Application of lactobacillus paracasei A-2 in corrosion prevention of oil field

Abstract

The invention provides an application of Lactobacillus paracasei A-2 in corrosion prevention of an oil field, the Lactobacillus paracasei A-2 is preserved in China General Microbiological Culture Collection Center (CGMCC) on December 11, 2024, and the preservation number is CGMCC No.33023. The Lactobacillus paracasei A-2 has the advantages that the Lactobacillus paracasei A-2 can be applied to corrosion prevention of the oil field, and the Lactobacillus paracasei A-2 can be applied to corrosion prevention of the oil field; the oil field corrosion prevention comprises the steps of inhibiting growth of sulfate reducing bacteria in the oil field environment, reducing the concentration of hydrogen sulfide in the oil field environment and slowing down corrosion of oil field metal facilities. The lactobacillus paracasei A-2 can generate a remarkable inhibition effect on bacteria which cause acid corrosion of an oil field, such as desulfurization vibrio, desulfurization monad, desulfurization sarcina, desulfurization leaf bacteria and desulfurization enterobacteria, and effectively fills up the blank of the existing antibacterial and antiseptic lactic acid bacteria, wherein the bacteria comprise desulfurization vibrio, desulfurization monad, desulfurization sarcina, desulfurization leaf bacteria and desulfurization enterobacteria.

Description

Technical Field

[0001] This invention belongs to the field of microbial and oilfield chemical technology, and specifically relates to the application of Lactobacillus paracasei A-2 in oilfield corrosion prevention. Background Technology

[0002] From development to production and transportation, many processes in an oil field, including drilling, well completion, acid fracturing, gathering and transportation, produced water, and reinjection systems, will generate [damage / effects]. gas. Hydrogen sulfide is an extremely toxic gas that can easily cause death. It is a potent neurotoxin, second only to cyanide in its toxicity. It affects the quality of drilling fluids, especially water-based drilling fluids, causing significant pollution. Furthermore, it reacts with substances in the formation, clogging the bottom layer and hindering extraction efficiency. When dissolved in water, hydrogen sulfide forms a weak acid that corrodes metals, causing hydrogen embrittlement of metal tubing, sulfide stress corrosion cracking, and electrochemical weightlessness. Downhole metal tubing can suddenly break due to hydrogen sulfide corrosion. Hydrogen sulfide corrosion can also cause wellhead equipment malfunctions and surface instrument explosions, and in severe cases, can lead to blowouts and major fires. Hydrogen sulfide not only seriously endangers human life but also pollutes the environment and causes severe corrosion damage to equipment.

[0003] The formation of hydrogen sulfide in nature is mainly attributed to five key factors. First, during biodegradation, sulfur-containing organic matter decomposes under environmental changes, releasing hydrogen sulfide. However, this process usually occurs at the Earth's surface, and the amount of hydrogen sulfide produced is limited, making it difficult to accumulate in large quantities. Second, in microbial sulfate reduction, sulfate-reducing bacteria (SRB) reduce sulfates using organic matter or hydrocarbons under anaerobic conditions, directly generating hydrogen sulfide. This process is conducive to the preservation and accumulation of hydrogen sulfide. Third, during thermochemical decomposition, sulfur-containing organic compounds in crude oil break down under thermal action, forming hydrogen sulfide, but the concentration is generally low. Fourth, in the thermochemical reduction of sulfate, under high-temperature conditions, sulfur-containing organic matter in the surrounding rock reacts with sulfate rocks to generate hydrogen sulfide gas. Finally, in magmatic origin, sulfur from the Earth's interior is released during magmatic activity, forming volatiles containing hydrogen sulfide. The content of these volatiles is influenced by the magma composition and gas transport conditions. These factors together constitute the generation mechanism of hydrogen sulfide in nature, among which sulfate-reducing bacteria are the main reported cause in oil reservoir environments.

[0004] The most common and effective method for controlling hydrogen sulfide in oilfield environments is chemical disinfection. Chemical disinfection is simple to operate, has good bactericidal effects, and is fast-acting, thus it is widely used in the treatment of hydrogen sulfide in oilfield wastewater systems. The most commonly used bactericides in chemical disinfection include quaternary ammonium salts, quaternary phosphate salts, glutaraldehyde, formaldehyde, ozone, and their compound formulations. However, long-term use of a single bactericide can lead to resistance in sulfate-reducing bacteria, thereby reducing the bactericidal effect and causing hydrogen sulfide production. In such cases, it is necessary to promptly replace the bactericide or use a higher concentration of the bactericide. Furthermore, treating hydrogen sulfide solely through chemical disinfection cannot completely eliminate its hazards. First, chemical disinfectants cannot penetrate the sludge and scale layers in oilfield wastewater systems, where sulfate-reducing bacteria can proliferate. Second, oilfield wastewater systems differ significantly from typical cooling water systems; they are not closed-loop systems. This means that chemical disinfectants entering the wastewater system are discharged along with the system's circulation, requiring continuous addition of disinfectants, which inevitably incurs substantial costs. Moreover, from a cost control perspective, relying solely on chemical disinfection presents certain challenges.

[0005] However, biological desulfurizers have enormous potential in terms of long-lasting effectiveness, environmental friendliness, and cost-effectiveness. Once beneficial bacteria successfully colonize and establish a dominant community in a system (such as oil reservoirs, pipelines, and wastewater treatment systems), they can work continuously, providing long-term and stable desulfurization. Control effects. In the long run, it can reduce the frequency of chemical agent additions, thereby reducing costs. It not only inhibits SRB, but also directly treats SRB metabolites— It transforms SRB into harmless substances. Simultaneously, it inhibits SRB activity at its source by competing for nutrients and ecological niches. Its mechanism of action is ecological competition and biotransformation, rather than direct poisoning. Therefore, SRB is unlikely to develop resistance like it does to chemical fungicides. As long as the biological sulfur-removing agent strain remains active, its effectiveness is stable.

[0006] Compared to nitrate-reducing bacteria, antibiotic-producing Bacillus strains, and bacteriophages, which can inhibit SRB (storage-reducing bacteria), lactic acid bacteria possess multiple antibacterial mechanisms. Lactic acid bacteria can simultaneously produce organic acids (such as lactic acid and acetic acid) to lower the environmental pH, inhibiting SRB growth; and secrete antimicrobial peptides that directly form pores on the SRB cell membrane, leading to leakage of cell contents and cell death. Furthermore, lactic acid bacteria are highly adaptable to their environment, rapidly growing and forming dominant flora in many natural environments. They are also recognized as safe probiotics and have a certain effect on deodorization. In practical applications, antimicrobial lactic acid bacteria can be used as microbial agents to achieve zero addition of chemical preservatives by inhibiting the growth of putrefactive microorganisms. Although antimicrobial lactic acid bacteria have begun to emerge in the food preservation field, their application in the petroleum industry is currently limited, especially in inhibiting SRB.

[0007] Therefore, developing lactic acid bacteria strains with broad-spectrum and highly efficient antiseptic and antibacterial activities is of great significance and has broad application prospects for promoting the development of the petroleum industry towards natural and safe antiseptic methods. Summary of the Invention

[0008] In view of the problems existing in the prior art, the purpose of this invention is to provide the application of Lactobacillus paracasei A-2 in oilfield preservation. This strain can significantly inhibit bacteria including desulfovibrio, desulfomonas, desulfocobacillus octococcus, desulfophylloxera, and desulfoenterobacteria, effectively filling the gap in existing antibacterial and preservative lactic acid bacteria.

[0009] The objective of this invention is achieved through the following technical solution: The first aspect of this invention provides the application of Lacticaseibacillus paracasei A-2 in oilfield corrosion prevention. The Lacticaseibacillus paracasei A-2 was deposited on December 11, 2024, at the China General Microbiological Culture Collection Center (CGMCC) with accession number CGMCC No. 33023.

[0010] Furthermore, the oilfield corrosion prevention includes inhibiting the growth of sulfate-reducing bacteria in the oilfield environment, reducing the concentration of hydrogen sulfide in the oilfield environment, and slowing down the corrosion of oilfield metal facilities.

[0011] Furthermore, the sulfate-reducing bacteria include desulfovibrio, desulfomonas, desulfodiacetic bacteria, desulfoleaf bacteria, and desulfoenterobacteria.

[0012] Furthermore, the *Lactobacillus paracasei* A-2 is either a live or inactivated bacterium.

[0013] A second aspect of the present invention provides an formulation for oilfield corrosion prevention, the formulation comprising the culture supernatant of Lactobacillus paracasei A-2 as described in claim 1.

[0014] Furthermore, the formulation also contains acceptable excipients.

[0015] Furthermore, the culture supernatant of Lactobacillus paracasei A-2 was prepared by the following method: Lactobacillus paracasei A-2 was inoculated into MRS liquid medium, cultured at 37 ℃ for 72 h, and then the supernatant was collected by centrifugation at 12000 r / min for 2 min.

[0016] Information on strain preservation: Lactobacillus paracasei A-2, deposited at: China General Microbiological Culture Collection Center (CGMCC); Address: No. 3, No. 1 Beichen West Road, Chaoyang District, Beijing, 100101, China; Deposit date: December 11, 2024; Accession number: CGMCC No. 33023; Classification: Lactobacillus paracasei.

[0017] The advantages of this invention compared to the prior art are as follows: 1. Highly efficient and broad-spectrum antibacterial and antiseptic properties: *Lactobacillus paracasei* A-2 exhibits significant inhibitory effects against various sulfate-reducing bacteria. When screened using *Vibrio desulfuriae* as an indicator bacterium, it demonstrates strong antibacterial ability. Subsequent antibacterial spectrum tests showed inhibitory effects against various bacteria, including *Desulfomonas*, *Desulfococcus*, *Desulfobacterium*, and *Desulfurenterobacter*. This characteristic effectively compensates for the narrow antibacterial spectrum of existing antibacterial lactic acid bacteria, particularly their insufficient inhibitory activity against sulfate-reducing bacteria. It provides stronger protection for corrosion prevention in the petroleum industry and can be widely applied in oil reservoirs, pipelines, and wastewater treatment systems, significantly reducing on-site hydrogen sulfide concentration and lowering the risk of corrosion caused by hydrogen sulfide in pipelines. 2. Excellent ability to inhibit hydrogen sulfide: In terms of hydrogen sulfide inhibition rate, adding 5% A-2 can achieve an inhibition rate of up to 80%, suggesting that A-2 may be able to remove hydrogen sulfide. Therefore, in practical applications, it can effectively improve hydrogen sulfide pollution and reduce hydrogen sulfide concentration from the source, with more significant effects. 3. Excellent antibacterial effect: When the concentration of sulfate-reducing bacteria is... When the concentration of sulfate-reducing bacteria is low, adding 2.5% A-2 can achieve a 90% antibacterial rate. If the concentration of sulfate-reducing bacteria on-site is low, this dosage can be reduced while still achieving the same effect. A-2's excellent antibacterial effect necessitates a low dosage, making it more economical for large-scale applications. Lactic acid bacteria can significantly reduce hydrogen sulfide generation at the source, thus preventing highly corrosive hydrogen sulfide from reacting with the pipe wall and greatly reducing the risk of pitting and uniform corrosion. This not only provides oilfields with a thorough and highly efficient microbial control strategy that is less likely to induce drug resistance, but also directly extends the service life of pipelines, achieving a green transformation from "sterilization" to "corrosion prevention." 4. High Safety and Environmental Friendliness: As a recognized "green" microbial preparation, lactic acid bacteria's outstanding safety stems from its long history of harmonious coexistence with humans and the environment. It is widely found in traditional fermented foods such as yogurt and kimchi, and is globally recognized as a safe probiotic, non-toxic and harmless to plants, animals, and ecosystems, achieving environmentally friendly governance. In terms of environmental protection, lactic acid bacteria exert their effects through their natural metabolic activities, effectively inhibiting harmful bacteria in the environment and reducing malodorous gases such as hydrogen sulfide. Its action does not introduce any exogenous chemicals, and its metabolic products, such as organic acids and bacteriocins, are naturally degraded, posing no risk of secondary pollution, perfectly aligning with the core concept of green and sustainable development. Therefore, whether in agriculture, environmental protection, or industrial production, lactic acid bacteria provide a reassuring biological solution that achieves a win-win situation with nature. 5. Broad Application Prospects: Based on the aforementioned excellent characteristics, *Lactobacillus paracasei* A-2 demonstrates disruptive application prospects in the industrial field, especially in oilfield microbial control. This end-to-end advantage, from "sterilization" to "corrosion prevention" to "environmental protection," makes lactic acid bacteria technology not only a sustainable solution to oilfield corrosion problems but also heralds an industry revolution from chemical to biological treatment, with extremely broad market potential and promotional value. Attached Figure Description

[0018] The present invention will be further described below with reference to the accompanying drawings and embodiments: Figure 1 The screening results of the antibacterial lactic acid bacteria described in Example 1 are shown; wherein, A: Lactobacillus paracasei inhibits Desulfovibrio; B: Lactobacillus bulgaricus inhibits Desulfovibrio; C: Streptococcus thermophilus inhibits Desulfovibrio; D: Leuconostoc mesenteroides inhibits Desulfovibrio. Figure 2 The results show the inhibition of *Lactobacillus paracasei* on *Desulfovibrio*, *Desulfomonas*, *Desulfococcus*, *Desulfospirochetes*, and *Desulfoenterobacter* using the A-2 double-layer streak plate method. Figure 3 The radius of the inhibition zone of Lactobacillus paracasei A-2 double-layer plate streak method against desulfovibrio, desulfomonas, desulfodiacetic bacteria, desulfoleaf bacteria, and desulfoenterobacteria is shown. Figure 4 The study demonstrated the inhibitory effects of Lactobacillus paracasei A-2 liquid live bacteria method on desulfovibrio, desulfomonas, desulfodiacetic bacteria, desulfoleaf bacteria, and desulfoenterobacteria. Figure 5 The study shows the removal of hydrogen sulfide by Lactobacillus paracasei A-2 after co-culturing with desulfovibrio, desulfomonas, desulfodiacetic bacteria, desulfoleaf bacteria, and desulfoenterobacteria. Figure 6 The macroscopic corrosion morphology of the corrosion model is shown; Figure 7 The microscopic corrosion morphology of the corrosion model. Detailed Implementation

[0019] The embodiments described are provided to better illustrate the present invention, but are not intended to limit the scope of the invention to the embodiments described. Therefore, non-essential improvements and adjustments made to the embodiments by those skilled in the art based on the above description are still within the scope of protection of the present invention.

[0020] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0021] The present invention will be described in detail below through embodiments. It should be understood that the following embodiments are only used to exemplify and further explain and illustrate the content of the present invention, and are not intended to limit the present invention.

[0022] Example 1: Screening of antibacterial lactic acid bacteria In this embodiment, desulfurized Vibrio was used as an indicator bacterium. Lactic acid bacteria with high activity against sulfate-reducing bacteria were screened from 20 strains of bacteria preserved in the laboratory, including 5 strains each of Lactobacillus paracasei, Lactobacillus bulgaricus, Streptococcus thermophilus, and Leuconostoc mesenteroides.

[0023] The Oxford cup method was selected for screening antibacterial activity. First, the lactic acid bacteria were activated by transferring them from glycerol tubes onto MRS medium and incubating at 37 °C for 48 h. The indicator bacteria were then incubated in liquid Postgate medium at 37 °C for 72 h. A small amount of Postgate medium containing 1.5% agar was poured into a sterile petri dish as a substrate. After the medium solidified, a sterilized Oxford cup was placed on the medium using forceps, and then 10 mL of Postgate medium containing the indicator bacteria (0.7% agar, bacterial culture: medium = 1:100) was poured on top. After the medium solidified, the Oxford cup was removed, and 100 μL of fermentation supernatant from *Lactobacillus paracasei* A-2 was added to each well. The plates were placed at 4 °C for 12 h for low-temperature diffusion, and then incubated in a 37 °C anaerobic incubator for 72 h. The antibacterial phenomenon was observed, and the diameter of the inhibition zone was measured. The strength of the antibacterial effect was compared based on the diameter of the inhibition zone.

[0024] After testing the antibacterial ability of the above 20 lactic acid bacteria strains, strains that could effectively inhibit desulfurization Vibrio were screened. Lactic acid bacteria numbered A-2 showed the strongest inhibitory ability against the indicator bacteria, with an average inhibition zone diameter of 19.15 mm. The inhibition diameters of other lactic acid bacteria ranged from 11 to 17 mm. Figure 1 ).

[0025] This strain was deposited at the China General Microbiological Culture Collection Center (CGMCC) on December 11, 2024, with accession number CGMCC No. 33023.

[0026] Example 2: Antibacterial spectrum test of Lactobacillus paracasei A-2 To determine whether *Lactobacillus paracasei* A-2 also possesses highly efficient inhibitory capabilities against other sulfate-reducing bacteria, this embodiment selected desulfovibrio, desulfomonas, desulfocobacillus, and desulfurized enterobacteria indicator bacteria for antibacterial spectrum testing. The bacterial assay was performed using the streak plating method, as detailed below: First, activate the lactic acid bacteria by transferring them from glycerol tubes onto MRS medium and incubating at 37°C for 48 hours. For the bottom layer, streak the plates by drawing two 2 cm long, 1.5 cm apart lines on the MRS plate using a ruler and marker. Then, streak a single colony of the activated lactic acid bacteria along the drawn lines. For the top layer, incubate the indicator bacteria in liquid medium until the logarithmic growth phase. Then, inoculate the indicator bacteria at a 1:100 ratio into semi-solid Postgate medium cooled to approximately 45°C and incubate at 37°C for 72 hours. Record the inhibition results, measure the inhibition zone, and compare the strength of the inhibition based on the inhibition zone range.

[0027] Figure 2 China A and Figure 3 The results showed that viable *Lactobacillus paracasei* A-2 could inhibit all indicator bacteria with strong inhibitory abilities. No indicator bacteria growth was observed within the plate area, meaning the inhibition range was the distance from *Lactobacillus paracasei* A-2 to the edge of the plate. Figure 2 B was the blank control; the plate was covered with indicator bacteria, further confirming the broad-spectrum antibacterial activity of this strain, which is of great application value.

[0028] Example 3: Analysis of the antibacterial effect of liquid Lactobacillus paracasei A-2 This embodiment quantitatively analyzed the antibacterial effect of *Lactobacillus paracasei* A-2 on various sulfate-reducing bacteria in a liquid system, clarified the inhibition rate of this strain at different inoculum amounts, determined its minimum inhibitory concentration (MIC), and the economically effective dosage for practical application. Specifically: After activating the *Lactobacillus paracasei* A-2 strain stored at -80 °C for three generations, a single colony was picked and inoculated into 100 mL of MRS liquid medium and cultured at 37 °C for 72 h. Similarly, the indicator strain, also stored at -80 °C, was activated for three generations and inoculated into 20 mL of Postgate liquid medium at a 10% inoculum, and cultured at 37 °C for 72 h. Subsequently, *Lactobacillus paracasei* A-2 was inoculated into anaerobic tubes at inoculum rates of 0%, 2.5%, 5%, 10%, 15%, and 20%, and the indicator strain was inoculated into anaerobic tubes at a 10% inoculum rate. The inoculum was then replenished with Postgate liquid medium, and cultured at 37 °C for 72 h. After 72 h, the anaerobic tubes were removed, and the indicator bacteria were counted using the dilution plating method.

[0029] like Figure 4 As shown, when the inoculum concentration of *Lactobacillus paracasei* A-2 is 15%, the inhibition rate against *Desulfococcus occulta* reaches 100%; for other sulfate-reducing bacteria, an inoculum concentration of 20% is required to achieve 100% inhibition. To achieve a 99.9% inhibition rate against all indicator bacteria, the inoculum concentration of A-2 is 5% or 10%, which is the minimum inhibitory concentration. Furthermore, when the inoculum concentration of *Lactobacillus paracasei* A-2 is 2.5%, the inhibition rate against sulfate-reducing bacteria can reach 90%–99%. When conducting large-scale experiments, the concentration of sulfate-reducing bacteria in the field environment is... This concentration can be used when the concentration is around 1000-2000 mmol / L, as it is more economical and effective. The amount of A-2 added can be adjusted according to the concentration of sulfate-reducing bacteria on site.

[0030] Example 4: Analysis of the inhibitory effect of Lactobacillus paracasei A-2 on hydrogen sulfide This embodiment quantitatively analyzed the inhibitory effect of *Lactobacillus paracasei* A-2 on hydrogen sulfide in the oilfield environment, clarifying the hydrogen sulfide inhibition rate of this strain at different inoculation amounts, specifically including: Lactobacillus paracasei A-2 and sulfate-reducing bacteria were activated for three generations each. Then, Lactobacillus paracasei A-2 was inoculated into anaerobic tubes at inoculum rates of 0%, 5%, and 10%, and indicator bacteria were inoculated into anaerobic tubes at an inoculum rate of 10%. The culture was then supplemented with Postgate liquid medium and incubated at 37 °C for 72 h. After 72 h, the anaerobic tubes were removed, and the sulfide content of the mixed bacterial culture was determined.

[0031] The sulfide content in water and oil samples was determined according to the "Determination of Sulfides in Water - Methylene Blue Spectrophotometric Method HJ 1226-2021". The main testing methods are as follows: a. Preparation of the standard curve: Take six 100 mL colorimetric tubes. Add 20 mL of 10 g / L sodium hydroxide solution to each tube, then add sulfide standard working solution with volume gradients of 0, 0.50, 1.00, 2.00, 4.00, and 7.00 mL. Dilute each tube to 60 mL with water to obtain sulfide standard solutions with concentration gradients of 0, 5.0, 10.0, 20.0, 40.0, and 70.0 μg / L. Mix 1 mL of ferric ammonium sulfate solution and 10 mL of N,N-dimethyl-p-phenylenediamine solution, let stand for 10 min, and add each mixture to the six tubes above, diluting to 100 mL. Measure the concentrations of the six solutions. Prepare a standard curve (the operation for low-concentration standard curves is basically the same as above, with a concentration range of 0~20 μg / L).

[0032] b. Centrifuge the sample (12000 r / min, 2 min), measure 200 μL of the supernatant after centrifugation and mix it with 8 μL of sodium hydroxide and 250 μL of zinc acetate sodium acetate solution in a 1.5 mL centrifuge tube, continue centrifuging (12000 r / min, 2 min) and take the supernatant. This process is used to fix hydrogen sulfide in the sample.

[0033] c. Measure 500 μL of N,N-dimethyl-p-phenylenediamine solution and mix it with 50 μL of ferric ammonium sulfate solution. After shaking and mixing, let it stand for 10 min and then centrifuge (12000 r / min, 12 s).

[0034] d. Add 550 μL of the centrifuged solution to 4450 μL of water and mix well (dilute 10 times).

[0035] e. Take 200 μL of the above solution, spot it, and measure... .

[0036] f. Based on the standard curve and absorbance measurements at 665 nm wavelength, the concentration of sulfides in the sample can be quantitatively analyzed.

[0037] The results are as follows Figure 5 As shown, the inhibition rate of hydrogen sulfide increased with the increase of A-2 addition. When the addition amount was 10%, the scavenging rate of hydrogen sulfide was 80.19-91.23%. When the addition amount was 5%, the hydrogen sulfide had the best inhibition effect on desulfurized Vibrio, at 81.64%.

[0038] Example 5: Verification of the preservative effect of Lactobacillus paracasei A-2 This embodiment verifies the actual anti-corrosion effect of Lactobacillus paracasei A-2 on oilfield metal facilities under simulated oilfield environmental conditions. After activating Lactobacillus paracasei A-2 stored at -80 ℃ for 3 generations, single colonies were picked and inoculated into 100 mL of MRS liquid medium and incubated at 37 ℃ for 72 h. Samples were then collected from oilfield produced wells. During collection, samples needed to be quickly transferred into sterile sampling containers pre-filled with high-purity nitrogen. The samples were transported under low-temperature conditions and transported to the laboratory as soon as possible for appropriate processing, minimizing the time the samples were exposed to air during the process.

[0039] The cultured Lactobacillus paracasei A-2 was mixed with oilfield produced water at inoculation rates of 0% and 2.5% (groups A and C, respectively; group B was supplemented with 2.5% MRS liquid medium). J55 steel sheets were placed on the mixture to construct a corrosion weight loss model. After reacting at 40 ℃ for 10 days, the corrosion morphology was observed and the corrosion rate, SRB concentration (counted using the extinction dilution method), and hydrogen sulfide content were measured.

[0040] Measure the dimensions of the test piece with vernier calipers, accurate to 0.02 mm, and calculate the area of ​​the test piece. First, wipe the test piece clean with filter paper, then place it in a container filled with petroleum ether with a boiling range of 60 ℃~90 ℃. Remove the surface grease with degreasing cotton, then immerse it in anhydrous ethanol for 5 min for further degreasing and dehydration. Remove the test piece, place it on filter paper, dry it with cold air, then wrap it with filter paper and store it in a desiccator. Weigh it after 1 h, accurate to 0.1 mg. Test pieces in each test container must not contact the container wall; the spacing between test pieces should be at least 1 cm, and the top of the test piece should be at least 3 cm from the liquid surface. Place the test apparatus in a constant temperature chamber and maintain the set temperature for one test cycle. After the test cycle has ended, remove the test pieces, observe and record the surface corrosion morphology, immediately rinse with clean water, and wipe dry with filter paper.

[0041] Remove the test specimens that have reached the test cycle, observe and record the surface corrosion morphology, and immediately rinse with clean water and dry with filter paper. Place the specimens in a container of petroleum ether with a boiling range of 60 ℃~90 ℃, remove the oil stains on the surface of the specimens with degreased cotton, remove the specimens and immerse them in acid cleaning solution for 5 min, while gently wiping the corrosion products on the surface of the specimens with degreased cotton. Remove the specimens from the cleaning solution, rinse off the residual acid on the surface with tap water, and then dehydrate them in anhydrous ethanol. Remove the specimens and place them on filter paper, dry them with cold air, then wrap the specimens with filter paper and store them in a desiccator. After 1 h, weigh them to an accuracy of 0.1 mg.

[0042] Calculate the uniform corrosion rate r using the following formula. c :

[0043] In the formula: — Uniform corrosion rate, expressed in millimeters per year (mm / year); m—Mass of the test piece before the experiment, in grams (g); —The mass of the test specimen after the experiment, in grams (g); S—Total area of ​​the test piece, in square centimeters ( ); ρ — density of the sample material, in grams per cubic centimeter (g / cm³) ); t — Test time, in hours (h).

[0044] The results are shown in Table 1. Adding A-2 reduced the uniform corrosion rate by approximately 63.19%, effectively alleviating pipeline corrosion and reducing the economic losses associated with pipeline replacement. Table 2 shows that adding A-2 reduced the SRB concentration by approximately 98%.

[0045] Figure 6 A, B, and C in the table correspond to groups A, B, and C, respectively. It can be observed that the degree of corrosion is greater in group B than in group A, which is greater than in group C. Group B has more corrosion pits, while no corrosion was observed in group C. This indicates that the metabolites of A-2 can alleviate corrosion, rather than the components of the MRS culture medium. Figure 7 A, B, and C in the diagram correspond to groups A, B, and C, respectively. Group A has larger and deeper corrosion pits, while after adding A-2, the corrosion pits become smaller, shallower, and fewer in number.

[0046] Table 1 Uniform corrosion rate

[0047] Table 2 SRB Concentration

[0048] Finally, it should be noted that the above description is only used to illustrate the technical solutions of the present invention and is not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention.

Claims

1. Lactobacillus paracasei ( Lacticaseibacillus paracasei The application of A-2 in oilfield corrosion prevention is characterized by, The Lactobacillus paracasei A-2 was deposited on December 11, 2024, at the China General Microbiological Culture Collection Center (CGMCC) with accession number CGMCC No. 33023.

2. The application according to claim 1, characterized in that, The oilfield corrosion prevention measures include inhibiting the growth of sulfate-reducing bacteria in the oilfield environment, reducing the concentration of hydrogen sulfide in the oilfield environment, and slowing down the corrosion of oilfield metal facilities.

3. The application according to claim 2, characterized in that, The sulfate-reducing bacteria include desulfurized Vibrio, desulfurized Monoclonal bacteria, desulfurized Diplococcus, desulfurized Leaf bacteria, and desulfurized Enterobacteriaceae.

4. The application according to claim 1, characterized in that, The *Lactobacillus paracasei* A-2 is either a live or inactivated bacterium.

5. A formulation for corrosion prevention in oil fields, characterized in that, The formulation comprises the culture supernatant of Lactobacillus paracasei A-2 as described in claim 1.

6. The formulation for oilfield corrosion prevention according to claim 5, characterized in that, The formulation also contains acceptable excipients.

7. The formulation for oilfield corrosion prevention according to claim 5, characterized in that, The culture supernatant of Lactobacillus paracasei A-2 was prepared by the following method: Lactobacillus paracasei A-2 was inoculated into MRS liquid medium and cultured at 37 ℃ for 72 h. The supernatant was then collected by centrifugation at 12000 r / min for 2 min.

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