Method for detecting concentration of surfactant in oilfield field produced water

Abstract

The invention relates to a method for detecting the concentration of a surfactant in oilfield field produced water, which comprises the following steps: preparing standard aqueous solutions of surfactants with different concentrations and testing the interfacial tension between each standard aqueous solution and oil to obtain a relation curve between the interfacial tension and the concentration of the surfactant; the method comprises the following steps: sucking produced water from oilfield field produced liquid, and filtering the produced water to remove impurities to obtain a to-be-detected produced water sample; testing the interfacial tension of the produced water sample to be detected and oil; and obtaining the concentration of the surfactant in the produced water sample based on the relation curve between the interfacial tension and the concentration of the surfactant and the interfacial tension of the produced water sample to be detected and the oil. According to the method, the specific molecular structure of the surfactant does not need to be defined, the concentration of the surfactant is measured through the interfacial tension method, efficiency is high, and the method is simple, convenient to operate and easy to use in oil field sites or indoor laboratories.

Description

Technical Field

[0001] This invention relates to oilfield chemical detection technology, belonging to the field of petrochemical technology, and more specifically to a method and system for detecting the concentration of surfactants in produced water from oilfields. Background Technology

[0002] Currently, many oilfields have entered the middle and late stages of production. Surfactant flooding / huff-and-puff, as an enhanced oil recovery technology, reduces oil-water interfacial tension and alters reservoir wettability by injecting surfactant solutions underground, thereby improving oil washing efficiency and crude oil recovery. In recent years, surfactant flooding / huff-and-puff tests have been conducted in conventional and heavy oil reservoirs, as well as pilot tests for surfactant huff-and-puff in shale oil, achieving good results. During field tests in oilfields, monitoring the surfactant concentration in produced water is a crucial method for monitoring drainage cycles.

[0003] However, because the surfactants used in oil fields are mostly complex formulations with unknown structures and compositions, it is difficult to establish standard curves for chromatographic detection, making the operation complex and time-consuming. Ultraviolet spectroscopy requires surfactants with strong ultraviolet absorption peaks, resulting in poor adaptability to the field environment. In particular, surfactant huff and puffing in shale oil is still in the exploratory stage, and many detection methods and techniques are currently lacking in the industry.

[0004] Patent document with patent application number CN202111012183.5 discloses a rapid detection kit and detection method for surfactants in edible oils. This patent is only applicable to the detection of surfactants in edible oils and is difficult to apply to the detection of surfactant concentration in produced water from oil fields.

[0005] Patent document with patent application number CN202410046425.X discloses a method for detecting surfactant content. This patent uses a spectrophotometer to measure the absorbance at the maximum wavelength, and then obtains the surfactant concentration according to the standard curve. This method has poor applicability and is difficult to apply to surfactants with low absorption intensity.

[0006] Patent application CN201510796231.2 discloses a method for detecting the concentration of components in a polymer-surfactant binary composite oil displacement system. This patent is based on the chemical oxygen demand (COD) to detect the concentration of components in a polymer and surfactant oil displacement system. It requires seven steps to complete, is relatively complex to operate, and is not applicable to the detection of surfactant concentration in produced water in oilfields.

[0007] Therefore, existing detection methods are insufficient to meet the requirements of field testing in oilfields. There is an urgent need to establish an accurate and rapid detection method for surfactant concentration in produced water from oilfields to meet the needs of field testing and practical applications. Summary of the Invention

[0008] To address the challenges and limited applicability of surfactant concentration detection in produced water from oilfields, this invention aims to provide a method for detecting surfactant concentration in produced water from oilfields. This method rapidly and accurately determines the surfactant concentration in produced water by measuring the interfacial tension between produced water and oil (e.g., white oil).

[0009] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: According to the present invention, a method for detecting the concentration of surfactants in produced water from an oilfield is provided, comprising the following steps: 1) By preparing standard aqueous solutions of surfactants with different concentrations and testing the interfacial tension between each standard aqueous solution and oil, the relationship curve between interfacial tension and surfactant concentration was obtained. 2) Extract produced water from the produced fluid at the oilfield site, and filter the produced water to remove impurities to obtain a produced water sample to be tested; 3) Test the interfacial tension between the produced water sample and the oil; 4) Based on the relationship curve between interfacial tension and surfactant concentration and the interfacial tension between the produced water sample and the oil, the concentration of surfactant in the produced water sample is obtained.

[0010] In one embodiment of the present invention, in step 1), the relationship curve between interfacial tension and surfactant concentration is obtained by means of: By preparing standard aqueous solutions of surfactants with different concentrations and testing the interfacial tension between each standard aqueous solution and oil, the curve of interfacial tension as a function of surfactant concentration was plotted. Based on the curve of interfacial tension as a function of surfactant concentration, the relationship curve between interfacial tension and surfactant concentration was obtained by fitting.

[0011] In one embodiment of the present invention, the relationship curve between interfacial tension and surfactant concentration is obtained by linear fitting.

[0012] In one embodiment of the present invention, the linear fitting formula is: lg(γ)=Alg(c)+B, where γ is the interfacial tension, mN / m; c is the surfactant concentration, mg / L; and A and B are constants.

[0013] In one embodiment of the present invention, in step 1), standard aqueous solutions of surfactants of different concentrations are prepared using on-site water injection and / or on-site injected surfactant stock solution.

[0014] In one embodiment of the present invention, in step 1), standard aqueous solutions of 9-15 surfactants of different concentrations are prepared.

[0015] In one embodiment of the present invention, in step 1), the surfactant concentration range of the standard aqueous solution is 1-1000 mg / L.

[0016] In one embodiment of the invention, the oil includes white oil.

[0017] In one embodiment of the present invention, in step 2), a syringe is used to draw 5 mL of collected water from the collected fluid. The syringe is 10 mL and the collected water is drawn from the collected fluid.

[0018] In one embodiment of the present invention, in step 2), the extracted water is filtered and impurities are removed using a needle filter.

[0019] In one embodiment of the present invention, in step 2), the extracted water sample to be tested is stored for up to three days.

[0020] In one embodiment of the present invention, the testing apparatus and testing conditions for testing the interfacial tension between each standard aqueous solution and oil in step 1) are the same as those for testing the interfacial tension between the extracted water sample to be tested and oil in step 3).

[0021] In one embodiment of the present invention, the interfacial tension is tested using a rotating drop interfacial tension meter at 30-90°C and a rotation speed of 5000-5500 r / min.

[0022] In one embodiment of the present invention, in step 3), the interfacial tension between the produced water sample and the oil is tested repeatedly, and the average value is taken to obtain the interfacial tension between the produced water sample and the oil.

[0023] In one embodiment of the present invention, the concentration of surfactant in the produced water sample is the concentration of surfactant in the produced water after shale oil surfactant huff and puff, or the concentration of surfactant in the produced water after reservoir surfactant flooding.

[0024] By adopting the above technical solution, the present invention has the following advantages compared with the prior art: This invention provides a method for detecting the concentration of surfactants in produced water. This method does not require knowing the specific molecular structure of the surfactant. It uses the interfacial tension method to determine the surfactant concentration, which is highly efficient, simple, easy to operate, and easy to use in oilfields or indoor laboratories. Attached Figure Description

[0025] Figure 1 A schematic flowchart of a method for detecting surfactant concentration in produced water from an oilfield, provided by the present invention, is shown. Figure 2The curve showing the change of interfacial tension with surfactant concentration, as plotted in Example 1 of the present invention, is shown. Figure 3 The linear standard curve fitted in Embodiment 1 of the present invention is shown. Detailed Implementation

[0026] It should be understood that the embodiments of the invention shown in the exemplary embodiments are merely illustrative. Although only a few embodiments have been described in detail in this invention, those skilled in the art will readily recognize that various modifications are possible without substantially departing from the teachings of the invention. Accordingly, all such modifications should be included within the scope of the invention. Other substitutions, modifications, variations, and deletions can be made to the design, operating conditions, and parameters of the following exemplary embodiments without departing from the spirit of the invention.

[0027] like Figure 1 As shown, the present invention provides a method for detecting the concentration of surfactants in produced water from oil fields, comprising the following steps: S101: By preparing standard aqueous solutions of surfactants with different concentrations and testing the interfacial tension between each standard aqueous solution and oil, the relationship curve between interfacial tension and surfactant concentration is obtained. S102: Extract produced water from the produced fluid at the oilfield site, filter and remove impurities from the produced water to obtain a produced water sample to be tested; S103: Test the interfacial tension between the produced water sample and the oil; S104: Based on the relationship curve between interfacial tension and surfactant concentration and the interfacial tension between the produced water sample and the oil, the concentration of surfactant in the produced water sample is obtained.

[0028] This invention provides a method for detecting the concentration of surfactants in produced water. This method does not require knowing the specific molecular structure of the surfactant. It uses the interfacial tension method to determine the surfactant concentration, which is highly efficient, simple, easy to operate, and easy to use in oilfields or indoor laboratories.

[0029] In a preferred embodiment of the above detection method, in step S101, the relationship curve between interfacial tension and surfactant concentration is obtained in the following manner: By preparing standard aqueous solutions of surfactants with different concentrations and testing the interfacial tension between each standard aqueous solution and oil, the curve of interfacial tension as a function of surfactant concentration was plotted. Based on the curve of interfacial tension as a function of surfactant concentration, the relationship curve between interfacial tension and surfactant concentration was obtained by fitting.

[0030] In a preferred embodiment of the above detection method, the relationship curve between interfacial tension and surfactant concentration is obtained by linear fitting.

[0031] In a preferred embodiment of the above detection method, the linear fitting formula is: lg(γ)=Alg(c)+B, where γ is the interfacial tension (unit: mN / m), c is the surfactant concentration (unit: mg / L), and A and B are constants.

[0032] In a preferred embodiment of the above detection method, in step S101, standard aqueous solutions of surfactants of different concentrations are prepared using on-site injected water and / or on-site injected surfactant stock solution.

[0033] In a preferred embodiment of the above detection method, in step S101, standard aqueous solutions of 9-15 surfactants with different concentrations are prepared.

[0034] In a preferred embodiment of the above detection method, in step S101, the surfactant concentration range of the standard aqueous solution is 1-1000 mg / L.

[0035] In a preferred embodiment of the above detection method, the oil includes white oil.

[0036] In a preferred embodiment of the above detection method, in step S102, a syringe is used to draw 5 mL of collected water from the collected fluid. The syringe is 10 mL.

[0037] In a preferred embodiment of the above detection method, in step S102, the extracted water is filtered and impurities are removed using a needle filter.

[0038] In a preferred embodiment of the above detection method, in step S102, the extracted water sample to be tested is stored for up to three days.

[0039] In a preferred embodiment of the above detection method, the testing device and testing conditions for testing the interfacial tension between each standard aqueous solution and oil in step S101 are the same as those for testing the interfacial tension between the extracted water sample to be tested and oil in step S103.

[0040] In a preferred embodiment of the above detection method, a rotating drop interfacial tension meter is used to test the interfacial tension under conditions of 30-90℃ and a rotation speed of 5000-5500 r / min.

[0041] In a preferred embodiment of the above detection method, in step S103, the interfacial tension between the produced water sample and the oil is tested repeatedly (e.g., three times), and the average value is taken to obtain the interfacial tension between the produced water sample and the oil.

[0042] In a preferred embodiment of the above detection method, the concentration of surfactant in the produced water sample is the concentration of surfactant in the produced water after shale oil surfactant huff and puff, or the concentration of surfactant in the produced water after reservoir surfactant flooding.

[0043] The technical solutions of the present invention will be described in detail below through specific embodiments.

[0044] This invention provides a method for detecting the concentration of surfactants in produced water from oilfields, the specific steps of which are as follows: (1) Establishing the standard curve and calculation method of interfacial tension: Prepare 9-15 different concentrations of standard aqueous solutions of surfactants using on-site injection water and on-site injected surfactant mother liquor (the concentration range of the standard aqueous solution is 1-1000 mg / L). Then, use CNG701 rotating drop interfacial tension meter to test the interfacial tension with white oil under the conditions of 30-90℃ and rotation speed of 5000-5500 r / min. Plot the curve of interfacial tension with surfactant concentration, and fit the linear standard curve according to the curve of change. The linear calculation formula lg(γ)=Alg(c)+B is obtained, where γ is the interfacial tension (unit: mN / m), c is the surfactant concentration (unit: mg / L), and A and B are constants. (2) Separate the produced water from the produced fluid: Use a 10mL syringe to draw 5mL of produced water from the produced fluid, and use a 0.45μm needle filter to filter the produced water to remove suspended impurities, and obtain the produced water sample to be tested (the produced water sample to be tested shall be kept for no more than three days). (3) Detect the concentration of surfactant in the actual produced fluid: Use a rotating drop interfacial tension meter to test the interfacial tension between the produced water sample and white oil at 30-90℃ and 5000-5500 r / min. Repeat three times and take the average value to obtain the interfacial tension between the produced water sample and white oil. (4) Calculate the concentration: Based on the linear calculation formula and the interfacial tension between the produced water sample to be tested and the white oil, calculate the concentration of surfactant in the actual produced water.

[0045] Example 1 The concentration of surfactant in produced water after shale oil huff and puff was measured in an oilfield. The effective concentration of the Nano S1 mother liquor used for field huff and puff in the oilfield was 40%, and the concentrations for field injection were 2000 mg / L and 4000 mg / L.

[0046] The concentration of surfactants in the extracted water was tested according to the following steps: (1) Nano S1 standard aqueous solutions with concentrations of 1, 4, 6, 10, 15, 20, 30, 40, 50, 80, 100, 200, 400, 600 and 1000 mg / L were prepared using on-site water and Nano S1 mother liquor. The interfacial tension between the standard aqueous solutions and white oil was tested using a CNG701 rotating drop interfacial tensiometer at 90℃ and 5000 r / min. The interfacial tension curve I (e.g., surfactant concentration c (mg / L) was plotted on the x-axis and interfacial tension γ (mN / m) was plotted on the y-axis. Figure 2 As shown), then fit the linear standard curve II (as shown). Figure 3 As shown), the linear calculation formula is obtained as lg(γ) = -2.3403lg(c) + 2.7630(R). 2 =0.9970); (2) Use a 10mL syringe to draw 5mL of produced water from the produced fluid, and use a 0.45μm needle filter to filter the produced water to remove suspended impurities, so as to obtain the produced water sample to be tested. (3) Test the interfacial tension between the above-mentioned produced water sample and white oil, repeat the test three times and record the average interfacial tension. (4) Substitute the above interfacial tension value into the linear calculation formula lg(γ)=-2.3403lg(c)+2.7630 to obtain the concentration of surfactant in the sampled water to be tested, as shown in Table 1.

[0047] Table 1. Concentration test results of surfactants in produced water from a certain oilfield

[0048] As can be seen from Table 1, the method of Embodiment 1 of the present invention has good repeatability and high accuracy.

[0049] Example 2 The concentration of surfactant in the produced water after surfactant flooding in Block XX of a certain oilfield was measured. The effective concentration of the mother liquor of surfactant for field flooding in this oilfield is 30%, and the concentration for field injection is 3000 mg / L.

[0050] The concentration of surfactants in the extracted water was determined by following these steps: (1) Standard aqueous solutions of surfactant with concentrations of 1, 5, 10, 25, 50, 75, 100, 200, 400, 600, 800 and 1000 mg / L were prepared using on-site water and surfactant stock solution, respectively. The interfacial tension between the standard aqueous solution and white oil was tested using a CNG701 rotating drop interfacial tensiometer at 50℃ and 5000 r / min. The interfacial tension curve I was plotted with the surfactant concentration c (mg / L) as the abscissa and the interfacial tension γ (mN / m) as the ordinate. Then, a linear standard curve II was fitted, and the linear calculation formula was obtained as lg(γ) = -1.9772lg(c) + 2.5471(R 2 =0.9978).

[0051] (2) Use a 10mL syringe to draw 5mL of produced water from the produced fluid, and use a 0.45μm needle filter to filter the produced water to remove suspended impurities, so as to obtain the produced water sample to be tested. (3) Test the interfacial tension between the above-mentioned produced water sample and white oil, repeat the test three times and record the average interfacial tension. (4) Substitute the above interfacial tension value into the linear calculation formula lg(γ)=-1.9772lg(c)+2.5471 to obtain the concentration of surfactant in the sample to be tested, as shown in Table 2.

[0052] Table 2. Test results of surfactant concentration in produced water from Block XX of a certain oilfield.

[0053] As can be seen from Table 2, the method of Embodiment 2 of the present invention has good repeatability and high accuracy.

[0054] Therefore, the present invention provides a method for detecting the concentration of surfactants in produced water. This method does not require specific molecular structures of surfactants. It uses the interfacial tension method to determine the surfactant concentration, which is efficient, simple, easy to operate, and easy to use in oilfields or indoor laboratories.

[0055] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of the present invention. Any modifications or equivalent substitutions made to the present invention without departing from the spirit and scope thereof should be covered within the protection scope of the claims of the present invention.

Claims

1. A method for detecting the concentration of surfactants in produced water from an oilfield, characterized in that, Includes the following steps: 1) By preparing standard aqueous solutions of surfactants with different concentrations and testing the interfacial tension between each standard aqueous solution and oil, the relationship curve between interfacial tension and surfactant concentration was obtained; 2) Extract produced water from the produced fluid at the oilfield site, and filter the produced water to remove impurities to obtain a produced water sample to be tested; 3) Test the interfacial tension between the produced water sample and the oil; 4) Based on the relationship curve between interfacial tension and surfactant concentration and the interfacial tension between the produced water sample and the oil, the concentration of surfactant in the produced water sample is obtained.

2. The method for detecting surfactant concentration in produced water from oilfields according to claim 1, characterized in that, In step 1), the relationship curve between interfacial tension and surfactant concentration is obtained in the following ways: By preparing standard aqueous solutions of surfactants with different concentrations and testing the interfacial tension between each standard aqueous solution and oil, the curve of interfacial tension as a function of surfactant concentration was plotted. Based on the curve of interfacial tension as a function of surfactant concentration, the relationship curve between interfacial tension and surfactant concentration was obtained by fitting.

3. The method for detecting surfactant concentration in produced water from oilfields according to claim 2, characterized in that, The relationship curve between interfacial tension and surfactant concentration was obtained by linear fitting.

4. The method for detecting surfactant concentration in produced water from oilfields according to claim 3, characterized in that, The linear fitting formula is: lg(γ)=Alg(c)+B, where γ is the interfacial tension, mN / m; c is the surfactant concentration, mg / L; and A and B are constants.

5. The method for detecting surfactant concentration in produced water from oilfields according to claim 1, characterized in that, In step 1), standard aqueous solutions of surfactants of different concentrations are prepared using on-site water and / or on-site injected surfactant stock solution.

6. The method for detecting surfactant concentration in produced water from oilfields according to claim 5, characterized in that, In step 1), standard aqueous solutions of 9-15 different concentrations of surfactants are prepared.

7. The method for detecting surfactant concentration in produced water from oilfields according to claim 1, characterized in that, In step 1), the surfactant concentration range of the standard aqueous solution is 1-1000 mg / L.

8. The method for detecting surfactant concentration in produced water from oilfields according to claim 1, characterized in that, The oil includes white oil.

9. The method for detecting surfactant concentration in produced water from oilfields according to claim 1, characterized in that, In step 2), a syringe is used to draw 5 mL of the collected water from the collected fluid.

10. The method for detecting surfactant concentration in produced water from oilfields according to claim 1, characterized in that, In step 2), the extracted water is filtered and impurities are removed using a needle filter.

11. The method for detecting surfactant concentration in produced water from oilfields according to claim 1, characterized in that, In step 2), the extracted water sample to be tested shall be kept for no more than three days.

12. The method for detecting surfactant concentration in produced water from oilfields according to claim 1, characterized in that, The testing apparatus and conditions for testing the interfacial tension between each standard aqueous solution and oil in step 1) are the same as those for testing the interfacial tension between the extracted water sample to be tested and the oil in step 3).

13. The method for detecting surfactant concentration in produced water from oilfields according to claim 12, characterized in that, Interfacial tension was tested using a rotating drop interfacial tensiometer at 30-90℃ and a rotation speed of 5000-5500 r / min.

14. The method for detecting surfactant concentration in produced water from oilfields according to claim 1, characterized in that, In step 3), the interfacial tension between the produced water sample and the oil is tested repeatedly, and the average value is taken to obtain the interfacial tension between the produced water sample and the oil.

15. The method for detecting surfactant concentration in produced water from oilfields according to claim 1, characterized in that, The concentration of surfactant in the produced water sample is either the concentration of surfactant in the produced water after shale oil surfactant huff and puff, or the concentration of surfactant in the produced water after reservoir surfactant flooding.

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