An emulsified oil displacement composition and its use in low-permeability reservoirs

Abstract

This invention provides an emulsified oil displacement composition and its application in low-permeability reservoirs. The emulsified oil displacement composition includes an extended surfactant, a betaine-type surfactant, an additive, and water. The emulsified oil displacement composition can utilize interfacial mixing and adsorption to adjust the interfacial vacancy size, enhance the synergistic effect with the active components of crude oil, and develop an oil displacement system with controllable emulsification strength. It achieves both ultra-low interfacial tension and emulsification performance, with the cost controlled within RMB 10,500 / ton, and has broad application prospects in low-permeability reservoirs.

Description

Technical Field

[0001] This invention relates to the field of oil displacement technology, and more particularly to an emulsified oil displacement composition and its use in low-permeability reservoirs. Background Technology

[0002] With the continuous improvement and expansion of tertiary oil recovery technology, the focus of research on enhancing oil recovery has gradually shifted from conventional reservoirs to low-permeability reservoirs with poor physical properties. Compared with ordinary reservoirs, the smaller pore size and larger specific surface area of ​​low-permeability reservoirs pose serious challenges to traditional chemical flooding systems. The adsorption and retention of surfactant-polymer binary composite systems prevent the effective utilization of the original technical advantages of the flooding formulation, leading to a bottleneck of "injection failure and recovery failure." At this point, in addition to possessing basic temperature and salt resistance properties, surfactants also need to address issues such as oil film stripping and pressure reduction / injection enhancement based on their own wetting regulation; increase capillary bundles, enhance emulsification strength, and strengthen initiation and migration by reducing oil-water interfacial tension; and control the mobility ratio and increase the viscosity of the bulk phase or front-end oil wall by constructing a certain film strength, ultimately achieving a significant increase in oil recovery.

[0003] In other words, the construction of an optimal chemical flooding system requires simultaneous consideration of factors such as pore structure, reservoir environment, and oil phase properties. Regarding pore structure, the permeability and heterogeneity of reservoir rock pores constrain the sweep capacity and permeability of the displacing fluid, which are prerequisites for formulation construction. The reservoir environment primarily imposes requirements on the stability of the displacing fluid; high-temperature, high-salinity reservoir environments can cause ionic surfactants to salt out and nonionic surfactants to become turbid, which is a necessary condition for formulation construction. Oil phase properties mainly affect the interfacial behavior of surfactant molecules. Different types of active components in crude oil can generate synergistic or anti-synergistic effects with surfactant molecules at the interface, regulating the tightness of the adsorption film, which is an important condition for formulation construction.

[0004] Laboratory characterization methods for enhancing oil recovery through chemical flooding mainly include sand-filling methods, CT scanning imaging, nuclear magnetic resonance T2 spectroscopy, and core displacement. These methods effectively simulate rock composition and pore structure characteristics, establishing a link between laboratory characterization and actual oilfield applications, thus increasing the reliability of chemical flooding formulation screening. However, these methods generally emphasize quantitative concepts, providing relatively little feedback on the initiation and migration of crude oil and emulsions in the pores. Information on the occurrence and distribution of remaining oil is also lacking, which is detrimental to the theoretical design of chemical flooding systems. Summary of the Invention

[0005] In view of the problems existing in the prior art, the present invention provides an emulsified oil displacement composition and its use in low-permeability reservoirs. The emulsified oil displacement composition has a high oil displacement effect targeting the reservoir environment, pore structure and crude oil properties, and the cost is controlled within RMB10,500 / ton, which has broad application prospects in low-permeability reservoirs.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides an emulsified oil displacement composition comprising an extended surfactant, a betaine surfactant, an additive, and water.

[0008] This invention reveals the mechanism of action of surfactant interfaces and bulk molecules, deepens the synergistic effect of oil displacement systems, and develops a high-efficiency and low-cost oil displacement system by using betaine-type surfactants with excellent ability to increase the strength of oil-water interfacial film as the main agent and extended surfactants and additives as auxiliary agents, targeting the reservoir environment, pore structure and crude oil properties.

[0009] This invention is based on the quantitative characterization of the surface and interface properties of the emulsion-regulated oil displacement system at the macroscopic scale, clarifying the relationship between the system's emulsification regulation capability and physicochemical parameters such as interfacial tension and film strength, and verifying the oil displacement effect of the above-mentioned emulsion-regulated oil displacement composition at the macroscopic scale.

[0010] Furthermore, based on the quantitative characterization of the surface and interface properties of the emulsion-controlled oil displacement system at the microscale, the relationship between the characterization at normal temperature, normal pressure, and macroscale and the actual application effect at high temperature, high pressure, and confined space was clarified, revealing the key technical indicators of emulsion control, and verifying the excellent oil displacement effect of the above-mentioned oil displacement composition at the microscale.

[0011] Preferably, the extended surfactant is a novel surfactant formed by embedding polyoxypropylene between the alkyl chain and hydrophilic group of the initial surfactant.

[0012] The present invention uses an extended surfactant that is temperature and salt resistant and reduces the oil-water interfacial tension to an ultra-low level. When combined with betaine-type surfactants and additives, it exerts a synergistic effect and significantly improves the oil displacement efficiency.

[0013] Preferably, the initial surfactant in the extended surfactant comprises an anionic nonionic surfactant.

[0014] Preferably, the anionic nonionic surfactant comprises any one or a combination of at least two of alkyl alcohol ether carboxylates, alkyl alcohol sulfates, or alkyl alcohol polyoxypropylene polyoxyethylene carboxylates, wherein typical but non-limiting combinations are combinations of alkyl alcohol ether carboxylates and alkyl alcohol sulfates, combinations of alkyl alcohol ether carboxylates and alkyl alcohol polyoxypropylene polyoxyethylene carboxylates, and combinations of alkyl alcohol polyoxypropylene polyoxyethylene carboxylates and alkyl alcohol sulfates.

[0015] Preferably, the number of addition groups in the embedded segment of the extended surfactant is 2 to 6 PO groups, for example, 2, 3, 4, 5 or 6.

[0016] The present invention preferably controls the number of addition segments of the embedded segment to be between 2 and 6, which can better balance the water-oil group ratio in the extended surfactant and has a better oil displacement effect.

[0017] Preferably, the betaine-type surfactant includes arylalkyl long-chain sulfobetaine.

[0018] Preferably, the mass ratio of the extended surfactant to the betaine surfactant in the emulsified oil displacement composition is (3-10):1, for example, it can be 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1 or 10:1, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0019] In this invention, when the mass ratio of the extended surfactant to the betaine surfactant is too high, the emulsion stability is poor; when the mass ratio of the extended surfactant to the betaine surfactant is too low, the pores and throats are blocked, affecting the emulsion migration.

[0020] Preferably, the mass fraction of the extended surfactant in the emulsified oil displacement composition is 0.2% to 0.28%, for example, it can be 0.2%, 0.21%, 0.22%, 0.23%, 0.24%, 0.25%, 0.26%, 0.27%, 0.28%, or 0.28%, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0021] In this invention, when the amount of the extended surfactant is too large, there are problems of difficulty in dissolving and low cost-effectiveness; when the amount of the extended surfactant is too small, there are problems of poor interfacial performance and low oil displacement efficiency.

[0022] Preferably, the mass fraction of the additive in the emulsified oil displacement composition is 0.01% to 0.3%, for example, it can be 0.01%, 0.05%, 0.08%, 0.11%, 0.14%, 0.18%, 0.21%, 0.24%, 0.27%, or 0.3%, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0023] In this invention, when the amount of additive is too large, it may affect the effect of the surfactant or even cause the surfactant to fail; when the amount of additive is too small, there may be significant adsorption loss during the oil displacement process, resulting in limited efficacy.

[0024] Preferably, the additive comprises any one or a combination of at least two of nanoparticles, alkaline substances, or neutral salts, wherein typical but non-limiting combinations are combinations of nanoparticles and alkaline substances, combinations of nanoparticles and neutral salts, and combinations of neutral salts and alkaline substances.

[0025] The present invention preferably uses the above-mentioned additives. Compared with other acidic salts, metal substances and other additives, the above substances have excellent temperature and salt resistance, good biodegradability, and can promote the activation and stripping of oil film by surfactants. They can also interact with betaine-type surfactants and extended surfactants to improve oil recovery efficiency.

[0026] Preferably, when the additive is nano-black card, the content of nano-black card in the emulsified oil displacement composition is 0.01-0.2%, for example, it can be 0.01%, 0.04%, 0.06%, 0.08%, 0.1%, 0.12%, 0.14%, 0.16%, 0.18%, or 0.2%, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0027] Preferably, the nanoparticles include nano-black cards.

[0028] The present invention does not impose any special limitation on the size of the nanoparticles. For example, the particle size of the nanoparticles can be a sheet-like material with a diameter of 5×300×300nm.

[0029] Preferably, when the additive is an alkaline substance, the content of the alkaline substance in the emulsified oil displacement composition is 0.01% to 0.3%, for example, it can be 0.01%, 0.05%, 0.08%, 0.11%, 0.14%, 0.18%, 0.21%, 0.24%, 0.27%, or 0.3%, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0030] Preferably, the alkaline substance includes sodium carbonate and / or sodium bicarbonate.

[0031] Preferably, when the additive is a neutral salt, the content of the neutral salt in the emulsified oil displacement composition is 0.1% to 0.5%, for example, it can be 0.1%, 0.15%, 0.19%, 0.24%, 0.28%, 0.33%, 0.37%, 0.42%, 0.46%, or 0.5%, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0032] Preferably, the neutral salt includes sodium chloride.

[0033] In a second aspect, the present invention provides the use of the emulsified oil displacement composition described in the first aspect for oil displacement in low-permeability reservoirs.

[0034] Preferably, the total salinity of water in the low-permeability reservoir is 15,000 to 30,000 mg / L, for example, it can be 15,000 mg / L, 16,000 mg / L, 18,000 mg / L, 20,000 mg / L, 21,000 mg / L, 23,000 mg / L, 25,000 mg / L, 26,000 mg / L, 28,000 mg / L or 30,000 mg / L, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0035] Preferably, the viscosity of the oil in the low-permeability reservoir is 5 to 10 cp, for example, it can be 5 cp, 5.6 cp, 6.2 cp, 6.7 cp, 7.3 cp, 7.8 cp, 8.4 cp, 8.9 cp, 9.5 cp or 10 cp, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0036] Preferably, the permeability of the low-permeability reservoir is 0.01–0.05 μm. 2 For example, it could be 0.01μm 2 0.015μm 2 0.019μm 2 0.024μm 2 0.028μm 2 0.033μm 2 0.037μm 2 0.042μm 2 0.046μm 2 or 0.05μm 2 This includes, but is not limited to, the listed values; other unlisted values ​​within this range also apply.

[0037] The emulsified oil displacement composition provided by this invention can be well applied to oil recovery in low-permeability reservoirs.

[0038] Preferably, the reservoir temperature of the low-permeability reservoir is 65-80℃, for example, it can be 65℃, 67℃, 69℃, 70℃, 72℃, 74℃, 75℃, 77℃, 79℃ or 80℃, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0039] Compared with the prior art, the present invention has at least the following beneficial effects:

[0040] (1) The emulsified oil displacement composition provided by the present invention adopts molecular design methods, changes the number and molecular weight of PO groups, uses an extended surfactant with excellent emulsifying performance, utilizes interfacial mixing adsorption, adjusts the interfacial vacancy size, enhances the synergistic effect with the active components of crude oil, and develops an emulsified oil displacement composition with controllable emulsification strength, achieving both ultra-low interfacial tension and emulsifying performance, with the cost controlled within RMB10,500 / ton, and has broad application prospects;

[0041] (2) The emulsified oil displacement composition provided by the present invention has excellent oil displacement efficiency for low-permeability reservoirs. The oil recovery rate of microscopic visualization oil displacement test can reach more than 89%, and the oil recovery rate of core displacement can reach more than 41%. Attached Figure Description

[0042] Figure 1 This is a test diagram of the droplet coalescence ability of the emulsified oil displacement composition provided in Example 1 of the present invention in a microscopic visualization oil displacement test.

[0043] Figure 2 This is a microscopic visualization of the oil displacement effect of the emulsified oil displacement composition provided in Example 1 of the present invention.

[0044] Figure 3 This is a graph showing the pressure data processing of multiple pressure measurement points during core displacement of the emulsified oil displacement composition provided in Example 1 of the present invention.

[0045] Figure 4 This is a one-dimensional wave displacement diagram of the emulsified oil displacement composition provided in Example 1 of the present invention during core displacement. Detailed Implementation

[0046] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0047] The present invention will now be described in further detail. However, the examples described below are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention is determined by the claims.

[0048] Examples 1-12 and Comparative Examples 1-6 provide different oil displacement compositions, the composition and formulation of which are shown in Table 1.

[0049] Table 1

[0050]

[0051] The simplified structural formula of S126 in Table 1 is shown below:

[0052]

[0053] In Table 1, "Same as 1" indicates that the same scheme is used as in Example 1.

[0054] The octadecyl dimethyl mixed betaine in Table 1 is the octadecyl dimethyl mixed betaine prepared in Example 1 of CN108531157A.

[0055] To verify the advantages of the emulsified oil displacement composition of this application, the following method was used to comprehensively test various properties of the emulsified oil displacement composition. Before the experiment, diluted crude oil was injected into different types of glass models at a rate of 20 μL / min until the crude oil filled the entire glass model and no air bubbles were present in the pore throat. During the experiment, different types of surfactant solutions were injected into the glass models at a constant injection rate of 0.1 μL / min. The entire process of crude oil displacement in the glass models (hydrophilic simulation, hydrophobic simulation, and heterogeneous) was recorded using a microscope in video recording mode, and the pressure changes during the displacement process were accurately recorded using the microfluidic uProcess software. The results are shown in Table 2.

[0056] Table 2

[0057]

[0058]

[0059] The droplet coalescence ability test of the emulsified oil displacement composition in Example 1 is shown in the figure below. Figure 1 As shown, from Figure 1 It can be seen that Example 1 has a suitable interfacial film strength, and the droplets do not rapidly coalesce.

[0060] Table 2 shows the migration mode W, which is a qualitative characterization of the initiation and migration capabilities of diluted crude oil in the glass model, including bulk migration, string migration, droplet migration, and emulsification migration. Among these, systems with ultra-low oil-water interfacial tension often migrate in string and droplet forms, while systems with higher tension generally migrate in a bulk manner.

[0061] The quantity M of residual film oil refers to the classification of residual oil in the glass model after displacement. Residual oil with a film thickness less than 1 / 3 of the pore throat diameter is defined as residual film oil. The quantity of residual film oil is a measure of the oil film removal capability of the emulsion displacement system; the lower the quantity, the better the oil film removal capability.

[0062] The microscopic contact angle C is another characterization of the system's ability to strip oil film. It is calculated by statistically analyzing the contact angle distribution of the remaining oil in the glass model after displacement; the larger the contact angle, the stronger the ability to strip oil film. Here, it refers to the oil phase contact angle.

[0063] Pressure P refers to the instantaneous pressure generated when the emulsion-modified displacement system breaks through and enters the glass model of saturated oil. The magnitude of the pressure is closely related to the interfacial film strength and interfacial tension. For emulsion-modified displacement systems with high film strength and high interfacial tension formed with diluted crude oil, the breakthrough pressure value is relatively high, and vice versa. The test results in Example 1 are as follows. Figure 2 As shown, from Figure 2 It can be seen that Example 1 has an excellent oil displacement effect.

[0064] Oil displacement efficiency K is the most intuitive quantitative description of the oil displacement effect of different types of emulsion-modified displacement systems in microscopic visualization tests. It is the ratio of the change in the oil phase pixel during the entire experiment to the initial pixel. The larger the ratio, the more porous crude oil is displaced, and the better the oil displacement effect.

[0065] The following points can be observed from Table 2:

[0066] (1) As can be seen from the comprehensive examples 1 to 12, the emulsified oil displacement composition provided by the present invention has excellent oil displacement effect. Its oil displacement efficiency in microscopic visualization test is above 49%, preferably up to 92%, and its core displacement oil displacement efficiency is above 17%, preferably up to 45%.

[0067] (2) As can be seen from Examples 1 and Comparative Examples 1-6, each component and its content in the emulsified oil displacement composition provided by the present invention are crucial, and the components work synergistically to significantly improve the oil displacement efficiency. Furthermore, as can be seen from Examples 1 and Examples 6-12, the present invention achieves a better oil displacement effect by selecting the content of each component and the substances within the preferred range.

[0068] Application of the emulsified oil displacement composition in tertiary oil recovery in Example 1

[0069] The oil displacement experiment was conducted according to the petroleum industry standard SY / T 6424-2014. Based on the pressure data at the end of water flooding, the one-dimensional core chemical flooding swept volume was calculated. First, the pressure at both ends of the core at the end of the subsequent water flooding was virtually extended. Virtual pressure points with equal values ​​to the core endpoints were assigned at positions with equal spacing between pressure measurement points outside the core, and Akima interpolation was performed on multiple pressure measurement points. Second, the interpolated pressure was differentiated to obtain the core pressure gradient distribution at the end of the subsequent water flooding. Finally, the pressure gradient was integrated, and the swept volume was represented by the area where the pressure gradient integration area was 50%. This quantitative swept volume value effectively includes system channeling swept volume, the main swept location of the system, and the degree of system retention. Example 1 illustrates the core displacement effect as follows: Figures 3-4 As shown, from Figures 3-4 It can be seen that the formulation of Example 1 has a good ability to start up and strip the original pores, and also has a certain sweep efficiency. The interfacial film strength is not too high, which can ensure the smooth injection and displacement of the oil displacement composition. The core displacement effect is good. The oil displacement efficiency of core displacement in other examples and comparative examples is shown in Table 2, denoted by R.

[0070] The applicant declares that the detailed structural features of the present invention are illustrated through the above embodiments, but the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must rely on the above detailed structural features to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for the components selected in the present invention, additions of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. An emulsified oil displacement composition, characterized in that, The emulsified oil displacement composition includes a spreadable surfactant, a betaine-type surfactant, an additive, and water; The extended surfactant is a novel surfactant formed by embedding polyoxypropylene between the alkyl chain and hydrophilic group of the initial surfactant, wherein the number of addition segments in the extended surfactant is 2 to 6 PO groups. The initial surfactant includes S126, the structural formula of which is shown below: ； The betaine-type surfactant includes octadecyl dimethyl betaine; The mass ratio of extended surfactant to betaine surfactant in the emulsified oil displacement composition is (3~10):1; The mass fraction of the extended surfactant in the emulsified oil displacement composition is 0.2-0.28%; The mass fraction of the additive in the emulsified oil displacement composition is 0.01~0.3%; The additives include any one or a combination of at least two of nanoparticles, alkaline substances, or neutral salts. The preparation method of the octadecyldimethyl mixed betaine includes the following steps: Step 1: In a 250mL three-necked flask equipped with a thermometer and a reflux condenser, add 29.7g of octadecyl dimethyl tertiary amine, 4.64g of sodium chloroacetate, 10g of propylene glycol, 10g of propylene glycol polyoxyethylene ether, and 5g of ethylene glycol monobutyl ether. Then place the three-necked flask in an oil bath and control the reaction temperature at 110-115°C for 1 hour to produce a mixed solution containing carboxylated betaine. Step 2: Continue heating to 125-130°C, and add 13.76g of sodium trichlorodihydroxypropanesulfonate to the mixture from Step 1. Continue the reaction for 2 hours. Detect the reaction by measuring the residual amine value. After the reaction, the conversion rate was 99.7% based on the amine value. Add 26.9g of deionized water while hot to obtain a pale yellow octadecyldimethyl mixed betaine.

2. The emulsified oil displacement composition according to claim 1, characterized in that, The nanoparticles include nano-black cards.

3. The emulsified oil displacement composition according to claim 2, characterized in that, When the additive is nano-black card, the content of nano-black card in the emulsified oil displacement composition is 0.01~0.2%.

4. The emulsified oil displacement composition according to claim 1, characterized in that, When the additive is an alkaline substance, the content of the alkaline substance in the emulsified oil displacement composition is 0.01~0.3%.

5. The emulsified oil displacement composition according to claim 4, characterized in that, The alkaline substances include sodium carbonate and / or sodium bicarbonate.

6. The emulsified oil displacement composition according to claim 1, characterized in that, When the additive is a neutral salt, the content of the neutral salt in the emulsified oil displacement composition is 0.1~0.3%.

7. The emulsified oil displacement composition according to claim 6, characterized in that, The neutral salt includes sodium chloride.

8. Use of the emulsified oil displacement composition according to any one of claims 1 to 7 in oil displacement in low-permeability reservoirs.

9. The use according to claim 8, characterized in that, The total salinity of water in the low-permeability reservoir is 15,000~30,000 mg / L.

10. The use according to claim 8, characterized in that, The viscosity of the oil in the low-permeability reservoir is 5-10 cp.

11. The use according to claim 8, characterized in that, The permeability of the low-permeability reservoir is 0.01~0.05 μm. 2 .

12. The use according to claim 8, characterized in that, The reservoir temperature of the low-permeability reservoir is 65~80℃.

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