High internal phase tackifying in-situ emulsification oil displacement system

Abstract

The invention discloses a high internal phase tackifying type in-situ emulsification oil displacement system which is suitable for strengthening the oil displacement effect of CO2 flooding and chemical combination flooding by cooperatively regulating and controlling the oil-water mobility ratio and interfacial tension, and belongs to the technical field of oilfield chemistry and recovery efficiency improvement. The in-situ emulsification oil displacement system disclosed by the invention is prepared from 0.1 to 0.12 percent of modified xanthan gum, 0.15 to 0.18 percent of lignosulfonate, 0.02 to 0.05 percent of glycerol stearin, 0.02 to 0.05 percent of nano calcium carbonate and the balance of water. The interfacial tension of the in-situ emulsification oil displacement system and crude oil can reach 10 <-2 >-10 <-3 > mN / m, in the water displacement process, the crude oil and water can form a W / O emulsion slug which is large enough and stable, the viscosity of the emulsion is larger than that of the crude oil, the mobility ratio of a displacement phase to a displaced phase can be obviously reduced, the water displacement swept volume is increased, and the oil displacement efficiency is improved. And a very strong flow control effect is achieved in a heterogeneous stratum.

Description

Technical Field

[0001] The present invention belongs to the technical fields 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 an oil reservoir, injecting an 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 water flooding swept volume, and has a strong flow control effect.

[0003] The water-in-oil high internal phase emulsion is generally composed 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 oil 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 oil 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 often cannot be industrially produced due to high costs. Therefore, more researchers tend to compound existing industrially produced surfactants and find that they will show a synergistic effect when compounded in appropriate proportions, 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, efficient 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: A high internal phase viscosity-increasing in-situ emulsifying oil displacement system, in terms of mass percentage, consists of the following components: Xanthan gum modified by long-chain alkyl silane, where the carbon chain of the long-chain alkyl is 12 - 16, 0.1 - 0.12%; Lignosulfonate, 0.15 - 0.18%; Glycerol stearate, 0.02 - 0.05%; Nano calcium carbonate, 0.02 - 0.05%; The balance is water.

[0006] As a specific embodiment of the present invention, the xanthan gum modified by long-chain alkyl silane is xanthan gum modified by hexadecyltrimethoxysilane.

[0007] As a specific embodiment of the present invention, the xanthan gum modified by hexadecyltrimethoxysilane is prepared by the following method: S1. Add hexadecyltrimethoxysilane to an ethanol aqueous solution for hydrolysis to obtain a hexadecyltrimethoxysilane hydrolysis solution; The hydrolysis in this step is a conventional reaction, and its specific conditions can be selected as needed. 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.

[0008] S2. Gradually add a pH regulator to the solution obtained in S1 under stirring conditions to adjust the pH value of the solution to acidic; In this step, the pH regulator can be selected from conventional reagents 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.

[0009] S3. Add xanthan gum to the solution obtained in S2 and react under stirring at 35 - 40 °C for 4 - 5 h to obtain a hydrophobically modified xanthan gum solution; the mass ratio of xanthan gum to hexadecyltrimethoxysilane is 1:5 - 1:10; S4. Centrifuge the hydrophobically modified xanthan gum solution, wash and dry the separated solid matter to obtain the target product.

[0010] Beneficial effects: High internal phase synergistic viscosity-increasing effect: Through the combined 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 the synergistic effect of 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%).

[0011] 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. Description of the drawings

[0012] 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 ratios; Figure 2 is the oil displacement effect diagram of the high internal phase viscosity-increasing in-situ emulsifying oil displacement system. Detailed implementation manners

[0013] 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 the embodiments.

[0014] 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 ethanol (purity 95 v%) aqueous solution, stir magnetically 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 under 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 centrifuge and separate multiple times until the pH value of the washing solution is neutral. Place the obtained product in a vacuum oven to dry to obtain a white powder, which is the modified xanthan gum.

[0015] 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 4mg / 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.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] Test Example 1 Put the high internal phase viscosity-increasing in-situ emulsified oil displacement systems of Examples 2 to 5 and four kinds of crude oils into a test tube, and use a TX500C rotary drop interfacial tension meter to measure the interfacial tension between the high phase transition point in-situ emulsified viscosity-increasing system and the degassed crude oil at 65°C for 1 h to obtain a stable interfacial tension value, as shown in Table 1.

[0020] Table 1 Stable interfacial tension between the high internal phase viscosity-increasing in-situ emulsified oil displacement system and crude oil

[0021] As can be seen from Table 1, the interfacial tension between oil and water can be maintained at the order of 10 4 mN / m under the condition of mineralized water with a salinity of 0.1 - 20×10 -2 mg / L for each oil displacement system, showing good performance in reducing the oil-water interfacial tension.

[0022] Test Example 2 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 degassed crude oil (crude oil viscosity 212.64 mPa·s) respectively according to the volume ratios of 1:9, 2:8, 3:7, 4:6, 5:5, 6:4, 7:3, 8:2, and 9:1, and use an emulsifying homogenizer to shear them for 30 min, and measure the viscosity of the emulsion after shearing (the test temperature is 65°C), and the results are shown in Tables 2 to 5.

[0023] Table 2 Viscosity of emulsions formed by mixing Example 2 and crude oil in different ratios

[0024] Table 3 Viscosity of emulsions formed by mixing Example 3 and crude oil in different ratios

[0025] Table 4 Viscosity of Emulsions Formed by Mixing Example 4 with Crude Oil in Different Proportions

[0026] Table 5 Viscosity of Emulsions Formed by Mixing Example 5 with Crude Oil in Different Proportions

[0027] 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 a water-in-oil emulsion with a mobility control function. When the water cut of the system breaks through 80%, a high internal phase water-in-oil emulsion with relatively high viscosity can still be formed, and the viscosity of the emulsion 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 emulsion to strengthen mobility control through structural viscosity at the high water cut stage and maintain the effective migration of the emulsion in the porous medium through a moderate fluid morphology, achieving a dynamic balance between the viscoelasticity and transportability of the displacement phase.

[0028] Example 6: Taking 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 by mass percentage, and the balance being 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.

[0029] The composition of the simulated formation water is as follows:

[0030] Test Example 3 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 shear them with an emulsifying homogenizer for 30 min, and measure the viscosity of the emulsion after shearing. The results are as Figure 1 shown.

[0031] Test Example 4 Oil Displacement Performance of the High Internal Phase Viscosity-Increasing In-Situ Emulsifying Oil Displacement System: Conduct a displacement experiment through a homogeneous core (permeability 800 mD, length 8 cm, diameter 3.8 cm) at 65 °C to study the oil displacement performance of the high internal phase viscosity-increasing in-situ emulsifying oil displacement system (Example 5). The results are as Figure 2As shown, during the water flooding stage (water flooding rate: 2.0 mL / min), affected by the imbalance between the mobility ratios of the water phase and crude oil, the water flooding exhibits significant fingering characteristics. When the water cut rapidly rises to 98% after water flooding breakthrough, the oil recovery factor only reaches about 35%. Subsequently, when injecting a highly viscous in-situ emulsifying oil displacement system with a high internal phase (injection rate: 0.4 mL / min), it is found that the injection pressure gradient increases, indicating that the system achieves mobility control through viscoelastic regulation. An oil-in-water (W / O) emulsion (internal phase ratio > 74%) is continuously produced at the core outlet end, which proves that in-situ phase transition can still be triggered under residual oil saturation conditions. The emulsion enhances oil recovery through two aspects: on the one hand, the high-viscosity continuous phase improves the macroscopic mobility ratio and inhibits the channeling of the displacement fluid; on the other hand, the interfacial tension is 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 factor is increased to 48% in a single stage during the chemical flooding stage, and the cumulative oil recovery factor reaches 83%, which verifies the technical advantages of the viscosity-increasing and emulsifying synergistic enhancement mechanism.

[0032] As mentioned above, this is not any form of limitation to the present invention. Although the present invention has been disclosed through the above embodiments, it is not intended to limit the present invention. Any person skilled in the art, without departing from the scope of the technical solution of the present invention, may make some changes or modifications to the 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 shall 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.

2. A high internal phase viscosity-enhancing in-situ emulsification flooding system as claimed in claim 1, characterized in that: The long-chain alkylsilane-modified xanthan gum is hexadecyltrimethoxysilane-modified xanthan gum.

3. A high internal phase viscosity-enhancing in-situ emulsification flooding system as claimed in claim 2, characterized in that: The hexadecyltrimethoxysilane-modified xanthan gum 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.

4. A high internal phase viscosity-enhancing in-situ emulsification flooding system as claimed in claim 3, 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.

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

10.

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

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