Method for detecting viscosity thermal stability of polymer for oil displacement

Abstract

The present application belongs to the technical field of oil and gas field development, and particularly relates to a method for detecting viscosity thermal stability of oil displacement polymer. The method comprises the following steps: establishing a standard curve of the relationship between the hydrolysis degree and the viscosity of the water solution of the oil displacement polymer; aging the water solution of the oil displacement polymer to be detected at high temperature, testing the hydrolysis degree of the water solution of the oil displacement polymer to be detected, and obtaining the viscosity thermal stability of the oil displacement polymer to be detected after aging through the established standard curve. The method can obtain the viscosity thermal stability of the polymer under the condition of no oxygen removal, avoids the defect that the traditional evaluation method of thermal stability has a large error in the test result of the thermal stability of the polymer due to incomplete oxygen removal, and improves the accuracy of the test result of the viscosity thermal stability of the polymer.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of oil and gas field development, and particularly relates to a method for detecting viscosity thermal stability of a polymer for oil displacement. BACKGROUND

[0002] In the field of oil and gas field development, polymer flooding has a good effect of improving oil recovery. The mechanism of polymer flooding is to reduce the water-oil mobility ratio during the migration in the formation, expand the sweep, and improve the recovery ratio by relying on the high viscosity. Since the polymer needs to migrate in the formation for more than half a year after being injected into the formation, the long-term stability of the viscosity of the polymer under the temperature condition of the oil reservoir has an important influence on the oil displacement effect. At present, the type of the polymer used for polymer flooding is mainly partially hydrolyzed polyacrylamide polymer. The viscosity thermal stability evaluation of the polymer is mainly performed by vacuuming and removing oxygen from the polymer solution, sealing the solution after the removal of oxygen is completed, placing the solution in an oven, setting the temperature of the oven as the temperature of the oil reservoir where the polymer is to be injected, testing the viscosity of the polymer solution by using a viscometer every certain time, and finally obtaining the ratio of the viscosity of the polymer after three months to the initial viscosity, which is the long-term viscosity retention rate of the polymer.

[0003] Chinese patent CN104857743A discloses a sealing oxygen removal device and method for polymer solution. The device includes a sealed container for containing the polymer solution, at least two connecting ports including a first connecting port and a second connecting port in the upper part of the sealed container, and a liquid outlet in the lower part. The first connecting port is connected with an inert gas generator, and an evacuation mechanism is connected with the second connecting port for evacuating and removing oxygen from the sealed container and the polymer solution contained therein. A sampling mechanism is connected with the liquid outlet for detecting the oxygen content of the polymer contained in the sealed container. The main purpose of the device is to efficiently remove oxygen from the polymer solution, thereby realizing the evaluation of the long-term thermal stability of the polymer.

[0004] Chinese patent CN108579133A discloses an oxygen removal device and method for polymer solution. The device includes a source steel bottle, a buffer bottle, a spherical valve, a gas flow meter, a glass conduit, a reagent bottle, a gas distributor, a puncture needle, and a narrow-mouth glass bottle. The device is used for oxygen removal, and the method includes primary oxygen removal and deep oxygen removal. The invention solves the problem that the general oxygen removal method is not complete and is not suitable for high-viscosity aqueous solutions, and is used for oxygen removal of high-viscosity polymer solutions.

[0005] Chinese invention patent CN105571988B discloses a polymer thermal stability detection device and a detection method. The inlet of the first constant-rate displacement pump is connected to a first displacement liquid storage device. The outlet of the first constant-rate displacement pump is connected to the inlet of a first intermediate container group. The outlet of the first intermediate container group is connected to the inlet of a homogeneous sand filling pipe series. The outlet of the homogeneous sand filling pipe series is connected to the inlet of a second intermediate container group. The outlet of the second intermediate container group is connected to the outlet of the second constant-rate displacement pump. The inlet of the second constant-rate displacement pump is connected to a second displacement liquid storage device. The homogeneous sand filling pipe series is placed in a thermostat. A porous medium short section is installed between the inlet of the homogeneous sand filling pipe series and the outlet of the first intermediate container group. The main effect of the method is to solve the problem that the existing technology lacks the influence of combining actual conditions on the evaluation of polymer stability, thereby realizing dynamic stability detection of polymer solution.

[0006] The polymer viscosity long-term thermal stability tested by the above method has the following disadvantages.

[0007] (1) The oxygen removal process is time-consuming and complicated. In the traditional method for testing the long-term thermal stability of polymer viscosity, the polymer needs to be deoxygenated for 2-5 hours by a vacuum pump or a vacuum glove box. After deoxygenation, the sample needs to be packaged. The entire deoxygenation process is time-consuming and complicated.

[0008] (2) The deoxygenation effect seriously affects the thermal stability results of the polymer solution. The polymer solution is in an anaerobic state in the formation, so it is necessary to completely deoxygenate the polymer solution when testing the long-term thermal stability of the polymer solution. However, during the actual deoxygenation operation, it is difficult to completely remove the oxygen due to the high viscosity of the polymer, which ultimately leads to different oxygen contents in different bottles. Therefore, it is difficult to make parallel tests on the viscosity thermal stability of the same sample.

[0009] Therefore, there is an urgent need for an evaluation method that can simply and accurately test the viscosity thermal stability of the polymer in a high-temperature and high-calcium and magnesium reservoir environment. SUMMARY

[0010] The main purpose of the present application is to provide a method for detecting the viscosity thermal stability of the polymer used for oil displacement. The method of the present application obtains the viscosity thermal stability of the polymer by testing the hydrolysis degree of the polymer. The obtained results have high accuracy, and the method is simple, which overcomes the above problems existing in the prior art.

[0011] The present application provides a method for detecting the viscosity thermal stability of the polymer used for oil displacement, which comprises the following steps:

[0012] The method for establishing the standard curve of the relationship between the hydrolysis degree and the viscosity of the polymer solution for oil displacement comprises the following steps: preparing polymer solutions with different hydrolysis degrees by using formation simulated water, testing the viscosity of the polymer solutions with different hydrolysis degrees by using a rheometer, testing the hydrolysis degree of the polymer solution by using an automatic potentiometric titrator, and drawing the standard curve.

[0013] Further, the method for establishing the standard curve of the relationship between the hydrolysis degree and the viscosity of the polymer solution for oil displacement comprises the following steps: preparing polymer solutions with different hydrolysis degrees by using formation simulated water, testing the viscosity of the polymer solutions with different hydrolysis degrees by using a rheometer, testing the hydrolysis degree of the polymer solution by using an automatic potentiometric titrator, and drawing the standard curve.

[0014] Further, the total content of calcium and magnesium ions in the formation simulated water is 200-5000 mg / L.

[0015] Further, the concentration of the polymer solutions with different hydrolysis degrees prepared by using the formation simulated water is 1500-2000 mg / L.

[0016] Further, the polymer for oil displacement is a polyacrylamide polymer, and the hydrolysis degree ranges from 10% to 70%.

[0017] Further, when the rheometer is used to test the viscosity of the polymer solutions with different hydrolysis degrees, the testing temperature is 60-95 ℃.

[0018] Further, before the automatic potentiometric titrator is used to test the hydrolysis degree of the polymer solution, blank titration is first performed, the titration end point selected for the blank titration is pH=3.4-3.5, and the blank titration is performed at least 3 times to obtain the arithmetic mean value.

[0019] Further, the method for high-temperature aging of the polymer solution for oil displacement comprises the following steps: placing the polymer solution for oil displacement to be tested into a high-temperature resistant container and sealing the container, and then performing high-temperature aging.

[0020] Further, the high-temperature aging temperature is 60-95 ℃.

[0021] Further, the aging time is greater than or equal to 90 days.

[0022] The present application first discovers that the polymer hydrolysis degree and the viscosity have an inverse relationship under high-temperature and high-calcium and magnesium conditions. The method of the present application first establishes the standard curve of the polymer hydrolysis degree and the viscosity, then places the polymer solution to be tested into a high-temperature oven, tests the hydrolysis degree of the polymer after different heat aging times, and obtains the long-term heat stability of the viscosity of the polymer to be tested according to the polymer viscosity corresponding to the hydrolysis degree value of the polymer after heat aging on the standard curve.

[0023] Compared with the prior art, the present application has the following advantages:

[0024] The method can obtain the thermal stability of the viscosity of the polymer under the condition of no oxygen removal, avoids the defect that the traditional evaluation method of the thermal stability of the polymer has a larger error of the test result of the thermal stability of the polymer due to incomplete oxygen removal, and simultaneously improves the accuracy of the detection result of the thermal stability of the viscosity of the polymer due to the high accuracy and good parallelism of the automatic potentiometric titration method for testing the hydrolysis degree. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 A test flow chart of the method for detecting the viscosity thermal stability of the partially hydrolyzed polyacrylamide polymer for oil displacement in a high-temperature high-calcium-magnesium oil reservoir according to the application;

[0026] Figure 2 A standard curve of the hydrolysis degree and the viscosity of the partially hydrolyzed polyacrylamide polymer for oil displacement with a hydrolysis degree of 20%-60% under the conditions of a salinity of 19334 mg / L, calcium-magnesium ions of 514 mg / L and a temperature of 75℃;

[0027] Figure 3 A corresponding curve of the hydrolysis degree and the viscosity of the 1# polymer with a hydrolysis degree of 21.3% after 90 days of thermal aging at 75℃;

[0028] Figure 4 A corresponding curve of the hydrolysis degree and the viscosity of the 2# polymer with a hydrolysis degree of 28.5% after 90 days of thermal aging at 75℃;

[0029] Figure 5 A standard curve of the hydrolysis degree and the viscosity of the partially hydrolyzed polyacrylamide polymer for oil displacement with a hydrolysis degree of 20%-60% under the conditions of a salinity of 19334 mg / L, calcium-magnesium ions of 514 mg / L and a temperature of 85℃;

[0030] Figure 6 A corresponding curve of the hydrolysis degree and the viscosity of the 3# polymer with a hydrolysis degree of 22.8% after 90 days of thermal aging at 75℃;

[0031] Figure 7 A corresponding curve of the hydrolysis degree and the viscosity of the 3# polymer with a hydrolysis degree of 22.8% after 90 days of thermal aging at 85℃. DETAILED DESCRIPTION

[0032] It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0033] It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments in accordance with the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and / or "comprising," when used in this specification, specify the presence of stated features, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and / or groups thereof.

[0034] In order to enable a person skilled in the art to more clearly understand the technical solutions of the present application, the technical solutions of the present application will be described in detail below in combination with specific embodiments.

[0035] Embodiment 1

[0036] A method for detecting viscosity thermal stability of an oil displacement polymer, comprising the following steps:

[0037] (1) Using formation simulation water with a salinity of 19334 mg / L and a total calcium and magnesium ion content of 514 mg / L, a partially hydrolyzed polyacrylamide polymer solution with a concentration of 1500 mg / L and a hydrolysis degree of 20% to 60% is prepared. The viscosity of the polymer solution with different hydrolysis degrees is tested at a reservoir temperature of 75°C using a rheometer, and the hydrolysis degree of the polymer solution is tested using an automatic potentiometric titrator. Before testing the hydrolysis degree of the polymer using the automatic potentiometric titrator, blank titration is required. The titration end point selected for the blank titration is pH = 3.4, and the blank titration is performed three times, and the arithmetic mean value is taken. A standard curve corresponding to the hydrolysis degree and viscosity of the polymer is established, as shown in Figure 2 .

[0038] (2) Using formation simulation water, a partially hydrolyzed polyacrylamide polymer with an initial hydrolysis degree of 21.3% (denoted as 1# polymer) is prepared with a concentration of 1500 mg / L. The polymer is directly placed in an ampoule under non-oxygen removal conditions, sealed with a cap, and then placed in a high-temperature oven with a temperature of 75°C.

[0039] (3) After the polymer is aged for 7 days, 15 days, 30 days, 60 days, and 90 days, respectively, the polymer solution is taken out and the hydrolysis degree of the polymer solution is tested (the hydrolysis degree testing method is the same as step 1), and compared with the standard curve to obtain the long-term thermal stability of the viscosity of the polymer after aging.

[0040] Table 1 Hydrolysis degree and viscosity thermal stability of 1# polymer aged at 75°C for different periods of time

[0041] Days of heat aging Test hydrolysis values Viscosity / mPa-s 0 21.3％ 18.3 7 24.5％ 18.1 15 28.4％ 17.5 30 32.3％ 16.5 60 37.5％ 14.5 90 43.3％ 12.2

[0042] 1# polymer after aging for 7 days, 15 days, 30 days, 60 days and 90 days under the conditions of salinity of 19334 mg / L, calcium and magnesium ion content of 514 mg / L and reservoir temperature of 75℃, the hydrolysis degree of the polymer increases from the initial 21.3% to 43.3% after 90 days, and the viscosity retention rate of the polymer after aging for 90 days is 66.7%.

[0043] Example 2

[0044] A viscosity thermal stability detection method for an oil displacement polymer, comprising the following steps:

[0045] (1) Using formation simulation water with salinity of 19334 mg / L and total calcium and magnesium ion content of 514 mg / L, a partially hydrolyzed polyacrylamide polymer solution with a concentration of 1500 mg / L and a hydrolysis degree of 20%-60% is prepared, the viscosity of the polymer solution with different hydrolysis degrees is tested at a reservoir temperature of 75℃ by using a rheometer, and the hydrolysis degree of the polymer solution is tested by using an automatic potentiometric titrator. Before testing the hydrolysis degree of the polymer by the automatic potentiometric titrator, blank titration is required, the titration end point pH is selected to be 3.4, the blank titration is performed for 3 times, and the arithmetic mean value is taken; a corresponding standard curve of the polymer hydrolysis degree and viscosity is established, as shown in Figure 2 .

[0046] (2) The partially hydrolyzed polyacrylamide polymer solution with an initial hydrolysis degree of 28.5% (denoted as 2# polymer) is prepared by using the formation simulation water, and the concentration is all 1500 mg / L. The polymer solution is directly placed in an ampoule without oxygen removal, sealed after pressing the lid, and then placed in a high-temperature oven with a temperature of 75℃.

[0047] (3) After the polymer is aged for 7 days, 15 days, 30 days, 60 days and 90 days, respectively, the polymer solution is taken out, the hydrolysis degree of the polymer solution is tested (the hydrolysis degree testing method is the same as step 1), and compared with the standard curve to obtain the long-term thermal stability of the viscosity of the polymer after aging.

[0048] Table 2 Hydrolysis degree and viscosity thermal stability of 2# polymer aged for different time at 75℃

[0049] Days of heat aging Test hydrolysis values Viscosity / mPa-s 0 28.5％ 17.8 7 32.9％ 16.3 15 35.2％ 15.4 30 37.9％ 14.4 60 42.9％ 12.3 90 48.8％ 10.5

[0050] 2# polymer after aging for 7 days, 15 days, 30 days, 60 days and 90 days under the conditions of salinity of 19334 mg / L, calcium and magnesium ion content of 514 mg / L and reservoir temperature of 75℃, the hydrolysis degree of the polymer increases from the initial 21.3% to 43.3% after 90 days, and the viscosity retention rate of the polymer after aging for 90 days is 66.7%.

[0051] Example 3

[0052] A method for detecting viscosity thermal stability of polymer for oil displacement, comprising the following steps:

[0053] (1) Using formation simulation water with salinity of 19334 mg / L and total calcium and magnesium ion content of 514 mg / L, a partially hydrolyzed polyacrylamide polymer solution with concentration of 1500 mg / L and hydrolysis degree of 20%-60% is prepared, the viscosity of the polymer solution with different hydrolysis degrees at reservoir temperature of 75 ℃ is tested by a rheometer, and the hydrolysis degree of the polymer solution is tested by an automatic potentiometric titrator, before testing the hydrolysis degree of the polymer by the automatic potentiometric titrator, blank titration is required, the titration end point pH is 3.4, the blank titration is performed for 3 times, and the arithmetic mean value is taken; the corresponding standard curve of the hydrolysis degree and the viscosity of the polymer is established, as shown in Figure 2 .

[0054] (2) The partially hydrolyzed polyacrylamide polymer solution (denoted as 3# polymer) with initial hydrolysis degree of 22.8% is prepared by using the formation simulation water, the concentration is 1500 mg / L, and the solution is directly placed in an ampoule under non-oxygen removal condition, sealed after pressing the cover, and then placed in a high-temperature oven with temperature of 75 ℃.

[0055] (3) After the polymer is aged for 7 days, 15 days, 30 days, 60 days and 90 days respectively, the polymer solution is taken out, the hydrolysis degree of the polymer solution is tested (the hydrolysis degree testing method is the same as step 1), and compared with the standard curve, to obtain the long-term thermal stability of the viscosity of the polymer after aging.

[0056] Table 3 Hydrolysis degree and viscosity thermal stability of 3# polymer aged at 75 ℃ for different time

[0057] Days of heat aging Test hydrolysis values Viscosity / mPa-s 0 22.8％ 18.2 7 25.9％ 18.1 15 30.3％ 17.3 30 33.5％ 16.2 60 39.6％ 13.5 90 46.4％ 11.3

[0058] After the 3# polymer is aged for 7 days, 15 days, 30 days, 60 days and 90 days respectively under the condition of salinity of 19334 mg / L, calcium and magnesium ion content of 514 mg / L and reservoir temperature of 75 ℃, the hydrolysis degree of the polymer increases from the initial 22.8% to 46.4% after 90 days, and the viscosity retention rate of the polymer aged at 75 ℃ for 90 days is 62.1%.

[0059] Example 4

[0060] A method for detecting viscosity thermal stability of polymer for oil displacement, comprising the following steps:

[0061] (1) Using formation simulation water with salinity of 19334 mg / L and total calcium and magnesium ion content of 514 mg / L, a partially hydrolyzed polyacrylamide polymer solution with a concentration of 1500 mg / L and a hydrolysis degree of 20%-60% is prepared. The viscosity of the polymer solution with different hydrolysis degrees is tested at a reservoir temperature of 85°C using a rheometer, and the hydrolysis degree of the polymer solution is tested using an automatic potentiometric titrator. Before testing the hydrolysis degree of the polymer using the automatic potentiometric titrator, blank titration is required. The titration end point selected for the blank titration is pH = 3.4, and the blank titration is performed three times, and the arithmetic mean value is taken. A standard curve corresponding to the hydrolysis degree and viscosity of the polymer is established, as shown in Figure 5 .

[0062] (2) A partially hydrolyzed polyacrylamide polymer solution (denoted as 3# polymer) with an initial hydrolysis degree of 22.8% is prepared using formation simulation water at a concentration of 1500 mg / L. The polymer is directly placed in an ampoule without oxygen removal, sealed with a cap, and then placed in a high-temperature oven at a temperature of 85°C.

[0063] (3) After the polymer is aged for 7 days, 15 days, 30 days, 60 days, and 90 days, respectively, the polymer solution is taken out and the hydrolysis degree of the polymer solution is tested (the hydrolysis degree testing method is the same as step 1). The long-term thermal stability of the viscosity of the polymer after aging is obtained by comparing with the standard curve.

[0064] Table 4 Hydrolysis degree and viscosity thermal stability of 3# polymer aged at 85°C for different periods of time

[0065] Days of heat aging Test hydrolysis values Viscosity / mPa-s 0 22.8％ 16.5 7 28.5％ 14.9 15 35.6％ 12.6 30 40.2％ 11 60 46.2％ 8.6 90 51.3％ 7.1

[0066] After the 3# polymer is aged for 7 days, 15 days, 30 days, 60 days, and 90 days, respectively, under the conditions of a salinity of 19334 mg / L, a total calcium and magnesium ion content of 514 mg / L, and a reservoir temperature of 85°C, the hydrolysis degree of the polymer increases from the initial 22.8% to 51.3% after 90 days. The viscosity retention rate of the polymer aged at 85°C for 90 days is 43.0%.

[0067] Example 5

[0068] A method for detecting the viscosity thermal stability of an oil displacement polymer, which is different from Example 1 in that the total calcium and magnesium ion content of the formation simulation water is 200 mg / L, and the other conditions are the same as those in Example 1.

[0069] Example 6

[0070] A method for detecting the viscosity thermal stability of an oil displacement polymer, which is different from Example 1 in that the total calcium and magnesium ion content of the formation simulation water is 5000 mg / L, and the other conditions are the same as those in Example 1.

[0071] Example 7

[0072] A viscosity thermal stability detection method of the polymer for oil displacement, which is different from example 1 in that the concentration of the polymer aqueous solution prepared by the formation water simulation water is 2000 mg / L, and the others are the same as example 1.

[0073] Example 8

[0074] A viscosity thermal stability detection method of the polymer for oil displacement, which is different from example 1 in that the determination temperature is 60℃, and the others are the same as example 1.

[0075] Example 9

[0076] A viscosity thermal stability detection method of the polymer for oil displacement, which is different from example 1 in that the determination temperature is 95℃, and the others are the same as example 1.

[0077] The above examples are the preferred embodiments of the present application, but the embodiments of the present application are not limited to the above examples, and any changes, modifications, substitutions, combinations, simplifications made without departing from the spirit and principles of the present application are equivalent replacement methods and are included in the protection scope of the present application.

Claims

1. A method for detecting the viscosity thermal stability of a polymer for oil displacement, characterized by, The method comprises the following steps: The standard curve of the relationship between the hydrolysis degree and the viscosity of the polymer solution for oil displacement is established, including: preparing polymer solutions with different hydrolysis degrees using formation simulation water, testing the viscosity of the polymer solutions with different hydrolysis degrees by using a rheometer, testing the hydrolysis degree of the polymer solution by using an automatic potentiometric titrator, and drawing the standard curve, wherein the total content of calcium and magnesium ions in the formation simulation water is 200-5000 mg / L; The polymer solution for oil displacement to be tested is subjected to high-temperature aging, and the method is as follows: the polymer solution for oil displacement to be tested is placed in a high-temperature resistant container and sealed, and then subjected to high-temperature aging, wherein the high-temperature aging temperature is 60-95 DEG C, and the aging time is greater than or equal to 90 days; The hydrolysis degree of the polymer solution for oil displacement to be tested is tested, and according to the standard curve, the viscosity of the polymer after thermal aging is obtained according to the hydrolysis degree value corresponding to the standard curve.

2. The method for detecting viscosity thermal stability of the polymer for oil displacement according to claim 1, characterized in that, The concentration of the polymer solution with different hydrolysis degrees prepared by using the formation simulation water is 1500-2000 mg / L.

3. The method for detecting viscosity thermal stability of the polymer for oil displacement according to claim 1, characterized in that, The polymer for oil displacement is a polyacrylamide polymer, and the hydrolysis degree ranges from 10% to 70%.

4. The method for detecting viscosity thermal stability of the polymer for oil displacement according to claim 1, characterized in that, When the rheometer is used to test the viscosity of the polymer solution with different hydrolysis degrees, the test temperature is 60-95 DEG C.

5. The method for detecting the viscosity thermal stability of the polymer for oil displacement according to claim 1, characterized in that, Before the automatic potentiometric titrator is used to test the hydrolysis degree of the polymer solution, blank titration is required, the selected titration end point of the blank titration is pH = 3.4-3.5, and the blank titration is performed at least three times to obtain the arithmetic mean value.

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