GLEB SPESHILOV
Director General of the Biospark contract biotech
laboratory

Up to 40% of all cases of corrosion that affects equipment and pipelines are caused by bacterial activity. That said, traditional methods of corrosion prevention prove to be ineffective when it comes to microbial corrosion. Nevertheless, modern technologies are not only capable of detecting the harmful bacteria, but they are also efficient in combating them. And these are not overseas technologies. The innovative diagnostic tool for detection of biocorrosion in petroleum industry with the genetic method was developed exactly here in our country.

Corrosion in equipment and pipelines is one of the acutest problems in oil industry that translates into huge economic losses. On a global scale, annual corrosion-induced costs stand at billions of dollars and include unplanned shutdowns of units and pipelines, ineffective operation or decline in production, increased repair costs and payment of incurred penalties. Corrosion costs may be significantly reduced if it is duly detected, identified and monitored properly.

Among the best studied types of corrosion are that of chemical and electrochemical origin. Traditional analytical methods allow for systematic identification and effective handling of these types of corrosion. At the same time, causes of up to a third of all cases of corrosion were not clear for a long time. It was only after a number of recent studies that specialists have come to conclusion that corrosion can also be attributed to microorganisms among other things. The recent studies quote the following figures:

• 20–40 % of corrosion is caused by microorganisms and products of their activity (so-called microbially induced corrosion, or biocorrosion);
• 70 to 95 % of all pipeline leakages are due to local internal corrosion of microbiological origin.

Corrosion in equipment and pipelines is one of the acutest problems in oil industry that translates into huge economic losses.

Biocorrosion is corrosion in metals that occurs as a result of microbial activity. Soils and surface waters contain a huge amount of microorganisms–bacteria, fungi, algae, protozoa, etc. As of today the following has been confirmed: corrosion in metals is in most cases particularly attributed to bacteria due to the high rate of their reproduction and activity in chemical transformations of environment. When the surface of metal is affected by water, microorganisms that inhabit it attach to the surface of pipes and form resistant films — highly organized, mobile and continuously changing heterogeneous communities.

Biofilms change electrochemical conditions along the metal–solution interface, which induces biocorrosion. For example, biofilms can trigger corrosion in various ways: by production of acids, through direct oxidation of iron in pipelines or through generation of hydrogen sulphide that can damage protective coatings. Also, biofilms alter the acid-base balance of liquids and create a physical barrier between the anode and cathode areas. It was noted that higher pH in the infested solution creates more favorable conditions for bacteria growth.

In the course of biofilm development, cells detach from the surface and move inside the pipelines carried away by the transported liquids, which causes microbiological damage to other areas of the pipeline system. As a result, corrosive biofilms significantly reduce durability and reliability of equipment.

Of many various microorganisms that can inhabit pipeline networks, the biggest hazard for petroleum and natural gas industry is imposed by sulphate reducing microorganisms (SRM) that live by consuming sulphates contained in water and produce sulphites and sulphides that have high chemical activity. Also, as part of their metabolism, bacteria generate a lot of hydrogen sulphide.

Therefore, SRM infestation of systems leads to:

• pit corrosion that is frequently found in places of biofilm attachment;
• aggregation of insoluble ferrous sulphide that clogs the pipeline system;
• hydrogen-sulphide corrosion in various system units.

During pipeline maintenance, in order to eliminate and prevent the corrosion-inducing microorganisms from growing, it is common to use biocides (highly effective specialized “antibiotics”) or special comprehensive inhibitors of various types of corrosion that have antibacterial properties. However, without precise identification of the type of microorganisms that cover the surface of the metal, biocide treatment often proves to be ineffective. It is important to point out that inhibition of biocorrosion is a long-term task due to high resistance of biofilms and variety of microorganisms in them. Uncontrollable application of inadequate strategies in biocide treatment leads to the opposite effect — explosive acceleration of growth of pathogenic bacteria resistant to utilized biocides.

It means that microbiological infestation has to be diagnosed way earlier than one can observe the consequences of the SRM activity. Early detection and relevant measures to “recover” the pipeline will cut the ad hoc costs of repairing and maintaining the damaged equipment. It is important to remember that SRM are living organisms that are capable of developing resistance to applied biocides, which creates necessity not only to select the reagent thoroughly but also to control its efficiency regularly.

Corrosion costs may be significantly reduced if it is duly detected, identified and monitored properly

Depending on the source of hydrogen sulphide inflow, SRM and the stage of microbiological infestation, oilfields can be basically divided into 3 groups:

• new oilfields where oil is extracted at the initial level of intensification and oil well fluids do not contain hydrogen sulphide or SRM;
• oilfields at a later stage of development where producing formations are flooded, and it eventually generates hydrogen sulphide and SRM;
• oilfields where extracted products already contain hydrogen sulphide and SRM from the very beginning of their development.

To address the first group of oilfields, it is necessary to select the flooding source with no or minimum SRM content and continuously treat it with bactericides in the lowest concentration. Besides, the type of bactericides should be changed 2–3 times a year to prevent SRM from adaptation to the reagent.

To tackle the second group of oilfields, SRM control shall be carried out in two directions: inhibition of SRM in the formation by treating injection wells with bactericides in loading concentration and protection of the oilfield equipment from corrosion with the help of reagents with comprehensive effect (bactericides-inhibitors).

The third group of oilfields is recommended to be approached with anti-corrosive measures using corrosion inhibitors and bactericides-inhibitors. Most oilfields of Russia belong to the second group in the above-mentioned classification, so bacterial infestation shall be prevented in several directions:

• inhibition of bacteria in the formation;
• protection of the oilfield equipment from corrosion.

Plan of actions to inhibit bacteria in the formation:

• Stage 1 – detailed study, identification of microorganisms, determination of their amount;
• Stage 2 – selection of appropriate bactericides;
• Stage 3 – elaboration of the bactericide application method on a test site;
• Stage 4 – extensive use of an inhibitor in oilfields.

In order to neutralize bacterial infestation, a complete survey shall be carried out — it will make it possible to demonstrate which groups of microorganisms inhabit the pipe and how many of them are. Retrieved data will allow to carry out less extensive express testing in the future and check only for those microorganisms that are particularly hazardous to a specific client.

In order to neutralize bacterial infestation, a complete survey shall be carried out — it will make it possible to demonstrate which groups of microorganisms inhabit the pipe and how many of them are

Such tests used to take weeks, as the process of testing included cultivation of microorganisms in the growth medium, visual identification using microscopy and determination of microbial count. However, the life cycle of most bacteria varies from several hours to several days, and different types of microorganisms reproduce at various rate in the lab setting. It means that results obtained through traditional methods do not reliably show the properties of analyzed samples, because the number of microorganisms and their variety are bound to change significantly in the course of cultivation. There is also a high risk of erroneous identification of the type of microorganisms, especially of rare uncultured forms that often amount to 70 % of the total biomass. Application of such methods makes its too complicated to select the right biocide and control its efficiency in the future.

To tackle these challenges, the BioSpark laboratory, first ever in Russia, suggests using molecular-genetic technologies to identify microorganisms and control bacterial contamination. These technologies work directly with the initial sample and skip the classical stage of biomass cultivation, and also reduce duration of testing to a matter of several hours.

With modern methods of DNA extraction and decoding, it is possible to analyze samples of microorganisms with the maximum detection sensitivity of up to 0.005 %, which means finding a single bacterium among 20 000 others! It allows for timely detection of new pathogenic microorganisms way ahead of the appearance of the first signs of biocorrosion. When you have all the data in place, the strategy of bactericide selection becomes purpose-oriented: the process uses the bactericide designed to specifically address particular types of bacteria. At the same time there is a continuous control of efficiency of its application.

At the second stage, the diagnostic results define the choice of bactericides that inhibit specific groups of microorganisms. Moreover, bactericides have to be marked by the following properties:

• they shall not leave sediments after contact with mineralized oilfield environments;
• they shall be technologically versatile (liquid state, low viscosity, low solidifying temperature);
• they shall be stable in long-term storage;
• they shall have low toxicity;
• their raw materials shall be available;
• they shall be compatible with components of drilling muds without changing their physical and chemical properties (in case bactericides are used to protect drilling equipment from corrosion);
• they shall not dissolve in oil and oil products to prevent breakdown of catalysts in refineries (in case bactericides are used in oilfields).

The bactericide concentration is considered effective if it eliminates at least 99 % of bacteria. As the modern-day practice suggests, companies put most efforts into combating the consequences of corrosion rather than preventing oil formations from being contaminated by harmful corrosion-inducing bacteria. This new highly sensitive diagnostic method does not only allow to determine the cause of existing biocorrosion, where necessary, but also helps to signal a high risk of its appearance well in advance.

To combat the cause of biocorrosion effectively, it is necessary to work out and implement a multi-stage plan that will start with the process of identification of microorganisms and determination of their quantitative content in the extracted products and injected waters. It is only after completion of the detailed study, identification of microorganisms and determination of their count that one can duly select and utilize bactericides to control biocorrosion effectively, reduce costs by a fair amount and prolong the lifetime of equipment.

Source: Neftegazovaya Vertikal Journal, March 2019 No.6 (450)
Date: March 27, 2019