A high internal phase viscosity-increasing in-situ emulsified oil displacement system

Abstract

The present invention discloses a high internal phase viscosity-increasing in-situ emulsifying oil displacement system, which is applicable to enhancing the oil displacement effect of CO2 flooding and chemical compound flooding by synergistically regulating the oil-water mobility ratio and interfacial tension, and belongs to the technical fields of oilfield chemistry and enhanced oil recovery. The in-situ emulsifying oil displacement system of the present invention comprises 0.1-0.12% of modified xanthan gum, 0.15-0.18% of lignosulfonate, 0.02-0.05% of glyceryl monostearate, 0.02-0.05% of nano calcium carbonate, and the balance is water. The interfacial tension between the in-situ emulsifying oil displacement system and crude oil can reach 10 ‑2 ~10 ‑3 mN / m. During the water flooding process, the crude oil and water can form a sufficiently large and stable W / O emulsion slug. The viscosity of this emulsion is greater than that of the crude oil, which can significantly reduce the mobility ratio of the displacing phase and the displaced phase, improve the water flooding swept volume, and has a strong flow control effect in heterogeneous formations.

Description

Technical Field

[0001] The present invention belongs to the technical field of oilfield chemistry and enhanced oil recovery, and particularly relates to a high internal phase viscosity-increasing in-situ emulsifying oil displacement system. Background Art

[0002] As one of the important technologies in chemical flooding, emulsifying oil displacement mainly improves oil recovery by injecting a surfactant system or alkaline water to achieve oil-water emulsification. In the reservoir, injecting the active system can not only reduce the oil-water interfacial tension, but also make the crude oil and formation water form a water-in-oil (W / O) emulsion. The viscosity of the W / O emulsion is greater than that of the crude oil, which can significantly reduce the mobility ratio of the displacement phase and the displaced phase, improve the waterflood sweep volume, and has a strong flow control effect.

[0003] The water-in-oil high internal phase emulsion generally consists of an oil phase, a water phase, and a surfactant with a relatively low hydrophilic-lipophilic balance value. The amphiphilic surfactant can spontaneously migrate to the oil-water interface and form a protective film between adjacent droplets, which not only prevents the collision between droplets spatially, but also increases the repulsive force between droplets by adsorbing on the droplet surface to improve the stability of the emulsion. As is well known, the environment of the reservoir is relatively complex and the formation structure is also relatively special, which results in the actual oil displacement ability being weaker than that measured in the laboratory when using surfactants for oil displacement in the reservoir. When using a single surfactant for oil displacement, these effects are more significant. To solve this problem, it is necessary to focus on the development of new surfactants or find a better surfactant compounding system. However, it is not easy to design a new surfactant, and the synthesized products are often unable to be industrially produced due to high costs. Therefore, more researchers tend to compound existing industrially produced surfactants and find that when compounded in appropriate proportions, they will exhibit a synergistic effect, that is, the performance is better than that of a single surfactant. More importantly, the interaction between them can reduce the adsorption of surfactants on the formation. For the compounding system, there are many forms that can be paired, such as anion-anion, anion-zwitterionic, and anion-nonionic surfactants. As long as the pairing is appropriate, high-efficiency oil displacement can be achieved. When the traditional compounding system improves the emulsification performance, although it can reduce the interfacial tension, the viscosity-increasing effect is limited, and it is difficult to optimize the sweep coefficient and oil displacement efficiency simultaneously. Summary of the Invention

[0004] Aiming at the above problems, the purpose of the present invention is to provide a high internal phase viscosity-increasing in-situ emulsifying oil displacement system. The oil displacement system of the present invention forms a high internal phase W / O emulsion during the oil displacement process, which can significantly reduce the interfacial tension and increase the viscosity of the emulsion, and is beneficial to improving the crude oil recovery rate.

[0005] To achieve the above technical objectives, the present invention adopts the following technical solutions:

[0006] A high internal phase viscosity-increasing in-situ emulsifying oil displacement system, calculated by mass percentage, consists of the following components:

[0007] Xanthan gum modified by long-chain alkylsilane, the carbon chain of the long-chain alkyl is 12 - 16, 0.1 - 0.12%;

[0008] Lignosulfonate, 0.15 - 0.18%;

[0009] Glycerol stearate, 0.02 - 0.05%;

[0010] Nano calcium carbonate, 0.02 - 0.05%;

[0011] The balance is water.

[0012] As a specific embodiment of the present invention, the xanthan gum modified by long-chain alkylsilane is xanthan gum modified by hexadecyltrimethoxysilane.

[0013] As a specific embodiment of the present invention, the xanthan gum modified by hexadecyltrimethoxysilane is prepared by the following method:

[0014] S1. Add hexadecyltrimethoxysilane to an ethanol aqueous solution for hydrolysis to obtain a hexadecyltrimethoxysilane hydrolysis solution;

[0015] The hydrolysis in this step is a conventional reaction, and its specific conditions can be selected according to needs. For example, in some embodiments, hexadecyltrimethoxysilane accounts for 5 - 10% of the total mass of hexadecyltrimethoxysilane and the ethanol aqueous solution, the ethanol purity is 95v%, during the hydrolysis process, magnetic stirring is used, the stirring rate is 200 - 500 rpm, the hydrolysis temperature is 35 - 40 °C, and the hydrolysis time is 1 - 2 h.

[0016] S2. Under stirring conditions, gradually add a pH regulator to the solution obtained in S1 to adjust the pH value of the solution to acidic;

[0017] In this step, the pH regulator can be selected from conventional agents such as hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, etc. For safety considerations, low-concentration acidic substances are preferably selected, and the product performance will be better when the pH value is adjusted to 3 - 4.

[0018] S3. Add xanthan gum to the solution obtained in S2, and react for 4 - 5 h under stirring at 35 - 40 °C to obtain a hydrophobically modified xanthan gum solution; the mass ratio of xanthan gum to hexadecyltrimethoxysilane is 1:5 - 1:10;

[0019] S4. Centrifuge the hydrophobically modified xanthan gum solution, wash and dry the separated solid matter to obtain the target product.

[0020] Beneficial effects: High internal phase synergistic viscosity increasing effect: Through the synergistic effect of a composite surfactant system of modified xanthan gum (with both viscosity increasing and emulsification regulation functions), lignosulfonate, and glyceryl stearate (with both anionic and nonionic characteristics), as well as nano-calcium carbonate particles, double breakthroughs of "ultra-low interfacial tension" and "high-viscoelastic emulsion" are achieved at a low total concentration (0.29 - 0.4%).

[0021] Green economic breakthrough: The combined use of lignosulfonate (an industrial by-product) and bio-based glyceryl stearate significantly reduces the chemical agent cost while ensuring performance (30 - 50% lower than synthetic surfactants), and the temperature and salt resistance of nano-calcium carbonate endows the system with a wider reservoir adaptability. Brief description of the drawings

[0022] Figure 1 is the curve of increasing the viscosity of crude oil by the high internal phase viscosity increasing in-situ emulsifying oil displacement system with different water cut rates;

[0023] Figure 2 is the oil displacement effect diagram of the high internal phase viscosity increasing in-situ emulsifying oil displacement system. Detailed implementation manners

[0024] In order to make the objectives, technical solutions, and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with embodiments.

[0025] Example 1: Preparation of modified xanthan gum: Weigh 5.0 g of hexadecyltrimethoxysilane (HDTMS), add it to a three-necked flask containing 95 g of an ethanol (purity 95 v%) aqueous solution, magnetically stir at a speed of 500 rpm, and gradually add dilute hydrochloric acid dropwise to the solution to adjust the pH value of the solution to 3 - 4. Then react at 40 °C for 1.5 h to obtain hydrolyzed hexadecyltrimethoxysilane; add 1.0 g of xanthan gum to the hydrolyzed hexadecyltrimethoxysilane solution, and react at 40 °C with magnetic stirring (500 rpm) for 4 h to obtain a modified xanthan gum solution; use a centrifuge to separate the modified xanthan gum solution (set the centrifuge speed to 1200 rpm and the centrifugation time to 5 min) to remove the solvent; after centrifugation, wash the solid product with ethanol solution multiple times and perform multiple centrifugation separations until the pH value of the washing liquid is neutral, and place the obtained product in a vacuum oven to dry to obtain a white powder, which is the modified xanthan gum.

[0026] Example 2: By mass percentage, take 0.12% of the modified xanthan gum (prepared in Example 1), 0.15% of lignosulfonate, 0.04% of glyceryl stearate, 0.04% of nano-calcium carbonate, and the balance is simulated formation water (the salinity is 0.1×10 4(mg / L), add each raw material into the simulated formation water and stir for 2.0 hours to obtain a high internal phase viscosity-increasing in-situ emulsified oil displacement system.

[0027] Example 3: The steps are the same as those in Example 2, except that the salinity of the simulated formation water is 1×10 4 mg / L.

[0028] Example 4: The steps are the same as those in Example 2, except that the salinity of the simulated formation water is 10×10 4 mg / L.

[0029] Example 5: The steps are the same as those in Example 2, except that the salinity of the simulated formation water is 20×10 4 mg / L.

[0030] Test Example 1

[0031] Add the high internal phase viscosity-increasing in-situ emulsified oil displacement systems of Examples 2 to 5 and four kinds of crude oils into the test tubes. Measure the interfacial tension between the high-phase-transition-point in-situ emulsified viscosity-increasing system and the degassed crude oil at 65°C using a TX500C rotary drop interfacial tensiometer for 1 h to obtain stable interfacial tension values, as shown in Table 1.

[0032] Table 1 Stable interfacial tension between the high internal phase viscosity-increasing in-situ emulsified oil displacement system and crude oil

[0033]

[0034] As can be seen from Table 1, each oil displacement system can keep the interfacial tension between oil and water at the order of magnitude of 10 4 mN / m under the condition of mineralized water with a salinity of 0.1 - 20×10 -2 mg / L, showing good performance in reducing the oil-water interfacial tension.

[0035] Test Example 2

[0036] Emulsifying performance of the high internal phase viscosity-increasing in-situ emulsified oil displacement system: Mix the high internal phase viscosity-increasing in-situ emulsified oil displacement systems prepared in Examples 2 to 5 and the degassed crude oil (crude oil viscosity 212.64 mPa·s) at volume ratios of 1:9, 2:8, 3:7, 4:6, 5:5, 6:4, 7:3, 8:2, and 9:1 respectively. Use an emulsifying homogenizer to shear them for 30 min, and measure the viscosity of the emulsion after shearing (test temperature is 65°C). The results are shown in Tables 2 to 5.

[0037] Table 2 Viscosity of emulsions formed by mixing Example 2 and crude oil in different ratios

[0038]

[0039] Table 3 Viscosity of Emulsions Formed by Mixing Example 3 with Crude Oil in Different Proportions

[0040]

[0041] Table 4 Viscosity of Emulsions Formed by Mixing Example 4 with Crude Oil in Different Proportions

[0042]

[0043] Table 5 Viscosity of Emulsions Formed by Mixing Example 5 with Crude Oil in Different Proportions

[0044]

[0045] As can be seen from Tables 2 to 5, the high internal phase viscosity-increasing in-situ emulsifying oil displacement system triggers the reconstruction of oil-water phase states under the action of the formation shear field, forming water-in-oil emulsions with the function of mobility control. When the water cut of the system breaks through 80%, high internal phase water-in-oil emulsions with relatively high viscosities can still be formed, and the viscosity of the emulsions is 1.2 to 7.8 times that of the viscous oil within the entire water cut range, showing significant non-Newtonian fluid characteristics. This viscosity gradient evolution mechanism enables the emulsions to strengthen mobility control through structural viscosity at high water cut stages and maintain the effective migration of the emulsions in porous media through appropriate fluid forms, achieving the dynamic balance of the viscoelasticity and transportability of the displacement phase.

[0046] Example 6: By mass percentage, take 0.1% of modified xanthan gum (prepared in Example 1), 0.18% of lignosulfonate, 0.05% of glyceryl stearate, 0.05% of nano-calcium carbonate, and the balance is simulated formation water. Add each raw material to the simulated formation water and stir for 2.0 hours to obtain a high internal phase viscosity-increasing in-situ emulsifying oil displacement system.

[0047] The composition of the simulated formation water is as follows:

[0048]

[0049] Test Example 3

[0050] Emulsifying Performance of the High Internal Phase Viscosity-Increasing In-Situ Emulsifying Oil Displacement System: Mix the high internal phase viscosity-increasing in-situ emulsifying oil displacement system of Example 6 with crude oil (crude oil viscosity 126.3 mPa·s) at volume ratios of 1:9, 2:8, 3:7, 4:6, 5:5, 6:4, 7:3, 8:2, and 9:1 respectively, and use an emulsifying homogenizer to shear it for 30 min, and measure the viscosity of the sheared emulsion. The results are as Figure 1 shown.

[0051] Test Example 4

[0052] Oil displacement performance of the high internal phase visco-increasing in-situ emulsification oil displacement system: Through displacement experiments on a homogeneous core (permeability 800 mD, length 8 cm, diameter 3.8 cm) at 65 °C, the oil displacement performance of the high internal phase visco-increasing in-situ emulsification oil displacement system (Example 5) was studied. The results are as Figure 2 shown. During the water flooding stage (water flooding rate 2.0 mL / min), affected by the imbalance of the mobility ratio between the water phase and the crude oil, the water flooding showed significant fingering characteristics. When the water cut rapidly rose to 98% after water flooding breakthrough, the oil recovery was only about 35%; Subsequently, when injecting the high internal phase visco-increasing in-situ emulsification oil displacement system (injection rate 0.4 mL / min), it was found that: the injection pressure gradient increased, which indicated that the system achieved mobility control through viscoelastic regulation; The W / O emulsion (internal phase ratio > 74%) was continuously produced at the outlet end of the core, which proved that the in-situ phase transition could still be triggered under the residual oil saturation condition. The emulsion improved the oil recovery through dual effects: on the one hand, the high-viscosity continuous phase improved the macroscopic mobility ratio and inhibited the channeling of the displacement fluid; on the other hand, the interfacial tension was reduced to the order of 10 -2 mN / m and accompanied by the regulation of the phase transition point, realizing the stripping of crude oil at the microscopic pore level. Finally, the oil recovery was increased to 48% in a single stage during the chemical flooding stage, and the cumulative oil recovery reached 83%, which verified the technical advantages of the viscosity-increasing and emulsification synergistic strengthening mechanism.

[0053] As mentioned above, it is not a restriction on the present invention in any form. Although the present invention has been disclosed through the above embodiments, it is not used to limit the present invention. Any person skilled in the art, within the scope of the technical solution of the present invention, can make some changes or modifications to equivalent embodiments with equivalent changes by using the technical content disclosed above. However, as long as it does not depart from the content of the technical solution of the present invention, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention all fall within the scope of the technical solution of the present invention.

Claims

1. A high internal phase viscosity-enhancing in-situ emulsification flooding system, characterized in that: In terms of mass percentage, it is composed of the following components: Xanthan gum modified with long-chain alkyl silane, the carbon chain of the long-chain alkyl is 12~16, 0.1~0.12%; Lignin sulfonate, 0.15-0.18%; Glycerol stearate, 0.02~0.05%; Nano calcium carbonate, 0.02~0.05%; The rest is water; The long-chain alkylsilane-modified xanthan gum is hexadecyltrimethoxysilane-modified xanthan gum, which is prepared by the following method: S1, adding hexadecyltrimethoxysilane into an ethanol aqueous solution for hydrolysis to obtain a hexadecyltrimethoxysilane hydrolyzed solution; S2, adding a pH adjuster dropwise to the solution obtained in S1 under stirring to adjust the pH value of the solution to acidic; S3, adding xanthan gum to the solution obtained in S2, reacting for 4-5 hours under stirring at 35-40° C. to obtain a hydrophobically modified xanthan gum solution; S4. Centrifugally separate the hydrophobically modified xanthan gum solution, and wash and dry the separated solid matter to obtain the target product.

2. A high internal phase viscosity-enhancing in-situ emulsification flooding system as claimed in claim 1, characterized in that: In step S1, the hydrolysis conditions are as follows: stirring rate is 200-500 rpm, hydrolysis temperature is 35-40° C., and hydrolysis time is 1-2 h.

3. A high internal phase viscosity-enhancing in-situ emulsification flooding system as claimed in claim 1, characterized in that: In step S3, the mass ratio of xanthan gum to hexadecyltrimethoxysilane is 1:5-1:

10.

4. A high internal phase viscosity-enhancing in-situ emulsification flooding system as claimed in claim 1, characterized in that: In step S4, the pH value of the solution is adjusted to 3-4.

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