Control of Sulfate-Reducing Bacteria in Oil and Gas Pipelines

Abstract

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 118410, "Control of Sulfate-Reducing Bacteria in Oil and Gas Pipelines," by M.D. Lohithesh and A.K. Agnihotri, ONGC, and Banwari Lal, SPE, TERI, prepared for the 2008 Abu Dhabi International Petroleum Exhibition and Conference, Abu Dhabi, UAE, 3-6 November. The paper has not been peer reviewed. A major economic loss faced by oil and gas companies is pipeline corrosion. Internal pipeline corrosion is, basically, caused by sulfate-reducing bacteria (SRB). The growth of SRB and their secondary metabolites in pipelines causes surface modifications, which can induce a more-complex corrosion process. A strategy was studied for controlling the SRB population of oil and gas pipelines. Introduction Microbial-induced corrosion (MIC) has been implicated widely in the deterioration of metal pipelines and offshore structures in the oil industry. Though several studies have reported the use of chemicals as biocides for controlling MIC, these conventional methods generally are inadequate against bacterial biofilms. Metabolically active bacteria exhibit an increased tendency to attach to metal surfaces and, depending on the availability of nutrients, to produce exopolymers to form mature biofilms. The exopolysaccharide matrix that helps form the biofilm may be involved in reducing the reactivity of chemical biocides. Attempts to circumvent this problem have focused on use of very high concentrations of chemical biocides, which may in turn pose environmental hazards. Further, after a long period of contact, corrosion-causing bacterial microflora might adapt to a given biocide and develop resistance. It is established that even if biocides are effective against planktonic population (i.e., dispersed in the water phase), their effectiveness against sessile forms (i.e., embedded within biofilm) is reduced by approximately 90%. Therefore, development continues for effective biocides, appropriate procedure for their application, and innovative measures for microbial control. This study explored the effect of biocides on the inhibition of SRB in oil pipelines. The objectives were to screen efficient and effective biocides for inhibition of MIC in oil pipelines, examine the potential of effective biocides by measuring the total sulfide production, and demonstrate the ability of biocides against biofilm (sessile population). Materials and Methods Oil and water samples were collected from the pipeline network of Oil and Natural Gas Corporation (ONGC), India, at the Bombay high offshore, Gandhar, and Ahmedabad areas. Production fluid was collected directly from the production wellheads. The SRB consortium was developed from formation water collected from corroded oil pipelines The SRB medium was prepared by adding 25 g of NaHCO3, 0.2 g of CaCl2•2H2O, 0.1 g of KCl, 1.5 g of NH4Cl, 0.6 g of NaH2PO4•H2O, 10.0 mL of vita-min, and 10 mL of trace element with a molarity of 50 mM (millimolar =mol/m3) ferric citrate in 1 L of double-distilled water. The pH of the medium was adjusted to 7.5±0.1 by use of 1 M NaOH. The SRB consortium was purified by the roll-tube method, and individual strains were identified by use of 16S rDNA analysis.