An in-situ emulsified water plugging system for oil well and a preparation method thereof

Abstract

The present application relates to the technical field of petroleum chemical industry, in particular to an in-situ emulsified water plugging system for oil well and a preparation method thereof.The system comprises an oil phase, modified molybdenum disulfide nanosheets and an emulsifier; the modified molybdenum disulfide nanosheets are obtained by modifying molybdenum disulfide nanosheets with an organic solvent.The oil-based water plugging system prepared by using modified molybdenum disulfide nanosheets and an emulsifier can realize in-situ emulsification of water phase in the ground, improve the selective plugging capacity of the plugging agent in the formation, that is, only in the water producing layer can plugging effect be produced, and through the synergistic effect of nanosheets and emulsifiers, the viscosity of the emulsion and the emulsification capacity of water are improved, and the plugging efficiency is further improved.

Description

Technical Field

[0001] This invention relates to the field of petrochemical technology, specifically to an in-situ emulsified water shut-off system for oil wells and its preparation method. Background Technology

[0002] Emulsions are an important water shut-off system for oil wells. They primarily use surfactants as emulsifiers to emulsify the oil phase and water, forming a relatively stable controlled-drive system. However, water-in-oil emulsion water shut-off systems undergo emulsification at the surface, resulting in excessively high initial viscosity and making injection difficult. Oil-in-water emulsions, on the other hand, have lower injection pressure but weaker plugging power. Traditional active oil water shut-off systems utilize emulsifiers added to the oil phase to emulsify with produced water underground, increasing viscosity and thus shutting off water. However, in emulsions stabilized by oil-based emulsifiers, the active oil's ability to emulsify formation water is poor. When the mass ratio of formation water to active oil exceeds 7:1, water-in-oil emulsions cannot form, leading to an emulsion type reversal into an oil-in-water emulsion, resulting in decreased viscosity and poorer plugging effect.

[0003] Chinese patent document CN202110396640.9 discloses a water-in-oil emulsion water-blocking agent based on ethylene tar, its preparation method, and its application. The water-in-oil emulsion water-blocking agent based on ethylene tar comprises the following components by weight percentage: 1.0%–2.0% oil-soluble anionic surfactant, 1.0%–2.0% nonionic surfactant, 0.05%–0.15% co-surfactant, 1.0%–2.0% modified nanoparticles, 30%–45% ethylene tar, and the balance being water.

[0004] Chinese patent document CN201510535437.X discloses a heavy oil emulsion phase inversion profile control and water shut-off agent. The heavy oil emulsion phase inversion profile control and water shut-off agent comprises: 50g of active heavy oil, 30g of water, 10g of limestone powder, 0.5-0.7g of emulsifier, 2-7g of phase inversion agent, and 0.3-0.7g of stabilizer. This invention uses heavy oil, which does not damage the oil layer, as the main profile control and water shut-off material. Before injection into the bottom layer, it is first prepared as a low-viscosity water-in-oil emulsion. After injection into the formation, the formation temperature and the added phase inversion agent transform the water-in-oil emulsion into a higher-viscosity water-in-oil emulsion. Because the stabilizer and limestone powder are added to the profile control and water shut-off agent, the water-in-oil emulsion entering the formation is more stable and has a high viscosity, thus providing excellent water shut-off effect even in rock layers with large fractures.

[0005] Chinese patent document CN02128876.3 discloses a method for phase inversion profile control and water shut-off using heavy oil emulsions, along with a phase inversion agent. This method involves adding 0.4–1.0% oil-in-water emulsion and 3%–10% of a phase inversion agent to a heavy oil system, followed by injection into the formation. The oil-in-water emulsion is a mixture of nonionic surfactants such as OP series, Tween series, Span series, and sodium carboxylate, along with inorganic salts such as sodium carbonate. The phase inversion agent is a mixture of oil-soluble surfactants such as OP series or Span series, or nonionic surfactants such as organic acid esters, and solid powders such as rosin powder, asphalt powder, coal powder, or bentonite.

[0006] The water-blocking system described above forms an emulsion on the ground and then reverses phase to form a water-in-oil emulsion after entering the underground, thereby achieving the purpose of water blocking. However, since a large amount of water is emulsified during the injection process, the ability to further emulsify water in the formation is greatly weakened. At the same time, traditional stable emulsions mainly use oil-soluble surfactants, whose ability to emulsify water and the stability of the emulsion are lower than those of emulsions stabilized by nanoparticles. Currently reported technologies mainly use spherical particles such as nano-silica to stabilize emulsions.

[0007] Nanomaterials can be adsorbed onto oil-water interfaces to stabilize emulsions. Based on their shape, they can be categorized into spherical, nanosheet, and rod-shaped nanomaterials. Spherical and rod-shaped nanoparticles exist at the oil-water interface in a "point-to-surface" contact manner, resulting in a small effective contact area between the particles and the interface, requiring a large amount of material and leading to unsatisfactory economic benefits. Therefore, there is an urgent need to improve the sealing efficiency of water-blocking systems. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention provides an in-situ emulsified water shut-off system for oil wells and its preparation method. The oil-based water shut-off system prepared by this invention using modified molybdenum disulfide nanosheets and emulsifiers can achieve in-situ injection of underground emulsified aqueous phase, improving the selective plugging ability of the plugging agent in the formation, that is, the plugging effect only occurs at the water-producing layer. Furthermore, the synergistic effect of nanosheets and emulsifiers improves the viscosity of the emulsion and its ability to emulsify water, further enhancing the plugging efficiency.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] This invention provides an in-situ emulsified water shut-off system for oil wells, the system comprising an oil phase, modified molybdenum disulfide nanosheets, and an emulsifier; the modified molybdenum disulfide nanosheets are obtained by modifying molybdenum disulfide nanosheets with an organic solvent.

[0011] Furthermore, the modified molybdenum disulfide nanosheets constitute 0.05%-1.0% of the oil phase by mass; the emulsifier constitutes 1%-10% of the oil phase by mass.

[0012] Furthermore, the method for preparing the modified molybdenum disulfide nanosheets is as follows:

[0013] (1) Add ammonium molybdate and thiourea to an aqueous solution, dissolve them completely, transfer the solution to a high-pressure reactor and heat it to carry out the reaction. After the reaction is completed, centrifuge, wash the precipitate, and dry it to obtain molybdenum disulfide nanosheets.

[0014] (2) Molybdenum disulfide nanosheets were placed in a solvent, n-octadecyl mercaptan was added, the mixture was stirred to carry out the reaction, and after centrifugation, washing and drying, modified molybdenum disulfide nanosheets were obtained.

[0015] Furthermore, the reaction time in step (1) is 8-16 h and the reaction temperature is 180-220 °C.

[0016] Furthermore, in step (1), the weight ratio of ammonium molybdate to thiourea is 1:1 to 10.

[0017] Furthermore, in step (2), the mass ratio of molybdenum disulfide nanosheets to n-octadecyl mercaptan is 1:0.05-0.15.

[0018] Furthermore, the solvent mentioned in step (2) is water or ethanol.

[0019] Furthermore, the oil phase is a light oil.

[0020] Furthermore, the emulsifier is a fatty acid ester oil-based emulsifier.

[0021] This invention also provides a method for preparing the above-described in-situ emulsified water shut-off system for oil wells, the method comprising the following steps:

[0022] Add an emulsifier to the thin oil and stir to dissolve; then add modified molybdenum disulfide nanosheets and stir thoroughly.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] 1. This invention uses molybdenum disulfide nanosheets and modifies them to change the molybdenum disulfide from strongly hydrophilic to weakly hydrophilic, thereby enabling it to be adsorbed on the oil-water interface.

[0025] 2. The oil-based water plugging system prepared by the present invention using modified molybdenum disulfide nanosheets and emulsifiers can achieve in-situ injection of underground emulsified aqueous phase, which improves the selective plugging ability of the plugging agent in the formation—the plugging effect is only produced at the water-producing layer.

[0026] 3. This invention improves the viscosity of the emulsion and its ability to emulsify water through the synergistic effect of modified molybdenum disulfide nanosheets and emulsifiers, thereby further improving the sealing efficiency. Detailed Implementation

[0027] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0028] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments of the present invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, and / or combinations thereof.

[0029] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0030] Unless otherwise specified, all reagents and materials used in the examples are commercially available or prepared using existing technologies; and all methods used are existing technologies unless otherwise specified.

[0031] Example 1

[0032] An in-situ emulsified water shut-off system for oil wells, the system comprising an oil phase, modified molybdenum disulfide nanosheets, and an emulsifier.

[0033] The modified molybdenum disulfide nanosheets comprise 0.2% by mass in the oil phase; the emulsifier comprises 1% by mass in the oil phase.

[0034] The oil phase is a thin oil, and the emulsifier is a fatty acid ester oil-based emulsifier.

[0035] The modified molybdenum disulfide nanosheets are prepared by the following method:

[0036] (1) Mix ammonium molybdate and thiourea in 100 mL of deionized water at a mass ratio of 1:10 g and stir for 2 h. Transfer the resulting solution to a high-pressure reactor with a capacity of 150 mL and heat it in an oven at 200 °C for 12 h.

[0037] (2) After the reaction is completed and the reactor is cooled to room temperature, the product is centrifuged and washed several times to remove impurities and reaction byproducts. It is then placed in a vacuum drying oven at 60°C overnight to obtain molybdenum disulfide nanosheets.

[0038] (3) Disperse 1g of molybdenum disulfide nanosheets in 100mL of ethanol solution and sonicate at room temperature for 30min; then add 0.1g of n-octadecyl alcohol and stir for 24h.

[0039] (4) Centrifuge and wash the reaction solution to remove ungrafted modifiers and reaction byproducts, and dry it in a vacuum drying oven at 60°C to obtain modified molybdenum disulfide nanosheets.

[0040] The method for preparing the water-blocking system:

[0041] Add a fatty acid ester-based oil emulsifier to the oilfield's light oil and stir to dissolve it; then add the modified molybdenum disulfide nanosheets prepared by the above method and stir to disperse them thoroughly to obtain the final product.

[0042] When the above-mentioned water-blocking system is mixed with eight times its own mass of formation water in a beaker, an oil-in-water emulsion is formed, indicating that the system can emulsify eight times its own mass of formation water without reversing to form an oil-in-water emulsion.

[0043] The water-blocking system was injected into an area with a permeability of 1842 × 10⁻⁶. -3 μm 2 The sand-filled pipe and subsequent water drive showed that the water phase permeability of the water-blocking system decreased by 85% after in-situ emulsification of water.

[0044] Example 2

[0045] An in-situ emulsified water shut-off system for oil wells, the system comprising an oil phase, modified molybdenum disulfide nanosheets, and an emulsifier.

[0046] The modified molybdenum disulfide nanosheets comprise 0.05% by mass in the oil phase; the emulsifier comprises 5% by mass in the oil phase.

[0047] The oil phase is a thin oil, and the emulsifier is a fatty acid ester oil-based emulsifier.

[0048] The modified molybdenum disulfide nanosheets are prepared by the following method:

[0049] (1) Mix ammonium molybdate and thiourea in 100 mL of deionized water at a mass ratio of 1:10 g and stir for 2 h. Transfer the resulting solution to a high-pressure reactor with a capacity of 150 mL and heat it in an oven at 220 °C for 8 h.

[0050] (2) After the reaction is completed and the reactor is cooled to room temperature, the product is centrifuged and washed several times to remove impurities and reaction byproducts. It is then placed in a vacuum drying oven at 60°C overnight to obtain molybdenum disulfide nanosheets.

[0051] (3) Disperse 1g of molybdenum disulfide nanosheets in 100mL of ethanol solution and sonicate at room temperature for 30min; then add 0.05g of n-octadecyl alcohol and stir for 24h.

[0052] (4) Centrifuge and wash the reaction solution to remove ungrafted modifiers and reaction byproducts, and dry it in a vacuum drying oven at 60°C to obtain modified molybdenum disulfide nanosheets.

[0053] The preparation method of the water-blocking system is the same as that described in Example 1.

[0054] The water-blocking system was injected into an area with a permeability of 1229 × 10⁻⁶. -3 μm 2 The sand-filled pipe and subsequent water drive showed that the water phase permeability of the water-blocking system decreased by 82% after in-situ emulsification of water.

[0055] Example 3

[0056] An in-situ emulsified water shut-off system for oil wells, the system comprising an oil phase, modified molybdenum disulfide nanosheets, and an emulsifier.

[0057] The modified molybdenum disulfide nanosheets comprise 0.1% by mass in the oil phase; the emulsifier comprises 3% by mass in the oil phase.

[0058] The oil phase is a thin oil, and the emulsifier is a fatty acid ester oil-based emulsifier.

[0059] The modified molybdenum disulfide nanosheets are prepared by the following method:

[0060] (1) Mix ammonium molybdate and thiourea in 100 mL of deionized water at a mass ratio of 1:10 g and stir for 2 h. Transfer the resulting solution to a high-pressure reactor with a capacity of 150 mL and heat it in an oven at 180 °C for 16 h.

[0061] (2) After the reaction is completed and the reactor is cooled to room temperature, the product is centrifuged and washed several times to remove impurities and reaction byproducts. It is then placed in a vacuum drying oven at 60°C overnight to obtain molybdenum disulfide nanosheets.

[0062] (3) Disperse 1g of molybdenum disulfide nanosheets in 100mL of ethanol solution and sonicate at room temperature for 30min; then add 0.15g of n-octadecyl alcohol and stir for 24h.

[0063] (4) Centrifuge and wash the reaction solution to remove ungrafted modifiers and reaction byproducts, and dry it in a vacuum drying oven at 60°C to obtain modified molybdenum disulfide nanosheets.

[0064] The preparation method of the water-blocking system is the same as that described in Example 1.

[0065] The water-blocking system was injected into an area with a permeability of 1286×10. -3 μm 2The saturated crude oil sand-filled pipe, and subsequent oil flooding showed that the water shut-off system had no effect on the oil phase permeability in the oil-bearing sand-filled pipe, indicating that it has excellent water shut-off but not oil shut-off characteristics.

[0066] Example 4

[0067] An in-situ emulsified water shut-off system for oil wells, the system comprising an oil phase, modified molybdenum disulfide nanosheets, and an emulsifier.

[0068] The modified molybdenum disulfide nanosheets contain 1.0% by mass in the oil phase; the emulsifier contains 1.0% by mass in the oil phase.

[0069] The oil phase is a thin oil, and the emulsifier is a fatty acid ester oil-based emulsifier.

[0070] The modified molybdenum disulfide nanosheets are prepared by the following method:

[0071] (1) Mix ammonium molybdate and thiourea in 100 mL of deionized water at a mass ratio of 1:1 g and stir for 2 h. Transfer the resulting solution to a high-pressure reactor with a capacity of 150 mL and heat it in an oven at 200 °C for 12 h.

[0072] (2) After the reaction is completed and the reactor is cooled to room temperature, the product is centrifuged and washed several times to remove impurities and reaction byproducts. It is then placed in a vacuum drying oven at 60°C overnight to obtain molybdenum disulfide nanosheets.

[0073] (3) Disperse 1g of molybdenum disulfide nanosheets in 100mL of water and sonicate at room temperature for 30min; then add 0.05g of n-octadecyl alcohol and stir for 24h.

[0074] (4) Centrifuge and wash the reaction solution to remove ungrafted modifiers and reaction byproducts, and dry it in a vacuum drying oven at 60°C to obtain modified molybdenum disulfide nanosheets.

[0075] The preparation method of the water-blocking system is the same as that described in Example 1.

[0076] Example 5

[0077] An in-situ emulsified water shut-off system for oil wells, the system comprising an oil phase, modified molybdenum disulfide nanosheets, and an emulsifier.

[0078] The modified molybdenum disulfide nanosheets comprise 0.05% by mass in the oil phase; the emulsifier comprises 10% by mass in the oil phase.

[0079] The oil phase is a thin oil, and the emulsifier is a fatty acid ester oil-based emulsifier.

[0080] The modified molybdenum disulfide nanosheets are prepared by the following method:

[0081] (1) Mix ammonium molybdate and thiourea in 100 mL of deionized water at a mass ratio of 1:5 g and stir for 2 h. Transfer the resulting solution to a high-pressure reactor with a capacity of 150 mL and heat it in an oven at 200 °C for 12 h.

[0082] (2) After the reaction is completed and the reactor is cooled to room temperature, the product is centrifuged and washed several times to remove impurities and reaction byproducts. It is then placed in a vacuum drying oven at 60°C overnight to obtain molybdenum disulfide nanosheets.

[0083] (3) Disperse 1g of molybdenum disulfide nanosheets in 100mL of water and sonicate at room temperature for 30min; then add 0.1g of n-octadecyl alcohol and stir for 24h.

[0084] (4) Centrifuge and wash the reaction solution to remove ungrafted modifiers and reaction byproducts, and dry it in a vacuum drying oven at 60°C to obtain modified molybdenum disulfide nanosheets.

[0085] The preparation method of the water-blocking system is the same as that described in Example 1.

[0086] Comparative Example 1

[0087] An in-situ emulsified water shut-off system for oil wells differs from Example 1 in that it uses unmodified molybdenum disulfide nanosheets.

[0088] The molybdenum disulfide nanosheets are prepared by the following method:

[0089] (1) Mix ammonium molybdate and thiourea in 100 mL of deionized water at a mass ratio of 1:10 g and stir for 2 h. Transfer the resulting solution to a high-pressure reactor with a capacity of 150 mL and heat it in an oven at 200 °C for 12 h.

[0090] (2) After the reaction is completed and the reactor is cooled to room temperature, the product is centrifuged and washed several times to remove impurities and reaction byproducts. It is then placed in a vacuum drying oven at 60°C overnight to obtain molybdenum disulfide nanosheets.

[0091] Everything else is the same as in Example 1.

[0092] The water-blocking system was injected into an area with a permeability of 1842 × 10⁻⁶. -3 μm 2 The sand-filled pipe and subsequent water drive showed that the water phase permeability of the water-blocking system decreased by only 37% after in-situ emulsification of water.

[0093] Comparative Example 2

[0094] An in-situ emulsified water shut-off system for oil wells differs from Example 1 in that the system consists of an oil phase and an emulsifier.

[0095] The water-blocking system is prepared by adding a fatty acid ester-based oil emulsifier to the oilfield's light oil, stirring and dissolving it. Everything else is the same as in Example 1.

[0096] The system can emulsify 6.5 times its own weight of formation water to form a water-in-oil emulsion, but when formation water is added further, the emulsion reverses to an oil-in-water emulsion.

[0097] Comparative Example 3

[0098] An in-situ emulsified water shut-off system for oil wells differs from Example 1 in that the system consists of an oil phase and modified molybdenum disulfide nanosheets.

[0099] The water-blocking system was prepared by adding 0.2% modified molybdenum disulfide nanosheets to oilfield light oil and stirring thoroughly to disperse them. All other steps were the same as in Example 1.

[0100] This system is difficult to mix with formation water to form a water-in-oil emulsion.

[0101] As can be seen from the above, the modified molybdenum disulfide nanosheets prepared in the embodiments of the present invention can adjust their wettability and participate in the formation of in-situ emulsions, significantly improving emulsification ability and blocking efficiency against the aqueous phase. The addition of modified molybdenum disulfide nanosheets effectively improves the system's ability to emulsify water, thereby enhancing the water-blocking effect of the emulsion. Furthermore, the synergistic effect of modified molybdenum disulfide nanosheets and emulsifiers has a unique role in the in-situ formation of water-in-oil emulsions underground.

[0102] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. An in-situ emulsified water shut-off system for oil wells, characterized in that, The water-blocking system includes an oil phase, modified molybdenum disulfide nanosheets, and an emulsifier; the modified molybdenum disulfide nanosheets are obtained by modifying molybdenum disulfide nanosheets with an organic solvent; The modified molybdenum disulfide nanosheets were prepared by the following method: (1) Add ammonium molybdate and thiourea to an aqueous solution, dissolve them completely, transfer the solution to a high-pressure reactor and heat it to carry out the reaction. After the reaction is completed, centrifuge, wash the precipitate, and dry it to obtain molybdenum disulfide nanosheets. (2) Molybdenum disulfide nanosheets were placed in a solvent, n-octadecyl mercaptan was added, the mixture was stirred to carry out the reaction, and after centrifugation, washing and drying, modified molybdenum disulfide nanosheets were obtained. The oil phase is a light oil; The emulsifier is a fatty acid ester oil-based emulsifier.

2. The in-situ emulsified water shut-off system for oil wells according to claim 1, characterized in that, The modified molybdenum disulfide nanosheets have a mass fraction of 0.05%-1.0% in the oil phase; the emulsifier has a mass fraction of 1%-10% in the oil phase.

3. The in-situ emulsified water shut-off system for oil wells according to claim 1, characterized in that, The reaction time in step (1) is 8-16 h and the reaction temperature is 180-220 ℃.

4. The in-situ emulsified water shut-off system for oil wells according to claim 1, characterized in that, In step (1), the weight ratio of ammonium molybdate to thiourea is 1:1~10.

5. The in-situ emulsified water shut-off system for oil wells according to claim 1, characterized in that, In step (2), the mass ratio of molybdenum disulfide nanosheets to n-octadecyl mercaptan is 1:0.05-0.

15.

6. The in-situ emulsified water shut-off system for oil wells according to claim 1, characterized in that, The solvent mentioned in step (2) is water or ethanol.

7. The preparation method of the in-situ emulsified water shut-off system for oil wells as described in claim 1, characterized in that, Includes the following steps: Add an emulsifier to the thin oil and stir to dissolve; then add modified molybdenum disulfide nanosheets and stir thoroughly.