Construction method of composite ionic surfactant system

Abstract

The invention discloses a construction method of a composite ionic surfactant system, which comprises the following steps: determining the relationship between the Zeta potential of a single inorganic salt lower-phase microemulsion and an ionic strength parameter I, establishing NaCl equivalence of the composite ion Zeta potential and the ionic strength parameter by taking a middle-phase microemulsion formed by taking NaCl as a water-phase ion as a benchmark, and combining with different ion molar concentration proportions to obtain the composite ionic surfactant system. And determining the optimal concentration of each inorganic salt in the composite ionic surfactant system. The problem that an HLD formula cannot be suitable for other salts is solved, and the composite ionic surfactant system constructed by the method can form a stable middle-phase microemulsion and can be used for middle-phase microemulsion oil displacement.

Description

Technical Field

[0001] The invention belongs to the technical field of petrochemical industry, and particularly relates to a method for constructing a composite ionic surfactant system. Background Art

[0002] Microemulsion flooding is a widely used chemical flooding technology for oil recovery. It reduces the oil-water interfacial tension, changes the wettability of reservoir rocks, solubilizes residual crude oil, and achieves efficient recovery by adding a flooding system composed of oil, water, surfactants, and additives.

[0003] Compared to other oil recovery methods, microemulsion flooding can effectively reduce displacement pressure, increase sweep coefficient, and improve oil removal efficiency during the flooding process, making it an important chemical flooding method with broad development prospects. Among them, mid-phase microemulsions, due to their ultra-low interfacial tension, have demonstrated excellent oil recovery capabilities in both laboratory experiments and field applications.

[0004] The phase state of microemulsion systems is significantly affected by the salt ion concentration in the aqueous phase. Therefore, experimental methods are often required to configure oil displacement systems suitable for field application. In recent years, foreign researchers have proposed empirical formulas for quantifying the different phase states of microemulsions. Among them, the hydrophilic-lipophilic deviation-net mean curvature formula (HLD) has been widely used in the construction of microemulsion systems.

[0005] In the process of realizing the present invention, the inventors discovered that there are at least the following problems in the prior art: the inorganic salt ions present in formation water under reservoir conditions are relatively complex, and the HLD equation is only applicable when the inorganic salt is sodium chloride. The current method of constructing a middle phase microemulsion using the HLD equation cannot be applied to the construction of a composite ion oil displacement system. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a method for constructing a composite ionic surfactant system in response to the above-mentioned deficiencies in the prior art. The composite ionic surfactant system constructed by this method can form a stable mesophase and can be applied to mesophase microemulsion flooding.

[0007] Compared with the prior art, the present invention has the following advantages:

[0008] 1. The present invention provides a method for constructing a composite ionic surfactant system, comprising establishing a correlation between the Zeta potential of a Winsor I phase microemulsion and an ionic strength parameter and determining, based on the correlation, the optimal concentration of each inorganic salt in the composite inorganic salt for forming a middle phase microemulsion. This method can obtain a stable middle phase microemulsion.

[0009] 2. Preferably, the method of the present invention includes establishing the relationship between the system Zeta potential and the ionic strength parameter using the following phase as a sample, which can effectively overcome the nonlinear response problem of the microemulsion micelles to the potential.

[0010] 3. The method of the present invention can correct the sodium chloride concentration in the conventional HLD equation by determining the effect of different salts on the micelles of the surfactant system, which can specifically solve the problem that the HLD equation cannot be applied to complex ions.

[0011] The technical solution of the present invention is further described in detail below with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is a schematic diagram of the construction process of the complex ionic surfactant system in Example 1;

[0013] Figure 2 is the phase state of each microemulsion in step 102 in Example 1;

[0014] Figure 3 Schematic diagram of the Zeta potential test results of Winsor I phase microemulsion;

[0015] Figure 4 The phase states of single NaCl aqueous phase ionic microemulsions with different concentrations;

[0016] Figure 5 The microemulsion phases of sodium chloride and potassium chloride with different molar concentration weights;

[0017] Figure 6 The microemulsion phases of sodium chloride and calcium chloride with different molar concentration weights;

[0018] Figure 7 The microemulsion phases of sodium chloride and magnesium chloride with different molar concentration weights;

[0019] Figure 8 Microemulsion phases of four inorganic salts with different molar concentration weights. DETAILED DESCRIPTION

[0020] The following will be combined with the embodiments of this application to clearly and completely describe the technical solution. Obviously, the embodiments described are part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0021] In the following description, the term "and / or" is used to describe the association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent: A exists alone, B exists alone, and A and B exist at the same time. A and B can be singular or plural.

[0022] In the following description, the terms "include", "comprising", "having" and "containing" are open-ended terms, meaning including but not limited to.

[0023] Those skilled in the art should understand that in the following description of the embodiments of the present application, the order of serial numbers does not mean the order of execution, some or all of the steps can be executed in parallel or sequentially, and the execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0024] It will be understood by those skilled in the art that the numerical ranges in the examples of the present application are to be understood as also specifically disclosing each intermediate value between the upper and lower limits of the ranges. Each smaller range between any intermediate value within a stated value or stated range and any other stated value or intermediate value within the stated range is also included in the present application. The upper and lower limits of these smaller ranges may independently be included or excluded in the range.

[0025] Unless otherwise indicated, the technical / scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which this application belongs. Although this application describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of this application. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In the event of any conflict with any incorporated document, the content of this specification shall prevail.

[0026] The technical principle adopted by the present invention is as follows: the intermediate phase microemulsion flooding is based on the ability of the flooding system to form a stable intermediate phase with the oil phase, and the optimal concentration of the composite inorganic salt is determined based on the linear relationship between the ionic strength parameter and the Zeta potential of the flooding system.

[0027] The present invention provides a method for constructing a composite ionic surfactant system, comprising:

[0028] S1. Determine the types of inorganic salts in the complex ionic surfactant system, use each inorganic salt as the aqueous phase ion, prepare a series of single inorganic salt surfactant systems with concentration gradients, and determine the salinity range (α1, α2) of the Winsor I phase microemulsion by salinity scanning;

[0029] The surfactant system of the composite inorganic salt is usually composed of a surfactant, a composite inorganic salt, an organic additive, an aqueous phase solvent and an oil phase solvent. When the other components are determined, the composition and content of the composite inorganic salt affect the phase state of the emulsion. One of the purposes of the present invention is to provide a method for constructing a composite ionic surfactant system that can form a stable intermediate phase.

[0030] The method for determining the type of inorganic salt in the complex ionic surfactant system to be formulated is not limited in the present invention and can be a component analysis method commonly used in the art, such as precipitation method, titration method or spectroscopy method.

[0031] The surfactant is an anionic surfactant. In some embodiments, the anionic surfactant is a sulfonate surfactant containing an EO group. In some specific embodiments, the surfactant is ALFOTERRA 123-4s 90 surfactant.

[0032] S2. Taking a value within the salinity range (α1, α2) as a preset salinity, preparing a Winsor I phase microemulsion according to the preset salinity, taking a lower phase from the Winsor I phase microemulsion, and measuring the zeta potential; the number of taken values ​​is ≥ 4, and the number of zeta potential measurements at each preset salinity is ≥ 5; in some specific embodiments, the method for taking the lower phase from the Winsor I phase microemulsion comprises using a rubber-tipped pipette to pass through the oil phase of the Winsor I phase microemulsion and aspirate the lower phase;

[0033] S3, define an ionic strength parameter I, set I = (cZ 2 ) -1 / 2 ;

[0034] Where, I is the microemulsion ionic strength parameter, in mol -1 / 2 ·L -1 / 2 ; c—concentration of inorganic salt in microemulsion, unit is g / 100mL; Z—cation valence of inorganic salt, unitless;

[0035] When setting up the relationship between composite inorganic salt and potential, when taking anionic surfactant as surfactant, ionic strength parameter is defined as cationic concentration and ion valence square product negative half power, can more accurately express the relationship between ionic strength parameter and Zeta potential.In the experimentation, the inventor found that the ionic concn in water and kind have an impact on the Zeta potential of micellar surface, macroscopically show as the phase state change of microemulsion, especially attempt to build the middle phase microemulsion, when taking the middle phase microemulsion group as Zeta potential extraction object, be difficult to clear and clarify the relationship rule between composite inorganic salt and Zeta potential, possible reason is that the middle phase microemulsion exists with bicontinuous component structure form conventionally, although interfacial charge distribution is uniform, but its Zeta potential is conventionally near zero, and measurement result fluctuation is larger, and there is larger error.By following phase microemulsion as the sample of determining the relationship between ionic strength parameter and microemulsion Zeta potential, can effectively overcome the nonlinear response problem of microemulsion to potential.

[0036] S4. Draw a scatter plot of I and Zeta potential, fit it into a straight line, and obtain the relationship between I and Zeta potential ζ = kI + b;

[0037] Where, ζ is the Zeta potential of the microemulsion, in mV; I is the ionic strength parameter of the microemulsion, in mol -1 / 2 ·L -1 / 2 ;

[0038] S5. Determine the optimal concentration of NaCl for preparing the middle phase microemulsion using NaCl as the aqueous phase ion, denoted as S NaCl * Specifically, the following steps are used: using the HLD equation, setting the HLD value to 0, and calculating the optimal NaCl concentration of the corresponding surfactant phase microemulsion, which is S NaCl * , the HLD formula is as follows:

[0039] HLD=ln(S NaCl )-K(EACN)-f(A)-α T (T-25)+Cc

[0040] Where S NaCl —NaCl concentration, i.e., aqueous phase salinity, in g / 100 mL; K—an empirical constant for the hydrophilicity of the surfactant head group, unitless; EACN—alkane equivalent carbon number, unitless; f(A)—a function of alcohol type and concentration, α T —Temperature coefficient, no unit; T—experimental temperature, unit is °C; Cc—characteristic curvature value of surfactant, no unit;

[0041] In the oil-water-surfactant system, when the conditions are suitable, the system will form a three-phase equilibrium middle phase microemulsion containing an upper phase (oil-in-water), a middle phase (bicontinuous phase) and a lower phase (water-in-oil). When the oil-water ratio in the middle phase is 1:1, the middle phase microemulsion system has the lowest interfacial tension and the best displacement effect. The NaCl concentration at this time is the optimal concentration.

[0042] The HLD equation is only applicable to microemulsion systems with NaCl as the aqueous phase ion, and its application range is limited. The inventors have found that for composite inorganic salt microemulsions, each cation will enter the double layer of the micelles, thereby affecting the charge of the micelles. To address the above problems, the corresponding relationship between ionic strength parameters and potential was established, and the relationship between the concentrations of sodium chloride and other inorganic salts was constructed.

[0043] S6, S NaCl * Substitute ζ=kI+b and I=(cZ 2 ) -1 / 2 , determine the optimal concentration of NaCl NaCl * , let ζ NaCl * Zeta potential of complex ionic surfactant system h Equal, we get: I h =(kI NaCl +b NaCl -b h ) / k, where

[0044]

[0045] I h —Ionic strength parameter of complex ionic surfactant system, unit is mol -1 / 2 ·L -1 / 2 ; b h —Intercept of the fitted straight line of the complex ionic surfactant system, unitless; I NaCl —Ionic strength parameter of the middle phase microemulsion prepared with NaCl as the aqueous phase ion, in mol -1 / 2 ·L -1 / 2 ; b NaCl —intercept b when NaCl is the aqueous phase ion; x i —molar concentration weight of inorganic salt i, %; b i —The intercept b when the corresponding inorganic salt i is the aqueous phase ion; Z i —cation valence of the inorganic salt i, unitless;

[0046] According to previous studies, the size and Zeta potential of micelles are affected by ionic strength. For anionic surfactants, the Zeta potential is mainly affected by the type and concentration of cations. 2 ) -1 / 2 In the process, it is considered that the ionic strength parameter can be weightedly calculated according to the molar concentration ratio of ions of different concentrations. After the total ionic strength of the mixed ions is calculated, the optimal mass concentration of each ion can be calculated according to the molar concentration ratio.

[0047] Previous studies have shown a correlation between microemulsion particle size and ion concentration, enabling the construction of microemulsions by fitting a particle size-salt concentration prediction model. However, during their research, the inventors discovered that under experimental conditions, instrumental particle size measurements exhibited significant errors, preventing effective fitting. This error stems from the interference of divalent ions, especially high concentrations, with particle size measurements. The present invention establishes a correlation between zeta potential and ionic strength parameters.

[0048] S7. Determine the theoretical optimal concentration S of each inorganic salt in the complex ionic surfactant system that can form a middle phase microemulsion i * :

[0049]

[0050] Where S i * —Theoretical optimal concentration of inorganic salt i, in g / 100mL: M i —molar mass of inorganic salt i, g / mol; x i —molar concentration weight of inorganic salt i, %; Z i —cation valence of the inorganic salt i, unitless;

[0051] S8, according to the theoretical optimal concentration S of each inorganic salt i * , a composite ionic surfactant system was prepared.

[0052] In some embodiments, a method for adjusting the accuracy is further included, comprising preparing a composite inorganic salt microemulsion according to the optimal concentration of each inorganic salt, and determining whether it is the middle phase through salinity scanning. If so, it indicates that the accuracy meets the requirements. If not, the Zeta potential is re-measured.

[0053] During the experiment, the inventors found that different valence states of cations have different effects on micelles, and cations of different valence states influence each other. When there are more divalent cations, the effect of monovalent cations on micelles is reduced. This interaction between ions of different valence states is the main reason for the error in the composite ion system. The present invention can effectively avoid the error in the function fitting process caused by experimental error and improve the accuracy.

[0054] The present invention has been subjected to a series of experiments before the application is filed. Some of the experimental results are listed below to further describe the invention in detail, and the following embodiments are used to describe the invention in detail.

[0055] Example 1

[0056] This embodiment provides a method for constructing a complex ionic surfactant system, the process is shown as follows Figure 1 As shown, the composite inorganic salt is composed of NaCl, KCl, CaCl2 and MgCl2, the surfactant is ALFOTERRA 123-4s 90, n-butanol is an auxiliary agent, deionized water is an aqueous phase solvent, and tetradecane is an oil phase solvent.

[0057] The construction method specifically includes:

[0058] Step 1: providing microemulsions of a single inorganic salt with different concentrations, and determining the phase state of each microemulsion; the inorganic salt includes NaCl, KCl, CaCl2 or MgCl2; the phase state includes Winsor I, Winsor II or Winsor III; wherein Winsor I corresponds to an oil-in-water microemulsion + an excess oil phase, Winsor II corresponds to an oil-in-water microemulsion + an excess water phase, and Winsor II is a middle phase microemulsion composed of an upper phase (oil-in-water), a middle phase (bicontinuous phase) and a lower phase (oil-in-water) in a three-phase equilibrium; the Winsor I phase has a clear oil-water interface boundary, wherein the upper layer is the excess oil phase, the lower layer is composed of the oil-in-water microemulsion and the excess water phase, and salts and excess surfactants are dissolved in the excess water phase;

[0059] Specifically include:

[0060] Step 101: Determine the raw materials of a single inorganic salt microemulsion and prepare a series of microemulsions according to a preset concentration gradient; wherein: ALFOTERRA 123-4s 90 is a surfactant, n-butanol is an auxiliary agent, a single inorganic salt is an aqueous phase ion, deionized water is an aqueous phase solvent, and tetradecane is an oil phase solvent. The single inorganic salt is NaCl, KCl, CaCl2 or MgCl2. In the microemulsion, the volumes of the aqueous phase solvent and the oil phase solvent are the same, both 5 mL. The mass percentage of the surfactant is 3 wt%, and the mass percentage of n-butanol is 1.5 wt%; the concentration range of the inorganic salt is 0.5-13 g / 100 mL, with a gradient of 0.5-2 g / 100 mL; the concentration of the inorganic salt = inorganic salt (g) / volume of aqueous phase solvent (mL); the mass percentage of the surfactant = mass of the surfactant / (mass of the aqueous phase solvent + mass of the surfactant + mass of the auxiliary agent + mass of the inorganic salt); the mass percentage of n-butanol = mass of n-butanol / (mass of the aqueous phase solvent + mass of the surfactant + mass of the auxiliary agent + mass of the inorganic salt);

[0061] Step 102: Determine the phase of each microemulsion through a salinity scanning experiment, comprising: mixing the above raw materials and placing them in a 20 mL test tube, sealing and vigorously shaking and constantly turning them over to fully mix, standing for 24 hours to allow the system to reach equilibrium, observing the appearance, and determining the phase type of each microemulsion; the phase of each microemulsion is shown in Table 1, and the appearance is shown in Table 1. Figure 2 As shown;

[0062] Table 1 Phase states of each microemulsion in step 102

[0063]

[0064]

[0065] Step 2: Based on the single inorganic salt concentration range corresponding to the Winsor I phase microemulsion, a series of Winsor I phase microemulsions are prepared and the zeta potential is measured. The number of prepared Winsor I phase microemulsions is ≥ 4, specifically comprising:

[0066] Step 201: According to Table 1 and Figure 2 It can be seen that the microemulsion phase of each single inorganic salt is as follows: Figure 2 In the table, the concentration unit for each test tube is g / 100mL:

[0067] When the inorganic salt in the microemulsion of a single inorganic salt is NaCl, when the inorganic salt concentration is ≤5g / 100mL, the microemulsion phase belongs to WinsorⅠ; when the inorganic salt concentration is 7-9g / 100mL, the microemulsion phase belongs to WinsorⅢ; when the inorganic salt concentration is 11-13g / 100mL, the microemulsion phase belongs to WinsorⅡ;

[0068] When the inorganic salt in the microemulsion of a single inorganic salt is KCl, when the inorganic salt concentration is ≤3g / 100mL, the microemulsion phase belongs to WinsorⅠ; when the inorganic salt concentration is 5-7g / 100mL, the microemulsion phase belongs to WinsorⅢ; when the inorganic salt concentration is 9-11g / 100mL, the microemulsion phase belongs to WinsorⅡ;

[0069] When the inorganic salt in the microemulsion of a single inorganic salt is CaCl2, when the inorganic salt concentration is ≤1g / 100mL, the microemulsion phase belongs to WinsorⅠ; when the inorganic salt concentration is 2-3g / 100mL, the microemulsion phase belongs to WinsorⅢ; when the inorganic salt concentration is 4g / 100mL, the microemulsion phase belongs to WinsorⅡ;

[0070] When the inorganic salt in the microemulsion of a single inorganic salt is MgCl2, when the inorganic salt concentration is ≤0.5g / 100mL, the microemulsion phase belongs to WinsorⅠ; when the inorganic salt concentration is 1-2g / 100mL, the microemulsion phase belongs to WinsorⅢ; when the inorganic salt concentration is 3-4g / 100mL, the microemulsion phase belongs to WinsorⅡ;

[0071] Step 202: Prepare a series of Winsor I phase microemulsions based on the inorganic salt concentrations of the microemulsions of each single inorganic salt belonging to Winsor I, wherein:

[0072] When the inorganic salt in the single inorganic salt microemulsion is NaCl, the inorganic salt concentrations in a series of Winsor I phase microemulsions are 0.2 g / 100 mL, 0.4 g / 100 mL, 0.6 g / 100 mL, 0.8 g / 100 mL and 1.0 g / 100 mL;

[0073] When the inorganic salt in the single inorganic salt microemulsion is KCl, the inorganic salt concentrations in a series of Winsor I phase microemulsions are 0.2 g / 100 mL, 0.4 g / 100 mL, 0.6 g / 100 mL, 0.8 g / 100 mL and 1.0 g / 100 mL;

[0074] When the inorganic salt in the single inorganic salt microemulsion is CaCl2, the inorganic salt concentrations in a series of Winsor I phase microemulsions are 0.05 g / 100 mL, 0.1 g / 100 mL, 0.15 g / 100 mL, 0.2 g / 100 mL and 0.25 g / 100 mL;

[0075] When the inorganic salt in the single inorganic salt microemulsion is MgCl2, the inorganic salt concentrations in a series of Winsor I phase microemulsions are 0.05 g / 100 mL, 0.1 g / 100 mL, 0.15 g / 100 mL, 0.2 g / 100 mL and 0.25 g / 100 mL;

[0076] In a microemulsion system with the same inorganic salt and other components and contents determined, the inorganic salt concentration and phase change show a relatively consistent change pattern, that is, when the inorganic salt concentration is lower than the known Winsor I phase concentration, the system remains in the Winsor I phase.

[0077] Step 203: Use a rubber-tipped pipette to penetrate the oil phase of the Winsor I phase microemulsion, draw the lower phase, and measure the Zeta potential of each lower phase using a Zeta potential analyzer. Repeat the test 10 times. The Zeta potential test results of each Winsor I phase lower phase are as follows: Figure 3 and Table 2; the Zeta potential analyzer is Zata PALS190Plus, and the Zeta potential range is -150 to 150 mV;

[0078] Table 2 Zeta potential test results of the lower phase in each WinsorⅠ phase microemulsion

[0079]

[0080]

[0081]

[0082] Step 3: Define an ionic strength parameter I, set I = (cZ 2 ) -1 / 2 ;

[0083] Where, I is the microemulsion ionic strength parameter, in mol -1 / 2 ·L -1 / 2 ; c—concentration of inorganic salt in microemulsion, unit is g / 100mL; Z—cation valence of inorganic salt, unitless;

[0084] In Winsor I phase microemulsions, there is a clear boundary between the oil phase and the water phase. The upper layer is the excess oil phase, and the lower layer is composed of the oil-in-water microemulsion and the excess water phase. Salts and excess surfactants are dissolved in the excess water phase. The zeta potential is the zeta potential of the oil-in-water micelles in the excess water phase. Ions exist only in the water phase. The concentration of inorganic salts in the microemulsion is equal to that in the lower system and the water phase.

[0085] Step 4: Draw a scatter plot with the zeta potential ζ as the ordinate and the ionic strength parameter I as the abscissa, and perform a linear fit on the scatter plot to obtain a straight line, which is the relationship between I and zeta potential ζ = kI + b, as shown in Table 3;

[0086] Where, ζ is the Zeta potential of the microemulsion, in mV; I is the ionic strength parameter of the microemulsion, in mol -1 / 2 ·L -1 / 2 ; k—slope of the relationship between I and Zeta potential, b—intercept of the relationship between I and Zeta potential;

[0087] Table 3 Relationship between I and Zeta potential

[0088]

[0089] According to the fitting results, the absolute values ​​of the slopes k of the four function expressions are basically the same, and the subsequent values ​​are uniformly taken as 18;

[0090] Step 5: Calculate the optimal NaCl concentration S for ALFOTERRA 123-4s 90 surfactant according to the HLD equation. NaCl *, the same Zeta potential has the same effect on the microemulsion micelles, and the same Zeta potential corresponds to the same phase state of the microemulsion. NaCl *Finally, based on this as a benchmark, the theoretical optimal concentration S of other inorganic salts is determined based on the following formula: i *, i.e. the concentration of inorganic salts forming the middle phase microemulsion, specifically including:

[0091]

[0092] Among them, S i *—Theoretical optimal concentration of inorganic salt i, in g / 100 mL. Other inorganic salts include KCl, CaCl2 or MgCl2; M i —molar mass of the inorganic salt i, in g / mol;

[0093] The HLD equation is as follows:

[0094] HLD=ln(S NaCl )-K(EACN)-f(A)-α T (T-25)+Cc;

[0095] Among them, S NaCl —water phase salinity, unit is g / 100 mL; K—empirical constant for the hydrophilicity of the surfactant head group; EACN—alkane equivalent carbon number, unitless, K(EACN)=0.049; f(A)—function of alcohol type and concentration, equal to -0.3, unitless; ɑ T—temperature coefficient, unitless; T—experimental temperature, 25°C; Cc—characteristic curvature value of surfactant, unitless, = -0.550;

[0096] Step 501: Calculate the optimal NaCl concentration S according to the HLD equation. NaCl * is 6.93 g / 100 mL. The salinity scanning experiment verified that when the NaCl concentration was 6.5 g / 100 mL and 7 g / 100 mL, the system was a middle phase microemulsion, indicating that when the NaCl concentration was 6.93 g / 100 mL, the system was a middle phase microemulsion. Figure 4 As shown, Figure 4 The corresponding concentration unit of each test tube is g / 100mL;

[0097] Step 502: According to S NaCl * The theoretical optimal concentrations of other inorganic salts determined are as follows:

[0098] S KCl * =5.385g / 100mL;

[0099] S CaC l2 * =2.033g / 100mL;

[0100] S MgCl2 * =1.073g / 100mL;

[0101] Step 6: Verification: Prepare microemulsions of each inorganic salt determined in step 5 according to the theoretical optimal concentration, and cross-compare with the phase range of the corresponding inorganic salt in step 2 to determine whether it belongs to the middle phase microemulsion. The results show that S KCl * Between 5 and 7 g / 100 mL, it belongs to Winsor III phase, S CaCl2 * Between 2 and 3 g / 100 mL, it belongs to Winsor III phase, S MgCl2 * Between 1 and 2 g / 100 mL, it belongs to Winsor III phase. In summary, the microemulsions prepared with the above theoretical optimal concentrations all belong to the middle phase microemulsion;

[0102] Step 7: Preset the molar concentration weight of each inorganic salt in the composite inorganic salt microemulsion, and determine the optimal concentration of each inorganic salt in the composite inorganic salt microemulsion based on the molar concentration weight, specifically including:

[0103] Step 701, the relationship between the ionic strength parameter I and the Zeta potential ζ of the composite inorganic salt microemulsion h =kI h +bh In the middle, the intercept b h as follows:

[0104]

[0105] Where n is the number of compound inorganic salts; x i is the molar concentration weight of inorganic salt i, %; b i is the intercept b when the corresponding inorganic salt i is the aqueous phase ion; Z i —cation valence of the inorganic salt i, unitless;

[0106] Step 702: Set h With ζ NaCl The same, according to the following formula to obtain the ionic strength parameter I of the composite inorganic salt microemulsion h :

[0107]

[0108] Among them, I NaCl For S NaCl *Corresponding ionic strength I NaCl *;

[0109] Step 703: Based on the molar concentration weight of the inorganic salt, determine the theoretical optimal concentration S of each inorganic salt according to the following formula: i * ;

[0110]

[0111] Step 8: Verification: According to the preset molar concentration weight, the theoretical optimal concentration of each inorganic salt is calculated according to the above formula, and two inorganic salt composite microemulsions are prepared. After salinity scanning experiments, it is determined whether it belongs to the middle phase microemulsion; the preset molar concentration weight, the corresponding inorganic salt type and the theoretical optimal concentration of the two inorganic salts calculated according to step 7 are shown in Table 4. The salinity scanning experimental results of the prepared microemulsion are shown in Table 4. Figures 5-7 As shown, 80% to 120% are multiples of the theoretical optimal concentration under the same molar concentration weight. For example, when the multiple is 80%, in the microemulsion composed of two inorganic salts of NaCl and KCl with a molar concentration weight ratio of 2:1, the concentration of NaCl is 3.095g / 100mL and the concentration of KCl is 1.970g / 100mL. Figures 5-7 It can be seen that compared with the two inorganic salt composite microemulsions at other concentrations, the two inorganic salt composite microemulsions at the optimal concentration clearly show a middle phase, indicating that the two inorganic salt surfactant system of the present invention can form a middle phase microemulsion with higher stability.

[0112] Table 4 Two inorganic salts compound and corresponding molar concentration weights

[0113]

[0114] Step 9: Verification: According to the preset molar concentration weight, the theoretical optimal concentration of each inorganic salt is calculated according to the above formula, and four inorganic salt compound microemulsions are prepared. After salinity scanning experiments, it is determined whether they belong to the middle phase microemulsion; the preset molar concentration weights of NaCl, KCl, CaCl2 and MgCl2 and the inorganic salt concentrations calculated according to step 7 are shown in Table 5. The salinity scanning experimental results of the prepared microemulsions are shown in Table 5. Figure 8 Compared with the four inorganic salt compound microemulsions at other concentrations, the four inorganic salt compound microemulsions at the theoretical optimal concentration clearly show a middle phase, indicating that the four inorganic salt surfactant system of the present invention can form a middle phase microemulsion with high stability.

[0115] Table 5 Four inorganic salts and their corresponding molar concentration weights

[0116]

[0117] Application Examples

[0118] The method for constructing a composite ionic surfactant system in Example 1 was used to construct a method for constructing a medium-phase microemulsion flooding system, wherein the oil-displacement phase was tetradecane and the volume was 5 mL, comprising:

[0119] Step 1. Prepare formation water under reservoir conditions for the experiment; in this application example, the formation water under reservoir conditions consists of NaCl, KCl, CaCl2, MgCl2 and water, wherein the volume of water is 5 mL, and the concentrations of NaCl, KCl, CaCl2 and MgCl2 are 0.5, 0.6, 0.4 and 0.4 g / 100 mL, respectively. That is, the masses of NaCl, KCl, CaCl2 and MgCl2 in the groundwater under reservoir conditions are 0.025 g, 0.03 g, 0.02 g and 0.02 g, respectively. In this application example, the concentrations of each inorganic salt in the formation water under reservoir conditions are all lower than the theoretical optimal concentration in Table 5. This is to consider the cheapness of adjusting the concentration. The optimal concentration can be achieved by only adding inorganic salts. When the inorganic salt concentration is higher than the theoretical optimal, it can be adjusted by increasing the amount of water added for dilution.

[0120] Step 2: Mix formation water under reservoir conditions, a surfactant, and n-butanol to obtain a mixed system; in the mixed system, the mass percentage of the surfactant is 3 wt%, and the mass percentage of n-butanol is 1.5 wt%; the mass percentage of the surfactant = the mass of the surfactant / (the mass of the water + the mass of the surfactant + the mass of the n-butanol + the mass of the inorganic salt); the mass percentage of the n-butanol = the mass of the n-butanol / (the mass of the water + the mass of the surfactant + the mass of the n-butanol + the mass of the inorganic salt); the surfactant is the same as that in Example 1;

[0121] Step 3, according to the preset molar concentration weight of 2:2:1:1, the theoretical optimal concentration of the four inorganic salts is calculated according to Example 1, that is, the concentrations of NaCl, KCl, CaCl2 and MgCl2 are 0.623 g / 100 mL, 0.795 g / 100 mL, 0.591 g / 100 mL and 0.507 g / 100 mL, respectively. According to the above optimal concentrations, the inorganic salts in the mixed system are replenished, that is, 0.00615 g NaCl, 0.00975 g KCl, 0.00955 g CaCl2 and 0.00535 g MgCl2 are added to the mixed system respectively to prepare a composite ionic surfactant system for oil displacement;

[0122] Step 4: Mix the composite ionic surfactant system for oil displacement with the oil phase to be displaced, and determine the formed phase by salinity scanning.

[0123] The results show that in this application example, an obvious middle phase appears in the emulsion after the composite ionic surfactant system for oil displacement is mixed with the phase to be displaced. The composite ionic surfactant system for oil displacement in this application example can form a middle phase microemulsion with high stability with the oil phase.

Claims

1. A method for constructing a complex ion surfactant system, wherein the complex ion comprises two or more inorganic salts, characterized in that: include: The Zeta potential of Winsor type I microemulsion was determined, and the relationship between ionic strength parameters and Zeta potential (1) and (2) was established: ζ=kI+b (1); I=(cZ 2 ) -1 / 2 (2); Where, I is the microemulsion ionic strength parameter, in mol -1 / 2 ·L -1 / 2 ; c - inorganic salt concentration in the microemulsion, unit is g / 100mL; Z - cationic valence of the inorganic salt, no unit; ζ - microemulsion Zeta potential, unit is mV; the aqueous phase ion in the WinsorI type microemulsion is an inorganic salt; According to formula (3), the theoretical optimal concentration S of each inorganic salt in the complex ionic surfactant system is determined. i * : Where S i * —Theoretical optimal concentration of inorganic salt i, in g / 100mL: M i —molar mass of inorganic salt i, g / mol; x i —molar concentration weight of inorganic salt i, %; Z i —cation valence of the inorganic salt i, unitless; I h —Ionic strength parameter of complex ionic surfactant system, unit is mol -1 / 2 ·L -1 / 2 ; According to the theoretical optimal concentration S of each inorganic salt i * , a composite ionic surfactant system was prepared.

2. The method for constructing a complex ionic surfactant system according to claim 1, wherein: Ionic strength parameter I of complex ionic surfactant system h for: I h =(kI NaCl +b NaCl -b h ) / k (4); b h —Intercept of the fitted straight line of the complex ionic surfactant system, unitless; I NaCl is the ionic strength parameter of the middle phase microemulsion prepared with NaCl as the aqueous phase ion, in mol -1 / 2 ·L -1 / 2 ; b NaCl is b in formula (1) when NaCl is the aqueous phase ion; x i —molar concentration weight of inorganic salt i, %; b i —b in formula (1) when the corresponding inorganic salt i is the aqueous phase ion; Z i —Cation valence of inorganic salt i, unitless.

3. The method for constructing a complex ionic surfactant system according to claim 2, wherein: Determine the ionic strength parameter I of the middle phase microemulsion prepared with NaCl as the aqueous phase ion NaCl The methods include: Determine the optimal NaCl concentration S for preparing the middle phase microemulsion using NaCl as the aqueous phase ion NaCl * ; S NaCl * Substituting into formula (2), we can obtain the microemulsion ionic strength parameter I of the middle phase microemulsion prepared with NaCl as the aqueous phase ion, which is I NaCl .

4. The method for constructing a complex ionic surfactant system according to claim 3, wherein: Determine the optimal NaCl concentration S for preparing the middle phase microemulsion using NaCl as the aqueous phase ion NaCl * , which is determined by the HLD equation.

5. The method for constructing a complex ionic surfactant system according to claim 1, wherein: The method for constructing a Winsor I type microemulsion includes: using a single inorganic salt as an aqueous phase ion to construct a single inorganic salt surfactant system of different concentrations, and using salinity scanning to determine the microemulsion phase of the system; the raw materials of the single inorganic salt surfactant system include: an inorganic salt, a surfactant, an adjuvant, an aqueous phase solvent, and an oil phase solvent; the single inorganic salt surfactant system of different concentrations is obtained by only changing the addition amount of the corresponding inorganic salt; the microemulsion phase includes Winsor I, Winsor III, or Winsor II.

6. The method for constructing a complex ionic surfactant system according to claim 1, wherein: Determining the Zeta potential of a Winsor type I microemulsion involves: Based on the single inorganic salt concentration range (α1, α2) corresponding to the phase state of Winsor type I microemulsion, a series of Winsor type I microemulsions were prepared by taking values ​​within the above range as the single inorganic salt concentration, and the phase was removed to measure the zeta potential.

7. The method for constructing a complex ionic surfactant system according to claim 6, characterized in that: The number of values ​​in the interval is ≥4.

8. The method for constructing a complex ionic surfactant system according to claim 1, wherein: The inorganic salts in the composite ionic surfactant system include two or more of NaCl, KCl, CaCl2 and MgCl2.

9. The method for constructing a complex ionic surfactant system according to claim 1, wherein: The surfactant in the composite ionic surfactant system is an anionic surfactant.

10. The method for constructing a complex ionic surfactant system according to claim 1, characterized in that: The method also includes a method for adjusting the accuracy, including: preparing a composite inorganic salt microemulsion according to the concentration of each inorganic salt that can form a middle phase microemulsion, and determining whether it is a middle phase through salinity scanning. If so, it indicates that the accuracy meets the requirements; if not, re-measuring the Zeta potential.

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