Middle-phase microemulsion, and preparation method therefor and use thereof

Abstract

The present invention relates to the technical field of tertiary oil recovery in oil fields. Disclosed are a middle-phase microemulsion, and a preparation method therefor and the use thereof. The middle-phase microemulsion contains 0.4-1.6 wt% of a main surfactant, 0.1-0.5 wt% of a co-surfactant, 7-14 wt% of an inorganic salt, 45-55 wt% of an oil phase and 35-45 wt% of water, wherein the main surfactant is selected from at least one of monoalkyl benzene sulfonate and dialkyl benzene sulfonate which have a C11-C22 alkyl chain, and the co-surfactant is sodium lauryl polyoxypropylene sulfate. When used for oil displacement, the middle-phase microemulsion of the present invention can greatly reduce the interfacial tension, and improve the recovery rate of crude oil; moreover, the middle-phase microemulsion does not require the addition of other auxiliaries such as an alkali, such that the concentration of the reagent used is low and the economic benefits are high. The middle-phase microemulsion can be used after chemical flooding to further increase the recovery rate.

Description

A medium-phase microemulsion and its preparation method and application

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of Chinese patent application 202211329487.9 filed on October 27, 2022, the contents of which are incorporated herein by reference. Technical Field

[0003] The present invention relates to the technical field of tertiary oil recovery in oil fields, and in particular to a middle-phase microemulsion and a preparation method and application thereof. Background Art

[0004] Crude oil production can be divided into three stages based on the stages and techniques used. In the early stages of oilfield development, oil is extracted through self-flowing through reservoir energy, with a recovery rate of only 15% to 20%. This stage is called primary oil recovery. To replenish insufficient formation energy, artificial water or gas injection is used to supplement reservoir energy and extract oil. This stage can reach a recovery rate of 25% to 40%. This stage is called secondary oil recovery. To recover the majority of the remaining crude oil, new physical, chemical, and biological technologies are used to further extract the remaining oil on top of secondary oil recovery. These methods are collectively referred to as tertiary oil recovery. Tertiary oil recovery primarily includes chemical flooding, gas flooding, and thermal flooding.

[0005] Among chemical flooding methods, microemulsion flooding has achieved breakthrough results in tertiary oil recovery (TER) from low-permeability reservoirs, significantly increasing crude oil recovery. A microemulsion is a thermodynamically stable, isotropic, low-viscosity, transparent or translucent dispersion of oil and water that spontaneously forms under certain conditions in the presence of surfactants and cosurfactants. In a microemulsion, two or more immiscible liquids are mixed and emulsified to form a system of droplets with diameters between 5 and 100 nm. The principle behind this process is to flood oil by first adding a surfactant and some polymers, followed by the injection of water. In the oil well, the surfactant-water solution and the original solution form a co-continuous microemulsion. The coexistence of the microemulsion with excess water and oil significantly reduces the interfacial tension between the crude oil and water.

[0006] Based on the number of microemulsion phases, microemulsions are classified as multiphase microemulsions (Winsor I, Winsor II, and Winsor III microemulsions) and single-phase microemulsions (Winsor IV microemulsions). Winsor I microemulsions, also known as lower-phase microemulsions, consist of an excess oil component coexisting with an O / W microemulsion. Surfactants are primarily dissolved in the lower microemulsion phase, while the upper oil component also contains a relatively low concentration of surfactant monomers. Winsor II microemulsions, also known as upper-phase microemulsions, consist of a W / O microemulsion coexisting with an excess water component. Surfactants are primarily dissolved in the upper microemulsion phase, while the lower water component also contains a relatively low concentration of surfactants. Winsor III microemulsions, also known as middle-phase microemulsions, consist of a microemulsion with both excess water and oil components. Winsor type III microemulsion is an intermediate structure in the continuous transition path between Winsor type I microemulsion and Winsor type II microemulsion. The system contains two interfaces and three phases, consisting of a surfactant-rich bicontinuous phase, an oil phase containing a small amount of surfactant at the top of the system, and an aqueous phase containing a small amount of surfactant at the bottom of the system. The intermediate phase of Winsor type III microemulsion is actually a bicontinuous microemulsion.

[0007] Generally, the construction of a middle-phase microemulsion requires a high surfactant concentration (>1%) and multiple additives, and the addition of alkali to the formulation creates a middle-phase microemulsion. This results in high costs, as the addition of alkali can cause problems such as pipeline corrosion and scaling.

[0008] Therefore, it is very necessary to develop a medium-phase microemulsion and its preparation process and application that can solve the above technical problems.

[0009] Summary of the Invention

[0010] The present invention aims to overcome the problems of existing middle-phase microemulsions and to provide a middle-phase microemulsion, its preparation method, and its application. The middle-phase microemulsion of the present invention is used for oil displacement, significantly reducing interfacial tension and improving crude oil recovery. Furthermore, the middle-phase microemulsion of the present invention does not require the addition of alkali and only requires a small amount of additives. The main agent concentration used is low, resulting in high economic benefits and significantly improving oil recovery. The microemulsion can be used to further improve oil recovery after chemical flooding, such as polymer flooding.

[0011] To achieve the above objectives, the present invention provides a middle-phase microemulsion comprising 0.4-1.6 wt% of a primary surfactant, 0.1-0.5 wt% of a co-surfactant, 7-14 wt% of an inorganic salt, 45-55 wt% of an oil phase, and 35-45 wt% of water, wherein the primary surfactant is selected from at least one of monoalkylbenzene sulfonate and dialkylbenzene sulfonate having an alkyl chain of C11-C22, and the co-surfactant is sodium dodecyl polyoxypropylene sulfate.

[0012] Preferably, the primary surfactant is selected from one or a mixture of at least two of monoalkylbenzene sulfonates and dialkylbenzene sulfonates with an alkyl chain of C14, C16, or C18.

[0013] Preferably, the structural formula of the co-surfactant is as shown in formula (I),

[0014] Here, n is an integer from 3 to 6.

[0015] Preferably, the inorganic salt is sodium chloride and / or potassium chloride.

[0016] Preferably, the oil phase is a straight-chain alkane or a mixture of normal alkanes and isoalkanes.

[0017] More preferably, the straight-chain alkane is n-tetradecane.

[0018] Further preferably, the mixture of normal paraffins and isoparaffins is white oil.

[0019] Preferably, the water is deionized water.

[0020] Preferably, the middle phase microemulsion is a transparent or translucent liquid.

[0021] The second aspect of the present invention provides a method for preparing the above-mentioned middle phase microemulsion, which comprises: mixing a main surfactant, a co-surfactant, an inorganic salt, an oil phase and water.

[0022] Preferably, the mixing process comprises: stirring and mixing the main surfactant, the co-surfactant, the inorganic salt, the oil phase and the water, and then letting them stand.

[0023] The third aspect of the present invention provides the use of the above-mentioned middle phase microemulsion as an oil displacement agent.

[0024] The middle phase microemulsion of the present invention can significantly reduce interfacial tension and improve crude oil recovery when used for oil displacement. In addition, the middle phase microemulsion does not require the addition of other additives such as alkali, and the concentration of the used agent is low, with high economic benefits. It can be used to further improve the recovery rate after chemical flooding.

[0025] The preparation process of the middle phase microemulsion of the present invention is simple and can be prepared by directly mixing the components evenly, which is conducive to large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] FIG1 is a small-angle X-ray image of the middle phase microemulsion prepared in Example 1;

[0027] FIG2 is a cryo-scanning electron micrograph of the middle phase microemulsion prepared in Example 1;

[0028] FIG3 is a small-angle X-ray image of the middle phase microemulsion prepared in Example 2;

[0029] FIG4 is a cryo-scanning electron micrograph of the middle phase microemulsion prepared in Example 2. DETAILED DESCRIPTION

[0030] The following describes the specific embodiments of the present invention in detail with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention and are not intended to limit the present invention.

[0031] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0032] The middle phase microemulsion of the present invention contains a main surfactant, a co-surfactant, an inorganic salt, an oil phase and water, but does not contain other auxiliary agents such as alkali.

[0033] In the middle phase microemulsion of the present invention, the primary surfactant is selected from at least one of monoalkylbenzene sulfonates and dialkylbenzene sulfonates having an alkyl chain of C11-C22. Specifically, the primary surfactant is selected from one or a mixture of at least two of monoalkylbenzene sulfonates and dialkylbenzene sulfonates having an alkyl chain of C14, C16, or C18.

[0034] In the middle phase microemulsion of the present invention, based on the total amount of the middle phase microemulsion being 100wt%, the content of the primary surfactant is 0.4-1.6wt%, the content of the cosurfactant is 0.1-0.5wt%, the content of the inorganic salt is 7-14wt%, the content of the oil phase is 45-55wt%, and the content of water is 35-45wt%. Preferably, the content of the primary surfactant is 0.4-1.2wt%, the content of the cosurfactant is 0.1-0.3wt%, the content of the inorganic salt is 8-12wt%, the content of the oil phase is 48-52wt%, and the content of water is 38-42wt%.

[0035] In the middle phase microemulsion of the present invention, the cosurfactant is sodium lauryl polyoxypropylene sulfate. In a preferred embodiment, the structural formula of the cosurfactant is as shown in formula (I):

[0036] Here, n is an integer of 3-6, and specifically can be 3, 4, 5 or 6.

[0037] In the middle phase microemulsion of the present invention, the inorganic salt may be sodium chloride and / or potassium chloride, preferably sodium chloride.

[0038] In the middle phase microemulsion of the present invention, the oil phase can be a straight-chain alkane or a mixture of normal alkanes and isoalkanes. The straight-chain alkane is preferably n-tetradecane. The mixture of normal alkanes and isoalkanes is preferably white oil.

[0039] In the middle phase microemulsion of the present invention, the water is preferably deionized water.

[0040] In the present invention, the middle phase microemulsion is a transparent or translucent liquid.

[0041] The preparation method of the middle phase microemulsion may include: mixing a main surfactant, a co-surfactant, an inorganic salt, an oil phase and water.

[0042] Preferably, the mixing process comprises: stirring and mixing the primary surfactant, the co-surfactant, the inorganic salt, the oil phase, and water, and then allowing the mixture to stand. Further preferably, the mixing process comprises: dissolving the primary surfactant, the co-surfactant, and the inorganic salt in water to obtain an aqueous phase, stirring and mixing the aqueous phase and the oil phase, and then allowing the mixture to stand. The stirring may be mechanical stirring, the stirring speed may be 50-200 rpm, and the stirring time may be 5-30 minutes.

[0043] The present invention also provides the use of the above-mentioned middle phase microemulsion as an oil displacement agent. The middle phase microemulsion can be used as an oil displacement agent to significantly reduce interfacial tension and improve crude oil recovery, and can be used to further improve recovery after chemical flooding such as polymer flooding.

[0044] The following examples further illustrate the middle phase microemulsion, preparation method, and application of the present invention. The examples are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operating processes, but the scope of protection of the present invention is not limited to the following examples.

[0045] The experimental methods in the following examples, unless otherwise specified, are all conventional methods in the art. The experimental materials used in the following examples, unless otherwise specified, are all commercially available.

[0046] Example 1

[0047] 0.4% heavy alkylbenzene sulfonate (primarily monoalkylbenzene sulfonate with a C16 alkyl chain), 0.2% sodium dodecylpolyoxypropylene sulfate (the compound represented by formula (I), where n is 3), 10% sodium chloride, 50% n-tetradecane, and 39.4% deionized water were weighed in percentage by weight. The surfactant and sodium chloride were dissolved in deionized water to obtain an aqueous phase. The oil phase and the aqueous phase were mixed uniformly and added to a beaker. The mixture was stirred at 100 rpm at room temperature for 10 minutes and then allowed to stand to obtain a middle phase microemulsion A1.

[0048] Heavy alkylbenzene sulfonate was provided by the Xinjiang Oilfield Company of PetroChina, sodium dodecyl polyoxypropylene sulfate was purchased from Sasol (Sandton, South Africa), n-tetradecane (99%) was purchased from Adamas-Beta (Shanghai), and NaCl (AR) was purchased from Kelon Reagent Company (Chengdu). Deionized water (resistivity 18.25 MΩ·cm) was prepared in-house using an ultrapure water purification unit CDUPT-Ш (Chengdu Ultrapure Technology Co., Ltd., China).

[0049] The prepared middle-phase microemulsion A1 was encapsulated in a quartz capillary and then placed in a SAXSpace (Anton Paar, Austria, Cu-Ka, λ = 0.154 nm) for SAXS measurement. The relationship between the scattering intensity and the scattering vector was obtained. The "Teubner-Strey" model was used to fit the SAXS curve to obtain the correlation length ξ and the periodicity d of the bicontinuous domains. The relevant results are shown in Figure 1.

[0050] As shown in Figure 1, the relationship between the scattering intensity and the scattering vector of this component conforms to the TS model, verifying that the intermediate phase is indeed a middle phase microemulsion with a bicontinuous structure.

[0051] The prepared middle phase microemulsion A1 was subjected to Cryo-SEM testing using a FEI-Helios G5 cryo-microscope (FEI, USA). Before sample preparation, it was stabilized at 40°C for 30 minutes, then dropped into a copper holder with conductive glue and mounted on a cryo-holder. The sample was then quenched in liquid nitrogen (-196°C) for 10 seconds. Then, two tweezers were used to bend the sample, break it and expose a new cross-section. The frozen sample was then moved into the sample chamber, sublimated at -90°C for 10 minutes, sputtered with gold at 10 mA, and moved into the observation chamber. The observation chamber temperature was -140°C and vacuumed to 1×10 -5 The image was captured using secondary or backscattered electrons (2 keV, 60 pA) at a pressure of 1.5 Pa. The relevant results are shown in Figure 2.

[0052] As can be seen from Figure 2, a typical bicontinuous structure appeared in the electron microscopy results, proving that the intermediate phase is indeed a middle phase microemulsion.

[0053] Example 2

[0054] 0.8% heavy alkylbenzene sulfonate (primarily monoalkylbenzene sulfonate with a C16 alkyl chain), 0.2% sodium lauryl polyoxypropylene sulfate (the compound represented by formula (I), where n is 3), 10% sodium chloride, 50% white oil, and 39% deionized water were weighed in percentage by weight. The surfactant and sodium chloride were dissolved in deionized water to obtain an aqueous phase. The oil phase and the aqueous phase were mixed uniformly and added to a beaker. The mixture was stirred at 100 rpm at room temperature for 10 minutes and then allowed to stand to obtain a middle phase microemulsion A2.

[0055] Heavy alkylbenzene sulfonate was provided by the Xinjiang Oilfield Company of PetroChina, sodium dodecyl polyoxypropylene sulfate was purchased from Sasol (Sandton, South Africa), white oil (#15) was purchased from Lingzhong Lubricating Oil Co., Ltd. (Chengdu), and NaCl (AR) was purchased from Kelon Reagent Co., Ltd. (Chengdu). Deionized water (resistivity, 18.25 MΩ·cm) was prepared in-house using an ultrapure water purification unit CDUPT-Ш (Chengdu Ultrapure Technology Co., Ltd., China).

[0056] The prepared middle phase microemulsion A2 was encapsulated in a quartz capillary and then placed in a SAXSpace (Anton Paar, Austria, Cu-Ka, λ = 0.154 nm) for SAXS measurement. The relationship between the scattering intensity and the scattering vector was obtained. The "Teubner-Strey" model was used to fit the SAXS curve to obtain the correlation length ξ and the periodicity d of the bicontinuous domain. The relevant results are shown in Figure 3.

[0057] As shown in Figure 3, the relationship between the scattering intensity and the scattering vector of this component conforms to the TS model, verifying that the intermediate phase is indeed a middle phase microemulsion with a bicontinuous structure.

[0058] The prepared middle phase microemulsion A2 was subjected to Cryo-SEM testing using a FEI-Helios G5 cryo-microscope (FEI, USA). Before sample preparation, it was stabilized at 40°C for 30 minutes, then dropped into a copper holder with conductive glue and mounted on a cryo-holder. The sample was then quenched in liquid nitrogen (-196°C) for 10 seconds. Then, two tweezers were used to bend the sample, break it and expose a new cross-section. The frozen sample was then moved into the sample chamber, sublimated at -90°C for 10 minutes, sputtered with gold at 10 mA, and moved into the observation chamber. The observation chamber temperature was -140°C and vacuumed to 1×10 -5 The images were captured using secondary or backscattered electrons (2 keV, 60 pA) at a pressure of 1.5 Pa. The relevant results are shown in Figure 4.

[0059] As can be seen from Figure 4, a typical bicontinuous structure appeared in the electron microscopy results, proving that the intermediate phase is indeed a middle phase microemulsion.

[0060] Example 3

[0061] 1.2% heavy alkylbenzene sulfonate (primarily monoalkylbenzene sulfonate with a C16 alkyl chain), 0.4% sodium lauryl polyoxypropylene sulfate (the compound represented by formula (I), where n is 6), 10% sodium chloride, 52% n-tetradecane, and 36.4% deionized water were weighed in percentage by weight. The surfactant and sodium chloride were dissolved in deionized water to obtain an aqueous phase. The oil phase and the aqueous phase were mixed uniformly and added to a beaker. The mixture was stirred at 100 rpm at room temperature for 10 minutes and then allowed to stand to obtain a middle phase microemulsion A3.

[0062] Example 4

[0063] 1.6% heavy alkylbenzene sulfonate (primarily monoalkylbenzene sulfonate with a C16 alkyl chain), 0.4% sodium lauryl polyoxypropylene sulfate (the compound represented by formula (I), where n is 4), 10% sodium chloride, 50% white oil, and 38% deionized water were weighed in percentage by weight. The surfactant and sodium chloride were dissolved in deionized water to obtain an aqueous phase. The oil phase and the aqueous phase were mixed uniformly and added to a beaker. The mixture was stirred at 100 rpm at room temperature for 10 minutes and then allowed to stand to obtain a middle phase microemulsion A4.

[0064] Example 5

[0065] Weigh 0.8% heavy alkylbenzene sulfonate (monoalkylbenzene sulfonate with a C18 alkyl chain), 0.2% sodium dodecylpolyoxypropylene sulfate (the compound represented by formula (I), where n is 5), 12% potassium chloride, 50% n-tetradecane, and 37% deionized water, calculated by weight. Dissolve the surfactant and sodium chloride in deionized water to obtain an aqueous phase. Mix the oil phase and aqueous phase, add the resulting mixture to a beaker, and stir at 100 rpm at room temperature for 10 minutes. Allow the mixture to stand to obtain a middle phase microemulsion A5.

[0066] Comparative Example 1

[0067] A middle phase microemulsion was prepared according to the method of Example 1, except that the heavy alkylbenzene sulfonate was replaced by the same weight of cycloalkylaryl sulfonate to obtain a middle phase microemulsion D1.

[0068] Comparative Example 2

[0069] A middle phase microemulsion was prepared according to the method of Example 1, except that the sodium dodecylbenzenesulfonate was used in place of the sodium dodecylpolyoxypropylene sulfate to obtain a middle phase microemulsion D2.

[0070] Test Case

[0071] The surfactant system selected from the above examples and comparative examples was used to conduct an oil displacement test. The specific test process was as follows:

[0072] The experiment was conducted using natural cores obtained from the target formation. First, the cores were cleaned and dried, and their basic physical properties were measured. The cores were saturated with simulated brine using a core vacuum saturation device and then soaked in simulated brine until ready for use. The core flooding experiment was conducted at a specific reservoir temperature of 40°C and consisted of three processes: oil saturation, water flooding, surfactant flooding, and post-water flooding. The specific steps are as follows:

[0073] 1) Oil saturation: Place the core in a holder and displace it with crude oil in the pressure line until the outlet stops discharging water and produces oil steadily. Collect and record the amount of water displaced V o , to obtain an oil-saturated core; after saturation, place it at high temperature for 1 to 2 days, the purpose of which is to allow the crude oil to be evenly distributed in the core and to simulate the crude oil distribution in a real oil reservoir as much as possible;

[0074] 2) Water flooding: 1 mL min -1 Inject simulated brine into the core until the water content of the produced fluid exceeds 98%, and record the volume of oil displaced V w Calculate the water flooding recovery factor E as follows: w :

[0075] 3) Surfactant flooding and subsequent water flooding: 1 mL min-1 After quantitatively injecting 1PV of surfactant solution, continue to use 1mL·min -1 Inject simulated brine, and when the water cut reaches above 98% again, end the subsequent water flooding. Record the cumulative total volume V of oil displaced during water flooding, surfactant flooding, and subsequent water flooding, and calculate the total crude oil recovery E and the enhanced oil recovery factor of surfactant flooding according to the following formula: E s =EE w (4)

[0076] The core parameters and test results are shown in Table 1 below. In the table, l is the core length, h is the core diameter, PV is the pore volume, φ is the porosity, Ke is the permeability, Ew is the water drive recovery factor, and Es is the surfactant drive factor.

[0077] Table 1

[0078] The results in Table 1 demonstrate that the surfactant flooding system of the present invention significantly improves oil recovery after water flooding, with the magnitude of this improvement increasing with increasing concentration of the active ingredient. Compared to the formulation of the present invention, the magnitude of this improvement is significantly reduced after changing the active ingredient and adjuvant, demonstrating the superiority of the system of the present invention.

[0079] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A middle phase microemulsion, characterized in that: The invention comprises 0.4-1.6 wt % of a main surfactant, 0.1-0.5 wt % of a co-surfactant, 7-14 wt % of an inorganic salt, 45-55 wt % of an oil phase and 35-45 wt % of water, wherein the main surfactant is selected from at least one of monoalkylbenzene sulfonate and dialkylbenzene sulfonate having an alkyl chain of C11-C22, and the co-surfactant is sodium dodecyl polyoxypropylene sulfate.

2. The middle phase microemulsion according to claim 1, characterized in that The main surfactant is selected from one or a mixture of at least two of monoalkylbenzene sulfonates and dialkylbenzene sulfonates with an alkyl chain of C14, C16, or C18.

3. The middle phase microemulsion according to claim 1, characterized in that The structural formula of the co-surfactant is shown in formula (I), Here, n is an integer from 3 to 6.

4. The middle phase microemulsion according to claim 1, characterized in that The inorganic salt is sodium chloride and / or potassium chloride.

5. The middle phase microemulsion according to claim 1, characterized in that The oil phase is a straight-chain alkane or a mixture of normal alkane and isoalkane.

6. The middle phase microemulsion according to claim 5, characterized in that The straight-chain alkane is n-tetradecane.

7. The middle phase microemulsion according to claim 5, characterized in that The mixture of normal paraffins and isoparaffins is white oil.

8. The middle phase microemulsion according to claim 1, characterized in that The water is deionized water.

9. The middle phase microemulsion according to any one of claims 1 to 8, characterized in that The middle phase microemulsion is a transparent or translucent liquid.

10. A method for preparing the middle phase microemulsion according to any one of claims 1 to 9, characterized in that: The method comprises: mixing a main surfactant, a co-surfactant, an inorganic salt, an oil phase and water.

11. The method according to claim 10, characterized in that The mixing process comprises: stirring and mixing the main surfactant, the co-surfactant, the inorganic salt, the oil phase and the water, and then letting the mixture stand.

12. Use of the middle phase microemulsion according to any one of claims 1 to 9 as an oil displacement agent.