Medium-phase microemulsion oil-displacing agent as well as preparation method and application thereof

Abstract

The invention provides a middle-phase microemulsion oil-displacing agent as well as a preparation method and application thereof. The middle-phase microemulsion oil-displacing agent comprises the following components: a main surfactant, a cosurfactant, an auxiliary agent and water, the main surfactant has a structural formula as shown in a formula I in the specification. In the invention, the main surfactant has excellent interfacial activity and crude oil adaptability and excellent temperature resistance and salt resistance, can form a middle-phase microemulsion with the cosurfactant, the auxiliary agent and water under the condition of low concentration, greatly improves the recovery efficiency, and has important significance for the development of different types of oil reservoirs.

Description

Technical Field

[0001] The invention belongs to the technical field of petroleum development and relates to a medium-phase microemulsion oil-displacing agent and a preparation method and application thereof. Background Art

[0002] Old oil fields are the cornerstone of domestic crude oil production stability and production increase. Most of the old oil fields in China have entered the high water content stage, and the problem of invalid water circulation is serious, which affects the economic benefits of oil field development. At the same time, the development level of most oil reservoirs is still low. Except for Daqing Changyuan, the water drive recovery of most oil reservoirs is below 40%. The development of tertiary oil recovery technology to further improve crude oil recovery is of vital significance for the development of old oil fields. Chemical flooding is one of the most promising tertiary oil recovery technologies, mainly including polymer flooding, strong alkali ternary composite flooding, weak alkali ternary composite flooding technology, binary composite flooding technology and other technologies. These technologies have been applied in Daqing, Shengli, Dagang, Xinjiang, Liaohe and other oil fields, and have shown good application prospects. The polymer flooding field test carried out in Daqing has increased the recovery rate by 8% to 12%, with good economic benefits, and has now entered the stage of industrial promotion. The field test of binary composite flooding has also achieved good results, with an average increase in recovery rate of 15%, which is one of the main technical directions for water flooding to improve recovery in Xinjiang, Liaohe and Dagang. However, after chemical flooding, there is still a large amount of residual oil remaining underground, which makes further tapping difficult. It is urgent to develop technologies that can significantly enhance oil recovery and realize deep tapping of the remaining oil in the reservoir.

[0003] The medium-phase microemulsion flooding technology has shown great potential in reducing residual oil saturation and significantly improving recovery. Microemulsion is a stable system formed by oil and water under the action of surfactants and additives. According to the different positions of the microemulsion in each phase, it can be divided into Winsor I microemulsion, Winsor II microemulsion and Winsor III microemulsion. Among them, Winsor III microemulsion, also known as medium-phase microemulsion, is an intermediate phase microemulsion formed by the mutual dissolution of oil and water. It is a bicontinuous structure rich in surfactants. The interfacial tension between this bicontinuous phase and oil and water is ultra-low, which makes it have the potential to significantly improve the recovery rate. In the later stage of water flooding development, the remaining oil is retained in the pores of the reservoir rock in the form of a discontinuous oil film. Capillary force is one of the key factors that bind crude oil and affect the development and utilization of the remaining oil. Under the optimal salt concentration conditions, the middle phase microemulsion surfactant can make oil and water miscible in equal proportions, and there is almost no interfacial tension between oil and water. The capillary force is ignored during the oil recovery process, and the mobilization of crude oil in small pores can be achieved to the greatest extent, so the oil recovery efficiency can reach more than 90%.

[0004] At present, medium-phase microemulsion has become the main technology for international oil companies to improve oil recovery, and a large number of field tests have been carried out, increasing oil recovery by more than 25%. However, the amount of surfactant used is more than 10%, and the high amount and high cost problems restrict the promotion and application of microemulsion flooding technology. my country also conducted research on microemulsion flooding in the 1980s and 1990s, and carried out high-concentration microemulsion flooding field tests in Daqing, Yumen and other oil fields and achieved good results, but it also faced the problem of high cost. Due to problems such as large dosage, it has not been widely promoted and applied.

[0005] Therefore, it is very necessary to design and develop new surfactants and oil-displacing agents, and systems that form middle-phase microemulsions at low concentrations and low dosages. Summary of the invention

[0006] In view of the shortcomings of the prior art, the object of the present invention is to provide a middle phase microemulsion oil displacement agent and its preparation method and application. The oil displacement agent provided by the present invention can form a stable middle phase microemulsion at a relatively low concentration, greatly improving the oil displacement efficiency and sweep efficiency, which is of great significance for the deep development of medium and high permeability old oil fields.

[0007] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a medium-phase microemulsion oil-displacing agent, the medium-phase microemulsion oil-displacing agent comprising the following components: a main surfactant, a co-surfactant, an auxiliary agent and water;

[0009] The main surfactant has the structural formula shown in the following formula I:

[0010]

[0011] In formula I, L is a linking group selected from C m H 2m , C p H 2p-2 or C q H 2q-8 ; m is an integer not less than 2 (e.g., 2, 3, 4, 5, 6, 7, 8, 9, 10, etc.), p is an integer not less than 4 (e.g., 4, 5, 6, 7, 8, 9, 10, 14, 16, 18, 20, etc.), q is an integer not less than 6 (e.g., 6, 8, 10, 14, 16, 18, 20, etc.);

[0012] R1 is a hydrophobic group, each occurrence of which is independently selected from alkane-C n H 2n+1 , olefin-C n H 2n-1 or alkyl aromatic hydrocarbon-C n H 2n-5; n is an integer of 6 to 22 (e.g., 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, etc.);

[0013] Each occurrence of R2 is independently selected from polyoxyethylene ether -(CH2CH2O) i -, Polyoxypropylene ether-(CH2CHCH3O) j -or a composition of polyoxyethylene ether and polyoxypropylene ether; i is an integer from 20 to 50 (for example, 20, 23, 25, 28, 30, 33, 35, 38, 40, 43, 45, 48, 50, etc.), j is an integer from 20 to 50 (for example, 20, 23, 25, 28, 30, 33, 35, 38, 40, 43, 45, 48, 50, etc.).

[0014] R3 is a hydrophilic group, each occurrence of which is independently selected from -CH2CO2 containing a sulfonic acid group or a carboxylic acid group - Na + 、-CH2CO2 - Na + 、-CH2PhCO2 - Na + 、-CH2CH2CH2CO2 - Na + 、-CH2CH2SO3 - Na + 、-CH2CH2CH2SO3 - Na + 、-CH2CH(OH)CH2SO3 - Na + or -CH2CH2CH2CH2SO3 - Na + .

[0015] In the present invention, the main surfactant has excellent interfacial activity and crude oil adaptability, excellent temperature and salt resistance, and can form a middle phase microemulsion with the co-surfactant, auxiliary agent and water under low concentration conditions, greatly improving the recovery rate, which is of great significance to the development of different types of oil reservoirs.

[0016] The medium-phase microemulsion oil-displacing agent provided by the present invention can achieve matching of the main surfactant with different types of crude oil by adjusting the length of the linking group and the polyether group according to the composition of the crude oil, thereby achieving the effect of greatly reducing the interfacial tension and emulsifying the crude oil.

[0017] Preferably, m is an integer of 2-6.

[0018] Preferably, n is an integer of 14-18.

[0019] Preferably, the primary surfactant has the following structural formula:

[0020]

[0021] Preferably, the primary surfactant is prepared by the following method:

[0022] (1) adding a dihalogenated hydrocarbon to an amine to react to obtain an intermediate I;

[0023]

[0024] (2) adding ethylene oxide and / or propylene oxide to intermediate I to react to obtain intermediate II;

[0025]

[0026] (3) adding a halogenated alkyl sulfonate or a halogenated alkyl carboxylate to the intermediate II for reaction to obtain the primary surfactant;

[0027]

[0028] Wherein, L, R1, R2, and R3 have the same defined ranges as above, and X is selected from chlorine, bromine, or iodine.

[0029] The present invention provides a main surfactant for a medium-phase microemulsion oil displacement agent prepared by using relatively common synthetic raw materials, halogenated hydrocarbons and amines, as raw materials and having high interfacial activity and high emulsification performance.

[0030] Preferably, step (1) specifically comprises the following steps: dissolving an amine in an organic solvent, heating to reflux, dropping a dihalogenated hydrocarbon into the amine, monitoring by TLC until the amine reaction is complete, and then washing, filtering and purifying the product to obtain intermediate I.

[0031] Preferably, the molar ratio of the amine to the dihalogenated hydrocarbon is (2.2-2.8):1, 2.2-2.8 can be, for example, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, etc.

[0032] Preferably, the reaction temperature in step (1) is 60-120°C, for example, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, etc.

[0033] Preferably, step (2) specifically comprises the following steps: adding intermediate I into a high-pressure reactor, filling with nitrogen to deoxygenate, adding a catalyst, heating, then adding ethylene oxide and / or propylene oxide, reacting, and purifying to obtain intermediate II.

[0034] Preferably, the molar ratio of intermediate I to ethylene oxide and / or propylene oxide is 1:(20-60), and 20-60 can be, for example, 20, 30, 40, 50, 60, etc.

[0035] Preferably, the reaction temperature in step (2) is 90-170°C, for example, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, etc.

[0036] Preferably, the reaction pressure in step (2) is 0.1-1 MPa, for example, 0.1 MPa, 0.2 MPa, 0.3 MPa, 0.5 MPa, 0.8 MPa, 1 MPa, etc.

[0037] Preferably, step (3) specifically comprises the following steps: adding intermediate II into a three-necked flask, adding halogenated alkyl sulfonate or halogenated alkyl carboxylate, and a catalyst, stirring, heating, and purifying after the reaction is complete to obtain the primary surfactant.

[0038] Preferably, the molar ratio of the intermediate II to the haloalkyl sulfonate or haloalkyl carboxylate is 1:(2-3.5), and 2-3.5 can be, for example, 2, 2.2, 2.3, 2.5, 2.8, 3, 3.4, 3.5, etc.

[0039] Preferably, the halogenated alkyl sulfonate or halogenated alkyl carboxylate comprises any one of sodium 2-chloroacetate, sodium 2-bromoacetate, sodium 3-chloropropionate, sodium 4-chlorobutyrate, sodium bromomethylbenzoate, sodium chlorosulfonate, sodium 2-chloroethylsulfonate, sodium 2-bromoethylsulfonate or sodium 3-chloropropylsulfonate, or a combination of at least two thereof.

[0040] Preferably, the reaction temperature in step (3) is 30-100°C, for example, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, etc.

[0041] Preferably, the co-surfactant comprises an anionic surfactant and / or a nonionic surfactant.

[0042] Preferably, the anionic surfactant includes any one of carboxylates, sulfonates, sulfates or phosphates, or a combination of at least two thereof.

[0043] Preferably, the nonionic surfactant comprises any one of alkyl polyether, alkanolamide or alkyl glycoside or a combination of at least two thereof.

[0044] Preferably, the auxiliary agent includes any one of alcohol, salt, polyelectrolyte or low molecular weight polymer, or a combination of at least two thereof.

[0045] Preferably, the alcohol comprises any one of methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, octanol, nonanol, decanol or dodecanol, or a combination of at least two thereof;

[0046] Preferably, the salt comprises any one or a combination of at least two of sodium chloride, sodium carbonate, sodium bicarbonate, sodium sulfate, potassium chloride, potassium carbonate, potassium sulfate, calcium chloride or magnesium chloride;

[0047] Preferably, the polyelectrolyte comprises any one or a combination of at least two of polyacrylic acid, polymethacrylic acid, polystyrene sulfonic acid (c), polyethylene sulfonic acid, polyethylene imine, polyethylene amine or polyvinyl pyridine;

[0048] Preferably, the low molecular weight polymer comprises any one of conventional partially hydrolyzed polyacrylamide, hydrophobically modified polyacrylamide, salt-tolerant polymer or attribute polymer, or a combination of at least two thereof.

[0049] Preferably, the medium-phase microemulsion oil-displacing agent comprises the following components by weight percentage:

[0050]

[0051] Preferably, the amount of the main surfactant in the middle phase microemulsion oil displacement agent can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, etc., calculated by weight percentage.

[0052] Preferably, the amount of the co-surfactant in the middle phase microemulsion oil-displacing agent can be 0.05%, 0.06%, 0.08%, 0.1%, 0.12%, 0.14%, 0.16%, 0.18%, 0.2%, etc., calculated by weight percentage.

[0053] Preferably, the amount of the auxiliary agent in the middle phase microemulsion oil displacement agent can be 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, etc., calculated by weight percentage.

[0054] In a second aspect, the present invention provides a method for preparing the medium-phase microemulsion oil-displacing agent as described in the first aspect, the preparation method comprising the following steps:

[0055] The main surfactant, the co-surfactant, the auxiliary agent and water are mixed to obtain the middle phase microemulsion oil displacement agent.

[0056] In a third aspect, the present invention provides a use of the medium-phase microemulsion oil displacement agent as described in the first aspect in oil field development.

[0057] Preferably, the medium-phase microemulsion oil-displacing agent can be used in combination with other displacement media, or can be used alone as an oil-displacing agent.

[0058] Preferably, the other displacement medium comprises a polymer and / or a gel.

[0059] Preferably, when the medium-phase microemulsion oil-displacing agent is used in combination with a polymer, the polymer slug can be injected first, and then the medium-phase microemulsion oil-displacing agent slug can be injected alternately. The medium-phase microemulsion oil-displacing agent and the polymer can also be formulated into a mixed liquid and injected into the ground at the same time to displace crude oil.

[0060] Preferably, when the middle phase microemulsion oil displacement agent is used in combination with the gel, the gel segment plug may be injected first, and then the middle phase microemulsion oil displacement agent segment plug may be injected alternately.

[0061] Preferably, the medium-phase microemulsion oil-displacing agent can be injected from a water well or an oil well as a displacement medium alone, and can be used in low-permeability and tight oil reservoirs to significantly increase the recovery rate.

[0062] Compared with the prior art, the present invention has the following beneficial effects:

[0063] (1) The intermediate phase microemulsion oil displacement agent provided by the present invention has high interfacial activity and strong crude oil emulsification ability, and can form intermediate phase microemulsion under low concentration conditions, thereby greatly improving the recovery rate.

[0064] (2) The medium-phase microemulsion oil-displacing agent provided by the present invention has good solubility, does not cause phase separation and precipitation, and is easy to prepare and use.

[0065] (3) The medium-phase microemulsion oil-displacing agent provided by the present invention has wide adaptability and can be used to improve the recovery rate of medium- and high-permeability oil reservoirs, low-permeability, ultra-low-permeability and tight oil reservoirs.

[0066] (4) The medium-phase microemulsion oil-displacing agent provided by the present invention has a simple preparation process, and its raw materials are cheap and readily available, so it is low in cost and easy to realize large-scale industrial production of the product, and has great application prospects and potential. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] Figure 1 The emulsion state of the mixed solution provided in Example 1.

[0068] Figure 2 The emulsion state of the mixed solution provided in Example 2.

[0069] Figure 3 The emulsion state of the mixed solution provided in Example 3. DETAILED DESCRIPTION

[0070] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0071] Preparation Example 1

[0072] This preparation example provides a primary surfactant having the following structural formula:

[0073]

[0074] The preparation method comprises the following steps:

[0075] 1) Preparation of intermediate I:

[0076] 0.28 mol of tetradecylamine and 80 mL of ethanol were added to a 250 mL three-necked flask, stirred at room temperature for 5 minutes, then heated to reflux, and 0.12 mol of 1,4-dibromobutane was slowly added dropwise using a constant pressure dropping funnel. After the addition was completed, the reaction was continued for 12 hours. After the reaction was completed, the mixture was transferred to a beaker, petroleum ether was added, and solids were obtained by suction filtration. The obtained solids were washed with ethyl acetate and petroleum ether for several times, and recrystallized from acetone and ethanol for three times to obtain a white solid, which was the hydrobromide of the product. The hydrobromide was dissolved in a 20% NaOH solution, extracted with anhydrous ether, and the organic phase was dried with anhydrous sodium sulfate, and then the solvent was removed by rotary evaporation, and further purified to obtain intermediate I.

[0077] 2) Preparation of intermediate II:

[0078] Add 0.1 mol of intermediate I and 0.1 mol of sodium hydroxide to a 250 mL autoclave at a time, and pass nitrogen while stirring to remove oxygen in the autoclave. Then heat to 145°C and pass cooling water, introduce ethylene oxide into the autoclave, keep the pressure of the autoclave at 0.5 MPa, and keep the temperature at 145°C, continue to add ethylene oxide to the designed reaction amount, continue the reaction until the pressure drops to near atmospheric pressure, stop heating, and finally add formic acid to neutralize potassium hydroxide to obtain intermediate II.

[0079] 3) Preparation and characterization of main surfactant:

[0080] Add 0.1 mol of intermediate II into a three-necked flask, heat and stir until melted, add 0.24 mol of sodium 3-chloropropanesulfonate, heat and stir for 30 minutes, then add 0.1 mol of sodium hydroxide, control the reaction temperature to 72° C., and continue the reaction for 16 hours to obtain the primary surfactant.

[0081] Preparation Example 2

[0082] This preparation example provides a primary surfactant having the following structural formula:

[0083]

[0084] The preparation method comprises the following steps:

[0085] 1) Preparation of intermediate I:

[0086] 0.30 mol hexadecylamine and 80 mL ethanol were added to a 250 mL three-necked flask, stirred, and then heated to reflux. 0.12 mol 1,2-dibromoethane was slowly added dropwise using a constant pressure dropping funnel. After the addition was completed, the reaction was continued for 8 hours. After the reaction was completed, the mixture was transferred to a beaker, petroleum ether was added, and solids were obtained by suction filtration. The obtained solids were washed with ethyl acetate and petroleum ether for several times, and recrystallized from acetone and ethanol for three times to obtain a white solid, which was the hydrobromide of the product. The hydrobromide was dissolved in a 20% NaOH solution, extracted with anhydrous ether, and the organic phase was dried with anhydrous sodium sulfate. The solvent was removed by rotary evaporation, and further purified to obtain intermediate I.

[0087] 2) Preparation of intermediate II:

[0088] Add 0.1 mol of intermediate I and 0.1 mol of sodium hydroxide to a 250 mL autoclave, and pass nitrogen while stirring to remove oxygen in the autoclave. Then raise the temperature to 155°C and pass cooling water, introduce ethylene oxide into the autoclave, keep the pressure of the autoclave at 0.6 MPa, and keep the temperature at 155°C, continue to add ethylene oxide to the designed reaction amount, continue the reaction until the pressure drops to near atmospheric pressure, stop heating, and finally add formic acid to neutralize the sodium hydroxide to obtain intermediate II.

[0089] 3) Preparation and characterization of main surfactant:

[0090] Add 0.05 mol of intermediate II into a three-necked flask, heat and stir until melted, add 0.13 mol of sodium 2-chloroethanesulfonate, heat and stir for 30 minutes, then add 0.05 mol of sodium hydroxide, control the reaction temperature to 92° C., and continue the reaction for 18 hours to obtain the primary surfactant.

[0091] Preparation Example 3

[0092] This preparation example provides a primary surfactant having the following structural formula:

[0093]

[0094] The preparation method comprises the following steps:

[0095] 1) Preparation of intermediate I:

[0096] 0.27 mol of octadecylamine and 90 mL of ethanol were added to a 250 mL three-necked flask, stirred, and then heated to reflux. 0.12 mol of 1,3-dibromopropane was slowly added dropwise using a constant pressure dropping funnel. After the addition was completed, the reaction was continued for 10 hours. After the reaction was completed, the mixture was transferred to a beaker, n-hexane was added, and solids were obtained by suction filtration. The obtained solids were washed with ethyl acetate and n-hexane for many times, and recrystallized from acetone and ethanol for three times to obtain a white solid, which was the hydrobromide of the product. The hydrobromide was dissolved in a 20% NaOH solution, extracted with anhydrous ether, and the organic phase was dried with anhydrous sodium sulfate. The solvent was removed by rotary evaporation, and further purified to obtain intermediate I.

[0097] 2) Preparation of intermediate II:

[0098] Add 0.1 mol of intermediate I and 0.1 mol of potassium hydroxide to a 250 mL autoclave, and pass nitrogen while stirring to remove oxygen in the autoclave. Then raise the temperature to 160°C and pass cooling water, introduce propylene oxide into the autoclave, keep the pressure of the autoclave at 0.6 MPa, and keep the temperature at 160°C, continue to add propylene oxide to the designed reaction amount, continue the reaction until the pressure drops to near atmospheric pressure, stop heating, and finally add formic acid to neutralize potassium hydroxide to obtain intermediate II.

[0099] 3) Preparation and characterization of main surfactant:

[0100] Add 0.05 mol of intermediate II into a three-necked flask, heat and stir until melted, add 0.12 mol of sodium 3-chloropropionate, heat and stir for 30 minutes, then add 0.05 mol of sodium hydroxide, control the reaction temperature to 72° C., and continue the reaction for 20 hours to obtain the primary surfactant.

[0101] Example 1

[0102] The main surfactant and heavy alkyl benzene sulfonate (CAS No. 68411-30-3) obtained in Preparation Example 1 are added successively into formation water and stirred evenly to be mixed with oil displacement surfactant solution, sodium chloride is added into the above-mentioned oil displacement surfactant solution, and the oil displacement agent having sodium chloride content of 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7% and 0.8% is mixed successively, wherein the content of the main surfactant is 0.22%, the content of heavy alkyl benzene sulfonate is 0.16%, and the formation water surplus. The contents in this embodiment and other embodiments refer to all weight percentages, which will not be repeated one by one.

[0103] The interfacial tension between the oil displacement agent and crude oil was tested using a TX500C spinning drop interfacial tension meter. The test temperature was 55°C and the test time was 2 hours. The test results are shown in Table 1.

[0104] The oil displacement agents with different salt concentrations were mixed with crude oil in a beaker at an oil-water volume ratio of 1:1, stirred, and the stirred mixture was poured into a graduated tube, and then placed in a 55°C thermostat to observe the emulsion state. Figure 1 shown.

[0105] It can be seen from the figure that the composite system can form an intermediate phase microemulsion under the condition of 0.4% to 0.7% salt concentration.

[0106] Table 1

[0107]

[0108]

[0109] Example 2

[0110] The main surfactant prepared in Preparation Example 2 and Daqing petroleum sulfonate were added to formation water in sequence and stirred evenly to prepare an oil-displacing surfactant solution. Sodium chloride was added to the above oil-displacing surfactant solution to prepare oil-displacing agents with sodium chloride contents of 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1% and 1.2%, respectively, wherein the content of the main surfactant was 0.25%, the content of Daqing petroleum sulfonate was 0.07%, and the balance was formation water.

[0111] The above-mentioned oil-displacing agents with different salt concentrations were mixed with oil and water from Daqing Oilfield at a volume ratio of 1:1 to obtain a mixed solution. The interfacial tension of the oil-displacing agent solution was tested using a TX500C spinning drop interfacial tension meter. The test temperature was 55°C and the test time was 2 hours. The test results are shown in Table 2.

[0112] The oil displacement agents with different salt concentrations were mixed with crude oil in a beaker at an oil-water volume ratio of 1:1, stirred, and the stirred mixture was poured into a graduated tube, and then placed in a 45°C thermostat to observe the emulsion state. Figure 2 shown.

[0113] It can be seen from the figure that the composite system can form an intermediate phase microemulsion under the condition of 0.7% to 1.0% salt concentration.

[0114] Table 2

[0115]

[0116]

[0117] Example 3

[0118] The main surfactant and octadecyl polyoxyethylene ether prepared in Preparation Example 3 were added to formation water in sequence and stirred evenly to prepare an oil-displacing surfactant solution. Sodium chloride was added to the above oil-displacing surfactant solution to prepare oil-displacing agents with sodium chloride contents of 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7% and 0.8%, respectively, wherein the content of the main surfactant was 0.28%, the content of octadecyl polyoxyethylene ether was 0.05%, and the balance was formation water.

[0119] The above-mentioned oil-displacing agents with different salt concentrations were mixed with the oil and water of Changqing Oilfield at a volume ratio of 1:1 to obtain a mixed solution. The interfacial tension of the oil-displacing agent solution was tested using a TX500C spinning drop interfacial tension meter. The test temperature was 55°C and the test time was 2 hours. The test results are shown in Table 3.

[0120] The oil displacement agents with different salt concentrations were mixed with crude oil in a beaker at an oil-water volume ratio of 1:1, stirred, and the stirred mixture was poured into a graduated tube, and then placed in a 55°C thermostat to observe the emulsion state. Figure 3 shown.

[0121] It can be seen from the figure that the composite system can form an intermediate phase microemulsion under the condition of 0.4% to 0.7% salt concentration.

[0122] Table 3

[0123]

[0124]

[0125] Test Example 1

[0126] The oil displacement efficiency of the oil displacement agent system prepared in Example 1 was evaluated by core flooding experiment. The specific steps are as follows: In the core saturated with oil, formation water was injected to carry out water flooding until the water content was 98%, then a 0.5PV oil displacement agent slug was injected, and finally a post-water flooding was carried out until the water content was 98%, and the produced oil, water, and injection pressure were recorded to calculate the recovery factor;

[0127] The oil and water used are the oil and water of Jilin Oilfield, the core used is 3.8*30cm Bailey core, the experimental temperature is 55°C, the displacement rate is 0.3mL / min, the oil displacement agent slug used is a mixture of the oil displacement agent system prepared in Example 1 (sodium chloride content is 0.5%) and a polymer, and the polymer used is partially hydrolyzed polyacrylamide, the molecular weight is 25 million, and the concentration is 0.12%. From the experimental results, it can be seen that the medium-phase microemulsion oil displacement system increases the recovery rate by 36.8% after water flooding, indicating that the medium-phase microemulsion oil displacement agent provided by the present invention has great advantages in the field of improving recovery rate.

[0128] Test Example 2

[0129] The oil displacement efficiency of the oil displacement agent system prepared in Example 1 was evaluated by core flooding experiment. The difference between this test example and test example 1 is that after injecting formation water for water flooding to 98% water content, 0.5PV of the oil displacement agent system prepared in Example 1 is first injected, then 0.5PV of polymer is injected, and finally post-water flooding is performed to 98% water content, and the produced oil, water, and injection pressure are recorded to calculate the recovery rate; the other conditions are the same as those in test example 1. The medium phase microemulsion oil flooding system increased the recovery rate by 33.2% after water flooding. It shows that changing the injection method can still significantly increase the recovery rate.

[0130] Test Example 3

[0131] The oil displacement efficiency of the oil displacement agent system prepared in Example 2 was evaluated by core flooding experiment. The specific steps are as follows: In the core saturated with oil, formation water was injected to carry out water flooding until the water content was 98%, then a 0.5PV oil displacement agent slug was injected, and finally a post-water flooding was carried out until the water content was 98%, and the produced oil, water, and injection pressure were recorded to calculate the recovery factor;

[0132] The oil and water used are the oil and water of Daqing Oilfield, the core used is 3.8*30cm Bailey core, the experimental temperature is 45°C, the displacement rate is 0.3mL / min, the oil displacement agent slug used is a mixture of the oil displacement agent system prepared in Example 2 (sodium chloride content is 0.9%) and a polymer, and the polymer used is partially hydrolyzed polyacrylamide, the molecular weight is 28 million, and the concentration is 0.10%. From the experimental results, it can be seen that the medium phase microemulsion oil displacement system has an enhanced recovery rate of 38.3% after water flooding.

[0133] Test Example 4

[0134] The oil displacement efficiency of the oil displacement agent system prepared in Example 3 was evaluated by core flooding experiment. The specific steps are as follows: In the core saturated with oil, formation water was injected to carry out water flooding until the water content was 98%, then a 0.5PV oil displacement agent slug was injected, and finally a post-water flooding was carried out until the water content was 98%, and the produced oil, water, and injection pressure were recorded to calculate the recovery factor;

[0135] The oil and water used are the oil and water of Changqing Oilfield, the core used is 3.8*30cm Bailey core, the experimental temperature is 55°C, the displacement rate is 0.3mL / min, the oil displacement agent slug used is a mixture of the oil displacement agent system prepared in Example 3 (the sodium chloride content is 0.5%) and a polymer, and the polymer used is salt-resistant polyacrylamide, the molecular weight is 20 million, and the concentration is 0.15%. From the experimental results, it can be seen that the medium phase microemulsion oil displacement system has an increased recovery rate of 37.2% after water flooding.

[0136] Comparative test example 1

[0137] The oil recovery efficiency of the binary flooding system was evaluated through core flooding experiments. The specific steps are as follows: In the oil-saturated core, formation water was injected to carry out water flooding until the water content was 98%, then a 0.5PV oil-displacing agent plug was injected, and finally a post-water flooding was carried out until the water content was 98%, and the produced oil, water, and injection pressure were recorded to calculate the recovery factor;

[0138] The oil and water used are from Jilin Oilfield, the core used is 3.8*30cm Bailey core, the experimental temperature is 55℃, the displacement rate is 0.3mL / min, the oil displacement agent segment plug used is a binary flooding system prepared by petroleum sulfonate and polymer with a mass ratio of 5:2, the polymer molecular weight used is 25 million, and the concentration is 0.12%. The binary flooding system can achieve ultra-low interfacial tension, but cannot form a mesophase microemulsion. From the experimental results, it can be seen that the oil displacement system that can form a mesophase microemulsion increases the recovery rate by 22.5% after water flooding.

[0139] Comparative test example 2

[0140] The oil recovery efficiency of the ternary flooding system was evaluated through core flooding experiments. The specific steps are as follows: In the oil-saturated core, formation water was injected to carry out water flooding until the water content was 98%, then a 0.5PV oil-displacing agent slug was injected, and finally a post-water flooding was carried out until the water content was 98%, and the produced oil, water, and injection pressure were recorded to calculate the recovery factor;

[0141] The oil and water used are from the Daqing Oilfield, the core used is a 3.8*30cm Bailey core, the experimental temperature is 45°C, the displacement rate is 0.3mL / min, and the oil displacement agent segment plug used is a ternary flooding system prepared with sodium carbonate, Daqing petroleum sulfonate and polymer (salt-resistant polyacrylamide) in a mass ratio of 10:3:1. The molecular weight of the polymer used is 28 million and the concentration is 0.10%. The ternary flooding system can achieve ultra-low interfacial tension, but cannot form an intermediate phase microemulsion. From the experimental results, it can be seen that the oil displacement system that can form an intermediate phase microemulsion increases the recovery rate by 26.1% after water flooding.

[0142] Comparative test example 3

[0143] The oil recovery efficiency of the binary flooding system was evaluated through core flooding experiments. The specific steps are as follows: In the oil-saturated core, formation water was injected to carry out water flooding until the water content was 98%, then a 0.5PV oil-displacing agent plug was injected, and finally a post-water flooding was carried out until the water content was 98%, and the produced oil, water, and injection pressure were recorded to calculate the recovery factor;

[0144] The oil and water used are from Changqing Oilfield, the core used is 3.8*30cm Bailey core, the experimental temperature is 55℃, the displacement rate is 0.3mL / min, and the oil displacement agent segment plug used is a binary flooding system prepared by Changqing petroleum sulfonate and polymer (hydrophobic associating polyacrylamide) with a mass ratio of 10:3. The molecular weight of the polymer used is 20 million and the concentration is 0.15%. The ternary flooding system can achieve ultra-low interfacial tension, but cannot form a mesophase microemulsion. From the experimental results, it can be seen that the oil displacement system that can form a mesophase microemulsion has an increased recovery rate of 21.7% after water flooding.

[0145] The oil displacement effects of the test examples of the present invention and the comparative test examples are shown in Table 4.

[0146] Table 4

[0147]

[0148] It can be seen that the main surfactant provided by the present invention has good emulsifying properties, can form an intermediate phase microemulsion under low concentration conditions, and greatly improve the recovery rate, and has great application prospects in the field of tertiary oil recovery.

[0149] The applicant declares that the present invention illustrates the medium-phase microemulsion oil-displacing agent and its preparation method and application through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned embodiments, that is, it does not mean that the present invention must rely on the above-mentioned embodiments to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of the raw materials selected by the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A medium phase microemulsion oil displacement agent, characterized in that: The medium-phase microemulsion oil displacement agent comprises the following components: a main surfactant, a co-surfactant, an auxiliary agent and water; The main surfactant has the structural formula shown in the following formula I: In Formula I, L is a linking group selected from C m H 2m , C p H 2p-2 or C q H 2q-8 ; m is an integer not less than 2, p is an integer not less than 4, and q is an integer not less than 6; R1 is a hydrophobic group, each occurrence of which is independently selected from -C n H 2n+1 , -C n H 2n-1 or -C n H 2n-5 ; n is an integer from 6 to 22; Each occurrence of R2 is independently selected from polyoxyethylene ether -(CH2CH2O) i -, Polyoxypropylene ether-(CH2CHCH3O) j - or a combination of polyoxyethylene ether and polyoxypropylene ether; i is an integer from 20 to 50, and j is an integer from 20 to 50; R3 is a hydrophilic group, each occurrence of which is independently selected from -CH2CO2 containing a sulfonic acid group or a carboxylic acid group - Na + 、-CH2CO2 - Na + 、-CH2PhCO2 - Na + 、-CH2CH2CH2CO2 - Na + 、-CH2CH2SO3 - Na + 、-CH2CH2CH2SO3 - Na + 、-CH2CH(OH)CH2SO3 - Na + or <h2 style=";text-align:left;direction:ltr">-CH2CH2CH2CH2SO3<h2 style=";text-align:left;direction:ltr"> - <h2 style=";text-align:left;direction:ltr"> Na<h2 style=";text-align:left;direction:ltr"> + <h2 style=";text-align:left;direction:ltr"> 。 2. The medium-phase microemulsion oil-displacing agent according to claim 1, characterized in that: m is an integer from 2 to 6; Preferably, n is an integer of 14-18.

3. The medium phase microemulsion oil displacing agent according to claim 1 or 2, characterized in that, The primary surfactant has the following structural formula:

4. The medium-phase microemulsion oil-displacing agent according to any one of claims 1 to 3, characterized in that: The main surfactant is prepared by the following method: (1) adding a dihalogenated hydrocarbon to an amine to react to obtain an intermediate I; (2) adding ethylene oxide and / or propylene oxide to intermediate I to react to obtain intermediate II; (3) adding a halogenated alkyl sulfonate or a halogenated alkyl carboxylate to the intermediate II for reaction to obtain the primary surfactant; Wherein, L, R1, R2, and R3 have the same definition as that of claim 1, and X is selected from chlorine, bromine, or iodine.

5. The medium phase microemulsion oil displacing agent according to claim 4, characterized in that: Step (1) specifically comprises the following steps: dissolving an amine in an organic solvent, heating to reflux, dropping a dihalogenated hydrocarbon into the amine, monitoring by TLC until the amine reaction is complete, and then washing, filtering and purifying the product to obtain an intermediate I; Preferably, the molar ratio of the amine to the dihalogenated hydrocarbon is (2.2-2.8):1; Preferably, the reaction temperature in step (1) is 60-120°C; Preferably, step (2) specifically comprises the following steps: adding intermediate I into a high-pressure reactor, filling with nitrogen to deoxygenate, adding a catalyst, heating, then adding ethylene oxide and / or propylene oxide, reacting, purifying, and obtaining intermediate II; Preferably, the molar ratio of intermediate I to ethylene oxide and / or propylene oxide is 1:(20-60); Preferably, the reaction temperature in step (2) is 90 to 170°C; Preferably, the reaction pressure in step (2) is 0.1-1 MPa; Preferably, step (3) specifically comprises the following steps: adding intermediate II into a three-necked flask, adding halogenated alkyl sulfonate or halogenated alkyl carboxylate, and a catalyst, stirring, heating, and purifying after the reaction is complete to obtain the primary surfactant; Preferably, the molar ratio of the intermediate II to the haloalkyl sulfonate or haloalkyl carboxylate is 1:(2-3.5); Preferably, the halogenated alkyl sulfonate or halogenated alkyl carboxylate comprises any one of sodium 2-chloroacetate, sodium 2-bromoacetate, sodium 3-chloropropionate, sodium 4-chlorobutyrate, sodium bromomethylbenzoate, sodium chlorosulfonate, sodium 2-chloroethylsulfonate, sodium 2-bromoethylsulfonate or sodium 3-chloropropylsulfonate, or a combination of at least two thereof; Preferably, the reaction temperature in step (3) is 30-100°C.

6. The medium-phase microemulsion oil-displacing agent according to any one of claims 1 to 5, characterized in that: The co-surfactant comprises an anionic surfactant and / or a nonionic surfactant; Preferably, the anionic surfactant comprises any one or a combination of at least two of carboxylates, sulfonates, sulfates or phosphates; Preferably, the nonionic surfactant comprises any one of alkyl polyether, alkanolamide or alkyl glycoside or a combination of at least two thereof.

7. The medium-phase microemulsion oil-displacing agent according to any one of claims 1 to 6, characterized in that: The auxiliary agent includes any one or a combination of at least two of alcohol, salt, polyelectrolyte or low molecular weight polymer; Preferably, the alcohol comprises any one of methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, octanol, nonanol, decanol or dodecanol, or a combination of at least two thereof; Preferably, the salt comprises any one or a combination of at least two of sodium chloride, sodium carbonate, sodium bicarbonate, sodium sulfate, potassium chloride, potassium carbonate, potassium sulfate, calcium chloride or magnesium chloride; Preferably, the polyelectrolyte comprises any one or a combination of at least two of polyacrylic acid, polymethacrylic acid, polystyrene sulfonic acid (c), polyethylene sulfonic acid, polyethylene imine, polyethylene amine or polyvinyl pyridine; Preferably, the low molecular weight polymer comprises any one of conventional partially hydrolyzed polyacrylamide, hydrophobically modified polyacrylamide, salt-tolerant polymer or attribute polymer, or a combination of at least two thereof.

8. The medium-phase microemulsion oil-displacing agent according to any one of claims 1 to 7, characterized in that: The medium-phase microemulsion oil-displacing agent comprises the following components by weight percentage:

9. A method for preparing a medium-phase microemulsion oil-displacing agent as claimed in any one of claims 1 to 8, characterized in that: The preparation method comprises the following steps: The main surfactant, the co-surfactant, the auxiliary agent and water are mixed to obtain the middle phase microemulsion oil displacement agent.

10. Use of the medium phase microemulsion oil displacement agent according to any one of claims 1 to 8 in oil field development; Preferably, the medium-phase microemulsion oil-displacing agent can be used in combination with other displacement media, or can be used alone as an oil-displacing agent; Preferably, the other displacement medium comprises a polymer and / or a gel; Preferably, when the medium-phase microemulsion oil-displacing agent is used in combination with a polymer, the polymer slug can be injected first, and then the medium-phase microemulsion oil-displacing agent slug can be injected alternately. The medium-phase microemulsion oil-displacing agent and the polymer can also be prepared into a mixed liquid and injected into the ground at the same time to displace crude oil. Preferably, when the middle phase microemulsion oil displacement agent is used in combination with the gel, the gel segment plug can be injected first, and then the middle phase microemulsion oil displacement agent segment plug can be injected alternately; Preferably, the medium-phase microemulsion oil-displacing agent can be injected from a water well or an oil well as a displacement medium alone, and can be used in low-permeability and tight oil reservoirs to significantly increase the recovery rate.

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