A method for retarding corrosion of oil well tubulars using microorganisms

Abstract

This invention relates to a method for delaying corrosion of oil well tubing using microorganisms, comprising the following steps: (1) initial screening of target oil well microorganisms; (2) screening of activators; (3) determining the amount of microorganisms and activators injected in the field using the dynamic mass loss method based on the corrosion rate and slow-release rate of the coated tubing; (4) determining the in-field injection cycle using the physical simulation method based on the concentration of biofilm-producing bacteria; (5) in-field implementation and effect evaluation, wherein the effect evaluation is based on the well-down rate in the test well area, the pump inspection cycle of the oil well, and the input-output ratio. Compared with the prior art, this invention has the following advantages: (1) wide applicability to oil reservoirs; (2) the activator is non-toxic and harmless to the human body and will not cause damage to the formation or pollution to the environment; (3) safe and convenient; (4) simple process, strong operability and good field test results, with a 100% success rate in field tests, an input-output ratio greater than 1:15, and a validity period of more than 5 years.

Description

Technical Field

[0001] This invention belongs to the field of oil well corrosion prevention, specifically relating to a method for delaying the corrosion of oil well tubing using microorganisms. Background Technology

[0002] Corrosion of oil well tubing is one of the main factors restricting normal production of oil wells in the field. The corrosion mechanisms mainly include electrochemical corrosion, microbial corrosion, dissolved gas corrosion, under-deposit corrosion, and temperature corrosion, as well as the combined corrosion of the above five mechanisms.

[0003] In conventional waterflooding reservoirs, well tubing corrosion is quite common, especially in carbon dioxide flooding reservoirs where corrosion is even more pronounced, severely shortening the service life of the tubing and impacting the economic benefits of the oilfield. Dry carbon dioxide gas is a non-corrosive gas, but when dissolved in water, it forms carbonic acid, causing continuous electrochemical corrosion of metal tubing and exacerbating the corrosion of downhole tubing, rods, and pumps.

[0004] Current methods for preventing oil pipe corrosion mainly include using corrosion-resistant alloy steel, using coated oil pipes, injecting corrosion inhibitors, and cathodic protection. Using corrosion-resistant alloy steel has the disadvantages of high initial investment and limited subsequent maintenance methods. The effectiveness of coated oil pipes is related to the coating material and process level, its performance is unstable, and there are processing leaks at the joints, resulting in long operation times. Injecting corrosion inhibitors requires large injection volumes, is expensive, has a significant impact on production, and involves toxic and harmful chemicals. Cathodic protection is complex in its operation, difficult to design, and has high operating costs.

[0005] Chinese invention patent CN101625063B discloses a method for manufacturing a nano-anti-corrosion coating for oil pipes. This method requires first removing the oil pipe and cleaning off any oil contaminants. Then, three layers of a nano-composite coating composed of nanoparticles are sequentially sprayed onto the inner and outer walls of the pipe. Due to the qualitative change in the physical properties of materials at the nanoscale, the three layers of the nano-composite coating produce a composite effect, significantly improving its impermeability, high-temperature resistance, and adhesion, effectively preventing scale from adhering to the coating surface. However, this method requires removing the oil pipe and then sandblasting it, and it needs to be cured at different temperatures for a considerable time. This method is costly due to the need to move the pipe string, and the time-consuming and complex process of curing at different temperatures further complicates the issue. Other Chinese patent applications for coatings, such as CN202521074U and CN109135501A, although using different materials, all suffer from the same drawbacks.

[0006] Chinese invention patent application CN109097765A discloses a surface treatment solution for galvanized materials containing complex biopolysaccharides and its preparation method. This invention discloses a surface treatment solution for galvanized materials containing complex biopolysaccharides, comprising inulin, organosilane, inorganic slow-release agent, nano-silica sol, pH adjuster, and deionized water. It can obtain a surface treatment solution for galvanized materials with good fluidity and better passivation and corrosion protection effects. However, this method requires fermentation of the treatment solution on the ground, which is labor-intensive, costly, and inconvenient to operate.

[0007] Biofilms are biological aggregates formed by extracellular polymers secreted by microorganisms. Biofilms are mainly composed of the extracellular matrix of microbial cell nuclei. The main components of the extracellular matrix are extracellular polymers composed of polysaccharides, proteins, nucleic acids and lipids. Summary of the Invention

[0008] Objective of the Invention: To address the shortcomings of the existing technology, this invention provides a method for delaying the corrosion of oil well tubing using microorganisms. This method has the advantages of strong reservoir adaptability, low processing cost, simple processing technology, and being environmentally friendly and pollution-free. By injecting activators and exogenous bacterial solutions into the oil well, the microorganisms, with their inherent ability to adhere to the surface of metal or clay minerals, form a biofilm—a biological aggregate—through the metabolic products produced by the fermentation of the bacterial solution within the wellbore and the microbial cells themselves. This biofilm forms a protective biological layer on the tubing wall, preventing contact between the tubing wall and the oil, gas, and water inside the wellbore, thus reducing the corrosion rate of the tubing, extending its service life, and significantly reducing maintenance costs.

[0009] Technical solution: A method for delaying corrosion of oil well tubing using microorganisms, comprising the following steps:

[0010] (1) Initial screening of target oil well microorganisms:

[0011] Based on the suitable temperature for microorganisms, microorganisms that can secrete extracellular polymers at deep temperatures below the tubing in the test wellbore were screened.

[0012] (2) Activator screening: including preliminary screening and secondary screening of activators, wherein:

[0013] The preliminary screening method for activators is static culture, and the basis for preliminary screening of activators is the concentration of biofilm-producing microorganisms;

[0014] Based on the initial screening of activators, a second screening of activators is conducted, and the final activator formulation is determined according to the amount of biofilm produced.

[0015] (3) Based on the corrosion rate and corrosion inhibition rate of the coupon, the dynamic mass loss method is used to determine the amount of microorganisms and activators injected on site;

[0016] (4) Based on the bacterial concentration of the biofilm-producing bacteria, the on-site injection cycle is determined by physical simulation method;

[0017] (5) On-site implementation and effect evaluation, the basis for effect evaluation is the well lying rate in the test well area, the pump inspection cycle of oil wells, and the input-output ratio.

[0018] Furthermore, the extracellular polymers in step (1) include xanthan gum, gellan gum, thermogelatin, pullulan, chitosan, starch, bacterial cellulose, and velan gum.

[0019] Further, the microorganism mentioned in step (1) is one or more of Pseudomonas, Alcaligenes, Budding Short-Stemmed Pseudomonas, Citric Acid Fermentation Waste Mycelium, Acetobacter, Aspergillus niger, and Acetobacter xylinum, preferably one of Pseudomonas, Alcaligenes, and Acetobacter.

[0020] Furthermore, the temperature at the tubing depth in the test wellbore described in step (1) is calculated based on the tubing depth and the geothermal gradient of the oil layer, and the calculation formula is as follows:

[0021] Temperature at the depth of the tubing in the test wellbore = 20℃ + geothermal gradient × (depth of tubing ÷ 100).

[0022] Furthermore, the initial screening index for the target oil well microorganisms in step (1) is: the concentration of the microbial cells and the extracellular polymers produced is greater than 3 g / L.

[0023] Furthermore, the specific steps for the preliminary screening of activators in step (2) are as follows:

[0024] Take multiple 50-60 mL portions of produced fluid from the test reservoir, and then add different activator mixtures to each portion, wherein:

[0025] The bacterial concentration of the activator mixture was 10%.

[0026] The activator mixture consists of 1-2 ml of microbial culture and an appropriate amount of activator;

[0027] Then they were placed in the test wellbore temperature and incubated for 5–15 days.

[0028] The bacterial concentration of biofilm-producing organisms in different culture media was measured, and 2-3 activator formulations with higher bacterial concentrations were preliminarily screened based on the bacterial concentration levels.

[0029] Furthermore, the specific steps of the secondary screening of the activator in step (2) are as follows:

[0030] Take multiple 50-60 mL portions of produced fluid from the test reservoir and add 10-20 mL of different activator mixtures to each.

[0031] The bacterial concentration of the activator mixture was 10%.

[0032] The activator mixture consists of 1-2 ml of microbial culture and an appropriate amount of pre-screened activator;

[0033] Then it was placed at the temperature of the test wellbore and incubated for 5–15 days.

[0034] Filter the mixture of cells and products, and dry it at an initial temperature of 35°C, increasing the temperature by 5°C every hour until it reaches a maximum of 50°C. Weigh the mixture separately and select the activator formulation with the largest weight in the mixture.

[0035] Furthermore, step (3) includes the following steps:

[0036] (31) Obtain the dimensions of the hanging piece and calculate its area;

[0037] (32) Wipe the strip clean, then immerse it in a container containing petroleum ether with a boiling range of 60-90℃, then take out the strip and remove the grease from the surface of the strip, and then soak it in anhydrous ethanol for 3-30 minutes.

[0038] (33) Remove the hanging piece, air dry it and weigh it;

[0039] (34) The clip is suspended in the dynamic corrosion test bottle, and the clip does not contact the inner wall of the dynamic corrosion test bottle. Then the clip is immersed in the activator mixture with different injection amounts and the produced water of the target oil well in the test reservoir. The air in the dynamic corrosion test bottle is evacuated, and a mixture of CO2 and air is injected. The dynamic corrosion test bottle is placed in an oven with the temperature inside the tubing for incubation.

[0040] (35) After 7 days of the experiment, the hanging plate was taken out, cleaned with cleaning solution, weighed, and the corrosion status of the hanging plate surface was observed. The corrosion rate was calculated according to formula (1), and the corrosion inhibition rate was calculated according to formula (2). Based on the corrosion rate and corrosion inhibition rate of the hanging plate, the amount of microorganisms and activators injected on site was determined.

[0041] r=8.76*10 4 *(m-m1) / s*t*ρ (1)

[0042] η1=(Δm0-Δm1) / Δm0(2)

[0043] In the formula: r is the uniform corrosion rate, mm / a;

[0044] m and m1 are the masses of the hanging pieces before and after the test, respectively, in grams;

[0045] S is the surface area of ​​the hanging piece, in cm² 2 ;

[0046] ρ is the density of the hanging sheet, in g / cm³. 3 ;

[0047] t is the reaction time, in hours;

[0048] η1 is the corrosion inhibition rate, %

[0049] Δm0 represents the mass loss of the substrate in the blank test, in grams.

[0050] Δm1 represents the mass loss of the tablets in the bacterial culture mixture, in grams.

[0051] Furthermore, the dynamic corrosion testing bottle is an anaerobic bottle with hooks attached inside, wherein the material of the hooks is the same as the tubing material of the target oilfield.

[0052] Furthermore, step (4) includes the following steps:

[0053] Take 50 ml of the produced fluid from the test reservoir and add the determined amount of microorganisms and activators to be injected in the field.

[0054] The concentration of biofilm-producing bacteria was monitored daily, and the concentration was lowered to 10 after rising. 7 When the bacterial culture is replenished at a rate of 1000 cells / ml, the on-site injection cycle should be determined.

[0055] Furthermore, the field test mentioned in step (5) refers to using a high-pressure plunger pump to inject microorganisms and activators from the middle section of the well in the test reservoir according to the injection volume determined in step (3), and replenishing the bacterial solution according to the field injection cycle determined in step (4).

[0056] Furthermore, the activator described in step (2) is composed of a carbon source, a nitrogen source, and a phosphorus source, wherein:

[0057] The carbon source is sucrose or glucose;

[0058] The nitrogen source is one of wheat bran, cottonseed meal, rapeseed cake meal, and corn steep liquor powder;

[0059] The phosphorus source is dipotassium hydrogen phosphate or potassium dihydrogen phosphate.

[0060] Furthermore, the activator contains carbon source, nitrogen source, and phosphorus source at mass concentrations of 1.0-5.0%, 0.2-0.8%, and 0.02-0.1%, respectively, with the remainder being water.

[0061] Furthermore, the mass concentrations of the carbon source, nitrogen source, and phosphorus source in the activator are 2.0-3.0%, 0.3-0.6%, and 0.04-0.08%, respectively.

[0062] Compared with the prior art, the present invention has the following advantages:

[0063] (1) This invention has a wide range of applications in oil reservoirs, especially in ordinary water-drive oil reservoirs and carbon dioxide-drive oil reservoirs;

[0064] (2) The activator injected in this invention is non-toxic and harmless to the human body, so it will not cause damage to the formation or pollution to the environment, and avoids the subsequent water treatment problems caused by chemical methods.

[0065] (3) This invention utilizes microorganisms to produce biopolymers such as polysaccharides and proteins in the wellbore, forming a biofilm on the pipe wall, transferring the reaction from the ground to the underground, which is safe and convenient.

[0066] (4) The invention has the characteristics of simple process, strong operability and good field test results. The field test success rate is 100%, the input-output ratio is greater than 1:8, and the validity period is greater than 5 years. Attached Figure Description

[0067] Figure 1 This is a morphological diagram of the detection data of bacterial concentration in the biofilm produced in Example 1.

[0068] Figure 2 This is a morphological diagram of the detection data of bacterial concentration in the biofilm produced in Example 2.

[0069] Figure 3 This is a morphological diagram of the detection data of bacterial concentration in the biofilm produced in Example 3. Detailed Implementation

[0070] 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.

[0071] The present invention will be further described below with reference to specific embodiments.

[0072] Example 1

[0073] Test Well Overview: Located in Block A1 of Shengli Oilfield, this well utilizes carbon dioxide flooding. The reservoir temperature is 108℃, the geothermal gradient is 3.3℃ / 100m, and the formation water salinity is 18765mg / L. Well SL-A1-1 has N80 grade tubing with an outer diameter of 88.9mm and a wall thickness of 6.5mm. The tubing depth is 1950m, the dynamic fluid level is 1800m, and the last pump inspection was conducted 68 days later due to tubing corrosion and leakage. This well meets the screening criteria for this invention and can be implemented.

[0074] A method for delaying oil well tubing corrosion using microorganisms, the specific steps of which are as follows:

[0075] (1) Screening of target oil well microorganisms:

[0076] The temperature at the bottom of the tubing in the test wellbore = 20℃ + 3.3℃ / 100m × (1950m ÷ 100) = 84.35℃;

[0077] Based on the temperature tolerance of the microbial strains, two types of Pseudomonas were selected, ST1 and ST2 (temperature tolerance range 85-90℃), whose metabolites are xanthan gum, vegan gum, or chitosan.

[0078] (2) Screening of activators, including preliminary screening and secondary screening:

[0079] The initial screening method for activators was static culture, and the basis for preliminary screening was the bacterial concentration of biofilm-producing organisms, with a bacterial concentration higher than 10⁻⁶. 8 / ml. The specific steps are as follows:

[0080] Take multiple 100mL conical flasks, add 50mL of the produced fluid from the test reservoir to each flask, and add 10mL of different activator mixtures to each flask.

[0081] The activator mixture consists of 9 ml of the activator to be screened and 1 ml of Pseudomonas ST1 bacterial culture, or

[0082] It consists of 9 ml of the activator to be screened and 1 ml of Pseudomonas ST2 bacterial culture;

[0083] Then it was placed in the test tubing and incubated at the temperature for 7 days.

[0084] The bacterial concentration of biofilm-producing organisms in the culture medium was measured, and three groups of activator formulations with higher bacterial concentrations were initially screened based on the bacterial concentration (as shown in Table 1).

[0085] The specific steps for secondary screening of activators are as follows:

[0086] The mixture of the three bacterial cells and products was then filtered, dried, and initially at 35°C, with the temperature increased by 5°C every hour until a maximum of 50°C was reached and constant weight was achieved. Based on the results, the activator formulation with the largest mixture weight was selected (as shown in Table 2).

[0087] Based on the bacterial concentration results, the activator formula for ST1 bacteria achieved a bacterial concentration of 4*10⁻⁶. 8 The concentrations of ST2 bacteria activator formulations 2 and 3 can both reach 10⁶ cells / mL. 8 per mL.

[0088] Table 1. Screening of suitable activators for oil well SL-A1-1

[0089]

[0090] The bacterial concentration above reached 10 8 Three samples per mL were dried and weighed. Based on the dry weight of the product mixture, the formulation of activator No. 1 corresponding to the highest ST1 was selected.

[0091] Table 2. Screening of suitable activators for oil well SL-A1-1

[0092]

[0093] (3) The amount of injection on site was determined by using the dynamic mass loss method to measure the corrosion rate and corrosion inhibition rate of the coupon.

[0094] Measure the dimensions of the hanging piece using a vernier caliper, repeat the measurement three times, take the average value, and then calculate the area of ​​the hanging piece.

[0095] Wipe the tablets clean with filter paper, then place them in a container filled with petroleum ether at a boiling point of 60°C. Remove the grease from the surface of the tablets with a cotton ball, and then soak them in anhydrous ethanol for 5 minutes to further degrease and dehydrate them.

[0096] Remove the tablets and place them on filter paper. Dry them with cold air, then wrap them in filter paper and place them in a desiccator. Weigh them after 1 hour, accurate to 0.1 mg.

[0097] The suspending strip is suspended inside the dynamic corrosion test bottle without contacting the bottle. The suspending strip is immersed in a mixture of activator solutions with different injection volumes. The air in the dynamic corrosion test bottle is evacuated, and a mixture of CO2 and air is injected. The corrosion test bottle is then placed in an oven at the temperature inside the oil pipe for incubation.

[0098] After 7 days of testing, the pads were removed, cleaned with cleaning solution, weighed, and their surface corrosion was observed. The injection volume was determined based on the corrosion rate and corrosion inhibition rate.

[0099] As shown in Table 3, considering economic benefits, a 2% injection volume results in a corrosion rate of 0.1162 mm / a and a corrosion inhibition rate of 94.9%.

[0100] Table 3 Design of Injection Volume for Oil Well SL-A1-1

[0101]

[0102] (4) Determination of the on-site injection cycle:

[0103] Take a 100mL conical flask, add 50mL of the produced fluid from the test reservoir, and add 2% (v / v) of activator mixture formula 1 (including 0.1ml of Pseudomonas ST1 and 0.9ml of activator formula 1 (activator formula 1 is prepared by mixing 3.0% sucrose, 0.6% cottonseed meal, 0.03% dipotassium hydrogen phosphate and 96.37% water).

[0104] The bacterial concentration of biofilm-producing bacteria was measured daily, and by day 21, the concentration had decreased to 10. 7 The bacterial count / ml was optimized to an injection cycle of 20 days. See the detailed bacterial concentration morphology diagram below. Figure 1 .

[0105] (5) On-site implementation and effect evaluation:

[0106] Oil well SL-A1-1 began injection on December 16, 2019, with injections every 20 days. Each injection consisted of 650 kg of activator mixture formula 1 (i.e., 65 kg of Pseudomonas ST1 bacterial solution and 585 kg of activator formula 1). The pump was inspected on January 31, 2021, with an inspection cycle of 411 days, which was extended by 346 days. The cost was 72,000 yuan, reducing the number of inspections by approximately 5 times. The input-output ratio was 1:8.5, and the field test results were good. This invention has broad prospects for promotion and application.

[0107] Example 2

[0108] Test Well Overview: Located in Block A2 of Shengli Oilfield, this well utilizes carbon dioxide flooding. The reservoir temperature is 110℃, the geothermal gradient is 3.5℃ / 100m, and the formation water salinity is 10765mg / L. Well SL-A2-33 uses N80 grade tubing with an outer diameter of 73mm and a wall thickness of 6.5mm. The tubing depth is 1750m, the dynamic fluid level is 1550m, and the last pump inspection was conducted 81 days later due to tubing corrosion and leakage. This well meets the screening criteria for this invention and can be implemented.

[0109] A method for delaying oil well tubing corrosion using microorganisms, the specific steps of which are as follows:

[0110] (1) Screening of target microorganisms:

[0111] The temperature at the bottom of the tubing in the test wellbore = 20℃ + 3.5℃ / 100m × (1750℃ ÷ 100) = 81.25℃;

[0112] Based on the temperature tolerance of the microbial strains, two types of Acetic Acid Bacillus, SL1 and SL2, were selected for screening. The temperature tolerance range of the microorganisms is 80-90℃, and their metabolic products are bacterial cellulose, vegan gum, or gellan gum.

[0113] (2) Activator screening:

[0114] The initial screening method was static culture, and the basis for the initial screening was the bacterial concentration of the biofilm-producing organisms, with a bacterial concentration higher than 10⁻⁶. 8 / ml.

[0115] Take a 100mL conical flask, add 60mL of the produced fluid from the test reservoir, and add 12mL of different activator mixtures respectively;

[0116] The activator mixture consists of 10 ml of the activator to be screened and 2 ml of Acetobacter SL1 bacterial culture, or

[0117] It consists of 10 ml of the activator to be screened and 2 ml of Acetobacter SL2 bacterial solution;

[0118] Then it was placed in the test tubing and incubated at the temperature for 5 days.

[0119] The bacterial concentration of biofilm-producing organisms in the culture medium was measured, and two groups of activator formulations with higher bacterial concentrations were initially screened based on the bacterial concentration (as shown in Table 4).

[0120] The specific steps for secondary screening of activators are as follows:

[0121] The mixture of the two groups of bacterial cells and products was then filtered and dried. The initial temperature was 35°C, and the temperature was increased by 5°C every hour thereafter, with a maximum temperature of 50°C, until constant weight was achieved. Based on the results (as shown in Table 5), the activator formulation with the largest mixture weight was selected.

[0122] Based on the bacterial concentration results, the activator formulations for both Acetobacter SL1 and Acetobacter SL2 achieved a bacterial concentration of 10⁻¹⁰. 8 per mL.

[0123] Table 4. Screening of suitable activators for oil well SL-A2-33 1

[0124]

[0125] The bacterial concentration above reached 10 8 Two samples of acetic acid bacteria per mL were dried and weighed. Based on the dry weight of the product mixture, the formulation of activator No. 1 corresponding to the highest acetic acid bacteria SL1 was selected.

[0126] Table 5. Screening of suitable anti-corrosion microorganisms for oil well SL-A2-33 2

[0127]

[0128] (3) The on-site injection volume was determined by using the dynamic mass loss method to measure the corrosion rate and corrosion inhibition rate of the coupons:

[0129] Measure the dimensions of the hanging piece using vernier calipers, repeat the measurement three times, take the average value, and then calculate the area of ​​the hanging piece.

[0130] Wipe the tablets clean with filter paper, then place them in a container filled with petroleum ether at a boiling point of 90°C. Remove the grease from the surface of the tablets with a cotton ball, and then soak them in anhydrous ethanol for 3 minutes to further degrease and dehydrate them.

[0131] Remove the tablets and place them on filter paper. Dry them with cold air, then wrap them in filter paper and place them in a desiccator. Weigh them after 1 hour, accurate to 0.1 mg.

[0132] The ferrule was suspended inside the bottle, without contacting the dynamic corrosion testing bottle, and immersed in activator mixtures of varying injection volumes. The air in the dynamic corrosion testing bottle was evacuated, and a mixture of CO2 and air was injected. The corrosion testing bottle was then placed in an oven at the temperature inside the oil pipe for incubation. After 7 days of testing with activator formulation 1, the ferrule was removed, cleaned with a cleaning solution, weighed, and its surface corrosion condition was observed. The injection volume was determined based on the corrosion rate and corrosion inhibition rate.

[0133] As shown in Table 6, considering economic benefits, a 1% injection rate results in a corrosion rate of 0.2444 mm / a and a corrosion inhibition rate of 92.5%.

[0134] Table 6. Design of Injection Volume for Oil Well SL-A2-33

[0135]

[0136] (4) Determination of the on-site injection cycle:

[0137] Take a 100mL conical flask, add 60mL of the produced fluid from the test reservoir, and add 1% (v / v) of bacterial activator mixture formula 1; measure the concentration of biofilm-producing bacteria daily, and on day 27, the concentration decreases to 10. 7 The bacterial count / ml was optimized to an injection cycle of 25 days. See the detailed bacterial concentration morphology diagram below. Figure 2 .

[0138] (5) On-site implementation and effect evaluation: Well SL-A2-33 started injection on March 1, 2020, and injected once every 25 days. Each injection was 175KG of 10% activator mixture. The pump was inspected on January 21, 2021. The pump inspection cycle was 326 days, which was extended by 245 days. The cost was RMB 20,000. The number of pump inspections was reduced by about 3 times. The input-output ratio was 1:12. The on-site test results were good. This invention has broad prospects for promotion and application.

[0139] Example 3

[0140] Test Well Overview: Located in Block A3 of Shengli Oilfield, this well utilizes water-drive development. The reservoir temperature is 98℃, the geothermal gradient is 3.4℃ / 100m, and the formation water salinity is 9800mg / L. Well SL-A3-6 has P80 tubing steel, an outer diameter of 73mm, a wall thickness of 6.5mm, a tubing depth of 1350m, a dynamic fluid level of 1120m, and a last pump inspection cycle of 71 days. The reason for the inspection was tubing corrosion and leakage. This well meets the screening criteria of this invention and can be implemented. The specific steps for implementing this invention in this block using the method of this invention are as follows:

[0141] (1) Screening of target microorganisms:

[0142] The temperature at the depth of the tubing in the test wellbore = 20℃ + 3.4℃ / 100m × (1350m ÷ 100) = 65.9℃.

[0143] Based on the temperature tolerance of the microbial strains, three types of Alcaligenes were selected: Alcaligenes SY1, Alcaligenes SY2, and Alcaligenes SY3 (temperature tolerance range 65-75℃). Their metabolic products are thermogelatin polysaccharides, starch, or chitosan.

[0144] (2) Activator screening:

[0145] The initial screening method was static culture, and the basis for the initial screening was the bacterial concentration of the biofilm-producing organisms, with a bacterial concentration higher than 10⁻⁶. 8 / ml.

[0146] Take several 100mL conical flasks, add 55mL of the produced fluid from the test reservoir, and add 15mL of a mixture of different activators;

[0147] The activator mixture consists of 13.5 ml of the activator to be screened and 1.5 ml of Alcaligenes SY1 bacterial culture, or

[0148] It consists of 13.5 ml of the activator to be screened and 1.5 ml of Alcaligenes SY2 bacterial culture, or

[0149] It consists of 13.5 ml of the activator to be screened and 1.5 ml of Alcaligenes SY3 bacterial culture;

[0150] Then it was placed in the test tubing and incubated at the temperature for 15 days.

[0151] The bacterial concentration of biofilm-producing organisms in the culture medium was measured, and three groups of activator formulations with higher bacterial concentrations were initially screened based on the bacterial concentration (as shown in Table 7).

[0152] The specific steps for secondary screening of activators are as follows:

[0153] The mixtures of the three bacterial cells and products were then filtered and dried. The initial temperature was 35°C, and the temperature was increased by 5°C every hour thereafter, with a maximum temperature of 50°C, until constant weight was achieved. Based on the results, the activator formulation with the largest mixture weight was selected (as shown in Table 8).

[0154] Based on the bacterial concentration results, the bacterial concentrations of SY1 and SY2 bacteria reached 10 under activator formulation 2. 8 For SY3 bacteria, activator formulation 3 can achieve a concentration of 10 cells / mL or higher. 8 per mL.

[0155] Table 7. Screening of suitable activators for oil well SL-A3-6 1

[0156]

[0157] The bacterial concentration above reached 10 8 Three samples per mL were dried and weighed. Based on the dry weight of the product mixture, the formulation of activator No. 2 corresponding to the highest SY2 was selected.

[0158] Table 8. Screening of suitable anti-corrosion microorganisms for oil well SL-A3-6 2

[0159]

[0160] (3) The amount of injection on site was determined by using the dynamic mass loss method to measure the corrosion rate and corrosion inhibition rate of the coupon.

[0161] Measure the dimensions of the hanging piece using vernier calipers, repeat the measurement three times, take the average value, and then calculate the area of ​​the hanging piece.

[0162] Wipe the tablets clean with filter paper, then place them in a container with petroleum ether at a boiling point of 80°C. Remove the grease from the surface of the tablets with a cotton ball, and then soak them in anhydrous ethanol for 30 minutes to further degrease and dehydrate them.

[0163] Remove the tablets and place them on filter paper. Dry them with cold air, then wrap them in filter paper and place them in a desiccator. Weigh them after 1 hour, accurate to 0.1 mg.

[0164] The clip is suspended inside the bottle without contacting the dynamic corrosion test bottle, and the clip is immersed in a mixture of activator solutions with different injection volumes. The air in the dynamic corrosion test bottle is evacuated, and a mixture of CO2 and air is injected. The corrosion test bottle is then placed in an oven at the temperature inside the oil pipe for incubation.

[0165] After 7 days of testing with the selected activator formulation, the tablets were removed, cleaned with a cleaning solution, weighed, and their surface corrosion was observed. The injection volume was determined based on the corrosion rate and corrosion inhibition rate.

[0166] As shown in Table 9, considering economic benefits, a 3% injection volume results in a corrosion rate of 0.2097 mm / a and a corrosion inhibition rate of 92.8%, meeting the screening criteria. Therefore, the preferred result is a 3% injection volume.

[0167] Table 9. Design of Injection Volume for Oil Well SL-A3-6

[0168]

[0169] (4) Determination of the on-site injection cycle: Take a 100mL conical flask, add 55mL of the produced fluid from the test reservoir, and add 3% (v / v) of bacterial activator mixture formula 2; test the bacterial concentration of biofilm-producing bacteria daily, and when the bacterial concentration drops to 10 on the 17th day. 7 The bacterial count / ml was optimized to an injection cycle of 15 days. See the detailed bacterial concentration morphology diagram below. Figure 3 .

[0170] (5) On-site implementation and effect evaluation: Oil well SL-A3-6 started injection on April 10, 2020, and was injected once every 15 days, with 380KG of bacterial solution and activator injected each time. The pump was inspected on December 26, 2020. The pump inspection cycle was 260 days, which was extended by 189 days. The cost was RMB35,000, which reduced the number of pump inspections by about 2 times. The input-output ratio was 1:8.6. The on-site test results were good. This invention has broad prospects for promotion and application.

[0171] Examples 4-8

[0172] Similar to Example 1, the only difference is that the temperature at different depths below the tubing in the test wellbore results in different microorganisms and extracellular polymers;

[0173]

[0174] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0175] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0176] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A method for delaying corrosion of oil well tubing using microorganisms, characterized in that, Includes the following steps: (1) Initial screening of target oil well microorganisms: Based on the suitable temperature for microorganisms, microorganisms that can secrete extracellular polymers at deep temperatures below the tubing in the test wellbore were screened. (2) Activator screening: including preliminary screening and secondary screening of activators, wherein: The preliminary screening method for activators is static culture, and the basis for preliminary screening of activators is the concentration of biofilm-producing microorganisms; Based on the initial screening of activators, a second screening of activators is conducted, and the final activator formulation is determined according to the amount of biofilm produced. (3) Based on the corrosion rate and corrosion inhibition rate of the coupon, the dynamic mass loss method is used to determine the amount of microorganisms and activators injected on site; (4) Based on the bacterial concentration of the biofilm-producing bacteria, the on-site injection cycle is determined by physical simulation method; (5) On-site implementation and effect evaluation, wherein the effect evaluation is based on the well-down rate in the test well area, the pump inspection cycle of the oil well, and the input-output ratio, wherein: The extracellular polymers in step (1) include xanthan gum, gellan gum, thermogelatin, pullulan, chitosan, starch, bacterial cellulose, and velan gum; The microorganisms mentioned in step (1) are one or more of the following: Pseudomonas aeruginosa, Alcaligenes acetogenes, budding short-stem mold, citric acid fermentation waste mycelium, Acetobacter, Aspergillus niger and Acetobacter xylinum.

2. The method for delaying oil well tubing corrosion using microorganisms as described in claim 1, characterized in that, The microorganism mentioned in step (1) is one of Pseudomonas, Alcaligenes, and Acetic Acid Bacillus.

3. The method for delaying oil well tubing corrosion using microorganisms as described in claim 1, characterized in that, The temperature at the tubing depth in step (1) of the test wellbore is calculated based on the tubing depth and the geothermal gradient of the oil layer, and the calculation formula is as follows: Temperature at the depth of the tubing in the test wellbore = 20℃ + geothermal gradient × (depth of tubing ÷ 100).

4. The method for delaying oil well tubing corrosion using microorganisms as described in claim 1, characterized in that, The initial screening index for the target oil well microorganisms in step (1) is: the concentration of the microbial cells and the extracellular polymers produced is greater than 3 g / L.

5. The method for delaying oil well tubing corrosion using microorganisms as described in claim 1, characterized in that, The specific steps for the preliminary screening of activators in step (2) are as follows: Take multiple 50-60 mL portions of produced fluid from the test reservoir, and then add different activator mixtures to each portion, wherein: The bacterial concentration of the activator mixture was 10%. The activator mixture consists of 1-2 ml of microbial culture and an appropriate amount of activator; Then they were placed in the test wellbore temperature and incubated for 5–15 days. The bacterial concentration of biofilm-producing organisms in different culture media was measured, and 2-3 activator formulations with higher bacterial concentrations were preliminarily screened based on the bacterial concentration levels.

6. The method for delaying oil well tubing corrosion using microorganisms as described in claim 5, characterized in that, The specific steps of the activator secondary screening in step (2) are as follows: Take multiple 50-60 mL portions of produced fluid from the test reservoir and add 10-20 mL of different activator mixtures to each. The bacterial concentration of the activator mixture was 10%. The activator mixture consists of 1-2 ml of microbial culture and an appropriate amount of pre-screened activator; Then it was placed at the temperature of the test wellbore and incubated for 5–15 days. Filter the mixture of cells and products, and dry it at an initial temperature of 35°C, increasing the temperature by 5°C every hour until it reaches a maximum of 50°C. Weigh the mixture separately and select the activator formulation with the largest weight in the mixture.

7. The method for delaying oil well tubing corrosion using microorganisms as described in claim 1, characterized in that, Step (3) includes the following steps: (31) Obtain the dimensions of the hanging piece and calculate its area; (32) Wipe the strip clean, then immerse it in a container containing petroleum ether with a boiling range of 60-90℃, then take out the strip and remove the grease from the surface of the strip, and then soak it in anhydrous ethanol for 3-30 minutes. (33) Remove the hanging piece, air dry it and weigh it; (34) The clip is suspended in the dynamic corrosion test bottle, and the clip does not contact the inner wall of the dynamic corrosion test bottle. Then the clip is immersed in the activator mixture with different injection amounts and the produced water of the target oil well in the test reservoir. The air in the dynamic corrosion test bottle is evacuated, and a mixture of CO2 and air is injected. The dynamic corrosion test bottle is placed in an oven with the temperature inside the tubing for incubation. (35) After 7 days of the experiment, the hanging plate was taken out, cleaned with cleaning solution, weighed, and the corrosion status of the hanging plate surface was observed. The corrosion rate was calculated according to formula (1), and the corrosion inhibition rate was calculated according to formula (2). Based on the corrosion rate and corrosion inhibition rate of the hanging plate, the amount of microorganisms and activators injected on site was determined. r = 8.76*10 4 (m-m1) / s*t*P (1) η1=(Δm0-Δm1) / Δm0(2) In the formula: r is the uniform corrosion rate, mm / a; m and m1 are the masses of the hanging pieces before and after the test, respectively, in grams; S is the surface area of ​​the hanging piece, in cm² 2 ; ρ is the density of the hanging sheet, in g / cm³. 3 ; t is the reaction time, in hours; η1 is the corrosion inhibition rate, % Δm0 represents the mass loss of the substrate in the blank test, in grams. Δm1 represents the mass loss of the tablets in the bacterial culture mixture, in grams.

8. A method for delaying oil well tubing corrosion using microorganisms as described in claim 7, characterized in that, The dynamic corrosion testing bottle is an anaerobic bottle with hooks attached inside, wherein the material of the hooks is the same as the tubing material of the target oilfield.

9. A method for delaying oil well tubing corrosion using microorganisms as described in claim 1, characterized in that, Step (4) includes the following steps: Take 50 ml of the produced fluid from the test reservoir and add the determined amount of microorganisms and activators to be injected in the field. The concentration of biofilm-producing bacteria was monitored daily, and the concentration was lowered to 10 after rising. 7 When the bacterial culture is replenished at a rate of 1000 cells / ml, the on-site injection cycle should be determined.

10. A method for delaying oil well tubing corrosion using microorganisms as described in claim 1, characterized in that, The field test mentioned in step (5) refers to injecting microorganisms and activators from the sluice gate of the test reservoir oil well using a high-pressure plunger pump according to the injection volume determined in step (3), and replenishing the bacterial solution according to the field injection cycle determined in step (4).

11. A method for delaying oil well tubing corrosion using microorganisms as described in claim 1, characterized in that, The activator described in step (2) consists of a carbon source, a nitrogen source, and a phosphorus source, wherein: The carbon source is sucrose or glucose; The nitrogen source is one of wheat bran, cottonseed meal, rapeseed cake meal, and corn steep liquor powder; The phosphorus source is dipotassium hydrogen phosphate or potassium dihydrogen phosphate.

12. The method for delaying oil well tubing corrosion using microorganisms as described in claim 11, characterized in that, The activator contains carbon source, nitrogen source and phosphorus source with mass concentrations of 1.0-5.0%, 0.2-0.8% and 0.02-0.1% respectively, with the remainder being water.

13. The method for delaying oil well tubing corrosion using microorganisms as described in claim 12, characterized in that, The activator contains carbon source, nitrogen source and phosphorus source with mass concentrations of 2.0-3.0%, 0.3-0.6% and 0.04-0.08% respectively, with the remainder being water.

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