Study of the sulfidogenic bacteria activity in the formation microflora of an oil field (Kazakhstan) and their potential contribution to corrosion processes

Background: Today at the oil field «N» there is an intensification of corrosion complications. Repeated monitoring of corrosion factors at all sites of the field has shown the localization of aggressive gases at site B, where thermal oil displacement technology is used, which could have triggered an increase in corrosion processes. In addition, large-scale studies of the microbial community of formation waters were conducted at field N, revealing the presence of sulfate-reducing and fermentative sulfidogenic bacteria, which could also contribute to the development of an aggressive environment. In this regard, the issue of the influence of the microbial community on corrosion processes remains a pressing task, and studies were conducted to identify the contribution of sulfidogenic bacteria to the formation of a corrosion-aggressive environment at this field. Aim: To study the contribution of sulfidogenic bacteria of production waters to the formation of aggressive environments and corrosion at the N field. Materials and methods: The objects of the study were samples of water extracted from group installations, wastewater from block cluster pumping stations, and vertical steel tanks. The studies were conducted using classical microbiological methods: anaerobic cultivation of bacteria, sowing using the tenfold dilution method, obtaining biofouling of the object under study in a natural environment, etc. A titrimetric method was used to determine the content of hydrogen sulfide and carbon dioxide. The dissolved oxygen content was determined by an express method using a Fibox 4 PreSens (Germany) fiber optic oxygen analyzer. The amount of mechanical impurities was determined by filtration followed by gravimetric analysis. The corrosion rate of steel coupons was determined gravimetrically by the loss of sample mass during their exposure at field facilities. Results: All studied objects showed high content of planktonic (105–108 cells/ml) and adherent (106–108 cells/ml) sulfidogenic bacteria. The productivity of different physiological groups of sulfidogenic bacteria was determined: sulfate-reducing bacteria contribute most to hydrogen sulfide formation (125.6–762.5 mg/L), while sulfur-reducing bacteria contribute least (59.6–298.2 mg/L). Site B of the field, where development is carried out using thermal technology, is characterized by the highest corrosion potential. At the same time, the number of sulfidogenic bacteria at site B is comparable to their number at other sites of the field. Conclusion: The microflora of the production waters of the N deposit has a high corrosion potential, but the greatest contribution to the formation of an aggressive environment is due to the use of thermal oil recovery technology at the deposit.