In-situ emulsification oil displacement agent for low-permeability reservoir and preparation method of in-situ emulsification oil displacement agent

Abstract

The invention discloses a low-permeability reservoir in-situ emulsification oil-displacing agent and a preparation method thereof, and belongs to the technical field of oil extraction. The in-situ emulsification oil-displacing agent for the low-permeability reservoir is obtained by compounding an emulsification low-tension oil-displacing agent and a sulfonate type surface active agent and has good stability, product performance cannot be influenced by adsorption of a stratum or dilution of stratum water in a reservoir migration process, chemical synthesis of the product cannot be influenced by the adsorption of the stratum or dilution of the stratum water, and the stability of the product is greatly improved. The chromatographic separation phenomenon of a traditional compound system is avoided, and the method has a huge application prospect in low-permeability oil reservoirs. Meanwhile, the emulsified low-tension oil-displacing agent disclosed by the invention is prepared by the following steps: by taking montmorillonite as a base material, carrying out intercalation modification on unsaturated double-bond quaternary ammonium salt to obtain a nano montmorillonite lamellar material; the oil-displacing agent has high interfacial activity, can emulsify crude oil in situ and can obviously improve the oil-displacing efficiency, the product synthesis process is mild, complex reactions such as high temperature and high pressure are not involved, and environmental pollution is avoided.

Description

Technical Field

[0001] The invention belongs to the technical field of oil production, and in particular relates to an emulsified low-tension oil displacement agent and a preparation method thereof, a low-permeability oil reservoir in-situ emulsified oil displacement agent and a preparation method thereof, and applications in low-permeability oil fields. Background Art

[0002] In recent years, with the continuous increase in my country's oil demand and the continuous reduction in production of medium and high permeability oil fields, the exploration and development of low permeability / ultra-low permeability oil reservoirs has continued to increase. The key to my country's future increase and stability of crude oil production depends on the development of low permeability / ultra-low permeability oil fields to enhance recovery technology. Proven oil reserves show that the country's low permeability crude oil production accounts for 40% of the country's total annual production, and the proportion is further increasing.

[0003] However, low-permeability / ultra-low-permeability reservoirs have the characteristics of very dense reservoirs, low abundance, low porosity, low permeability, low reservoir pressure, strong pressure sensitivity, large crude oil seepage resistance, strong heterogeneity, developed fractures, and insufficient natural energy. These characteristics make it difficult to effectively develop low-permeability reservoirs, resulting in a low degree of development. Even through fracturing, water injection and other production-increasing measures, there are still characteristics such as low single-well production, rapid capacity decline, and difficulty in stabilizing production.

[0004] In my country's medium and high permeability oil reservoirs, large-scale binary composite flooding (polymer + surfactant) and ternary composite flooding (polymer + surfactant + alkali) have been carried out, and significant results have been achieved in Daqing Oilfield, Shengli Oilfield and other oilfields. However, in composite flooding, polymers are used to increase the oil-water mobility ratio; however, due to the low porosity and low permeability characteristics of low permeability oilfields, polymers have problems such as difficult injection, high injection pressure, and formation blockage. Therefore, low permeability oilfields have not been able to use composite flooding on a large scale so far, which greatly limits the application of polymer flooding in low permeability oilfields.

[0005] Therefore, in view of the special physical properties of low-permeability oil fields, the in-situ emulsified oil displacement agent developed by the present invention solves the problem of low recovery rate of low-permeability oil fields by modifying and grafting functional groups on nanomaterials and utilizing their emulsification properties. Summary of the invention

[0006] The main purpose of the present invention is to provide an emulsified low-tension oil-displacing agent, an in-situ emulsified oil-displacing agent for low-permeability oil reservoirs, and a preparation method and application thereof. The emulsified low-tension oil-displacing agent has good temperature resistance and salt resistance, and compared with traditional sulfonate surfactants, has the advantages of no biological toxicity, easy degradation, no damage to the formation, etc.; and the in-situ emulsified oil-displacing agent for low-permeability oil reservoirs obtained by compounding the emulsified low-tension oil-displacing agent with a sulfonate surfactant can improve the emulsification effect of the surfactant, and at the same time, reduce the oil-water interfacial tension, ultimately improve the crude oil recovery rate, and can be used in low-permeability oil fields.

[0007] In order to achieve the purpose of the present invention, the emulsified low tension oil displacement agent provided by the present invention is the reaction product of a hydrophilic monomer and an emulsifier monomer grafted onto the surface of a nano-montmorillonite sheet material; The nano-montmorillonite sheet material is an unsaturated double-bond quaternary ammonium salt intercalated montmorillonite substrate; The hydrophilic monomer is selected from at least one of maleic anhydride monomers; The emulsifier monomer is selected from at least one of alkylphenol polyoxyethylene ether monomers.

[0008] Preferably, the hydrophilic monomer is at least one of maleic anhydride, vinyl maleic anhydride, and styrene maleic anhydride.

[0009] Preferably, the emulsifier monomer is at least one of OP-4, OP-7, OP-10, OP-15, and OP-20.

[0010] Furthermore, the preparation method of the nano-montmorillonite sheet material comprises the following steps: S1. The montmorillonite substrate was dissolved in water and nitrogen was passed through for 30 min to deoxygenate to obtain solution A; S2. The unsaturated double bond quaternary ammonium salt was added to solution A and stirred for 30 min to obtain solution B; S3. Place solution B in a reaction device and carry out intercalation reaction at 60-80°C. After the reaction is complete, dry, grind and sieve to obtain a nano-montmorillonite sheet material.

[0011] The nano-montmorillonite sheet material of the present invention adopts unsaturated double-bond quaternary ammonium salt for intercalation modification, which is specifically manifested as follows: The interlayer spacing increases. Montmorillonite is a layered silicate mineral with exchangeable cations between the layers. Unsaturated double-bonded quaternary ammonium salts enter the interlayers of montmorillonite through cation exchange reactions. Due to their large molecular size, they will expand the lamellar structure of montmorillonite and increase the interlayer spacing.

[0012] The surface properties change. The surface of montmorillonite is originally hydrophilic. Unsaturated double-bond quaternary ammonium salt has lipophilic groups and unsaturated double bonds. After entering the interlayer, it will change the surface of montmorillonite from hydrophilic to hydrophobic, improving its compatibility with organic matter.

[0013] Local adjustment of crystal structure. The intercalation process may cause some bond angles and bond lengths in the montmorillonite crystal structure to change slightly to accommodate the inserted unsaturated double-bonded quaternary ammonium salt molecules, but the overall crystal structure type of montmorillonite usually remains unchanged.

[0014] Introducing unsaturated double bonds. The insertion of unsaturated double bond quaternary ammonium salt introduces unsaturated double bonds into the montmorillonite structure, providing active sites for subsequent chemical reactions.

[0015] Therefore, after the nano-montmorillonite sheet material is chemically grafted with the combined hydrophilic monomer and emulsifier monomer, the obtained emulsified low-tension oil displacement agent can reduce rock adsorption in the reservoir, prevent chromatographic separation, and reduce losses in formation conditions. It has anti-adsorption and anti-dilution effects, and also has high temperature resistance.

[0016] Furthermore, the montmorillonite substrate is selected from at least one of sodium-based montmorillonite, calcium-based montmorillonite, and magnesium-based montmorillonite; The unsaturated double-bond quaternary ammonium salt is selected from at least one of allyl hexadecyltrimethylammonium chloride, allyl tetradecyltrimethylammonium chloride and allyl dodecyltrimethylammonium chloride.

[0017] Furthermore, the mass ratio of the unsaturated double-bond quaternary ammonium salt to the montmorillonite substrate is (8-10):1.

[0018] Furthermore, in step S3, the temperature of the intercalation reaction is 60-80° C., and the reaction time is 8-12 h.

[0019] The preparation method of the emulsified low tension oil displacement agent provided by the present invention specifically comprises the following steps: P1. Add an appropriate amount of water to the hydrophilic monomer and the emulsifier monomer to dissolve them, and pass nitrogen to deoxygenate to obtain a mixture A; P2. Then the mixture A is placed in an oil bath at 60-70°C for reaction, and a reaction product is obtained after the reaction is complete; P3. The nano-montmorillonite sheet material is added to the reaction product obtained in step P2 and stirred until fully dissolved to obtain a mixture B; P4. The initiator is added to an appropriate amount of water to dissolve and deoxygenate to obtain an initiator solution; P5. Preheat mixture B at 45-55°C for 30-40 min, then drop the initiator solution into mixture B for 7-10 min, and then carry out grafting reaction to obtain an emulsified low-tension oil displacement agent.

[0020] The present invention is to first react and combine the hydrophilic monomer and the emulsifier monomer, and then chemically graft them to the surface or interlayer of the nano-montmorillonite sheet material. According to different needs, corresponding products can be designed to obtain, which is conducive to precise control, and can also improve material performance, expand the application field and market competitiveness of the product. The present invention first reacts the hydrophilic monomer and the emulsifier monomer to form an intermediate product with a specific structure and activity, so that when the nano-montmorillonite sheet material is subsequently grafted and modified, the reaction is relatively more orderly, the designability is stronger, and the reaction selectivity is higher. Because the reactants are designed and pre-reacted, they can be grafted to the surface or interlayer of the nano-montmorillonite sheet material more evenly and stably, the grafting rate may be higher, and the distribution of the grafted chain is more uniform.

[0021] If the hydrophilic monomer and the emulsifier monomer are directly added to the nano-montmorillonite sheet material (i.e., the hydrophilic monomer and the emulsifier monomer are not reacted and combined first), they may first undergo their own diffusion, adsorption and other processes in the system, and then react with the nano-montmorillonite sheet material. The initial stage of the reaction is relatively complex and disordered, resulting in relatively poor controllability of the reaction, and uneven grafting may occur. The distribution of the monomer in the system and the disorder of the reaction may lead to uneven length and distribution of the grafted chain, affecting the performance consistency of the final product. Therefore, the performance of the product obtained by directly adding the hydrophilic monomer and the emulsifier monomer may have certain volatility and uncertainty, which in turn affects the overall performance of the material. In other words, the controllability of the reaction is poor, and the product performance is unstable.

[0022] Furthermore, the mass ratio of the hydrophilic monomer, the emulsifier monomer, the initiator and the nano-montmorillonite sheet material is 1: (0.5-1.5): (0.008-0.025): (0.5-0.2).

[0023] Furthermore, the initiator is selected from at least one of potassium persulfate, ammonium persulfate and sodium persulfate.

[0024] Further, in the step P2, the reaction temperature is 60-70°C and the reaction time is 3-5h; In the step P5, the temperature of the grafting reaction is 55-80° C., and the reaction time is 5-8 hours; and the dripping time of the initiator solution is 7-10 minutes.

[0025] The present invention also provides an in-situ emulsified oil displacement agent for low-permeability oil reservoirs. The in-situ emulsified oil displacement agent comprises a sulfonate surfactant and the emulsified low-tension oil displacement agent provided above.

[0026] Furthermore, the sulfonate surfactant is selected from SYD-YTS of Xi'an Petroleum Oil and Gas Technology Co., Ltd.

[0027] Further, the mass ratio of the emulsified low tension oil displacement agent and the SYD-YTS is (2-4): (1-2); Preferably, the mass ratio of the emulsified low tension oil displacement agent to the SYD-YTS is 2:(1-2).

[0028] The method for preparing the low-permeability reservoir in-situ emulsified oil displacement agent provided by the present invention comprises: mixing a solution A (the solvent is water) containing the emulsified low-tension oil displacement agent and a solution B (the solvent is water) containing a sulfonate type surfactant to obtain the emulsified low-tension oil displacement agent.

[0029] In the solution A, the mass percentage content of the emulsified low tension oil displacement agent is 20%-40%; In the solution B, the mass percentage content of the sulfonate surfactant is 10%-20%.

[0030] The low permeability reservoir in-situ emulsified oil displacement agent provided by the present invention can be used in low permeability oil fields, and the interfacial tension is lower than that of a single surfactant under the conditions of low permeability block reservoirs such as Changqing Oilfield and Yanchang Oilfield, reflecting the gain effect of in-situ emulsified crude oil in low permeability reservoirs.

[0031] The working principle of the low permeability reservoir in-situ emulsification oil displacement agent provided by the present invention is: (1) Reduce the interfacial tension between oil and water: Sulfonate surfactant molecules have hydrophilic sulfonate groups and lipophilic hydrocarbon chains, which can reduce the surface free energy of the oil-water interface, thereby reducing the interfacial tension between oil and water. Emulsified low-tension emulsifiers can also be adsorbed at the oil-water interface and work synergistically with sulfonate surfactants to further reduce the interfacial tension between oil and water. When the two are compounded, molecules with different structures and properties complement each other, which can more effectively reduce the interfacial tension, making it easier for oil droplets to peel off the rock surface and disperse in water, thereby improving the efficiency of oil washing.

[0032] (2) Formation of mixed micelles: After compounding, sulfonate surfactants and emulsifying low tension emulsifier molecules can form mixed micelles. The formation of mixed micelles not only changes the critical micelle concentration (CMC) of the surfactant, usually reducing the CMC, but also changes the structure and properties of the micelles. This mixed micelle can more effectively solubilize various components in crude oil, including some insoluble colloids, asphaltene, etc., making the dispersion of crude oil in water more stable, which is beneficial to improving the recovery rate of crude oil.

[0033] (3) Changes in rock surface properties: After the sulfonate surfactant and emulsified low-tension emulsifier system are adsorbed on the rock surface, the wettability of the rock surface will change. The originally oil-wet rock surface may change to a hydrophilic or weakly oil-wet state, weakening the adhesion between the crude oil and the rock surface, making the crude oil easier to be displaced. At the same time, this change in wettability can also reduce the retention of crude oil in the rock pores and reduce the flow resistance of the oil phase.

[0034] If other surfactants (such as nonionic surfactants, cationic surfactants, etc.) are used to compound with the emulsified low tension oil displacement agent of the present invention, the effects on low permeability oil fields are as follows: (1) Differences in interfacial tension control effects: Other surfactants, such as nonionic surfactants and cationic surfactants, may have different abilities and effects in reducing oil-water interfacial tension compared with sulfonate surfactants and emulsified low-tension emulsifier compound systems. Nonionic surfactants have a weaker ability to reduce interfacial tension in some cases, and it is difficult to achieve extremely low interfacial tension values, which is not conducive to the stripping and recovery of oil droplets. Cationic surfactants may strongly adsorb the negative charges on the rock surface, resulting in an increase in the retention of surfactants on the rock surface, which not only wastes surfactants, but may also change the pore structure of the rock and affect the seepage performance of the fluid.

[0035] (2) Uncertainty in regulating rock wettability: Different types of surfactants have different regulating effects on rock wettability after compounding. Some surfactant compounds may not be able to effectively change the rock surface from oil-wet to water-wet, or may excessively change the wettability, making the rock surface too hydrophilic, causing the water phase to form a continuous phase in the pores, hindering the flow of the oil phase and reducing the oil recovery efficiency.

[0036] (3) Compatibility with formation fluids: Formation fluids in low-permeability oil fields (such as formation water, crude oil, etc.) have specific chemical compositions and properties. Other surfactant compound systems may have poor compatibility with formation fluids, and are prone to precipitation, flocculation, and other phenomena, blocking formation pores, reducing formation permeability, and affecting oil recovery effects. For example, cationic surfactants may react with anions in formation water to form insoluble salt precipitates.

[0037] (4) Impact on capillary pressure: In low permeability oil fields, capillary pressure plays an important role in the flow of fluids. Different surfactant compound systems have different effects on capillary pressure. Some compound systems may not be able to effectively reduce capillary pressure, making it difficult for crude oil to flow in the pores, while sulfonate surfactant and emulsified low tension emulsifier compound systems can more effectively reduce capillary pressure and promote the flow of crude oil by reducing interfacial tension and changing wettability.

[0038] The present invention has achieved the following beneficial effects: The emulsified low-tension oil displacement agent of the present invention is obtained by combining a hydrophilic monomer with an emulsifier monomer through chemical grafting modification on the surface of an unsaturated double-bond quaternary ammonium salt intercalated montmorillonite substrate, thereby reducing rock adsorption in the reservoir, preventing chromatographic separation, reducing losses in formation conditions, and having anti-adsorption and anti-dilution effects.

[0039] The present invention compounds an emulsified low-tension oil-displacing agent with a sulfonate-type surfactant for oil displacement, and the obtained low-permeability reservoir in-situ emulsified oil-displacing agent can improve the emulsification effect of the surfactant, reduce the oil-water interfacial tension, and improve the stripping ability of crude oil in the reservoir; through a multifunctional displacement instrument displacement experiment, it is proved that the low-permeability reservoir in-situ emulsified oil-displacing agent formed by the compound system of the emulsified low-tension oil-displacing agent and the sulfonate-type surfactant of the present invention can significantly improve the recovery rate.

[0040] The present invention forms a W / O emulsion with crude oil under reservoir conditions by compounding an emulsified low-tension oil displacement agent with a sulfonate surfactant for oil displacement (i.e., obtaining an in-situ emulsified oil displacement agent for low-permeability reservoirs), thereby improving the mobility ratio of the displacement phase and achieving the effect of controlling water and increasing oil production.

[0041] The low-permeability reservoir in-situ emulsified oil displacement agent of the present invention has an interfacial tension much lower than that of traditional surfactants under the conditions of low-permeability oil reservoirs in Changqing Oilfield, Yanchang Oilfield, etc., and the recovery rate can be increased by 24.2%. The possible reasons are: first, the ultra-low interfacial tension of the low-permeability reservoir in-situ emulsified oil displacement agent; second, the system emulsifies crude oil in the formation, which has the effect of controlling water and increasing oil; third, the system has little loss during the migration of the reservoir.

[0042] The product cost of the present invention is relatively cheap, and the montmorillonite nanomaterial has a good biological and environmental protection effect and is non-toxic to the formation; at the same time, the in-situ emulsified oil displacement agent has a uniform particle size, a low degree of chromatographic separation, low interfacial tension, and improves the recovery effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 is the chemical formula of the emulsified low tension oil displacement agent of the present invention; Figure 2 This is an interfacial tension curve diagram of an in-situ emulsified oil displacement agent for a low permeability reservoir at different concentrations and temperatures according to an embodiment of the present invention; Figure 3 This is a graph showing changes in the comprehensive emulsification index of an in-situ emulsified oil displacement agent for a low permeability reservoir at different concentrations according to an embodiment of the present invention; Figure 4 It is a working principle diagram of the displacement test of the low permeability reservoir in-situ emulsified oil displacement agent of the present invention; Figure 5 This is a displacement test diagram of an in-situ emulsified oil displacement agent for a low permeability reservoir in an embodiment of the present invention when the gas permeability is about 8 mD. DETAILED DESCRIPTION

[0044] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0045] Unless otherwise specified, the raw materials in the examples of this application were purchased from commercial sources. Unless otherwise specified, the test methods all adopted conventional methods, and the instrument settings all adopted the settings recommended by the manufacturer.

[0046] like Figure 1 As shown, it is the chemical formula of the emulsified low tension oil displacement agent of the present invention. The emulsified low tension oil displacement agent of the present invention is first subjected to intercalation reaction of unsaturated double bond quaternary ammonium salt on montmorillonite matrix to obtain nano-montmorillonite sheet material, then a hydrophilic monomer and an emulsifier monomer are used for reaction, and then the reaction product of the two is grafted onto the nano-montmorillonite sheet to obtain the obtained material. The obtained emulsified low tension oil displacement agent has no biological toxicity, is easy to degrade, does not damage the formation, and has good temperature resistance and salt resistance. The present invention compounds the prepared emulsified low tension oil displacement agent with a sulfonate surfactant to obtain an in-situ emulsified oil displacement agent (also called in-situ emulsified oil displacement agent) for low permeability reservoirs, which can improve the emulsification effect of the surfactant, reduce the oil-water interfacial tension, and ultimately improve the crude oil recovery rate.

[0047] The preparation principle of the above-mentioned emulsified low-tension oil displacement agent is as follows: (1) Nano-montmorillonite is a layered silicate clay mineral with a large specific surface area and surface charge, good adsorption and ion exchange properties, and provides a basis for surface grafting reaction; (2) Nano-montmorillonite can introduce reactive functional groups to make it easier to react with monomers; (3) The monomer undergoes initiation, chain growth and chain termination reactions, and finally forms a composite material in which the hydrophilic monomer and emulsifier monomer reaction products are grafted on the surface of the nano-montmorillonite sheet material.

[0048] The preparation method of the nano-montmorillonite sheet material in the embodiment of the present invention is: S1. Weigh 1g of sodium montmorillonite raw material (selected from Hongfa Bentonite Factory in Wolong District, Nanyang City: sodium montmorillonite mesh number is 200-400 mesh) and dissolve it in 100g of water. Stir at 1000rpm until the montmorillonite raw material is completely dissolved, and introduce nitrogen for 30min to completely deoxygenate. S2. Add 10 g of allyl hexadecyltrimethylammonium chloride to the above solution, stir for 30 min, then put the reaction solution into a three-necked flask and adjust the temperature to 80°C.

[0049] S3. After the temperature reaches 80°C, the reaction begins, and the reaction time is 10 hours.

[0050] S4. After the reaction is complete, dry, grind, and sieve through 200 meshes to obtain nano-montmorillonite sheet material for later use.

[0051] Example 1 Preparation of emulsified low tension oil displacement agent 1# The preparation method of the emulsified low tension oil displacement agent 1# of this embodiment 1 is as follows: (1) Weigh 10 g of hydrophilic monomer maleic anhydride (MAH) and 15 g of emulsifier monomer OP-10 into a three-necked flask, add 100 mL of deionized water, stir to dissolve, and pass nitrogen for 30 min to eliminate oxygen in the solution and the container.

[0052] (2) Place the three-necked flask in an oil bath and heat it. When the temperature reaches 60°C, start timing. The reaction time is 5 hours to obtain the reaction product.

[0053] (3) Weigh 5 g of nano-montmorillonite sheet nanomaterial and add it to the three-necked flask in step (2). Stir for 30 min to fully dissolve.

[0054] (4) Weigh 0.25 g of initiator potassium persulfate, add 50 g of deionized water, stir to dissolve, and pass nitrogen for 30 min to remove oxygen from the solution (initiator concentration 0.5 wt%).

[0055] (5) When the temperature in the flask reaches 55°C, the potassium persulfate solution prepared in step (4) is added dropwise using a constant pressure funnel. The reaction temperature is set to 80°C. The initiator is added dropwise over 10-15 min. When the temperature of the reaction solution reaches 80°C, the timing is started. The reaction is continued for 8 hours to obtain the final product, emulsified low tension oil displacement agent 1#.

[0056] Example 2 Preparation of emulsified low tension oil displacement agent 2# The preparation method of the emulsified low tension oil displacement agent 1# of this embodiment 2 is as follows: (1) Weigh 10 g of hydrophilic monomer maleic anhydride (MAH) and 10 g of emulsifier monomer OP-10 into a three-necked flask, add 100 mL of deionized water, stir to dissolve, and pass nitrogen for 30 min to eliminate oxygen in the solution and the container.

[0057] (2) Place the three-necked flask in an oil bath and heat it. When the temperature reaches 70°C, start timing. The reaction time is 5 hours to obtain the reaction product.

[0058] (3) Weigh 3 g of nano-montmorillonite sheet nanomaterial and add it to the three-necked flask in step (2). Stir for 30 min to fully dissolve.

[0059] (4) Weigh 0.25 g of initiator potassium persulfate, add 50 g of deionized water, stir to dissolve, and pass nitrogen for 30 min to remove oxygen from the solution (initiator concentration 0.5 wt%).

[0060] (5) When the temperature in the flask reaches 55°C, the potassium persulfate solution in step (4) is added dropwise using a constant pressure funnel. The reaction temperature is set to 70°C. The initiator is added dropwise over 10-15 min. When the temperature of the reaction solution reaches 70°C, the timing is started. The reaction is continued for 8 h to obtain the final product, emulsified low tension oil displacement agent 2#.

[0061] Example 3 Preparation of emulsified low tension oil displacement agent 3# The preparation method of the emulsified low tension oil displacement agent 3# of this embodiment 3 is as follows: (1) Weigh 10 g of hydrophilic monomer maleic anhydride (MAH) and 15 g of emulsifier monomer OP-10 into a three-necked flask, add 100 mL of deionized water, stir to dissolve, and pass nitrogen for 30 min to eliminate oxygen in the solution and the container.

[0062] (2) Place the three-necked flask in an oil bath and heat it. When the temperature reaches 50°C, start timing. The reaction time is 3 hours to obtain the reaction product.

[0063] (3) Weigh 5 g of nano-montmorillonite sheet nanomaterial and add it to the three-necked flask in step (2). Stir for 30 min to fully dissolve.

[0064] (4) Weigh 0.25 g of initiator potassium persulfate, add 50 g of deionized water, stir to dissolve, and pass nitrogen for 30 min to remove oxygen from the solution (initiator concentration 0.5 wt%).

[0065] (5) When the temperature in the flask reaches 55°C, the potassium persulfate solution in step (4) is added dropwise using a constant pressure funnel. The reaction temperature is set to 60°C. The initiator is added dropwise over 10-15 min. When the temperature of the reaction solution reaches 60°C, the timing is started. The reaction is continued for 6 h to obtain the final product, emulsified low tension oil displacement agent 3#.

[0066] Example 4 Preparation of emulsified low tension oil displacement agent 4# The preparation method of the emulsified low tension oil displacement agent 4# of this embodiment 4 is as follows: (1) Weigh 10 g of hydrophilic monomer maleic anhydride (MAH) and 10 g of emulsifier monomer OP-10 into a three-necked flask, add 100 mL of deionized water, stir to dissolve, and pass nitrogen for 30 min to eliminate oxygen in the solution and the container.

[0067] (2) Place the three-necked flask in an oil bath and heat it. When the temperature reaches 70°C, start timing. The reaction time is 4 hours to obtain the reaction product.

[0068] (3) Weigh 5 g of nano-montmorillonite sheet nanomaterial and add it to the three-necked flask in step (2). Stir for 30 min to fully dissolve.

[0069] (4) Weigh 0.25 g of initiator potassium persulfate, add 50 g of deionized water, stir to dissolve, and pass nitrogen for 30 min to remove oxygen from the solution (initiator concentration 0.5 wt%).

[0070] (5) When the temperature in the flask reaches 55°C, the potassium persulfate solution in step (4) is added dropwise using a constant pressure funnel. The reaction temperature is set to 60°C. The initiator is added dropwise over 10-15 min. When the temperature of the reaction solution reaches 60°C, the timing is started. The reaction is continued for 5 h to obtain the final product, emulsified low tension oil displacement agent 4#.

[0071] Example 5 Preparation of emulsified low tension oil displacement agent 5# The preparation method of the emulsified low tension oil displacement agent 5# of this embodiment 5 is as follows: (1) Weigh 10 g of hydrophilic monomer maleic anhydride (MAH) and 15 g of emulsifier monomer OP-5 into a three-necked flask, add 100 mL of deionized water, stir to dissolve, and pass nitrogen for 30 min to eliminate oxygen in the solution and the container.

[0072] (2) Place the three-necked flask in an oil bath and heat it. When the temperature reaches 60°C, start timing. The reaction time is 5 hours to obtain the reaction product.

[0073] (3) Weigh 3 g of nano-montmorillonite sheet nanomaterial and add it to the three-necked flask in step (2). Stir for 30 min to fully dissolve.

[0074] (4) Weigh 0.25 g of initiator potassium persulfate, add 50 g of deionized water, stir to dissolve, and pass nitrogen for 30 min to remove oxygen from the solution (initiator concentration 0.5 wt%).

[0075] (5) When the temperature in the flask reaches 55°C, the potassium persulfate solution prepared in step (4) is added dropwise using a constant pressure funnel. The reaction temperature is set to 80°C. The initiator is added dropwise over 10-15 min. When the temperature of the reaction solution reaches 80°C, the timing is started. The reaction is continued for 8 hours to obtain the final product, emulsified low tension oil displacement agent 5#.

[0076] Example 6 Preparation of emulsified low tension oil displacement agent 6# The preparation method of the emulsified low tension oil displacement agent 6# of this embodiment 6 is as follows: (1) Weigh 10 g of hydrophilic monomer maleic anhydride (MAH) and 15 g of emulsifier monomer OP-20 into a three-necked flask, add 100 mL of deionized water, stir to dissolve, and pass nitrogen for 30 min to eliminate oxygen in the solution and the container.

[0077] (2) Place the three-necked flask in an oil bath and heat it. When the temperature reaches 60°C, start timing. The reaction time is 5 hours to obtain the reaction product.

[0078] (3) Weigh 5 g of nano-montmorillonite sheet nanomaterial and add it to the three-necked flask in step (2). Stir for 30 min to fully dissolve.

[0079] (4) Weigh 0.25 g of initiator potassium persulfate, add 50 g of deionized water, stir to dissolve, and pass nitrogen for 30 min to remove oxygen from the solution (initiator concentration 0.5 wt%).

[0080] (5) When the temperature in the flask reaches 55°C, the potassium persulfate solution prepared in step (4) is added dropwise using a constant pressure funnel. The reaction temperature is set to 80°C. The initiator is added dropwise over 10-15 min. When the temperature of the reaction solution reaches 80°C, the timing is started. The reaction is continued for 8 h to obtain the final product, emulsified low tension oil displacement agent 6#.

[0081] Comparative Example 1: Monomer is directly added to the formula The preparation method of the oil displacing agent of this comparative example 1 is as follows: (1) Weigh 10 g of hydrophilic monomer maleic anhydride (MAH) and 15 g of emulsifier monomer OP-10 into a three-necked flask, add 100 mL of deionized water, stir to dissolve, and pass nitrogen for 30 min to eliminate oxygen in the solution and the container.

[0082] (2) Weigh 5 g of nano-montmorillonite sheet nanomaterial and add it to the three-necked flask in step (1). Stir for 30 min to fully dissolve.

[0083] (3) Weigh 0.25 g of initiator potassium persulfate, add 50 g of deionized water, stir to dissolve, and pass nitrogen for 30 min to remove oxygen from the solution (initiator concentration 0.5 wt%).

[0084] (4) When the temperature in the flask reaches 55°C, the potassium persulfate solution prepared in step (4) is added dropwise using a constant pressure funnel. The reaction temperature is set to 80°C. The initiator is added dropwise over 10-15 min. When the temperature of the reaction solution reaches 80°C, the timing is started. The reaction is continued for 8 h to obtain an oil displacement agent.

[0085] Interfacial tension test of emulsified low tension oil displacement agent: The emulsified low tension oil displacement agents prepared in Examples 1-6 and Comparative Example 1 were diluted with water to prepare emulsified low tension oil displacement agents of different concentrations, and their interfacial tension values ​​were tested at a test temperature of 60° C. The specific data are shown in Table 1 below.

[0086] Note: The on-site water is the water for injection of Changqing Oilfield No. 9 Plant; the preparation method of simulated water is 500.0g (accurate to 0.0001g) deionized water, start the stirrer to make the solution form a vortex, and add the following substances in order: 5.5g anhydrous calcium chloride, 4.5g magnesium chloride, 50.0g sodium chloride, and 20.0g potassium chloride (accurate to 0.0001g).

[0087]

[0088] Note: The existing oil displacement agent formula in the table is from a company's product purchased directly on the market.

[0089] As shown in Table 1, the interfacial tension of the emulsified low tension oil displacement agent 1# prepared in Example 1 is low under different concentration conditions. When the concentration is over 0.1%, the interfacial tension can reach 10 -2 mN / m, with excellent interfacial activity. At the same time, compared with the existing oil-displacing agent, the oil-displacing agent can only reach 10-2mN / m in simulated water, and the interfacial tension of the oil-displacing agent obtained by direct monomer addition is relatively high. Therefore, in the subsequent preparation of the in-situ emulsified oil-displacing agent, the 1# sample in Example 1 was used for preparation.

[0090] Example 7 Preparation of in-situ emulsified oil displacement agent ZRQ-01 The preparation method of the in-situ emulsified oil displacement agent ZRQ-01 of this embodiment 7 is as follows: Prepare 20wt% SYD-YTS solution (solvent is water) and 30wt% emulsified low tension oil displacement agent 1# solution (solvent is water) prepared in Example 1; mix the SYD-YTS solution and 1# solution at a solution mass ratio of 1:3, stir at 50°C for 30min until the solution is mixed evenly and no obvious stratification occurs, and then obtain the in-situ emulsified oil displacement agent ZRQ-01.

[0091] Example 8 Preparation of in-situ emulsified oil displacement agent ZRQ-02 The preparation method of the in-situ emulsified oil displacement agent ZRQ-02 of this embodiment 8 is as follows: Prepare 20wt% SYD-YTS solution (solvent is water) and 30wt% emulsified low tension oil displacement agent 1# solution (solvent is water) prepared in Example 1; mix the SYD-YTS solution and 1# solution at a solution mass ratio of 1:2, stir at 50°C for 30min until the solution is mixed evenly and no obvious stratification occurs, and the in-situ emulsified oil displacement agent ZRQ-02 can be obtained.

[0092] Example 9 Preparation of in-situ emulsified oil displacement agent ZRQ-03 The preparation method of the in-situ emulsified oil displacement agent ZRQ-03 of this embodiment 9 is as follows: Prepare 20wt% SYD-YTS solution (solvent is water) and 30wt% emulsified low tension oil displacement agent 1# solution (solvent is water) prepared in Example 1; mix the SYD-YTS solution and 1# solution in a solution mass ratio of 1:1, stir at 50°C for 30min until the solution is mixed evenly and no obvious stratification occurs, and the in-situ emulsified oil displacement agent ZRQ-03 can be obtained.

[0093] Comparative Example 2 Preparation of in-situ emulsified oil displacement agent ZRQ-04 The preparation method of the in-situ emulsified oil displacement agent ZRQ-04 of this comparative example 2 is as follows: Prepare 20wt% of anionic surfactant Y1 solution (solvent is water) and 30wt% of emulsified low tension oil displacement agent 1# solution (solvent is water) prepared in Example 1; mix the Y1 solution and 1# solution in a solution mass ratio of 1:1, stir at 50°C for 30min until the solution is mixed evenly and no obvious stratification occurs, and the in-situ emulsified oil displacement agent ZRQ-04 can be obtained.

[0094] Comparative Example 3 Preparation of in-situ emulsified oil displacement agent ZRQ-05 The preparation method of the in-situ emulsified oil displacement agent ZRQ-05 of this comparative example 3 is as follows: Prepare 20wt% of cationic surfactant Y2 solution (solvent is water) and 30wt% of emulsified low tension oil displacement agent 1# solution (solvent is water) prepared in Example 1; mix Y2 solution and 1# solution in a solution mass ratio of 1:1, stir at 50°C for 30min until the solution is mixed evenly and no obvious stratification occurs, and the in-situ emulsified oil displacement agent ZRQ-05 can be obtained.

[0095] Performance testing of in-situ emulsified oil displacement agent: 1. In-situ emulsified oil displacement agent interfacial tension test The in-situ emulsified oil displacement agents prepared in Examples 7-9 and Comparative Examples 1-2 were diluted with water to prepare in-situ emulsified oil displacement agents of different concentrations, and their interfacial tension values ​​were tested at a test temperature of 60° C. The specific data are shown in Table 2 below.

[0096] like Figure 2 Shown is the interfacial tension curve of in-situ emulsified oil displacement agent at different concentrations and different temperatures (50°C, 70°C and 90°C).

[0097] Note: The on-site water is the water for injection of Changqing Oilfield No. 9 Plant; the preparation method of simulated water is 500.0g (accurate to 0.0001g) deionized water, start the stirrer to make the solution form a vortex, and add the following substances in order: 5.5g anhydrous calcium chloride, 4.5g magnesium chloride, 50.0g sodium chloride, and 20.0g potassium chloride (accurate to 0.0001g).

[0098]

[0099] Note: The SYD-YTS in Table 2 is the test data of using sulfonate surfactant alone as an oil displacement agent.

[0100] As can be seen from Table 2, the in-situ emulsified oil displacement agents obtained with different concentration ratios have reduced interfacial tension. Among them, the interfacial tension of ZRQ-01 can reach an ultra-low level when the concentration reaches 0.1% to 0.2%, that is, 10 -3 mN / m, it has excellent interfacial activity. However, when used in combination with other types of surfactants, the interfacial tension effect can only reach 10 -2 mN / m, the interfacial tension of sulfonate surfactant alone as an oil displacement agent can reach 10 -3 mN / m. The development of this product has a significant effect on improving the recovery rate of low permeability / ultra-low permeability oil fields.

[0101] from Figure 2 It can be seen that the higher the test temperature, the greater the interfacial tension of the in-situ emulsified oil-displacing agent of the present invention; the lower the concentration of the in-situ emulsified oil-displacing agent, the lower its interfacial tension.

[0102] 2. Evaluation of emulsification performance of in-situ emulsified oil displacement agent (1) Emulsion preparation In a 100 mL stoppered conical flask, weigh m3g of in-situ emulsified oil displacement agent (calculated according to the active matter content c, m3=100*10% / c, accurate to 0.01g), add m4g of simulated water (m4=100-m3), put in a magnetic stirring bar, place it on a magnetic stirrer and stir evenly for standby use.

[0103] Weigh crude oil W0 (about 50.00 g, accurate to 0.01 g) in a 100 mL beaker, add the above-mentioned in-situ emulsified oil displacement agent solution WS (about 50.00 g, accurate to 0.01 g), stir at a speed of 1400 r / min to 1500 r / min for 30 min, and use the prepared emulsified mixture immediately.

[0104] (2) Emulsifying power Add 25 mL of simulated water to a 50 mL volumetric flask, then add the newly prepared emulsified mixture specified in (1) (m9 about 0.50 g, accurate to 0.01 g), and then make up to the mark with simulated water. Transfer to a 60 mL separatory funnel and shake 200 times. Place it vertically on a stand and let it stand for 30 seconds. Place the lower aqueous phase in a beaker and use a pipette to draw the upper 10 mL of emulsion into another separatory funnel. Use a volumetric flask to measure 50 mL of carbon tetrachloride and extract it 3 to 5 times. Cover and shake each time. If the extract is turbid, add anhydrous sodium sulfate to dehydrate it so that the solution becomes a brown transparent liquid. Collect the extract in a volumetric flask.

[0105] The oil content was determined according to HJ 637-2012 "Water quality - Determination of petroleum, animal and vegetable oils - Infrared spectrophotometry". The determination was performed three times in parallel, and the arithmetic mean of the three times was taken as the determination result.

[0106] The emulsifying force is calculated according to formula (3).

[0107] …… ... Where: F e is the emulsifying power, %; W0 is the weight of crude oil, g; W S is the mass of 10% surfactant solution weighed, g; C0 is the oil concentration in the emulsion, C0=50%; m9 is the mass of the emulsified mixture weighed, g.

[0108] Note: The above results are automatically calculated by the instrument system.

[0109] (3) Emulsification comprehensive index Use a pipette to take 10 mL of the emulsion prepared in (1) into a graduated tube and keep it at 50°C for 1 h. Read the volume of water separated (V1) and the water separation rate (S). w According to formula (4), the emulsion stability S te Calculate according to the following formula (5). Parallel measurements were performed three times, and the difference between the three measurements did not exceed 1%. The arithmetic mean of the three measurements was taken as the measurement result.

[0110] …… ... S te = (1-S w )…… ... Where: V1 is the amount of water separated from the emulsion after standing and keeping warm, mL; W S is the mass of 10% surfactant solution weighed, g; c is the active matter content of surfactant, %; S w is the water separation rate, %; S te is emulsion stability, %.

[0111] Note: Since the density of water is considered to be 1g / cm3, the volume and mass of water read are numerically equal.

[0112] The comprehensive emulsification index is calculated according to formula (6): …… ... Where: f e is the emulsifying power, %; S te is emulsion stability, %; S ei Is the comprehensive emulsification index, %.

[0113] like Figure 3 As shown, it is the comprehensive emulsification index of three in-situ emulsification oil displacement agents (i.e., ZRQ-01, ZRQ-02 and ZRQ-03), among which ZRQ-01 has the best emulsification performance.

[0114] 3. Long-term stability of in-situ emulsified oil displacement agent The in-situ emulsified oil displacement agent ZRQ-01 sample prepared in Example 5 was diluted with simulated water to a concentration of 0.2%, placed in a 60°C oven, and its particle size and interfacial tension were continuously tracked and observed. From Table 3 below, we can see that after 35 days of continuous observation, the interfacial tension and particle size of the in-situ emulsified oil displacement agent ZRQ-01 sample have almost no change, and can still be used for oil displacement.

[0115] Table 3 Stability test results of in-situ emulsified oil displacement agent

[0116] In-situ emulsified oil displacement agent displacement performance test In order to better simulate the effect of in-situ emulsified oil displacement agent in the reservoir, the displacement performance test was carried out in the core displacement instrument.

[0117] (1) Experimental water: simulated mineral water.

[0118] (2) Experimental oil: Dehydrated Changqing crude oil was mixed with kerosene. The viscosity of underground crude oil was 37.2 mPa.s (60°C).

[0119] (3) Injection system: In-situ emulsified oil displacement agent ZRQ-01, the performance test of which is shown in Table 4 below.

[0120]

[0121] The experimental steps of displacement performance test are as follows: (1) Take the dried core and weigh its dry weight. After vacuum saturation with simulated water, weigh its wet weight and calculate the pore volume.

[0122] (2) Water permeability test (not performed this time): Inject water at a rate of 0.5 mL / min. After the injection pressure stabilizes, calculate the water permeability of the core.

[0123] (3) Oil saturation: Place the core in a 55°C oven to saturate it with crude oil until the produced fluid contains no water. Record the amount of produced water and calculate the oil saturation.

[0124] (4) Water flooding: Water flooding was performed at a rate of 0.1 mL / min. The liquid production, water production, oil production and pressure were recorded at regular intervals until the comprehensive water content reached 98%.

[0125] (5) Agent flooding: Prepare 0.8 PV of the prepared flooding agent at a rate of 0.1 mL / min, and record the liquid production, water production, oil production and pressure at regular intervals.

[0126] (6) Subsequent water flooding: Water flooding was performed at a rate of 0.1 mL / min. The liquid production, water production, oil production and pressure were recorded at regular intervals until the comprehensive water content reached 98%.

[0127] The experimental results and data analysis are shown in Tables 5, 6 and 7 below.

[0128]

[0129]

[0130]

[0131] like Figure 4 As shown in the figure, it is the working principle diagram of the displacement instrument. Figure 5This is a displacement test diagram of the in-situ emulsified oil displacement agent ZRQ-01. From the displacement data, it can be seen that the pressure increased significantly during the migration of the oil displacement agent, from the initial 4.9MPa to 9.9MPa, and finally to 14.7MPa. This is because ZRQ-01 emulsified with crude oil in situ to form a W / O emulsion, which then played a role in profile adjustment / displacement adjustment in the deep, and ultimately increased the oil recovery rate.

[0132] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0133] The above embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present invention. It should be pointed out that, for those of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention.

Claims

1. An emulsified low tension oil displacement agent, characterized in that: The emulsified low-tension oil displacement agent is a reaction product of a hydrophilic monomer and an emulsifier monomer grafted onto the surface of a nano-montmorillonite sheet material; The nano-montmorillonite sheet material is an unsaturated double-bond quaternary ammonium salt intercalated montmorillonite substrate; The hydrophilic monomer is selected from at least one of maleic anhydride monomers; The emulsifier monomer is selected from at least one of alkylphenol polyoxyethylene ether monomers.

2. The emulsified low tension oil displacement agent according to claim 1, characterized in that: The preparation method of the nano-montmorillonite sheet material comprises the following steps: S1. The montmorillonite substrate was dissolved in water and nitrogen was passed through for 30-50 min to deoxygenate to obtain solution A; S2. The unsaturated double bond quaternary ammonium salt was added to solution A and stirred for 30-50 min to obtain solution B; S3. Place solution B in a reaction device for intercalation reaction. After the reaction is complete, dry, grind and sieve to obtain nano-montmorillonite sheet material.

3. The emulsified low tension oil displacement agent according to claim 2, characterized in that: The montmorillonite substrate is selected from at least one of sodium-based montmorillonite, calcium-based montmorillonite and magnesium-based montmorillonite; The unsaturated double-bond quaternary ammonium salt is selected from at least one of allyl hexadecyl trimethyl ammonium chloride, allyl tetradecyl trimethyl ammonium chloride, and allyl dodecyl trimethyl ammonium chloride; The mass ratio of the unsaturated double-bond quaternary ammonium salt to the montmorillonite substrate is (8-10):

1.

4. A method for preparing an emulsified low tension oil displacement agent as claimed in any one of claims 1 to 3, characterized in that: The specific steps include: P1. Add an appropriate amount of water to the hydrophilic monomer and the emulsifier monomer to dissolve them, and pass nitrogen to deoxygenate to obtain a mixture A; P2. Then the mixture A is placed in an oil bath to react to obtain a reaction product; P3. The nano-montmorillonite sheet material is added to the reaction product obtained in step P2 and stirred until fully dissolved to obtain a mixture B; P4. The initiator is added to an appropriate amount of water for dissolution, deoxygenation, to obtain an initiator solution; P5. Preheat mixture B at 45-55°C for 30-40 min, then drop the initiator solution into mixture B for 7-10 min, and then carry out grafting reaction to obtain an emulsified low-tension oil displacement agent.

5. The method for preparing the emulsified low tension oil displacement agent according to claim 4, characterized in that: The mass ratio of the hydrophilic monomer, emulsifier monomer, initiator and nano-montmorillonite sheet material is 1: (0.5-1.5): (0.008-0.025): (0.5-0.2); The initiator is selected from at least one of potassium persulfate, ammonium persulfate and sodium persulfate.

6. The method for preparing the emulsified low tension oil displacement agent according to claim 4, characterized in that: In the step P2, the reaction temperature is 60-70°C and the reaction time is 3-5h; In the step P5, the temperature of the grafting reaction is 55-80° C., and the reaction time is 5-8 hours.

7. An in-situ emulsified oil displacement agent for a low permeability reservoir, wherein the low permeability reservoir original emulsified oil displacement agent comprises a sulfonate surfactant and the emulsified low tension oil displacement agent described in any one of claims 1 to 3, or the emulsified low tension oil displacement agent prepared by the preparation method described in any one of claims 5 to 6.

8. The low permeability reservoir in-situ emulsification oil displacement agent according to claim 7, characterized in that: The mass ratio of the emulsified low tension oil displacement agent to the SYD-YTS is (2-4): (1-2).

9. A method for preparing an in-situ emulsified oil displacement agent for low permeability reservoirs according to any one of claims 7 to 8, characterized in that: include: The solution A containing the emulsified low tension oil displacement agent and the solution B containing the sulfonate type surfactant are mixed to obtain; In the solution A, the mass percentage content of the emulsified low tension oil displacement agent is 20%-40%; In the solution B, the mass percentage content of the sulfonate surfactant is 10%-20%.

10. Use of an in-situ emulsified oil displacement agent for low permeability oil reservoirs according to any one of claims 7 to 8, or an in-situ emulsified oil displacement agent obtained by the preparation method described in claim 9 in low permeability oil fields.

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