A method for quickly testing the hydrodynamic size of an oil-displacing system

Abstract

The present invention relates to the technical field of oil and gas field development, and particularly relates to a method for rapidly testing the hydrodynamic size of an oil displacement system. By plotting the viscosity-hydrodynamic size matching relationship curve, the hydrodynamic size of the polymer solution is preliminarily determined through viscosity, and then through a simple and small amount of microporous membrane flow rate test, the more accurate hydrodynamic size of the polymer solution can be calculated. Compared with the traditional method of testing the viscosity and concentration of the polymer and obtaining the result by making tangents on both sides of the inflection point using the plotting method, the method of the present invention is faster and more concise.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas field development, and particularly relates to a method for quickly testing the hydrodynamic size of an oil displacement system. Background Art

[0002] The polymer used for oil displacement forms a random coil in solution, which is composed of one or more molecular chains. The size of the coil is affected by factors such as the molecular weight of the polymer, concentration, and salinity of the water used for sample preparation. Traditional methods for studying the size of polymer solutions usually include mathematical methods, atomic force microscopy (SEM), and dynamic light scattering (DLS). Among them, the mathematical method uses the semi-empirical formula of the FLORY characteristic viscosity number theory for characterizing the molecular size of polymer solutions for calculation. The representation methods include the radius of gyration and the root-mean-square end-to-end distance. These representation methods do not consider the influence of other factors such as concentration and water quality on the molecular size. At the same time, this method is applicable to non-electrolytes and is not suitable for the actual situation of oil fields. The atomic force microscopy method is to make a dry film of the polymer solution and then observe it. Its characteristic is that it can visually observe the aggregation morphology of the polymer system. The disadvantage is that after making the dry film, the morphology of the polymer may have changed, and the size of the hydrated molecular structure in the solution cannot be measured. The dynamic light scattering method can directly measure the morphology and size of the coils in a pure polymer solution. However, this method has high requirements for the cleanliness of the sample and the solution, and can only measure the hydrodynamic size of low-concentration polymer solutions, which is very different from the polymer concentration used in actual use. In addition, when using the dynamic light scattering method to measure the hydrodynamic radius of a low-concentration polymer solution, only the properties of the polymer are measured unilaterally, and the influence relationship between the hydrated radius of the polymer solution and the pore throat radius of the reservoir cannot be well studied.

[0003] The hydrodynamic radius of a single polymer molecule cannot be measured by using the microporous membrane method. Instead, it reflects the hydrodynamic size of the polymer solution under specific conditions and the ability of the polymer solution to pass through a pore throat of a specific size under specific conditions. It reflects the compatibility of the polymer as an aggregate with the pore throat, and is closer to the state and size of the polymer solution under the actual conditions of the oil layer. In the literature report, when using the microporous membrane method to test the hydrodynamic size of the polymer, under a certain experimental pressure, the polymer solution is passed through microporous membranes with different pore sizes, the concentration and viscosity of the polymer solution are measured, and a curve is plotted. According to the inflection point of the curve of the polymer concentration and viscosity changing with the pore size of the microporous membrane, the hydrodynamic characteristic size of the polymer solution is analyzed and determined. This method requires testing the viscosity and concentration under a series of microporous membranes with different pore sizes, which takes a long time and has low efficiency.

[0004] Chinese Patent Application CN105547934A discloses a method for measuring the hydrodynamic size of a polymer. The method uses a microporous membrane filtration device, and includes passing a mother liquor to be measured through the microporous membrane filtration device under a constant pressure, measuring the concentration, molecular weight or viscosity of the polymer in the filtrate; changing the pore sizes of a first filter membrane and a second filter membrane in the microporous membrane filtration device, and repeatedly measuring the concentration or viscosity respectively; establishing a curve of the pore size of the second filter membrane and the concentration of the polymer or its relative concentration, or the viscosity of the polymer filtrate or its relative viscosity; obtaining the inflection point of the curve, and the pore size of the second filter membrane corresponding to the inflection point is the hydrodynamic size of the mother liquor of the polymer to be measured.

[0005] Chinese Patent Application CN110243714A discloses a method for determining the hydrodynamic size of a polymer, which includes: obtaining the initial hydrodynamic size of a polymer solution to be measured under a plurality of preset pressure values, obtaining a target working pressure according to each pressure value and its corresponding initial hydrodynamic size, performing a continuous filtration test on the polymer solution to be measured under the target working pressure, obtaining the target filtration volume corresponding to the filter membrane with each preset pore size, calculating the filtrate rate of the polymer solution to be measured passing through the filter membrane with each preset pore size respectively according to the target working pressure and the target filtration volume corresponding to the filter membrane with each preset pore size, generating a relationship curve between the pore size and the filtrate rate according to each preset pore size and its corresponding filtrate rate, obtaining the pore size corresponding to the inflection point of the relationship curve, and taking the pore size corresponding to the inflection point as the hydrodynamic size of the polymer solution to be measured, without requiring the concentration and cleanliness of the polymer solution to be measured, and improving the accuracy of the measured hydrodynamic size. Summary of the Invention

[0006] The object of the present invention is to more quickly and accurately obtain the hydrodynamic size of a polymer solution, and provide a method for quickly testing the hydrodynamic size of an oil displacement system. This method can be applied to the detection of oil displacement systems with different formulation waters, different molecular weights and concentrations, and is especially used for testing the hydrodynamic size of oil displacement systems in polymer flooding, binary composite flooding and ternary composite flooding.

[0007] The object of the present invention is achieved by the following technical solutions.

[0008] A method for quickly testing the hydrodynamic size of an oil displacement system includes the following steps:

[0009] S1: Plot a viscosity-hydrodynamic size matching relationship curve to obtain a viscosity-hydrodynamic size relationship equation;

[0010] S2: Measure the viscosity of the polymer solution to be measured;

[0011] S3: Substitute the viscosity value measured in S2 into S1 to obtain an equation, calculate the hydrodynamic size value, and determine the required pore size B0 of the microfiltration membrane according to the hydrodynamic size value d0;

[0012] S4: Pass the polymer solution to be tested through a microfiltration membrane with a pore size of B0, and record the flow rate V0 passing through the microfiltration membrane at time T;

[0013] S5: Compare the values of V0 and the preset V. If V0 > V, replace the filter membrane with a pore size smaller than B0. At this time, the filter membrane pore size is denoted as B1, repeat S4 to obtain V1; and so on until a filter membrane with a pore size of B n is used to make V n ≤V;

[0014] Calculate the hydrodynamic size of the polymer solution through Equation I,

[0015]

[0016] S7: In S5, compare the values of V0 and the preset V. If V0 ≤ V, calculate the hydrodynamic size of the polymer solution through Equation II.

[0017]

[0018] Here, B is the value greater than B0 among the preset values of the filter membrane pore size.

[0019] Further, in S1, the viscosity-hydrodynamic size matching relationship curve is obtained by the following method:

[0020] Test the hydrodynamic size of the polymer solution at different viscosities, plot a scatter diagram with viscosity as the abscissa and hydrodynamic size as the ordinate, and finally obtain the viscosity-hydrodynamic size matching relationship curve through linear fitting.

[0021] Further, the polymer is selected from at least one of partially hydrolyzed polyacrylamide, ultra-high relative molecular weight AM / AHPE copolymer with a comb-shaped molecular structure, core-shell associative polymer, or hexadeca-arm star-shaped polycaprolactone polymer.

[0022] Further, the equation of the viscosity-hydrodynamic size matching relationship curve is y = 0.0019x + 0.2511, where y is the hydrodynamic size value and x is the viscosity value.

[0023] Further, the range of the viscosity is 0 - 250 mPa·s.

[0024] Further, the preset values of the filter membrane pore size are 0.15 μm, 0.22 μm, 0.3 μm, 0.45 μm, 0.65 μm, 0.8 μm, 1.0 μm, 2.0 μm, 3.0 μm, 5.0 μm, and 8.0 μm. Among them, B0, B1, ..., B n is selected from the preset values of the filter membrane.

[0025] In step S3 of the present invention, when determining B0, the filter membrane pore size closest to d0 is selected.

[0026] Further, in step S4, the time T is 100 - 200 min.

[0027] Further, in step S5, the preset V is 40 - 50 mL.

[0028] Further, in step S7, among the preset values where B is greater than B0, the value closest to B0 is selected.

[0029] For example, in step S7, when B0 is 0.3 μm, B is selected as 0.45 μm; when B0 is 0.8 μm, B is selected as 1.0 μm, and so on.

[0030] Further, the molecular weight of the polymer is 3 million - 35 million, preferably 10 million - 20 million.

[0031] Further, the concentration of the polymer is 500 mg / L - 2500 mg / L, preferably 1000 mg / L - 2000 mg / L.

[0032] The advantages of the present invention are as follows:

[0033] When using the traditional microfiltration membrane method for hydrodynamic size detection, it is necessary to test the viscosities and concentrations of the oil displacement systems at a series of different microfiltration membrane pore sizes, and use the plotting method to draw the tangents on both sides of the inflection point to obtain the results. After determining the viscosity - hydrodynamic size matching relationship curve in the early stage of the present invention, only the flow rates at a few pore sizes need to be tested in the later stage to calculate the final result. The present invention is faster and more concise, and does not require repeated determination of the concentration and viscosity of the analyte and multiple plotting.

[0034] The method of the present invention can be applied to the detection of oil displacement systems with different formulation waters, different molecular weights, and concentrations, and is particularly suitable for the testing of the hydrodynamic sizes of polymer, binary composite, or ternary composite oil displacement systems. Description of the Drawings

[0035] Figure 1 : Viscosity - hydrodynamic size relationship curve of the oil displacement system in Example 1. Detailed Description of the Invention

[0036] Determination of the viscosity - hydrodynamic size matching relationship curve

[0037] A series of solutions with different viscosities were prepared from partially hydrolyzed polyacrylamide, and their hydrodynamic sizes were measured and plotted as a scatter plot. The curve equation of the viscosity-hydrodynamic size matching relationship obtained by linear fitting is y = 0.0019x + 0.2511.

[0038] In the following examples, the preset values of the filter membrane pore sizes are 0.15 μm, 0.22 μm, 0.3 μm, 0.45 μm, 0.65 μm, 0.8 μm, 1.0 μm, 2.0 μm, 3.0 μm, 5.0 μm, and 8.0 μm. The time T is 150 min, and the preset V = 45 mL.

[0039] Example 1

[0040] (1) Preparation of the polymer solution to be tested: A solution of partially hydrolyzed polyacrylamide (KYKAM, Beijing Hengju Co., Ltd.) with a polymer molecular weight of 10 million and a concentration of 1500 mg / L was prepared with fresh water (mineralization degree 353 mg / L). After stirring for 2 h, it was aged for 12 h and then used.

[0041] (2) Determination of viscosity: The viscosity of the polymer solution was measured using a viscometer to be 25.83 mPa·s. Substituting it into the viscosity-hydrodynamic size matching relationship curve equation, y = 0.3002 was obtained. Therefore, the required microporous filter membrane pore size B0 = 0.3 μm.

[0042] (3) Take 55 ml of the polymer solution in step (1) and pass it through a microporous filter membrane with a pore size of 0.3 μm under a pressure of 0.5 MPa. The flow rate at 150 min was V0 = 12.4 mL, which is less than the preset V = 45 mL.

[0043] (4) Calculate the hydrodynamic size of the polymer solution: Since V0 < V, according to the formula, therefore according to the formula

[0044]

[0045] where B = 0.45 μm, B0 = 0.3 μm, V0 = 12.4 mL, T = 150 min, and d = 0.4004 μm was calculated.

[0046] According to the above, repeat the experiment 6 times. The hydrodynamic sizes of the polymer are: 0.4087 μm, 0.4125 μm, 0.4201 μm, 0.3996 μm, 0.4138 μm, 0.4015 μm. After calculation, the relative standard deviation is: 1.73%.

[0047] Example 2

[0048] The difference from Example 1 is that the mineralization degree of the fresh water in (1) is 3456 mg / L.

[0049] The viscosity of the prepared polymer solution is 13.51 mPa·s. Calculating y = 0.2768, so the required pore size B0 of the microporous filter membrane is 0.3 μm. At this time, V0 = 38.7 mL which is less than V = 45 mL.

[0050] Therefore, according to the formula

[0051]

[0052] where B = 0.45 μm, B0 = 0.3 μm, V0 = 38.7 mL, T = 150 min, and calculating gives d = 0.2952 μm.

[0053] Example 3

[0054] The difference from Example 1 is that a binary oil displacement system is used, and the formulation is: polymer molecular weight 15 million, concentration 1500 mg / L, surfactant concentration 3000 mg / L.

[0055] The viscosity of the prepared polymer solution is 27.32 mPa·s. Calculating y = 0.3030, so the required pore size B0 of the microporous filter membrane is 0.3 μm. At this time, V0 = 20.4 mL which is less than V = 45 mL.

[0056] Therefore, according to the formula

[0057]

[0058] where B = 0.45 μm, B0 = 0.3 μm, V0 = 20.4 mL, T = 150 min, and calculating gives d = 0.3684 μm.

[0059] Example 4

[0060] The difference from Example 1 is that a binary oil displacement system is used, and the formulation is: polymer molecular weight 15 million, concentration 1500 mg / L, surfactant concentration 3000 mg / L, sodium carbonate concentration 6000 mg / L.

[0061] The viscosity of the prepared polymer solution is 6.54 mPa·s. Calculating y = 0.2633, so the required pore size B0 of the microporous filter membrane is 0.3 μm. At this time, V0 = 48.5 mL which is greater than V = 45 mL. Therefore, a microporous filter membrane with pore size B1 = 0.22 μm is replaced, and testing gives V1 = 23.5 mL which is less than V = 45 mL.

[0062] Therefore, according to the formula

[0063]

[0064] where Bn-1 = B0 = 0.3 μm, B n = B1 = 0.22 μm, V n = V1 = 23.5 mL, T = 150 min, and the calculated d = 0.2499 μm.

[0065] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than a limitation on the protection scope of the present invention. Any simple modification or equivalent replacement made by those of ordinary skill in the art to the technical solution of the present invention shall not depart from the essence and scope of the technical solution of the present invention.

Claims

1. A method for rapidly testing the hydrodynamic size of an oil-displacing system, comprising the following steps: S1: Plot a viscosity-hydrodynamic size matching relationship curve for the polymer solution to obtain a viscosity-hydrodynamic size relationship equation; S2: Measure the viscosity of the polymer solution to be tested; S3: Substitute the viscosity value obtained in S2 into the equation obtained in S1 to calculate the hydrodynamic size value. According to the hydrodynamic size value d0, determine the pore size B0 of the microporous filter membrane required; The B0 is the value closest to d0; S4: Pass the polymer solution to be tested through a microporous filter membrane with a pore size of B0, and record the flow rate V0 flowing through the microporous filter membrane at time T; S5: Compare the value of V0 with the preset value of V. If V0 > V, replace the filter membrane with a pore size smaller than B0. At this time, the pore size of the filter membrane is denoted as B1. Repeat S4 to obtain V1; and so on until a filter membrane with a pore size of B n is used to make V n ≤ V; Calculate the hydrodynamic size of the polymer solution through Equation I, wherein, the unit of d is μm, B n and B n-1 have the unit of μm; V n has the unit of mL; the unit of T is min; S6: Compare the values of V0 and the preset V in S5. If V0 ≤ V, calculate the hydrodynamic size of the polymer solution through Equation II; In the formula, the unit of d is μm, the units of B0 and B are μm; the unit of V0 is mL; the unit of T is min; B is the value greater than B0 and closest to B0 among the preset values of the filter membrane pore size; The preset values of the filter membrane pore sizes are 0.15 μm, 0.22 μm, 0.3 μm, 0.45 μm, 0.65 μm, 0.8 μm, 1.0 μm, 2.0 μm, 3.0 μm, 5.0 μm and 8.0 μm, where B0, B1, ..., B n are selected from the preset values of the filter membrane.

2. The method according to claim 1, characterized in that, In S1, the range of the viscosity is 0 - 250 mPa·s.

3. The method according to claim 1, characterized in that, In S1, the polymer is selected from at least one of partially hydrolyzed polyacrylamide, ultra-high relative molecular mass AM / AHPE copolymer with a comb-shaped molecular structure, core-shell associative polymer, or hexadeca-arm star-shaped polycaprolactone polymer.

4. The method according to claim 1, wherein In S1, the viscosity-hydrodynamic size matching relationship curve equation is y = 0.0019x + 0.2511, where y is the hydrodynamic size value and x is the viscosity value.

5. The method according to claim 1, characterized in that In S4, the time T is 100 - 200 min.

6. The method according to claim 1, wherein In S5, the preset V is 40 - 50 mL.

7. The method according to claim 1, wherein In S7, B is selected as the value greater than B0 and closest to B0 among the preset values.

8. The method according to claim 1, wherein The molecular weight of the polymer is 3 million - 35 million.

9. The method according to claim 1, characterized in that The concentration of the polymer is 500 mg / L - 2500 mg / L.

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