Medium-phase microemulsion as well as oil displacement method and application thereof

Abstract

The invention relates to the field of tertiary oil recovery of oil fields, in particular to a middle-phase microemulsion as well as an oil displacement method and application thereof. The middle-phase microemulsion is prepared from the following components in parts by weight: 4 to 8 parts of alkylolamide, 1 to 5 parts of alkyl polyoxypropylene ether sulfate and 1 to 4.5 parts of alkylphenol polyoxyethylene ether sulfate. The oil displacement method comprises the following steps: (1) injecting a polymer oil displacement system into a reservoir of a target oil reservoir; (2) injecting a middle-phase microemulsion oil displacement system, wherein the middle-phase microemulsion oil displacement system comprises the middle-phase microemulsion; optionally, (3) injecting a foam flooding system; optionally, (4) injecting a PPG oil displacement system; and (5) injecting a polymer oil displacement system. By adopting the middle-phase microemulsion oil displacement system, the sweep efficiency and the oil displacement efficiency can be greatly improved, and huge application potential is shown in the field of improving the recovery efficiency.

Description

Technical Field

[0001] The invention relates to the field of tertiary oil recovery in oil fields, and in particular to a medium-phase microemulsion and an oil recovery method and application thereof. Background Art

[0002] The distribution range of pore throat size in conglomerate reservoirs is wide, mainly with filling complex mode and bimodal characteristics. There are significant differences in the pore structure mode and throat radius distribution characteristics of different lithologies. The complex lithology and pore structure lead to strong spatial heterogeneity of conglomerate reservoir physical properties, with great differences in plane, interlayer and intralayer. At the same time, compared with sandstone reservoirs, the water content rises quickly, the water-free oil production period is short, and the water drive recovery rate is low. After more than half a century of water injection development, the reservoir structure and oil-water distribution are more complicated.

[0003] Among the tertiary oil recovery technologies, fire drive and natural gas gravity miscible drive can increase the recovery rate by more than 35%, meeting the technical requirements for significantly increasing the recovery rate (more than 25%), but the technical application conditions are harsh. At present, the technologies applied and promoted in major oil fields are polymer drive technology, binary composite drive technology and ternary composite drive technology, and all three technologies cannot meet the technical requirements for significantly increasing the recovery rate. Medium-phase microemulsion drive is a technology similar to miscible drive that can significantly increase the recovery rate. It has the characteristics of significantly reducing the residual oil saturation and is one of the most effective ways to achieve a significant increase in recovery. The total oil recovery efficiency can reach more than 90%. Without increasing the cost of chemicals, it is expected that the field test will increase by 5 percentage points compared with composite drive, and the cost of chemicals per ton of oil can be reduced by more than 20%. Medium-phase microemulsion drive is to displace the crude oil in the formation by in-situ formation of Winsor III type microemulsion in the reservoir. Winsor III microemulsion solubilizes oil and water at the same time, and has extremely low interfacial tension with oil and water. There is almost no capillary force in the displacement process, and it has a strong solubilizing ability for the residual oil along the way, and the microscopic sweep efficiency and oil displacement efficiency are greatly improved. The formation of the middle phase microemulsion is closely related to the structure of the surfactant. Conventional surfactants can also form a stable intermediate phase under the action of alcohol and salt, and the required concentration is usually above 1%. The first petroleum sulfonate (YM-3A) suitable for the L layer performance of Laojunmiao Oilfield was developed in China, and the oil displacement system formula 4401 (4.0% YM-3A, 4.0% n-butanol, 0.1% BPA) was screened out. After testing, it was found that its performance was excellent and reached the level of similar foreign research, but the dosage was large, which affected the economic benefits. Therefore, it is urgent to explore the system and method for significantly improving the recovery rate in the later stage of water injection development of conglomerate reservoirs. Summary of the invention

[0004] The purpose of the present invention is to overcome the problem of low recovery rate in the later stage of water injection development of conglomerate oil reservoirs in the prior art, and to provide a middle phase microemulsion and an oil recovery method and application thereof. The oil recovery method containing the middle phase microemulsion can greatly improve the sweep efficiency and oil recovery efficiency.

[0005] 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.

[0006] The second aspect of the present invention provides the use of the aforementioned middle phase microemulsion in oil displacement.

[0007] A third aspect of the present invention provides an oil recovery method, comprising:

[0008] (1) injecting a polymer flooding system into a reservoir of a target oil reservoir;

[0009] (2) injecting a middle phase microemulsion flooding system, wherein the middle phase microemulsion flooding system comprises the aforementioned middle phase microemulsion;

[0010] Optionally, (3) injecting a gas foam flooding system;

[0011] Optionally, (4) injecting a PPG flooding system;

[0012] (5) Injection of polymer flooding system.

[0013] A fourth aspect of the present invention provides the use of the aforementioned middle phase microemulsion or the aforementioned oil recovery method in a conglomerate reservoir.

[0014] Through the above technical solution, the beneficial technical effects achieved by the present invention are as follows:

[0015] 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 made to reach about 1, which makes it easier to form a middle phase system.

[0016] 2) The present invention adopts a medium-phase microemulsion flooding system for oil displacement, and improves the displacement effect by combining different slugs during the oil displacement process, including 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 highlight the displacement effect, which can greatly improve the sweep efficiency and oil displacement efficiency, and shows great application potential in the field of enhanced oil recovery. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the structure of the microemulsion state observation device. DETAILED DESCRIPTION

[0018] The endpoints and any values ​​of the ranges disclosed in this article 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 endpoint values ​​of each range, the endpoint values ​​of each range and the 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 as specifically disclosed in this article.

[0019] 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.

[0020] In the present invention, alkyl alcohol amide is a nonionic surfactant; alkyl polyoxypropylene ether sulfate and alkylphenol polyoxyethylene ether sulfate are anionic surfactants.

[0021] 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.

[0022] 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.

[0023] In some embodiments of the present invention, the general formula of the alkyl alcohol amide is R 1 CON(CH 2 CH 2 OH) n , R 1 C 10 -C 20 The alkyl group of n=1-40, preferably 10-30.

[0024] In the present invention, R 1 Preferred is decyl, dodecyl, tetradecyl, hexadecyl, octadecyl or eicosyl.

[0025] In some preferred embodiments of the present invention, the alkyl alcohol amide is selected from one or more of dodecyl diethanolamide, coconut oil alkyl alcohol amide phosphate and coconut oil fatty acid diethanolamide, preferably dodecyl diethanolamide.

[0026] In some embodiments of the present invention, the general formula of the alkyl polyoxypropylene ether sulfate is C m H 2m+1 (CH 2 CH 2 CH 2 O) mSO 3 X, wherein m=1-30, preferably 10-20; X is selected from Li, Na or K.

[0027] In some preferred embodiments of the present invention, 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, preferably sodium dodecyl polyoxypropylene ether sulfate or sodium hexadecyl polyoxypropylene ether sulfate.

[0028] In some embodiments of the present invention, the alkylphenol polyoxyethylene ether sulfate has a structural formula shown in Formula I:

[0029]

[0030] In Formula I, R 2 C 10 -C 20 wherein P=3-15, preferably 5-12, and Y is selected from Li, Na or K.

[0031] In the present invention, R 2 Preferred is nonyl, undecyl, tridecyl, pentadecyl, heptadecyl or nonadecyl.

[0032] In some preferred embodiments of the present invention, the alkylphenol polyoxyethylene ether sulfate is selected from one or more of undecylphenol polyoxyethylene ether sodium sulfate, tridecylphenol polyoxyethylene ether sodium sulfate, tridecylphenol polyoxyethylene ether lithium sulfate, tridecylphenol polyoxyethylene ether potassium sulfate, pentadecylphenol polyoxyethylene ether sodium sulfate, heptadecylphenol polyoxyethylene ether sodium sulfate and nonadecylphenol polyoxyethylene ether sodium sulfate, preferably undecylphenol polyoxyethylene ether sodium sulfate or tridecylphenol polyoxyethylene ether sodium sulfate.

[0033] The second aspect of the present invention provides the use of the aforementioned middle phase microemulsion in oil displacement.

[0034] 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 improve the recovery rate.

[0035] The use of the medium phase microemulsion of the present invention for oil displacement can greatly increase the crude oil recovery rate.

[0036] A third aspect of the present invention provides an oil recovery method, comprising:

[0037] (1) injecting a polymer flooding system into a reservoir of a target oil reservoir;

[0038] (2) injecting a middle phase microemulsion flooding system, wherein the middle phase microemulsion flooding system comprises the aforementioned middle phase microemulsion;

[0039] Optionally, (3) injecting a gas foam flooding system;

[0040] Optionally, (4) injecting a PPG flooding system;

[0041] (5) Injection of polymer flooding system.

[0042] 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 that forms a star-shaped or three-dimensional network structure by initiating polymerization of polymer monomers, cross-linking agents, proppants, etc.), which is a particle-type flooding agent with viscoelasticity and deformable migration in porous media, and has the characteristics of good viscoelasticity, temperature and salt resistance, and strong migration ability. PPG has three different particle sizes, namely (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 application in mines, which is conducive to solving the problem of improving the recovery rate of oil reservoirs after polymer flooding.

[0043] The method of the present invention adopts a medium-phase microemulsion flooding system, supplemented by a nitrogen foam flooding system, and can greatly improve the crude oil recovery rate. The concentration of the agent used in the present invention is low, and has good economic benefits.

[0044] 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 PPG is 1:1-3; and the viscosity of the polymer is 30-80 mPa·s.

[0045] 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.

[0046] In some embodiments of the present invention, the polymer flooding system is formulated with in situ water.

[0047] 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%.

[0048] In some embodiments of the present invention, in step (1), the injection volume of the polymer flooding system is 0.02-0.07 PV.

[0049] In some embodiments of the present invention, in step (2), the medium phase microemulsion flooding system is prepared with on-site water having a salinity of 1-9%.

[0050] 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%.

[0051] In the present invention, the mass concentration of the middle phase microemulsion is preferably between 0.2-0.5% to have a better oil displacement effect. If the mass concentration of the middle phase microemulsion is too small, 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%, a good oil displacement effect can also be achieved, but it will lead to increased costs. It has been found through research that the mass concentration of the middle phase microemulsion is as high as 2%, which is similar to the oil displacement effect of the mass concentration of 0.5%. Therefore, considering the cost and oil displacement effect, the present application preferably has a mass concentration of 0.2-0.5% for the middle phase microemulsion.

[0052] In some embodiments of the present invention, the injection volume of the medium-phase microemulsion flooding system is 0.05-0.7 PV.

[0053] In some embodiments of the present invention, step (2) further comprises: before injecting the middle phase microemulsion flooding system, adding a polymer having a viscosity of 10-50 mPa·s into the middle phase microemulsion flooding system.

[0054] 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.

[0055] 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%.

[0056] 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%.

[0057] In the present invention, in step (2), a polymer is added to the middle phase microemulsion oil displacement system to control fluidity and increase the volume of the middle phase microemulsion, thereby further improving the oil displacement efficiency; sodium carbonate is added to increase the volume of the middle phase, thereby further improving the recovery rate.

[0058] 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 comprises an anionic surfactant, a polymer compound and urea.

[0059] In some embodiments of the present invention, the foam flooding system is prepared with water having a salinity of 1-9%.

[0060] 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%.

[0061] In the present invention, in the foam flooding system, the total mass concentration of the anionic surfactant, the polymer compound and the urea is 0.1-3.5%.

[0062] 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 R 3 CONHR 4 COOA, where R 3 C 8 -C 12 Alkyl groups with carbon chain lengths of 8 to 12, such as C 8 H 17 , C 10 H 21 , C 12 H 23 ; R 4 C 1 -C 8 A is H, Na or K.

[0063] In the present invention, R 4 An aliphatic group which is an amino group.

[0064] 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.

[0065] In some preferred embodiments of the present invention, the anionic surfactant further contains sodium dodecyl sulfate and / or sodium dodecyl sulfonate.

[0066] 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.

[0067] In some embodiments of the present invention, the volume ratio of the gas to the foam flooding system is 2:1-6:1.

[0068] In some embodiments of the present invention, the gas is selected from one or more of nitrogen, air, oxygen and hypoxic air.

[0069] In some particularly preferred embodiments of the present invention, the gas foam flooding system comprises: 0.4% sodium dodecyl sulfate, 0.15% xanthan gum and 1% urea; nitrogen is introduced at a ratio of 3:1 (nitrogen to foam flooding system volume ratio).

[0070] In some embodiments of the present invention, the injection volume of the gas foam flooding system is 0-0.7 PV.

[0071] In some embodiments of the present invention, in step (4), the PPG flooding system is prepared using on-site water having a salinity of 1-9%.

[0072] In some embodiments of the present invention, in the PPG flooding system, the mass concentration of PPG is 0.1-0.3%.

[0073] In some embodiments of the present invention, the injection volume of the PPG flooding system is 0-0.15 PV.

[0074] 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 PPG is 1:1-3; and the viscosity of the polymer is 30-80 mPa·s.

[0075] In some embodiments of the present invention, in step (5), the injection volume of the polymer flooding system is 0.03-0.07 PV.

[0076] 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;

[0077] In some embodiments of the present invention, the polymer flooding system is formulated with in situ water;

[0078] 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%.

[0079] In some embodiments of the present invention, the on-site water with a mineralization degree of 1-9% is prepared by adding sodium chloride to the on-site water.

[0080] 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.

[0081] In the present invention, the order of step (2) and step (3) can be changed at will. Step (2) can be performed first and then step (3), or step (3) can be performed first and then step (2). Step (2) and step (3) can also be injected alternately.

[0082] A fourth aspect of the present invention provides the use of the aforementioned middle phase microemulsion or the aforementioned oil recovery method in a conglomerate reservoir.

[0083] In some embodiments of the present invention, the conglomerate reservoir has a complex modal pore structure.

[0084] According to a particularly preferred embodiment of the present invention, an oil recovery method using a low-concentration medium-phase microemulsion oil recovery system assisted by a nitrogen foam oil recovery system comprises the following steps:

[0085] (1) injecting a polymer flooding system into a reservoir of a target oil reservoir; the injection amount of the polymer flooding system is 0.02PV-0.07PV;

[0086] A polymer flooding system with a mass concentration of 0.03%-0.15% is prepared using on-site water, wherein the polymer flooding system comprises 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;

[0087] (2) injecting a middle phase microemulsion flooding system after step (1), wherein the injection amount of the middle phase microemulsion flooding system is 0.05-0.7 PV;

[0088] Sodium chloride is used to adjust the mineralization of on-site water to obtain water for preparation with a mineralization of 1%-9%; the 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 acyl 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;

[0089] (3) injecting a foam flooding system after step (2), wherein the injection amount of the foam flooding system is 0-0.7 PV;

[0090] A foam flooding system with a mass concentration of 0.1% to 3.5% is prepared using a solution water with a salinity of 1% to 9%, wherein the foam flooding system comprises an anionic surfactant, a polymer compound and urea, wherein the anionic surfactant is a fatty acyl-peptide condensate, and nitrogen is added, and the volume ratio of nitrogen to the volume of the foam flooding system is 2:1 to 6:1.

[0091] The anionic surfactant is selected from one or more of sodium dodecyl sulfate, sodium dodecyl sulfonate, sodium lauroyl sarcosinate, and sodium lauric acid monoglyceride sulfate; the polymer compound is selected from one or more of xanthan gum, sodium carboxymethyl cellulose, and sodium carboxymethyl starch;

[0092] (4) injecting a PPG flooding system after step (3), wherein the injection amount of the PPG flooding system is 0-0.15 PV;

[0093] Use water with a salinity of 1%-9% to prepare a PPG flooding system with a mass concentration of 0.1%-0.3%;

[0094] (5) injecting a polymer flooding system after step (4), wherein the injection amount of the polymer flooding system is 0.03-0.07 PV;

[0095] 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.

[0096] 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).

[0097] The order of step (2) and step (3) can be interchanged or used alternately.

[0098] 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, such as Figure 1As shown, it comprises: 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 a suitable 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.

[0099] 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 the boundary between each phase can be determined more accurately.

[0100] The device can be used to more clearly observe the phase transition of the middle phase microemulsion. The phase state varies with the salt concentration or surfactant concentration added to the system, and the volume of the middle phase is also different. The higher the volume of the middle phase, the more conducive it is to improving the oil recovery efficiency. The present invention adjusts the salinity and compounding ratio of the oil recovery system according to the formation crude oil and the water used for liquid preparation.

[0101] The present invention will be described in detail below through examples.

[0102] In the following examples and comparative examples,

[0103] A conglomerate reservoir in Xinjiang Oilfield was selected as the target reservoir, and water-saturated cores produced from well area A were used to measure permeability; then the oil well crude oil was used to drive water until no water was produced; the water produced from well area A was used to drive to a water content of 98%, and the water drive recovery rate was calculated; an oil drive system with a certain PV number (the oil drive system in the embodiment and the comparative example) was injected, and then the water produced from well area A was used to drive to a water content of 98%, and the chemical drive recovery rate was calculated.

[0104] Preparation of polymer flooding system: On-site water is used to prepare the polymer flooding system, which includes partially hydrolyzed polyacrylamide and PPG, and the mass ratio of partially hydrolyzed polyacrylamide to PPG is 1:1; in the polymer flooding system, the total mass concentration of partially hydrolyzed polyacrylamide and PPG is 0.1%.

[0105] Preparation of a medium-phase microemulsion oil displacement system: sodium chloride is used to adjust the mineralization of on-site water to 3% as the preparation water to prepare the medium-phase microemulsion oil displacement system; the medium-phase microemulsion in the medium-phase microemulsion oil displacement system includes: 5 parts of coconut oil fatty acyl amino acid ethyl ester sodium, 1 part of hexadecyl polyoxypropylene sodium sulfate, and 1 part of nonylphenol polyoxyethylene ether sodium sulfate, and the mass concentration of the medium-phase microemulsion in the medium-phase microemulsion oil displacement system is 0.5%. The medium-phase microemulsion oil displacement system also adds a hyperbranched associative polymer with a mass concentration of 0.15% and sodium carbonate with a mass concentration of 0.6%, wherein the viscosity of the hyperbranched associative polymer is 50 mPa·s.

[0106] Preparation of nitrogen foam flooding system: Sodium chloride is used to adjust the mineralization of on-site water to 3%, and the foam flooding system is prepared as liquid preparation water. The foam flooding system includes: sodium dodecyl 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 is introduced into the foam flooding system so that the volume ratio of nitrogen to the foam flooding system is 3:1, thereby obtaining the nitrogen foam flooding system.

[0107] Preparation of PPG flooding system: Sodium chloride was used to adjust the mineralization of the on-site water to 3%, and the PPG flooding system with a mass concentration of 0.1% was prepared as the liquid preparation water.

[0108] Adopt SYT 5862-2020 Technical requirements for polymers for oil recovery.

[0109] The interfacial tension parameters are measured according to SY / T5370-2018 "Surface and interfacial tension determination method".

[0110] The permeability, water drive recovery and chemical drive recovery are measured according to QS / Y 1583-2013 Technical Specifications for Surfactants for Binary Flooding.

[0111] Example 1

[0112] An oil displacement method specifically comprises the following steps:

[0113] (1) injecting the polymer flooding system into the reservoir of the target oil reservoir at an injection volume of 0.05 PV;

[0114] (2) injecting the above-mentioned middle phase microemulsion flooding system after step (1) at an injection volume of 0.2 PV;

[0115] (3) injecting the nitrogen foam flooding system after step (2) at an injection volume of 0.15 PV;

[0116] (4) injecting the above-mentioned PPG flooding system after step (3) at an injection volume of 0.05 PV;

[0117] (5) After step (4), the polymer flooding system is injected at an injection volume of 0.05 PV.

[0118] The measured permeability, interfacial tension, water flooding recovery and chemical flooding recovery are shown in Table 1.

[0119] Example 2

[0120] The oil displacement method of Example 1 is used, except that the sodium hexadecyl polyoxypropylene sulfate in the microemulsion oil displacement system in step (2) is replaced by sodium tetradecyl polyoxypropylene sulfate. The rest is the same as Example 1. The results are shown in Table 1.

[0121] Example 3

[0122] The oil displacement method of Example 1 is different in that the coconut oil fatty acylamin acid ethyl sodium in the microemulsion oil displacement system in step (2) is replaced by a mixture of coconut oil fatty acylamin acid ethyl sodium (80wt%) and coconut oil fatty acid diethanolamide (20wt%). The rest is the same as in Example 1. The results are shown in Table 1.

[0123] Example 4

[0124] The oil recovery method of Example 1 was used, except that step (4) was not performed, that is, the step of injecting the nitrogen foam oil recovery system was not performed. The rest was the same as Example 1. The results are shown in Table 1.

[0125] Example 5

[0126] The oil recovery method of Example 1 is different in that step (4) is not performed, that is, the step of injecting the PPG oil recovery system is not performed. The rest is the same as Example 1. The results are shown in Table 1.

[0127] Example 6

[0128] The oil displacement method of Example 1 was used, except that step (1) and step (5) were not performed, that is, the step of injecting the polymer oil displacement system was not performed. The rest was the same as Example 1. The results are shown in Table 1.

[0129] Example 7

[0130] The oil displacement method of Example 1 was used, except that the viscosity of the hyperbranched associative polymer was 10 mPa·s. The rest was the same as Example 1. The results are shown in Table 1.

[0131] Example 8

[0132] 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 Example 1. The results are shown in Table 1.

[0133] Comparative Example 1

[0134] The oil displacement method of Example 1 is different in that the middle phase microemulsion oil displacement system of step (2) comprises: 1 part of coconut oil fatty acyl amino acid ethyl ester sodium, 1 part of hexadecyl polyoxypropylene sodium sulfate, and 1 part of nonylphenol polyoxyethylene ether sodium sulfate. The rest is the same as that of Example 1. The results are shown in Table 1.

[0135] Comparative Example 2

[0136] The oil displacement method of Example 1 is different in that the middle phase microemulsion oil displacement system of step (2) does not contain sodium nonylphenol polyoxyethylene ether sulfate. The rest is the same as Example 1. The results are shown in Table 1.

[0137] Comparative Example 3

[0138] The oil displacement method of Example 1 is used, except that the middle phase microemulsion oil displacement system of step (2) does not contain sodium hexadecyl polyoxypropylene sulfate. The rest is the same as Example 1. The results are shown in Table 1.

[0139] Comparative Example 4

[0140] The oil displacement method of Example 1 is different in that step (2) is not performed, that is, the step of injecting the middle phase microemulsion oil displacement system is not performed. The rest is the same as Example 1. The results are shown in Table 1.

[0141] Table 1

[0142]

[0143] It can be seen from the results in Table 1 that, under the premise of similar water drive recovery, the chemical drive recovery obtained by the oil recovery methods of Examples 1-7 of the present invention is greater than 20%, and Example 1 even reaches 51.3%, while the oil recovery methods of Comparative Examples 1-4 are all less than 20%. Therefore, the oil recovery methods of Examples 1-7 of the present invention have significantly better oil recovery effects than the oil recovery methods of Comparative Examples 1-4.

[0144] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope 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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