitation of heavy oil steam injection reservoirs;

[0020] (2) The alkyl imidazole ionic liquid used in the present invention has a good synergistic effect with the surfactant, and the surface activity of the composite system is stronger, which can greatly reduce the oil-water interfacial tension and can reduce the oil-water interfacial tension to 10 -2 mN / m;

[0021] (3) The alkyl imidazole ionic liquid used in the present invention has more intermolecular and intramolecular forces, is a good polar / non-polar solvent, has a unique solubility for surfactants, reduces the adsorption and stagnation of surfactants during oil recovery, and can increase oil recovery efficiency by 12-15%;

[0022] (4) The alkyl imidazole ionic liquids used in the present invention have strong van der Waals forces and can form hydrogen bonds between the ionic liquids, so their viscosity is relatively large, which increases the viscosity of the composite oil displacement system, effectively improving the displacement phase viscosity and the sweep coefficient of the displacement process. DETAILED DESCRIPTION

[0023] In order to fully understand the purpose, features and effects of the present invention, the present invention is described in detail through the following specific embodiments. Except for the following contents, the process method of the present invention adopts conventional methods or devices in the art. Unless otherwise specified, the following terms have the meanings commonly understood by those skilled in the art.

[0024] When a numerical range is disclosed in the present invention, the above range is considered to be continuous and includes the minimum and maximum values ​​of the range, as well as each value between such minimum and maximum values. Further, when a range refers to an integer, each integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be merged. In other words, unless otherwise indicated, all ranges disclosed in the present invention should be understood to include any and all subranges included therein.

[0025] Specifically, the ionic liquid-surfactant oil recovery system provided by the present invention comprises: an ionic liquid, a surfactant and formation water.

[0026] In the oil displacement system of the present invention, the ionic liquid and the surfactant have good synergistic effects, the surface activity of the composite system is stronger, and the oil-water interfacial tension is greatly reduced. The following is a detailed introduction to each component in the oil displacement system:

[0027] Ionic Liquids

[0028] Ionic liquids refer to salts that are liquid at or near room temperature and are composed entirely of anions and cations, also known as low-temperature molten salts. Ionic liquids can maintain a relatively low vapor pressure at higher temperatures due to the large Coulomb force inside them, eliminating the problem of environmental pollution caused by volatile co-solvents during oil recovery.

[0029] Preferably, in the oil displacement system of the present invention, the ionic liquid is an alkyl imidazole ionic liquid, [Cnmim][Br] (n=12, 14, 16), and its molecular structure is as follows:

[0030]

[0031] The alkyl imidazole ionic liquid used in the present invention has a wide range of liquid states and can stably exist from room temperature to 300° C., so the oil displacement system has good physical and chemical stability. In addition, there is a strong van der Waals force between the alkyl imidazole ionic liquids, and hydrogen bonds can be formed between the ionic liquids, so the viscosity is relatively large, which increases the viscosity of the composite oil displacement system, effectively improving the displacement phase viscosity and the sweep coefficient of the displacement process.

[0032] Preferably, the concentration of the ionic liquid in the oil displacement system of the present invention is 0.75-1.20wt%. When the concentration is less than 0.75wt%, the hydrogen bonding between the ionic liquids is weakened, the viscosity of the oil displacement system does not increase significantly, and the sweep efficiency cannot be effectively improved. When the concentration is greater than 1.20wt%, as the concentration of the ionic liquid increases, the hydration water around the micro-micelles formed by the ionic liquid and the surfactant decreases and the chains curl up, the electrostatic repulsion between different groups is weakened, so that the original polymer long chain is further bent, resulting in a decrease in its viscosity and a decrease in the sweep coefficient.

[0033] More preferably, the concentration of the ionic liquid is between 0.80 wt% and 1.00 wt%.

[0034] Surfactants

[0035] Surfactant refers to a substance with fixed hydrophilic and lipophilic groups, which can be arranged in a directional manner on the surface of a solution and can significantly reduce the surface tension.

[0036] Among them, the surfactant used in the present invention is a cationic surfactant. Compared with other surfactants, cationic surfactants are more easily dissolved in ionic liquids, can reduce adsorption losses in formations, and have high salt resistance and chemical stability, and can be stored for a long time without decomposition.

[0037] Preferably, the cationic surfactant is one of dodecyltrimethylammonium chloride or hexadecyltrimethylammonium chloride.

[0038] Further preferably, the cationic surfactant is hexadecyltrimethylammonium chloride.

[0039] Wherein, the concentration of the surfactant in the oil displacement system of the present invention is 0.30-0.60wt%. When the concentration of the surfactant is less than 0.30wt%, the oil-water interfacial tension cannot be effectively reduced, and the improvement of the displacement efficiency is not obvious. When the concentration of the surfactant is greater than 0.60wt%, the excess surfactant forms a non-interfacial active component, which will increase the interfacial tension between oil and water and reduce the oil displacement effect.

[0040] Preferably, the concentration of the surfactant is 0.4 wt%-0.50 wt%.

[0041] Formation water

[0042] Formation water refers to the edge water and bottom water at the edge and bottom of the reservoir, interlayer water, and bound water in the same layer as crude oil.

[0043] The formation water used in the oil displacement system of the present invention is high-mineralization formation water. The use of high-mineralization formation water in the oil displacement system can indicate that the system does not fail in a high-salinity environment. The system has a high salt tolerance and is capable of achieving a high oil displacement efficiency within the salinity range.

[0044] Preferably, the mineralization of the formation water is 20000-40000 mg / L, and the calcium ion content is 1500-4000 mg / L.

[0045] Further preferably, the formation water has a mineralization of 35000 mg / L and a calcium ion content of 2000 mg / L.

[0046] On the other hand, the present invention also provides a method for preparing the above-mentioned ionic liquid-surfactant oil recovery system, comprising: weighing the formulated amount of ionic liquid and surfactant, dissolving the surfactant with formation water at room temperature, and then mixing the surfactant evenly with the ionic liquid to obtain the ionic liquid-surfactant oil recovery system.

[0047] The types and concentrations of the ionic liquid, surfactant and formation water are the same as those of the ionic liquid-surfactant flooding system provided in the first aspect of the present invention, and will not be described repeatedly herein.

[0048] Through practice, the ionic liquid-surfactant oil recovery system of the present invention has good temperature and salt resistance, can stably exist for about 35 days in formation water at 300°C and a salinity of 35,000 mg / L, and is suitable for the exploitation of heavy oil steam injection reservoirs.

[0049] Example

[0050] The present invention is further described below by way of examples, but the present invention is not limited to the scope of the examples. The experimental methods in the following examples without specifying specific conditions are carried out according to conventional methods and conditions. The raw materials used in the following examples are all conventionally purchased.

[0051] Example 1

[0052] At room temperature, 0.3g of hexadecyltrimethylammonium chloride was added to 98.95g of seawater, and after it was fully dissolved, 0.75g of ionic liquid [C12mim][Br] was added and mixed evenly to obtain the composite oil displacement system required for the experiment. The displacement experiment was carried out using a sand-filled tube model. The experimental temperature was 300°C, the reservoir formation temperature. First, water was driven until the volume percentage of the water content of the output fluid was greater than 98%, and then a 0.5PV composite oil displacement system segment was injected. Finally, subsequent water drive was carried out until the volume percentage of the water content was greater than 98% again. The displacement rate in the experiment was fixed at 0.5mL / min. The experimental measurement showed that the water drive oil displacement efficiency was 17.6%, the chemical drive oil displacement efficiency was 12.3%, and the total oil displacement efficiency was 29.9%.

[0053] Example 2

[0054] At room temperature, 0.55g of hexadecyltrimethylammonium chloride was added to 98.25g of seawater, and after it was fully dissolved, 1.2g of ionic liquid [C12mim][Br] was added and mixed evenly to obtain the composite oil displacement system required for the experiment. The displacement experiment was carried out using a sand-filled tube model. The experimental temperature was 300°C, the reservoir formation temperature. First, water was driven until the volume percentage of the water content of the output fluid was greater than 98%, and then a 0.5PV composite oil displacement system plug was injected. Finally, subsequent water drive was carried out until the volume percentage of the water content was greater than 98% again. The displacement rate in the experiment was fixed at 0.5mL / min. The experimental measurement showed that the water drive oil displacement efficiency was 17.4%, the chemical drive oil displacement efficiency was 13.5%, and the total oil displacement efficiency was 30.7%.

[0055] Example 3

[0056] At room temperature, 0.3g of hexadecyltrimethylammonium chloride was added to 98.95g of seawater, and after it was fully dissolved, 0.75g of ionic liquid [C14mim][Br] was added and mixed evenly to obtain the composite oil displacement system required for the experiment. The displacement experiment was carried out using a sand-filled tube model. The experimental temperature was 300°C, the reservoir formation temperature. First, water was driven until the volume percentage of the water content of the output fluid was greater than 98%, and then a 0.5PV composite oil displacement system plug was injected. Finally, subsequent water drive was carried out until the volume percentage of the water content was greater than 98% again. The displacement rate in the experiment was fixed at 0.5mL / min. The experimental measurement showed that the water drive oil displacement efficiency was 18.1%, the chemical drive oil displacement efficiency was 13.1%, and the total oil displacement efficiency was 31.2%.

[0057] Example 4

[0058] At room temperature, 0.60g of hexadecyltrimethylammonium chloride was added to 98.20g of seawater, and after it was fully dissolved, 1.2g of ionic liquid [C14mim][Br] was added and mixed evenly to obtain the composite oil displacement system required for the experiment. The displacement experiment was carried out using a sand-filled tube model. The experimental temperature was 300℃, the reservoir formation temperature. First, water was driven until the volume percentage of the water content of the output fluid was greater than 98%, and then a 0.5PV composite oil displacement system segment was injected. Finally, subsequent water drive was carried out until the volume percentage of the water content was greater than 98% again. The displacement rate in the experiment was fixed at 0.5mL / min. The experimental measurement showed that the water drive oil displacement efficiency was 17.9%, the chemical drive oil displacement efficiency was 14.2%, and the total oil displacement efficiency was 32.1%.

[0059] Example 5

[0060] At room temperature, 0.3g of hexadecyltrimethylammonium chloride was added to 98.95g of seawater, and after it was fully dissolved, 0.75g of ionic liquid [C16mim][Br] was added and mixed evenly to obtain the composite oil displacement system required for the experiment. The displacement experiment was carried out using a sand-filled tube model. The experimental temperature was 300°C, the reservoir formation temperature. First, water was driven until the volume percentage of the water content of the output fluid was greater than 98%, and then a 0.5PV composite oil displacement system segment was injected. Finally, subsequent water drive was carried out until the volume percentage of the water content was greater than 98% again. The displacement rate in the experiment was fixed at 0.5mL / min. The experimental measurement showed that the water drive oil displacement efficiency was 17.8%, the chemical drive oil displacement efficiency was 13.9%, and the total oil displacement efficiency was 31.7%.

[0061] Example 6

[0062] At room temperature, 0.6g of hexadecyltrimethylammonium chloride was added to 98.20g of seawater, and after it was fully dissolved, 1.2g of ionic liquid [C16mim][Br] was added and mixed evenly to obtain the composite oil displacement system required for the experiment. The displacement experiment was carried out using a sand-filled tube model. The experimental temperature was 300°C, the reservoir formation temperature. First, water was driven until the volume percentage of the water content of the output fluid was greater than 98%, and then a 0.5PV composite oil displacement system segment was injected. Finally, subsequent water drive was carried out until the volume percentage of the water content was greater than 98% again. The displacement rate in the experiment was fixed at 0.5mL / min. The experimental measurement showed that the water drive oil displacement efficiency was 18.2%, the chemical drive oil displacement efficiency was 14.7%, and the total oil displacement efficiency was 32.9%.

[0063] Comparative Example 1

[0064] At room temperature, 1.05g of hexadecyltrimethylammonium chloride was added to 98.95g of seawater to fully dissolve it to obtain the surfactant solution required for the experiment. A displacement experiment was carried out using a sand-filled tube model. The experimental temperature was 300°C, the reservoir formation temperature. First, water was driven until the volume percentage of the water content of the output fluid was greater than 98%, and then 0.5PV of surfactant drive plug was injected. Finally, subsequent water drive was carried out until the volume percentage of the water content was greater than 98% again. The displacement rate in the experiment was fixed at 0.5mL / min. The experimental measurement showed that the water drive oil recovery efficiency was 16.6%, the chemical drive oil recovery efficiency was 7.3%, and the total oil recovery efficiency was 23.9%.

[0065] Comparative Example 2

[0066] At room temperature, 1.75g ​​of hexadecyltrimethylammonium chloride was added to 98.25g of seawater to fully dissolve it to obtain the surfactant solution required for the experiment. A displacement experiment was carried out using a sand-filled tube model. The experimental temperature was 300°C, the reservoir formation temperature. First, water was driven until the volume percentage of the water content of the output fluid was greater than 98%, and then 0.5PV of surfactant drive segment plug was injected. Finally, subsequent water drive was carried out until the volume percentage of the water content was greater than 98% again. The displacement rate in the experiment was fixed at 0.5mL / min. The experimental measurement showed that the water drive oil recovery efficiency was 15.6%, the chemical drive oil recovery efficiency was 8.7%, and the total oil recovery efficiency was 24.3%.

[0067] Performance Testing

[0068] In order to investigate the temperature and salt resistance of the composite ionic liquid-surfactant flooding system, the long-term thermal stability of the system at formation temperature was evaluated.

[0069] Taking the oil displacement systems prepared in Comparative Example 1, Comparative Example 2 and Example 1 as examples, the oil displacement systems were placed at a temperature of 300° C. and the conditions of the composite solution systems were observed at time intervals of 1 d, 7 d, 14 d, 28 d and 35 d.

[0070] The experiment showed that comparative example 1 precipitated after 28 days of stability test, comparative example 2 precipitated after 14 days of test, and the system had no obvious change after 35 days, indicating that the composite oil displacement system has good stability under high temperature and high salt conditions.

[0071] Ionic liquid and hexadecyltrimethylammonium chloride have good synergistic effects and can significantly reduce the interfacial tension between oil and water. The effects of comparative example 1, comparative example 2 and the composite system on the interfacial tension between oil and water were determined by the hanging drop method. The specific test steps are as follows:

[0072] Test standard: SY / T 5370-2018 Surface and interfacial tension

[0073] Test steps: Place the sample receiver in an air constant temperature bath. Turn on the power supply and adjust the pointer on the thermostat to set the test temperature. Adjust the position and brightness of the light source and the focal length of the camera recorder to make the edge of the droplet image clear. Place the quartz tank and syringe with the sample (1-5mL of test liquid is inhaled, and the viscous or solid sample is placed in a beaker and heated to reduce the viscosity before inhalation) in an air constant temperature bath, and keep the needle vertical. The liquid is kept at a constant temperature for 60 minutes, and the micromotor is started to make the sample in the syringe form a droplet at the needle end of the syringe. When the droplet approaches the maximum diameter, press the shutter to record the droplet image.

[0074] The experimental results show that the oil-water interfacial tension of Comparative Example 1 and Comparative Example 2 is 0.235mN / m and 0.106mN / m respectively. Within the scope of investigation, the compound system can significantly reduce the oil-water interfacial tension. The interfacial tension is within 10 -2 mN / m, and the lowest interfacial tension is 0.054mN / m. Different ionic liquids have similar trends in reducing oil-water interfacial tension, that is, there is an optimal value. When the concentration of ionic liquid is higher than this value, the oil-water interfacial tension gradually increases. Therefore, the addition of an appropriate amount of ionic liquid can effectively reduce the oil-water interfacial tension and improve oil recovery efficiency.

[0075] The present invention has been disclosed above with preferred embodiments, but those skilled in the art should understand that these embodiments are only used to describe the present invention and should not be understood as limiting the scope of the present invention. It should be noted that all changes and substitutions equivalent to these embodiments should be deemed to be included in the scope of the claims of the present invention. Therefore, the scope of protection of the present invention should be based on the scope defined in the claims.

Claims

1. An ionic liquid-surfactant flooding system, characterized in that: In terms of weight percentage, it comprises: 0.75-1.20 wt% of ionic liquid, 0.30-0.60 wt% of surfactant, and the rest is formation water; Wherein, the ionic liquid is an alkyl imidazole ionic liquid, and its molecular structure is as follows: Where n=12, 14 or 16; Wherein, the surfactant is hexadecyltrimethylammonium chloride.

2. The ionic liquid-surfactant flooding system according to claim 1, characterized in that: Calculated by weight percentage, it includes: 0.80-1.00 wt% of ionic liquid, 0.40-0.50 wt% of surfactant, and the rest is formation water.

3. The ionic liquid-surfactant flooding system according to claim 1, characterized in that: The mineralization of the formation water is 20000-40000 mg / L, and the calcium ion content is 1500-4000 mg / L.

4. The ionic liquid-surfactant flooding system according to claim 3, characterized in that: The mineralization of the formation water is 35000 mg / L, and the calcium ion content is 2000 mg / L.

5. The method for preparing the ionic liquid-surfactant flooding system according to any one of claims 1 to 4, characterized in that: The method comprises: weighing a formula amount of ionic liquid and surfactant, dissolving the surfactant with formation water at room temperature, and then uniformly mixing the surfactant with the ionic liquid to obtain an ionic liquid-surfactant oil displacement system.

6. Use of the ionic liquid-surfactant flooding system according to any one of claims 1 to 4 or the ionic liquid-surfactant flooding system obtained by the preparation method according to claim 5 in tertiary oil recovery in an oil field.

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