Medium-phase microemulsion based on biological surfactant as well as preparation method and application of medium-phase microemulsion

Abstract

The invention provides a middle-phase microemulsion based on a biological surfactant and a preparation method and application of the middle-phase microemulsion, and the middle-phase microemulsion is prepared from the following raw materials in percentage by weight: 0.2-0.8% of the biological surfactant; 0.1 to 0.4 percent of a cosurfactant; 8-12% of inorganic salt; 45-55% of an oil phase; 35-45% of water; the biological surfactant comprises single rhamnolipid and / or double rhamnolipid. The middle-phase microemulsion is used for oil displacement, interfacial tension can be greatly reduced, alkali does not need to be added into the middle-phase microemulsion, only a small amount of auxiliaries are needed, the concentration of the used main agent is low, economic benefits are high, the recovery efficiency can be greatly improved, and the middle-phase microemulsion can be used for polymer flooding and other chemical flooding to further improve the recovery efficiency.

Description

Technical Field

[0001] The invention belongs to the technical field of tertiary oil recovery in oil fields, and particularly relates to a middle-phase microemulsion based on a biological surfactant, a preparation method and an application thereof. Background Art

[0002] 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.

[0003] In chemical flooding, microemulsion flooding has achieved breakthrough results in tertiary oil recovery 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 main principle behind this process is that during oil recovery, oil is first flooded by adding surfactants and some polymer compounds, followed by the injection of water. In the oil well, the aqueous surfactant solution and the original solution form a bicontinuous microemulsion. The coexistence of the microemulsion with excess water and oil significantly reduces the interfacial tension between the crude oil and water.

[0004] 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 microemulsion phase at the bottom of the system, 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 phase of the system, while the lower water component also contains a relatively low concentration of surfactants. Winsor III microemulsions, in which microemulsions coexist with excess water and oil components, are called middle-phase microemulsions. Winsor III microemulsion is an intermediate structure in the continuous transition path of Winsor I microemulsion and Winsor II microemulsion. The system contains two interfaces and three phases, consisting of a bicontinuous phase rich in surfactant, 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 III microemulsion is actually a bicontinuous microemulsion.

[0005] 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.

[0006] Therefore, it is very necessary to develop a middle phase microemulsion that can solve the above technical problems. Summary of the Invention

[0007] To address the shortcomings of the prior art, the present invention aims to provide a biological surfactant-based middle-phase microemulsion, its preparation method, and its application. The middle-phase microemulsion provided by the present invention can significantly reduce interfacial tension and improve crude oil recovery when used for oil displacement. Furthermore, the middle-phase microemulsion does not require the addition of alkali, uses a low concentration of reagents, and has high economic benefits. It can be used to further improve oil recovery after chemical flooding.

[0008] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0009] In a first aspect, the present invention provides a middle-phase microemulsion based on a biological surfactant, wherein the raw materials for preparing the middle-phase microemulsion include the following components in terms of weight percentage:

[0010]

[0011]

[0012] The biological surfactant includes monorhamnolipid and / or disrhamnolipid.

[0013] The middle phase microemulsion of the present invention is used for oil displacement, can significantly reduce interfacial tension, and improve crude oil recovery rate. The middle phase microemulsion of the present invention does not require the addition of alkali and only requires a small amount of auxiliary agent. The main agent concentration used is low, the economic benefit is high, and the recovery rate can be significantly improved. It can be used to further improve the recovery rate after chemical flooding such as polymer flooding.

[0014] The biosurfactant of the present invention is selected from monorhamnolipids and / or dirhamnolipids. It has oil-water amphiphilicity, can reduce water surface tension, and can be used as a wetting agent, emulsifier, and foaming agent. The rhamnolipid biosurfactant can be used under extreme conditions of temperature, pH, and salinity, is non-toxic, and is biodegradable. When used in oil displacement, it is highly stable and does not cause environmental stress.

[0015] The bio-based surfactants used in this formulation are low in concentration, and the mono- and di-rhamnolipids are widely available, biodegradable, and environmentally friendly.

[0016] In the present invention, the amount of the biological surfactant used in the preparation of the middle phase microemulsion can be 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, etc., calculated by weight percentage.

[0017] In the present invention, the amount of the co-surfactant used in the preparation of the middle phase microemulsion can be 0.1%, 0.2%, 0.3%, 0.4%, etc., calculated by weight percentage.

[0018] In the present invention, the amount of inorganic salt used in the preparation of the middle phase microemulsion can be 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, 11.5%, 12%, etc., calculated by weight percentage.

[0019] In the present invention, the amount of the oil phase in the preparation of the middle phase microemulsion can be 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, etc., calculated by weight percentage.

[0020] In the present invention, the amount of water used in the preparation of the middle phase microemulsion can be 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, etc., calculated by weight percentage.

[0021] The structural formula of the monorhamnolipid of the present invention is shown in the following formula (A):

[0022]

[0023] The structural formula of the dirhamnolipid of the present invention is shown in the following formula (B):

[0024]

[0025] Preferably, the biological surfactant comprises monorhamnolipid and disrhamnolipid. As a preferred technical solution of the present invention, when monorhamnolipid and disrhamnolipid are used simultaneously as surfactants, the emulsification performance, stability, antioxidant properties and surface activity of the middle phase microemulsion can be synergistically improved.

[0026] Preferably, the co-surfactant comprises sodium lauryl polyoxypropylene sulfate.

[0027] Preferably, the structural formula of the co-surfactant is shown in the following formula (I):

[0028]

[0029] Wherein, n is an integer of 3-6 (eg, 3, 4, 5 or 6).

[0030] Preferably, the inorganic salt comprises sodium chloride and / or potassium chloride.

[0031] Preferably, the oil phase comprises a mixture of linear alkanes and isoalkanes, or white oil.

[0032] Preferably, the linear alkane comprises n-tetradecane.

[0033] Preferably, the water is deionized water.

[0034] Preferably, the middle phase microemulsion is a transparent or translucent liquid.

[0035] In a second aspect, the present invention provides a method for preparing the middle phase microemulsion as described in the first aspect, the preparation method comprising the following steps:

[0036] The biological surfactant, co-surfactant, inorganic salt, oil phase and water in the formulated amount are mixed to obtain the middle phase microemulsion.

[0037] The preparation process of the middle-phase microemulsion provided by the present invention is simple and can be prepared by directly mixing the components evenly, which is conducive to large-scale production.

[0038] Preferably, the mixing specifically includes the following process:

[0039] The biological surfactant, the co-surfactant, the inorganic salt and the water in the formulated amount are mixed to obtain the aqueous phase, and the aqueous phase and the oil phase are mixed.

[0040] Preferably, the mixing further includes a step of standing.

[0041] In a third aspect, the present invention provides a use of the middle phase microemulsion as described in the first aspect in an oil displacement agent.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] (1) The middle phase microemulsion of the present invention is used for oil displacement, which can significantly reduce interfacial tension and improve crude oil recovery. In addition, the middle phase microemulsion of the present invention does not require the addition of alkali and only requires a small amount of auxiliary agent. The concentration of the main agent used is low, the economic benefit is high, and the recovery rate can be significantly improved. It can be used to further improve the recovery rate after chemical flooding such as polymer flooding.

[0044] (2) The biosurfactant of the present invention is selected from monorhamnolipids and / or disrhamnolipids, which are amphiphilic to both oil and water, can reduce the surface tension of water, and can be used as a wetting agent, emulsifier, and foaming agent. Rhamnolipid biosurfactants can be used under extreme conditions of temperature, pH, and salinity, are non-toxic, and are biodegradable. They are highly stable when used in oil displacement and do not cause stress on the environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 is a photograph of the middle phase microemulsion prepared in Example 1;

[0046] Figure 2 This is a cryo-scanning electron micrograph of the middle phase microemulsion prepared in Example 2. DETAILED DESCRIPTION

[0047] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0048] Unless otherwise specified, the raw materials used in the examples and comparative examples of the present invention are as follows:

[0049] Monorhamnolipid: provided by China Petroleum Exploration and Development Research Institute;

[0050] Rhamnolipid: provided by PetroChina Xinjiang Oilfield Company;

[0051] Sodium lauryl polyoxypropylene sulfate: purchased from Sasol (Sandton, South Africa);

[0052] n-Tetradecane (99%): purchased from Adamas-Beta (Shanghai);

[0053] White oil (15#): purchased from Lingzhong Lubricating Oil Co., Ltd. (Chengdu);

[0054] NaCl (AR): purchased from Kelon Reagent Company (Chengdu):

[0055] Deionized water (resistivity: 18.25 MΩ·cm) was prepared in the laboratory using an ultrapure water purification device CDUPT-Ш (Chengdu Ultrapure Technology Co., Ltd., China).

[0056] Example 1

[0057] In this embodiment, a middle-phase microemulsion based on a biological surfactant is provided. The raw materials for preparing the middle-phase microemulsion include the following components in terms of weight percentage:

[0058]

[0059] The biological surfactant is monorhamnolipid; the co-surfactant is sodium dodecylpolyoxypropylene sulfate (a compound represented by formula (I), where n is 3); the inorganic salt is sodium chloride; the oil phase is a mixture of n-tetradecane and its isomers (the content of n-tetradecane in the mixture is 99%); and the water is deionized water.

[0060] The preparation method comprises the following steps:

[0061] The formulated amount of biological surfactant, co-surfactant and inorganic salt is dissolved in water to obtain an aqueous phase. The aqueous phase and the oil phase are mixed evenly and added to a beaker. The mixture is stirred at a speed of 100 rpm at room temperature for 10 minutes and then allowed to stand to obtain the middle phase microemulsion.

[0062] The photo of the middle phase microemulsion provided in this example is as follows Figure 1 As shown in the figure, it can be seen that there are obvious upper, middle and lower phases, and the middle phase is the middle phase microemulsion.

[0063] Example 2

[0064] In this embodiment, a middle-phase microemulsion based on a biological surfactant is provided. The raw materials for preparing the middle-phase microemulsion include the following components in terms of weight percentage:

[0065]

[0066] Among them, the biological surfactant is disrhamnolipid; the co-surfactant is sodium dodecyl polyoxypropylene sulfate (a compound represented by formula (I), n is 3); the inorganic salt is sodium chloride; the oil phase is white oil; and the water is deionized water.

[0067] The preparation method is the same as that of Example 1.

[0068] The middle phase microemulsion provided in this embodiment 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 temperature of the observation chamber was -140°C and vacuumed to 1×10 -5 The image was captured using secondary or backscattered electrons (2keV, 60pA) at a pressure of 1.5 Pa. The test results are shown in Figure 2 ,from Figure 2 It can be seen that a typical bicontinuous structure appears in the electron microscopy results, proving that the intermediate phase is indeed a middle phase microemulsion.

[0069] Example 3

[0070] In this embodiment, a middle-phase microemulsion based on a biological surfactant is provided. The raw materials for preparing the middle-phase microemulsion include the following components in terms of weight percentage:

[0071]

[0072] The biological surfactants are monorhamnolipid and disrhamnolipid (the mass ratio of the two is 1:1); the co-surfactant is sodium dodecylpolyoxypropylene sulfate (a compound represented by formula (I), where n is 3); the inorganic salt is sodium chloride; the oil phase is a mixture of n-tetradecane and its isomers (the content of n-tetradecane in the mixture is 99%); and the water is deionized water.

[0073] The preparation method is the same as that of Example 1.

[0074] Example 4

[0075] In this embodiment, a middle-phase microemulsion based on a biological surfactant is provided. The raw materials for preparing the middle-phase microemulsion include the following components in terms of weight percentage:

[0076]

[0077] Among them, the biological surfactant is disrhamnolipid; the co-surfactant is sodium dodecyl polyoxypropylene sulfate (a compound represented by formula (I), n is 3); the inorganic salt is sodium chloride; the oil phase is white oil; and the water is deionized water.

[0078] The preparation method is the same as that of Example 1.

[0079] Example 5

[0080] In this embodiment, a middle-phase microemulsion based on a biological surfactant is provided. The raw materials for preparing the middle-phase microemulsion include the following components in terms of weight percentage:

[0081]

[0082] Among them, the biological surfactant is disrhamnolipid; the co-surfactant is sodium dodecyl polyoxypropylene sulfate (a compound represented by formula (I), n is 3); the inorganic salt is sodium chloride; the oil phase is white oil; and the water is deionized water.

[0083] The preparation method is the same as that of Example 1.

[0084] Comparative Example 1

[0085] The only difference between this comparative example and Example 1 is that the amount of the biological surfactant used is 1% and the amount of water used is 38.8%.

[0086] Comparative Example 2

[0087] The only difference between this comparative example and Example 1 is that the amount of the biological surfactant used is 0.1% and the amount of water used is 39.7%.

[0088] Comparative Example 3

[0089] The only difference between this comparative example and Example 1 is that the biological surfactant (monorhamnolipid) is replaced by an equal weight of a glycerolipid surfactant (glyceryl monocaprate).

[0090] The oil displacement test was performed on the middle phase microemulsion provided in the examples and comparative examples. The specific test process is as follows:

[0091] 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 subsequent water flooding. The specific steps are as follows:

[0092] 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 2 days, the purpose of which is to make the crude oil evenly distributed in the core, and try to simulate the crude oil distribution in the real oil reservoir;

[0093] 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 Vw Calculate the water flooding recovery factor E as follows: w , where S o is the volume of saturated oil in the core:

[0094]

[0095] 3) Surfactant flooding and subsequent water flooding: 1 mL min -1 After quantitatively injecting 1 PV of surfactant solution (i.e., the middle phase microemulsion provided by the present invention), continue to use 1 mL·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 recovery due to surfactant flooding according to the following formula:

[0096]

[0097] E s =EE w (4)

[0098] 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, K e is the permeability, E w is the water flooding recovery factor, E s Surfactant flooding enhances oil recovery.

[0099] Table 1

[0100] serial number l(cm) h(cm) PV (mL) φ(%) <![CDATA[K e (mD)]]> <![CDATA[E w (%)]]> <![CDATA[E s (%)]]> Example 1 29.8 3.8 33.1 9.9 152.6 45.96 10.38 Example 2 29.4 3.8 32.5 9.7 151.4 46.53 13.51 Example 3 29.1 3.8 32.0 9.8 154.4 44.2 14.2 Example 4 29.7 3.8 33.5 9.9 155.0 43.91 13.0 Example 5 30.0 3.8 33.8 9.7 147.9 47.9 14.7 Comparative Example 1 29.5 3.8 33.2 9.8 154.2 48.12 6.50 Comparative Example 2 29.6 3.8 33.4 9.9 150.0 47.65 4.72 Comparative Example 3 29.8 3.8 33.8 9.9 155.0 43.9 5.12

[0101] As can be seen from Table 1, the middle phase microemulsions provided by the embodiments of the present invention significantly increased the recovery factor (10.38%-14.70%) after being used for water flooding.

[0102] Compared with Examples 1-5, the middle phase microemulsions provided in Comparative Examples 1-3 did not increase the recovery factor by more than 10% after being used for water flooding, and could not achieve a significant increase in the recovery factor.

[0103] The applicant declares that the present invention uses the above-mentioned embodiments to illustrate the biosurfactant-based middle-phase microemulsion, its preparation method, and application. However, the present invention is not limited to the above-mentioned embodiments, and it does not mean that the present invention must rely on the above-mentioned embodiments for implementation. Those skilled in the art should understand that any improvements to the present invention, equivalent replacements of the raw materials used in the present invention, addition of auxiliary components, and selection of specific methods, etc., fall within the scope of protection and disclosure of the present invention.

Claims

1. A middle phase microemulsion based on a biological surfactant, characterized in that: The raw materials for preparing the middle phase microemulsion include the following components in terms of weight percentage: The biological surfactant includes monorhamnolipid and / or disrhamnolipid.

2. The middle phase microemulsion according to claim 1, characterized in that The raw materials for preparing the middle phase microemulsion include the following components in terms of weight percentage:

3. The middle phase microemulsion according to claim 1 or 2, characterized in that The co-surfactant includes sodium lauryl polyoxypropylene sulfate; Preferably, the structural formula of the co-surfactant is shown in the following formula (I): Here, n is an integer from 3 to 6.

4. The middle phase microemulsion according to any one of claims 1 to 3, characterized in that The inorganic salt includes sodium chloride and / or potassium chloride.

5. The middle phase microemulsion according to any one of claims 1 to 4, characterized in that The oil phase includes a mixture of linear alkanes and isoalkanes or white oil; Preferably, the linear alkane comprises n-tetradecane.

6. The middle phase microemulsion according to any one of claims 1 to 5, characterized in that The water is deionized water.

7. The middle phase microemulsion according to any one of claims 1 to 6, characterized in that The middle phase microemulsion is a transparent or translucent liquid.

8. A method for preparing a middle phase microemulsion according to any one of claims 1 to 7, characterized in that: The preparation method comprises the following steps: The biological surfactant, co-surfactant, inorganic salt, oil phase and water in the formulated amount are mixed to obtain the middle phase microemulsion.

9. The preparation method according to claim 8, characterized in that The mixing specifically includes the following process: The biological surfactant, the co-surfactant, the inorganic salt and the water in the formulated amount are mixed to obtain the aqueous phase, and the aqueous phase and the oil phase are mixed.

10. Use of the middle phase microemulsion according to any one of claims 1 to 7 in an oil displacement agent.

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