A method for evaluating the disintegration and dispersion effect of chemical flooding system on heavy oil

Abstract

The present invention discloses a method for evaluating the disintegration and dispersion effect of a chemical flooding system on heavy oil. The method comprises the following steps: preparing a solution of the chemical flooding system, then adding at least one drop of heavy oil to the surface of the solution and allowing the solution to stand; using a stirring rod to stir the oil film on the surface of the solution and observing the oil-water dispersion state; measuring the spreading coefficient of the heavy oil on the solution. If the spreading coefficient is less than 0, determining whether the chemical flooding system has a disintegration and dispersion effect on the heavy oil is performed according to the following 1) or 2): 1) if the oil film does not spread on the surface of the solution and the heavy oil cannot be dispersed after stirring and adheres to the stirring rod, it indicates that the heavy oil has not undergone self-disintegration and dispersion on the surface of the solution; 2) if the oil film spreads uniformly on the surface of the solution, that is, after stirring, the oil film evenly separates and does not adhere to the stirring rod, it indicates that the heavy oil has undergone self-disintegration and dispersion on the surface of the solution. The method of the present invention can quickly and accurately evaluate the disintegration and dispersion effect of the chemical flooding system on heavy oil.

Description

Technical Field

[0001] The invention relates to a method for evaluating the disassembly and dispersion effect of a chemical oil flooding system on heavy oil, and belongs to the field of oil field development. Background Art

[0002] 60% of the Bohai Oilfield's reserves are heavy or viscous oil. Waterflooding recovery is relatively low for highly viscous oil reservoirs, making efficient heavy oil development a pressing challenge. Chemical flooding viscosity reduction technology, as the most economical and effective viscosity reduction technology, is crucial for heavy oil production in my country, garnering significant attention for its potential in enhancing oil recovery. Currently, the interfacial behavior, viscosity reduction, and flooding effectiveness of chemical flooding systems for heavy oil viscosity reduction are hot topics. The efficiency and effectiveness of chemical flooding solutions are determined by their ability to disintegrate and disperse heavy oil, but research on these effects and rates is limited, and our understanding of the viscosity reduction mechanisms remains incomplete. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for evaluating the dismantling and dispersing effect of a chemical flooding system on heavy oil, which is intuitive, simple and reliable and can quantitatively characterize the efficiency and effect of different agents on the dismantling and dispersing effect of heavy oil.

[0004] The method provided by the present invention for evaluating the dismantling and dispersing effect of a chemical flooding system on heavy oil comprises the following steps:

[0005] S1. Prepare a solution of a chemical flooding system, then add at least one drop of heavy oil to the surface of the solution and let it stand;

[0006] S2. Use a stirring rod to stir the oil film on the surface of the solution and observe the oil-water dispersion state;

[0007] S3. Determine the spreading coefficient of the heavy oil on the solution of the chemical flooding system. If the spreading coefficient is less than 0, determine whether the chemical flooding system has a disintegration and dispersion effect on the heavy oil according to the following 1) or 2):

[0008] 1) The oil film does not spread on the surface of the solution, and the heavy oil cannot be dispersed after stirring and adheres to the stirring rod, indicating that the heavy oil does not undergo self-disassembly and dispersion on the surface of the solution of the chemical flooding system, that is, the chemical flooding system does not have a disassembly and dispersion effect on the heavy oil;

[0009] 2) The oil film spreads evenly on the surface of the solution, that is, after stirring, the oil film separates evenly and does not adhere to the stirring rod, indicating that the heavy oil undergoes self-disassembly and dispersion on the surface of the solution of the chemical flooding system, that is, the chemical flooding system has a disassembly and dispersion effect on the heavy oil.

[0010] In the above method, the viscosity of the heavy oil is ≥50 mPa·s.

[0011] In the above method, the chemical flooding system includes a heavy oil activator, a conventional polymer and a small molecule viscosity reducer;

[0012] The structure of the heavy oil activator is shown in Formula I, and can be prepared according to the method described in the Chinese patent application with application number 201710659444.X. In Formula I, x, y, z, m and n are respectively the mass fractions of the corresponding segments in the polymer, m is 0.75-0.85, y is 0.20-0.24, and x, z and n are all 0.001-0.01;

[0013]

[0014] The conventional polymer may be conventional polyacrylamide, xanthan gum, hydroxyethyl cellulose, etc.;

[0015] The small molecule viscosity reducer can be octylphenol polyoxyethylene ether (OP-10, OP-15), nonylphenol polyoxyethylene ether (TX-10), or sodium α-olefin sulfonate (AOS).

[0016] In the above method, in the solution of the chemical flooding system, the mass concentration of the chemical flooding system is 50 ppm to 10,000 ppm, preferably 200 ppm to 1,000 ppm.

[0017] In the above method, step S1 is carried out at 5 to 80° C., preferably room temperature;

[0018] The standing time is 1 to 10 minutes, preferably 5 to 10 minutes.

[0019] In the above method, in step S1, preferably about 50 μL of the thick oil is added dropwise.

[0020] In the above method, in step S2, the stirring rod is a glass rod.

[0021] In the above method, in step S1, the diameter of the oil film formed after standing is measured, and the dispersion rate of the oil film is obtained according to formula (1);

[0022] v=(Dd) / (2×t) Formula (1)

[0023] In formula (1), D represents the diameter of the oil film, d represents the diameter of the original oil droplet, t represents the standing time, and v represents the dispersion rate.

[0024] In the above method, the surface tension of the solution of the chemical flooding system, the surface tension of the oil phase, and the interfacial tension between the oil phase and the solution of the chemical flooding system are tested, and the spreading coefficient of the heavy oil on the surface of the solution of the chemical flooding system is calculated according to formula (2):

[0025] S O / W =γ w -γ O -γ O / W (2)

[0026] In formula (2), S O / W represents the spreading coefficient, γ w represents the surface tension of the solution of the chemical flooding system, γ O represents the surface tension of the oil phase, γ O / W Represents the interfacial tension between the oil phase and the solution of the chemical flooding system; wherein the oil phase refers to the heavy oil or its components.

[0027] The present invention characterizes the dismantling and dispersing effect and dispersion rate of different chemical flooding systems on heavy oil by testing the spreading coefficient of the oil film on the solution surface and the surface oil film size. This method is intuitive, simple, and reliable, and can quantitatively characterize the dismantling and dispersing efficiency and effect of different agents on heavy oil.

[0028] Experiments of the present invention confirm that when heavy oil is dropped onto the surface of an aqueous solution of a heavy oil activator represented by Formula I, it spreads evenly and has a large oil film radius. After stirring, the oil film separates evenly and does not stick to a glass rod. Moreover, theoretical calculation results show that the spreading coefficient is less than 0, demonstrating that the heavy oil can undergo a good self-disassembly and dispersion effect on the surface of the activator solution represented by Formula I. The activator of the present invention has a strong dispersing effect on the heavy oil structure and can disperse the continuous phase of the oil into a dispersed phase at the micron level or even hundreds of nanometers. At an oil-to-water ratio of 1:1, the activator can achieve a viscosity reduction rate of over 85% for the heavy oil.

[0029] When the concentration of the activator solution is 200ppm, the oil film can be quickly and evenly dispersed and spread on its surface, while the polymer and small molecule viscosity reducer solutions of the same concentration cannot disperse the oil film, and a viscous core appears; when the concentration increases to 1000ppm, the small molecule viscosity reducer solution has a weaker dispersing effect on the oil film, and after stirring, it is dispersed in the form of small oil droplets, while the polymer solution still has no obvious dispersing effect on the oil film.

[0030] Experiments confirmed that at low concentrations, the activator had a rapid dispersion rate of 5.1 mm / min for heavy oil, resulting in a thin oil film thickness of approximately 27.9 μm. At high concentrations, the activator's dispersion rate increased by approximately 2 times, and the final oil film thickness was reduced to half that of the low concentration. However, the small-molecule viscosity reducer had a limited oil film dispersion effect, with a dispersion rate of only 2.1 mm / min and a final oil film thickness of 262 μm. The present method demonstrates that the activator represented by Formula I has significantly greater dispersibility for heavy oil than the small-molecule viscosity reducer. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The oil film dispersion state (200ppm) on the surface of the activator / conventional polymer / small molecule viscosity reducer solution.

[0032] Figure 2 The oil film dispersion state on the surface of the activator / conventional polymer / small molecule viscosity reducer solution (1000ppm)

[0033] Figure 3 This is a microscopic photograph of the oil film dispersion state on the surface of the activator / conventional polymer / small molecule viscosity reducer solution (1000ppm). DETAILED DESCRIPTION

[0034] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0035] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0036] The materials, reagents, and instruments used in the following examples are as follows:

[0037] Potassium chloride, sodium chloride, calcium chloride, sodium bicarbonate, sodium sulfate, potassium sulfate, analytical grade, Beijing Modern Oriental Fine Chemicals Co., Ltd.; magnesium chloride hexahydrate, analytical grade, Beijing Yili Fine Chemicals Co., Ltd.; simulated water for the experiment, mineralization 9374ppm, main ion mass concentration (unit ppm): Na + +K + 3091.96, Ca 2+ 276.17, Mg 2+ 158.68, CO3 2- 14.21, HCO3 - 311.48, SO4 2- 85.29、Cl - 5436.34. The crude oil is Bohai S3 heavy oil.

[0038] Waring stirrer (Beijing Taiya Saifu Technology Development Co., Ltd.), TEXAS-500C spinning drop interfacial tensiometer (KINO Company, USA), DV-Ⅲ Bookfield viscometer (Brookfield Company, USA), DCAT 21 surface tensiometer (Dataphysics Company, Germany), BX-41 optical microscope (Olympus Company, Japan).

[0039] The heavy oil activator used in the following examples was prepared according to the method described in Example 1 of Chinese patent application (201710659444.X).

[0040] The polymer used in the following examples is conventional polyacrylamide, with a weight average molecular weight (M w ) is 750×10 4 .

[0041] The small molecule viscosity reducer used in the following examples is octylphenol polyoxyethylene ether OP-15.

[0042] Example 1: Disintegration and dispersion of heavy oil by different chemical flooding systems

[0043] 1. Test of the dynamic process of crude oil dispersion

[0044] At room temperature (25°C), a single droplet (0.05 mL) of thick oil (4000 mPa·s) was added to the surface of the activator solution, polymer solution, and small molecule viscosity reducer solution at concentrations of 200 and 1000 ppm, respectively. After 5 minutes of stabilization, the oil film on the surface of each solution was moved with a clean glass rod. The spreading of the oil film was observed and compared, and the spreading speed was calculated.

[0045] 2. Results of the dynamic process of crude oil dispersion

[0046] During the crude oil dispersion process, the spreading process of crude oil on the surface of different solutions was recorded by video, and the radius of the oil film on the solution surface was measured ( Figure 1 (a) Figure 2 (a)), calculate the oil film thickness and spreading rate; and use a clean glass rod to move the oil film on the surface of the three solutions ( Figure 1 (b) Figure 2 (b)), observe and compare the dispersion state of the oil film.

[0047] After spreading for 4 minutes, there are obvious differences in the dispersion state of the oil film on the surface of 200ppm activator solution, conventional polymer solution, and small molecule viscosity reducer solution ( Figure 1The oil film on the activator solution surface spreads evenly and has a large oil film radius. After stirring, the oil film separates evenly and does not stick to the glass rod, indicating that the heavy oil can be well dispersed on the activator solution surface. The oil film on the conventional polymer surface has a large radius, but the middle part of the oil film is darker in color, with a clear viscous core. After stirring, the central core still cannot disperse and adheres to the glass rod. The oil film on the surface of the small molecule viscosity reducer solution does not spread, and after stirring, the oil droplets still cannot disperse and adhere to the glass rod.

[0048] After spreading for 2 minutes, the dispersion state of the oil film on the surface of 1000ppm activator solution, conventional polymer solution, and small molecule viscosity reducer solution also showed obvious differences ( Figure 2 Compared with the 200ppm solution, the radius of the oil film on the surface of the 1000ppm activator solution was larger and equally uniform. After stirring, the oil film separated evenly and did not stick to the glass rod, indicating that the heavy oil was well dispersed on the surface of the activator solution and the dispersion rate was faster. The oil film dispersion phenomena on the surface of the 200ppm and 1000ppm conventional polymer solutions were similar, with the core of the oil film unable to disperse and adhering to the glass rod. Unlike the 200ppm solution, the oil film on the surface of the 1000ppm small molecule viscosity reducer solution partially spread but at a slower rate, and after stirring, it dispersed as small oil droplets.

[0049] The oil film dispersed on the surface of 1000ppm activator solution, conventional polymer solution and small molecule viscosity reducer solution was stirred and sampled for observation ( Figure 3 ) , the microscopic state of the oil film after dispersion shows significant differences. Activators have a strong dispersing effect on the structure of heavy oil, dispersing the continuous phase of oil into dispersed phases at the micron level or even hundreds of nanometers. Polymers, on the other hand, have a poor ability to disperse heavy oil, resulting in irregularly shaped dispersed oil phases and large droplet diameters. Small molecule viscosity reducers also have a weaker ability to disperse heavy oil, resulting in spherical dispersed oil phases and larger droplet sizes than those after activator action.

[0050] Example 2: Disintegration and dispersion rates of heavy oil by different chemical flooding systems

[0051] 1. Solution surface tension test

[0052] Platinum foils were used to measure the surface tension of 200ppm and 1000ppm activator solutions, polymer solutions, and small molecule viscosity reducer solutions. The test temperature was 25°C and the test pressure was standard atmospheric pressure. Before testing, the platinum foil was soaked in ethanol and then placed over an alcohol burner to burn off the alcohol and completely remove any adsorbed contaminants.

[0053] 2. Oil-water interfacial tension test

[0054] The interfacial tensions between crude oil and 200ppm and 1000ppm activator solutions, polymer solutions, and small molecule viscosity reducer solutions at 25℃ were measured using a TEXAS-500C video rotating drop tensiometer produced by KINO Corporation of the United States.

[0055] 3. Effect of different chemical flooding systems on the disassembly and dispersion rate of heavy oil

[0056] In order to study the driving force of oil film spreading on the solution surface, the surface tension of the solution and the oil-water interfacial tension were measured. The surface tension of the oil phase was represented by the surface tension of three components (alkanes, aromatic hydrocarbons, and polar components). The theoretical value of the spreading coefficient (S O / W =γ w -γ O -γ O / W ), as shown in Table 1.

[0057] Table 1 Spreading coefficients of different components in the oil film on the surface of activator / conventional polymer / small molecule viscosity reducer solution

[0058]

[0059]

[0060] Theoretical values and experimental spreading phenomena of heavy oil spreading coefficients can be used to characterize whether the heavy oil undergoes self-disassembly on the solution surface. At a concentration of 200 ppm, the theoretical spreading coefficients of the activator solution and the small molecule viscosity reducer solution are similar, with short-chain alkanes exhibiting positive values (≈7 mN / m) and highly aromatic polycyclic aromatic hydrocarbons and polar components exhibiting negative values (≈-1 mN / m and ≈-17 mN / m). However, the dispersion states differ significantly. This is due to the activator's strong disassembly and dispersion effect on the heavy oil, which weakens the interaction between the heavy components of the crude oil and allows the oil film to spread evenly on the activator solution surface. Comparing the theoretical values of spreading coefficients at different concentrations, the solution concentration has little effect on the spreading coefficients of crude oil components on their surfaces. However, at high concentrations, the oil film spreading rate on the surface of the activator solution and the small molecule viscosity reducer solution increases significantly, further indicating that the two solutions have a disassembly and dispersion effect on the crude oil components, resulting in a weakening of the interaction between the crude oil components and a decrease in the surface tension of the oil phase. After the disassembly and dispersion effect, the spreading coefficient increases with the increase in the concentration of the activator and small molecule viscosity reducer solutions. Ultimately, the oil film spreading rate is determined by the disassembly and dispersion rate of the chemical agents on the heavy oil.

[0061] For polymer solutions, the theoretical spreading coefficient of light crude oil components (alkanes and simple condensed-ring aromatic hydrocarbons) on the surface of conventional polymer solutions is large, making them easier to spread; the spreading coefficient of heavy crude oil components (condensed-ring aromatic hydrocarbons with high aromaticity and polar components) is negative, making them difficult to spread. The derivation of the theoretical value of the spreading coefficient is consistent with the phenomenon observed in the dynamic process experiment of crude oil dispersion: after the oil film spreads on the surface of the polymer solution, there is an obvious viscous core, and a very light-colored oil film is distributed around the core, indicating that the polymer has no disassembly and dispersion effect on the heavy oil and does not change the interaction between crude oil components.

[0062] To quantitatively describe the degree and rate of crude oil disintegration and dispersion by activators and small-molecule viscosity reducers, the oil film thickness and spreading rate after equilibrium dispersion were calculated (Table 2). At low concentrations, the activator exhibited a rapid dispersion rate on the heavy oil, reaching 5.1 mm / min, and a thin final film thickness of approximately 27.9 μm, while the small-molecule viscosity reducer showed no significant dispersing effect on the oil film. At high concentrations, the activator's dispersion rate increased by approximately 2-fold, and the final film thickness decreased to 13.1 μm, while the small-molecule viscosity reducer's dispersing effect on the oil film was still limited, with a dispersion rate of only 2.1 mm / min. This suggests that the activator's ability to disintegrate and disperse heavy oil is significantly stronger than that of the small-molecule viscosity reducer.

[0063] Table 2 Effect of activator / small molecule viscosity reducer on the dispersion rate of heavy oil

[0064]

[0065]

Claims

1. A method for evaluating the dismantling and dispersing effect of a chemical flooding system on heavy oil, comprising the following steps: S1. Prepare a solution of a chemical flooding system, then add at least one drop of heavy oil to the surface of the solution and let it stand; In step S1, the diameter of the oil film formed after standing is measured, and the dispersion rate of the oil film is obtained according to formula (1); In formula (1), D represents the diameter of the oil film, d represents the diameter of the original oil droplet, and t represents the standing time. v represents the dispersion rate; The surface tension of the solution of the chemical flooding system, the surface tension of the oil phase, and the interfacial tension between the oil phase and the solution of the chemical flooding system were measured, and the spreading coefficient of the heavy oil on the surface of the solution of the chemical flooding system was calculated according to formula (2): In formula (2), S O / W represents the spreading coefficient, γ w represents the surface tension of the solution of the chemical flooding system, γ O represents the surface tension of the oil phase, γ O / W represents the interfacial tension between the oil phase and the solution of the chemical flooding system; wherein, The oil phase refers to the thick oil or its components; S2. Use a stirring rod to stir the oil film on the surface of the solution and observe the oil-water dispersion state; S3. If the spreading coefficient is less than 0, determining whether the chemical flooding system has a disintegration and dispersion effect on the heavy oil is performed according to the following 1) or 2): 1) The oil film does not spread on the surface of the solution, and the heavy oil cannot be dispersed and adheres to the stirring rod after stirring, indicating that the heavy oil does not undergo self-disassembly and dispersion on the surface of the solution of the chemical flooding system, that is, the chemical flooding system does not have a disassembly and dispersion effect on the heavy oil; 2) The oil film spreads evenly on the surface of the solution, and after stirring, the oil film separates evenly and does not adhere to the stirring rod, indicating that the heavy oil undergoes self-disassembly and dispersion on the surface of the solution of the chemical flooding system, that is, the chemical flooding system has a disassembly and dispersion effect on the heavy oil.

2. The method according to claim 1, wherein: The viscosity of the heavy oil is ≥50 mPa·s.

3. The method according to claim 1 or 2, characterized in that: The chemical flooding system includes a heavy oil activator, a conventional polymer and a small molecule viscosity reducer; The conventional polymer is polyacrylamide, xanthan gum or hydroxyethyl cellulose.

4. The method according to claim 1 or 2, characterized in that: In the solution of the chemical flooding system, the mass concentration of the chemical flooding system is 50ppm~10000ppm.

5. The method according to claim 1 or 2, characterized in that: Step S1 is carried out at 5-80°C; The standing time is 1 to 10 minutes.

6. The method according to claim 1 or 2, characterized in that: In step S2, the stirring rod is a glass rod.

Images