Screening method of surfactant for oil displacement

Abstract

The invention discloses a screening method of a surfactant for oil displacement, which comprises the following steps: (1) measuring the interfacial tension of the surfactant, and screening the surfactant meeting the interfacial tension parameter requirement; (2) measuring the adsorption quantity of the surfactants on the quartz sand, and screening out the surfactants meeting the adsorption quantity parameter requirements; (3) measuring the stability of the surfactants screened out in the step (1) and the step (2) by taking the concentration retention rate as an evaluation parameter, and screening out the surfactant meeting the concentration retention rate requirement; and (4) testing the long-term stability of the surfactant screened out in the step (3) by taking the concentration retention rate as an evaluation parameter, and screening out the surfactant meeting the requirement of the concentration retention rate, namely the finally screened surfactant. The method can be applied to screening of oil displacement surfactants under harsh oil reservoir conditions of high temperature, high salt and the like; the workload and manpower for screening the surfactant for oil displacement are reduced, and the screening method is quicker, simpler, more convenient and more accurate.

Description

Technical Field

[0001] The invention belongs to the technical field of improving crude oil recovery, and in particular relates to a method for screening a surfactant for oil displacement. Background Art

[0002] Faced with the current global situation of rapid development of new energy industry, oil still plays an important role in national economy and development. However, through traditional primary and secondary oil recovery, about 60% to 65% of crude oil cannot be driven out. In the past few decades, due to the contradiction between crude oil supply and demand in the market, tertiary oil recovery (EOR) method came into being to recover the remaining oil in the primary and secondary oil recovery stages. The tertiary oil recovery process mainly includes thermal recovery, gas drive and chemical drive. Chemical drive has become a research hotspot in the petroleum industry due to its high crude oil recovery rate in application. Among them, surfactant drive is one of the most promising EOR technologies.

[0003] Surfactants are amphiphilic substances with lipophilic and hydrophilic groups. They are easily distributed at the oil-water interface, reducing the interfacial tension between oil and water, changing the rock surface from oil-wet to water-wet, reducing the adsorption of oil droplets on the rock surface, and promoting the flow of oil droplets, thereby improving the oil recovery efficiency. At the same time, surfactants have an emulsifying and aggregating effect on crude oil, making it easier for oil droplets to be carried away by water, which can further improve the oil recovery efficiency. At present, it has been successfully applied to China's Shengli Oilfield and Daqing Oilfield, and the recovery rate has increased by 10wt% to 20wt% on the basis of water flooding.

[0004] With the deepening of oil field exploitation, the oil reservoir is getting deeper and deeper. The reservoir conditions of many proven and exploitable oil reservoirs in the world are very bad. The temperature and salinity of these reservoirs are relatively high, which seriously affects the application of surfactants. In the face of oil reservoirs with bad reservoir conditions, most surfactants cannot have ultra-low interfacial tension for a long time in a high temperature and high salt environment, which makes the recovery rate of these oil reservoirs relatively low. At the same time, crude oil often stays in the finer capillary channels of the reservoir, and it is difficult to extract it with water drive. Therefore, in order to drive these crude oils out of the pores, it is necessary for the surfactant to have ultra-low oil-water interfacial tension, low rock adsorption loss value and low cost, and at the same time have the performance of high salt resistance and high temperature resistance. Therefore, the research on temperature-resistant and salt-resistant surfactants has attracted more and more attention. However, in the prior art, there are problems such as large workload and difficulty in screening for oil displacement surfactants. Summary of the invention

[0005] The present invention is proposed to solve the problems existing in the prior art, and its purpose is to provide a method for screening surfactants for oil displacement.

[0006] The present invention is achieved through the following technical solutions:

[0007] A method for screening a surfactant for oil displacement comprises the following steps:

[0008] (I) Determine the interfacial tension of the surfactant and select the surfactant that meets the interfacial tension parameter requirements;

[0009] (II) Determine the adsorption amount of the surfactant on quartz sand and screen out the surfactant that meets the adsorption amount parameter requirements;

[0010] (III) using the concentration retention rate as an evaluation parameter to determine the stability of the surfactants screened in steps (I) and (II), and screen out surfactants that meet the concentration retention rate requirements;

[0011] (IV) Using the concentration retention rate as an evaluation parameter, the long-term stability of the surfactant screened out in step (III) is tested, and the surfactant that meets the concentration retention rate requirement is screened out, which is the final screened surfactant.

[0012] In the above technical solution, the interfacial tension parameter of step (I) is required to be 10 -3 mN / m~10 -1 mN / m.

[0013] In the above technical solution, the adsorption amount parameter requirement of step (II) is 0.5 mg / g to 10 mg / g.

[0014] In the above technical solution, the concentration retention rate requirement of step (III) is: 60%≤concentration retention rate<100%.

[0015] In the above technical solution, the stability test time of step (III) is 1 to 3 days.

[0016] In the above technical solution, the concentration retention rate requirement of step (IV) is: 20%<concentration retention rate<60%.

[0017] In the above technical solution, the test duration of the long-term stability of step (IV) is longer than the test duration of the stability of step (III), and is no more than 150 days.

[0018] In the above technical solution, in the determination of steps (I), (II) and (III), the concentration range of the surfactant solution is 0 to 10000 mg / L.

[0019] In the above technical scheme, the method for determining the adsorption amount in step (II) is specifically as follows: using a total organic carbon analyzer to determine the total organic carbon content of the unadsorbed surfactant solution and the supernatant after adsorption, which are TOC a、 TOC b , then the calculation formula of adsorption amount is:

[0020] Γ 0 =(TOC a -TOC b )*c 0 *n / TOC a

[0021] Where: 0 is the adsorption loss, in mg / g;

[0022] TOC a is the total organic carbon content of the unadsorbed surfactant solution, in mg / L;

[0023] TOC b is the total organic carbon content of the supernatant after adsorption, in mg / L;

[0024] c 0 The initial concentration of the surfactant solution prepared is c 0 , the unit is mg / L;

[0025] n is the mass ratio of the surfactant solution volume to the quartz sand in the adsorption experiment, in L / g.

[0026] In the above technical solution, the method for determining the concentration retention rate is specifically as follows: using a total organic carbon analyzer to determine the total organic carbon content TOC of the surfactant solution before and after placement 0 、TOC 后 , concentration retention rate = TOC 后 / TOC 0 .

[0027] The beneficial effects of the present invention are:

[0028] The invention provides a rapid, simple and accurate screening method for an oil recovery surfactant, which can be applied to the screening of oil recovery surfactants under harsh reservoir conditions such as high temperature and high salinity. The screening method of the invention greatly reduces the workload and manpower in the screening of oil recovery surfactants: 1) different solution properties (interfacial tension, wettability, emulsification performance, oil recovery effect, etc.) in a long-term stability evaluation experiment can be directly characterized by testing a single parameter of the surfactant solution, which saves the testing time of multiple properties and the vacuum sealing time of a large number of sample ampoules on the one hand; on the other hand, simplifies the complexity of performance testing under harsh conditions of high temperature and high salinity, and improves the accuracy and efficiency of the long-term stability performance characterization of the surfactant; 2) a total organic carbon analyzer is used to determine the surfactant concentration and its adsorption amount on quartz sand, so that the screening is faster, simpler and more accurate. The screening method of the invention has a good application prospect in the screening of oil recovery surfactants. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 1 is a graph showing the interfacial tension and concentration of three surfactants in Example 1 of the present invention.

[0030] For ordinary technicians in this field, other relevant drawings can be obtained based on the above drawings without any creative work. DETAILED DESCRIPTION

[0031] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention is further described below with reference to the accompanying drawings and through specific implementation methods.

[0032] Example 1

[0033] The formation simulation water used in this embodiment is prepared as follows:

[0034] Weigh 2.2617 g of CaCl using an analytical balance 2 , 52.6588g NaCl and 1.4932g KCl, add them to container A containing 1L deionized water, stir with a glass rod until dissolved; then weigh 14.4257g MgSO 4 7H 2 O and 5.1027 g MgCl 2 Add it to another container B containing 0.5L deionized water and stir until dissolved, then pour it into container A. Finally, weigh 0.4204g NaHCO 3 Add it to container A, continue stirring until all reagents are dissolved, and finally rinse container B and the glass rod used in the experiment three times with 0.5L of water, pour the washing liquid into container A, and shake until mixed evenly to obtain the target oilfield seawater simulation water.

[0035] A method for screening and long-term stability evaluation of a surfactant for oil displacement comprises the following steps:

[0036] (I) Determine the interfacial tension of surfactants and screen out surfactants that meet the long-term stability test screening requirements based on the interfacial tension parameters (interfacial tension <σ 0 ) of a surfactant; 10 -3 mN / m<σ 0 <10 1 mN / m;

[0037] The surfactant interfacial tension determination method refers to the standard SY / T5370 "Surface and interfacial tension determination method", and the interfacial tension between the surfactant and the two crude oils is tested using an SVT-20N interfacial tension meter;

[0038] Determining the surfactant interfacial tension specifically comprises the following steps:

[0039] (I-i) The surfactant solution and crude oil WZ1 were placed in a 130°C constant temperature oven for preheating for 20 min, the interfacial tension meter sample tube was rinsed three times with petroleum ether and ethanol in sequence, and then rinsed three times with deionized water, the instrument was turned on, the temperature was set to the reservoir temperature, and the experiment was started when the temperature reached the reservoir temperature;

[0040] (I-ii) First, rinse the interfacial tension test tube with the test liquid, add the sample to fill the sample tube, use a 5μL microsyringe to extract 1μL of the crude oil to be tested and inject it into the water phase of the test tube, keeping the oil drop balanced and centered. In order to prevent bubbles in the tube, it is best to add a few more drops of sample;

[0041] (I-III) Insert the test tube into the interfacial tension meter, cover the instrument cap, and after confirming that it is correct, use the lens to capture the oil droplet, and gradually adjust the speed from small to large, from slow to fast, until the speed reaches 6000r / min, set the parameters, fine-tune the lens and the tester, keep the oil droplet in the lens at all times, and select the appropriate test mode to capture the interface between the oil droplet and water;

[0042] (I-IV) The oil droplet deforms under high-speed rotation. By testing and capturing the outer dimensions of the oil droplet, the radius R and length L of the oil droplet can be obtained, and the oil-water interfacial tension can be fitted by the following calculation formula;

[0043] When the measured oil-water interfacial tension is high, the oil droplet is ellipsoidal and the following formula (1) applies:

[0044]

[0045] When the measured oil-water interfacial tension is low, the oil droplet is in the shape of a strip, and the following formula (2) applies:

[0046]

[0047] In formulas (1) and (2), R(x) is the radius of the oil droplet, in cm; ω is the rotation frequency, in Hz; R max is the radius of the liquid column, in cm; γ L is the oil-water interfacial tension, in mN / m; R 1 , R 2 is the oil droplet curvature radius, in cm; Δρ 12 is the density difference between the oil droplet in the sample tube and the solution outside, in g / cm 3 ;

[0048] The curves of interfacial tension and concentration of the three surfactants in this example are as follows: Figure 1 As shown. Figure 1It can be observed that the interfacial tension between crude oil and simulated formation water is 14 mN / m, and the interfacial tension decreases significantly after the addition of surfactant. At low concentrations, the interfacial tension between S1, S2, and S3 and crude oil decreases with the increase of surfactant concentration; the interfacial tension between S1 and crude oil slowly decreases to 10 with the increase of surfactant concentration. -2 mN / m, the interfacial tension between S2 and crude oil decreases rapidly to 10 with the increase of surfactant concentration. -2 mN / m, the interfacial tension between S3 and crude oil decreases rapidly to 10 with the increase of surfactant concentration. -3 mN / m.

[0049] Depend on Figure 1 It can be seen that the interfacial tension between 3000 mg / L S1, S2, and S3 solutions and crude oil is less than 10 -1 mN / m, which meets the requirements. Based on the interfacial tension parameters, these three surfactants meet the long-term stability test screening requirements.

[0050] (II) Determine the amount of surfactant adsorbed on quartz sand, and select surfactants that meet the long-term stability test screening requirements (adsorption <Γ 0 mg / g) of surfactant; 0.5mg / g<Γ 0 <10mg / g

[0051] (II-i) Select 100 mesh quartz sand, rinse it with deionized water for 5 times and dry it for later use; prepare a solution with a concentration of c 0 The surfactant solution was placed in three conical flasks respectively, and stirred at 3000r / min on a turbine stirrer for 20s. Then, 5g of quartz sand was accurately weighed and placed in a high-temperature tank. After adding 15mL of the surfactant solution, the tank was sealed. Then, the sand and the surfactant were separated in the high-temperature tank at 130℃, and the supernatant was taken. <c 0 <10000mg / L;

[0052] (Ⅱ-ⅱ) The total organic carbon content (TOC) of the unadsorbed surfactant solution and the supernatant after adsorption was measured using a total organic carbon analyzer (TOC-V), which was recorded as TOC a and TOC b ;

[0053] All carbon-containing compounds in the surfactant sample are transported by the carrier gas (O 2 ) is brought into the quartz combustion tube of the instrument and converted into CO after being burned at high temperature (900℃, Pt as catalyst) 2 The non-dispersive infrared gas analyzer inside the instrument can measure the total carbon content (TC); then the surfactant sample is burned at a low temperature (150°C, with hydrochloric acid as a catalyst), and the inorganic carbonates can be converted into CO2 , the inorganic carbon content (IC) can be measured; the organic carbon content (TOC) can be obtained by subtracting the inorganic carbon content from the total carbon content: TOC = TC-IC; since the amount of organic carbon in the surfactant solution is proportional to the surfactant content, the amount of organic carbon lost by adsorption of the surfactant solution is the adsorption amount; therefore, by measuring the total organic carbon content of the unadsorbed surfactant solution and the supernatant after adsorption, the TOC a 、TOC b At this time, the concentration of surfactant before and after adsorption can be obtained from the TOC value, and finally the adsorption amount is calculated using formula 3:

[0054] Γ 0 =(TOC a -TOC b )*c 0 *n / TOC a (3)

[0055] In the formula (3): Γ 0 is the adsorption amount, the unit is mg / g;

[0056] TOC a is the total organic carbon content of the unadsorbed surfactant solution, in mg / L;

[0057] TOC b is the total organic carbon content of the supernatant after adsorption, in mg / L;

[0058] c 0 The initial concentration of the surfactant solution prepared is c 0 , the unit is mg / L;

[0059] n is the mass ratio of the surfactant solution volume to the quartz sand in the adsorption experiment, in L / g;

[0060] The TOC and adsorption loss of surfactants S1, S2 and S3 before and after adsorption are shown in Table 1. As shown in Table 1, the adsorption loss of surfactants S2 and S3 on quartz sand is small, which meets the requirements. These two surfactants meet the long-term stability test screening requirements.

[0061] Table 1 TOC and adsorption amount of surfactant solution before and after adsorption

[0062]

[0063] (III) Determine the stability of the surfactants screened in steps (I) and (II), based on the concentration retention rate k of the surfactants 1 Screen out the products that meet the long-term stability test screening requirements (60% ≤ concentration retention rate k 1<100%) surfactant; the stability test time is p 1 , 1≤p 1 ≤3;

[0064] Prepare 10-50mL of 3000mg / L surfactant solution with formation simulated water, stir at 40℃ for 0.5h, filter part of the solution, measure the surfactant concentration in the filtrate, and inject the remaining solution into ampoules, evacuate with a vacuum device for 5h, seal with an alcohol burner and number. Put the ampoules in a constant temperature oven at the target temperature (130℃) for aging for 3 days, cool to room temperature, filter the supernatant, and measure the surfactant concentration in the supernatant after filtration and the interfacial tension between the surfactant and crude oil;

[0065] The method for determining the surfactant concentration is specifically as follows:

[0066] The total organic carbon content (TOC) of the surfactant in the filtrate was determined by a total organic carbon analyzer (TOC-V). All carbon-containing compounds in the surfactant sample were transported by the carrier gas (O 2 ) is brought into the quartz combustion tube of the instrument and converted into CO after being burned at high temperature (900℃, Pt as catalyst) 2 The non-dispersive infrared gas analyzer inside the instrument can measure the total carbon content (TC); then the surfactant sample is burned at a low temperature (150°C, with hydrochloric acid as a catalyst), and the inorganic carbonates can be converted into CO 2 , the inorganic carbon content (IC) can be measured. The organic carbon content (TOC) can be obtained by subtracting the inorganic carbon content from the total carbon content: TOC = TC-IC. Since the amount of organic carbon in the surfactant solution is proportional to the surfactant content, the total organic carbon content of the supernatant before and after aging at high temperature (130°C) for 3 days is measured, which are TOC, 0 、TOC 1 , then the concentration retention rate k = TOC 1 / TOC 0 .

[0067] This example tests the concentrations of three surfactant solutions before and after standing, and the specific data are shown in Table 2.

[0068] Table 2 Surfactant stability

[0069] serial number Surfactant S1 Surfactant S2 Surfactant S3 Concentration before placement, mg / L 3000 3000 3000 Concentration after standing, mg / L 2652 2778 2930 Concentration retention rate, % 88.4 92.6 97.7 Interfacial tension, mN / m 0.041 0.012 0.016

[0070] As shown in Table 2, after aging at 130°C for 3 days, the concentration retention rates of S2 and S3 reached 90%, which met the requirements. These two surfactants met the long-term stability test screening requirements.

[0071] At the same time, it can be seen from Table 2 that after aging at 130°C for 3 days, the interfacial tension and concentration retention rate of the three surfactants S1, S2 and S3 with crude oil are very similar. Therefore, it can be inferred that the surfactant concentration parameters after aging can be used to characterize other properties of the surfactant, including interfacial tension, wettability, emulsification performance and oil displacement effect.

[0072] (IV) Test step (III) The long-term stability of the surfactants screened out, and screen out those that meet the requirements (20% < concentration retention rate k 2 <60%) of surfactant

[0073] (IV-i) Test the concentration retention rate k of surfactant after long-term aging 2

[0074] Prepare a surfactant solution (surfactant S2 and S3) with a concentration of 3000 mg / L using formation simulated water. After stirring at 40°C for 0.5 h, take part of the solution and filter it to determine the concentration of the surfactant in the filtrate. Inject the remaining solution into ampoules, evacuate them with a vacuum device for 5 h, seal them with an alcohol burner and number them. Place the ampoules in a constant temperature oven at the target temperature (90°C) for aging. Take part of the supernatant every 3 days and filter it, determine the concentration of the surfactant in the filtrate, and calculate the surfactant concentration retention rate.

[0075] The long-term stability test duration is p 2 , p 1 <p 2 ≤150;

[0076] Surfactant concentration retention rate k = TOC p / TOC 0

[0077] TOC 0 、TOC p are the total organic carbon contents of the surfactant solution before and after placement for p days, respectively.

[0078] The aging time was 90 days in total. The concentration retention rate is shown in Table 3 (partial data).

[0079] Table 3 Surfactant concentration retention rate

[0080]

[0081]

[0082] It can be seen from Table 3 that the 90-day retention rate of surfactant S3 is above 80%, which meets the requirements.

[0083] As can be seen from the above, the screening method of the present invention can greatly reduce the workload and can quickly and accurately screen out surfactants for oil displacement with good effects.

[0084] (IV-ii) Testing the performance of surfactant solutions after long-term aging

[0085] A. Interfacial tension test: Same as step (Ⅰ).

[0086] B. Wettability test: Wash the quartz plate and place it in a 90℃ oven to dry for 2 hours, then take it out and place it in a container filled with crude oil and seal it, then place the container in a 130℃ constant temperature box for aging for 8 hours to simulate reservoir rock. Use lens paper to wipe off the excess crude oil on the surface of the quartz plate soaked in crude oil, measure the contact angle of formation simulated water on the core and record it; use formation simulated water to prepare surfactant solution, and use the high temperature and high pressure interfacial rheological tensiometer of French Teclis Company to test the contact angle between the surfactant solution and the core treated with crude oil at room temperature.

[0087] C. Oil displacement experiment: A single-tube core oil displacement experiment was conducted using homogeneous cores, with a core size of 2.5cm×2.5cm×10cm. Experimental steps: After the cores were dried and vacuum-saturated with water, the core porosity was calculated based on the core mass difference before and after saturation with water, and the cores were saturated with crude oil using the variable flow rate method, and aged at 130°C for more than 24 hours; the pump rate was set to 1mL / min, and water was driven at 65°C until the water content of the produced fluid reached 98%, and then 0.3PV of surfactant solution was injected, and then water was driven until the water content of the produced fluid exceeded 98%.

[0088] From the above experimental results, it can be seen that the solution concentration retention rates of S3 surfactant after constant temperature placement for 3 days and 90 days are 97.7% and 85.9% respectively, that is, the solution concentrations of S3 surfactant after constant temperature placement for 3 days and 90 days are 2931 mg / L and 2577 mg / L respectively. The solution performance after aging for 3 days and 90 days is tested: the interfacial tension is 0.0018 mg / L and 0.0023 mg / L respectively, the contact angle is 27° and 35° respectively, and the enhanced recovery factor is 18.2% and 14.5% respectively.

[0089] Due to the long-term stability, the amount of solution sample in each ampoule is limited, and the amount of solution in a single ampoule is insufficient to test the various properties of the aged solution. If the solution performance is tested for each group of aged solutions, the vacuum sealing time of a large number of sample ampoules and the time for testing the sample performance will increase. For this reason, the long-term stability of the surfactant is characterized by testing the concentration of the solution after aging, and its reliability is verified: the initially prepared 3000 mg / L surfactant solution is diluted to the target concentrations of 2931 mg / L and 2577 mg / L, and then the performance of the target concentration solution is tested: the interfacial tension is 0.0017 mg / L and 0.0022 mg / L, respectively, the contact angle is 28° and 34°, respectively, and the enhanced oil recovery is 17.6% and 14.1%, respectively. The test results show that the performance of the solution diluted to the target concentration with the initially prepared 3000 mg / L surfactant solution is basically the same as the performance of the aged solution, so the concentration of the solution after aging can be used to characterize the long-term stability of the surfactant.

[0090] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for screening a surfactant for oil displacement, characterized in that: The following steps are involved: (I) Determine the interfacial tension of the surfactant and select the surfactant that meets the interfacial tension parameter requirements; (II) Determine the adsorption amount of surfactant on quartz sand and screen out surfactants that meet the adsorption amount parameter requirements; (III) using the concentration retention rate as an evaluation parameter to determine the stability of the surfactants screened in steps (I) and (II), and screen out surfactants that meet the concentration retention rate requirements; (IV) Using the concentration retention rate as an evaluation parameter, the long-term stability of the surfactant screened out in step (III) is tested, and the surfactant that meets the concentration retention rate requirement is screened out, which is the final screened surfactant.

2. The method for screening an oil displacement surfactant according to claim 1, wherein: The interfacial tension parameter of step (I) is required to be 10 -3 mN / m~10 -1 mN / m.

3. The method for screening an oil displacement surfactant according to claim 1, wherein: The adsorption amount parameter requirement of step (II) is 0.5 mg / g to 10 mg / g.

4. The method for screening an oil displacement surfactant according to claim 1, wherein: The concentration retention rate requirement of step (III) is: 60%≤concentration retention rate<100%.

5. The method for screening an oil displacement surfactant according to claim 1, wherein: The stability test duration of step (III) is 1 to 3 days.

6. The method for screening an oil displacement surfactant according to claim 1, wherein: The concentration retention rate requirement of step (IV) is: 20%<concentration retention rate<60%.

7. The method for screening an oil displacement surfactant according to claim 1, wherein: The long-term stability test duration of step (IV) is longer than the stability test duration of step (III), and is no more than 150 days.

8. The method for screening an oil displacement surfactant according to claim 1, wherein: In the determination of steps (I), (II) and (III), the concentration range of the surfactant solution is 0 to 10000 mg / L.

9. The method for screening an oil displacement surfactant according to claim 1, wherein: The method for determining the adsorption amount in step (II) is specifically as follows: using a total organic carbon analyzer to determine the total organic carbon content of the unadsorbed surfactant solution and the supernatant after adsorption, which are TOC a、 TOC b , then the calculation formula of adsorption amount is: Γ0=(TOC a -OCD b )*c0*n / OCD a Where: Γ0 is the adsorption loss, unit is mg / g; TOC a is the total organic carbon content of the unadsorbed surfactant solution, in mg / L; TOC b is the total organic carbon content of the supernatant after adsorption, in mg / L; c0 is the initial concentration of the prepared surfactant solution, in mg / L; n is the mass ratio of the surfactant solution volume to the quartz sand in the adsorption experiment, in L / g.

10. The method for screening an oil displacement surfactant according to claim 1, characterized in that: The method for determining the concentration retention rate is specifically as follows: using a total organic carbon analyzer to determine the total organic carbon content TOC0 and TOC1 of the surfactant solution before and after placement. 后 , concentration retention rate = TOC 后 / TOC0.

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