Method for evaluating under-scale sterilization effect of bactericide

Abstract

The invention discloses a method for evaluating the under-scale sterilization effect of a bactericide, which comprises the following steps: culturing SRB bacteria in a water body and under the scale in a closed environment, and removing a film and a covering on the surface of a metal sample through an electrolytic method to obtain a solution with the under-scale SRB bacteria so as to evaluate the content of the under-scale SRB bacteria. According to the method, the sterilization effect (sterilization rate) of the bactericide in the water body and under the scale is obtained through calculation by combining the measured values of the SRB content of the water body and under the scale before and after the bactericide is injected, the defects that the content of the bacteria under the scale cannot be detected and the performance of the bactericide under the scale cannot be evaluated in a traditional evaluation method are overcome, and the method has important popularization value.

Description

Technical Field

[0001] This invention relates to the field of oilfield development technology, and in particular to a method for evaluating the bactericidal effect of a bactericide under scale. Background Technology

[0002] Various microorganisms are prevalent in oilfield production, such as sulfate-reducing bacteria (SRB), saprophytic bacteria (TGB), iron bacteria (IB), sulfur bacteria, yeast, algae, and protozoa. These bacteria can cause metal corrosion, formation blockage, and chemical deterioration. Among them, sulfate-reducing bacteria are the most harmful; it has been reported that 70% of oil well corrosion in the United States is caused by sulfate-reducing bacteria.

[0003] Currently, the indoor evaluation method for the performance of bactericides in the oil and gas industry is based on SY-T5890-93 "Evaluation Method for Performance of Bactericides". However, this standard can only test the bactericidal performance of bactericides in water. It cannot effectively evaluate whether bactericides can penetrate scale layers or have a bactericidal effect on bacteria under the scale.

[0004] Industrial pipelines, containers, and other related equipment are prone to bacterial growth during operation. This is especially true in oil and gas field production, where complex deposits generated during processes adhere to metal surfaces, easily forming a sealed environment under the scale, leading to bacterial proliferation. The growth of sulfate-reducing bacteria (SRB), in particular, can cause severe under-scale corrosion and the release of large amounts of H2S, seriously affecting safe production. Traditional SRB detection and bactericide evaluation primarily target SRB bacteria in water bodies, failing to address SRB detection and bactericide evaluation in the under-scale environment. This can result in incomplete SRB eradication, shortened dosing cycles, and exacerbated under-scale corrosion, among other problems. Therefore, effectively detecting under-scale SRB content and evaluating the bactericidal effect of under-scale bactericides has significant engineering practical value.

[0005] However, current methods for detecting sulfate-reducing bacteria under deposits and evaluating under-deposit bactericides have shortcomings or deficiencies. These mainly include the inability to establish reliable evaluation methods for sulfate-reducing bacteria under deposits, and the lack of corresponding evaluation methods for detecting SRB content under deposits and the bactericidal effect of under-deposit bactericides. Summary of the Invention

[0006] This invention aims to provide a method for evaluating the bactericidal effect of bactericides under deposits. By artificially simulating the under-deposit environment, SRB bacteria in the water and under the deposits are cultured in a closed environment. Then, the surface covering of the metal sample is removed by electrolysis, resulting in a solution containing under-deposit SRB bacteria, thereby assessing the SRB bacteria content. By combining the measured values ​​of SRB bacteria content in the water and under the deposits before and after adding the bactericide, the bactericidal effect (bactericidal rate) of the bactericide in the water and under the deposits is calculated. This method fills the gap in traditional evaluation methods, which cannot detect under-deposit bacteria content and cannot evaluate the performance of under-deposit bactericides, and has significant potential for widespread application.

[0007] To achieve the above-mentioned objectives, the technical solution of the present invention is as follows: S1. An electrochemical cathode polarization pre-scaling method is used to form a scale coating layer on the surface of the metal sample; S2. Prepare an anaerobic solution containing sulfate-reducing bacteria, wherein the concentration of sulfate-reducing bacteria in the anaerobic solution is greater than or equal to 100 bacteria / mL; S3. Immerse the metal sample from step S1 in the oxygen-free solution from step S2 in a sealed container for 3-5 hours at a temperature of 35℃±1℃, and then detect the concentration of sulfate-reducing bacteria in the solution after immersion. S4. After soaking in step S3, add a bactericide to the solution for sterilization, and test the concentration of sulfate-reducing bacteria in the water after adding the bactericide. S5. Place the metal sample soaked in step S3 and the metal sample sterilized in step S4 into an anaerobic closed electrolytic cell, respectively, and remove the membrane by electrolysis. After membrane removal, the solution is ultrasonically treated for 3-8 minutes, and the concentration of sulfate-reducing bacteria under the deposit is detected when no bactericide is added and when bactericide is added. S6. Calculate the bactericidal rate of the bactericide in water and under scale by using the concentration of sulfate-reducing bacteria detected in steps S3-S5.

[0008] In step S1, the electrochemical cathode polarization pre-scaling method is carried out in an artificially prepared simulated solution; The simulated solution in step S1 is a mixed solution of 0.5-1 g / L Ca(NO3)2 and 0.5-1 g / L NaHCO3. 100-1000 sulfate-reducing bacteria / ml are added to the solution to ensure that the formed scale contains bacteria. In step S1, the electrochemical cathode polarization pre-scaling method employs a three-electrode method, applying a cathode potential of -1.0 V (relative to the open circuit potential) to the surface of the working electrode. In step S1, the electrochemical cathode polarization pre-scaling time is 5-8 hours. In step S1, the electrochemical cathode polarization pre-scaling is carried out at room temperature.

[0009] In step S2, the anoxic solution is a NaCl solution with a mass concentration of 1.5-3.5% prepared according to the on-site formation water quality; In step S5, the electrolytic membrane removal method uses a graphite or platinum anode, and the scaled metal sample after immersion is used as the cathode. In step S5, the cathode current density during electrolytic membrane removal is 100 A / m. 2 The membrane removal time is 5 minutes; In step S5, the electrolytic membrane removal is carried out in an oxygen-free ammonium citrate solution (concentration of 10%). The volume of ammonium citrate solution V (mL) and the exposed area S (cm²) of the scaled metal sample are determined by the specific ratio of the electrolytic membrane removal process. 2 The ratio (V / S) is greater than 20 mL / cm 2 .

[0010] In step S5, the electrolytic membrane removal is carried out at room temperature.

[0011] In step S6, the sterilization rate of the bactericide in the water body is calculated as follows: in, E s The disinfection rate (%) of the disinfectant against SRB bacteria in the water. C s0 The concentration of SRB bacteria in the water (cFU / mL) without the addition of bactericides. C s1 The concentration of SRB bacteria in the water after the addition of a bactericide (cFU / mL).

[0012] The bactericidal effect (bactericidal rate) of the bactericide under the deposit is calculated as follows: in, E d The bactericidal rate (%) of the bactericide against sulfate-reducing bacteria under the deposits; C d0 The concentration of sulfate-reducing bacteria under the deposits (CFU / mL) without the addition of bactericides. C d1 The concentration of sulfate-reducing bacteria under the deposits (CFU / mL) after the addition of bactericide.

[0013] The beneficial effects of this invention are: 1. The evaluation method of this invention fills the gaps in traditional evaluation methods, which cannot detect the content of bacteria under deposits and cannot evaluate the performance of under-deposit bactericides. By artificially simulating scaling, a scale sample containing sulfate-reducing bacteria is formed, and operational steps and methods for evaluating sulfate-reducing bacteria under deposits are established. Using existing sulfate-reducing bacteria evaluation methods as a framework, this invention achieves an evaluation method for the quantity of sulfate-reducing bacteria under deposits and the under-deposit bactericidal performance of bactericides. This evaluation method overcomes the limitations of existing evaluation methods for bacteria and bactericides under deposits and has significant potential for widespread application.

[0014] 2. This invention employs electrolysis to remove the film layer from the metal surface. The reaction is relatively mild and does not cause significant damage to the substrate surface. This method overcomes the drawback of traditional acid pickling methods, where strong oxidizing acids can cause corrosion to the substrate. The electrolytic film removal method allows for more precise control of the removal speed and effect by adjusting the current, making it safer, more reliable, more adaptable, and highly adjustable.

[0015] 3. In this invention, the solution after membrane removal is treated with ultrasound. Ultrasound can generate strong shearing and impact forces, which can better disperse the bacteria in the liquid, making the distribution of sulfate-reducing bacteria in the solution more uniform and the bacterial content detection results more accurate.

[0016] 4. In this invention, the method used for cathodic polarization pre-scaling is the three-electrode method. This method can increase the deposition rate on the electrode surface, accelerate the deposition of ion scale, and effectively improve the scale deposition efficiency. It overcomes the shortcomings of natural scaling, such as long time consumption and low efficiency. Attached Figure Description

[0017] Figure 1 This is a schematic diagram illustrating the bactericidal effect of bactericide A in Example 1 of the present invention.

[0018] Figure 2 This is a schematic diagram illustrating the bactericidal effect of bactericide B in Embodiment 2 of the present invention.

[0019] Figure 3 This is a schematic diagram illustrating the bactericidal effect of bactericide C in Example 3 of the present invention. Detailed Implementation

[0020] The present invention will be further described in detail below with reference to embodiments, but the implementation of the present invention is not limited thereto.

[0021] Example 1 This embodiment provides a method for evaluating the under-deposit bactericidal effect of a bactericide, comprising the following steps: S1. An electrochemical cathode polarization pre-scaling method is used to form a scale coating layer on the surface of the metal sample; The exposed area is 5 cm 2A Q235 steel sheet was placed in 500 mL of a simulated solution (a mixed solution of 0.5 g / L Ca(NO3)2 and 0.5 g / L NaHCO3). 100 bacteria / mL (SRB) were added to the solution. A three-electrode system was used (Q235 steel sheet as the working electrode, platinum sheet as the auxiliary electrode, and saturated calomel electrode as the reference electrode). A voltage of -1.0 V (relative to the open circuit potential) was applied to the working electrode at room temperature and maintained at room temperature for 6 hours. A scale coating was formed on the surface of the metal sample. S2. Prepare an anaerobic solution containing sulfate-reducing bacteria, wherein the concentration of sulfate-reducing bacteria in the anaerobic solution is 100 bacteria / mL; The anoxic solution was a 3.5% NaCl solution prepared according to the site's formation water quality. S3. The metal sample described in step S1 is placed in the oxygen-free solution described in step S2 and soaked in a sealed container for 4 hours at a soaking temperature of 35℃±1℃. The concentration of sulfate-reducing bacteria in the water without the addition of bactericide is also measured. S4. After soaking in step S3, bactericidal experiments were conducted by adding different concentrations of bactericide A (5 mg / L, 10 mg / L, 20 mg / L, and 40 mg / L) to the solution; and the concentration of sulfate-reducing bacteria in the water was measured after adding the bactericide. S5. Place the metal sample soaked in step S3 and the metal sample sterilized in step S4 into an anaerobic closed electrolytic cell, respectively, and remove the membrane by electrolysis. The solution after membrane removal is ultrasonically treated for 5 minutes. The concentration of sulfate-reducing bacteria under the deposit is detected when no bactericide is added and the concentration of sulfate-reducing bacteria under the deposit is detected when bactericide is added. Prepare 125 mL of a 10% ammonium citrate solution as the membrane removal electrolyte and purge with nitrogen for 1 hour to remove oxygen. After soaking, rinse the scale-laden metal sample with clean water and then place it in the membrane removal electrolyte (in a sealed container to avoid oxygen exposure). Set the scale-laden sample as the cathode and graphite or platinum as the anode. Control the cathode current density at room temperature to 100 A / m. 2 The membrane removal time is 5 minutes; After the membrane removal is completed, remove the three electrodes and ultrasonically disperse the membrane-removed solution at room temperature for 5 minutes, maintaining a nitrogen atmosphere during this period and avoiding oxygen exposure. In steps S3-S5, the method for detecting the concentration of sulfate-reducing bacteria is as follows: Take 1 mL of different water samples respectively, and use the "Analysis Method of Bacteria in Oilfield Injection Water - Extinction Dilution Method (SY / T0532-2012)" to detect the sulfate-reducing bacteria concentration in the solution after soaking in step S3, the solution after sterilization in step S4, the solution after ultrasonic treatment of the metal sample after soaking in step S5, and the solution after ultrasonic treatment of the metal sample after sterilization in step S5. S6. Calculate the bactericidal rate of the bactericide in water and under scale by using the concentration of sulfate-reducing bacteria detected in steps S3-S5. The sterilization rate of the bactericide in water is calculated as follows: in, E s The disinfection rate (%) of the disinfectant against SRB bacteria in the water. C s0 The concentration of SRB bacteria in the water (cFU / mL) without the addition of bactericides. C s1 The concentration of SRB bacteria in the water after the addition of a bactericide (cFU / mL).

[0022] The bactericidal effect (bactericidal rate) of the bactericide under the deposit is calculated as follows: in, E d The bactericidal rate (%) of the bactericide against sulfate-reducing bacteria under the deposits; C d0 The concentration of sulfate-reducing bacteria under the deposits (CFU / mL) without the addition of bactericides. C d1 The concentration of sulfate-reducing bacteria under the deposits (CFU / mL) after the addition of bactericide.

[0023] In this embodiment, the bactericide A used is glutaraldehyde; in this embodiment, different concentrations of bactericide A are added, and the number of bacteria (SRB) in the water and under-deposit (SDB) and the bactericidal rate of the bactericide in the water and SDB are as follows: Figure 1 As shown.

[0024] Example 2 This embodiment provides a method for evaluating the under-deposit bactericidal effect of a bactericide, comprising the following steps: S1. An electrochemical cathode polarization pre-scaling method is used to form a scale coating layer on the surface of the metal sample; The exposed area is 10cm 2 An N80 steel sheet was placed in a 500 mL simulated solution (a mixed solution of 1 g / L Ca(NO3)2 and 0.5 g / L NaHCO3). 500 bacteria / mL (SRB) were added to the solution. A three-electrode system was used (the working electrode was an N80 steel sheet, the auxiliary electrode was a platinum sheet, and the reference electrode was a saturated calomel electrode). A voltage of -1.0 V (relative to the open circuit potential) was applied to the working electrode at room temperature and maintained at room temperature for 8 hours. A scale coating was formed on the surface of the metal sample. S2. Prepare an anaerobic solution containing sulfate-reducing bacteria, wherein the concentration of sulfate-reducing bacteria in the anaerobic solution is 500 bacteria / mL; The anoxic solution was a 1.5% NaCl solution prepared according to the site's formation water quality. S3. The metal sample described in step S1 is placed in the oxygen-free solution described in step S2 and soaked in a sealed container for 5 hours at a soaking temperature of 35℃±1℃. The concentration of sulfate-reducing bacteria in the water without the addition of bactericide is also measured. S4. After soaking in step S4, bactericidal experiments were conducted by adding different concentrations of bactericide B (10 mg / L, 20 mg / L, 40 mg / L and 80 mg / L) to the solution; and the concentration of sulfate-reducing bacteria in the water was detected after adding the bactericide. S5. Place the metal sample soaked in step S3 and the metal sample sterilized in step S4 into an anaerobic closed electrolytic cell, respectively, and remove the membrane by electrolysis. The solution after membrane removal is ultrasonically treated for 8 minutes. The concentration of sulfate-reducing bacteria under the deposit is detected when no bactericide is added and when bactericide is added. Prepare 300 mL of a 10% ammonium citrate solution as the membrane removal electrolyte and purge with nitrogen for 1 hour to remove oxygen. After soaking, rinse the scale-laden metal sample with clean water and then place it in the membrane removal electrolyte (in a sealed container to avoid oxygen exposure). Set the scale-laden sample as the cathode and graphite or platinum as the anode. Control the cathode current density at room temperature to 100 A / m. 2 The membrane removal time is 5 minutes; After the membrane removal is completed, remove the three electrodes and ultrasonically disperse the membrane-removed solution at room temperature for 5 minutes, maintaining a nitrogen atmosphere during this period and avoiding oxygen exposure. In steps S3-S5, the method for detecting the concentration of sulfate-reducing bacteria is as follows: Take 1 mL of different water samples respectively, and use the "Analysis Method of Bacteria in Oilfield Injection Water - Extinction Dilution Method (SY / T0532-2012)" to detect the sulfate-reducing bacteria concentration in the solution after soaking in step S3, the solution after sterilization in step S4, the solution after removing the membrane from the soaked metal sample in step S5, and the solution after removing the membrane from the sterilized metal sample in step S5. S6. Calculate the bactericidal rate of the bactericide in water and under scale by using the concentration of sulfate-reducing bacteria detected in steps S3-S5. The sterilization rate of the bactericide in water is calculated as follows: in, E s The disinfection rate (%) of the disinfectant against SRB bacteria in the water. C s0 The concentration of SRB bacteria in the water (cFU / mL) without the addition of bactericides. C s1 The concentration of SRB bacteria in the water after the addition of a bactericide (cFU / mL).

[0025] The bactericidal effect (bactericidal rate) of the bactericide under the deposit is calculated as follows: in, E d The bactericidal rate (%) of the bactericide against sulfate-reducing bacteria under the deposits; C d0 The concentration of sulfate-reducing bacteria under the deposits (CFU / mL) without the addition of bactericides. C d1 The concentration of sulfate-reducing bacteria under the deposits (CFU / mL) after the addition of bactericide.

[0026] In this embodiment, the bactericide B used is isothiazolinone; in this embodiment, different concentrations of bactericide B are added, and the number of bacteria (SRB) in the water and under-deposit, as well as the bactericidal rate of the bactericide in the water and under-deposit are as follows: Figure 2 As shown.

[0027] Example 3 This embodiment provides a method for evaluating the under-deposit bactericidal effect of a bactericide, comprising the following steps: S1. An electrochemical cathode polarization pre-scaling method is used to form a scale coating layer on the surface of the metal sample; The exposed area is 8cm 2 An X65 steel sheet was placed in 500 mL of a simulated solution (a mixed solution of 0.5 g / L Ca(NO3)2 and 1 g / L NaHCO3). 100 bacteria / mL (SRB) were added to the solution. A three-electrode system was used (X65 steel sheet as the working electrode, platinum sheet as the auxiliary electrode, and saturated calomel electrode as the reference electrode). A voltage of -1.0 V (relative to the open circuit potential) was applied to the working electrode at room temperature and maintained at room temperature for 5 hours. A scale coating was formed on the surface of the metal sample. S2. Prepare an anaerobic solution containing sulfate-reducing bacteria, wherein the concentration of sulfate-reducing bacteria in the anaerobic solution is 1000 bacteria / mL; The anoxic solution was a 3% NaCl solution prepared according to the site's formation water quality. S3. The metal sample described in step S1 is placed in the oxygen-free solution described in step S2 and soaked in a sealed container for 3 hours at a soaking temperature of 35℃±1℃. The concentration of sulfate-reducing bacteria in the water without the addition of bactericide is also measured. S4. After soaking in step S3, bactericidal experiments were conducted by adding different concentrations of bactericide B (10 mg / L, 25 mg / L, 50 mg / L and 75 mg / L) to the solution; and the concentration of sulfate-reducing bacteria in the water was detected after adding the bactericide. S5. Place the metal sample soaked in step S3 and the metal sample sterilized in step S4 into an anaerobic closed electrolytic cell, respectively, and remove the membrane by electrolysis. The solution after membrane removal is ultrasonically treated for 3 minutes. The concentration of sulfate-reducing bacteria under the deposit is detected when no bactericide is added and when bactericide is added. Prepare 250 mL of a 10% ammonium citrate solution as the membrane removal electrolyte and purge with nitrogen for 1 hour to remove oxygen. After soaking, rinse the scale-laden metal sample with clean water and then place it in the membrane removal electrolyte (in a sealed container to avoid oxygen exposure). Set the scale-laden sample as the cathode and graphite or platinum as the anode. Control the cathode current density at room temperature to 100 A / m. 2 The membrane removal time is 5 minutes; After the membrane removal is completed, remove the three electrodes and ultrasonically disperse the membrane-removed solution at room temperature for 5 minutes, maintaining a nitrogen atmosphere during this period and avoiding oxygen exposure. In steps S3-S5, the method for detecting the concentration of sulfate-reducing bacteria is as follows: Take 1 mL of different water samples respectively, and use the "Analysis Method of Bacteria in Oilfield Injection Water - Extinction Dilution Method (SY / T0532-2012)" to detect the sulfate-reducing bacteria concentration in the solution after soaking in step S3, the solution after sterilization in step S4, the solution after removing the membrane from the soaked metal sample in step S5, and the solution after removing the membrane from the sterilized metal sample in step S5. S6. Calculate the bactericidal rate of the bactericide in water and under scale by using the concentration of sulfate-reducing bacteria detected in steps S3-S5. The sterilization rate of the bactericide in water is calculated as follows: in, E s The disinfection rate (%) of the disinfectant against SRB bacteria in the water. C s0 The concentration of SRB bacteria in the water (cFU / mL) without the addition of bactericides. C s1 The concentration of SRB bacteria in the water after the addition of a bactericide (cFU / mL).

[0028] The bactericidal effect (bactericidal rate) of the bactericide under the deposit is calculated as follows: in, E d The bactericidal rate (%) of the bactericide against sulfate-reducing bacteria under the deposits; C d0 The concentration of sulfate-reducing bacteria under the deposits (CFU / mL) without the addition of bactericides. C d1The concentration of sulfate-reducing bacteria under the deposits (CFU / mL) after the addition of bactericide.

[0029] In this embodiment, the bactericide C used is dithiocarbamate (DTC); in this embodiment, different concentrations of bactericide C are added, and the number of surface bacteria (SRB) in the water and the bactericide kill rate in the water and under the scale are as follows: Figure 3 As shown.

[0030] from Figures 1-3 It can be seen that with the increase of the concentration of bactericide A, the number of SRB in the water and under the scale decreased significantly, and the sterilization rate increased significantly. When the concentration reached 40 mg / L, the sterilization effect was close to 100%. Figure 2 As the concentration of fungicide B increases, the growth of SRB begins to decrease, reaching its lowest point at 80 mg / L. The inhibitory effect increases significantly with the increase of fungicide concentration, approaching 100% at 80 mg / L. Figure 3 The results showed that the number of SRB in the water and under the scale decreased sharply and then remained at a low level with the increase of the concentration of bactericide C. The bactericidal effect reached its maximum, approaching 100%, when the concentration reached 75 mg / L. It was also observed that all three bactericides shared the characteristic of significant effectiveness in killing SRB in the water, with a high bactericidal rate. However, when comparing the effects of the bactericides on SRB under the scale, the bactericidal efficiency decreased significantly.

[0031] It is understood that the present invention has been described through some embodiments, and those skilled in the art will recognize that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the invention. Furthermore, under the teachings of the present invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the protection scope of the present invention.

Claims

1. A method for evaluating the bactericidal effect of a bactericide under scale, characterized in that: Includes the following steps: S1. An electrochemical cathode polarization pre-scaling method is used to form a scale coating layer on the surface of the metal sample; S2. Prepare an anaerobic solution containing sulfate-reducing bacteria, wherein the concentration of sulfate-reducing bacteria in the anaerobic solution is greater than or equal to 100 bacteria / mL; S3. Immerse the metal sample from step S1 in the oxygen-free solution from step S2 in a sealed container for 3-5 hours at a temperature of 35℃±1℃, and detect the concentration of sulfate-reducing bacteria in the water without the addition of bactericide. S4. After soaking in step S3, add a bactericide to the solution for sterilization, and test the concentration of sulfate-reducing bacteria in the water after adding the bactericide. S5. Place the metal sample soaked in step S3 and the metal sample sterilized in step S4 into an anaerobic closed electrolytic cell, respectively, and remove the membrane by electrolysis. After membrane removal, the solution is ultrasonically treated for 3-8 minutes. The concentration of sulfate-reducing bacteria under the deposit is detected when no bactericide is added and the concentration of sulfate-reducing bacteria under the deposit is detected when bactericide is added. S6. Calculate the bactericidal rate of the bactericide in water and under scale by using the concentration of sulfate-reducing bacteria detected in steps S3-S5.

2. The method for evaluating the under-deposit bactericidal effect of a bactericide according to claim 1, characterized in that: In step S1, the electrochemical cathode polarization pre-scaling method is carried out in an artificially prepared simulated solution, which is a mixed solution of 0.5-1 g / L Ca(NO3)2 and 0.5-1 g / L NaHCO3.

3. The method for evaluating the bactericidal effect of a bactericide under deposits according to claim 2, characterized in that: The simulated solution contains 100-1000 sulfate-reducing bacteria per ml.

4. The method for evaluating the under-deposit bactericidal effect of a bactericide according to claim 1, characterized in that: In step S1, the electrochemical cathode polarization pre-scaling method employs a three-electrode method, applying a cathode potential of -1.0 V to the surface of the working electrode.

5. The method for evaluating the under-deposit bactericidal effect of a bactericide according to claim 1, characterized in that: In step S1, the electrochemical cathode polarization pre-scaling time is 5-8 hours.

6. The method for evaluating the under-deposit bactericidal effect of a bactericide according to claim 1, characterized in that: In step S2, the anoxic solution is a NaCl solution with a mass concentration of 1.5-3.5% prepared according to the on-site formation water quality.

7. The method for evaluating the under-deposit bactericidal effect of a bactericide according to claim 1, characterized in that: Electrolytic membrane removal uses a graphite or platinum anode, and the scaled metal sample after immersion serves as the cathode; the cathode current density during electrolytic membrane removal is 100 A / m2, and the membrane removal time is 5 minutes.

8. The method for evaluating the under-deposit bactericidal effect of a bactericide according to claim 1, characterized in that: In step S5, the electrolytic membrane removal is carried out in an oxygen-free ammonium citrate solution. The volume of ammonium citrate solution V (mL) is related to the exposed area S (cm) of the scaled metal sample. 2 The ratio (V / S) is greater than 20 mL / cm 2 .

9. The method for evaluating the under-deposit bactericidal effect of a bactericide according to claim 1, characterized in that: In step S6, the sterilization rate of the bactericide in the water body is calculated as follows: Among them, E s The bactericidal rate (%) of the bactericide against sulfate-reducing bacteria in water; C s0 The concentration of sulfate-reducing bacteria in the water without the addition of bactericides (Cb / mL); s1 The concentration of sulfate-reducing bacteria in the water after the addition of bactericide (CFU / mL).

10. The method for evaluating the under-deposit bactericidal effect of a bactericide according to claim 1, characterized in that: The bactericidal effect (bactericidal rate) of the bactericide under the deposit is calculated as follows: Among them, E d The bactericidal rate (%) of the bactericide against sulfate-reducing bacteria under deposits; C d0 The concentration of sulfate-reducing bacteria under the deposits (Cb / mL) without the addition of bactericides; C d1 The concentration of sulfate-reducing bacteria under the deposits (CFU / mL) after the addition of bactericide.

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