Preparation method of temperature-resistant nano-emulsion and application of temperature-resistant nano-emulsion in shale oil reservoir imbibition oil displacement

Abstract

The invention belongs to the technical field of oil and gas exploitation and oilfield chemistry, and relates to a preparation method of a temperature-resistant nano-emulsion and application of the temperature-resistant nano-emulsion in shale oil reservoir imbibition oil displacement. The method comprises the following steps: preparing an oil-water mixture by taking D-limonene as an oil phase and a sodium chloride aqueous solution as a water phase; the preparation method comprises the following steps: mixing an amide propyl betaine zwitterionic surfactant, an alpha-olefin sulfonate anionic surfactant and an organic alcohol cosurfactant to obtain an emulsifier; dropwise adding the emulsifier into the oil-water mixture, and continuously stirring until the mixture is changed into a uniform transparent phase, so as to obtain a homogeneous microemulsion; and adding water into the micro-emulsion, fully stirring, and diluting to obtain the nano-emulsion. The nano-emulsion prepared by the invention has ultra-low interfacial tension, relatively strong wetting reversal capability and high-temperature thermal stability, and is suitable for shale oil imbibition oil displacement to improve the recovery ratio.

Description

Technical Field

[0001] The invention belongs to the technical field of oil and gas exploitation and oilfield chemistry, and relates to a method for preparing a temperature-resistant nanoemulsion and application thereof in imbibition flooding of shale oil reservoirs. Background Art

[0002] As a significant unconventional oil and gas resource, shale oil holds a crucial position in the global energy mix and has gradually become a key replacement for oil and gas resources. With the application and promotion of the "long horizontal well combined with multi-stage hydraulic fracturing" technology, shale oil industry development in China has taken off. However, shale oil reservoirs differ significantly from conventional reservoirs in terms of reservoir and fluid characteristics. Their reservoir space consists of a coexistence of nanoscale pores and microfractures. Furthermore, the rock surface is oil-wet, and shale oil is primarily stored in an adsorbed state. Fracturing can significantly improve the permeability of the stimulated zone, but it still faces challenges such as high production decline rates and low predicted oil recovery. Replenishing formation energy and improving displacement efficiency have become key constraints to improving shale oil recovery. Practice has shown that conventional water injection and huff-and-puff recharge methods are prone to fracture-induced water breakthrough, making it difficult to establish an effective recharge system. While carbon dioxide recharge and refracturing offer advantages such as high recharge efficiency, they are significantly constrained by reservoir conditions and economic benefits.

[0003] In recent years, imbibition flooding has attracted industry attention due to its simple injection technology, low operating costs, and excellent oil-increasing performance. Imbibition can be divided into spontaneous imbibition and forced imbibition. The former is initiated solely through capillary forces, while the latter requires external forces to complete imbibition. Nanoemulsions, with their tiny dispersed phase, stable emulsion systems, and low oil-water interfacial tension, can alter rock wettability, facilitate access to pore throats, and reduce injection pressure. They also effectively solubilize crude oil, making them widely used in imbibition flooding. However, due to the deep burial depth of shale reservoirs, formation temperatures are generally high. For example, formation temperatures in the Jiyang Sag and Gulong, Daqing, are both above 100°C, ranging from 130°C to 200°C and 100°C to 120°C, respectively. Temperatures in the middle of the Lucaogou Formation in Jimusar reach as high as 92°C. Studies have shown that as temperature increases, nanoemulsion particle size increases, causing emulsion aggregation and decreased stability. Therefore, developing temperature-resistant nanoemulsions is crucial for improving shale oil recovery. Summary of the Invention

[0004] Aiming at the problem of emulsion aggregation and poor stability under high temperature conditions, the present invention constructs a microemulsion-nanoemulsion conversion system suitable for high-temperature shale oil reservoir imbibition flooding through the synergistic action of multiple components. Based on a mixture of D-limonene and sodium chloride aqueous solution, an amidopropyl betaine zwitterionic surfactant, αThe synergistic effect of anionic olefin sulfonate surfactants and organic alcohol co-surfactants forms a homogeneous microemulsion with interfacial control capabilities and high-temperature thermal stability. After dilution with water, dynamic interfacial reorganization yields a nanoemulsion that can meet varying concentration requirements. Ultra-low interfacial tension drives crude oil emulsification and dispersion, wettability reversal enhances water-phase imbibition, and strong thermal stability ensures long-lasting action at high temperatures. By combining interfacial control, wettability modification, and thermal stability, this solution provides a highly efficient and reliable solution for imbibition flooding in high-temperature shale reservoirs.

[0005] The present invention solves the above technical problems with the following technical solutions: a method for preparing a temperature-resistant nanoemulsion and its application in imbibition flooding of shale oil reservoirs, comprising the following steps: Step 1: Prepare an oil-water mixture using D-limonene as the oil phase and sodium chloride aqueous solution as the water phase; Step 2: Amidopropyl betaine zwitterionic surfactant, α -Olefin sulfonate anionic surfactant and organic alcohol co-surfactant are mixed as emulsifier; Step 3: Add the emulsifier in step 2 dropwise to the oil-water mixture and continue stirring until the mixture becomes a homogeneous transparent phase, which is a homogeneous microemulsion; Step 4: Add water to the microemulsion in step 3, and after sufficient stirring and dilution, a nanoemulsion is obtained; Furthermore, in step 1, the mass ratio of the oil phase to the water phase is 4:6~6:4, the mass concentration of the sodium chloride aqueous solution is 6%~12%; the amidopropyl betaine type zwitterionic surfactant, α - The mass ratio of olefin sulfonate anionic surfactant to organic alcohol cosurfactant is 0.25:0.75:1~0.75:0.25:2; the mass ratio of dilution water to microemulsion in step 4 can be adjusted according to usage requirements; Furthermore, the amidopropyl betaine zwitterionic surfactant includes one or a combination of two or more of lauryl amide propyl betaine, cocamidopropyl betaine, palmitamide propyl betaine and oleamidopropyl betaine; α -Olefin sulfonate anionic surfactants include carbon chain length C 12 ~C 18 of α - one or a combination of two or more of sodium, magnesium and potassium olefin sulfonates; the organic alcohol cosurfactant includes one or a combination of two or more of n-butanol, n-pentanol and isopentanol.

[0006] The present invention also provides an application of the nanoemulsion prepared by the above preparation method in imbibition flooding of shale oil reservoirs, wherein the mass concentration of the nanoemulsion is 0.2% to 0.5%, the formation temperature of the shale oil reservoir is higher than 120°C, and the core permeability is less than 1.0 mD.

[0007] The beneficial effects of the present invention are: The present invention constructs a stable microemulsion-nanoemulsion conversion system through the synergistic action of multiple components. The prepared nanoemulsion has ultra-low interfacial tension, strong wetting reversal ability and high-temperature thermal stability, overcoming the problems of emulsion agglomeration and poor stability of nanoemulsion in high-temperature shale oil reservoirs, providing a more efficient and reliable solution for improving oil recovery by imbibition flooding in high-temperature shale oil reservoirs, conforming to social and economic benefits, and having broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 ( a ) is the interfacial tension between nanoemulsions of different concentrations and kerosene at room temperature; Figure 1 ( b ) is the interfacial tension between the nanoemulsion with a mass concentration of 0.3% and kerosene at different temperatures; Figure 2 The contact angles of the core slices before and after aging after immersion in nanoemulsion with a mass concentration of 0.3%; Figure 3 The state characteristics of the nanoemulsion with a mass concentration of 0.3% at different standing times; Figure 4 Figure 2 shows the oil displacement capacity of nanoemulsion with a mass concentration of 0.3% in shale core at different injection rates. DETAILED DESCRIPTION

[0009] The principles and features of the present invention are described below. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0010] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0011] The present invention provides a method for preparing a temperature-resistant nanoemulsion and its application in imbibition flooding of shale oil reservoirs, comprising the following steps: Step 1: Prepare an oil-water mixture using D-limonene as the oil phase and sodium chloride aqueous solution as the water phase; Step 2: Amidopropyl betaine zwitterionic surfactant, α -Olefin sulfonate anionic surfactant and organic alcohol co-surfactant are mixed as emulsifier; Step 3: Add the emulsifier in step 2 dropwise to the oil-water mixture and continue stirring until the mixture becomes a homogeneous transparent phase, which is a homogeneous microemulsion; Step 4: Add water to the microemulsion in step 3, and after sufficient stirring and dilution, a nanoemulsion is obtained; Furthermore, in step 1, the mass ratio of the oil phase to the water phase is 4:6~6:4, the mass concentration of the sodium chloride aqueous solution is 6%~12%; the amidopropyl betaine type zwitterionic surfactant, α - The mass ratio of olefin sulfonate anionic surfactant to organic alcohol cosurfactant is 0.25:0.75:1~0.75:0.25:2; the mass ratio of dilution water to microemulsion in step 4 can be adjusted according to usage requirements; Furthermore, the amidopropyl betaine zwitterionic surfactant includes one or a combination of two or more of lauryl amide propyl betaine, cocamidopropyl betaine, palmitamide propyl betaine and oleamidopropyl betaine; α -Olefin sulfonate anionic surfactants include carbon chain length C 12 ~C 18 of α - one or a combination of two or more of sodium, magnesium and potassium olefin sulfonates; the organic alcohol cosurfactant includes one or a combination of two or more of n-butanol, n-pentanol and isopentanol.

[0012] The present invention also provides an application of the nanoemulsion prepared by the above preparation method in imbibition flooding of shale oil reservoirs, wherein the mass concentration of the nanoemulsion is 0.2% to 0.5%, the formation temperature of the shale oil reservoir is higher than 120°C, and the core permeability is less than 1.0 mD.

[0013] Example 1: Based on a mixture of D-limonene and sodium chloride aqueous solution, a zwitterionic surfactant cocamidopropyl betaine, an anionic surfactant α -Sodium olefin sulfonate (carbon chain length C 12 ~C 14 ) and the organic alcohol cosurfactant n-butanol synergistically form a homogeneous microemulsion with interface control ability and high temperature thermal stability; after dilution, a nanoemulsion that can meet different concentration requirements can be obtained through dynamic interface reorganization; the specific implementation steps are as follows: Step 1: Prepare an oil-water mixture with D-limonene as the oil phase and sodium chloride aqueous solution as the water phase, wherein the mass ratio of the oil phase to the water phase is 5:5 and the mass concentration of the sodium chloride aqueous solution is 10%; Step 2: Add the zwitterionic surfactant cocamidopropyl betaine and anionic surfactant α -Sodium olefin sulfonate (carbon chain length C 12 ~C14 ) and organic alcohol co-surfactant n-butanol, mixed in a mass ratio of 1:1:2 as an emulsifier; Step 3: Add the emulsifier in step 2 dropwise to the oil-water mixture and continue stirring until the mixture becomes a homogeneous transparent phase, which is a homogeneous microemulsion; Step 4: Add water to the microemulsion in step 3, and dilute it to a nanoemulsion with a mass concentration of 0.3% after sufficient stirring.

[0014] The nanoemulsion prepared in the above example was tested for its interface control ability and high-temperature thermal stability, and core flooding experiments were conducted to further evaluate its ability to improve the recovery rate of high-temperature shale reservoirs through imbibition flooding. The relevant test results are as follows: 1. Nanoemulsion interface control capability The interfacial tension between the nanoemulsion and kerosene was tested using a spinning drop interfacial tension meter, and the optimal emulsion concentration was selected. The nanoemulsion with this concentration was aged at different temperatures for 12 hours to investigate the effect of temperature on its interfacial tension. An optical contact angle meter was used to test the effect of nanoemulsion on the wettability of rocks. The rock core was sliced ​​and polished, then aged in crude oil for 48 hours to make it oil-wettable. The contact angle between the rock core slice and water was measured. The aged rock core slice was then immersed in the nanoemulsion for 48 hours, and the changes in contact angle before and after the nanoemulsion were compared. The relevant experimental results are as follows. Figure 1 、 Figure 2 shown.

[0015] Figure 1 ( a ) is the interfacial tension between nanoemulsions of different concentrations and kerosene at room temperature. As the mass concentration of the nanoemulsion increases, the interfacial tension decreases. The surfactant increases the stability of the emulsion. Due to the formation of the film, the oil droplets are prevented from agglomerating, thereby reducing the interfacial tension. When the mass concentration exceeds 0.3%, the interfacial tension remains relatively stable. Therefore, the optimal mass concentration for preparing the nanoemulsion is 0.3%. After aging the nanoemulsion with a mass concentration of 0.3% at different temperatures for 12 hours, the interfacial tension between it and kerosene was tested, as shown in FIG. Figure 1 ( b ). As the nanoemulsion ages at elevated temperatures, its interfacial tension increases from 0.012 mN / m to 0.015 mN / m. The temperature increase intensifies Brownian motion, increasing collisions between oil droplets and causing droplet aggregation. This, in turn, increases interfacial tension, but the increase is small and remains low.

[0016] Figure 2The contact angles of core slices before and after immersion and aging in a 0.3% nanoemulsion. Contact angle testing of the core slices revealed a hydrophobic contact angle of 104°. After 12 hours of immersion and aging in the nanoemulsion, the contact angle decreased to 43°, indicating that the nanoemulsion, when injected into the formation, transformed the oil-wetting surface of the rock from being oleophilic to being hydrophilic. The rock, primarily composed of hydrophilic dolomite, undergoes aging with crude oil, resulting in a layer of crude oil molecules adhering to the surface and becoming oleophilic. Further immersion in the nanoemulsion removes the crude oil from the rock surface, leaving it covered with the nanoemulsion and forming a new wetting film that is hydrophilic. This facilitates the entry of subsequent water injection, increasing the water phase pressure to a greater value than the oil phase pressure. Capillary forces allow the water phase to enter the rock pores, displacing the crude oil and preventing its reattachment.

[0017] 2. High temperature thermal stability of nanoemulsion The nanoemulsion was injected into the aging tank and aged for a long time at different temperatures. After cooling, the nanoemulsion was observed to see if it became turbid or stratified to evaluate the long-term stability of the nanoemulsion. Figure 3 As shown. The nanoemulsion with a mass concentration of 0.3% is translucent, as shown Figure 3 ( a ). At 100℃, 120℃, and 140℃, after standing for 12 hours and 5 days, the nanoemulsion showed no stratification, indicating good stability. Figure 3 ( b )、3( c ) as shown.

[0018] 3. Nanoemulsion oil displacement capability The core was fractured, vacuumed and dried for 24 hours, and the dry weight of the core was measured. Then, it was immersed in crude oil and aged at 140°C for 1 month to restore it to the original state of the reservoir. The wet weight of the saturated core was measured, and the oil saturation of the core was calculated based on this. Formation water was then injected into the core for a water drive. When the water cut reached 98%, nanoemulsion (mass concentration of 0.3%) was injected, and the inlet and outlet ends were closed. After "holding the well" for 20 hours, a second water drive was carried out to obtain the oil-infiltration and displacement capacity of the nanoemulsion in the shale core at different injection rates.

[0019] Figure 4Figure 3 shows the imbibition recovery capability of nanoemulsion in shale cores at different injection rates. Injection rates of 0.2 PV, 0.5 PV, 0.8 PV, and 1 PV were used, followed by a 20-hour soak at 140°C and a confining pressure of 12 MPa. At each injection rate, the final recovery of nanoemulsion imbibition flooding significantly increased compared to conventional water flooding, with increases ranging from 5.96% to 9.23%. At an injection rate of 0.5 PV, the final recovery increased by 3.05% compared to 0.2 PV. Beyond 0.5 PV, the enhanced recovery effect was no longer significant.

[0020] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a temperature-resistant nanoemulsion, characterized in that: The following steps are involved: Step 1: Prepare an oil-water mixture using D-limonene as the oil phase and sodium chloride aqueous solution as the water phase; Step 2: Amidopropyl betaine zwitterionic surfactant, α -Olefin sulfonate anionic surfactant and organic alcohol co-surfactant are mixed as emulsifier; Step 3: Add the emulsifier in step 2 dropwise to the oil-water mixture and continue stirring until the mixture becomes a homogeneous transparent phase, which is a homogeneous microemulsion; Step 4: Add water to the microemulsion in step 3, and after sufficient stirring and dilution, a nanoemulsion is obtained; Wherein, in step 1, the mass ratio of the oil phase to the water phase is 4:6~6:4, the mass concentration of the sodium chloride aqueous solution is 6%~12%; the amidopropyl betaine zwitterionic surfactant, α -The mass ratio of olefin sulfonate anionic surfactant to organic alcohol co-surfactant is 0.25:0.75:1~0.75:0.25:2; the mass ratio of dilution water to microemulsion in step 4 can be adjusted according to usage requirements.

2. A method for preparing a temperature-resistant nanoemulsion according to claim 1, characterized in that, The amidopropyl betaine zwitterionic surfactant includes one or a combination of two or more of lauryl amide propyl betaine, cocamidopropyl betaine, palmitamide propyl betaine and oleamidopropyl betaine; α -Olefin sulfonate anionic surfactants include carbon chain length C 12 ~C 18 of α - one or a combination of two or more of sodium, magnesium and potassium olefin sulfonates; the organic alcohol cosurfactant includes one or a combination of two or more of n-butanol, n-pentanol and isopentanol.

3. An application of the nanoemulsion prepared by the preparation method according to any one of claims 1 to 2 in imbibition flooding of shale oil reservoirs, characterized in that: The mass concentration of the nanoemulsion is 0.2% to 0.5%, the formation temperature of the shale oil reservoir is higher than 120° C., and the core permeability is less than 1.0 mD.

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