Middle-phase microemulsion, method for oil displacement using same, and use of middle-phase microemulsion

Abstract

Disclosed in the present invention are a middle-phase microemulsion, a method for oil displacement using same, and the use of the middle-phase microemulsion. The middle-phase microemulsion comprises, in parts by weight: 4-8 parts of alkylolamide, 1-5 parts of alkyl polyoxypropylene ether sulfate, and 1-4.5 parts of alkylphenol polyoxyethylene ether sulfate. The oil displacement method comprises: (1) injecting a polymer oil displacement system into a reservoir bed of a target oil reservoir; (2) injecting a middle-phase-microemulsion oil displacement system thereinto, wherein the middle-phase-microemulsion oil displacement system comprises the middle-phase microemulsion; optionally, (3) injecting a foam oil displacement system thereinto; and optionally, (4) injecting a PPG oil displacement system thereinto; and (5) injecting a polymer oil displacement system thereinto. In the present invention, a middle-phase-microemulsion oil displacement system is used, and therefore the sweep efficiency and the oil displacement efficiency can be greatly improved; and the present invention shows great application potential in the field of enhanced oil recovery.

Description

Middle phase microemulsion and its oil displacement method and application

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of Chinese patent application No. 202310827687.5 filed on July 6, 2023, the contents of which are incorporated herein by reference. Technical Field

[0003] The present invention relates to the field of tertiary oil recovery in oil fields, and in particular to a medium-phase microemulsion and an oil displacement method and application thereof. Background Art

[0004] Conglomerate reservoirs have a wide range of pore throat sizes, primarily exhibiting filling-type, complex, and bimodal characteristics. Pore structure modalities and throat radius distributions vary significantly across lithologies. Complex lithology and pore structure lead to strong spatial heterogeneity in conglomerate reservoir properties, with significant variations in planar, inter-layer, and intra-layer properties. Furthermore, years of waterflooding in sandstone reservoirs have resulted in even more complex reservoir structure and oil-water distribution, with significant heterogeneity both in plan and vertical directions.

[0005] Among tertiary oil recovery technologies, fire flooding and natural gas gravity miscible flooding increase oil recovery by over 35%, meeting the technical requirement for a significant increase in oil recovery (over 25%). However, these technologies are subject to stringent application requirements. Currently, polymer flooding, binary composite flooding, and ternary composite flooding are being promoted in major oil fields. None of these technologies meet the technical requirements for a significant increase in oil recovery. Medium-phase microemulsion flooding, similar to miscible flooding, significantly reduces residual oil saturation and is one of the most effective methods for achieving a significant increase in oil recovery, with a total displacement efficiency exceeding 90%. Without increasing chemical costs, field trials are expected to show a 5 percentage point improvement over composite flooding, reducing chemical costs per ton of oil by over 20%. Medium-phase microemulsion flooding displaces crude oil from the formation by generating a Winsor III microemulsion in situ within the reservoir. Winsor III microemulsions solubilize both oil and water simultaneously, exhibiting extremely low interfacial tension with both oil and water. Capillary forces are virtually absent during the displacement process, resulting in strong solubilization of residual oil along the way. This significantly improves microscopic sweep efficiency and oil displacement efficiency. The formation of a mesophase microemulsion is closely related to the structure of the surfactant. Conventional surfactants can also form a stable mesophase in the presence of alcohols and salts, typically requiring concentrations above 1%. China was the first to develop a petroleum sulfonate (YM-3A) suitable for the L formation of the Laojunmiao Oilfield. The displacement system formula 4401 (4.0% YM-3A, 4.0% n-butanol, 0.1% BPA) was selected. Testing revealed excellent performance, reaching the level of similar research conducted internationally. However, the high dosage required compromises economic efficiency. Therefore, there is an urgent need to explore systems and methods for significantly improving oil recovery in sandstone and conglomerate reservoirs during the later stages of waterflooding.

[0006] Summary of the Invention

[0007] The purpose of the present invention is to overcome the problem of low recovery rate in the late stage of water injection development of sandstone conglomerate oil reservoirs in the prior art, and to provide a middle phase microemulsion and its oil displacement method and application. The oil displacement method using the middle phase microemulsion can greatly improve the sweep efficiency and oil displacement efficiency.

[0008] In order to achieve the above object, the first aspect of the present invention provides a middle phase microemulsion, which comprises, by weight, 4-8 parts of alkyl alcohol amide, 1-5 parts of alkyl polyoxypropylene ether sulfate and 1-4.5 parts of alkylphenol polyoxyethylene ether sulfate.

[0009] The second aspect of the present invention provides the use of the aforementioned middle phase microemulsion in oil displacement.

[0010] A third aspect of the present invention provides an oil displacement method, comprising:

[0011] (1) Injecting a polymer flooding system into the reservoir of the target oil reservoir;

[0012] (2) injecting a middle phase microemulsion flooding system, wherein the middle phase microemulsion flooding system includes the aforementioned middle phase microemulsion;

[0013] Optionally, (3) injecting a gas foam flooding system;

[0014] Optionally, (4) injecting a PPG flooding system;

[0015] (5) Injection of polymer flooding system.

[0016] A fourth aspect of the present invention provides the use of the aforementioned middle phase microemulsion or the aforementioned oil displacement method in a conglomerate reservoir.

[0017] Through the above technical solution, the beneficial technical effects achieved by the present invention are as follows:

[0018] 1) The middle phase microemulsion of the present invention comprises: at least one nonionic surfactant (alkyl alcohol amide) and at least two anionic surfactants (alkyl polyoxypropylene ether sulfate and alkylphenol polyoxyethylene ether sulfate). By compounding these three substances, the HLB can be adjusted to about 10, and the system stacking parameter can be adjusted to about 1, thereby facilitating the formation of a middle phase system.

[0019] 2) The present invention adopts a medium-phase microemulsion flooding system for oil displacement. During the oil displacement process, different slug combinations are used to improve the displacement effect. This includes adding PPG to the front slug to adjust the profile, adding nitrogen foam flooding to further adjust the reservoir heterogeneity, and adding a protective slug to further enhance the displacement effect. This can significantly improve the sweep efficiency and oil recovery efficiency, showing great application potential in the field of enhanced oil recovery. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] FIG1 is a schematic structural diagram of a microemulsion state observation device. DETAILED DESCRIPTION

[0021] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0022] The first aspect of the present invention provides a middle phase microemulsion, which comprises, by weight, 4-8 parts of alkylolamide, 1-5 parts of alkyl polyoxypropylene ether sulfate and 1-4.5 parts of alkylphenol polyoxyethylene ether sulfate.

[0023] In the present invention, alkyl alcohol amide is a nonionic surfactant; alkyl polyoxypropylene ether sulfate and alkylphenol polyoxyethylene ether sulfate are anionic surfactants.

[0024] The present invention can adjust the HLB to about 10 by compounding these three substances, and at the same time can make the system stacking parameter reach about 1, making it easier to form a middle phase system.

[0025] In some preferred embodiments of the present invention, the middle phase microemulsion comprises, by weight, 5-7 parts of alkyl alcohol amide, 2-4 parts of alkyl polyoxypropylene ether sulfate, and 2-4 parts of alkylphenol polyoxyethylene ether sulfate.

[0026] In some embodiments of the present invention, the general formula of the alkylolamide is R1CON(CH2CH2OH) n , R1 is C 10 -C 20 wherein n=1-40, preferably 10-30.

[0027] In the present invention, R1 is preferably decyl, dodecyl, tetradecyl, hexadecyl, octadecyl or eicosyl.

[0028] In some preferred embodiments of the present invention, the alkylolamide is selected from one or more of lauryl diethanolamide, coconut oil alkylolamide phosphate and coconut oil fatty acid diethanolamide, preferably lauryl diethanolamide.

[0029] In some embodiments of the present invention, the general formula of the alkyl polyoxypropylene ether sulfate is C m H 2m+1 (CH2CH2CH2O) m SO3X, wherein m=1-30, preferably 10-20; X is selected from Li, Na or K.

[0030] In some preferred embodiments of the present invention, the alkyl polyoxypropylene ether sulfate is selected from one or more of sodium lauryl polyoxypropylene ether sulfate, sodium tetradecyl polyoxypropylene ether sulfate, sodium hexadecyl polyoxypropylene ether sulfate, potassium octadecyl polyoxypropylene ether sulfate and lithium octadecyl polyoxypropylene ether sulfate, preferably sodium lauryl polyoxypropylene ether sulfate or sodium hexadecyl polyoxypropylene ether sulfate.

[0031] In some embodiments of the present invention, the alkylphenol polyoxyethylene ether sulfate has the structural formula shown in Formula I:

[0032] In formula I, R2 is C 10 -C 20 wherein p=3-15, preferably 5-12, and Y is selected from Li, Na or K.

[0033] In the present invention, R2 is preferably nonyl, undecyl, tridecyl, pentadecyl, heptadecyl or nonadecyl.

[0034] In some preferred embodiments of the present invention, the alkylphenol polyoxyethylene ether sulfate is selected from one or more of sodium undecylphenol polyoxyethylene ether sulfate, sodium tridecylphenol polyoxyethylene ether sulfate, lithium tridecylphenol polyoxyethylene ether sulfate, potassium tridecylphenol polyoxyethylene ether sulfate, sodium pentadecylphenol polyoxyethylene ether sulfate, sodium heptadecylphenol polyoxyethylene ether sulfate and sodium nonadecylphenol polyoxyethylene ether sulfate, preferably sodium undecylphenol polyoxyethylene ether sulfate or sodium tridecylphenol polyoxyethylene ether sulfate.

[0035] The second aspect of the present invention provides the use of the aforementioned middle phase microemulsion in oil displacement.

[0036] When the middle phase microemulsion of the present invention is used for oil displacement, only a relatively low mass concentration (≤0.5%) is required to significantly increase the recovery rate.

[0037] The use of the middle phase microemulsion of the present invention for oil displacement can greatly increase the crude oil recovery rate.

[0038] A third aspect of the present invention provides an oil displacement method, comprising:

[0039] (1) Injecting a polymer flooding system into the reservoir of the target oil reservoir;

[0040] (2) injecting a middle phase microemulsion flooding system, wherein the middle phase microemulsion flooding system includes the aforementioned middle phase microemulsion;

[0041] Optionally, (3) injecting a gas foam flooding system;

[0042] Optionally, (4) injecting a PPG flooding system;

[0043] (5) Injection of polymer flooding system.

[0044] In the present invention, the PPG (Preformed Particle Gel) in the PPG flooding system refers to a viscoelastic particle flooding agent (a viscoelastic particle-type flooding agent in which polymer monomers, cross-linking agents, proppants, etc. are polymerized to form a star-shaped or three-dimensional network structure). It is a particle-type flooding agent with viscoelasticity and the ability to deform and migrate in porous media. It has good viscoelasticity, temperature and salt resistance, and strong migration ability. PPG has three different particle sizes: (75-150) μm, (100-300) μm, and (300-900) μm. The heterogeneous composite flooding method using it as the main agent is a new chemical flooding method with great potential for field application, which is conducive to solving the problem of improving the recovery rate of oil reservoirs after polymer flooding.

[0045] The method of the present invention adopts a medium-phase microemulsion flooding system supplemented by a nitrogen foam flooding system, which can greatly improve the crude oil recovery rate. The concentration of the reagent used in the present invention is low, and has good economic benefits.

[0046] In some embodiments of the present invention, in step (1), the polymer flooding system comprises a polymer and PPG, wherein the mass ratio of the polymer to the PPG is 1:1-3; and the viscosity of the polymer is 30-80 mPa·s.

[0047] In some embodiments of the present invention, the polymer is selected from one or more of a hyperbranched associative polymer, a salt-resistant polymer, a temperature-resistant and salt-resistant polymer, and a partially hydrolyzed polyacrylamide.

[0048] In some embodiments of the present invention, the polymer flooding system is formulated with in situ water.

[0049] In some embodiments of the present invention, in the polymer flooding system, the total mass concentration of the polymer and PPG is 0.03-0.15%.

[0050] In some embodiments of the present invention, in step (1), the injection volume of the polymer flooding system is 0.02-0.07 PV.

[0051] In some embodiments of the present invention, in step (2), the middle phase microemulsion flooding system is prepared with on-site water having a salinity of 1-9%.

[0052] In some embodiments of the present invention, in the middle phase microemulsion flooding system, the mass concentration of the middle phase microemulsion is 0.2-0.5%.

[0053] In the present invention, the mass concentration of the middle phase microemulsion is preferably between 0.2-0.5%, which has a better oil displacement effect. If the mass concentration of the middle phase microemulsion is too low, less than 0.2%, especially less than 0.1%, the oil displacement effect is poor; although the mass concentration of the middle phase microemulsion is higher than 0.5%, it can also achieve a good oil displacement effect, but it will lead to increased costs. Studies have found that the mass concentration of the middle phase microemulsion as high as 2% has an oil displacement effect similar to that of a mass concentration of 0.5%. Therefore, considering the cost and oil displacement effect, the present application preferably uses a mass concentration of 0.2-0.5% of the middle phase microemulsion.

[0054] In some embodiments of the present invention, the injection volume of the middle phase microemulsion flooding system is 0.05-0.7 PV.

[0055] In some embodiments of the present invention, step (2) further comprises: adding a polymer having a viscosity of 10-50 mPa·s to the middle-phase microemulsion flooding system before injecting the middle-phase microemulsion flooding system.

[0056] In some preferred embodiments of the present invention, the polymer is selected from one or more of a hyperbranched associative polymer, a salt-resistant polymer, a temperature-resistant and salt-resistant polymer, and a partially hydrolyzed polyacrylamide.

[0057] In some preferred embodiments of the present invention, in the middle-phase microemulsion flooding system, the mass concentration of the polymer is 0.05-0.25%.

[0058] Furthermore, a hyperbranched associative polymer and sodium carbonate are added to the middle-phase microemulsion flooding system, wherein the mass concentration of the hyperbranched associative polymer is 0.15%, and the mass concentration of the sodium carbonate is 0.6%.

[0059] In the present invention, in step (2), a polymer is added to the middle phase microemulsion flooding system to control the fluidity and increase the volume of the middle phase microemulsion, thereby further improving the oil recovery efficiency; sodium carbonate is added to increase the volume of the middle phase, thereby further improving the recovery rate.

[0060] In some embodiments of the present invention, in step (3), the gas foam flooding system is obtained by filling a foam flooding system with gas; the foam flooding system includes an anionic surfactant, a polymer compound and urea.

[0061] In some embodiments of the present invention, the foam flooding system is prepared with water having a salinity of 1-9%.

[0062] In some embodiments of the present invention, in the foam flooding system, the mass concentration of the anionic surfactant is 0.1-0.8%, the mass concentration of the polymer compound is 0.1-0.5%, and the mass concentration of urea is 0.5-2%.

[0063] In the present invention, in the foam flooding system, the total mass concentration of the anionic surfactant, the high molecular compound and urea is 0.1-3.5%.

[0064] In some embodiments of the present invention, the anionic surfactant contains at least one of a fatty acyl-peptide condensate; the fatty acyl-peptide condensate has the general formula R3CONHR4COOA, wherein R3 is C8-C 12 Alkyl groups with carbon chain lengths of 8-12, such as C8H 17 、C 10 H 21 、C 12 H 23 ; R4 is a C1-C8 alkyl group; A is H, Na or K.

[0065] In the present invention, R4 is an aliphatic group of an amino group.

[0066] In some preferred embodiments of the present invention, the fatty acyl-peptide condensate is selected from sodium lauroyl sarcosinate and / or sodium lauric monoglyceride sulfate.

[0067] In some preferred embodiments of the present invention, the anionic surfactant further contains sodium lauryl sulfate and / or sodium lauryl sulfonate.

[0068] In some embodiments of the present invention, the polymer compound is selected from one or more of xanthan gum, sodium carboxymethyl cellulose and sodium carboxymethyl starch.

[0069] In some embodiments of the present invention, the volume ratio of the gas to the foam flooding system is 2:1-6:1.

[0070] In some embodiments of the present invention, the gas is selected from one or more of nitrogen, air, oxygen and hypoxic air.

[0071] In some particularly preferred embodiments of the present invention, the gas foam flooding system comprises: 0.4% sodium lauryl sulfate, 0.15% xanthan gum and 1% urea; nitrogen is introduced at a ratio of 3:1 (nitrogen to foam flooding system volume ratio).

[0072] In some embodiments of the present invention, the injection volume of the gas foam flooding system is 0-0.7 PV.

[0073] In some embodiments of the present invention, in step (4), the PPG flooding system is prepared using on-site water with a salinity of 1-9%.

[0074] In some embodiments of the present invention, in the PPG flooding system, the mass concentration of PPG is 0.1-0.3%.

[0075] In some embodiments of the present invention, the injection volume of the PPG flooding system is 0-0.15 PV.

[0076] In some embodiments of the present invention, in step (5), the polymer flooding system comprises a polymer and PPG, wherein the mass ratio of the polymer to the PPG is 1:1-3; and the viscosity of the polymer is 30-80 mPa·s.

[0077] In some embodiments of the present invention, in step (5), the injection volume of the polymer flooding system is 0.03-0.07 PV.

[0078] In some embodiments of the present invention, the polymer flooding system further comprises one or more of a hyperbranched associative polymer, a salt-resistant polymer, a temperature-resistant and salt-resistant polymer, and a partially hydrolyzed polyacrylamide;

[0079] In some embodiments of the present invention, the polymer flooding system is formulated with in situ water;

[0080] In some embodiments of the present invention, in the polymer flooding system, the total mass concentration of the polymer and PPG is 0.03-0.15%.

[0081] In some embodiments of the present invention, the on-site water with a salinity of 1-9% is prepared by adding sodium chloride to on-site water.

[0082] In some embodiments of the present invention, the order of step (2) and step (3) can be interchanged; and / or, step (2) and step (3) can be injected alternately.

[0083] In the present invention, the order of step (2) and step (3) can be interchanged at will. Step (2) can be performed first and then step (3), or step (3) can be performed first and then step (2), or step (2) and step (3) can be injected alternately.

[0084] A fourth aspect of the present invention provides the use of the aforementioned middle phase microemulsion or the aforementioned oil displacement method in a conglomerate reservoir.

[0085] In some embodiments of the present invention, the conglomerate reservoir has a complex modal pore structure.

[0086] According to a particularly preferred embodiment of the present invention, an oil displacement method using a low-concentration middle-phase microemulsion flooding system assisted by a nitrogen foam flooding system comprises the following steps:

[0087] (1) injecting a polymer flooding system into a reservoir of a target oil reservoir; the injection volume of the polymer flooding system is 0.02PV-0.07PV;

[0088] A polymer flooding system with a mass concentration of 0.03% to 0.15% is prepared using on-site water. The polymer flooding system comprises a polymer and PPG, wherein the mass ratio of the polymer to the PPG is 1:1 to 1:3, and the viscosity of the polymer is 30 mPa·s to 80 mPa·s. The polymer is selected from one or more of a hyperbranched associative polymer, a salt-resistant polymer, a temperature-resistant and salt-resistant polymer, and a partially hydrolyzed polyacrylamide.

[0089] (2) injecting a medium-phase microemulsion flooding system after step (1), wherein the injection amount of the medium-phase microemulsion flooding system is 0.05-0.7 PV;

[0090] Sodium chloride is used to adjust the mineralization of on-site water to obtain water for preparation with a mineralization of 1%-9%; water for preparation with a mineralization of 1%-9% is used to prepare a middle-phase microemulsion flooding system with a mass concentration of 0.2%-0.5%; the middle-phase microemulsion flooding system includes: a nonionic surfactant and an anionic surfactant, wherein the nonionic surfactant is an alkyl alcohol amide, and the anionic surfactant is an alkyl polyoxypropylene ether sulfate and an alkylphenol polyoxyethylene ether sulfate. The middle-phase microemulsion flooding system also includes one or more of dodecyl diethanolamide, coconut oil fatty acid amino acid ethyl sodium and coconut oil fatty acid diethanolamide. Furthermore, in this step, a polymer with a viscosity of 10mPa·s-50mPa·s is also added; the polymer is selected from one or more of hyperbranched associative polymers, salt-resistant polymers, temperature-resistant and salt-resistant polymers and partially hydrolyzed polyacrylamide;

[0091] (3) injecting a foam flooding system after step (2), wherein the injection amount of the foam flooding system is 0-0.7 PV;

[0092] A foam flooding system with a mass concentration of 0.1% to 3.5% is prepared using water with a salinity of 1% to 9%. The foam flooding system includes an anionic surfactant, a polymer compound, and urea. The anionic surfactant is a fatty acyl-peptide condensate. Nitrogen is added with a nitrogen volume to foam flooding system volume ratio of 2:1 to 6:1.

[0093] The anionic surfactant is selected from one or more of sodium lauryl sulfate, sodium lauryl sulfonate, sodium lauroyl sarcosinate, and sodium lauric monoglyceride sulfate; the polymer compound is selected from one or more of xanthan gum, sodium carboxymethyl cellulose, and sodium carboxymethyl starch;

[0094] (4) injecting a PPG flooding system after step (3), wherein the injection volume of the PPG flooding system is 0-0.15 PV;

[0095] Use water with a salinity of 1%-9% to prepare a PPG flooding system with a mass concentration of 0.1%-0.3%;

[0096] (5) injecting a polymer flooding system after step (4), wherein the injection amount of the polymer flooding system is 0.03-0.07 PV;

[0097] A polymer flooding system with a mass concentration of 0.03%-0.15% is prepared using on-site water. The polymer flooding system includes a polymer and PPG, wherein the mass ratio of the polymer to the PPG is 1:1-1:3, and the viscosity of the polymer is 30mPa·s-80mPa·s. The polymer is selected from one or more of a hyperbranched associative polymer, a salt-resistant polymer, a temperature-resistant and salt-resistant polymer, and a partially hydrolyzed polyacrylamide.

[0098] The polymer flooding system in step (5) may be the same as or different from the polymer flooding system in step (1). In order to reduce the number of preparation steps, it is preferred that the polymer flooding system in step (5) is the same as the polymer flooding system in step (1).

[0099] The order of step (2) and step (3) can be interchanged or used alternately.

[0100] In the present invention, in order to more conveniently observe the formation process of the middle phase microemulsion and whether the middle phase microemulsion is formed in the produced fluid, the present invention also provides a microemulsion state observation device, as shown in Figure 1, which includes: a fixing device 1, a background light 2, a lifting plate 3 and a fixing screw 4, wherein the fixing device 1 is provided with a through hole 11 and an adjustable test tube rack 12, and the test tube rack 12 can be inserted into the through hole 11. The test tube rack 12 is used to clamp the test tube and keep the test tube 12 balanced. The lifting plate 3 can be adjusted in height to support the test tube to prevent the test tube from falling. The fixing screw 4 is used to fix the lifting plate 3, and when the lifting plate 3 is lifted to the appropriate position, it is fixed with the fixing screw 4. The background light 2 is a rectangular white transparent background light, and the color and intensity of the light can be adjusted to clearly observe the phase transition of the microemulsion.

[0101] The device can be used to visually observe the differences between the oil phase, water phase and intermediate phase formed after the surfactant is emulsified, and can more accurately determine the boundary between each phase.

[0102] This device allows for clearer observation of the phase transitions in the middle phase microemulsion. The phase transitions vary with the salt or surfactant concentration added to the system, and the volume of the middle phase also varies. A higher middle phase volume is associated with improved oil recovery efficiency. The present invention adjusts the salinity and formulation ratio of the oil recovery system based on the formation crude oil and the water used for the formulation.

[0103] The present invention will be described in detail below through examples.

[0104] In the following examples and comparative examples,

[0105] A conglomerate reservoir in the Xinjiang Oilfield was selected as the target reservoir. Water-saturated cores were produced from well area A and the permeability was measured using water. The crude oil from the oil well was then used to drive water until no water was produced. The water produced from well area A was used to drive the oil to a water content of 98%, and the water drive recovery factor was calculated. A flooding system with a certain PV number (the flooding system in the embodiment and comparative example) was injected, and then the water produced from well area A was used to drive the oil to a water content of 98%, and the chemical drive recovery factor was calculated.

[0106] Preparation of polymer flooding system: On-site water was used to prepare the polymer flooding system, which included partially hydrolyzed polyacrylamide and PPG, with the mass ratio of partially hydrolyzed polyacrylamide to PPG being 1:1; in the polymer flooding system, the total mass concentration of partially hydrolyzed polyacrylamide and PPG was 0.1%.

[0107] Preparation of a medium-phase microemulsion flooding system: Sodium chloride is used to adjust the salinity of on-site water to 3%, and this is used as the preparation water to prepare the medium-phase microemulsion flooding system. The medium-phase microemulsion in this medium-phase microemulsion flooding system includes 5 parts of sodium ethyl coconut oil fatty acylaminate, 1 part of sodium cetyl polyoxypropylene sulfate, and 1 part of sodium nonylphenol polyoxyethylene ether sulfate. The mass concentration of the medium-phase microemulsion in this medium-phase microemulsion flooding system is 0.5%. A hyperbranched associative polymer at a mass concentration of 0.15% and sodium carbonate at a mass concentration of 0.6% are also added to this medium-phase microemulsion flooding system. The viscosity of the hyperbranched associative polymer is 50 mPa·s.

[0108] Preparation of a nitrogen foam flooding system: Sodium chloride was used to adjust the salinity of on-site water to 3%, and the solution was used as the preparation water to prepare a foam flooding system. The foam flooding system included: sodium lauryl sulfate with a mass concentration of 0.4%, xanthan gum with a mass concentration of 0.15%, and urea with a mass concentration of 1.0%. Nitrogen was introduced into the foam flooding system so that the volume ratio of nitrogen to the foam flooding system was 3:1, thereby obtaining a nitrogen foam flooding system.

[0109] Preparation of PPG flooding system: Sodium chloride was used to adjust the salinity of the on-site water to 3%, and the solution was used as the preparation water to prepare a PPG flooding system with a mass concentration of 0.1%.

[0110] Adopt SYT 5862-2020 Technical Requirements for Polymers for Oil Displacement.

[0111] The interfacial tension parameters were measured according to SY / T5370-2018 “Surface and interfacial tension determination method”.

[0112] The permeability, water flooding recovery rate, and chemical flooding recovery rate were measured according to QS / Y 1583-2013 “Technical Specifications for Surfactants for Binary Flooding”.

[0113] Example 1

[0114] An oil displacement method specifically comprises the following steps:

[0115] (1) injecting the polymer flooding system into the reservoir of the target oil reservoir at an injection volume of 0.05 PV;

[0116] (2) injecting the above-mentioned middle phase microemulsion flooding system after step (1) at an injection volume of 0.2 PV;

[0117] (3) injecting the nitrogen foam flooding system after step (2) at an injection rate of 0.15 PV;

[0118] (4) injecting the above-mentioned PPG flooding system after step (3) at an injection volume of 0.05 PV;

[0119] (5) After step (4), the polymer flooding system is injected at an injection volume of 0.05 PV.

[0120] The measured permeability, interfacial tension, water flooding recovery and chemical flooding recovery are shown in Table 1.

[0121] Example 2

[0122] The oil displacement method of Example 1 was followed, except that the sodium hexadecyl polyoxypropylene sulfate in the microemulsion oil displacement system in step (2) was replaced with sodium tetradecyl polyoxypropylene sulfate. The rest was the same as in Example 1. The results are shown in Table 1.

[0123] Example 3

[0124] The oil displacement method of Example 1 was followed, except that the sodium ethyl coconut oil fatty acylaminate in the microemulsion flooding system in step (2) was replaced with a mixture of sodium ethyl coconut oil fatty acylaminate (80 wt%) and coconut oil fatty acid diethanolamide (20 wt%). The rest was the same as in Example 1. The results are shown in Table 1.

[0125] Example 4

[0126] The oil displacement method of Example 1 was followed, except that step (4), that is, the step of injecting the nitrogen foam flooding system, was not performed. The rest was the same as in Example 1. The results are shown in Table 1.

[0127] Example 5

[0128] The oil displacement method of Example 1 was followed, except that step (4), that is, the step of injecting the PPG oil displacement system, was not performed. The rest was the same as in Example 1. The results are shown in Table 1.

[0129] Example 6

[0130] The oil displacement method of Example 1 was followed, except that step (1) and step (5) were not performed, that is, the step of injecting the polymer flooding system was not performed. The rest was the same as in Example 1. The results are shown in Table 1.

[0131] Example 7

[0132] The oil displacement method of Example 1 was followed, except that the viscosity of the hyperbranched associative polymer was 10 mPa·s. The rest was the same as in Example 1. The results are shown in Table 1.

[0133] Example 8

[0134] The oil displacement method of Example 1 was followed, except that the mass concentration of the middle phase microemulsion was 0.3%. The rest was the same as in Example 1. The results are shown in Table 1.

[0135] Comparative Example 1

[0136] The oil displacement method of Example 1 was used, except that the middle phase microemulsion oil displacement system in step (2) included: 1 part of sodium ethyl coconut oil fatty acylaminate, 1 part of sodium hexadecyl polyoxypropylene sulfate, and 1 part of sodium nonylphenol polyoxyethylene ether sulfate. The rest were the same as in Example 1. The results are shown in Table 1.

[0137] Comparative Example 2

[0138] The oil displacement method of Example 1 was followed, except that the middle phase microemulsion oil displacement system in step (2) did not contain sodium nonylphenol polyoxyethylene ether sulfate. The rest was the same as in Example 1. The results are shown in Table 1.

[0139] Comparative Example 3

[0140] The oil displacement method of Example 1 was followed, except that the middle phase microemulsion oil displacement system in step (2) did not contain sodium hexadecyl polyoxypropylene sulfate. The rest was the same as in Example 1. The results are shown in Table 1.

[0141] Comparative Example 4

[0142] The oil displacement method of Example 1 was followed, except that step (2), that is, the step of injecting the middle phase microemulsion oil displacement system, was not performed. The rest was the same as in Example 1. The results are shown in Table 1.

[0143] Table 1

[0144] The results in Table 1 show that, under the premise of similar water flooding recovery factors, the chemical flooding recovery factors achieved by the oil flooding methods of Examples 1-7 of the present invention were all greater than 20%, with Example 1 even reaching 51.3%. The oil flooding methods of Comparative Examples 1-4 were all less than 20%. Therefore, the oil flooding methods of Examples 1-7 of the present invention significantly achieved better oil recovery results than the oil flooding methods of Comparative Examples 1-4.

[0145] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A medium phase microemulsion, characterized in that: In parts by weight, the middle phase microemulsion comprises: 4-8 parts of alkyl alcohol amide, 1-5 parts of alkyl polyoxypropylene ether sulfate and 1-4.5 parts of alkylphenol polyoxyethylene ether sulfate.

2. The middle phase microemulsion according to claim 1, wherein The general formula of the alkyl alcohol amide is R1CON(CH2CH2OH) n , R1 is C 10 -C 20 An alkyl group, n=1-40.

3. The middle phase microemulsion according to claim 2, wherein The alkyl alcohol amide is selected from one or more of lauryl diethanolamide, coconut oil alkyl alcohol amide phosphate and coconut oil fatty acid diethanolamide.

4. The middle phase microemulsion according to claim 1 or 2, wherein The general formula of the alkyl polyoxypropylene ether sulfate is C m H 2m+1 (CH2CH2CH2O) m SO3X, wherein m=1-30; X is selected from Li, Na or K.

5. The middle phase microemulsion according to claim 4, wherein The alkyl polyoxypropylene ether sulfate is selected from one or more of sodium dodecyl polyoxypropylene ether sulfate, sodium tetradecyl polyoxypropylene ether sulfate, sodium hexadecyl polyoxypropylene ether sulfate, potassium octadecyl polyoxypropylene ether sulfate and lithium octadecyl polyoxypropylene ether sulfate.

6. The middle phase microemulsion according to claim 1 or 2, wherein: The alkylphenol polyoxyethylene ether sulfate has a structural formula shown in Formula I: In formula I, R2 is C 10 -C 20 wherein p=3-15, and Y is selected from Li, Na or K.

7. Use of the middle phase microemulsion according to any one of claims 1 to 6 in oil displacement.

8. An oil displacement method, characterized in that: The oil displacement method comprises: (1) injecting a polymer flooding system into a reservoir of a target oil reservoir; (2) injecting a middle phase microemulsion flooding system, wherein the middle phase microemulsion flooding system comprises the middle phase microemulsion according to any one of claims 1 to 7; Optionally, (3) injecting a gas foam flooding system; Optionally, (4) injecting a PPG flooding system; (5) Injection of polymer flooding system.

9. The oil displacement method according to claim 8, wherein: In step (1) and step (5), the polymer flooding system comprises a polymer and PPG, wherein the mass ratio of the polymer to the PPG is 1:1-3; the viscosity of the polymer is 30-80 mPa·s; and / or, in step (1), the injection volume of the polymer flooding system is 0.02-0.07 PV; And / or, in step (5), the injection volume of the polymer flooding system is 0.03-0.07 PV.

10. The oil displacement method according to claim 9, wherein: The polymer is selected from one or more of a hyperbranched associative polymer, a salt-resistant polymer, a temperature-resistant and salt-resistant polymer, and a partially hydrolyzed polyacrylamide; and / or, the polymer flooding system is formulated with on-site water; And / or, in the polymer flooding system, the total mass concentration of the polymer and PPG is 0.03-0.15%.

11. The oil displacement method according to claim 8, wherein: In step (2), the middle phase microemulsion flooding system is prepared with on-site water having a salinity of 1-9%; and / or, in the middle phase microemulsion flooding system, the mass concentration of the middle phase microemulsion is 0.2-0.5%; And / or, the injection volume of the medium-phase microemulsion flooding system is 0.05-0.7 PV.

12. The oil displacement method according to claim 8, wherein: Step (2) further comprises: before injecting the middle phase microemulsion oil displacement system, adding a polymer having a viscosity of 10-50 mPa·s into the middle phase microemulsion oil displacement system.

13. The oil displacement method according to claim 8, wherein: In step (3), the gas foam flooding system is obtained by filling a foam flooding system with gas; the foam flooding system comprises an anionic surfactant, a polymer compound and urea; And / or, the injection volume of the gas foam flooding system is 0-0.7 PV.

14. The oil displacement method according to claim 13, wherein: The foam flooding system is prepared with water having a salinity of 1-9%; And / or, in the foam flooding system, the mass concentration of the anionic surfactant is 0.1-0.8%, the mass concentration of the polymer compound is 0.1-0.5%, and the mass concentration of urea is 0.5-2%.

15. The oil displacement method according to claim 13, wherein: The anionic surfactant contains at least one of the fatty acyl-peptide condensation compounds; the general formula of the fatty acyl-peptide condensation compound is R3CONHR4COOA, wherein R3 is C8-C 12 R4 is a C1-C8 alkyl group; A is H, Na or K; And / or, the polymer compound is selected from one or more of xanthan gum, sodium carboxymethyl cellulose and sodium carboxymethyl starch.

16. The oil displacement method according to claim 13, wherein: The fatty acyl-peptide compound is selected from sodium lauroyl sarcosinate and / or sodium lauric monoglyceride sulfate; And / or, the anionic surfactant further contains sodium dodecyl sulfate / or sodium dodecyl sulfonate.

17. The oil displacement method according to claim 13, wherein: The volume ratio of the gas to the foam flooding system is 2:1-6:1; And / or, the gas is selected from one or more of nitrogen, air, oxygen and hypoxic air.

18. The oil displacement method according to claim 8, wherein: In step (4), the PPG flooding system is prepared with on-site water having a salinity of 1-9%; and / or, in the PPG flooding system, the mass concentration of PPG is 0.1-0.3%; And / or, the injection volume of the PPG flooding system is 0-0.15 PV.

19. The oil displacement method according to any one of claims 11 to 18, wherein: The on-site water with a mineralization degree of 1-9% is prepared by adding sodium chloride to the on-site water.

20. The oil displacement method according to claim 8, wherein: The order of step (2) and step (3) can be interchanged; And / or, step (2) and step (3) can be injected alternately.

21. Use of the middle phase microemulsion according to any one of claims 1 to 6 or the oil displacement method according to any one of claims 8 to 20 in a conglomerate reservoir.

22. The use according to claim 21, wherein: The conglomerate reservoir has a complex modal pore structure.

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